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Plant density studies with direct seeded tomatoes in Ontario, Canada
Scientia Horticulturae, 1 (1973) 309 320 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
PLANT DENSITY STUDIES WITH DIRECT SEEDED TOMATOES IN ONTARIO, CANADA
M.A. NICHOLS*, I.L. NONNECKE and S.C. PHATAK**
Department of Horticultural Science, University of Guelph, Guelph, Ontario (Canada) *Department of Horticulture, Massey University, Palmerston North (New Zealand) **Ontario Department of Agriculture and Food Research Station, Simeoe, Ontario (Canada) (Received April 25th, 1973)
In direct seeded t o m a t o density experiments with constant rectangularity of 1.0 carried out at Preston and Simcoe Research Stations, Ontario, Canada in 1971, the effect o f increasing plant density from 4.2 to 62.1 plants/m 2 was to increase total plant weight, total fruit weight and ripe fruit weight per unit area. The proportion o f ripe fruit to total fruit increased with increased density, and ripe fruit yields from a single harvest of up to 14 kg/m 2 were obtained. Using the reciprocal y i e l d - d e n s i t y equation 1/W = A p + B (when W is the mean weight per plant (or plant part) at density p, A and B are constants, and density is the only variable) to analyse the experiments, showed that b o t h the A and B constants were influenced by cultivar while the A constant was influenced more b y fertilizer application than was the B constant. In general the effect of increased fertilizer was to increase the yield potential (1/A ) for total plant weight and total fruit weight, but this effect was not so marked for ripe fruit weight. INTRODUCTION The production o f processing tomatoes for mechanical harvesting requires that a very high proportion of the fruit should be ripe when harvested. In California, and similar mediterranean-type climates, the near absence of rainfall over the harvesting period enables this to be achieved b y a process of 'field storage' in which the ripe fruit remains on the plant in the field in good condition, while the rest of the fruit ripens. Although this technique appears to work well in arid climates, it has major defects
310 in more humid climates such as the Eastern half of North America in that the first fruit to ripen may deteriorate before the others have ripened. Concentrated ripening can be obtained b y increasing the plant density (Fery & Janick, 1971) or b y spraying onto the growing crop the ethylene generator, ethephon (Dostal & Wilcox, 1971 ). The majority of plant density studies with processing tomatoes have involved a constant row spacing, and varied within row spacings, although Nicklow & Downes (1971) have attempted to obtain a near square arrangement b y direct drilling, and Fery & Janick (1970) used a square arrangement in some of their plant density studies. The objective of the present work was to determine the effect of plant density, nutrition and cultivar on yield and uniformity of maturity. M A T E R I A L S A N D METHODS
Two experiments were carried out: (1) A plant density and fertilizer study at the University of Guelph's Horticultural Research Station at Preston, Ontario. (2) A plant density and cultivar study at the Ontario Ministry of Agriculture and F o o d Horticultural Research Station at Simcoe, Ontario. In b o t h experiments the seed had been 'hardened' b y soaking in a nutrient solu'tion (Ells, 1963) to give more rapid germination, and defuzzed (removing the hairs on the seed) to ensure that when drilling the seeds did not stick together. The seed was sown into fiat beds using a precision drill (Stanhay R) calibrated to sow from 3 - 5 seeds per site at the spacings shown in Table I. A constant rectangularity of 1.0 (an equidistant spacing) was used for all densities. Soon after seedling emergence the areas were sprayed against flea beetle and the seedlings thinned to one per site. t
TABLEI Spacings used in the experaments Plot
Spacing (cm)
Plant p o p u l a t i o n / m ~
Rows/bed
Sample rows
1 2 3 4 5 6 7 8 (Simcoe) 8 (Preston)
12.7 15.9 19.0 22.9 25.4 28.6 34.3 45.7 45.7
62.1 39.6 27.6 19.1 15.5 12.2 8.5 4.8 4.8
9 9 9 7 7 6 6 4 3
3 3 3 3 3 2 2 2 1
x x x x x x x x x
12.7 15.9 19.0 22.9 25.4 28.6 34.3 45.7 45.7
311 At Preston (Experiment 1), seed was sown on 2 9 - 3 0 May 1971 into a seed bed, wherein the fertilizer had been cultivated with the addition o f the herbicide trifluoralin at 0.5 g/m 2 a.i. There was one variety, 'Fireball', and the experimental design was a split-split plot, with two replications. Fertilizer levels were the main treatments, densities the sub plots, and harvests the s u b - s u b plots. The five fertilizer treatments used were: 0, 0.125, 0.250, 0.375, and 0.500 kg/m z of 1 0 - 1 0 - 1 0 . Destructive harvests were taken on 5 July, 20 July, 6 August, 23 August, 1 September, 8 September, 15 September and 22 September, when the following per plant attributes were measured : Total weight (of aerial parts) Total fruit weight (and number) Ripe fruit weight (and number). All sample plants were guarded by a minimum of 50 cm of plants at the same density. At Simcoe (Experiment 2), seed was sown on 21 May 1971 into a seed bed wherein had been cultivated 0.25 kg/m ~ of 1 0 - 1 0 - 1 0 fertilizer. The cultivars examined were: 'Fireball' 'H 1706' 'L 1626' ' R o m a V.F.' The experimental design was a split-split plot, with two replications. Cultivars were the main treatments, densities the sub plots, and harvests the s u b - s u b plots. Destructive harvests were taken on 30 August, 8 September, 15 September, and 22 September, when the same per plant attributes as in the Preston experiment were determined. All sample plants were guarded b y a minimum of 50 cm o f plants at the same density. Weed control was b y pre-emergence application of the herbicide diphenamid (0.5 g/m 2 a.i.), followed by hand weeding where required. In b o t h experiments regular application of insecticides and fungicides were made against pathogens and irrigation was used to ensure that the soil moisture deficit did not exceed 3 cm, measured using a soil moisture budget. RESULTS A N D DISCUSSION 0 estimates
