LESSONS FROM LONG TERM FERTILISER EXPERIMENTS

Dhakshinamoorthy, M., Santhy, P., Selvi, D., Savithri, P. and T.M.ThiyagarajanDirectorate of Soil and Crop Management Studies

Tamil Nadu Agricultural University, Coimbatore-641 003

The continuously growing population and increasing demand for food call for greater reliance on agriculture than had ever been witnessed. The mining of nutrients from soil for ages along with their losses due to erosion and other causes if allowed to continue would severely limit crop production in the coming years. Fertiliser inputs have undoubtedly proved to be one of the major components of raising the soil productivity. The increasing demand for plant nutrients grew by leaps and bounds with the introduction of high yielding varieties which even under the best possible management cannot be met from the inherent soil fertility . The present day agriculture all over the world has therefore become much dependent upon chemical fertilisers to produce more and more from the shrinking land area.

Since the early days of use of chemical fertilisers there has been some apprehensions regarding the soil fertility and crop yield being adversely affected by their prolonged usage. As a sequel to these had come the world's oldest classical manurial experiments started by Lawes and Gilbert at Broadbalk fields in Rothamsted (England). The succeeding decades saw permanent manurial experiments being set up in several parts of the world. India started three such experiments after the Rothamsted model towards the end of the last and the beginning of the present century at Kanpur (U.P.), Coimbatore (Tamil Nadu) and Pusa (Bihar) followed by some more permanent field trials at other locations.

These classical experiments did provide valuable information on the effect of rotational cropping , use of bulky organic manures, nutrient application alone or in combinations on crop yields, nutrient uptake and on changes in soil physico - chemical properties of the soil. The change over of the cropping pattern based on high yielding technology and multiple cropping and breaking of the age old yield barrier gave new dimensions to agricultural production strategy in the country. The yield levels and the nutrient input requirements have gone up several folds with a rapid turnover of the nutrients in the soil plant systems. Multiple cropping, irrigation and pest control measures, all directed towards achieving higher levels of production, necessarily have a much greater impact on soil and crop environment than ever conceived before. It becomes imperative, therefore, to examine how far the soil, which is one of the greatest natural resources can be manipulated without seriously damaging the long term viability of the farm on which the livelihood of all ultimately depends. There is a general agreement that long term experiments play an important role in identifying the soil constraints that limit crop yields and help in monitoring the soil conditions so as to protect the crop plants and food chain from attaining harmful concentrations of various environmental pollutants in the years to come, besides maintaining soil fertility and productivity through suitable soil ameliorative measures as necessary warrants.

The Indian Council of Agricultural Research sponsored an All India Coordinated Research Project on Long Term Fertiliser Experiments during the Fourth Plan Period to examine as to what would happen to soil fertility and productivity on a long term basis under high input soil management technology. Thus, a new set of statistically designed field experiments in keeping with the modern intensive system of agriculture were started at eleven selected centres in 1971. Six more centres were added during 1996 to provide more wider representations for the major soil-climatic zones of the country.

The treatments adopted at these centres essentially consisted of 50, 100 and 150 % optimum NPK, 100 % NPK with handweeding , ZnSO4 application @ 25kg ha-1 , S free sources of NPK fertilisers and FYM @ 10 t ha-1, 100 % optimum NP, 100 % optimum N and a control. The lessons learnt from these Long Term Fertiliser Experiments will be discussed in this paper.

