Yield components and fruit development in ‘Golden Delicious’ apples as affected by the timing of nitrogen supply

Scientia Horticulturae, 12 (1980) 243--257 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

243

Y I E L D COMPONENTS A N D F R U I T D E V E L O P M E N T IN ' G O L D E N D E L I C I O U S ' APPLES AS A F F E C T E D BY THE TIMING OF N I T R O G E N SUPPLY

POUL HANSEN State Research Centre for Horticulture, Institute for Pomology, Blangstedgaardsvej 133, DK-5220 Odense S (~ (Denmark) (Accepted for publication 7 August 1979)

ABSTRACT Hansen, P., 1980. Yield components and fruit development in 'Golden Delicious' apples as affected by the timing of nitrogen supply. Scientia Hortic., 12: 243--257. The nitrogen (N) supply of 'Golden Delicious' was changed in various ways during the growing season by altering the N concentration of nutrient solutions or by urea sprays. The terminal shoot growth increased with the duration of "high" N supply, especially with the early summer application where some degree of correlation with the N values of the leaves was established. Blossom density was decreased only at continuously low N supply, when evaluated on the basis of the previous year's crop level. Fruit set was reduced when N in spur leaves, immediately after bloom, dropped below 2.8--3.0%, which occurred with continuously low N, or with high N supply only in the early summer. Growth of fruits at a definite fruit/leaf ratio increased with N supply and, with some variation between years, the N supply during the early part of the fruit growth period was the more important. The yellow colouring of the fruit at certain fruit/leaf ratios was greater at low N levels or when the N supply was low during the later part of the fruit growth period. Other effects on fruit quality and composition were small or experimentally inconsistent when the more N-deficient treatments were excluded. The relative importance of the timing of N supply on the different components of yield and fruit quality is discussed. INTRODUCTION With a few e x c e p t i o n s , N a p p l i c a t i o n in winter, spring, s u m m e r or a u t u m n has n o t increased t h e yield o f apple trees in Danish e x p e r i m e n t s , where t h e soil was clean-cultivated t h r o u g h t h e first p a r t o f the g r o w i n g season, a l t h o u g h a fairly high N status o f the trees is n o r m a l l y achieved u n d e r such c o n d i t i o n s ( D u l l u m and R a s m u s s e n , 1 9 5 2 ; D u l l u m and Dalbro, 1 9 5 6 ; J e p s e n et al., 1 9 6 2 ; Sandvad a n d J e p s e n , 1 9 6 6 ; Vang-Petersen, 1 9 7 5 a , b; Vang-Petersen et al., 1977). H o w e v e r , u n d e r c o n d i t i o n s w i t h a p e r m a n e n t c o v e r c r o p substantial yield increase has b e e n attained. Also, well k n o w n d e t r i m e n t a l effects o f N s u p p l y o n t h e c o l o u r a n d storage q u a l i t y o f the fruits have been c o n f i r m e d . In a t t e m p t s t o balance the effects o f N o n yield and fruit quality, t o o b t a i n the best possible c o m p r o m i s e , t h e t i m i n g o f t h e N availability b e c o m e s an

244

important consideration. It has been the object of several pot experiments to study this balance, where exact timing is easier to establish than under field conditions (Hill-Cottingham, 1963; Mori et al., 1963; Delap, 1967; Liidders and Biinemann, 1969a, b). Under Danish conditions, only the vegetative growth was investigated and was found to be dependent on available N in the early summer in particular; less effect was found if good reserves of N were carried over from the year before (Hansen, 1968). The present pot experiment describes effects of seasonal changes in the N supply on yield and fruit development. Not only was the soil application of N varied, but urea sprays were also included, as they would allow more abrupt changes in the N supply both under experimental and field conditions. Attemps were made to elucidate the effects of N application on the separate components of yield, and to evaluate these effects in relation to other major factors influencing the components, such as fruit/leaf ratios (Hansen, 1977).

