Chapter 7 Cassava Mineral Nutrition and...

Chapter 7Cassava Mineral Nutrition and

Fertilization

Reinhardt H. HowelerCIAT Regional Office in Asia, Department of Agriculture, Chatuchak,

Bangkok 10900, Thailand

Introduction

Cassava is generally grown by poor farmersliving in marginal areas with adverse climaticand soil conditions. The crop is very suitablefor these conditions because of its exceptionaltolerance to drought and to acid, infertile soils.It is often grown on sloping land because of itsminimal requirement for land preparation, andits ability to produce reasonably good yields oneroded and degraded soils, where other cropswould fail. It has been shown (Quintiliano et al.,1961; Margolis and Campos Filho, 1981;Putthacharoen et al., 1998), however, thatgrowing cassava on slopes can result in severeerosion, with high soil and nutrient losses. Thuscassava cultivation on slopes requires adequatecultural and soil conservation practices thatminimize erosion (Howeler, 1994).

Cassava is well adapted to poor or degradedsoils because of its tolerance to low pH, highlevels of exchangeable aluminium (Al) and lowconcentrations of phosphorus (P) in the soilsolution. Studying the effect of pH on the growthof several crops grown in flowing nutrientsolution, Islam et al. (1980) reported thatcassava and ginger (Zingiber officinale) were moretolerant of low pH (< 4) than tomatoes(Lycopersicon esculentum), wheat (Triticumaestivum L.) or maize (Zea mays L.). Centro

Internacional de Agricultura Tropical (CIAT;1978) and Howeler (1991a) also reported thatcassava and cowpeas (Vigna unguiculata) weremore tolerant of acid soils with high levelsof exchangeable Al, and were much lessresponsive to lime applications than commonbeans (Phaseolus vulgaris), rice (Oryza sativa),maize and sorghum (Sorghum vulgaris).

Effect of Cassava Production onSoil Fertility

Nutrient absorption, distribution andremoval in harvested products

As cassava may grow well in poor and/ordegraded soils and few other crops will growwell on those same soils after cassava, it is oftenbelieved that cassava is a ‘scavenger crop’, thatis, highly efficient in nutrient absorption from alow-nutrient soil, leaving that soil even poorerthan before. Thus it is often concluded thatcassava extracts more nutrients from the soilthan most other crops, resulting in nutrientdepletion and a decline in soil fertility.

Table 7.1 shows the average removal of themajor nutrients by cassava roots as compared tothat for the harvested products of other crops(Howeler, 1991b). Nitrogen (N) and P removal

©CAB International 2002. Cassava: Biology, Production and Utilization(eds R.J. Hillocks, J.M. Thresh and A.C. Bellotti) 115

per tonne of dry matter (DM) in cassava roots wasactually much lower than that removed by mostother crops, while that of potassium (K) was simi-lar or lower than that of other crops. When cas-sava root yield was very high, as in Table 7.1, theN and P removal per hectare was similar to that ofother crops, while K removal was indeed higherthan that of any other crop. Similar results werereported by Prevot and Ollagnier (1958) andAmarasiri and Perera (1975). Putthacharoenet al. (1998), however, reported that with anaverage root yield of 11 t ha−1 cassava rootsremoved much less N and P than other crops,while K removal was similar to that of other cropsand much less than that removed by pineapple.

Nutrient absorption and distribution areclosely related to plant growth rate, whichdepends on soil fertility and climatic conditionsas well as on varietal characteristics. In poor soilsfertilizers can markedly increase plant growthand nutrient absorption; while in areas witha long dry season, irrigation can do the same(Fig. 7.1). At 2–3 months after planting (MAP),the tuberous roots become the major sink of DM.At harvest DM is always highest in the roots, usu-ally followed by stems, fallen leaves, leaf bladesand petioles (Fig. 7.1). Table 7.2 shows the DMand nutrient distribution at time of harvest for

fertilized and unfertilized plants in Carimagua,Colombia. Fertilization increased total DMproduction and root yield by about 30%, butnearly doubled the total absorption of P and K,and increased that of N by 61%. Total nutrientabsorption was highest for N, followed by K, Ca,Mg, P and S; absorption of micronutrients wasvery low (Paula et al., 1983). The roots generallyaccumulated more K than N, followed by P, Ca,Mg and S, while fallen leaves and stems werehigh in N and Ca. Similar results were reportedby Nijholt (1935), Asher et al. (1980), CIAT(1980, 1985a,b), Howeler and Cadavid (1983),Paula et al. (1983) and Putthacharoen et al.(1998).

As indicated above, the amount of nutrientsabsorbed by the plant or that removed in theroot harvest is highly dependent on growth rateand yield, which in turn depend on climate, soil-fertility conditions and variety. Table 7.3 showsthe fresh and dry matter production, as well asthe nutrient content in the roots and in the totalplant from 15 experiments reported in the litera-ture, with yields ranging from 6 to 65 t ha−1.The amounts of nutrients in the roots or in thewhole plant were quite variable, but tended to bevery high when yields were high and quite lowwhen yields were low. If nutrient removal were

116 R.H. Howeler

Yield (t ha−1) (kg ha−1) (kg t−1 DM produced)

Crop/plant part Fresh Drya N P K N P K

Cassava/fresh rootsSweet potatoes/fresh rootsMaize/dry grainRice/dry grainWheat/dry grainSorghum/dry grainCommon beansb/dry grainSoybeans/dry grainGroundnuts/dry podSugarcane/fresh caneTobacco/dry leaves

35.725.2

6.54.62.73.61.11.01.5

75.22.5

13.535.055.563.972.323.100.940.861.29

19.552.10

5561966056

1343760

1054352

13.213.317.4

7.512.029.0

3.615.3

6.520.2

6.1

112972613132922673596

105

4.512.017.317.124.143.339.669.881.4

2.324.8

0.832.633.132.405.179.403.83

17.795.040.912.90

6.619.2

4.74.15.69.4

23.477.927.1

4.450.0

Source: Howeler (1991b).aAssuming cassava to have 38% DM, grains 86%, sweet potatoes 20%, sugarcane 26%, dry tobaccoleaves 84%.bPhaseolus vulgaris.DM, dry matter.

Table 7.1. Average nutrient removal by cassava and various other crops, expressed in both kg ha−1

and kg t−1 harvested product, as reported in the literature.

proportional to yield, an average root yieldof 15 t ha−1 would remove about 35 kg N,5.8 kg P, 46 kg K, 7.0 kg Ca and 4.1 kg Mg ha−1.The relationship between dry root yield and rootnutrient content is, however, not linear (Fig. 7.2)because high-yielding plants generally havehigher nutrient concentrations in the roots thanlow-yielding plants. Thus at lower yield levels,nutrient removal is considerably lower thanindicated above. Figure 7.2 shows that at a freshroot yield level of 15 t ha−1the nutrients removed

in the harvested roots would be about 30 kg N,3.5 kg P and 20 kg K ha−1, considerably lowerfor P and K than previously estimated (Howeler,1981). This may be the reason why cassavayields of less than 10 t ha−1 (about 3.7 t ha−1 ofdry roots) do not seriously deplete the nutrientlevel of the soil. Yields can be sustained at thoselevels for several cropping seasons, even when nofertilizers or manures are applied, as long as planttops are re-incorporated into the soil. The ratherclose fit of the experimental data reported in the

Mineral Nutrition and Fertilization 117

(t ha−1)DM

(kg ha−1)

N P K Ca Mg S B Cu Fe Mn Zn

UnfertilizedTopRootsFallen leavesTotal

FertilizedTopsRootsFallen leavesTotal

5.1110.75

1.5517.41

6.9113.97

1.8622.74

69.130.323.7

123.1

99.967.330.5

197.7

7.47.51.5

16.4

11.716.8

2.030.5

33.654.9

4.092.5

74.3102.1

7.1183.5

37.45.4

24.767.5

55.015.531.9

102.4

16.26.54.0

26.7

15.38.44.7

28.4

8.23.32.5

14.0

9.67.02.6

19.3

0.070.080.040.19

0.080.070.050.20

0.030.020.010.06

0.030.030.020.08

0.450.38

––

0.780.90

––

0.330.020.370.72

0.570.060.461.09

0.260.100.180.54

0.300.170.190.66

Source: Howeler (1985a).

Table 7.2. Dry matter (DM) and nutrient distribution in 12-month-old cassava cv. M Ven 77, grown withand without fertilization in Carimagua, Colombia.

Fig. 7.1. Dry matter distribution among roots, stems, leaf blades, petioles and fallen leaves of fertilizedcassava during a 12-month growth cycle in Carimagua (Colombian Eastern Plains), with (B) or without(A) irrigation. (Source: CIAT, 1985b.)

literature for the relationship between P and Kremoval with dry root yield (Fig. 7.2B and C) indi-cates that yields may be more closely associatedwith the concentrations of P and K in the rootsthan with that of N.

To prevent nutrient depletion of the soil,about 60 kg N, 10–20 kg P2O5 and 50 kg K2Oha−1 should be applied if the expected yield levelis 15 t ha−1 and all stems and leaves are returnedto the soil. If leaves and stems are also removed,at least twice this much needs to be applied.Removal of P, Ca and Mg is quite low if onlyroots are harvested but increases considerably(especially Ca and Mg) if plant tops are alsoremoved.

Nutrient losses by runoff and erosion

When cassava is grown on slopes, nutrientlosses in eroded sediments and runoff can besubstantial. The detachment of soil particlesby the impact of raindrops and the subsequentmovement down slope, together with runoffwater, not only physically removes part ofthe top soil with the associated organic matter(OM), nutrients and microorganisms, but alsofertilizers, plant litter and earthworm castings.This leaves a soil that is lighter in texture andlower in OM and nutrients. Given the reduceddepth of the topsoil, a highly acid, infertilesubsoil may be exposed. Consequently, cassava

118 R.H. Howeler

Yield (t ha−1) Nutrient content (kg ha−1)

Plant part Fresh Dry N P K Ca Mg Source/cultivar

RootsWhole plantRootsWhole plantRootsWhole plantRootsWhole plantRootsWhole plantRootsWhole plantRootsWhole plantRootsWhole plantRootsWhole plantRootsWhole plantRootsWhole plantRootsWhole plantRootsWhole plantRootsWhole plantRootsWhole plant

64.7110.6

59.0–

52.7111.1

37.5–

~ 33.9–

32.3–

~ 27.6–

26.6–

26.0–

18.3–

16.1–

~ 15.0–

~ 8.7–8.7–6.0–

26.5939.9921.6730.0825.2144.6513.9722.7412.6020.9215.3925.0410.2819.5612.8119.1010.7517.41

5.529.013.64

10.555.58

10.623.246.542.684.231.524.37

45124152315

38132

67198161330127243100353

91167

30123

329530

19366

197379313391891

28.245.322.037.027.948.517.031.010.020.519.134.4

8.724.811.319.1

8.016.0

3.69.94.7

27.02.78.11.54.00.93.22.2

12.2

317487163238268476102184

53100

71147107174

47765592356545

13717612340

4101555

51155

207734

16116

1021688

65615

1335

325

675

379

1228

1004

303

215

46

184311321952

8281230

5251337

619

727

415

527

520

29282

15

Nijholt (1935)São Pedro PretoHoweler and Cadavid (1983)M Col 22, fertilizedNijholt (1935)MangiHoweler (1985b)M Col 22, unfertilizedPaula et al. (1983)Branco SC, fertilizedCadavid (1988)CM 523–7, fertilizedPaula et al. (1983)Riqueza, fertilizedCadavid (1988)CM 523–7, unfertilizedHoweler (1985a)M Ven 77, unfertilizedSittibusaya, unpublishedRayong 1, fertilizedPutthacharoen et al. (1998)Rayong 1, 1990/91Paula et al. (1983)Riqueza, unfertilizedPaula et al. (1983)Branca SC, unfertilizedSittibusaya, unpublishedRayong 1, unfertilizedPutthacharoen et al. (1998)Rayong 1, 1989/90

Table 7.3. Fresh and dry yield, as well as nutrient content in cassava roots and in the whole plant attime of harvest, as reported in the literature.

yields on eroded soils are substantially lowerthan on nearby non-eroded soil (Howeler, 1986,1987).

Research has shown (Quintiliano et al.,1961; Margolis and Campos Filho, 1981; Putt-hacharoen et al., 1998; Wargiono et al., 1998)


Fig. 7.2. Relation between the N, P and K contents of cassava roots and dry root yield, as reported inthe literature (see Table 7.3); arrows indicate the approximate nutrient contents corresponding to a freshroot yield of 15 t ha−1. (In Fig. 7.2A two points corresponding to data of Nijholt (1935) were not consid-ered when drawing the line, as the reported levels of N removal were too low for the high yields obtained.This may have been due to faulty analytical procedures at the time. Data for P and K removal from thesame author seem to be correct and are therefore included.)

that cultivating cassava on slopes results in moreerosion than for most other crops. This is mainlydue to the wide plant spacing used and the slowinitial growth of cassava, which result in soilbeing exposed to the direct impact of rainfallduring the first 3–4 MAP. Recent research hasshown that erosion can be markedly reducedby simple agronomic practices such as selectingvarieties with rapid initial growth, minimumtillage, closer plant spacing (0.8 × 0.8 m), verti-cal planting, intercropping, mulching, fertilizerapplication, planting at the end rather than thebeginning of the rainy season, and the plantingof contour hedgerows of grasses such as vetiver(Vetiveria zizanioides), leguminous trees or foragespecies (Howeler, 1998; Nguyen Huu Hy et al.,1998; Tongglum et al., 1998; Wargiono et al.,1998).