RESPONSE IN CROP YIELDS

Balanced application of 100 % NPK with FYM @ 10 t ha-1, produced highest grain yield response in almost all the soils and cropping systems. However , 150 % NPK recorded the highest yield response in alluvial soil of Barrackpore and New Delhi and the red loam of Bangalore and Hyderabad. Among the various cropping systems studied, rice-wheat rotation followed at Pantnagar on foot hill (Terai) soil produced the highest average grain yield of the order of 10.7 t / ha / year over the years with an additional output of about 4 t / ha of cowpea fodder. Similarly, the grain yield under maize-wheat, rice-rice and soybean-wheat cropping systems averaged from 7.5 to 7.7, 6.9 to 7.5 and 4.1 to 6.5 t/ha/year, respectively. Thus, the importance of balanced NPK nutrition and FYM incorporation was very much evinced in maintaining yield stability.(Santhy et al., 1998a)

In order to evaluate the net trend in yield over years in each treatment and crop the average yield in each treatment in each year was related to time in a semilog function as

Y = at b,where Y is yield in kg ha_1, t is the time in months and a and b are constants. A negative b value is an indication of declining trend and a positive one , for yield sustainability.

The results indicated that in finger millet a declining yield growth over years occurred in control and 100% N treatment whereas in other treatments the yield growth was sustainable. In maize sustainable yield growth over years occurred in all treatments including control. But in grain cowpea the yield growth was sustainable only in 100% NP, 100% NPK + ZnSO4 and 100% NPK + FYM treatments whereas in other treatments the yield growth was found to be declining (Table 1).

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Table 1. Temporal effect of Treatments on yield

Treatments Finger millet Maizea b a b

Control 639 (-) 0.0006 118 0.0103100% N 916 (-) 0.0010 317 0.0061100% NP 2392 0.0007 1525 0.004050% NPK 2101 0.0015 1212 0.0048100% NPK 2101 0.0015 1480 0.0045150% NPK 2416 0.0012 1737 0.0040100% NPK + ZnSO4 2276 0.0010 1772 0.0035100% NPK + FYM 2724 0.0011 1920 0.0039100% NPK + HW 2441 0.0006 1669 0.0037100% NPK (S free) 2392 0.0006 1604 0.0040

(Murugappan et. al., 1997)

RESPONSE TO NPK

Mean response of rice to N ( kg grain / kg N ) was found to be 18 kg in new alluvium of Barrackpore, 6 to 10 kg in red loam of Hyderabad, 8 to 14 kg in laterite soil of Bhubaneswar and 12 kg in Terai soil of Pantnagar. While response of wheat to N was 17 kg at Pantnagar, it was only 4 to 5 kg in medium black and acidic sub-montane soil. The N failed to give any response in acidic red loam soils(Ranchi and Bangalore). Poor response to N in medium black and acidic red loam soil was to be due to inadequate availability of P.

Response to P was found to be very high in acidic red loams (Bangalore and Hyderabad) medium black soils (Jabalpur and Coimbatore) and acidic sub-montane (Palampur) soils where P has been found to be one of the major soil constraints limiting crop production. Response to P in alluvial soils of New Delhi and Ludhiana have been found to be quite encouraging (8 to 13 kg grain / kg P2O5 ).

Effect of K on yield was found to be quite high in light alluvial sandy soil of Ludhiana and red loam of Hyderabad . Increasing response to K was recorded in acidic red loam, acidic sub-montane, foot hill and even in K rich medium black (Jabalpur) soil when N and P were not limiting. Response to K was not observed in the mixed black soils of Long Term Fertiliser Experiments at Coimbatore centre.

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EFFECT OF CONTINUOUS N APPLICATION

Application of N alone had a deleterious effect on soil productivity resulting in diminishing yields in acidic red loam (Ranchi and Bangalore) and sub-montane (Palampur) soils where P and K were deficient. Even though the mixed black soils of Coimbatore centre have medium P and high K status, continuous application of N alone has reduced the yield to a tune of 70% over 100% NPK in finger millet and maize (Santhy et. al. 1998 b) and Jayasree et. al. 2000). This ensures the importance of P and K in determining the response to N suggesting the need for balanced nutrition.

EFFECT ON SOIL PHYSICAL PROPERTIES

Bulk Density

Ploughing and cultivation increase soil aeration and the physical disruption caused by intensive cultivation can result in break down of soil aggregates and produce a tilth that is very fine and loose. The reduced aggregate stability is associated with increased porosity and aeration and a decrease in bulk density within the plough depth. Such a reduction in bulk density was observed due to combined application of 100 % NPK + FYM in some intensive cropping systems (Table 2).

