J. Sci. Fd Agric. 1975,26,769-778

Some Responses of Chrysanthemum morifolium (cv. “Hurricane”), Grown as a Year-Round Crop in a Peat-Sand Substrate, to Micronutrients and Liming

Peter Adams, Christopher J. Graves and Geoffrey W. Winsor

Glasshouse Crops Research Institute, Littlehampton, Sussex, England (Manuscript received 26 July 1974 and accepted I0 December 1974)

The effects of a fritted micronutrient mixture on the growth and flowering of spray chrysanthemums (cv. “Hurricane”) were studied in relation to pH in a peat- sand substrate (3: l by volume). The treatments consisted of three rates of ap- plication of a fritted micronutrient mixture (0, 200, 500 g/m3) in factorial com- bination with four rates of liming (average pH values 4.2,5.0,6.3 and 7.1). Five suc- cessive crops were grown under conditions, including controlled day-length, used commercially for year-round chrysanthemum production.

Bud initiation and development were greatly delayed in the absence of micro- nutrients, particularly at high pH, and some plants failed to flower. The proportion of marketable sprays was decreased by omission of micronutrients (P < 0.001) and by liming (P < 0.001), and those that were saleable were reduced in size. Omission of micronutrients decreased the numbers of flowers per spray (P < 0.001). Plants grown without added micronutrients developed more leaves and bracts on their lateral shoots (P < 0.001), particularly at high pH (6.3-7.1); the interaction between lime and micronutrients was significant at P < 0.01.

Leaf samples were anaIysed for micronutrient content (B, Fe, Mn, Cu and Zn). Symptoms of boron deficiency (“quilling” of the petals) were recorded and shown to be significantly correlated with the boron content of the leaves (P < 0.001). The copper content of plants grown without added micronutrients was well below the published critical level, and this deficiency is considered re- sponsible for many of the effects observed.

1. Introduction Peat and peat-sand mixtures are now used extensively as substrates for commercial pot-grown plants. In countries with abundant supplies of peat this medium is also widely used for crop production in greenhouse beds and borders. Interest in the extended use of peat as a rooting medium in the United Kingdom led to nutritional studies at the Glasshouse Crops Research Institute, including trials with both macro- and micro- nutrients.

Micronutrient deficiencies readily develop in soilless substrate~,l-~ and it is al- ready normal practice to incorporate a complete micronutrient mixture in peat and peat-sand mixtures. Fritted trace element mixtures4* have proved a reasonably satis- factory means of controlling deficiencies. Problems still arise, however, due to im- balance between micronutrients, uncertainty concerning the need to repeat the treat- ment in continuously cropped beds, and failure to appreciate the extent to which pH

769

770 P. Adams el al.

regulates micronutrient availability. Furthermore, the use of complete micronutrient mixtures has tended to divert attention away from the role of specific elements.

The experiment now reported was designed to test the responses of spray chrysanthe- mums, grown as a year-round crop in glasshouse beds, to a fritted micronutrient mixture over a range of pH values. The results are discussed in relation to published data for leaf composition and deficiency symptoms, much of which is based on studies in sand and solution

2. Experimental 2.1. Plots and layout A concrete bed was partitioned into 24 plots, each of 1.42 m2 (1.22 x 1.16 m internally) in area, with a guard plot at either end. The plots were filled to a depth of 17.5 cm with a mixture of three parts by volume of sphagnum peat and one part of sand.

The bed was divided into two blocks of 12 plots, the treatments being randomised independently within each block.

2.2. Treatments The treatments consisted of three levels of a fritted micronutrient mixture (0, 200 and 500 g/m3, subsequently referred to as FI-3) in factorial combination with four levels of lime (ground chalk at 0.8,2.0,4.4 and 8.0 kg/m3 for treatments Ca 1-4 respectively). The frit (253A) contained 12 % Fe, 5 % Mn, 4 % Zn, 2 % B, 2 % Cu and 0.13 % Mo, and was supplied as a fine powder (87% passing a 100 mesh, sieve) by Ferro (Great Britain) Ltd, Wolverhampton. The lime was of horticultural grade, obtained from quarries at Cocking, Sussex and ground to pass a 0.125 in mesh sieve. The plots received only one application of micronutrients, but supplementary additions of lime totalling 0.3, 1.3, 1.8 and 3.2 kg/m3 at Ca 1-4 were necessary to maintain the different pH values in crops 2-5.