MATERIALS AND METHODS

Two-year-old 'Golden Delicious'/MM 104 trees were planted in a porous soil in 15-1 drained plastic pots in the spring of 1970. They were transferred to 30-1 pots before the growing season of 1972. In a similar way, two-yearold 'Golden Delicious'/M 7a (a virus-tested selection of M 7, not identical to the EMLA clone) were planted in 15-1 pots in the spring of 1971 and transferred to 30-1 pots in the spring of 1973. Each of the following treatments comprised 12 replicate trees, where 4 were from the MM 104 lot, and 8 from the M 7a l o t . Treatments comprised combinations of N supply through the roots and urea spraying on the tops (Fig. 1). The experiment started 12 July 1971 and continued until October 1974. During this period the pots were drip-irrigated to run-off with 1--6 1 of nutrient solution per pot per day from 15 May until 1 November. Once a week, pure tap water was used for irrigation. Nutrient solutions of the "high" N content contained 10 meq N/1 (60% NO3-N, 40% NH4-N); those of low N contained 1 meq N/1 in 1971--72, but 2.3 meq N/1 during 1973 and 1974. In all cases, the nutrient solutions contained 2 K, 1 Na, 4 Mg, 4 P, all in meq/1, as well as micro-elements and the natural Ca of the water (ca. 5 meq/1). The trees were sprayed to run-off with a 0.5% urea solution (in late fall 2%) approximately once a week during the periods designated. At the same time, the trees received nutrient solutions of "low" N. The trees were kept indoors during the winters. Cropping was not undertaken until 1972, when the trees flowered abundantly. Bloom was at the end of May, and the blossom density per tree in 1972, 1973, and 1974 was assessed by a scale from 5 (completely covered with flowers) to 0 (without flowers). Similarly, natural fruit set was estimated on 26 June, before the essential part of the June drop, where trees densely covered with fruits were designated as 5, and trees without fruits as 0. Trees

245

I 1/6

I 1/7

I0 meq N / l l l r e

1-2.3

! 1/8 nutrient

! 1/9

I 1/10

l 1/11

solution

-

1-Z.3 urea at each snctlon

+ Indicaind

n spray with 1/2% (=:2% urea)

F i g . 1. T r e a t m e n t s .

were hand-thinned to various extents a b o u t 1 July in 1972 and 1973 to obtain trees of different fruit loads within each treatment. In 1974, the trees randomly developed different fruit numbers. Composite leaf samples of 4 replicate trees were taken at intervals throughout the season. In June, well developed spur leaves were sampled, otherwise leaves sampled were from the middle part of extension shoots. In late autumn, each tree was enclosed in a piece of net to collect the leaves. After drying at 80°C, the total leaf d r y weight per tree was determined. Fruits were harvested in late October and the number and weight per tree was determined. The colour of the fruits from each tree was assessed independently b y 3 individuals using a scale where 5 was very yellow and 0, completely green. The fruits were kept in a cold store for observation o f differences in storage quality. Number and length o f extension shoots were measured each winter. In the autumn o f 1974, the trees were cut up into different parts and their dry weights were determined. The mineral content of the leaves was determined by standard procedures (Hansen, 1973) and expressed as % dry matter. RESULTS

Mineral c o m p o s i t i o n o f leaves. ~ The N concentration of the leaves was affect-

ed distinctly b y the N supply (Fig. 2). It remained low with the " l o w " N application alone (Treatment 9). "High" N supply via the roots in the autumn

246

and by urea spraying in the spring (Treatment 7) gave high spring values and also prevented definite deficiency for the remainder of the season. "High" soil-N in part of June and in July alone (Treatment 8) raised the N level during the application period, but the spring value was low. "High" N from 1 August yielded higher leaf concentrations, when given via the roots (Treatments 3, 5) than by urea spraying (Treatments 4, 6). Urea spraying in part of May and June (Treatments 3, 4) may increase the value slightly. Whole-season supply with 10 meq N/1 (Treatment 1) yielded the maximum values. The concentrations of P and K were high at "low" N supply (Treatment 9) and decreased with the duration of high N supply (Table I). The K content, of the leaves especially, was higher with top rather than root application of N, and this effect seems greater than the corresponding lower N values would suggest. Ca and Mg in the leaves were affected less by the method of N supply. '/,N 2e