It was intended to analyse the results from b o t h experiments b y fitting the reciprocal y i e l d - d e n s i t y equation: W -0 =Ap +B
312 (when W is the mean weight per plant, or plant part, at density p and A, B, and 0 are constants when density is the only variable) to the total plant weight, the total fruit weight, and the ripe fruit weight data, using weighted least squares criteria (Nelder, 1963) to obtain estimates o f 0. 0 describes the effect of density on the ratio of plant part (e.g. economic yield) / total plant yield. When 0 = 1.0 (an asymptotic yield/density relationship) it can be shown that: (1) When p -+ 0 then 1/B = W, the yield/plant in a non-competitive situation. (2) When p -+ o~ then 1/A = Wp, the asymptotic yield/unit area. When 0 < 1.0 ( a parabolic yield/density relationship) it can be shown that yield per unit area is maximised at p = BO/A ( 1 - 0 ). In b o t h experiments the estimates o f 0 for total plant, total fruit, and ripe fruit weight were found to vary widely from plot to plot when fitting this equation. Fitting all the total plant weight (aerial parts) data resulted in b o t h experiments to a 0 of 1.2. However, if those plot for which 0 estimates were outside a meaningful range ( 0 . 1 - 2 . 0 ) were discarded, then the 0 estimate for b o t h experiments was found to be close to 1.0. It is considered that the failure to derive useful 0 estimates from some plots was due to the occasional plot which did not conform to the general pattern because of the rolling nature of the sites causing variations in soil depth and drainage. The use o f a systematic spacing design (Nelder, 1962) would, possibly, have permitted more meaningful estimates of 0 using this equation, b y providing a more homogeneous soil environment. Bleasdale (1967) has proposed that 0 can be estimated from a knowledge of the relationship between weight of the plant, and the weight of the plant part using the equation: log1 o W = K + 0 log~ o Wp when W is the weight of a plant, and Wp is the weight of the plant part (e.g. fruit or ripe fruit), and K is a constant, provided that the yielddensity relationship for the total plant weight is asymptotic. This relationship was used to determine 0 for b o t h total fruit weight and for ripe fruit weight in b o t h experiments. In the fertilizer experiment an analysis o f variance o f these 0 estimates for total fruit weight for the last five harvests was unable to detect any significant difference between harvests or between fertilizer treatments. The mean 0 estimate was 0.97 (S.E. = 0.009), however, estimates of 0 for ripe fruit weight for the final two harvests showed a reduced 0 with increased fertilizer (Table II). In the cultivar experiment 0 estimates for total fruit weight were not
313 TABLE II Effect o f fertilizer level on the 0 estimate for ripe fruit (Preston experiment)* Fertilizer rate: 0 estimate*:
0 1.009
1 1.074
2 0.983
3 0.900
4 0.838
*S.E. = 0.037 (D.F. = 9).
TABLE III K parameters for total fruit (Simcoe experiment) Cultivar
K
'Firebalr 'H 1706' 'L 1626' ' R o m a V.F.'
0.96 1.43 1.53 2.22
significantly altered b y cultivar or harvest date, the mean being 0.96 (S.E. --- 0.02). K was however significantly effected b y cultivar (Table III). Fery and Janick (1971) have suggested that the constancy of 0 regardless of genotype or harvest date indicates that total fruit is a constant proportion o f total plant yield, b u t in fact 0 is a measure of the effect o f density on the proportion o f total fruit to total plant yield. 0< 1 indicates that the total fruit/total plant yield decreases with increasing density (i.e. a parabolic yield/density relationship). It is the K parameter which describes the ratio. Analysis of the 0 parameters for the final three harvests for ripe fruit showed no significant differences between cultivar or harvest date. It is pertinent to note the similarity in the estimates of 0 for total fruit yield (calculated from the log ~ log relationship) not only between the cultivars and fertilizer treatments in these experiments, b u t also b e t w e e n these experiments and those of Fery & Janick (1971). Because estimates of 0, using the reciprocal equation proved difficult to obtain, and 0 estimates from the log10 W ~ log~ 0 Wp relationship were close to 1.0, the simpler reciprocal y i e l d - d e n s i t y equation:
1/W = A p + B was used, and an analysis of variance was done on the A and B constants for blocks, harvests, and treatments (cultivars or fertilizers, depending on
314 the experiment), for total plant weight, total fruit weight and ripe fruit weight. In fact results from the use o f the simpler yield density equation probably approximate very closely those one might, obtain using the more sophisticated, equation.