2.3. Glasshouse procedure

Adequate levels of nitrogen, phosphorus, potassium and magnesium were applied as base fertiliser before planting; supplementary nitrogen and potassium were supplied in solution via trickle irrigation equipment.

Each plot was planted with 90 cuttings of cv. “Hurricane”, a widely grown variety, spaced at 12 x 13 cm. The crops were grown under commercial conditions, using stan- dard lighting and shading schedules to control day 1ength;l’ all cuttings used were from the same commercial supplier. The planting dates and pH values are summarised in Table 1.

2.4. Crop recording

All sprays were graded to commercial standards after cutting for market. The saleable product was classified into size grades; the “large” sprays referred to in section 3.3 were those of which 30 or less were sufficient to fill the commercial pack. Detailed ob- servations, including the numbers of buds, flowers, leaves and shoots per spray, were

Responses of Chrysanthemum morifolium to micronutrients 771

also recorded on a representative sample of 20 plants per plot; in crop 1 these observa- tions were limited to the top three lateral shoots only.

Table 1. Planting dates, duration of cropping and pH for chrysanthemum crops 1-5

Crop 1 Crop 2 Crop 3 Crop4 Crop 5 Mean

Planted July December May September January Duration (weeks) 13 17 12 14 15

pH Cal 4.5 4.1 4.2 3.9 4.1 4.2 pH Ca2 5.1 4.9 5.1 4.7 5.0 5.0 pH Ca3 6.6 6.0 6.4 6.2 6.2 6.3 pH Ca4 7.4 6.9 7.2 7.1 6.7 7.1

2.5. Sampling and analysis Cores of peat-sand were taken to a depth of 12.5 cm; pH was determined on the fresh material, using a saturated solution of calcium sulphate at an extractant to substrate ratio of 2.5:l (v/v). This extractant, used for salinity testing in glasshouse soils,11 was shown to give pH values within 0.03 units of those measured in 0.01 M-CaCl, as proposed by Schofield and Taylor.''

Samples of the seventh leaf below the top were collected when the terminal bud was removed to encourage axillary bud formation ("disbudding"). The leaves were dried at 80 "C and ground in a porcelain mortar to avoid metallic contamination. Samples other than for boron determination were ashed at 550 "C; a lower temperature (450 "C) was used for boron, with calcium hydroxide added. Boron (Gorfinkiel and Pollard13) and copper (Andrus14) were estimated colorimetrically ; iron, manganese and zinc were determined with a Unicam SP 90 atomic absorption spectrometer.

3. Results

The crops showed little response to micronutrient treatment during the early stages of growth, though heavy liming (Ca4) shortened the plants in crops 3 and 4 (P < 0.001). Once the buds developed, however, responses to treatment became more obvious. Plants receiving adequate levels of micronutrients were dark green and flowered normally. In contrast, those without micronutrients tended to remain pale green; bud formation was delayed and many of the sprays were unmarketable. When harvested, the plants grown without micronutrients in crops 1-4 were significantly taller than those in the F3 treatments (P < 0.001 in each crop); the average stem lengths were 94.3 and 86.3 cm at F1 and F3 respectively. The main features of the results are summarised in the sections which follow.