3.0

l~ '~,

2.6

/_

"~,,i

s,

1

2.2

1.8

1.4 I

I

I

I

1/6

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1/8

118

I

1110

I

1/11

I

I

I

l/

116

1/7

119

1 9

I

l/tO

I

1/11

Fig. 2. Seasonal c h a n g e s in t h e N c o n c e n t r a t i o n o f leaves as a f f e c t e d b y N s u p p l y . Average o f 1972, 1973 a n d 1974. Signatures as Fig. 1. J u n e samples s p u r leaves, o t h e r w i s e leaves f r o m t h e m i d d l e p a r t o f e x t e n s i o n s h o o t s . LSD = least significant d i f f e r e n c e (P < 0.05). TABLEI N u t r i e n t c o n c e n t r a t i o n s o f leaves as i n f l u e n c e d b y N s u p p l y . Averages o f s a m p l e s t a k e n o n 1 A u g u s t 1972, 1973 a n d 1974; % o f d r y m a t t e r N Supply

LSD

1

2

3

4

5

6

7

8

9

N P

2.97 0.26

2.51 0.33

2.24 0.39

2.22 0.40

2.12 0.49

2.03 0.55

2.17 0.49

2.64 0.39

1.72 0.70

K

1.06

1.47

1.40

1.64

1.57

1.98

1.86

1.65

2.96

0.17

Ca Mg

1.23 0.45

1.24 0,42

1.26 0.44

1.27 0.42

1.20 0.45

1.33 0.39

1.20 0.39

1.25

1.06 0.31

n.s. 0.09

0.44

0.24 0.13

247

The total dry matter production during the experimental period generally decreased, as the duration of "high" N supply was reduced, to about half of the maximum value at "low" N {Table II). The effect of N supply on the vegetative growth was small, although the effect on different parts of the tree varied distinctly. Decreased top growth by reduced N supply was, to some degree, compensated for by improved root growth. The vigorous growth after additional N in June--July alone (Treatment 8) was partly due to a reduced fruit set (see below), but the total dry-matter production was slightly reduced due to the rather short period of "high" N application. The terminal shoot growth was particularly affected by the N supply and correlated fairly well with the duration of "high" N supply (Fig. 3). Also, a fair degree of correlation was shown between the shoot length and the N concentration of the leaves in July or August, except where the N of the leaves was raised by application in late autumn and spring {Treatment 7) or by high N in June-July alone {Treatment 8). Vegetative

growth.

--

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/

20

/,

16

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12 ? t~

¢

I

I

i

1.2

1.6

2.0

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2.6 %N

Fig. 3. Accumulated terminal shoot growth 1971--1974 versus average N concentration of their leaves at the beginning of July (o) and on 1 August (a). Numbers refer to treatments (see Fig. 1).

Yield components. - - The yield of a tree is determined by different components of growth and development. Yield depends on the size of the tree, which is fairly well correlated to the amount of leaves, which again gives an idea of the ability of assimilate production per tree. The diversion of this into fruit growth is again influenced by fruit/leaf ratios as determined by blossom density, fruit set etc., and by the fruit growth potential at a given fruit/ leaf ratio. The different yield components may be influenced by the mode of N supply and to varying extents and should therefore be examined in further detail.

248

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249 B l o s s o m d e n s i t y . - - This factor is influenced in particular by the formation of

flower buds the year before flowering. The yield here, or the fruit/leaf ratio, is a decisive factor. A negative correlation between flower density and fruit/ leaf ratio o f the preceding growing season was established (Fig. 4), but the scatter of individual trees within this relationship was considerable. So only the "low" N application (Treatment 9) can be proven significantly to demand a lower fruit/leaf ratio (perhaps only half), to attain a certain blossom density, than the other treatments. In 1973 the bloom was delayed at "low" N (Treatment 9) and at "high" N in June--July only (Treatment 8). blossom density

x,

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I I

i

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I

I

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200

400

600

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number of f r u i t s /

1973

kg l e a f dry m a t t e r

Fig. 4. B l o s s o m density and fruit/leaf ratios o f the preceding year within 3 groups o f N treatments (see Fig. 1). Parentheses s h o w the range o f N concentration o f leaves, averages o f July and August samples the year before b l o s s o m evaluation. 5 = c o m p l e t e l y covered with flowers. 0 = no flowers.