Table 7.4 shows the soil and associatednutrient losses measured in cassava trialsconducted in Thailand and Colombia. Nutrientlosses were much higher in Thailand than inColombia due to the higher soil losses, even on a‘gentle’ slope of only 7%. Losses of P, K and Mgare in terms of available P and exchangeable Kand Mg. If the unavailable or non-exchangeablefractions had been measured, these losses wouldhave been about ten times higher. Thus annualN losses in eroded sediments in Thailand werealmost twice as high as in the harvested roots(Putthacharoen et al., 1998), while in ColombiaN losses in sediments were one to two times as

high as those estimated in the harvested roots(Ruppenthal, 1995; Ruppenthal et al., 1997).

There is little quantitative informationabout nutrient losses from cassava fields inrainfall runoff. Naturally this depends on rainfallintensity, amount of runoff, fertilizers applied,etc. Data reported for upland rice grown on25–35% slope in Luang Prabang, Laos, indicatethat total N and P losses in runoff (3.6 kg N and0.85 kg P ha−1 year−1) were considerably lowerthan in the eroded sediments (35.5 kg N and5.6 kg P ha−1 year−1), but that total K losses werehigher (52 kg ha−1 year−1) in the runoff than inthe sediment (33 kg ha−1 year−1; Phommasacket al., 1995, 1996).

Long-term effect of cassava productionon soil productivity

When cassava is grown continuously on thesame soil without adequate fertilizer or manureinputs, soil productivity may decline due tonutrient depletion and soil loss by erosion.Sittibusaya (1993) reported that cassava yieldsin unfertilized plots declined from 26–30 to10–12 t ha−1 after 20–30 years of cassavacultivation. Similar or even faster yield declineshave been observed for other annual crops(Ofori, 1973; Nguyen Tu Siem, 1992).

Cong Doan Sat and Deturck (1998)compared the effect of long-term cultivation

120 R.H. Howeler

Dry soil loss(t ha−1 year−1)

(kg ha−1 year−1)

Location and treatments Na Pb Kb Mgb

Cassava on 7% slope in Sriracha, Thailandc

Cassava on 7–13% slope in Quilichao, Colombiad

Cassava + leguminous cover crops in Quilichao, Colombiad

Cassava + grass hedgerows in Quilichao, Colombiad

Cassava on 12–20% slope in Mondomo, Colombiad

Cassava + leguminous cover crops in Mondomo, Colombiad

Cassava + grass hedgerows in Mondomo, Colombiad

71.45.1

10.62.75.22.71.5

37.111.524.0

5.813.3

6.53.5

2.180.160.240.061.090.040.02

5.150.450.970.220.450.240.13

5.350.450.810.240.360.200.10

aTotal N.bAvailable P and exchangeable K and Mg.cSource: Putthacharoen et al. (1998).dSource: Ruppenthal et al. (1997).

Table 7.4. Nutrients in sediments eroded from cassava plots with various treatments in Thailand andColombia.

of cassava with that of natural forest, rubber,cashew and sugarcane grown on similar soils insouthern Vietnam. Cassava cultivation resultedin the lowest levels of soil organic C, total N andexchangeable K and Mg, and an intermediatelevel of P because of some P fertilizer applications.Cassava cultivation also resulted in the lowestclay content, soil aggregate stability and waterretention, as well as intermediate bulk densityand infiltration rates. Compared to native forest,grasslands or perennial plantation crops, long-term cassava cultivation has a negative impacton soil productivity, especially when grown onslopes with inadequate management and nofertilizer. This is also true, however, for otherannual food crops, which all require frequentland preparation, resulting in erosion and morerapid decomposition of OM. Moreover, fertilizerinputs may not compensate for nutrient removalin harvested products, or losses by leaching anderosion.

When cassava was grown for 8 consecutiveyears without fertilizers in Quilichao, Colombia,root yields declined from 22 t ha−1 in the firstyear to 13 t ha−1 in the last year (Fig. 7.3). Withapplication of only N or P, yields declined from 27and 29 t ha−1 in the first year to 20 and 15 t ha−1,respectively, in the last year. This yield declinewas due to the increasing intensity of Kdeficiency. When only K was applied (150 kgK2O ha−1) yields could be maintained at about30 t ha−1, while with the annual application of100 kg N, 200 kg P2O5 and 150 kg K2O ha−1,yields actually increased from about 32 to nearly40 t ha−1. Without K application the exchange-able K content of the soil decreased in 2–3 yearsfrom 0.2 to about 0.1 meq 100 g−1 and remainedat that level for the following five crop cycles.With application of 150 kg K2O ha−1, the soilK level remained constant at about 0.2 meq100 g−1, while with applications of 300 kg K2Oha−1 it increased gradually to 0.45 meq 100 g−1.Thus high yields and adequate levels of Kcould be maintained with annual applications of150 kg K2O ha−1 (Howeler and Cadavid, 1990;Howeler, 1991b).

On mineral soils in Malaysia, very high cas-sava yields of about 50 t ha−1 were maintainedfor 9 years with annual applications of 112 kg N,156 kg P2O5 and 187 kg K2O ha−1, but withoutfertilizers yields declined from 32 t ha−1 in thefirst year to about 20 t ha−1 in the 9th year

(Chan, 1980; Howeler, 1992). This was alsoattributed mainly to increasing K deficiency. InKerala, India, continuous cropping for 10 yearsalso resulted in declining yields when no Kwas applied, while annual applications of 100 kgK2O ha−1 maintained high yields of 20–30 t ha−1

(Kabeerathumma et al., 1990).Figure 7.4 shows similar results for a

long-term (> 20 year) fertility trial conductedin Khon Kaen, Thailand. Without K applicationyields declined from 28 t ha−1 in the first year to10 t ha−1 in the second, and then slowly declinedto about 5 t ha−1 during the subsequent 17cropping cycles. With application of NK or NPK,yields could be maintained at a level of 20 t ha−1

for the entire period. Figure 7.4B also shows thatwhen plant tops were re-incorporated into thesoil, the yield decline without fertilizer applica-tion was much slower. After 19 years the yieldwas still about 10 t ha−1, i.e. twice as high aswhen all plant parts were removed. Thus, whenplant tops were returned to the soil, yields ofabout 10 t ha−1 could be maintained, even in avery poor soil and without any application offertilizers. With adequate fertilization high yieldsof at least 20 t ha−1 could be maintained for19 years of continuous cropping.

Diagnosis of Nutritional Disorders

If plant growth is not optimal and/or yields arelow, and if other causes such as insect pests anddiseases, drought, shade or cold have been ruledout, plants may be suffering from nutritionaldeficiencies and/or toxicities. Before effectiveremedial measures can be taken, it is essentialto diagnose the problem correctly. This can bedone in several ways, but the best diagnosis isusually obtained from a combination of differentmethods.

Observation of deficiency and toxicitysymptoms

Cassava plants do not readily translocatenutrients from the lower to the upper leaves;instead, when certain nutrients are in deficientsupply, plants respond by slowing the growthrate, producing fewer and smaller leaves andsometimes shorter internodes. Leaf life is also


reduced. As nutrients are not readily mobilizedto the growing point, symptoms for NPK defi-ciencies, normally found in the lower leaves,tend to be less pronounced in cassava than inother crops. For that reason farmers may notbe aware that plant growth is reduced becauseof nutritional deficiencies. The initial diagnosisbased on deficiency or toxicity symptoms needsto be confirmed by soil or plant tissue analyses or

from experiments. Nevertheless, visual identifi-cation is a quick, easy method to diagnose manynutritional problems. Symptoms have beendescribed and colour photos have been includedin several publications (Asher et al., 1980;Howeler, 1981, 1989, 1996a,b; Lozano et al.,1981; Howeler and Fernandez, 1985). Thesymptoms of nutrient deficiencies and toxicitiesare summarized in Table 7.5.

122 R.H. Howeler

Fig. 7.3. Effect of various levels of annual applications of N, P and K on cassava root yield (A), and onthe exchangeable K content of the soil (B) during eight consecutive cropping cycles in a long-term NPKtrial conducted at CIAT-Quilichao, Colombia.

Soil analysis

This method is advantageous in that problemscan be detected before planting and, if necessary,lime and/or nutrients can be applied before plantgrowth is affected by the problem. Soil analysesare particularly useful for detecting P, K, Ca, Mgand Zn deficiencies, while soil pH will indicatewhether Al and/or Mn toxicity or micronutrientdeficiencies are likely to occur. Analysis for OMcontent is not very reliable in predicting Nresponses as high-OM soils may still produce a

significant N response if N mineralization isslow, especially in very acid soils.

Soil analyses usually determine the amountof available or exchangeable nutrient as this partof the total soil nutrient is best correlated withplant uptake. These ‘available’ fractions are usu-ally determined by shaking the soil sample withcertain extracting solutions and determiningthe amount of nutrient in the extract. Differentlaboratories may use different extracting agentsas there is no one method that is optimal for allsoil types; thus results from one laboratory may


Fig. 7.4. Effect of annual applications of various combinations of N, P and K (A) and crop residuemanagement (B) on cassava yield during 19 consecutive crops grown in Khon Kaen, Thailand, from1977–1995. (Source: Howeler, 2000.)

124 R.H. Howeler

Deficiencies Symptoms

Nitrogen (N)

Phosphorus (P)

Potassium (K)

Calcium (Ca)(rare in the field)

Magnesium (Mg)(often seen in field)Sulphur (S) (similar to Ndeficiency; seldom seen in field)Boron (B)

Copper (Cu)(mainly in peat soils)

Iron (Fe) (mainly incalcareous soils)

Manganese (Mn)(mainly in sandyand high pH soils)Zinc (Zn) (oftenseen in high pH orcalcareous soils;also in acid soils)

Reduced plant growthIn some cultivars, uniform chlorosis of leaves, starting with lower leaves, but soonspreading throughout the plantReduced plant growth, thin stems, short petioles; sometimes pendant leavesUnder severe conditions 1–2 lower leaves turn yellow to orange, become flaccid andnecrotic; may fall offIn some cultivars lower leaves turn purplish/brownReduced plant growth with excessive branching, resulting in prostrate plant typeSmall, sometimes chlorotic upper leaves; thick stems with short internodesUnder severe conditions premature lignification of upper stems with very shortinternodes, resulting in zigzag growth of upper stemsIn some cultivars purple spotting, yellowing and border necrosis of lower leavesIn other cultivars upward curling of lower leaf borders, similar to drought stresssymptomsReduced root and shoot growthChlorosis, deformation and border necrosis of youngest leaves with leaf tips ormargins bending downwardsMarked intervenal chlorosis or yellowing in lower leavesSlight reduction in plant heightUniform chlorosis of upper leaves, which soon spreads throughout the plant

Reduced plant height, short internodes, short petioles and small deformed upperleavesPurple–grey spotting of mature leaves in middle part of plantUnder severe conditions gummy exudate on stem or petioles (almost never seen infield)Suppressed lateral development of fibrous rootsDeformation and uniform chlorosis of upper leaves, with leaf tips and marginsbending up- or downwardPetioles of fully expanded leaves long and bending downReduced root growthUniform chlorosis of upper leaves and petioles; under severe conditions leaves turnwhite with border chlorosis of youngest leavesReduced plant growth; young leaves small, but not deformedIntervenal chlorosis or yellowing of upper or middle leaves; uniform chlorosis undersevere conditionsReduced plant growth; young leaves small, but not deformed.Intervenal yellow or white spots on young leavesLeaves become small, narrow and chlorotic in growing point; necrotic spotting onlower leaves as wellLeaf lobes turn outward away from stemReduced plant growth; under severe conditions, death of young plants

Toxicities Symptoms

Aluminium (Al) (only in veryacid mineral soils)Boron (B) (only observedafter excessive B application)Manganese (Mn) (mainly inacid soils and when plantgrowth stagnates)Salinity (observedonly in saline/ alkaline soils)

Reduced root and shoot growthUnder very severe conditions yellowing of lower leavesNecrotic spotting of lower leaves, especially along leaf margins

Yellowing or oranging of lower leaves with purple-brown spots along veinsLeaves become flaccid and drop off

Uniform yellowing of leaves, starting at bottom of plant but soon spreading throughoutSymptoms very similar to Fe deficiencyUnder severe conditions border necrosis of lower leaves, poor plant growth and deathof young plants

Table 7.5. Symptoms of nutrient deficiencies and toxicities in cassava.

differ from those of another. In interpreting theresults, therefore, it is important to consider themethodology used.

Representative soil samples should be takenin areas that appear to be uniform in terms ofplant growth and previous management. About10–20 subsamples are taken in zigzag fashionacross the whole area. These subsamples arethoroughly mixed together and then about300–500 g are air dried or dried at about 65°C ina forced-air oven. This combined sample is thenfinely ground, screened and sent to the lab foranalysis.

Results of the soil analysis can be comparedwith published data obtained from correlationstudies, which indicate either the ‘critical level’of the nutrient, as determined with a specificextracting agent or the nutrient ranges accord-ing to the particular nutritional conditions of thecrop. Table 7.6 gives the ranges correspondingto the nutritional requirements of cassava deter-mined with particular methodologies.

These data were determined from manyfertilizer experiments conducted in Colombia andin various Asian countries by relating the rela-tive yield in the absence of N, P or K fertilizers(yield without the nutrient over the highest yield

obtained with the nutrient) with the OM, avail-able P and exchangeable K content of the soil,respectively. Figure 7.5 gives an example fromnine locations in four Asian countries. A line wasdrawn visually through the points to show therelationship and to estimate the ‘critical level’ ofthe nutrient or soil parameter. This critical levelis interpreted as the concentration of the nutrientin the soil or plant tissue above which there isno further significant response to application ofthe nutrient (usually defined as corresponding to95% of maximum yield). Critical levels are 3.2%for OM, 7 µg g−1 for P (Bray II) and 0.14 meq100 g−1 for exchangeable K. The critical levels forP and K are close to those reported earlier in theliterature (Table 7.7). Those for available soil-Preported for cassava (4–10 µg g−1) are muchlower than for most other crops (10–18 µg g−1),indicating that cassava will grow well insoils that are low in P and where other cropswould suffer from P deficiency. This is due tothe effective association between cassava rootsand vesicular–arbuscular mycorrhizas (VAM)occurring naturally in the soil (Howeler, 1990).