3.1. Delayed flowering The effects of micronutrients on the proportion of sprays harvested when 60-70% of the total crop had been cleared are shown in Table 2. Flowering was greatly delayed in the F1 treatments, particularly in crops 1 and 4. Only in crop 3 was there a significant

772 P. Adams et al.

Table 2. Effect of three levels of micronutrients on the proportion of sprays harvested when 60-70% of the total crop had been cleared

Micronutrient treatment Crop 1 Crop2 Crop3 Crop4 Crop5 Mean

F1 9 54 34 24 41 32 F2 100 78 75 85 74 82 F3 100 83 82 83 72 84

1.s.d. (P = 0.05) 3 9 6 14 22

overall delay in flowering at the intermediate (F2) level of trace elements. Heavy liming delayed flowering significantly in crops 2 (P < 0.05), 3 (P < 0.001) and 4 (P < 0.01); the response to lime was greatest in the absence of micronutrients, though the inter- action was significant (P < 0.01) only in crop 3.

Since some of the plants in the F1 plots failed to flower within the period of observa- tion, the data for crop 3 have been recalculated to distinguish between delay and failure to flower. Thus in Figure 1 the numbers of sprays harvested within the first nine days are shown as a percentage of those ultimately flowering. High pH tended to delay flowering at all levels of micronutrients, but the effect was particularly marked in the absence of trace elements.

3.2. Proportion of marketable sprays The pH of the beds had no overall significant effect on the proportion of marketable sprays grown with added micronutrients (Figure 2; F2 and F3 treatments). Where micronutrients were omitted (FI), however, pH values greater than 5.0 decreased the proportion of saleable produce; the effect of pH was greatest between 5.0 and 6.5. The first three crops were the most responsive, the percentage of marketable produce from the Ca4 F1 plots being only 34, 18 and 26% in crops 1-3 respectively. Averaged over five crops the main effects of lime and micronutrients, and the interaction between them, were all significant at P < 0.001.

I I I O< 5.0 6.0 7.0 4.0 5.0 6.0 7.0

O h 4.0

pH of subslrate pH of substrate

Figure 1. Effects of micronutrients and pH on the number of sprays cut in the first nine days of harvesting, expressed as a percentage of those ultimately flowering (Crop 3). 0, F1; A, F2; B, F3.

Figure 2. Effects of micronutrients and pH on the proportion of marketable sprays (mean of crops 1-5). 0 , F1; A, F2; W, F3.

Responses of Chrysanthemum morifollirn to micronutrients 773

Table 3. Effects of micronutrients and pH on the proportion of large‘sprays in five successive chrysan- themum crops

Treatment Crop 1 Crop2 Crop 3 Crop4 Crop5 Mean

Micronutrients: F1 F2 F3

1.s.d. (P = 0.05) Lime:

Cal Ca2 Ca3 Ca4

1.s.d. (P = 0.05)

14.9 23.1 14.4 2.8 18.3 14.7 63.0 39.6 48.0 14.7 31.4 39.3 64.9 44.3 54.7 17.5 37.4 43.8 8.1 7.0 7.3 4.8 8.5

49.2 34.3 45.3 14.6 38.9 36.5 50.7 39.0 45.4 16.3 30.1 36.3 44.8 34.4 39.2 11.6 29.6 31.9 45.7 34.7 26.3 4.1 17.2 25.6 n.s. n.s. 8.4 5.5 9.8

a As defined in section 2.4.

3.3. Proportion of large sprays As a further aspect of quality the main effects of lime and micronutrients on the size of the marketable sprays are summarised in Table 3 ; the data shown are the percentages of plants graded commercially as large (commercial grade “30” or larger; see section 2). Relatively few plants grown without added micronutrients (Fl) developed into large sprays. Lime had no overall effect in crops 1 or 2, but decreased the proportion of large marketable sprays in crops 3-5 (P < 0.01). There was no significant interaction between lime and micronutrients in any of the five crops.

3.4. Flowering When plots receiving adequate micronutrients (F3) had been cleared, the percentage of sprays without any visible buds in the F1 plots, averaged over crops 1-5, ranged from 0.1-0.6% at Cal and Ca2 (pH 4.2-5.0) to 7.5 and 8.7% at Ca3 and Ca4 (PH 6.3-7.1). The proportion of sprays in the F1 plots on which one or more lateral shoots failed to produce visible buds increased still more markedly with pH (Table 4; P < 0.001). The response was greatest in crops 1 and 3, grown during the summer, and occurred mainly between pH 5.0 and 6.3.