F r u i t set. - - Assessment o f the final fruit set in relation to blossom density revealed that the fruit set depended to a certain extent on the N status of the trees as indicated by leaf values immediately after b l o o m (Fig. 5) where the N concentration of the spur leaves should be 2.8--3.0% or more to ensure a proper fruit set. In 1973 the leaves were sampled later, and the general N lev-

250

el of the leaves had dropped. The fruit set was low in treatment " l o w " N (Treatment 9) in all 3 years, and with "high" N during June--July (Treatment 8) in 2 of the years. This contributed to the low yields per tree under these 2 treatments. Conversely, additional N in late autumn and in spring only (Treatment 7) showed an adequate fruit set even when the N level was comparatively low later in the season, as was shown in Fig. 2. FRUIT SET

I.O

/

/® 0.9

®/ LSD,set,

/

0.6

/ ®

0.4

~/

/ I,

1973

"13

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74

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A 1974

0.2 [] ,

Jtso~N

t

1972 I

I

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1.6

2.9

2.4

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3.9 % N

Fig. 5. Fruit set and N concentrations of spur leaves in 3 years. Fruit set expressed as ratios between estimates of fruit density before June drop and estimates o f blossom density. Leaves sampled 2, 19 and 10 days after full bloom, in 1972, 1973 and 1974, respectively. Numbers indicate treatments (Fig. 1). - - The growth of individual fruits depends inter alia on fruit/leaf ratios (Hansen, 1977) and the effects of N supply on fruit growth and thus on fruit size should therefore be compared at identical fruit/leaf ratios (Fig. 6). Separation of some of the treatments was possible, b u t n o t in the same way in all years; variations in fruit growth were greatest in 1972, as were the variations in the N status. The tendency is for a more rapid fruit growth with increasing duration o f "high" N supply. Minimum fruit growth was, at least in 1972 and 1974, found at " l o w " N throughout the season (Treatment 9), where the N concentration of the leaves was also very low. The lack of response in 1973 m a y be due to the increase from 1 to 2.3 meq N/1 nutrient soFruit growth.

Fig. 6. Yield versus fruit number on a leaf a m o u n t basis, within different groups o f treatments. Solid curves differ significantly, but n o t the treatments included in the same graph. Based on 12 trees per treatments included in the graph. Parentheses s h o w the range of N c o n c e n t r a t i o n s o f leaves, averages of July and August samplings.

251

kg f r u i t

fw I

kg

leaf

dm

69

1,2,4 {1.8-2.5) ~

3,7 (.w.'r-l.e:)

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1973

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,~J6

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9 (I.6 .l

(2,3)~ ,~. "°* io* #

1974

/o,° t" 200

l 400 number

I 600 of f r u i t s /

I 800 kg

loaf

i 1000 dry mattor

252 lution. However, the seasonal distribution of N may also play a role. "High" N from August only (Treatments 5, 6) was found to relate to the lower growth intensities, whereas Treatment 7, with part of the additional N in the spring, showed a better result in some cases. Additional N in June + July only (Treatment 8) assured a fairly good fruit size at low fruit/leaf ratios, but the size was decreased in 1973 at higher fruit/leaf ratios. So the N supply in the early part of the growing season may be the most important for the growth of the fruits. This does not always correlate with the N status of the leaves during the fruit growth period, as Treatment 4 was among the best in 2 of the years, but its N level was not particularly high (see Fig. 2). - - The colour of the fruit skin is another important factor of yield components. The degree of yellow colouring decreases with increasing fruit/leaf ratio of the tree, which also reduces the average fruit size (Hansen, 1977). Visual assessment of the fruit of individual trees at harvest was related to fruit/leaf ratios (Fig. 7), and the results of size and colour grading after storage (Table III), with few exceptions, show similar trends. "Low" N throughout the season (Treatment 9) in all cases yielded fruits of a stronger yellow colour, even in 1973, when the growth of fruits was not distinctly reduced (see Fig. 6). Continuous "high" N (Treatments 1, 2) resulted in greener fruits. The timing of an additional N supply may play a role; an early application may yield more yellow fruits, as additional N supplied in late autumn and spring alone (Treatment 7) gave more yellow fruits than other treatments and no strong reduction in fruit growth was observed. In 1973, this effect was noticed only in the grading results after storage. "High" N in June--July alone (Treatment 8) resulted in substantial yields only in 1973, here turning the fruits a little more yellow than most other treatments. A high correlation between colour response and the N status of the trees, as judged by leaf analysis during late summer, is not proven; the major trend was, however, higher leaf values and greener fruits with increasing duration of "high" N supply. In all cases, "low" N throughout the season (Treatment 9) yielded fruits with higher contents of total and soluble dry matter and of titratable acid (results not presented). Also, the fruits from the remaining treatments difFruit development.