Table 2. Bulk density of soils (Mg m-3) under intensive cropping systems

Treatments Location/Soil type/Cropping systemBarrackpore Hyderabad Bhubaneswar Pantnagar Coimbatore

Alluvial Red loam Laterite Silty clay loam

Inceptisol

Rice-Wheat-Jute

Rice-Rice Rice-Rice Rice-Wheat-Cowpea fodder

Finger millet - Maize - Cowpea fodder

1. 100 % NPK 1.44 1.68 1.63 1.32 1.402. 150 % NPK 1.40 1.62 1.55 1.33 1.413. 100 % NP 1.41 1.58 1.62 1.29 1.424. 100 % N 1.46 1.78 1.61 1.28 1.365. 100 % NPK + FYM

1.40 1.34 1.56 1.31 1.30

6. Control 1.46 1.53 1.65 1.33 1.44C.D.(P=0.05) 0.014 0.12 0.08 0.008 0.063

(Anon., 1989 and 1999)

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No appreciable changes in B.D. were observed between the uncultivated A2

horizon and the cultivated Ap horizon of an Andisol under long term cultivation in Japan. This has been attributed to the fact that the depletion of organic matter associated with cultivation was low (Table 3). The application of 100% NPK with FYM recorded a reduced bulk density value of 1.30 Mg m-3 compared to other treatments which could be ascribed to better aggregation. (Anon., 1999)

Table 3. Effect of cultivation on soil properties

Property Uncultivated A2 horizon Cultivated Ap horizonOrganic C (g.kg-1) 93.9 ± 7.3 81.2 ± 14.2Total N (g.kg-1) 5.76 ± 0.53 5.46 ± 0.76C/N ratio 16.3 ± 0.7 14.8 ± 0.9Bulk density (Mg.m-3) 0.56 ± 0.06 0.61 ± 0.04

(Higuchi & Kashiwagi, 1993 )

Porosity

Soil porosity is influenced by the amount of clay and the arrangement of soil particles. An increase in clay content is likely to increase the capillary porosity. Aggregation of soil particles into stable structure is bound to result in the proper distribution of capillary and noncapillary porosity. Continuous incorporation of cattle manure increased the porespace in the OPM and NPM experiments at Coimbatore. Increase in total and noncapillary porosity and a decrease in capillary porosity due to the continuous incorporation of 100 % NPK have been observed in an intensive cropping system involving Fingermillet-Maize-Cowpea fodder (Table 4 ).

Table 4. Effect of intensive cropping and continuous fertilisation on soil porosity(%)

Treatment Total porosity Capillary porosity Non capillary porosity

100 % NPK 56.14 38.26 17.87150 % NPK 56.98 39.47 17.51100 % NP 52.11 35.76 17.15100 % N 52.24 34.88 17.36100 % NPK + FYM 58.85 40.86 20.50Control 54.18 36.61 17.57C. D. (P=0.05) 2.04 2.82 2.85

(Anon., 1999)

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Hydraulic conductivity

Intensive cultivation results in less organic carbon, low porosity, few water stable aggregates, a smaller mean weight diameter of water stable aggregates and lower saturated hydraulic conductivity (Arvidsson and Hakansson, 1996). This is due to the fact that ploughing largely restores the macroporosity of the soil within the plough layer. A slight increase in saturated hydraulic conductivity has been observed in Barrackpore alluvial sandy loam soil and in Vertic Ustropept of Coimbatore under FYM treatment. But a reduction in hydraulic conductivity was observed in laterite soils of Bhubaneswar under FYM treatment due to reduction in non capillary porosity.(Table 5 )

Table 5. Hydraulic conductivity under intensive cropping (cm.hr-1)