Table 4. Percentage of sprays on which one or more lateral shoots in the flowering zone failed to form a visible bud when grown without added micronutrients (Fl)

Treatment Crop 1 Crop2 Crop3 Crop4 Crop5 Mean”

Lime: Cal Ca2 Ca3 Ca4 Mean

2.9 9.0 - 4.7 0.6 - 3.3 10.6 - 4.4 1.7 -

32.4 11.4 30.3 22.2 1.2 19.5 30.7 11.7 23.9 17.3 9.1 18.5 20.7 5.8 15.8 10.5 2.6

a 1.s.d. (P= 0.05) between lime treatments (means of crops 1-5) = 6.7.

114

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Figure 3. Effects of micronutrients and pH on the numbers of flowers per spray (mean of crops 2-5). (a) Open flowers; (b) buds and flowers combined. *, F1; A , F2; W, F3.

0-

6 -

5 1 I I I

The numbers of open flowers per spray when judged ready for market, averaged over crops 2-5, are shown in Figure 3(a). Addition of micronutrients at the F2 or F3 level increased the numbers of flowers (P < 0.001) and largely eliminated the effect of pH. In contrast, high pH values seriously impaired flowering where micronutrients were omitted (FI); the interaction between lime and micronutrients was significant at P < 0.01 *

In addition to data for open flowers, the total numbers of flowers and buds were also recorded. As shown in Figure 3(b), omission of micronutrients decreased the num- bers of buds and flowers (P < 0.001), particularly at high pH, but the effects were smaller than for open flowers alone. This lesser response was due to the fact that lime without micronutrients, though decreasing the numbers of open flowers, increased the numbers of unopened and partly opened buds. The proportion of buds fully opened when har- vested was lower overall at F1 (55%) than at F2 or F3 (70-71 %), falling to 45% in the F1 Ca4 plots.

3.5. Bracts and leaves on lateral shoots Omission of micronutrients at high pH generally increased the numbers of bracts and leaves on the lateral (flowering) shoots (Table 5). Spray chrysanthemums commonly have one or more small bracts per lateral shoot, though these are rarely conspicuous; the data for the F2 and F3 treatments are thus quite typical. Plants grown without added micronutrients at pH 6.2 and 7.0 (Ca3 and Ca4) carried almost twice as many bracts and leaves on the lateral shoots, however. The main effect of micronutrient treatment and the interaction with liming were significant at P < 0.001 and 0.01 respectively.

Apart from increased numbers of bracts per spray in the F1 treatments at high pH, the bracts were often unusually large. In extreme cases, normal leaves were also present

Responses of Chrysanthemum moriforirrm to micronutrients 775

Table 5. Numbers of bracts and leaves per spray on lateral shoots

Bracts + leaves (crops 2-5)

Treatment F1 F2 F3 Normal leaves (crop 1)'

Lime: cal ca2 Ca3 ca4

Mean 1.s.d. (P = 0.05)

14.6 13.9 13.3 0 14.3 12.7 15.4 0.8 25.4 13.6 14.1 9.8 25.2 11.6 12.6 12.1 19.9 12.9 13.8

Between means Fl-F3; 2.2 Within body of table; 4.4

Top three lateral shoots only.

on the lateral shoots, together with intermediate forms. The first experimental crop proved particularly leafy in the F1 plots, and data for normal leaves on the three uppermost lateral shoots per spray are included in Table 5.

3.6. Leaf analysis

The contents of copper, manganese, iron and zinc in the foliage, determined for all plots in crop 3, are shown in Table 6.

