Proceedings of the Sixth International Citrus Congress

663

Tel Aviv, Israel, March 6-11, 1988, R. Goren and K. Mendel (Eds) © 1988 Balaban Publishers, Philadelphia/Rehovot Margraf Scientific Books, D-6992 Weikersheim ISBN 3-8236-1136-4

The Effect of N and K Fertilisation on Yield and Fruit Size of Valencia S.F. DUPLESSIS AND T.J. KOEN

Citrus and Subtropical Fruit Research Institute, Nelspruit, 1200. Republic of South Africa. Additional Index words: N/K ratio.

Abstract The purpose of this investigation was to determine the leaf N and K levels for maximum yield, optimum fruit size and net income. A field experiment using old Valencia trees and with five levels of N and K in all combinations, was used for this purpose. Results were obtained over a period of five seasons. It was shown that maximum yield did not necessarily ensure maximum income in an area known for small fruit. It was also evident that the N/K ratio in the leaves of fruit bearing twigs was more important in determining yield or fruit size than the absolute N or K values. In the case of maximum yield the optimal N/K ratio was between 2,4 and 3,0 with N higher than 2,1% and K higher than 0,8%. For maximum fruit size the ratio was 1,6 and 2,2 with N higher than 1,8% and K higher than 0,9%. Therefore, to obtain maximum yield the N level should be relatively high and to obtain optimum fruit size and income, theN level should be relatively low.

Introduction Numerous researchers have proposed a relationship between N and K fertilisation on yield and fruit size of citrus (4, 5, 7, 9, 10, 11). Leaf analyses employing the 'critical value' approach where critical norms are used to evaluate the nutritional status of the trees, are very widely used in all citrus producing countries (3, 5, 6, 8). Bar-Akiva (1) claimed that N03-N in citrus leaves was a better indicator for the response to applied N than total N. Sumner (12) suggested that the so called 'Dris' approach was superior to the critical value approach for corn, soybeans and sugarcane. Beverly, Stark, Ojala and Embleton (2) tested the Dris system on Valencias and concluded that it agreed well with the sufficiency range method for

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diagnostic purposes. The Dris approach used the ratios between elements in plant tissue to determine which elements are likely to become lacking. The present investigation was undertaken to determine the leaf N and K levels for maximum yield, optimum fruit size and net income with Valencias, and to investigate the possible use of N/K ratios combined with the sufficiency range concept for fertiliser advisory purposes.

Statistical analyses

Materials and Methods

Effect of N and K on fruit size

This experiment was started in 1981 on 29 year old Valencia trees on sweet orange rootstocks, that received uniformly low fertiliser applications for at least 5 seasons. The trees were grown on the Experimental Farm at Nelspruit on a sandy clay loam soil with a pH (water) of 6.4 and a planting distance of 6.4 x 7.3 m.

Experimental design A factorial design was used with 5 x N and 5 x K levels in all combinations, replicated. three times, with three trees per plot. The N and K levels applied over the 5 seasons 1981/82 to 1985/86 are shown in Table 1. N was applied in two split applications in July and August as limestone ammonium nitrate (28% N) and K also in two split applications in September and October as potassium chloride (50% K). Care was taken to maintain the soil pH above 6.0 in water for the different treatments, over the 5 year period.

Relationships between leaf analyses and yield data were determined by means of polynomial regression analysis. The data were also subjected to analysis of variance.

Results and Discussion Fig. 1 indicates the typical effect of increasing the leaf N or K levels on the mass of small fruit per tree. These data represent the average over five seasons. From these results it is clear that the negative effect of Non fruit size was less consistent that the positive effect of K on fruit size (R2 of 68 as against 87%). Furthermore, with an increase in leaf N of 0.1% at a given K level the mass of small fruit (diam. < 63mm) was increased by roughly 3.6%. Similarly, an increase in leaf K of 0.1% at a given N level decreased the mass of small fruit by approximately 4%. (Yn = 102,26 + 103,26 Xn, where %N (Xn) varies from 1.51 to 2.32% and Yk = 191,9097,42 Xk, where %K (Xk) varies from 0,58 to 1,64%. Yn and Yk is the mass of fruit< 63mm diameter). Q; Q) ~

Q; 170! c. OJ

Table 1: Annual Nand K levels applied {g/tree) during the 5 seasons N applications

K applications

Levels

1981/82 0

0

1

210 420 630 840

2 3 4

1982-1986 210 420 630 840 1050

1981-1986 0

500 1000 1500 2000

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(R 2 •68%)