The critical levels for exchangeable K forcassava (0.08–0.18 meq K 100 g−1; Table 7.7)are also lower than for most other crops


Soil parameter Very low Low Medium High Very high

pHa

Organic matterb (%)Al saturationc (%)Salinity (mS cm−1)Na saturation (%)Pd (µg g−1)Kd (meq 100 g−1)Cad (meq 100 g−1)Mgd (meq 100 g−1)Sd (µg g−1)Be (µg g−1)Cue (µg g−1)Mne (µg g−1)Fee (µg g−1)Zne (µg g−1)

< 3.5< 1.0

< 2.5< 0.10< 0.25< 0.2

< 20.25.5< 0.2< 0.1< 5.5< 1.5< 0.5

3.5–4.51.0–2.0

2–40.10–0.150.25–1.0

0.2–0.420–40

0.2–0.50.1–0.3

5–101–10

0.5–1.0

4.5–7.52.0–4.0< 75.5

< 0.5< 2.54–15

0.15–0.251.0–5.00.4–1.040–70

0.5–1.00.3–1.010–10010–100

1.0–5.0

7–8> 4.0

75–850.5–1.0

2–10> 15.0

> 0.25> 5.0> 1.0

> 70.01–21–5

100–250> 100.0

5–50

> 8

> 85.0> 1.0> 10

> 2> 5

> 250

> 50

apH in H2O.bOM = Walkley and Black method.cAl saturation = 100 × Al (Al + Ca + Mg + K) in meq 100 g−1.dP in Bray II; K, Ca, Mg and Na in 1N NH4-acetate; S in Ca phosphate.eB in hot water; and Cu, Mn, Fe and Zn in 0.05 N HCl + 0.025 N H2SO4.Source: Howeler (1996a,b).

Table 7.6. Approximate classification of soil chemical characteristics according to the nutritionalrequirements of cassava.

126 R.H. Howeler

Fig. 7.5. Relationship between relative yield of cassava (i.e. without nutrient as % of highest yield withnutrient) and organic matter available P and exch. K content of the soil in nine NPK trials conducted inAsia (1993–1996). (Source: Howeler, 1998.)


Soil parameter Methodc Crop Critical level Source

Organic matter (%)P (µg g−1)

K (meq 100 g−1)

Ca (meq 100 g−1)

Mg (meq 100 −1)pH

Al (% sat.)

Walkley and BlackBray I

Bray II

Olsen-EDTA

North Carolina

NH4-acetate

Bray II

North CarolinaNH4-acetate

NH4-acetate1 : 1 in water

KCl

CassavaCassavaCassavaCassavaCassavaMaizeSoybeansCassavaCassavaCassavaCassavaCassavaCassavaCassavaCassavaCassavaCommon beansd

CassavaCassavaCassavaCassavaCassavaCommon beansCassavaCassavaCassavaCassavaCassavaCassavaCassavaCassavaRicePotatoesSugarcaneCassavaCassavaCassavaCassavaCassavaCassavaCassavaCassavaCassavaCommon beansCassavaCassavaCommon beansCassavaCommon beans

3.17.175

b8b.1754.27.175

14.17515.175

8.1754.1756.175

b5.8b

10.17510.175

4.1754.57.175

10–153.175

b7.5b

8.175b5.0b

9.17518.175

0.09–0.15< 0.15< 0.15

0.18b0.175b

0.150.18

0.08–0.100.21

0.20–1.000.16–0.51

0.150.170.16

b0.175b

0.170.120.140.150.254.5

< 0.204.6 and 7.8

4.980.17510–20

Howeler (1998)Howeler (1978)Kang et al. (1980)Cadavid (1988)Howeler (1989)Kang et al. (1980)Kang et al. (1980)CIAT (1982)Howeler (1985a)CIAT (1985a)Cadavid (1988)Howeler (1989)Hagens and Sittibusaya (1990)Howeler and Cadavid (1990)Howeler (1995)Howeler (1998)Howeler and Medina (1978)van der Zaag et al. (1979)Cadavid (1988)Howeler (1989)Cadavid (1988)Howeler (1989)Goepfert (1972)Obigbesan (1977)Kang (1984)Kang and Okeke (1984)Howeler (1985b)Cadavid (1988)Howeler (1989)Howeler and Cadavid (1990)Hagens and Sittibusaya (1990)Jones et al. (1982)Roberts and McDole (1985)Orlando Filho (1985)CIAT (1985a)Howeler (1985b)CIAT (1988b)Cadavid (1988)Howeler and Cadavid (1990)Howeler (1995)Howeler (1998)Howeler (1989)CIAT (1979)Howeler and Medina (1978)Kang (1984)CIAT (1977, 1979)Abruña et al. (1974)CIAT (1979)Abruña et al. (1974)

footnote on next page

Table 7.7. Critical levelsa of nutrients for cassava and other crops according to various methods of soilanalysis, as reported in the literature.

(0.16–0.51 meq K 100 g−1), indicating thatdespite the crop’s relatively high K requirement,it will still grow well on soils with only inter-mediate levels of K.

As mentioned above, there is seldom a goodrelationship between the relative response to Nand the soil OM content (Howeler, 1995). Usingdata from 56 NPK trials conducted in Brazil from1950 to 1983 (Gomes, 1998), the critical leveldetermined for OM was only 1.3%, considerablylower than the 3.1% determined in Asia(Howeler, 1998).

Using data from 20 NPK cassava trialsconducted in Colombia to compare differentmethods of extracting available P, Cadavid(1988) reported the highest correlation betweenrelative cassava yields and available soil P usingBray I, followed by Bray II, North Carolinaand Olsen-EDTA extractants. For determiningexchangeable K, Cadavid (1988) found no signif-icant difference between the use of Bray II andNH4-acetate; both resulted in a critical level of0.175 meq K 100 g−1.

Plant tissue analysis

Analysis of plant tissue indicates the actualnutritional status of the plants. The totalamount of a certain nutrient is determined,resulting in data that are fairly similar amongdifferent laboratories. These analyses are partic-ularly useful for diagnosing N and secondary ormicronutrient deficiencies.

Given that nutrient concentrations varyamong different tissues, it is imperative to use an‘indicator’ tissue, the nutrient concentration ofwhich is best related to plant growth or yield. Forcassava, the best ‘indicator’ tissue is the blade

of the youngest fully expanded leaf (YFEL), i.e.normally about the fourth to fifth leaf fromthe top. Blades without petioles are analysedas nutrient concentrations are quite differentin these two tissues (Table 7.8). Nutrient con-centrations also change during the growthcycle, depending on the rate of plant growth(Howeler and Cadavid, 1983; CIAT, 1985a,b).As they tend to stabilize after about 4 months,leaf samples should be taken at about 4 MAP.

About 20 leaf blades (without petioles) arecollected from a plot or uniform area in the fieldand combined into one sample (Howeler, 1983).If leaves are dusty or have received chemicalsprays, they should be washed gently and rinsedin distilled or deionized water. To prevent con-tinued respiration with consequent loss of DM,leaves should be dried as soon as possible at60–80°C for 24–48 h. If no oven is available,leaves should be dried as quickly as possible in thesun, preferably in a hot but well-ventilated area,and away from dust. After drying, samples arefinely ground in a lab mill. For Cu analysissamples should be passed through a stainlesssteel sieve. For Fe analysis the dry leaves shouldbe ground with an agate mortar and pestle.Samples are normally collected in paper bags tofacilitate drying, but for analysis of B, plastic bagsshould be used. Once ground and sieved, samplesare stored in plastic vials until analysis.

To diagnose nutritional problems, the resultsare compared with the nutrient ranges corre-sponding to the various nutritional states of theplant (Table 7.9), or with critical levels reportedin the literature (Table 7.10). While the numbersmay vary somewhat given the different varieties,soil and climatic conditions (Howeler, 1983), thedata in these tables can be used as a general guidefor interpreting plant tissue analyses.

128 R.H. Howeler

Footnote for Table 7.7.aCritical level defined as 95% of maximum yield.bCritical level defined as 90% of maximum yield.cMethods:

Bray I = 0.025 N HCl + 0.03 N NH4F.Bray II = 0.10 N HCl + 0.03 N NH4F.Olsen-EDTA = 0.5 N NaHCO3 + 0.01N Na-EDTA.North Carolina = 0.05 N HCl + 0.025 N H2SO4.NH4-acetate = 1 N NH4 -acetate at pH 7.

dPhaseolus vulgaris.

Greenhouse and field experiments

If analysis of soil or plant tissue is notpossible, one can also diagnose nutritionalproblems by planting cassava in pot experi-ments using the soil in question, or directlyin the field. To diagnose nutrient deficienciesin a particular soil in either pot or field

experiments, it is recommended to use the‘missing element’ technique, where all nutrientsare applied to all treatments at rates thatare expected to be non-limiting, while onenutrient is missing in each treatment (i.e.-N, -P, -K, etc.). Treatments with the poorestgrowth or yield indicate the element that is mostdeficient.


(%) (µg g−1)

N P K Ca Mg S Fe Mn Zn Cu B

UnfertilizedLeaf blades

UpperMiddleLowerFallena

PetiolesUpperMiddleLowerFallen

StemsUpperMiddleLower

RootsRootletsa

Thickened roots

4.573.663.312.31

1.500.700.630.54

1.641.030.78

1.520.42

0.340.250.210.13

0.170.100.090.05

0.200.180.21

0.150.10

1.291.181.090.50

1.601.321.350.54

1.220.870.81

1.020.71

0.681.081.481.69

1.322.202.693.52

1.531.451.19

0.770.13

0.250.270.250.25

0.370.430.450.41

0.320.300.32

0.380.06

0.290.250.250.22

0.100.100.130.13

0.190.160.16

0.160.05

198267335

4850

797692

271

13374

184

5985127

128185191209

172304361429

115103

95

19110

496689

121

4072

11094

363954

16516

9.98.77.69.4

4.42.92.82.5

9.78.97.9

–3.0

26374239

16151518

141310

104

FertilizedLeaf blades

UpperMiddleLowerFallena

PetiolesUpperMiddleLowerFallen

StemsUpperMiddleLower

RootsRootletsa

Thickened roots

5.194.003.551.11

1.490.840.780.69

2.131.571.37

1.710.88

0.380.280.240.14

0.170.090.090.06

0.230.210.28

0.190.14

1.611.361.300.54

2.181.841.690.82

2.091.261.14

1.031.05

0.761.081.401.88

1.582.583.543.74

2.091.301.31

0.710.16

0.280.270.220.23

0.360.410.420.20

0.470.260.23

0.330.06

0.300.260.230.19

0.100.070.070.08

0.140.110.09

0.200.05

298430402

3333

878895

294

94110210

3780127

177207220247

238359417471

140120

99

36815

476377

120

334970

155

374636

13615

10.69.68.58.9

4.93.03.23.1

9.810.810.0

–3.9

26303738

17141517

141210

104

aFallen leaves and rootlets were probably contaminated with micronutrients from the soil.Source: Howeler (1985a).

Table 7.8. Nutrient concentration in various plant parts of fertilized and unfertilized cassava cv. M Ven77 at 3–4 MAP in Carimagua, Colombia.

For pot experiments it is recommended notto sterilize or fumigate the soil, in order not tokill the native mycorrhizas. Rooted plant shootsrather than stakes should be used as the stakeshave high nutrient reserves and their use wouldtherefore delay responses to nutrient additions.In pot experiments cassava plants are generallyharvested 3–4 MAP, and dry weights of topgrowth are used as indicators of nutrientresponse.

Correcting Nutritional Disorders

Chemical fertilizers

While cassava performs better than most cropson infertile soils, the crop is highly responsiveto fertilizer applications. High yields can beobtained and maintained only when adequateamounts of fertilizers and/or manures areapplied. Thousands of fertilizer experiments con-ducted by FAO worldwide indicate that cassavais as responsive to fertilizer applications as othercrops, with yield increases of 49% (West Africa)

to 110% (Latin America) versus increases of43% (yams and rice in West Africa) to 102%(rice in Latin America) for other crops. In WestAfrica (Ghana) cassava responded mainly toK, in Latin America (Brazil) to P, and in Asia(Indonesia and Thailand) to N (Richards, 1979;Hagens and Sittibusaya, 1990).

Cassava is sensitive to over-fertilization,especially with N, which will result in excessiveleaf formation at the expense of root growth.Cock (1975) reported that cassava has anoptimal leaf area index (LAI) of 2.5–3.5 and thathigh rates of fertilization may lead to excessiveleaf growth and an LAI > 4. High N applicationsnot only reduce the harvest index (HI) and rootyield, but can also reduce the starch and increasethe HCN content of the roots. Moreover, nutri-ents generally interact with each other, and theexcessive application of one nutrient may inducea deficiency of another. Howeler et al. (1977) andEdwards and Kang (1978) have shown that highrates of lime application may actually reduceyields by inducing Zn deficiency. Spear et al.(1978b) showed that increasing the K con-centration in nutrient solution decreased the

130 R.H. Howeler

Nutritional statesa

Nutrient Very deficient Deficient Low Sufficient High Toxic

N (%)P (%)K (%)Ca (%)Mg (%)S (%)B (µg g−1)Cu (µg g−1)Fe (µg g−1)Mn (µg g−1)Zn (µg g−1)

< 4.0< 0.25< 0.85< 0.25< 0.15< 0.20< 7.25< 1.5

< 100.25< 30.25< 25.25

4.1–4.80.25–0.360.85–1.260.25–0.410.15–0.220.20–0.27

7–151.5–4.8

100–11030–4025–32

4.8–5.10.36–0.381.26–1.420.41–0.500.22–0.240.27–0.30

15–184.8–6.0

110–12040–5032–35

5.1–5.80.38–0.501.42–1.880.50–0.720.24–0.290.30–0.36

18–286–10

120–14050–15035–57

> 5.8> 0.50

1.88–2.400.72–0.88

> 0.29> 0.3628–6410–15

140–200150–250

57–120

b−b

–> 2.40> 0.88

––

> 64.10> 15.10

> 200.10> 250.10> 120.10

aVery deficient, < 40% maximum yield.aDeficient, 40–80% maximum yield.aLow, 80–90% maximum yield.aSufficient, 90–100% maximum yield.aHigh, 100–90% maximum yield.aToxic, < 90% maximum yield.b– = no data available.Source: Howeler (1996a,b).