Preston experiment It was found that the variances in the early harvests precluded the carrying out o f an analysis o f variance which included the first three harvests for total plant weight, for harvests 3 and 4 for total fruit weight or for harvest 6 for ripe fruit weight. The analysis o f variance showed in all cases that the fertilizer treatments had no effect on the B parameters for total plant, for total fruit, or for ripe fruit. The A parameter was significantly influenced by fertilizer level for total plant weight and total fruit weight. The same pattern was apparent for the analysis of ripe fruit, although the differences were not significant (Table IV). The A parameters fertilizer response was examined by means o f orthogonal polynomial analysis and showed b o t h a significant linear and quadratic component. An exception was the analysis of ripe fruit, which showed no significant fertilizer response, although the pattern was the same as for the other analyses. One possible explanation o f this may be due to a different ripening pattern with levels o f fertilizer (Table V). This may be due to enhanced ripening at low plant nitrogen levels, or to the higher rates of fertilizer producing heavier fruit yields. The latter would have a greater spread of
TABLE IV Results from fitting reciprocal yield-density equation to Preston experiment data A = kg-I m 2 ; B = kg-l. Fertilizer level
0 1 2 3 4
Total weight
Total fruit weight
Ripe fruit weight
A
B
A
B
A
0.1006 0.0581 0.0514 0.0442 0.0502 Last eight
0.281 0.409 0.233 0.353 0.286 harvests
0.1.174 0.0766 0.0690 0.0597 0.0661 Last four
0.344 0.390 0.200 0.317 0.226 harvests
0.1199 0.0940 0.0874 0.0801 0.0986 Last two
B 0.824 0.706 0.382 0.523 0.409 harvests
315 TABLE V Yield (kg/m: ) of fruit (with % of ripe fruit in parentheses) Means of last two harvests at Preston, derived from y i e l d - d e n s i t y equation. Density
Fertilizer level:
(plants/m 2 )
0
62.1 39.6 27.6 19.1 15.5 12.2 8.5 4.8
8.3 8.0 7.8 7.4 7.1 6.8 6.0 5.0
1 (91) (88) (86) (83) (81) (78) (77) (68)
12.5 12.1 11.7 11.0 10.6 10.1 9.1 7.3
2 (76) (74) (72) (69) (68) (65) (62)
15.3 14.9 14.4 13.8 13.4 12.8 11.7 9.7
(55)
3 (70) (69) (68) (67) (67) (66) (64) (62)
4
16.1 15.4 14.7 13.8 13.1 12.3 10.9 8.5
(70) (69) (69) (67) (67) (66) (65) (62)
15.2 14.6 14.0 13.2 12.6 11.9 10.6 8.4
(63) (62) (63) (63) (63) (63) (64) (65)
TABLE VI Mean weight (kg) per fruit at Preston over the last six harvests for five fertilizer levels Harvest
Fertilizer level
Mean
0
1
2
3
4
3 4 5 6 7 8
0.0339 0.0707 0.0794 0.0903 0.1014 0.1014
0.0342 0.0719 0.0815 0.0943 0.1008 0.1035
0.0370 0.0705 0.0786 0.0916 0.0967 0.1041
0.0400 0.0704 0.0745 0.0868 0.0922 0.0969
0.0371 0.0680 0.0711 0.0786 0.0880 0.0904
Mean
0.0795
0.0810
0.0798
0.0768
0.0722
0.0364 0,0703 0.0770 0.0883 0.0958 0.0992
maturity due to the development of laterals which were virtually absent at the higher populations and low (or zero) fertilizer levels. The mean fruit weight was significantly influenced by the fertilizer level (Table VI), plant density, harvest date, and the harvest fertilizer interaction (Table VII). The mean ripe fruit weight was significantly affected only by harvest date and density. These results support those o f Nicklow & D o w n e s (1971) in that in general higher levels of fertilizer tend to reduce the fruit size (except when comparing zero fertilizer with the next level). It is clear that although the mean weight per fruit increases with maturity, there is a reduction in mean weight per ripe fruit with maturity, especially at the lower densities (Table VII).
316 TABLE VII
Mean weight (kg) per fruit at Preston showing the effect of harvest date and plant density Density
Ripe fruit
(plants/m 2)
Harvest 6
Harvest 7
Harvest 8
Harvest 6
Harvest 7
Harvest 8
62.1 39.6 27.6 19.1 15.5 12.2 8.5 4.8
0.1043 0.1165 0.1271 0.1520 0.1310 0.1484 0.1579 0.1789
0.1039 0.1136 0.1160 0.1356 0.1286 0.1371 0.1484 0.1470
0.0994 0.1156 0.1104 0.1207 0.1150 0.1312 0.1239 0.1363
0.0805 0.0833 0.0844 0.0923 0.0931 0.0932 0.0858 0.0939
0.0844 0.0896 0.0931 0.0986 0.1024 0.0990 0.0992 0.1002
0.0894 0.0987 0.0923 0.1009 0.1023 0.1064 0.0951 0.1089
Total fruit
An analysis of variance done on the number of fruit per m 2 showed significant differences only between harvests, densities and fertilizers. The harvest differences occurred only while the fruits were still setting (harvest 3 and 4), and for the final four harvests there was no significant difference. Increasing fertilizer resulted in increased fruit number, as did increasing plant density (Table VIII). The similarity between the fruit number/density, and yield/density relationships stimulated interest in examining the fruit number data using the reciprocal yield/density relationship:
1/N=Ao +B when N is the number of fruit per plant at density p and A and B are TABLE VIII F r m t number/plant at five levels of fertilizer
Density
Fertilizer level:
(plants/m 2)
0
1
2
3
4
62.1 39.6 27.6 19.1 15.5 12.2 8.5 4.8
1.4 1.9 3.2 4.0 3.7 6.5 8.0 12.8
2.6 2.6 4.0 4.8 6.8 8.4 9.9 15.9
3.1 3.6 4.5 6.7 6.4 11.5 12.8 23.8
3.2 3.6 5.1 7.1 9.1 13.6 12.7 16.5
3.3 3.8 6.0 7.9 9.2 12.5 13.5 22.1
317 04 []
0.3 ~T
[]
o.2 [] []
o.1
[]
lb
[]
2'0
~o
~o
~o
do
7'o
Plant density (P) (plants/rn 2) Fig. 1. Relationship between the reciprocal o f number of fruit per plant and plant density; Preston experiment, mean o f five fertilizer levels
constants when density is the only variable. This appears to provide a reasonable fit to the data (Fig. 1). The mean fruit count data from the final four harvests were fitted to this reciprocal equation, and an analysis of variance done on the A and B constants. Only the A constants for fertilizer were significantly different, thus the major effect o f fertilizer application is to increase fruit number, and that unlike the effect o f fertilizer on fruit weight yield (where the response is parabolic), there is no down turn in fruit number with increasing fertilizer. Thus a major effect o f fertilizer on yield may be by increasing the fruit number, which b y providing more sinks thus increases the photosynthetic efficiency. As shown earlier, the higher the rate o f fertilizer application, the lower the percentage o f ripe fruit at any one destructive harvest. This may be simply a function o f fruit number, for example at 62 plants/m 2 the highest fertilizer rate plants have 3.4 fruits/plant, while the lowest fertilizer rate plants have only 1.4 fruits/plant. Clearly one might anticipate a greater spread of maturity because of this fact alone, but for confirmation we would require data from plants grown at even higher densities than 62 plants/m 2 . The reduced percentage o f ripe fruit at high densities with increased fertilizer application may be due to: (1) The greater spread o f maturity because o f more fruit per plant. This could be tested by using even higher plant populations. (2) A greater between-plant variation. (3) A higher N content in the plant, affecting maturity.