Treatments Barrackpore* Alluvial sandy

loam

Bhubaneswar* Laterite sandy loam

CoimbatoreInceptisol sandy clay

loam100 % NPK 0.095 3.02 1.81150 % NPK 0.099 3.00 1.87100 % NP 0.095 3.02 1.66100 % N 0.095 3.03 1.73100 % NPK + FYM 0.106 2.90 2.61Control 0.088 3.09 1.44 *(Nambiar and Abrol, 1989)

(Anon., 1999)PHYSICO-CHEMICAL PROPERTIES

Soil reaction ( pH )Suresh Lal and Mathur (1988) reported that continuous application of fertilisers

for eight years lowered the soil pH. However application of FYM alone had either maintained or slightly increased the pH but the incorporation of fertilisers with it decreased the same (Prasad et al., 1983). The rise in pH under FYM treatment was due to the deactivation of Fe3+ and Al3+ with concomitant release of basic cations (Ca2+,Mg2+

and K+ ) during its decomposition. They also stated that the pH of the control plot had also increased after 28 years of continuous cropping. This may be due to the release of HCO3

-1 and OH-1 into the soil solution for the uptake of anions such as nitrate, phosphate, sulphate, molybdate and borate.

However, no perceptible change in soil reaction was observed in near neutral to alkaline soils after a decade of intensive cropping and manuring under the ICAR's Long Term Fertiliser Experiments including Coimbatore centre (Santhy et. al., 1999) (Table 6). But there was an increase in acidity in acidic red loam soil of Bangalore and Ranchi and sub-montane soil of Palampur. Maximum acidity was observed in 100 % N treatment, the effect being more pronounced in acidic red loam soil where urea and

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ammonium sulphate were used as N source. The increased acidity may lead to a decline in productivity in acid soils in the long run.

Electrical conductivity ( EC )The major source of salts to the soil is irrigation water and wherever the irrigation

water used contains considerable quantities of salts, it will result in increased electrical conductivity of the soil over the years (Wang and Fang, 1978 ). In general, the electrical conductivity of the soil does not vary markedly due to long term manurial practices (Anon., 1979), unless the schedule involves the addition of heavy doses as in the case of gypsum (Singh and Abrol,1988). Long term application of lime and K to a Typic Haplustalfs soil increased the soil electrical conductivity where as continuous application of inorganic fertilisers alone (N, NP and NPK) for 14 years did not change the electrical conductivity in a sandy loam soil (Kapur et al., 1986). In the Long Term Fertiliser Experiments at Coimbatore centre, continuous cropping and manuring did not alter the soil electrical conductivity to any appreciable extent (Table 6).

Table 6. Effect of intensive cropping on soil physico-chemical properties

Treatments pH Electrical conductivity (dSm-1)

50 % NPK 8.1 0.95100 % NPK 8.2 0.75150 % NPK 8.2 0.80100 % NPK + FYM 8.1 0.63Control 8.1 0.62CD (P=0.05) 0.05 0.03

(Santhy et. al., 1999)Cation exchange capacity ( CEC )

The cation exchange capacity of a soil is influenced mainly by the content of organic matter and clay fraction. Since long term application of manures and fertilisers is likely to alter the organic carbon status of the soil, significant changes in soil cation exchange capacity as a result of manurial practices over the years has been quoted in the past (Krishnamoorthy and Ravikumar, 1973). Continuous application of N and compost to rice crop in a permanent manurial experiment at Cuttack increased the cation exchange capacity of the soil (Table 7).

Table 7. Effect of N and compost on CEC of rice soils ( C mol. p+ kg-1 )

N levels (kg ha-1) Compost levels ( t.ha-1)0 9.2 Mean

0 21.6 22.1 21.822.4 21.7 22.1 21.944.8 21.6 22.9 22.267.2 22.2 22.9 22.589.6 21.3 22.6 21.9

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Mean 21.6 22.5 (Patnaik et al., 1989)

The cation exchange capacity of a sandy loam soil (Typic Ustochrept) was practically unaffected due to the continuous application of inorganic fertilisers to a fixed maize-wheat rotation (Kapur et al., 1986 ). Higher CEC was recorded under 100 % NPK + FYM in a Long Term Fertiliser Experiment at Coimbatore and this has been attributed to the build up of humus due to the application of FYM and the presence of higher amounts of crop residues (Sheeba, 1994).