·-130

E

"'

:0 E E 90 (') co v

-

K(%)

~

"'E

en

N(%)

10 1,8

1,6

Records taken Leaf samples from fruiting terminals were taken annually in April from each plot and analysed for N, P, K, Ca, Mg, Zn, Cu, Mn, Fe and B. Soil samples were taken every second year and analysed for pH, extractable P, AI and exchangeable cations. Fruit was harvested in August on a per tree basis and sized according to commercial standards. Counts used were 138 (smaller than 63 mm diameter), 112 (63-68 mm diameter), 88 (69-73 mm) and 72 (larger than 73 mm diameter). The mass of fruit in each count was recorded separately and expressed on a kg/tree basis.

~7%)

~ 50

0,4

0,6

2,0 0,8

2,2 1,0

2,4 1,2

2,6 1,4

K(%)

Figure 1:

Effect of increasing theN or K concentration in the leaf on mass of small fruit (kg/tree)

In Fig. 2 the effect of increasing K levels on yield, mass of small and large fruit and consequently income, is indicated. Despite a relatively small effect on yield, the effect on net income was quite significant. The reason was the higher prices paid for

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larger fruit. The histogram clearly indicates the reduction of the mass of small fruit and the increase of large fruit due to higher K applications. Similarly, Fig. 3 demonstrates the negative effect of increasing N application levels on net income, due mainly to a drastic reduction in mass of large fruit. From these results it was concluded that and optimal N/K ratio in the leaves will probably exist for maximum yield or optimal fruit size. 3001

or optimal fruit size can be achieved by a combination of different N and K values and not by one value only.

Effect of decreasing NIK ratio In Fig. 6 a summary of the results are given showing the optimal N/K ratio for different sizes of fruit as compared to total yield. Maximum yield (mean for 5 seasons) was obtained with a N/K ratio of 2.8. To obtain a maximum number of fruit with a diameter of 63mm or larger the ratio should be decreased to 2.2; to 1.6 for larger fruit (> 68mm diameter) and even lower for fruit with a diameter of 73mm or more. With these data in mind it is thus easy to adapt to market preferences for smaller or larger fruit without changing the analysis norms.'

a; ~200

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lilt

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300

100

50

201

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K 0 K1 K 2 K 3 K 4

K 0 K 1 K 2 K3 K 4

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Yield

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160 120

180

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4 ,0

5,0

40

6 ,0

Diam . NIK in blare I in leaves

3

2

>

73rnm (d)

4

Leaf NIK ratio

Figure 4 : The relationship between increasing N/K ratio's in the leaves and total yield for 5 seasons.

Figure 6

Effect of increasing the N/K ratio (X) in the leaves on yield and fruit size (mass of fruitY, mean of 5 seasons).

Optimal NIK ratio

Ya = 60.17 + 188.49 X- 33.40 X 2 Yb = 77,.33 + 123.14 X -26,88X 2 Yc = 76,54 + 41,39X -12,08 X 2 Yd = 63 .30- 12.31 X

:-j '

260

i

240,

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I

(R 2 = 65%) (R2 = 67%) (R2 = 86%) (R2 = 87%)

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Lower limits for

220 E 200 E

N and K in the leaf: (Table 2)

Yield

68mm

327 342

77 61

43 25

670

671

Fruit size Examination of the data revealed that the minimum K in this case should be 0,9% with a minimum N level of 1.8%. However, trees with a N level of this magnitude had sparse foliage with a yellowish colour, but bore a relatively large crop with excellent fruit size (Table 2). The data in Table 2 showed that these minimum values correspond very well with the optimum values in Table 3 (N1K3 for fruit size and N4K3 for yield.)

Maximum yield or optimal fruit size This question can only be answered in monetary terms and will therefore differ from country to country and even season to season . In Table 3 the effect of increasing K levels at two N levels (N 1 and N4) is shown. Optimal fruit size is obtained at the NtK3 level and optimal yield at N4K3. Comparing net income per tree N1K2 gave similar values to N4K3, the latter having received 500 g K and 630 g N per tree more than the former. From these results it follows that by increasing the K level from K2 to K4 netcome improved, but to increase theN from Nt to N4 will, despite the higher yield (approximately 48 kg/tree), not be worthwhile in net income terms. Table 3: Effect of increasing K levels at the N 1 and N4 level on the N/K ratio in the leaves, yield (kg/tree), fruit size (kg/tree) and net income of Valencias (Average of 5 seasons) N1 Level K level