318
Simcoe experiment Analysis of variance of the A and B parameters of the reciprocal yield density equation with 0 =1.0, for total plant weight, total fruit weight and ripe fruit weight was carried out. There was no significant difference for the B parameters for harvests or cultivars for total plant or total fruit weight. In both cases the A parameter was significant (P < 0.01) for cultivar, but not significant for harvests. The analysis on the final three harvests for ripe fruit showed that cultivars had a significant (P < 0.05) effect on the A parameter, but both cultivars and harvest (P < 0.01) and their interaction (P < 0.05) were significant for the B parameter (Table IX). These results are different from those obtained by Fery and Janick (1971), who found that genotype did not effect the A parameter for total
TABLE IX
Results from fitting reciprocal yield-density equation to Simcoe experimental data A = k g -l m 2: B = k g "x
Cultivar
Total weight A
'Fireball'
0.0366 'H 1706' 0.0561 'L 1626' 0.0574 'Roma V.F.' 0.0633
Total fruit
Ripe fruit
B
A
B
A
B
0.1809 0.1118 0.1264 0.1324
0.0441 0.0830 0.0947 0.0925
0.2960 0.1916 0.2676 0.1677
0.0663 0.0918 0.1355 0.1063
0.3493 0.2852 3.5130 1.0180
TABLE X
Yields of ripe fruit (kg/m2), mean of 4 varieties from Simcoe Derived from yield-density equation. Density
Harvest:
(plants/m 2)
2
3
4
62.1 39.6 27.6 19.1 15.5 12.2 8.5 4.8
6.9 5.9 5.0 4.1 3.6 3.0 2.3 1.5
9.1 8.6 8.1 7.5 7.1 6.6 5.7 4.3
9.4 9.0 8.6 8.1 7.8 7.4 6.6 5.2
319 plant weight. The major difference between their work and ours is that they used transplants, while our experiment was direct seeded. In view of the different methods used in plant establishment, further work is required to explain these differences in yield potential. The differences between the A parameters for total plant, and total fruit yields, particularly when comparing 'Fireball' with the other three cultivars suggests that there might be some advantage in selection on a basis o f fruit/total plant ratio. The pattern o f ripening (Table X) supports Fery and Janick's (1971) statement that the higher densities mature earlier. This alone could offer potential in producing mechanically harvested processing tomatoes in short season districts. CONCLUSIONS It appears from the results of these two experiments that the production of processing tomatoes for mechanical harvesting could be successfully done by direct seeding the drop at densities in excess o f 40/m 2 . At this density the need for field storage o f ripe fruit is minimized, as all the crop tends to mature at the same time. These results apply only for a square planting pattern (rectangularity 1.0), and may not be the same when using similar densities and between the row spacings o f 1.5 or 2 meters. Thus if a high density, low rectangularity planting system is used, efficient chemical weed control becomes more critical. It is relevant to note that, at high density, and with a low rectangularity, there is a tendency for the plants to remain more upright, so that the fruit could perhaps be harvested easier, although some modification to existing harvesting machinery would be necessary. At high density, evenness of maturity within each plant will become less important, but between-plant differences b e c o m e increasingly important, hence the need with such plantings will be to minimize betweenplant differences. As the application of fertilizer was found to reduce the maturity concentration, it remains to be seen whether this effect can be reduced by even higher plant populations. Theoretically it would be desirable to find o u t whether the y i e l d density relationship for fruit is asymptotic, or parabolic, because if the latter, then there is an obvious constraint as to how high the densities can go in order to concentrate maturity. However, because the highest densities used already greatly exceed present day agronomic practise, there might be no practical gain from such an approach, especially as our 0 estimates for total fruit were b e t w e e n 0.96 and 0.97, when 0 for an asymptotic relationship is 1.0.
320
ACKNOWLEDGEMENTS The authors wish to acknowledge the financial assistance o f the National Research Council o f Canada, which provided support to the senior author while on sabbatical leave, and Mr. C. van Dyken for his technical assistance.
REFERENCES Bleasdale, J.K.A. (1967), The relationship between the weight of a plant part and total weight as affected by plant density, J. hort. Sei. 42, 51-58. Dostal, H.C. & Wilcox, G.E. (1971), Chemical regulation of fruit ripening of field-grown tomatoes with (2-chloroethyl) phosphoric acid, J. Amer. Soc. hort. Sci. 96,656-660. Ells, J.F. (1963), The influence of treating tomato seed with nutrient solutions on emergence rate and seedling growth, Proc. Amer. Soc. hort. Sci. 83,684-687. Fery, R.L. & Janick, J. (1970), Response of the tomato to population pressure, or. Amer. Soc. hort. SeL 95, 614-624. Fery, R.L. & Janick, J. (1971), Effect of time of harvest on the response of tomato to population pressure, Z Amer. Soc. hort. Sei. 96, 172-176. Nelder, J.A. (1962), New kinds of systematic designs for spacing experiments, Biometrics 18, 283-307. Nelder, J.A. (1963), Yield-density relations and Jarvis's lucerne data, Jr. Agric. Sci., Camb. 61. 427-429. Nicklow, C.W. &Downes, J.D, (1971), Influence of nitrogen, potassium and plant population on the maturity of field seeded tomatoes for once-over harvest, J. A mer. Soc. hort. Sci. 96, 46-49.