SOIL NUTRIENT STATUS

Nitrogen In a Long Term Fertiliser Experiment at Coimbatore, continuous intensive

cropping was found to have a general depletion in the total N status of the soil. The order of depletion of soil N reserve with crops in the rotation was found to be Maize > Cowpea fodder > Finger millet. The available N was also depleted in all plots including the control due to intensive cropping except in plots receiving 100 % NPK + FYM ( Table 8 ).

Table 8. Total and available N status in a Long Term Fertiliser Experiment(mg kg -

1)

Treatments Total N (mg. kg-1) Available N (mg. kg-1)

Finger millet

Maize Cowpea Finger millet

Maize Cowpea

Control 288 293 281 62 66 62100%N 516 509 510 72 71 75100%NP 516 511 512 77 73 7950%NPK 434 432 432 73 69 74100%NPK 523 531 532 76 74 77150%NPK 553 544 544 77 80 80100%NPK+ ZnSO4 553 540 541 75 74 77100%NPK + FYM 664 593 631 92 86 91100%NPK + HW 490 492 487 77 73 75100%NPK (S free) 497 486 487 74 72 72

*C.D.(P=0.05) 12.59 5.59 *Treatment Crop interaction effect (Velusamy, 1996)

Cultivation is an oxidative process since it typically promotes good aeration and consequently promotes rapid decomposition of organic matter and mineralization of organically bound N. Mineralized N may be denitrified or leached besides fulfilling crop uptake and this may explain the reasons for depletion of N under intensive cropping.

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Crop rotations have been suggested to reduce soil N depletion. Olsen et al.(1970) found that crop rotation reduced NO3 leaching at a depth of 1.2 to 1.5 m by 34 to 82 per cent compared to continuous corn. They found that the decrease in solution NO3 was directly proportional to the number of years in oats, meadow or alfalfa and attributed this to the combined recovery of NO3 by shallow rooted oat crops followed by deep rooted alfalfa crops.

In a Long Term Fertiliser Experiment on sugarcane for 11 years in a slightly acidic soil, there was a drastic reduction in soil NPK status in the control treatment due to intensive cultivation . Application of NPK with FYM improved the soil fertility ( Rabindra and Gowda, 1986). Muthuvel et al.(1977) reported that the available N content was higher in the organic manure treatment than in the fertilised plots due to optimum microbial population and quicker mineralization enhanced by FYM application.

Balanced application of NPK at 100 % level reflected in a positive balance of N in alluvial soil of Barrackpore, Ludhiana and New Delhi , medium black soil of Coimbatore, red loam soils of Bangalore and Hyderabad, acidic sub-montane soil of Palampur and laterite soil of Bhubaneswar. Negative N balance was observed in medium black soil of Jabalpur, acidic red loam soil of Ranchi and Terai soil of Pantnagar. (Nambiar and Ghosh, 1984)

Phosphorus

In the Old and New Permanent Manurial experiments at Coimbatore, the plots receiving inorganic P and cattle manure recorded higher available and total P content. In the Long Term Fertiliser Experiments, considerable build up of P was noticed in 100 % and 150 % NPK treatments at Barrackpore, Ludhiana and Delhi. Depletion of P was noticed in 100 % N alone as compared to control, probably due to greater removal of P for enhanced plant growth brought about by N application. Depletion of P (from the initial level) after 10 years was 37, 47, and 77 % at New Delhi, Barrackpore and Ludhiana while it was 37, 42 and 66 %, respectively under control (Nambiar and Ghosh, 1984). Similar results have been observed at Coimbatore centre. The P reduction in the soil was for a continuous addition of N alone was from 490 to 423 ppm in total P and 4.92 to 2.00 ppm in available P over a period if 20 years in the medium black soils of Coimbatore (Jayasree et. al., 2000).