Table 7.9. Nutrient concentrations in youngest fully expanded leaf (YFEL) blades of cassava at 3–4MAP, corresponding to various nutritional states of the plants; data are averages of various greenhouseand field trials.


Element Method Plant tissue Critical levela Source

N deficiency

P deficiency

K deficiency

Ca deficiency

Mg deficiency

S deficiency

Zn deficiency

Zn toxicityB deficiency

B toxicity

Cu deficiencyCu toxicityMn deficiency

Mn toxicity

Al toxicity

FieldFieldFieldFieldNutrient solutionFieldFieldNutrient solutionNutrient solutionFieldFieldFieldFieldFieldFieldFieldFieldNutrient solutionFieldNutrient solutionNutrient solution

Nutrient solutionFieldNutrient solutionNutrient solutionFieldFieldNutrient solutionNutrient solutionFieldNutrient solutionFieldFieldNutrient solutionNutrient solutionFieldNutrient solutionNutrient solutionNutrient solutionNutrient solutionNutrient solutionNutrient solutionNutrient solutionNutrient solutionNutrient solutionNutrient solutionNutrient solutionNutrient solutionNutrient solution

YFEL bladesYFEL bladesYFEL bladesYFEL bladesShootsYFEL bladesYFEL bladesShootsYFEL bladesYFEL bladesYFEL bladesYFEL bladesYFEL bladesYFEL bladesYFEL bladesYFEL bladesYFEL bladesPetiolesPetiolesStemsShoots androotsYFEL bladesYFEL bladesShootsYFEL bladesYFEL bladesYFEL bladesYFEL bladesShootsYFEL bladesYFEL bladesYFEL bladesYFEL bladesYFEL bladesYFEL bladesYFEL bladesYFEL bladesYFEL bladesShootsYFEL bladesShootYFEL bladesYFEL bladesYFEL bladesShootsYFEL bladesShootsShootsRoots

5.1%5.7%4.6%5.7%4.2%0.41%

0.33–0.35%0.47–0.66%

1.1%1.2%1.4%1.5%

< 1.1%<1.5%1.7%1.9%1.9%0.8%2.5%0.6%0.8%

0.46%0.60–0.64%

0.4%0.29%

< 0.33% <0.29%0.24%0.26%0.32%0.27%

0.27–0.33%37–51 µg g−1

43–60 µg g−1

30 µg g−1

33 µg g−1

120 µg g−1

35 µg g−1

17 µg g−1

100 µg g−1

140 µg g−1

6 µg g−1

15 µg g−1

50 µg g−1

100–120 µg g−1

250 µg g−1

250–1450 µg g−1

70–97 µg g−1

2000–14,000 µg g−1

Fox et al. (1975)Howeler (1978)Howeler (1995)Howeler (1998)Forno (1977)CIAT (1985a)Nair et al. (1988)Jintakanon et al. (1982)Spear et al. (1978a)Howeler (1978)CIAT (1982)CIAT (1982)Kang (1984)CIAT (1985a)Howeler (1995)Nayar et al. (1995)Howeler (1998)Spear et al. (1978a)Howeler (1978)Spear et al. (1978a)Spear et al. (1978a)

CIAT (1985a)CIAT (1985a)Forno (1977)Edwards and Asher (unpublished)Kang (1984)Howeler (1985a)CIAT (1985a)Edwards and Asher (unpublished)Howeler (1978)CIAT (1982)Howeler, unpublishedCIAT (1978)Edwards and Asher (unpublished)Howeler et al. (1982c)CIAT (1985a)Howeler et al. (1982c)Howeler et al. (1982c)Forno (1977)Howeler et al. (1982c)Forno (1977)Howeler et al. (1982c)Howeler et al. (1982c)Howeler et al. (1982c)Edwards and Asher (unpublished)Howeler et al. (1982c)Edwards and Asher (unpublished)Gunatilaka (1977)Gunatilaka (1977)

aRange corresponds to values obtained in different varieties.YFEL, youngest fully expanded leaf.

Table 7.10. Critical nutrient concentrations for deficiencies and toxicities in cassava plant tissue.

absorption of Ca and especially Mg, leading toMg deficiency. However, in both nutrient solu-tion and field experiments with varying rates ofapplications of K, Ca and Mg, Howeler (1985b)did not find a significant effect of increasing Kon the Ca concentration in the leaves. The Mgconcentration decreased slightly in the field, butincreased in the nutrient solution experiment.Increasing Mg supply markedly decreased theconcentrations of K and Ca. Similarly, Ngongiet al. (1977) reported that high applicationsof KCl induced S deficiency in a low-S soil inColombia, while Nair et al. (1988) found thathigh rates of P application induced Zn deficiency.Hence, it is important not only to apply theright amount of each nutrient, but also the rightbalance among the various nutrients.

Nitrogen

Severe N deficiency is usually observed in verysandy soils low in OM, but may also be found inhigh-OM, but acid soils, mainly due to a low rateof N mineralization.

Significant responses to N have beenobserved more frequently in Asia than in LatinAmerica or Africa. In nearly 100 NPK trials con-ducted by FAO on farmers’ fields in Thailand,there was mainly a response to N, followed by Kand P (Hagens and Sittibusaya, 1990). Similarresults were obtained in 69 trials conducted inIndonesia (FAO, 1980). In Africa relatively fewfertilizer trials have been conducted with cas-sava, mainly because very few cassava farmersapply fertilizers. In West Africa the responses to N

were probably the most frequent (Okogun et al.,1999). In Latin America responses to N werethe least frequent, with significant responsesreported in only five out of 41 trials conducted inBrazil (Gomes, 1998) and in five out of 22 trialsconducted in Colombia (Howeler and Cadavid,1990).

On a very sandy soil (89% sand, 0.7% OM)in Jaguaruna, Santa Catarina, Brazil, two localvarieties showed a nearly linear response up to150 kg N ha−1. For both varieties highest yieldswere obtained with a split application of N, withone-third applied at 30, 60 and 90 days afterplanting (Moraes et al., 1981). A similarly spec-tacular response to N was also observed in a claysoil with 1.2% OM in Jatikerto, East Java, Indone-sia (Fig. 7.6). In this case, cassava was intercrop-ped with maize, which competed strongly for thelimited supply of N in the soil (Wargiono et al.,1998). In Nanning, Guangxi, China, there wasalso a highly significant response to N (ZhangWeite et al., 1998), up to 200 kg N ha−1 in onecultivar (SC205), but only up to 50 kg N ha−1

in the other (SC201). As the latter cultivar isextremely vigorous, high N levels produced toomuch top growth at the expense of root pro-duction. Similar negative responses to high Napplications have been reported by Acosta andPerez (1954), Vijayan and Aiyer (1969), Foxet al. (1975) and Obigbesan and Fayemi (1976).Krochmal and Samuels (1970) reported a rootyield reduction of 41% and top growth increaseof 11% due to high N applications. These highrates also stimulate production of N-containingcompounds, such as protein and HCN, and mayresult in a decrease in root starch content. High

132 R.H. Howeler

Fig. 7.6. Response of cassava cv. Faroka to the annual application of different levels of N, P and Kduring the seventh cycle in Jatikerto, East Java, Indonesia in 1994/95. (Source: Wargiono et al., 1998.)

rates of N application may also increase theintensity of diseases such as cassava bacterialblight (Kang and Okeke, 1984). Thus N ratesmust not only be adjusted to a particular soil butalso tailored to the needs of a particular cultivar.

Trials on optimum time and partitioningof N applications have generally shown non-significant differences between single applica-tions at planting, at 1 MAP or various partitions(0–3 MAP) using N rates up to 100 kg N ha−1

(Howeler, 1985a). At higher rates, partition ofthe nitrogen application was found to be betterthan a single application.

There are usually no significant differencesamong N sources such as urea, NH4NO3, mono-or di-ammonium phosphate. Vinod and Nair(1992) reported significantly higher yields withslow-release N sources such as neem cake-coatedurea or super-granules of urea.

When cassava is grown for forage produc-tion, spacing is greatly reduced (0.6 × 0.6 m),and green tops are cut off at 3–4 month intervals.The offtake of N is very high, sometimes> 300 kg N ha−1 year−1 (CIAT, 1988a,b;Putthacharoen et al., 1998). High rates of N(> 200 kg ha−1) need to be applied to sustainhigh levels of shoot and root production.

Phosphorus

Cassava’s tolerance to low P concentrations insoil solution is not due to the efficient uptake of Pby the root system; in fact, cassava grown inflowing nutrient solution required a muchhigher P concentration for maximum growththan rice, maize, cowpeas or common beans(Howeler et al., 1981; Jintakanon et al., 1982;Howeler 1990). When inoculated with endo-trophic VAM, the growth of cassava in nutrientsolution improved significantly (Howeler et al.,1982a). Masses of mycorrhizal hyphae growingin and around the fibrous roots of cassavamarkedly increased the plant’s ability to absorbP from the surrounding medium (Fig. 7.7).When planted in natural soil, the crop’s fibrousroots soon become infected with native soilmycorrhizas. The resulting hyphae grow intothe surrounding soil and help in the uptakeand transport of P to the cassava roots. Throughthis highly effective symbiosis, cassava is ableto absorb P from soils with low levels of available

P, mainly by extending the soil volume fromwhich P can be absorbed through the associatedmycorrhizal hyphae.

Responses of cassava to P applicationdepend on the available-P level of the soil, themycorrhizal population and the variety used.van der Zaag et al. (1979) reported highyields of 42 t ha−1 in an oxisol in Hawaii withonly 3 µg P g−1 (NaHCO3-extractant) using thecultivar Ceiba. CIAT (1988a) similarly reportedthat some varieties produced yields of 40–50 tha−1 without P application in a soil with only4.6 µg P g−1 (Bray II). In other soils with equallylow levels of available P but with a less-efficientmycorrhizal population, cassava responded verymarkedly to P applications. Thus in the oxisolsof the Eastern Plains of Colombia, with only1.0 µg P g−1 (Bray II), cassava respondedmarkedly to applications of 200–400 kg P2O5

ha−1 (Fig. 7.8). Of the seven P sources tested,banding of triple superphosphate (TSP) or broad-cast applications of basic slag were most effective.


Fig. 7.7. Comparison of a vesicular–arbuscularmycorrhizas (VAM)-inoculated plant (right) witha non-inoculated plant grown in a phosphorus-deficient nutrient solution.

Partially acidulated rock phosphate (RP) or RPmixed with elemental sulphur (S) were also quiteeffective in these acid soils (CIAT, 1978). Locallyproduced simple super phosphate (SSP) was lesseffective, except at high rates of application. Simi-larly, Santos and Tupinamba (1981) reportedsignificant responses to 60 or 120 kg P2O5 ha−1

in three soils of Sergipe, Brazil, with TSP andhyperphosphate being more effective than twolocal sources of RP. Soluble-P sources like TSP,SSP, mono- or di-ammonium phosphate shouldbe band applied near the stakes, while less-soluble sources such as basic slag and RPsshould be broadcast and incorporated. All Pshould be applied at or shortly after planting asfractionation of P had no significant effect onyield. Alternative methods of P application, suchas stake treatments or foliar sprays, are not aseffective as soil application in increasing yields(Howeler, 1985a).

Severe P deficiency has been reportedmainly in Latin America, particularly on oxisols,ultisols and inceptisols in Brazil and Colombia.These soils are highly P fixing and have available(Bray II or Mehlich I) P levels of only 1–2 µg g−1.During the first year(s) of cropping, cassavaresponds markedly to P application, but with

continuous cropping on the same land, res-ponses to P become less significant as soil Plevels build up from previous applications(Nair et al., 1988; Howeler and Cadavid, 1990;Kabeerathumma et al., 1990).

In Asia P deficiency is seldom the principallimiting factor for cassava production becausemost cassava is grown on soils with morethan 4 µg g−1 of available P and/or that havebeen previously fertilized with P. Nevertheless,significant responses to P application havebeen observed in Guangzhou (Guangdong),Nanning (Guangxi) and on Hainan Island ofChina; in northern and southern Vietnam; andon Leyte Island of the Philippines. In low-Psoils in Kerala State, India, significant initialresponses to 100 kg P2O5 ha−1 were reported,but these declined over time. Nair et al. (1988)determined an optimum economic rate of 45 kgP2O5 ha−1.

In Africa few P experiments have been con-ducted with cassava. Responses to P applicationhave been reported mainly in Ghana (Stephens,1960; Takyi, 1972) and Madagascar (Courset al., 1961). Ofori (1973) reported a negativeeffect of P application on cassava yields on aforest ochrosol in Ghana.

134 R.H. Howeler

Fig. 7.8. Response of cassava cv. Llanera to application of different levels and sources of P inCarimagua, Colombia. RP, rock phosphate; TSP, triple super-phosphate; SSP, single super-phosphate.(Source: CIAT, 1977.)

Large varietal differences have beenobserved in cassava’s ability to grow on low-Psoils (CIAT, 1988a,b). Pellet and El-Sharkawy(1993a,b) found that varietal differences inresponse to applied P were not due to geneticdifferences in P-uptake efficiencies, but ratherto contrasting patterns of DM distribution andP-use efficiency (root yield total per P in plant).Low-P tolerant cultivars had a high fine root-length density, moderate top growth, and a high,stable HI.