KO Kl K2 K3 K4

Yield

Net Income

Fruit size

N/K

(kg/tree

~63mm

3.2 2.6 1.8 1.7 1.7

291 281 293 300 298

169 187 217 227 227

>68mm 68 90 118 126 123

($/tree) 19.00 21.30 24.25 24.80 25.45

4.3 3.9 3.5 2.9 2.6

270 308 302 348 346

120

Table 4: The effect of increasing (a) N levels of application at the K4 level on leaf K and (b) K levels of application at the N4 level on leaf N ( 1986 data). N orK level

LeafK(%) (a)

LeaiN(%) (b)

0 1 2 3 4 p 0.05 0 O.Dl CV(%)

1.93 1.22 0.97 0.82 0.77 0.09 0.12 17.00

2.20 2.22 2.19 2.34 2.18 NS NS 17 .00

Antagonistic effects of Non K and vice versa: In Table 4 the antagonistic effect of increasing N application rates on leaf K is shown at the highest (2 kg K/tree) application level of K. These results show that by increasing the N level of application the leaf K status can be reduced from very high (1,93%) to deficient (0,77%). Increased K levels on the other hand had no effect on theN content of the leaves. These results imply that high K applications will only increase the leaf K level if relatively low N rates are applied, or that the N leaf levels should be reduced to improve the K status of the trees.

Literature Cited 1. Bar-Akiva, A. 1973. Nitrate estimation in citrus leaves as a means of evaluating nitrogen fertilizer requirement of citrus trees. I Congreso Mundia/ De Citricu/tura 1973. Murcia-Valencia Spairi. Vol. I, 159-164. 2. Beverly, R.B., Stark, J.A., Ojala, J.C. and Embleton, T.W. 1984. Nutrient diagnosis of Valencia oranges by DRIS . Jour. Amer. Soc. Horl . Sci. 109, 649-654.

N4 Level KO Kl K2 K3 K4

Therefore, for a market preferring larger fruit, it will not be worthwhile to go for maximum yield. It should also be borne in mind that these results were obtained in a "small fruit area". In hotter areas were fruit size is not a limiting factor, maximum yield will be the obvious choice.

172

37 64

173 231 237

106 111

72

13.55 18.30 19.05 24.50 25.10

3. Calvert, D.V.,l973. Fertilization of citrus on the Alfisols and Spodisols of Florida. I Congreso Mundia/ De Citricu/tura, 1973. Murcia - Valencia, Spain. Vol. 1, 207-211. 4. Chapman, J.C., 1982. The effect of potassium and nitrogen fertilizers on the yield, fruit quality and leaf analysis of~ lmperial mandarins. Aust. Jour . Exp . Agric. and Animal Hush . 22, 331-336. 5 . DuPlessis, S.F. and Koen, T.J., 1984. Effect of nutrition on fruit size of citrus. Proc . Int. Soc. Citricu/ture 1984. Sao Paulo, Brazil Vol. I, 148-150.

672 6 . Embleton, T.W. and Jones W.W., 1972. Correction of potassium deficiency in grapefruit. Calif. Citrograph 57, 227-231. 7 . Embleton, T.W., Jones, W.W., Platt, R.G. and Burns, R.M ., 1974. Potassium nutrition and deficiency in citrus. Calif. Agric. 28, 6-8. 8. Guardiola, J.L., Vivas, S. and Gonzalez-Sicilia, E., 1975. Effectiveness of foliar analysis of nitrogen as an indicator of nitrogen nutrition of citrus. Fruits D' Outre Mer 30, 113-118. 9 . Koen, T.J., du Plessis, S.F. and Langenegger, W.,l976 . The effect of nitrogen fertilisation on yield, fruit quality and leaf composition of Valencia trees. Citrus Subtrop. Fruit Jour . 55, 9-18. 10. Koo, R.C.J. and Reese, R.L.,1984. Influence of nitrogen, potassium and irrigation on citrus fruit quality. The Citrus Industry 65, 48 . 11. Sharples, G.C. and Hilgeman, R.H., 1969. Influence of differential nitrogen fertilization on production, trunk growth, fruit size and quality and foliage composition of Valencia orange trees in Central Arizona. Proc . First !nJern. Citrus Symp. 3,1569-1578. 12.- Sumner, M.E., 1979. Interprepatation of foliar analysis for diagnostic purposes. Agron. Jour . 71, 343-348.