TABLE

III

Effect of N supply on y e l l o w colouring, after 5--6 months of storage. 100 = all fruits strongly yellow, 33 = all fruits faintly yellow. Fruits o f equal size compared Year

1972 1973 1974

Treatment

LSD

1

2

3

4

5

6

7

8

9

55 46 53

57 43 48

81 70 52

79 50 67

87 72 66

87 69 58

94 84 68

68 76 73

100 96 96

8 7 10

253 colour 5-%- .................

9 (1.3)

4 \ 3 \\ \ ~

8

)

2 (2.6)

1972

g l . 9 - 2.2)

~ I

1.2 (2.4-2.8) I

"'''"

I

I

9 C1.9)

,88 ('2.3) "-.. ~"].6 ~ ~ - ' ( 2 . 1

1973 I

I

I

19,

I

I

~!73.,,,,,:,:,~4,5,6 I 200

I 400

i 600

n u m b e r of f r u / t s /

I 800 kg leaf

,5,6.7 - 2.3 I

(2.1-2.8) i 1000 dry matter

Fig. 7. Colour of fruits in late October at different fruit/leaf ratios within groups of N treatments. Parentheses show the range of N concentrations of leaves, averages of August and September samplings. Visual assessment, 5 = completely yellow, 0 ffi all green. Otherwise as Fig. 6. fered, b u t w i t h o u t a clear c o r r e l a t i o n w i t h N s u p p l y or o t h e r f e a t u r e s o f f r u i t d e v e l o p m e n t . Fruits assessed a f t e r s t o r a g e s h o w e d 1 - - 1 3 % h e a v y russeting a f t e r t h e 1 9 7 2 season a n d 3 - - 1 7 % o f slight russeting a f t e r the 1 9 7 3 season. T h e higher values w e r e f o u n d a f t e r e a r l y u r e a s p r a y i n g ( T r e a t m e n t s 3, 4), exc e p t f o r a high value in fruits o f T r e a t m e n t 8, in 1 9 7 3 . A f t e r t h e 1 9 7 3 a n d 1 9 7 4 seasons, 2 1 - - 3 4 a n d 4 0 - - 5 9 % o f t h e fruits, r e s p e c t i v e l y , d e v e l o p e d