Potassium

Although K is not a basic component of protein,carbohydrates or fats, it plays an important rolein their metabolism. Potassium stimulates netphotosynthetic activity of a given leaf area andincreases the translocation of photosynthatesto the tuberous roots. This results in low carbo-hydrate levels in the leaves, further increasingphotosynthetic activity (Kasele, 1980).

Blin (1905), Obigbesan (1973) and Howeler(1998) reported that K application not onlyincreased root yields but also their starchcontent. Similar increases in starch content withincreasing applications of K have been observedin Carimagua (CIAT, 1982) and Pescador,Colombia (Howeler, 1985a), as well as in south-ern Vietnam (Nguyen Huu Hy et al., 1998) andChina (Howeler, 1998). In general root starchcontent increases up to 80–100 kg K2O ha−1 andthen decreases at higher rates of K application.Obigbesan (1973) and Kabeerathumma et al.(1990) reported that K also decreased the HCNcontent of roots, while Payne and Webster(1956) found highest levels of HCN in rootsproduced in low-K soils.

Potassium deficiency in cassava is generallyfound in tropical soils with low-activity claysuch as oxisols, ultisols and inceptisols, as wellas in alfisols derived from sandstone. After landclearing the alfisols have a reasonable level ofexchangeable K, but often show a significant Kresponse in the second year of planting becauseof low K reserves in the parent material (Kangand Okeke, 1984).

Long-term experiments in Asia and Colom-bia have shown that K deficiency invariablybecomes the main limiting factor when cassavais grown continuously on the same soil without

adequate K fertilization. Figure 7.9 shows that,without K application, yields declined from 22.4to 6.3 t ha−1 during 10 years of continuouscropping in Trivandrum, Kerala, India (Kabe-erathumma et al., 1990). During that time,exchangeable K of the soil gradually declinedfrom 0.18 to 0.064 meq 100 g−1. High yields of20–30 t ha−1 could be maintained with annualapplications of 100 kg N, 100 P2O5 and 100 K2Oha−1. The high rate of P used led to a buildup ofsoil P to excessive levels (~100 µg P g−1). Therewas also a slight buildup of exchangeable K to alevel of 0.25 meq 100 g−1. This contrasts withreports by Howeler and Cadavid (1990), whichshow that 8 years of continuous cropping withannual applications of 150 kg K2O ha−1 inQuilichao, Colombia, maintained the exchange-able K content at only 0.2 meq 100 g−1. In avery poor sandy soil near the Atlantic Coastof Colombia, Cadavid et al. (1998) also foundthat annual applications of 50 kg N, 50 P2O5 and50 K2O ha−1 increased yields during 8 yearsof continuous cropping, but had no effect onsoil K, which remained at a low level (0.06 meq100 g−1).

Long-term NPK trials were conducted infour Asian countries. After 4–10 years of contin-uous cropping, there was a significant responseto N in eight out of 11 sites, to P in four and to K inseven. Responses to K increased most markedlywith time (Nguyen Huu Hy et al., 1998; Howeler,2000), but in Malang, Indonesia, responses toN increased more markedly than elsewhere(Wargiono et al., 1998).

Data from short-term NPK trials conductedin Brazil (Gomes, 1998) indicate that significantresponses to K were obtained in only nine outof 48 trials; similarly in Colombia there was asignificant K response in six out of 22 locations,mainly in the Eastern Plains.

In Africa, significant responses to K havebeen found on strongly acid soils of easternNigeria (Okeke, unpublished) and on slightlyacid soils (0.23 meq K 100 g−1) of southwesternNigeria (Kang and Okeke, 1984). No significantresponse to K was observed in field experimentsconducted in Nigeria (Obigbesan, 1977) nor inGhana (Takyi, 1972). In Madagascar, however,Roche et al. (1957) and Cours et al. (1961) foundthat K was the main limiting nutrient, and appli-cations of 110 kg K2O ha−1 were recommended(Anon, 1952, 1953).


Experiments on different sources of Khave generally shown no significant differencesbetween the use of KCl, K2SO4 or Sulphomag(CIAT, 1985a), while in southern India the use of

syngenite and schoenite (extracted from sea-water) were also found to be equally effective(Central Tuber Crops Research Institute; CTCRI,1974, 1975). In low-S soils in the Eastern Plains

136 R.H. Howeler

Fig. 7.9. Cassava yield (top) and the exchangeable K content of the soil (bottom) during 10 years ofcontinuous cropping with various NPK treatments in Trivandrum, Kerala, India. (Source: Kabeerathummaet al., 1990.)

of Colombia, Ngongi et al. (1977) obtained muchbetter yields with application of K2SO4 or KCl + Sthan with KCl. However, this was mainly aresponse to S; the same experiment conducted inJamundí, Colombia, did not show any differencebetween K sources.

Experiments on the optimum time of Kapplication have produced somewhat contra-dictory results, but generally there were nosignificant differences between single or splitapplications, or, among different times of appli-cation (CIAT, 1982). Overall, a single applica-tion at one MAP produced the highest yield.In India, Ashokan and Shreedharan (1980)recommended split application of K only whenlow rates were applied, but CTCRI (1972) foundno significant differences among different timesof application in Trivandrum, India.

Calcium and magnesium

Calcium plays an important role in the supplyand regulation of water in the plant, while Mg isa basic component of chlorophyll and as such isessential for photosynthesis.

Symptoms of Ca deficiency are seldomobserved in the field; but in very acid soilswith low levels of exchangeable Ca (< 0.25meq 100 g−1), the crop may respond to Caapplications. In Carimagua-Alegría, Colombia,highly significant responses to application ofCa were obtained on a sandy loam soil with apH of 5.1 and only 0.18 meq Ca 100 g−1 and0.05 meq Mg 100 g−1. Highest yields wereobtained with application of 200–400 kg Caha−1 as broadcast gypsum. Broadcast calcitic ordolomitic limes were less effective, while band-applied gypsum was ineffective in increasingcassava yields (CIAT, 1985a). As these Casources are relatively insoluble, they should allbe broadcast and incorporated before planting.The good response to gypsum was not a responseto S because either MgSO4 or S were applieduniformly to all plots.

In the same soil in Carimagua, an experi-ment was conducted to determine the optimumrates and best sources of Mg (CIAT, 1985a).There was a significant response up to thehighest level of 60 kg Mg ha−1, but there wereno overall significant differences among sources;the more soluble Sulphomag was more effective

at intermediate rates, while banded MgSO4

or broadcast MgO were better at higher rates ofapplication.

Experiments conducted in nutrient solutionculture showed that increasing concentrationsof Ca in solution markedly reduced the concen-trations of K and Mg in YFEL blades at 2 MAP,and that increasing concentrations of Mg insolution similarly decreased the concentrationsof K and Ca in the leaves. In field experiments inCarimagua, however, increasing levels of Caor Mg had no effect on leaf concentration of K,and only slightly decreased the concentrationsof Mg or Ca, respectively (Howeler, 1985b).There appears to be a strong antagonistic effectbetween K and Mg and between Ca and Mg, butnot between K and Ca.

Sulphur

This basic component of certain amino acidsis essential for producing protein. In industrialareas much of the plant’s S requirements aremet from S emissions into the atmosphere, butin isolated areas cassava may suffer from Sdeficiency. This has been reported only forCarimagua, Colombia, which is far removedfrom any industrial centres. Soils there con-tained only 23 µg of Ca phosphate-extractable Sg−1 of soil; with application of 40 kg S ha−1 aselemental S this increased to 36 µg g−1. Therewas a response to applying S up to 20–40 kgS ha−1. There were no significant differencesamong S sources although yields were slightlyhigher with banded K- and Mg-sulphate thanwith broadcast elemental S. Clear S-deficiencysymptoms were observed in the control plots.These plants had 0.20–0.25% S in YFEL blades,compared with 0.30–0.32% in plants thathad received S applications. Critical levels of0.27 and 0.33% S were estimated in two fieldexperiments (Howeler, unpublished).

Micronutrients

Deficiencies are generally observed in high pH orcalcareous soils, but deficiencies of Zn have beenobserved in both acid and alkaline soils. Limeapplication to acid soils with low levels of avail-able Zn may induce Zn deficiency, resulting in


low yields and even death of young plants (seeAcid soils, below).

Zinc

Cassava is quite susceptible to Zn deficiency,especially in the early stages of growth. Plantsshowing early symptoms of Zn deficiency maylater recuperate once the fibrous root system iswell established and roots become infected withmycorrhizas. If the deficiency is severe, however,plants may either die or produce very low yields.The response of two varieties to soil applicationof different levels of Zn as ZnSO4.7H2O was testedin Carimagua-Alegría after applying 2 t ha−1

of lime (CIAT, 1985a). Both varieties were seri-ously affected by Zn deficiency in the check plots,but reached maximum yields with applicationof 10 kg Zn ha−1, band applied with NPK atplanting. A critical level of 33 µg Zn g−1 in YFELblades was estimated. Broadcast application of10–20 kg ha−1 of Zn as ZnO was also effective inincreasing yields in acid soils (CIAT, 1978).

In high-pH soils, application of ZnSO4.7H2Oto the soil is not as effective because the appliedZn is precipitated rapidly (CIAT, 1978). Foliarapplication or stake treatments may be moreeffective. When 20 cassava cultivars were plantedin a high-pH (7.9), low-Zn (1.0 µg g−1) soil, withor without treating stakes for 15 min in a solu-tion of 4% ZnSO4.7H2O before planting, yieldsincreased from an average 11.5 to 25.0 t ha−1 dueto the Zn treatment (CIAT, 1985a). Large vari-etal differences in low-Zn tolerance were observed,with some cultivars dying off completely withoutthe Zn treatment, while others produced highyields with or without Zn. Dipping stakes for15 min in a ZnSO4.7H2O solution and air-dryingthe stakes overnight before planting is a veryinexpensive yet effective way to reduce Zn defi-ciency in cassava when grown on low-Zn soils.

Copper

This deficiency in cassava has been reportedonly on peat soils in Malaysia (Chew, 1971).Chew et al. (1978) recommended a basalapplication of 2.5 kg Cu ha−1 as CuSO4. 5H2O.

Iron and manganese

Deficiency symptoms of Fe are often observedin calcareous soils such as in the Yucatan

peninsula of Mexico, parts of northern Colom-bia, southeast Java of Indonesia and westernNakorn Rachasima province of Thailand. Mndeficiency has been observed in sandy soilsalong the coast in northeast Brazil, in alkalinesoils at CIAT, Colombia, and in northern Viet-nam, near houses where lime had been used fortheir construction. A practical solution is proba-bly a stake treatment with 2–4% FeSO4.H2O orMnSO4.4H2O before planting, or foliar sprayswith sulphates or chelates.

Boron

Symptoms of B deficiency have been observed inboth acid soils of Carimagua and Quilichao, aswell as in alkaline soils at CIAT, Colombia. Simi-lar symptoms were also observed in North Viet-nam and southern China, although the exactnature of that problem was never identified. InColombia, application of 1–2 kg B ha−1, bandapplied as borax at planting, eliminated thesymptoms, increased plant height, increased Bconcentrations in the leaves from 3 to 40 µg g−1,but had no significant effect on yield. Thus itseems that cassava is quite tolerant of low levelsof available B in the soil.

Soil Amendments

Soil amendments are usually applied to increasethe pH of acid soils or decrease the pH ofalkaline soils, but they can also serve to improvethe physical conditions of the soil or improvenutrient availability.

Acid soils

Very acid soils present a complex of problems forplant growth, including low pH, high concen-trations of Al and/or Mn, low levels of Ca, Mgand K, and sometimes low P and N. Cassava as aspecies is particularly tolerant of soil acidity andhigh levels of Al (Gunatilaka, 1977; CIAT,1979; Islam et al., 1980), but some varietal dif-ferences in acid soil tolerance have also beenobserved (CIAT, 1982, 1985a; Howeler, 1991a).In very acid (pH < 4.5) and high Al ( > 80% Alsaturation) soils, lime application may increasecassava yields, mainly by supplying Ca and Mg

138 R.H. Howeler

as nutrients. High rates of lime may, however,induce micronutrient deficiencies, particularlyZn, resulting in decreased yield (Spain et al.,1975; Edwards and Kang, 1978). Field trails(CIAT, 1976) showed that without Zn, cassavaresponded to lime applications only up to2 t ha−1, but with applied Zn there was a positiveresponse up to 6 t ha−1 of lime. Analysis of cas-sava leaves confirmed that liming reduced Znuptake and that with 6 t ha−1 of lime withoutZn, the Zn concentrating in YFEL blades droppedbelow the critical level of 40–50 µg g−1. Largevarietal differences have been found for bothhigh-Al and low-Zn tolerance (Spain et al.,1975).

Saline–alkaline soils

Cassava is not well adapted to saline and alka-line soils and may suffer from a combination ofhigh pH, high Na, high salt and low uptakeof micronutrients. Yields can be improved byapplying 1–2 t ha−1 of elemental S or 1–2 t ha−1

of H2SO4 (CIAT, 1977), but this is seldom justi-fied economically. Most cultivars will tolerate apH up to about 8.0, Na saturation up to about2%, and conductivity up to 0.5 mS cm−1 (CIAT,1977). Large varietal differences in tolerancehave been observed, and the use of tolerantvarieties is probably the most practical solution.

Animal manures and compost

Many cassava farmers apply animal manuresor compost to cassava with good results, butlittle research has been conducted to determineoptimum rates and methods of application.

In Vietnam and south China, most farmersapply 5–10 t ha−1 of pig manure, in Indonesia upto 9 t ha−1 of cattle manure, and in Cauca prov-ince of Colombia, 4–5 t ha−1 of chicken manure.Animal manures tend to have low nutrient con-tents (< 10% of that in most compound fertiliz-ers), but they do contain Ca, Mg, S and somemicronutrients not found in most chemicalfertilizers (Howeler, 1980b). In addition, theymay improve the physical conditions of the soil,although this has not been well documented.