Potassium

In ongoing Long Term Fertiliser Experiment at Coimbatore centre, continuous cropping even with the recommended dose of NPK + FYM had a declined on total as well as available K status of the soil. The depletion was of high magnitude in situation were no K additions were done (Murugappan et. al., 1999). The non exchangeable K generally showed a declining trend indicating the role of this form of K in meeting the crop requirement when the soil available pool remains constantly under K stress. The total K also showed a declining trend with the progress in the number of crops, as a result

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of K removal by the crops which far exceeded the fertiliser K input into the soil. The available K also decreased due to crop uptake over and the quantity of fertilisers applied (Table 9).

Table 9. Content of K fractions in soil under Long Term Fertiliser Experiments (mg. kg-1)

Treatments Water soluble-K

Exchange-able K

Nonexchangeable-K

Lattice-K Total K Available-K

50 % NPK 16 215 813 2621 3685 238100 % NPK 20 231 899 2620 3788 255150 % NPK 24 244 1036 2620 3939 273100 % NP 7 108 514 1621 3275 127100 % N 10 126 707 2627 3485 139100 % NPK + FYM

23 254 971 2618 3890 281

Control 12 183 813 2643 3665 198CD(P=0.05) 1 13 80 NS 89 13 (Santhy., et al.,1998b)

Similar results indicating a depletion in available K under intensive cropping had been observed by Nambiar and Ghosh (1984 ).

Organic matter

Organic matter is the centre of nearly all life activities in the soil. It serves as a source of food for microflora, fauna and other living matter in the soil. Long term recycling of crop residues can improve the organic matter content of soil as a result of increased dry matter production( Bhat et al., 1991). The rotation which included only a cereal crop gave only a lower organic matter status as against a rotation with a green manure or legume crop( Havanagi and Mann, 1970 ; Campbell et al., 1991). The organic matter is higher under continuous cropping than under fallow ( Jansen, 1987 ). The results of 15 years of Long Term Fertiliser Experiments at Ludhiana, Hyderabad, Bhubaneswar, Palampur and Coimbatore showed that organic matter levels increased due to intensive cropping ( Nambiar and Ghosh, 1984).

Secondary and micronutrients

A decrease in exchangeable Ca and Mg by fertiliser additions but increase under FYM treatment had been observed by several workers(Prasad and Singh, 1981 ; Suresh Lal and Mathur, 1988; Patiram and Singh, 1993 ).The results of Long Term Fertiliser Experiments from Barrackpore, Bhubaneswar and Coimbatore centres have shown that the available S content was decreased due to intensive cropping especially when S free fertilisers were added. Addition of S containing fertilisers and FYM with 100 % NPK maintained or improved the S status of the soil ( Nambiar and Ghosh, 1984).

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A steep decrease in DTPA-Zn over years due to intensive cultivation of Coimbatore centre was observed (2.58 to 0.90 mg kg-1). However the ZnSO4 application @ 25 kg ha-

1 to maize alone resulted in an increase in the available Zn status of the soil (2.86 mg kg -

1) (Selvi et. al., 2000). Zinc deficiency symptoms were not observed at Barrackpore even after the 14th crop cycle ( Anon.,1989). Prasad et al.(1994) observed a similar pattern of depletion of micronutrients under continuous maize - wheat rotations.

The biomass C, N and P were all found to be the highest for the content application of 100% NPK + FYM. The activity of phosphorus enzyme was higher for the intensive application of 100% NPK + FYM which was on par with 150% NPK (Santhy, et. al., 2000). The biomass C : N ratio was narrower in the case of 100% NPK + FYM and wider in unmanured control than 100% NPK. Depletion of P and K widened the ratio in case of 100% N application (Selvi, et. al., 2000).