254 heavy scald. Only where fruit growth had clearly been restricted were lower values observed (9% for Treatment 8 in 1973; 6% for Treatment 9 in 1974). Generally, variations between years were greater than between treatments. Other storage disorders occurred only to a minor extent. DISCUSSION Not only the direct supply of N, but also the N reserves of the trees are of importance. N reserves within the tree may be increased by soil or top application in the autumn. Reserves are mobilized and used for new growth in the spring (Tromp and Ovaa, 1967, 1973) and are thus of importance for early development. Substantial amounts of reserves may partly substitute for a direct supply of N in the early part of the growing season (Oland, 1959, 1963; Hill-Cottingham, 1963; Hansen, 1968; Tromp and Ovaa, 1976). Extension growth increases with N supply within a rather broad range (Fig. 3) and the uptake of N in young apple trees is rapid during the period of vigorous terminal growth in particular (Poulsen and ~rensen, 1964; Grasmanis and Nicholas, 1971; Mochizuki and Kamakura, 1971). It is therefore understandable that the availability of appreciable amounts of N during early to mid-summer is of major importance for the extension growth (Mori et al., 1963; Delap, 1967; Hansen, 1968}, whether applied via the roots or the tops (Liidders and Biinemann, 1969a, b). Sufficient N during the late summer may be of importance for flower bud formation (Liidders and Biinemann, 1970a) and NH4-N may be more efficient in promoting flower initiation than NO3-N (Grasmanis and Edwards, 1974). Flower bud formation was only severely checked in trees permanently "low" in N when the fruit/leaf ratios are considered (Fig. 4). Field experiments indicate a decrease in blossom density when summer leaf values are below 1.8% N (Sandvad and Jepsen, 1966), and a tendency to biennial bearing may occur (Williams and Billingsley, 1974). Due to large individual variations in flowering response, minor differences within a higher range of N cannot be excluded. However, in evaluating the effects of N on the yield, effects on flower bud formation will not be of primary importance. Effects on flower development and fruit set may play a greater role. Low or early application of N, as against summer or autumn application, inhibits flower bud differentiation and delays bloom, diminishes the flower quality as shown by the longevity of ovules or the degree of self-fertilization in some cultivars, and reduces fruit set (Hill-Cottingham, 1963; Williams, 1963, 1965; Hill-Cottingham and Williams, 1967; Delap, 1967; Liidders and Biinemann, 1970a; Shim et al., 1972; Terblanche et al., 1979). Similarly, the bloom was delayed in 1973 at "low" N (Treatment 9) and at "high" N in June--July only (Treatment 8). Also, these 2 treatments showed a poorer fruit set (Fig. 5). This stresses the importance of N reserves from the previous year for a proper fruit set as indicated by the N status of the trees around blooming time. Conversely, under conditions with good N reserves, additional N such as spring sprays with KNO3 did not show any benefits (Vang-Petersen, 1975b).

255 The size of fruits,and the yield itself, depend to a certain extent on the N nutrition (Sandvad and Jepsen, 1966; Williams and Billingsley, 1974; VangPetersen et al., 1977). To determine the exact effect on the growth of fruits, evaluation should take place on the basis of the fruit density of the tree (fruit/ leaf ratio; Hansen, 1977). In this study, some positive correlations between N supply and fruit growth were obtained (Fig. 6). Ample N during the early part of the period of fruit development may be more important than during the later part (Mori et al., 1963; Liidders and Biinemann, 1970a). While N supply within a certain range may increase the fruit size, adverse effects are normally found on the storage quality of fruits as well as on colour (Fig. 7). This applies equally to the red colour of red-fruited cultivars as well as the yellow colour of 'Golden Delicious', whereas the greenness of the ground colour and the chlorophyll content of the peel are enhanced by N supply. Leaf values below 1.8--2.1% N have been proposed to ensure a good fruit quality (Jepsen et al., 1962, Sandvad and Jepsen, 1966; Walter, 1967; Kva°le, 1971; Raese and Williams, 1974; Williams and BiUingsley, 1974; VangPetersen et al., 1977). Ample nitrogen availability in the period towards fruit harvest may be more detrimental to the colour than "high" N through the earlier period of fruit development (Fig. 7, Table III; Kaether, 1965; Liidders and Biinemann, 1970a, b) whereas the opposite was found by Mori et al. (1963). It is concluded that N has a pronounced effect on the terminal growth, which may be of importance in young trees. High N availability in early to mid summer, but low availability in the remainder of the year may favour vegetative growth at the expense of fruit. In cropping trees, the effects of N on other yield components should be emphasized. A moderate to good N status of the trees should be established through the late autumn and spring to ensure a proper fruit set. The best compromise between the positive effect of N on fruit growth and the negative one on the colour, etc., of the fruits may be achieved by keeping a rather high N status during the early part, but a lower one during the later part, of the fruit development period. Only if green fruit are the objective should a generally high N status be established. By a more specific timing of the N supply, the N contents of the leaves may be affected in ways which deviate from the effect found under more steady N conditions, so that the normal relationship between leaf contents of N and yield and fruit development will not always apply. ACKNOWLEDGEMENTS The technical assistance of Mr. Eigil Jcbrgensen in running the experiment is highly appreciated.

256

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