Silva (1970) reported good responses toapplications of 6–15 t ha−1 of cattle manure in

Rio Grande do Norte of Brazil; higher applica-tions decreased yields. Howeler (1985a) reportedthat 4.3 t ha−1 chicken manure (correspondingto 170 kg P2O5 ha−1) increased cassava yields inMondomo, Colombia, from 19 to 31 t ha−1. Thechicken manure was about twice as effective ascattle manure or 10–30–10 compound fertilizer,applied at equivalent levels of P. The totalamount of nutrients applied with the chickenmanure was considerably higher than thatapplied in the chemical fertilizer, but the greaterbeneficial effect must also be due to improvedsoil structure, the presence of essential elementsother than NPK, and the stimulation of beneficialmicroorganisms such as VAM. If these manureshave to be transported over long distances, thehigher cost of transport and application maymake them more expensive than chemical fertil-izers. Moreover, in many countries like Thailand,animal manures are not readily available.

In Bahia, Brazil, Gomes et al. (1983)obtained very high yields with a system called‘parcagem’, which is basically in situ applicationof cattle manure, where a large number of cattleare enclosed overnight on a small piece of land. Itwas calculated that 30 animals kept overnighton 1 ha for 60 days will produce about 8 t of drymanure containing 40 kg N (plus the N in theurine). At an equal dosage of 40 kg N ha−1, cas-sava yields with the parcagem system (combinedwith additional P and K) increased 30–90% ascompared to application of only chemical fertiliz-ers. This system may be economically viable inareas with large cattle populations. Good resultswere also obtained in Bahia when applying5 t ha−1 of cattle manure combined with 10 kgP2O5 ha−1 (Diniz et al., 1994).

Little information is available on the effec-tiveness of applying compost, which is consider-ably lower in nutrients than animal manures(Howeler et al., 2002); but when applied inlarge quantities (10–15 t ha−1), they maysupply considerable amounts of nutrients aswell as improving the soil’s physical condi-tion and water-holding capacity. Application of6–10 t ha−1 of compost made from cassava peelresidues in starch factories has given promisingresults in Thailand. In Brazil the application of5 t ha−1 of vinhoto (a by-product of alcoholproduction) increased yields, especially whenfortified with 60 kg P2O5 and 1 t lime (Souzaet al., 1992).


Green manures, cover crops and mulch

Planting of green manures and their subsequentmulching or incorporation into the soil have beenpractised traditionally as a form of ‘improvedfallow’ to maintain soil fertility. Research on theuse of green manures and cover crops to main-tain soil fertility in cassava fields was recentlyreviewed (Howeler et al., 2002a, b). In theabsence of chemical fertilizers, green manuresincreased yields slightly in Quilichao, Colombia,but significantly on sandy soils in Media Luna,Colombia. In the presence of fertilizers the effectwas minimal. Most effective were kudzu(Puerarea phaseoloides), Zornia (Zornia latifolium)and groundnuts (Arachis hypogea) in Quilichao,and local weeds and Canavalia ensiformis inMedia Luna. In Thailand, Crotalaria juncea wasthe most productive and effective in increasingyields. The growing of green manures beforeplanting cassava was found to be impractical,however, as cassava yields were markedlyreduced by planting too late in the wet season(Howeler, 1992, 1995).

Research on cover crops in both Colombia(Muhr et al., 1995; Ruppenthal, 1995) andThailand (Howeler, 1992; Tongglum et al.,1992, 1998) indicate that almost all speciescompete too strongly with cassava for soilwater and nutrients, resulting in unacceptablylow cassava yields, especially in the secondand third year after cover-crop establishment. Itis clear that cassava is a weak competitor, andyields are seriously reduced by competition fromweeds or cover crops.

Planting intercrops such as maize, ground-nut, cowpea, common bean, mungbean or soy-bean and incorporating the residue after harvestmay improve soil fertility (especially if the inter-crops are fertilized), help reduce erosion andprovide the farmer with additional food orincome, without reducing cassava yields tooseriously (Leihner, 1983).

Application of mulch of local weeds, cut-and-carry grass or crop residues such as ricestraw or maize stalks can also improve soilfertility and moisture, as well as reduce surfacetemperature and erosion. In Africa applicationof mulch, especially that of leguminous species,increased cassava yields in acid sandy soils(Ofori, 1973; Hulugalle et al., 1991). In sandysoils on the Atlantic Coast of Colombia, Cadavid

et al. (1998) reported that annual applicationsof 12 t ha−1 of dry Panicum maximum grassas mulch significantly increased cassava yieldsduring eight consecutive years of cropping, espe-cially in the absence of chemical fertilizers. It alsoincreased root DM content and decreased HCNlevels. Annual mulching gradually increased soilP and especially soil K, and prevented a decline insoil Ca and Mg. In addition, the mulch coverreduced soil temperatures in the top 20 cm ofsoil and enhanced the maintenance of soil C.Thus application of mulch, where available,can be another effective way of improving soilproductivity.

Inoculation with mycorrhizas

As indicated above, cassava can grow well inlow-P soils because of a highly efficient symbio-sis with VAM, which occur naturally in thesoil. Without VAM, cassava would require anapplication of at least 1–2 t ha−1 of P to obtainthe same yield as plants with VAM but withoutP (Howeler, 1980a; Howeler et al., 1982b).Compared with six other tropical crops andforages, cassava was found to be the mostdependent on VAM (Howeler et al., 1987).

Soils, however, differ in both quantity andquality of native mycorrhizae and, thus, in thecrop’s responses to P application (Sieverding andHoweler, 1985; Howeler et al., 1987). Of manyVAM species tested, Glomus manihotis was one ofthe most effective species for increasing cassavagrowth and yield in acid soils. G. manihotis wasalso found to compete strongly with other VAMspecies in the range of 50–200 kg ha−1 of appliedP. Inoculation with G. manihotis markedlyincreased cassava growth in greenhouse experi-ments using sterilized soils. The effect was sig-nificant but less dramatic in non-sterilized soil.When plots in the field were sterilized withmethyl bromide to kill the native VAM in thetopsoil, re-inoculation of the soil with VAMmarkedly improved initial plant growth (Fig.7.10). Non-inoculated plants grew poorly,showing clear symptoms of P deficiency. Oncethe roots of these non-inoculated plants reachedthe non-sterilized subsoil, however, they soonbecame infected with VAM and recuperated.In Quilichao, Colombia, which has a highlyeffective native VAM population dominated by G.

140 R.H. Howeler

manihotis, non-inoculated plants in the sterilizedplots attained as high yields as those in theunsterilized soil. Inoculated plants growingin the sterilized soil produced 40% higher yields(Howeler et al., 1982b). In other experimentsat Quilichao, soil sterilization markedly reducedyields, but inoculation of plants growing inunsterilized soil did not increase yields becauseof the highly effective native VAM population.

In soils with a less effective native VAMpopulation, such as in Carimagua, Colombia,inoculation of plants grown in sterilized soilincreased yields nearly threefold without appliedP and 164% with 100 kg P ha−1. In unsterilizedsoil the effect of inoculation was not significantwithout applied P, but significant with 100 kg Pha−1. In a similar trial in Carimagua, using differ-ent sources of P, VAM inoculation in unsterilizedsoil had no effect without P application butincreased yields significantly (22%) at an inter-mediate application of 100 kg P ha−1 (Howelerand Sieverding, 1983).

Numerous experiments on VAM inocula-tion of cassava growing in natural soils in Colom-bia indicate that responses vary from locationto location, depending on the efficiency of thenative VAM population and the ability of theintroduced species to compete with the nativepopulation. In areas with less-effective nativepopulations, such Carimagua, Colombia, yieldsincreased 23% by inoculation, but this maydecrease over time once cassava cultivation has

stimulated a build-up of native mycorrhizas.In other locations the effect of inoculationwas smaller and not consistent. It is clear thatmycorrhizas are absolutely essential for cassavagrowth, but it seems difficult to improve on analready highly efficient, naturally occurringsymbiosis.

References

Abruña, F., Perez-Escolar, R., Vicente-Chandler, J.,Figarella, J. and Silva, S. (1974) Response of greenbeans to acidity factors in six tropical soils. Journalof Agriculture (University of Puerto Rico) 58(1),44–58.

Acosta, J.R. and Perez, G.J. (1954) Abonamiento enyuca. Suelo Tico (Costa Rica) 7, 300–308.

Amarasiri, S.L. and Perera, W.R. (1975) Nutrientremoval by crops growing in the dry zone of SriLanka. Tropical Agriculturist 131, 61–70.

Anon. (1952) Le manioc. Recherche Agronomique deMadagascar 1, 49–52.

Anon. (1953) Essais de fumure du manioc. RechercheAgronomique de Madagascar. Compte Rendu 2,85–88.

Asher, C.J., Edwards, D.G. and Howeler, R.H. (1980)Nutritional Disorders of Cassava (Manihotesculenta Crantz). University of Queensland,St Lucia, Queensland, Australia.

Ashokan, P.K. and Sreedharan, C. (1980) Effect ofpotash on growth; yield and quality of tapiocavariety H. 97. In: Proceedings National Seminar onTuber Crops Production Technology, Tamil Nadu


Fig. 7.10. Comparison of plants inoculated with vesicular–arbuscular mycorrhizas (VAM); (right) andnon-inoculated plants in plots previously sterilized with methyl bromide.

Agricultural University, Coimbatore, TamilNadu, India, pp. 78–80.

Blin, H. (1905) La fumure du manioc. BulletinEconomique de Madagascar 3, 419–421.

Cadavid, L.F. (1988) Respuesta de la yuca (Manihotesculenta Crantz) a la aplicacion de NPK ensuelos con diferentes características. Monograph,Universidad Nacional de Colombia, Palmira,Colombia.

Cadavid, L.F., El-Sharkawy, M.A., Acosta, A. andSanchez, T. (1998) Long-term effects of mulch,fertilization and tillage on cassava grown in sandysoils of northern Colombia. Field Crops Research57, 45–56.

CTCRI (1972) Annual Report 1971. CTCRI, Trivan-drum, India.



CIAT (1976) Annual Report for 1975. CIAT, Cali,Colombia.



CIAT (1979) Annual Report for 1978. CIAT, Cassavaprogram. Cali, Colombia, pp. A76–84.

CIAT (1980) Cassava program. Annual Report for 1979.CIAT, Cali, Colombia.

CIAT (1982) Cassava program. Annual Report for 1981.CIAT, Cali, Colombia.

CIAT (1985a) Cassava program. Annual Report for1982 and 1983. CIAT, Cali, Colombia.

CIAT (1985b) Cassava program. Annual Report for1984. Working Document No. 1. CIAT, Cali,Colombia.

CIAT (1988a) Cassava program. Annual Report for1985. Working Document No. 38. CIAT, Cali,Colombia.

CIAT (1988b) Cassava program. Annual Report for1986. Working Document No. 43. CIAT, Cali,Colombia.

CIAT (1998) Improving Agricultural Sustainability inAsia. Integrated Crop-Soil Management forSustainable Cassava-Based Production Systems.End-of-Project Report, 1994–1998 submittedto the Nippon Foundation. CIAT, Cali,Colombia.

Chan, S.K. (1980) Long-term fertility considerations incassava production. In: Weber, E.J., Toro, J.C. andGraham, M. (eds) Workshop on Cassava CulturalPractices, Salvador, Bahia, Brazil, 18–21 March,IDRC-151e, pp. 82–92.

Chew, W.Y. (1971) The performance of tapioca, sweetpotato and ginger on peat at the Federal Experi-ment Station, Jalan Kebun, Selangor. Agronomy

Branch, Division of Agriculture, Kuala Lumpur,Malaysia.

Chew, W.Y., Ramli, K. and Joseph, K.T. (1978) Copperdeficiency of cassava (Manihot esculenta Crantz)on Malaysian peat soil. MARDI Research Bulletin6(2), 208–213.

Cock, J.H. (1975) Fisiología de la planta y desarrollo.In: Curso sobre Produccion de Yuca. InstitutoColombiano Agropecuario, Regional 4, Medellín,Colombia.

Cong Doan Sat and Deturck, P. (1998) Cassava soilsand nutrient management in South Vietnam. In:Howeler, R.H. (ed.) Cassava Breeding, Agronomyand Farmer Participatory Research in Asia, Proceed-ings 5th Regional Workshop, Danzhou, Hainan,China, 3–8 November 1996, pp. 257–267.

Cours, G., Fritz, J. and Ramahadimby, G. (1961) Eldiagnóstico felodérmico de la mandioca. Fertilité12, 3–20.

Diniz, M. de S., Gomes C. J. de and Caldas, R.C. (1994)Sistemas de adubação na cultura da mandioca.Revista Brasileira de Mandioca (Cruz das Almas,Bahia, Brazil) 13, 157–160.

Edwards, D.G. and Kang, B.T. (1978) Tolerance ofcassava (Manihot esculenta Crantz) to high soilacidity. Field Crops Research 1, 337–346.

EMBRAPA, CNPMF (1981) Relatória Técnico Annual.Projecto de Mandioca. Cruz das Almas, Bahia,Brazil, pp. 119–167.

EMBRAPA, CNPMF (1984) Relatória Técnico Annual doCNPMF 1983. Cruz das Almas, Bahia, Brazil.

FAO (1980) Review of Data on Responses of Tropical Cropsto Fertilizers, 1961–1977. FAO, Rome, Italy.

Forno, D.A. (1977) The mineral nutrition of cassava(Manihot esculenta Crantz) with particularreference to nitrogen. PhD thesis. University ofQueensland, St Lucia, Queensland, Australia.

Fox, R.H., Talleyrand, H. and Scott, T.W. (1975) Effectof nitrogen fertilization on yields and nitrogencontent of cassava, Llanera cultivar. Journalof Agriculture (University of Puerto Rico) 56,115–124.