PLANT DENSITY STUDIES WITH DIRECT SEEDED TOMATOES IN ONTARIO, CANADA
M.A. NICHOLS*, I.L. NONNECKE and S.C. PHATAK**
Department of Horticultural Science, University of Guelph, Guelph, Ontario (Canada) *Department of Horticulture, Massey University, Palmerston North (New Zealand) **Ontario Department of Agriculture and Food Research Station, Simeoe, Ontario (Canada) (Received April 25th, 1973)
In direct seeded t o m a t o density experiments with constant rectangularity of 1.0 carried out at Preston and Simcoe Research Stations, Ontario, Canada in 1971, the effect o f increasing plant density from 4.2 to 62.1 plants/m 2 was to increase total plant weight, total fruit weight and ripe fruit weight per unit area. The proportion o f ripe fruit to total fruit increased with increased density, and ripe fruit yields from a single harvest of up to 14 kg/m 2 were obtained. Using the reciprocal y i e l d - d e n s i t y equation 1/W = A p + B (when W is the mean weight per plant (or plant part) at density p, A and B are constants, and density is the only variable) to analyse the experiments, showed that b o t h the A and B constants were influenced by cultivar while the A constant was influenced more b y fertilizer application than was the B constant. In general the effect of increased fertilizer was to increase the yield potential (1/A ) for total plant weight and total fruit weight, but this effect was not so marked for ripe fruit weight. INTRODUCTION The production o f processing tomatoes for mechanical harvesting requires that a very high proportion of the fruit should be ripe when harvested. In California, and similar mediterranean-type climates, the near absence of rainfall over the harvesting period enables this to be achieved b y a process of 'field storage' in which the ripe fruit remains on the plant in the field in good condition, while the rest of the fruit ripens. Although this technique appears to work well in arid climates, it has major defects
310 in more humid climates such as the Eastern half of North America in that the first fruit to ripen may deteriorate before the others have ripened. Concentrated ripening can be obtained b y increasing the plant density (Fery & Janick, 1971) or b y spraying onto the growing crop the ethylene generator, ethephon (Dostal & Wilcox, 1971 ). The majority of plant density studies with processing tomatoes have involved a constant row spacing, and varied within row spacings, although Nicklow & Downes (1971) have attempted to obtain a near square arrangement b y direct drilling, and Fery & Janick (1970) used a square arrangement in some of their plant density studies. The objective of the present work was to determine the effect of plant density, nutrition and cultivar on yield and uniformity of maturity. M A T E R I A L S A N D METHODS
Two experiments were carried out: (1) A plant density and fertilizer study at the University of Guelph's Horticultural Research Station at Preston, Ontario. (2) A plant density and cultivar study at the Ontario Ministry of Agriculture and F o o d Horticultural Research Station at Simcoe, Ontario. In b o t h experiments the seed had been 'hardened' b y soaking in a nutrient solu'tion (Ells, 1963) to give more rapid germination, and defuzzed (removing the hairs on the seed) to ensure that when drilling the seeds did not stick together. The seed was sown into fiat beds using a precision drill (Stanhay R) calibrated to sow from 3 - 5 seeds per site at the spacings shown in Table I. A constant rectangularity of 1.0 (an equidistant spacing) was used for all densities. Soon after seedling emergence the areas were sprayed against flea beetle and the seedlings thinned to one per site. t
TABLEI Spacings used in the experaments Plot
Spacing (cm)
Plant p o p u l a t i o n / m ~
Rows/bed
Sample rows
1 2 3 4 5 6 7 8 (Simcoe) 8 (Preston)
12.7 15.9 19.0 22.9 25.4 28.6 34.3 45.7 45.7
62.1 39.6 27.6 19.1 15.5 12.2 8.5 4.8 4.8
9 9 9 7 7 6 6 4 3
3 3 3 3 3 2 2 2 1
x x x x x x x x x
12.7 15.9 19.0 22.9 25.4 28.6 34.3 45.7 45.7
311 At Preston (Experiment 1), seed was sown on 2 9 - 3 0 May 1971 into a seed bed, wherein the fertilizer had been cultivated with the addition o f the herbicide trifluoralin at 0.5 g/m 2 a.i. There was one variety, 'Fireball', and the experimental design was a split-split plot, with two replications. Fertilizer levels were the main treatments, densities the sub plots, and harvests the s u b - s u b plots. The five fertilizer treatments used were: 0, 0.125, 0.250, 0.375, and 0.500 kg/m z of 1 0 - 1 0 - 1 0 . Destructive harvests were taken on 5 July, 20 July, 6 August, 23 August, 1 September, 8 September, 15 September and 22 September, when the following per plant attributes were measured : Total weight (of aerial parts) Total fruit weight (and number) Ripe fruit weight (and number). All sample plants were guarded by a minimum of 50 cm of plants at the same density. At Simcoe (Experiment 2), seed was sown on 21 May 1971 into a seed bed wherein had been cultivated 0.25 kg/m ~ of 1 0 - 1 0 - 1 0 fertilizer. The cultivars examined were: 'Fireball' 'H 1706' 'L 1626' ' R o m a V.F.' The experimental design was a split-split plot, with two replications. Cultivars were the main treatments, densities the sub plots, and harvests the s u b - s u b plots. Destructive harvests were taken on 30 August, 8 September, 15 September, and 22 September, when the same per plant attributes as in the Preston experiment were determined. All sample plants were guarded b y a minimum of 50 cm o f plants at the same density. Weed control was b y pre-emergence application of the herbicide diphenamid (0.5 g/m 2 a.i.), followed by hand weeding where required. In b o t h experiments regular application of insecticides and fungicides were made against pathogens and irrigation was used to ensure that the soil moisture deficit did not exceed 3 cm, measured using a soil moisture budget. RESULTS A N D DISCUSSION 0 estimates