Table 6. Concentration of copper, manganese, iron and zinc in chrysanthemum leaves (parts/106 in dry matter; crop 3) in relation to lime and micronutrient treatments

Effluent Micronutrient treatment

Lime treatment F1 F2 F3

c u

Fe

Mn

Zn

Ca 1 Ca 2 Ca 3 Ca 4 Ca 1 Ca 2 Ca 3 Ca 4 Ca 1 Ca 2 Ca 3 Ca 4 C a l Ca 2 Ca 3 Ca 4

2.8 1.8 2.2 2.4

102 128 114 116 97 66 23 21 77 56 43 54

9.5 8.9 5.4 4.9

102 120 104 105 200 146 34 30 81 95 50 53

14.2 11.6 8.8 6.2

122 130 118 97

283 163 40 29

110 91 65 62

776 P. Adams et ul.

The copper content increased with micronutrient treatment and, except at F1 where the values were all very low, decreased with liming. The manganese content of the leaves was particularly responsive to liming. Whereas the F2 and F3 treatments raised the manganese content markedly under acid conditions they had relatively little effect at high pH. The data for iron show no obvious trends with treatments, and ana- lytical values for this nutrient appear to have little diagnostic value. The zinc content increased somewhat with micronutrient treatment and was decreased by liming, but none of the values is considered to be low.

loo-

.C 80-

60- 0 2 40-

a

0 -

c

.. L O

20 -

I I I 5.0 6.0 7.0

01 I 4.0

100 r

pH of substrate Parts/106 boron in leaf

Figure 4. Effect of pH on the boron content of the leaves (mean of crops 1-5). 0, F1; A, F2; ., F3.

Figure 5. Relation between the boron content of the foliage and the proportion of sprays with quilled petals in plots without added micro- nutrients (crops 1-4).

Because of recognisable symptoms of boron deficiency, the content of this element was determined throughout the trial; the results, averaged over the five crops, are shown in relation to pH in Figure 4. In plots receiving the highest (F3) level of micro- nutrients the boron status of the leaves was greatly affected by pH. Under acid condi- tions (Cal, pH 4.1) the boron content in leaves from the F3 plots averaged over 100 parts/106, and a slight marginal scorch indicated toxicity. The boron status of the crop was sub-optimal in the F1 plots, and particularly low values (5-6 parts/106) were recorded for the final crop. As shown in Figure 5, quilling of the petals, characteristic of mild to moderate boron deficiency, was significantly related to the boron content of leaves from the F1 plots in crops 1-4 ( r = - 0.88; P < 0.001).

4. Discussion

The experiment now reported provides quantitative data on the responses of spray chrysanthemums to a micronutrient mixture when grown as a year-round crop under semi-commercial conditions. Whereas in soil the occurrence of micronutrient defi- ciencies in chrysanthemums is relatively rare, in the present study it proved impossible to grow a satisfactory crop in a peat-sand substrate without supplying micronutrients. Apart from the loss of saleable produce, the delays in flowering would have disrupted the

Responses of Chrysanthemum morijolium to micronutrients 777

planned schedule of commercial year-round cropping. In view of the use of unwashed sand, commercial fertilisers and water from the nursery mains (bore-hole), the degree of response to micronutrient deficiency was unexpectedly large.

One feature of the response to omission of the micronutrient mixture was readily identified, namely quilling of the petals due to boron deficiency. The symptoms were as described by Messing and Owen,6 and the boron content of the plants confirmed this diagnosis. Leaves from plants grown without micronutrients (F1 treatment) averaged 10-20 parts/106 B (Figure 4), this being below the published critical levels of 20-25 p a r t ~ / l O ~ , ~ - ~ and quilling was well correlated with boron content (Figure 5).