Goepfert, C.F. (1972) Experimento sobre o efeito resid-ual da adubação fosfatada em feijoeiro (Phaseolusvulgaris). Agronomia Sulriograndense 8, 41–47.

Gomes, C.J. de (1998) Adubação de mandioca. CursoInternacional de Mandioca para Países Africanosde Lingua Portuguesa. Cruz das Almas, Bahia,Brazil, 13–30 April.

Gomes, C.J. de and Ezeta, F.N. (1982) Nutrição eadubação potássica da mandioca no Brasil.In: Anais de Simpósio Sobre Potássio na Agric-ultura Brasileira, Londrina, Paraná. Institutoda Potassa/IAPAR, Piracicaba, SP, Brazil,pp. 487–502.

Gomes, C.J. de, Souza, R.F., Rezende, J. de O. and Lemos,L.B. (1973) Efeitos de N, P, K, S, micronutrientes e

142 R.H. Howeler

calagem na cultura de mandioca. Boletim Técnico20. Instituto de Pesquisa Agropecuária doLeste (IPEAL). Cruz das Almas, Bahia, Brazil,pp. 49–67.

Gomes, C.J. de, Carvalho, P.C.L. de, Carvalho, F.L.C.and Rodrigues, E.M. (1983) Adubação orgânicona recuperação de solos de baixa fertilidade com ocultivo da mandioca. Revista Brasileira deMandioca (Cruz das Almas, Bahia, Brazil) 2(2),63–76.

Gunatilaka, A. (1977) Effects of aluminium con-centration on the growth of corn, soybean, andfour tropical root crops. MSc thesis. University ofQueensland, St. Lucia, Queensland, Australia.

Hagens, P. and Sittibusaya, C. (1990) Short and longterm aspects of fertilizer applications on cassavain Thailand. In: Howeler, R.H. (ed.) Proceedings8th Symposium International Society of TropicalRoot Crops, Bangkok, Thailand, 30 October–5November, 1988, pp. 244–259.

Howeler, R.H. (1978) The mineral nutrition andfertilization of cassava. In: Cassava ProductionCourse. CIAT, Cali, Colombia, pp. 247–292.

Howeler, R.H. (1980a) The effect of mycorrhizal inocu-lation on the phosphorus nutrition of cassava.In: Weber, E.J., Toro, J.C. and Graham, M. (eds)Cassava Cultural Practices, Proceedings Work-shop, Salvador, Bahia, Brazil, 18–21 March,International Development Research Centre(IDRC) 151e, Ottawa, Canada, pp. 131–137.

Howeler, R.H. (1980b) Soil-related cultural practicesfor cassava. In: Weber, E.J., Toro, J.C. and Gra-ham, M. (eds) Cassava Cultural Practices, Proceed-ings Workshop, Salvador, Bahia, Brazil, 18–21March, IDRC 151e, Ottawa, Canada, pp. 59–69.

Howeler, R.H. (1981) Mineral Nutrition and Fertilizationof Cassava. Series 09EC-4, CIAT, Cali, Colombia.

Howeler, R.H. (1983) Análisis del Tejido Vegetal enel Diagnóstico de Problemas Nutricionales: AlgunosCultivos Tropicales. CIAT, Cali, Colombia.

Howeler, R.H. (1985a) Mineral nutrition and fertiliza-tion of cassava. In: Cassava; Research, Productionand Utilization. UNDP-CIAT Cassava Program,Cali, Colombia, pp. 249–320.

Howeler, R.H. (1985b) Potassium nutrition of cassava.In: Potassium in Agriculture. International Sympo-sium, Atlanta, GA, 7–10 July. ASA, CSSA, SSSA,Madison, Wisconsin, USA, pp. 819–841.

Howeler, R.H. (1986) El control de la erosión con prác-ticas agronómicas sencillas. Suelos Ecuatoriales16, 70–84.

Howeler, R.H. (1987) Soil conservation practices incassava-based cropping systems. In: Tay, T.H.,Mokhtaruddin, A.M. and Zahari, A.B. (eds)Proceedings International Conference SteeplandAgriculture in the Humid Tropics, Kuala Lumpur,Malaysia, 17–21 August, pp. 490–517.

Howeler, R.H. (1989) Cassava. In: Plucknett, D.L. andSprague, H.B. (eds) Detecting Mineral Deficienciesin Tropical and Temperate Crops. Westview Press.Boulder, Colorado, pp. 167–177.

Howeler, R.H. (1990) Phosphorus requirements andmanagement of tropical root and tuber crops.In: Proceedings Symposium on Phosphorus Require-ments for Sustainable Agriculture in Asia andOceania. IRRI, Los Baños, Philippines. 6–10March, 1989, pp. 427–444.

Howeler, R.H. (1991a) Identifying plants adaptable tolow pH conditions. In: Wright, R.J., Baligar, V.C.and Murrmann, R.P. (eds) Plant-Soil Interactionsat Low pH. Kluwer Academic, The Netherlands,pp. 885–904.

Howeler, R.H. (1991b) Long-term effect of cassavacultivation on soil productivity. Field CropsResearch 26, 1–18.

Howeler, R.H. (1992) Agronomic research in the AsianCassava Network – an overview, 1987–1990. In:Howeler, R.H. (ed.) Cassava Breeding, Agronomyand Utilization Research in Asia, Proceedings 3rdRegional Workshop, Malang, Indonesia, 22–27October 1990, pp. 260–285.

Howeler, R.H. (1994) Integrated soil and crop manage-ment to prevent environmental degradationin cassava-based cropping systems in Asia. In:Bottema, J.W.T. and Stoltz, D.R. (eds) Upland Agri-culture in Asia, Proceedings Workshop, Bogor,Indonesia, 6–8 April 1993, pp. 195–224.

Howeler, R.H. (1995) Agronomy research in the AsianCassava Network – towards better productionwithout soil degradation. In: Howeler, R.H. (ed.)Cassava Breeding, Agronomy Research and Technol-ogy Transfer in Asia. Proceedings 4th RegionalWorkshop, Trivandrum, Kerala, India, 2–6November 1993, pp. 368–409.

Howeler, R.H. (1996a) Diagnosis of nutritional dis-orders and soil fertility maintenance of cassava.In: Kurup, G.T., Polaniswami, M.S., Potty, V.P.,Padmaja, G., Kabeerathumma, S. and Pillai, S.V.(eds) Tropical Tuber Crops: Problems, Prospects andFuture Strategies. Oxford and IBH Publishing Co.,New Delhi, India, pp. 181–193.

Howeler, R.H. (1996b) Mineral nutrition of cassava.In: Craswell, E.T., Asher, C.J. and O’Sullivan, J.N.(eds) Mineral Nutrient Disorders of Root Crops inthe Pacific. Proceedings Workshop, Nuku’alofa,Kingdom of Tonga, 17–20 April 1995,ACIAR Proceedings no. 5, Canberra, Australia,pp. 110–116.

Howeler, R.H. (1998) Cassava agronomy research inAsia – an overview, 1993–1996. In: Howeler,R.H. (ed.) Cassava Breeding, Agronomy and FarmerParticipatory Research in Asia. Proceedings 5thRegional Workshop, Danzhou, Hainan, China,3–8 November 1996, pp. 355–375.


Howeler, R.H. (2000) Cassava production practices –can they maintain soil productivity? In: Howeler,R.H., Oates, C.G. and O’Brien, G.M. (eds) Cassava,Starch and Starch Derivatives, Proceedings of anInternational Symposium, Nanning, Guangxi,China, 11–15 November 1996. pp. 101–117.

Howeler, R.H. and Cadavid, L.F. (1983) Accumulationand distribution of dry matter and nutrientsduring a 12-month growth cycle of cassava. FieldCrops Research 7, 123–139.

Howeler, R.H. and Cadavid, L.F. (1990) Short- andlong-term fertility trials in Colombia to determinethe nutrient requirements of cassava. FertilizerResearch 26, 61–80.

Howeler, R.H. and Fernandez, F. (1985) NutritionalDisorders of the Cassava Plant. Study Guide. CIAT,Cali, Colombia.

Howeler, R.H. and Medina, C.J. (1978) La fertilización enel frijol Phaseolus vulgaris: elementos mayores ysecundarios. Revisión de la literatura para el Cursode Producción de Frijol. CIAT, Cali, Colombia.

Howeler, R.H. and Sieverding, E. (1983) Potentials andlimitations of mycorrhizal inoculation illustratedby experiments with field grown cassava. Plantand Soil 75, 245–261.

Howeler, R.H., Cadavid, L.F. and Calvo, F.A. (1977)The interaction of lime with minor elementsand phosphorus in cassava production. In:Proceedings 4th Symposium International Society ofTropical Root Crops, Cali, Colombia. IDRC, Ottawa,Canada, pp. 113–117.

Howeler, R.H., Edwards, D.G. and Asher, C.J. (1981)Application of the flowing solution culture tech-niques to studies involving mycorrhizas. Plant andSoil 59, 179–183.

Howeler, R.H., Asher, C.J. and Edwards, D.G. (1982a)Establishment of an effective endomycorrhizalassociation in cassava in flowing solution cultureand its effect on phosphorus nutrition. NewPhytologist 90, 229–238.

Howeler, R.H., Cadavid, L.F. and Burckhardt, E.(1982b) Response of cassava to VA mycorrhizalinoculation and phosphorus application in green-house and field experiments. Plant and Soil 69,327–339.

Howeler, R.H., Edwards, D.G. and Asher, C.J. (1982c)Micronutrient deficiencies and toxicities of cas-sava plants grown in nutrient solutions. I. Criticaltissue concentrations. Journal of Plant Nutrition 5,1059–1076.

Howeler, R.H., Sieverding, E. and Saif, S. (1987) Practi-cal aspects of mycorrhizal technology in sometropical crops and pastures. Plant and Soil 100,249–283.

Howeler, R.H., El-Sharkawy, M.A. and Cadavid, L.F.(2002a) The use of grain and forage legumes for

soil fertility maintenance and erosion control incassava in Colombia (in press).

Howeler, R.H., Oates, C.G. and Costa Allem, A.C.(2002b) Strategic Assessment on the Impact ofSmall-holder Cassava Production and Processing onthe Environment and Biodiversity. InternationalFund for Agricultural Development (IFAD),Rome, Italy (in press).

Howeler, R.H., Thai Phien and Nguyen the Dang(2002) Sustainable cassava production on slop-ing lands in Vietnam. Proceedings of InternationalWorkshop on Sustainable Land Management in theNorthern Mountainous Region of Vietnam. Hanoi,Vietnam (in press).

Hulugalle, N.R., Lal, R. and Gichuru, M. (1991) Effect offive years of no-tillage and mulch on soil proper-ties and tuber yield of cassava on an acid ultisol insoutheastern Nigeria. IITA Research 1, 13–16.

Islam, A.K.M.S., Edwards, D.G. and Asher, C.J. (1980)pH optima for crop growth: results of flowingculture experiment with six species. Plant and Soil54(3), 339–357.

Jintakanon, S., Edwards, D.G. and Asher, C.J. (1982)An anomalous, high external phosphorusrequirement for young cassava plants in solutionculture. In: Proceedings 5th International Sympo-sium Tropical Root Crops, Manila, Philippines,17–21 September 1979, pp. 507–518.

Jones, U.S., Katyal, J.C., Mamaril, C.P. and Park, C.S.(1982) Wetland-rice nutrient deficienciesother than nitrogen. In: Rice Research Strategiesfor the Future. IRRI, Los Baños, Philippines,pp. 327–378.

Kabeerathumma, S., Mohankumar, B., Mohankumar,C.R., Nair, G.M., Prabhakar, M. and Pillai, N.G.(1990) Long range effect of continuous croppingand manuring on cassava production and fertilitystatus of soil. In: Howeler, R.H. (ed.) Proceedings8th Symposium International Society of TropicalRoot Crops, Bangkok, Thailand, 30 October–5November 1988, pp. 259–269.

Kang, B.T. (1984) Potassium and magnesiumresponses of cassava grown in ultisol in southernNigeria. Fertilizer Research 5, 403–410.

Kang, B.T. and Okeke, J.E. (1984) Nitrogen and potas-sium responses of two cassava varieties grownon an alfisol in southern Nigeria. In: Proceedings6th Symposium International Society of TropicalRoot Crops, Lima, Peru, 21–26 February 1983,pp. 231–237.

Kang, B.T., Islam, R., Sanders, F.E. and Ayanaba, A.(1980) Effect of phosphate fertilization andinoculation with VA-mycorrhizal fungi onperformance of cassava (Manihot esculenta,Crantz) grown on an alfisol. Field Crops Research 3,83–94.

144 R.H. Howeler

Kasele, I.N. (1980) Investigation on the efffect ofshading, potassium and nitrogen and drought onthe development of cassava tuber at the earlystage of plant growth. MSc thesis, University ofIbadan. Ibadan, Nigeria.

Krochmal, A. and Samuels, G. (1970) The influence ofNPK levels on the growth and tuber developmentof cassava in tanks. CEIBA 16, 35–43.

Leihner, D. (1983) Management and Evaluation ofIntercropping Systems with Cassava. CIAT, Cali,Colombia.

Lozano, J.C., Bellotti, A., Reyes, J.A., Howeler, R.,Leihner, D. and Doll, J. (1981) Field Problems inCassava. CIAT Series No. 07EC-1, Cali, Colombia.

Margolis, E. and Campos Filho, O.R. (1981)Determinação dos fatores da equação universal deperdas de solo num podzólico vermelho amarelode Glória do Goitá. In: Anais do 3rd EncontroNacional de Pesquisa Sobre Conservação do Solo,Rengife, Pernambuco, Brazil, 28 July–1 August1980, pp. 239–250.