CONCLUSIONS

The data collected from experiments conducted over a period of 30 years indicated little response to N fertilizer in the absence of P application on Vertic Ustochrepts (Coimbatore) and Chromusterts (Jabalpur). Application of N fertilizer alone had a deleterious effect on crop yields on both Haplustalfs (Ranchi) and Hapludalfs (Palampur), and the crop yields in respect of N treatment were lower than the yields from unmanured plots. The yield of crops appreciated markedly with the application of P fertilizer in combination with N, which showed further improvement with balanced use of N, P and K fertilizers. The integrated use of organic manures and chemical fertilizers was found to be quite promising in maintaining stability in crop production through correction of marginal deficiencies of secondary and micronutrient elements in the course of mineralization on the one hand and providing favourable physical and soil ecological conditions on the other. The deteriorating productivity was found to be associated with the imbalance in secondary nutrients like S and micronutrients like Zn. The original productivity could be restored with the application of nutrients which were otherwise yield-limiting. The role of S in maintaining productivity was more marked in respect of certain crops than others in the multiple-cropping systems. Its effect was more marked on kharif rice on both Eutrochrepts (Barrackpore) and Haplaquepts (Bhubaneswar) after 2 and 3 annual cropping cycles, respectively, as the available soil-S (Morgan’s-extractable S) dropped to around 4 mg kg-1 soil.

No perceptible change in soil pH was observed over the years (1971-99) in respect of soils with neutral to alkaline in reaction but the soil pH decreased by 0.9 - 1.0 from the initial values on both Haplustalfs (Ranchi) and Hapludalfs (Palampur) under N treatment. However, incorporation of farm yard manure along with NPK fertilizers showed some moderating effect on soil pH. Appreciable improvement in soil organic carbon over the initial level was noticed at optimal to superoptimal (100-150%) NPK doses on almost all the soils except on Hapludolls (Pantnagar), Eutrochrepts (Barrackpore) and Haplustalfs (Ranchi), where considerable reduction in organic carbon was noticed. However, the initial level of organic carbon was maintained with NPK + FYM treatment.

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The available soil-N improved appreciably at optimal to superoptimal (100-150%) NPK doses over the initial levels on almost all the soils. It declined to a very low level in unmanured plots. The available soil-P at optimal to superoptimal (100-150%) NPK doses was raised from low to high status on Chromisters (Jabalpur), medium to high on Ustochrepts (Delhi), Haplustalfs (Ranchi), Hapludolls (Pantnagar) and Vertic Ustropept (Coimbatore), high to very high on Eutrochrepts (Barrackpore) and Haplustalfs (Palampur) and low to very high on Ustochrepts (Ludhiana). An appreciable build-up in the available soil-K (N NH4Oac-extractable K) was noticed even at the optimal (100%) NPK dose on Ustochrepts (Ludhiana and Delhi) and Haplustalfs (Ranchi) and it was at superoptimal (150%) NPK dose on Hapludalfs (Palampur) and Hapludolls (Pantnagar). However, available soil-K declined over the years on Vertic Ustropepts (Coimbatore), Chromusterts (Jabalpur) and Tropaquepts (Hyderabad) even at superoptimal NPK dose, indicating considerable soil mining of its available K. The highest depletion in available soil-K was noted under NP treatment. Incorporation of farm yard manure (along with optimal NPK dose) improved soil physical properties like bulk density, total porosity and hydraulic conductivity over other treatments.

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TAMIL NADU AGRICULTURAL UNIVERSITY

From To

Dr.P.Savithri,Ph.D., The DirectorProfessor and Head CARDSDept. of Soil Science and Agrl.Chemistry Tamil Nadu Agrl.UniversityTNAU, Coimbatore 641 003. Coimbatore 641 003.

Through: The Director(SCMS)

Sir,

I submit to enclose an article entitled “Lessons from Long Term Fertiliser

Experiments” for favour of publication in the book to be released for the convocation.

PROFESSOR AND HEAD(SS & AC)

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