Quilling of the petals was by no means the most striking feature of the results, however. Many other aspects of flowering were affected adversely by micronutrient deficiency, including earliness (Table 2), proportion of marketable sprays (Figure 2), size of spray (Table 3) and the number of flowers per spray (Figure 3). In severe in- stances the buds, where present, failed to develop and no open flowers were produced. Although the present experiment was designed to examine responses to a micronutrient mixture rather than to individual nutrients, the analytical data in Table 6 strongly sug- gest that copper was the element primarily involved. Thus the iron content (102-128 parts/106 at Fl) was not considered to be at all low and was little influenced by the treat- ments. The zinc content of the leaves responded both to micronutrient application and to pH, but the values found for the F1 plots were well above the published critical level (7 p a r t ~ / l O ~ ) . ~ - ~ The manganese content of leaves from the FI plots at high pH was somewhat low (Table 6) , though not sufficiently so as to suggest acute deficiency. Ad- dition of the micronutrient mixture at high pH led to normal colour and flowering with- out greatly increasing the manganese content. Data obtained by Lunt et ~ 1 . ~ 3 ~ were considered inadequate to estimate the critical level for this element in chrysanthemums, and the critical value reported by Criley and Carlson9 from a commercial source (200 parts/106) seems unduly high; the corresponding value quoted for carnations and roses was 30 parts/106. Lunt et al.’ reported only 3-4 parts/106 Mn in chrysanthemum leaves showing “moderate or severe” deficiency, such values being far below those given in Table 6 . The increasing severity of the deficiency at high pH largely eliminates molybdenum from consideration, this element being least available under acid condi- tions. l5

The copper content of leaves from the F1 treatment (1.8-2.8 parts/106 in crop 3) was well below the critical levels found by Lunt et aL7p8 (5 parts/106) or quoted by Criley and Carlsong (<10parts/106). B u d 6 referred to delays in flowering of up to ten days for a pot-grown cultivar (“Golden Princess Anne”) deficient in copper. Suppression of bud initiation and development by copper deficiency does not appear to have been described previously for year-round spray chrysanthemums. A photograph published by Penning- sfeld and Forchthammer,17 however, showing a terminal flowering (“standard”) variety pot-grown in a mixture of peat and polystyrene granules, suggested a condition analogous to our results for spray varieties. In a later paper Penningsfeldl found no significant effect of copper deficiency on the number of flowers per plant (cv. “yellow Delaware”). As summarised elsewhere,18 direct evidence that copper deficiency can prevent bud development in spray varieties of year-round chrysanthemum has since been obtained, and further studies are in progress.

778 P. Adams et al.

References 1. Penningsfeld, F. Acta Horticulturae 1972, No. 26, p. 81. 2. Bunt, A. C. Acta Horticulturae 1971, No. 18, p. 66. 3. Spithost, L. S. Tuinbouwmededelingen 1969, 32,499. 4. Bunt, A. C. Acta Horticulturae 1972, No. 26, p. 129. 5. SmiIde, K. W. Evaluation of fritted trace elements on peat substrates. Rapport I , 1971, Institute

for Soil Fertility, Haren-Groningen, The Netherlands. 6. Messing, J. H. L.; Owen, 0. PI. Soil 1954,5,101. 7. Lunt, 0. R.; Kofranek, A. M.; Oertli, J. J. The Exchange, 1963,140,38. 8. Lunt, 0. R.; Kofranek, A. M.; Oertli, J. J. In Plant Anlaysis and Fertilizer Problems ZV 1964, p.

398 (Bould, C.; Prevot, P.; Magness, J. R., Eds) American Society for Horticultural Science, East Lansing.

9. Criley, R. A.; Carlson, W. H. Florists’ Review 1970,146, 19. 10. Searle, S. A.; Machin, B. J. Chrysanthemums the year round 1968, 3rd ed., Blandford Press,

London. 11. Ministry of Agriculture, Fisheries and Food. Bull. 209 Fertilizer recommendations 1973, HMSO,

London. 12. Schofield, R. K.; Taylor, A. W. Proc. Soil Sci. SOC. Am. 1955,19,164. 13. Gorfinkiel, E.; Pollard, A. G. J. Sci. Fd Agric. 1952,3,622. 14. Andrus, S. Analyst 1955,80,514. 15. Lucas, R. E.; Davis, J. F. SoiZSci. 1961,92,177. 16. Bunt, A. C. Acta Horticulturae 1973, No. 31, p. 163. 17. Penningsfeld, F. ; Forchthammer, L. Proceedings of the VZth Colloquium of the Znternational

Potash Institute, Florence 1968, p. 364. 18. Adams, P. ; Davies, J. N. ; Graves, C. J. ; Winsor, G. W. J. Sci. Fd Agric. 1974,25,1192.