Moraes, O. de, Mondardo, E., Vizzotto, J. and Machado,M.O. (1981) Adubação quimica e calagem damandioca. Boletim Técnico No.8. EmpresaCatarinense de Pesquisa Agropecuâria.Florianopolis, Santa Catarina, Brazil.

Muhr, L., Leihner, D.E., Hilger, T.H. and Müller-Sämann, K.M. (1995) Intercropping of cassavawith herbaceous legumes. II. Yields as affected bybelow-ground competition. Angewandte Botanik69, 22–26.

Nair, P.G., Mohankumar, B., Prabhakar, M. andKabeerathumma, S. (1988) Response of cassavato graded doses of phosphorus in acid lateritic soilsof high and low P status. Journal of Root Crops14(2), 1–9.

Nayar, T.V.R., Kabeerathumma, S., Potty, V.P. andMohankumar, C.R. (1995) Recent progress incassava agronomy in India. In: Howeler, R.H.(ed.) Cassava Breeding, Agronomy Research andTechnology Transfer in Asia. Proceedings 4thRegional Workshop, Trivandrum, Kerala, India,2–6 November 1993, pp. 61–83.

Ngongi, A.G.N., Howeler, R.H. and MacDonald, H.A.(1977) Effect of potassium and sulphur ongrowth, yield, and composition of cassava.In: Proceedings 4th Symposium InternationalSociety of Tropical Root Crops, Cali, Colombia,1–7 August 1976. IDRC, Ottawa, Canada,pp. 107–113.

Nguyen Huu Hy, Pham Van Bien, Nguyen The Dangand Thai Phien (1998) Recent progress in cas-sava agronomy research in Vietnam. In: Howeler,R.H. (ed.) Cassava Breeding, Agronomy and FarmerParticipatory Research in Asia. Proceedings 5thRegional Workshop, Danzhou, Hainan, China,3–8 November 1996, pp. 235–256.

Nguyen Tu Siem (1992) Organic matter recyclingfor soil improvement in Vietnam. In:Proceedings 4th Annual Meeting, IBSRAMAsialand Network.

Nijholt, J.A. (1935) Opname van voedingsstoffen uitden bodem bij cassave [Absorption of nutrientsfrom the soil by a cassava-crop]. Buitenzorg.Algemeen Proefstation voor den Landbouw.Korte Mededeelingen No. 15.

Normanha, E.S. and Pereira, A.S. (1950) Aspectosagronômicos da cultura da mandioca (Manihotutilissima Pohl). Bragantia (Campinas, SP, Brazil)10, 179–202.

Nunes, W.O., de, Brito, D.P.P.S., de, Meneguelli, C.A.,Arruda, N.B. de and Oliveira, A.B. de (1974)Resposta da mandioca a adubação mineral emétodos de aplicação do potássio em solos debaixa fertilidade. Pesquisa Agropecuária Brasileira(Série Agronomia) (Rio de Janeiro, Brazil) No. 9,pp. 1–9.

Obigbesan, G.O. (1973) The influence of potassiumnutrition on the yield and chemical compositionof some tropical root and tuber crops. In: 10thColoquium International Potash Institute, Abidjan,Ivory Coast, pp. 439–451.

Obigbesan, G.O. (1977) Investigations on Nigerianroot and tuber crops: effect of potassium onstarch yield, HCN content and nutrient uptakeof cassava cultivars (Manihot esculenta). Journal ofAgricultural Science 89, 29–34.

Obigbesan, G.O. and Fayemi, A.A.A. (1976) Investiga-tions on Nigerian root and tuber crops: influenceof nitrogen fertilization on the yield and chemicalcomposition of two cassava cultivars (Manihotesculenta). Journal of Agricultural Science 86,401–406.

Ofori, C.S. (1973) Decline in fertility status of a tropicalforest ochrosol under continuous cropping.Experimental Agriculture 9, 15–22.

Okogun, J.A., Sanginga, N. and Adeola, E.O. (1999)Soil Fertility Maintenance and Strategies for CassavaProduction in West and Central Africa. IITA,Ibadan, Nigeria (mimeograph).

Orlando Filho, J. (1985) Potassium nutrition of sugar-cane. In: Bishop, W.D. et al. (eds) Potassiumin Agriculture. ASA-CSSA-SSSA, Madison,Wisconsin, pp. 1045–1062.

Paula, M.B. de, Nogueira, F.D. and Tanaka, R.T. (1983)Nutrição mineral da mandioca: absorção denutrientes e produção de materia seca por duascultivares de mandioca. Revista Brasileira deMandioca, Cruz das Almas, 31–50.

Payne, H. and Webster, D.C. (1956) The toxicity ofcassava varieties on two Jamaican soil types ofdiffering K status. Ministry of Agriculture andFisheries. Crop Agronomy Division, Kingston,Jamaica.


Pellet, D. and El-Sharkawy, M.A. (1993a) Cassavavarietal response to phosphorus fertilization.I. Yield, biomass and gas exchange. Field CropsResearch 35, 1–11.

Pellet, D. and El-Sharkawy, M.A. (1993b) Cassavavarietal response to phosphorus fertilization. II.Phosphorus uptake and use efficiency. Field CropsResearch 35, 13–20.

Phommasack, T., Sengtaheuanghung, O. and Phan-thaboon, K. (1995) The management of slopinglands for sustainable agriculture in Laos. In:Sajjapongse, A. and Elliot, C.R. (eds) The Manage-ment of Sloping Lands for Sustainable Agriculture inAsia, (Phase 2, 1992–1994). IBSRAM/AsialandNetwork Doc. no. 12. IBSRAM, Bangkok,Thailand, pp. 87–101.

Phommasack, T., Sengtaheuanghung, O. and Phan-thaboon, K. (1996) The management of slopinglands for sustainable agriculture in Laos. In:Sajjapongse, A. and Leslie, R.N. (eds) The Manage-ment of Sloping Lands in Asia. IBSRAM/AsialandNetwork Doc. no. 20. IBSRAM, Bangkok,Thailand, pp. 109–136

Prevot, P. and Ollagnier, M. (1958) La fumurepotassique dans les regions tropicales etsubtropicales. In: Potassium Symposium, Berne,Switzerland, pp. 277–318.

Putthacharoen, S., Howeler, R.H., Jantawat, S. andVichukit, V. (1998) Nutrient uptake and soilerosion losses in cassava and six other crops ina Psamment in eastern Thailand. Field CropsResearch 57, 113–126.

Queiroz, G.M. de and Pinho, J.L.N. de (1981)Resultados do experimento efeito da fertilizaçãocom macronutrientes NPK em mandioca noEstado do Ceará. EPACE. Pacajús, Ceará, Brazil.

Queiroz, G.M. de, Pinho, J.L.N. de, Lima, A.R.C. da andVerde, N.G.L. (1980) Efeito da fertilização commacronutrientes NPK em mandioca (Manihotesculenta Crantz) no Estado do Ceará. In: EPACE,Relatório Annual de Pesquisa Fitotécnica. Fortaleza,Ceará, Brazil, pp. 83–96.

Quintiliano, J., Margues, A., Bertoni, J. and Barreto,G.B. (1961) Perdas por erosão no estado de SãoPaulo. Brigantia 20(2), 1143–1182.

Richards, I.R. (1979) Response of tropical crops tofertilizer under farmers conditions – analysis ofresults of the FAO Fertilizer Programme. Phos-phorus in Agriculture 76, 147–156.

Rio Grande do Norte (1976) Pesquisa e experi-mentação com culturas alimentares: mandioca,1971–1975. Secretaria da Agricultura. Rio Grandedo Norte, Brazil.

Roberts, S. and McDole, R.E. (1985) Potassium nutri-tion of potatoes. In: Bishop, W.D. et al. (eds) Potas-sium in Agriculture. International Symposium,

Atlanta, Georgia, 7–10 July. ASA-CSSA-SSSA,Madison, Wisconsin, pp. 800–818.

Roche, P., Velly, J. and Joliet, B. (1957) Essai de determi-nation des seuils de carence en potasse dans le solet dans les plantes. Revue de la Potasse 1957, 1–5.

Ruppenthal, M. (1995) Soil Conservation in AndeanCropping Systems. Hohenheim Tropical Agricul-ture Series no. 3, Hohenheim University,Germany.

Ruppenthal, M., Leihner, D.E., Steinmuller, N. andEl-Sharkawy, M.A. (1997) Losses of organicmatter and nutrients by water erosion incassava-based cropping systems. ExperimentalAgriculture 33, 487–498.

Santos, Z.G. dos and Tupinamba, E.A. (1981)Resultados do experimento de niveis e fontesde fósforo na produção de mandioca (Manihotesculenta Crantz). EMBRAPA-UEPAE, Aracaju,Sergipe, Brazil.

Sieverding, E. and Howeler, R.H. (1985) Influence ofspecies of VA mycorrhizal fungi on cassava yieldresponse to phosphorus fertilization. Plant and Soil88, 213–222.

Silva, J.R. da and Freire, E.S. (1968) Efeitos de dosescrescentes de nitrogênio, fósforo e potássio sobre aprodução de mandioca em solos de baixa e altafertilidade. Brigantia (Campinas, SP, Brazil) 27(29), 357–364.

Silva, L.G. (1970) Adubação NPK na cultura damandioca em Tabuleiró Costeiro no estado daParaiba. Pesquisas Agropecuárias no Nordeste 2(1),73–75.

Silva, L.G., Souza, J.B. de, Silva, J.C. da and Lucas, A.P.de (1969) Ação de macronutrientes e manganêsna cultura da mandioca em solos de tabuleiroscosteiros do Nordeste. SUDENE, Recife.Pernambuco, Brazil.

Sittibusaya, C. (1993) [Progress report of soil research onfertilization of field crops, 1992]. Annual CassavaProgram Review, Rayong, Thailand, 19–20January 1993 [in Thai].

Sobral, L.F., Barreto, A.C., Siqueira, L.A., Santos, Z.G.dos, Souza, R.F., Rezende, J.O. de and Ribeiro, J.V.(1976) Efeitos de macro e micronutrientesem produção da mandioca (Manihot esculentaCrantz). Comunicado Técnico, 1. EMBRAPA-Rep. No Estado de Sergipe, Aracaju, Sergipe,Brazil.

Souza, L.D., Gomes C.J. de and Caldas, R.C. (1992)Interação vinhoto, calage, e fósforo na cultura damandioca no Norte de Mato Grosso. RevistaBrasileira de Mandioca 11(2), 148–155.

Spain, J.M., Francis, C.A., Howeler, R.H. and Calvo, F.(1975) Differential species and varietal toleranceto soil acidity in tropical crops and pastures.In: Bosnemisza, E. and Alvarado, A. (eds) Soil

146 R.H. Howeler

Management in Tropical America. North CarolinaState University, Raleigh, North Carolina,pp. 308–329.

Spear, S.N., Asher, C.J. and Edwards, D.G. (1978a)Response of cassava, sunflower, and maize topotassium concentration in solution. I. Growthand plant potassium concentration. Field CropsResearch 1, 347–361.

Spear, S.N., Edwards, D.G. and Asher, C.J. (1978b)Response of cassava, sunflower, and maize topotassium concentration in solution. III. Inter-actions between potassium, calcium, and magne-sium. Field Crops Research 1, 375–389.

Stephens, D. (1960) Fertilizer trials on peasant farms inGhana. Empire Journal of Experimental Agriculture109, 1–22.

Takyi, S.K. (1972) Effects of potassium, lime andspacing on yields of cassava (Manihot esculentaCrantz). Ghana Journal of Agricultural Science 5(1),39–42.

Tongglum, A., Vichukit, V., Jantawat, S., Sittibusaya,C., Tiraporn, C., Sinthuprama, S. and Howeler,R.H. (1992) In: Howeler, R.H. (ed.) CassavaBreeding, Agronomy and Utilization Research inAsia. Proceedings 3rd Regional Workshop,Malang, Indonesia, 22–27 October 1990,pp. 199–223.

Tongglum, A., Pornpromprathan, V., Paisarncharoen,K., Wongwitchai, C., Sittibusaya, C., Jantawat, S.,Nual-on, T. and Howeler, R.H. (1998) Recentprogress in cassava agronomy research inThailand. In: Howeler, R.H. (ed.) CassavaBreeding, Agronomy and Farmer Participatory

Research in Asia. Proceedings 5th Regional Work-shop, Danzhou, Hainan, China, 3–8 November1996, pp. 211–234.

Vijayan, M.R. and Aiyer, R.S. (1969) Effect of nitrogenand phophorus on the yield and quality ofcassava. Agricultural Research Journal of Kerala 7,84–90.

Vinod, G.S. and Nair, V.M. (1992) Effect of slow-release nitrogenous fertilizers on the growthand yield of cassava. Journal of Root Crops 18,124–125.

Wargiono, J., Kushartoyo, Suyamto, H. and Guritno, B.(1998) Recent progress in cassava agronomyresearch in Indonesia. In: Howeler, R.H. (ed.) Cas-sava Breeding, Agronomy and Farmer ParticipatoryResearch in Asia. Proceedings 5th Regional Work-shop, Danzhou, Hainan, China, 3–8 November1996, pp. 307–330.

Zaag, P. van der (1979) The phosphorus requirementsof root crops. PhD thesis, University of Hawaii,Hawaii.

Zangrande, M.B. (1981) Resultados do experi-mento estudo de níveis de NPK para a culturada mandioca (Manihot esculenta Crantz) noEstado do Espírito Santo, EMCAPA. Cariacica, ES,Brazil.

Zhang Weite, Lin Xiong, Li Kaimian, Huang Jie, TianYinong, Lee Jun and Fu Quohui (1998) Cassavaagronomy research in China. In: Howeler, R.H.(ed.) Cassava Breeding, Agronomy and FarmerParticipatory Research in Asia. Proceedings 5thRegional Workshop, Danzhou, Hainan, China,3–8 November 1996, pp. 191–210.


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