It was intended to analyse the results from b o t h experiments b y fitting the reciprocal y i e l d - d e n s i t y equation: W -0 =Ap +B
312 (when W is the mean weight per plant, or plant part, at density p and A, B, and 0 are constants when density is the only variable) to the total plant weight, the total fruit weight, and the ripe fruit weight data, using weighted least squares criteria (Nelder, 1963) to obtain estimates o f 0. 0 describes the effect of density on the ratio of plant part (e.g. economic yield) / total plant yield. When 0 = 1.0 (an asymptotic yield/density relationship) it can be shown that: (1) When p -+ 0 then 1/B = W, the yield/plant in a non-competitive situation. (2) When p -+ o~ then 1/A = Wp, the asymptotic yield/unit area. When 0 < 1.0 ( a parabolic yield/density relationship) it can be shown that yield per unit area is maximised at p = BO/A ( 1 - 0 ). In b o t h experiments the estimates o f 0 for total plant, total fruit, and ripe fruit weight were found to vary widely from plot to plot when fitting this equation. Fitting all the total plant weight (aerial parts) data resulted in b o t h experiments to a 0 of 1.2. However, if those plot for which 0 estimates were outside a meaningful range ( 0 . 1 - 2 . 0 ) were discarded, then the 0 estimate for b o t h experiments was found to be close to 1.0. It is considered that the failure to derive useful 0 estimates from some plots was due to the occasional plot which did not conform to the general pattern because of the rolling nature of the sites causing variations in soil depth and drainage. The use o f a systematic spacing design (Nelder, 1962) would, possibly, have permitted more meaningful estimates of 0 using this equation, b y providing a more homogeneous soil environment. Bleasdale (1967) has proposed that 0 can be estimated from a knowledge of the relationship between weight of the plant, and the weight of the plant part using the equation: log1 o W = K + 0 log~ o Wp when W is the weight of a plant, and Wp is the weight of the plant part (e.g. fruit or ripe fruit), and K is a constant, provided that the yielddensity relationship for the total plant weight is asymptotic. This relationship was used to determine 0 for b o t h total fruit weight and for ripe fruit weight in b o t h experiments. In the fertilizer experiment an analysis o f variance o f these 0 estimates for total fruit weight for the last five harvests was unable to detect any significant difference between harvests or between fertilizer treatments. The mean 0 estimate was 0.97 (S.E. = 0.009), however, estimates of 0 for ripe fruit weight for the final two harvests showed a reduced 0 with increased fertilizer (Table II). In the cultivar experiment 0 estimates for total fruit weight were not
313 TABLE II Effect o f fertilizer level on the 0 estimate for ripe fruit (Preston experiment)* Fertilizer rate: 0 estimate*:
0 1.009
1 1.074
2 0.983
3 0.900
4 0.838
*S.E. = 0.037 (D.F. = 9).
TABLE III K parameters for total fruit (Simcoe experiment) Cultivar
K
'Firebalr 'H 1706' 'L 1626' ' R o m a V.F.'
0.96 1.43 1.53 2.22
significantly altered b y cultivar or harvest date, the mean being 0.96 (S.E. --- 0.02). K was however significantly effected b y cultivar (Table III). Fery and Janick (1971) have suggested that the constancy of 0 regardless of genotype or harvest date indicates that total fruit is a constant proportion o f total plant yield, b u t in fact 0 is a measure of the effect o f density on the proportion o f total fruit to total plant yield. 0< 1 indicates that the total fruit/total plant yield decreases with increasing density (i.e. a parabolic yield/density relationship). It is the K parameter which describes the ratio. Analysis of the 0 parameters for the final three harvests for ripe fruit showed no significant differences between cultivar or harvest date. It is pertinent to note the similarity in the estimates of 0 for total fruit yield (calculated from the log ~ log relationship) not only between the cultivars and fertilizer treatments in these experiments, b u t also b e t w e e n these experiments and those of Fery & Janick (1971). Because estimates of 0, using the reciprocal equation proved difficult to obtain, and 0 estimates from the log10 W ~ log~ 0 Wp relationship were close to 1.0, the simpler reciprocal y i e l d - d e n s i t y equation:
1/W = A p + B was used, and an analysis of variance was done on the A and B constants for blocks, harvests, and treatments (cultivars or fertilizers, depending on
314 the experiment), for total plant weight, total fruit weight and ripe fruit weight. In fact results from the use o f the simpler yield density equation probably approximate very closely those one might, obtain using the more sophisticated, equation.
Preston experiment It was found that the variances in the early harvests precluded the carrying out o f an analysis o f variance which included the first three harvests for total plant weight, for harvests 3 and 4 for total fruit weight or for harvest 6 for ripe fruit weight. The analysis o f variance showed in all cases that the fertilizer treatments had no effect on the B parameters for total plant, for total fruit, or for ripe fruit. The A parameter was significantly influenced by fertilizer level for total plant weight and total fruit weight. The same pattern was apparent for the analysis of ripe fruit, although the differences were not significant (Table IV). The A parameters fertilizer response was examined by means o f orthogonal polynomial analysis and showed b o t h a significant linear and quadratic component. An exception was the analysis of ripe fruit, which showed no significant fertilizer response, although the pattern was the same as for the other analyses. One possible explanation o f this may be due to a different ripening pattern with levels o f fertilizer (Table V). This may be due to enhanced ripening at low plant nitrogen levels, or to the higher rates of fertilizer producing heavier fruit yields. The latter would have a greater spread of
TABLE IV Results from fitting reciprocal yield-density equation to Preston experiment data A = kg-I m 2 ; B = kg-l. Fertilizer level
0 1 2 3 4
Total weight
Total fruit weight
Ripe fruit weight
A
B
A
B
A
0.1006 0.0581 0.0514 0.0442 0.0502 Last eight
0.281 0.409 0.233 0.353 0.286 harvests
0.1.174 0.0766 0.0690 0.0597 0.0661 Last four
0.344 0.390 0.200 0.317 0.226 harvests
0.1199 0.0940 0.0874 0.0801 0.0986 Last two
B 0.824 0.706 0.382 0.523 0.409 harvests
315 TABLE V Yield (kg/m: ) of fruit (with % of ripe fruit in parentheses) Means of last two harvests at Preston, derived from y i e l d - d e n s i t y equation. Density
Fertilizer level:
(plants/m 2 )
0
62.1 39.6 27.6 19.1 15.5 12.2 8.5 4.8
8.3 8.0 7.8 7.4 7.1 6.8 6.0 5.0
1 (91) (88) (86) (83) (81) (78) (77) (68)
12.5 12.1 11.7 11.0 10.6 10.1 9.1 7.3
2 (76) (74) (72) (69) (68) (65) (62)
15.3 14.9 14.4 13.8 13.4 12.8 11.7 9.7
(55)
3 (70) (69) (68) (67) (67) (66) (64) (62)
4
16.1 15.4 14.7 13.8 13.1 12.3 10.9 8.5
(70) (69) (69) (67) (67) (66) (65) (62)
15.2 14.6 14.0 13.2 12.6 11.9 10.6 8.4
(63) (62) (63) (63) (63) (63) (64) (65)
TABLE VI Mean weight (kg) per fruit at Preston over the last six harvests for five fertilizer levels Harvest
Fertilizer level
Mean
0
1
2
3
4
3 4 5 6 7 8
0.0339 0.0707 0.0794 0.0903 0.1014 0.1014
0.0342 0.0719 0.0815 0.0943 0.1008 0.1035
0.0370 0.0705 0.0786 0.0916 0.0967 0.1041
0.0400 0.0704 0.0745 0.0868 0.0922 0.0969
0.0371 0.0680 0.0711 0.0786 0.0880 0.0904
Mean
0.0795
0.0810
0.0798
0.0768
0.0722
0.0364 0,0703 0.0770 0.0883 0.0958 0.0992
maturity due to the development of laterals which were virtually absent at the higher populations and low (or zero) fertilizer levels. The mean fruit weight was significantly influenced by the fertilizer level (Table VI), plant density, harvest date, and the harvest fertilizer interaction (Table VII). The mean ripe fruit weight was significantly affected only by harvest date and density. These results support those o f Nicklow & D o w n e s (1971) in that in general higher levels of fertilizer tend to reduce the fruit size (except when comparing zero fertilizer with the next level). It is clear that although the mean weight per fruit increases with maturity, there is a reduction in mean weight per ripe fruit with maturity, especially at the lower densities (Table VII).
316 TABLE VII
Mean weight (kg) per fruit at Preston showing the effect of harvest date and plant density Density
Ripe fruit
(plants/m 2)
Harvest 6
Harvest 7
Harvest 8
Harvest 6
Harvest 7
Harvest 8
62.1 39.6 27.6 19.1 15.5 12.2 8.5 4.8
0.1043 0.1165 0.1271 0.1520 0.1310 0.1484 0.1579 0.1789
0.1039 0.1136 0.1160 0.1356 0.1286 0.1371 0.1484 0.1470
0.0994 0.1156 0.1104 0.1207 0.1150 0.1312 0.1239 0.1363
0.0805 0.0833 0.0844 0.0923 0.0931 0.0932 0.0858 0.0939
0.0844 0.0896 0.0931 0.0986 0.1024 0.0990 0.0992 0.1002
0.0894 0.0987 0.0923 0.1009 0.1023 0.1064 0.0951 0.1089
Total fruit
An analysis of variance done on the number of fruit per m 2 showed significant differences only between harvests, densities and fertilizers. The harvest differences occurred only while the fruits were still setting (harvest 3 and 4), and for the final four harvests there was no significant difference. Increasing fertilizer resulted in increased fruit number, as did increasing plant density (Table VIII). The similarity between the fruit number/density, and yield/density relationships stimulated interest in examining the fruit number data using the reciprocal yield/density relationship:
1/N=Ao +B when N is the number of fruit per plant at density p and A and B are TABLE VIII F r m t number/plant at five levels of fertilizer
Density
Fertilizer level:
(plants/m 2)
0
1
2
3
4
62.1 39.6 27.6 19.1 15.5 12.2 8.5 4.8
1.4 1.9 3.2 4.0 3.7 6.5 8.0 12.8
2.6 2.6 4.0 4.8 6.8 8.4 9.9 15.9
3.1 3.6 4.5 6.7 6.4 11.5 12.8 23.8
3.2 3.6 5.1 7.1 9.1 13.6 12.7 16.5
3.3 3.8 6.0 7.9 9.2 12.5 13.5 22.1
317 04 []
0.3 ~T
[]
o.2 [] []
o.1
[]
lb
[]
2'0
~o
~o
~o
do
7'o
Plant density (P) (plants/rn 2) Fig. 1. Relationship between the reciprocal o f number of fruit per plant and plant density; Preston experiment, mean o f five fertilizer levels
constants when density is the only variable. This appears to provide a reasonable fit to the data (Fig. 1). The mean fruit count data from the final four harvests were fitted to this reciprocal equation, and an analysis of variance done on the A and B constants. Only the A constants for fertilizer were significantly different, thus the major effect o f fertilizer application is to increase fruit number, and that unlike the effect o f fertilizer on fruit weight yield (where the response is parabolic), there is no down turn in fruit number with increasing fertilizer. Thus a major effect o f fertilizer on yield may be by increasing the fruit number, which b y providing more sinks thus increases the photosynthetic efficiency. As shown earlier, the higher the rate o f fertilizer application, the lower the percentage o f ripe fruit at any one destructive harvest. This may be simply a function o f fruit number, for example at 62 plants/m 2 the highest fertilizer rate plants have 3.4 fruits/plant, while the lowest fertilizer rate plants have only 1.4 fruits/plant. Clearly one might anticipate a greater spread of maturity because of this fact alone, but for confirmation we would require data from plants grown at even higher densities than 62 plants/m 2 . The reduced percentage o f ripe fruit at high densities with increased fertilizer application may be due to: (1) The greater spread o f maturity because o f more fruit per plant. This could be tested by using even higher plant populations. (2) A greater between-plant variation. (3) A higher N content in the plant, affecting maturity.
318
Simcoe experiment Analysis of variance of the A and B parameters of the reciprocal yield density equation with 0 =1.0, for total plant weight, total fruit weight and ripe fruit weight was carried out. There was no significant difference for the B parameters for harvests or cultivars for total plant or total fruit weight. In both cases the A parameter was significant (P < 0.01) for cultivar, but not significant for harvests. The analysis on the final three harvests for ripe fruit showed that cultivars had a significant (P < 0.05) effect on the A parameter, but both cultivars and harvest (P < 0.01) and their interaction (P < 0.05) were significant for the B parameter (Table IX). These results are different from those obtained by Fery and Janick (1971), who found that genotype did not effect the A parameter for total
TABLE IX
Results from fitting reciprocal yield-density equation to Simcoe experimental data A = k g -l m 2: B = k g "x
Cultivar
Total weight A
'Fireball'
0.0366 'H 1706' 0.0561 'L 1626' 0.0574 'Roma V.F.' 0.0633
Total fruit
Ripe fruit
B
A
B
A
B
0.1809 0.1118 0.1264 0.1324
0.0441 0.0830 0.0947 0.0925
0.2960 0.1916 0.2676 0.1677
0.0663 0.0918 0.1355 0.1063
0.3493 0.2852 3.5130 1.0180
TABLE X
Yields of ripe fruit (kg/m2), mean of 4 varieties from Simcoe Derived from yield-density equation. Density
Harvest:
(plants/m 2)
2
3
4
62.1 39.6 27.6 19.1 15.5 12.2 8.5 4.8
6.9 5.9 5.0 4.1 3.6 3.0 2.3 1.5
9.1 8.6 8.1 7.5 7.1 6.6 5.7 4.3
9.4 9.0 8.6 8.1 7.8 7.4 6.6 5.2
319 plant weight. The major difference between their work and ours is that they used transplants, while our experiment was direct seeded. In view of the different methods used in plant establishment, further work is required to explain these differences in yield potential. The differences between the A parameters for total plant, and total fruit yields, particularly when comparing 'Fireball' with the other three cultivars suggests that there might be some advantage in selection on a basis o f fruit/total plant ratio. The pattern o f ripening (Table X) supports Fery and Janick's (1971) statement that the higher densities mature earlier. This alone could offer potential in producing mechanically harvested processing tomatoes in short season districts. CONCLUSIONS It appears from the results of these two experiments that the production of processing tomatoes for mechanical harvesting could be successfully done by direct seeding the drop at densities in excess o f 40/m 2 . At this density the need for field storage o f ripe fruit is minimized, as all the crop tends to mature at the same time. These results apply only for a square planting pattern (rectangularity 1.0), and may not be the same when using similar densities and between the row spacings o f 1.5 or 2 meters. Thus if a high density, low rectangularity planting system is used, efficient chemical weed control becomes more critical. It is relevant to note that, at high density, and with a low rectangularity, there is a tendency for the plants to remain more upright, so that the fruit could perhaps be harvested easier, although some modification to existing harvesting machinery would be necessary. At high density, evenness of maturity within each plant will become less important, but between-plant differences b e c o m e increasingly important, hence the need with such plantings will be to minimize betweenplant differences. As the application of fertilizer was found to reduce the maturity concentration, it remains to be seen whether this effect can be reduced by even higher plant populations. Theoretically it would be desirable to find o u t whether the y i e l d density relationship for fruit is asymptotic, or parabolic, because if the latter, then there is an obvious constraint as to how high the densities can go in order to concentrate maturity. However, because the highest densities used already greatly exceed present day agronomic practise, there might be no practical gain from such an approach, especially as our 0 estimates for total fruit were b e t w e e n 0.96 and 0.97, when 0 for an asymptotic relationship is 1.0.
320
ACKNOWLEDGEMENTS The authors wish to acknowledge the financial assistance o f the National Research Council o f Canada, which provided support to the senior author while on sabbatical leave, and Mr. C. van Dyken for his technical assistance.
REFERENCES Bleasdale, J.K.A. (1967), The relationship between the weight of a plant part and total weight as affected by plant density, J. hort. Sei. 42, 51-58. Dostal, H.C. & Wilcox, G.E. (1971), Chemical regulation of fruit ripening of field-grown tomatoes with (2-chloroethyl) phosphoric acid, J. Amer. Soc. hort. Sci. 96,656-660. Ells, J.F. (1963), The influence of treating tomato seed with nutrient solutions on emergence rate and seedling growth, Proc. Amer. Soc. hort. Sci. 83,684-687. Fery, R.L. & Janick, J. (1970), Response of the tomato to population pressure, or. Amer. Soc. hort. SeL 95, 614-624. Fery, R.L. & Janick, J. (1971), Effect of time of harvest on the response of tomato to population pressure, Z Amer. Soc. hort. Sei. 96, 172-176. Nelder, J.A. (1962), New kinds of systematic designs for spacing experiments, Biometrics 18, 283-307. Nelder, J.A. (1963), Yield-density relations and Jarvis's lucerne data, Jr. Agric. Sci., Camb. 61. 427-429. Nicklow, C.W. &Downes, J.D, (1971), Influence of nitrogen, potassium and plant population on the maturity of field seeded tomatoes for once-over harvest, J. A mer. Soc. hort. Sci. 96, 46-49.