Annals of the Sri Lanka Department of Agriculture. 2008.10:81-95.
YIELD IMPROVEMENT OF GREENHOUSE TOMATOES (Lycopersicon esculentum) THROUGH PLANT DENSITY MANAGEMENT R.J.K.N. KULARATHNE1, C.K. WICKRAMATHUNGA1 and R.M.L.G.I. RAJASINGHE2 1 Horticultural Crops Research and Development Institute, Gannoruwa, Peradeniya 2 Faculty of Agriculture, Rajarata University, Sri Lanka
ABSTRACT Tomato is the most popular crop among greenhouse vegetables growers in the world. In Sri Lanka also, the crop ranks the same due to various social and economic reasons. Even though greenhouse tomato production is becoming more and more popular among growers, yields remain at low levels due to inadequate research information to improve yields under local conditions. This research was conducted to find out the effect of plant density on growth and yield of greenhouse tomatoes. Seven different spacing treatments, 180 x 40 cm (2.8plants/m2), 180 x 50 cm (2.2 plants/m2), 180 x 60 cm (1.9 plants/m2), 150 x 40 cm (3.3 plants/m2), 150 x 50 cm (2.7 plants/m2), 150 x 60 cm (2.2 plants/m2) and 80 x 50 cm (2.5 plants/m 2) were compared using the hybrid greenhouse tomato variety Volcano. The experiment was conducted in a Randomized Complete Block Design with three replicates in maha 2007/2008 in the greenhouse at Gannoruwa. Plant height, total leaf number, canopy diameter and total leaf area were not significantly different among treatments. Plant density of 3.3 plants/m 2 had the highest Leaf Area Index (LAI), 1.11 in contrast to lowest plant density treatment, at 6 weeks after transplanting. The marketable yield per plant was not significantly different among treatments. A population of 3.3 plants/m2 gave significantly higher marketable yield of 9.83 kg/m2. There was a 3.84 kg yield increase compared to the lowest plant density and 3.5 fold higher productivity compared to the open field tomato cultivation. The average number of fruits/plant and fruit quality parameters did not show any significant differences. The 3.3 plants/m2 treatment gave excellent results, and there is possibility of further decrease in inter-row spacing as it shows a positive co-relation with LAI and yield/ m2. KEYWORDS: Greenhouse tomatoes, Growth parameters, Plant density, Yield.
INTRODUCTION The fresh tomato production in the world at present is about 120 million mt, produced on 4.0 million hectares from 144 countries the (FAOSTAT Database, 2005). Much attention has been focused on the development of this crop due to its multifarious benefits in income, export potential, human nutrition, health and employment avenues (Kallo, 1985). In Sri Lanka, it is considered as one of the most important vegetable crops among farmers. The extent under open field cultivation was 6633 ha in 2006 with an average yield of 9.20 t/ha (AgStat, 2007) though the yield potential is 20-30 t/ha (Department of Agriculture, 2007). The large gap
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between the potential and the average yield under open field conditions is attributed to unpredictable rainfall distribution pattern, pest attacks, diseases, weed infestation and adverse influence of the soil. These factors cause severe crop failure and yield losses, which affect the economy of both growers and consumers. Growing tomatoes in greenhouses is a means of providing a protected environment to the crop with sufficient control over the abiotic and biotic environments, which enables the greater production of high quality products with greater economic benefits to the producer. A survey conducted by Sri Lanka Council for Agricultural Research Policy (CARP) in 2005 revealed that protected agriculture has high potential for expansion and diversification of agricultural production in the country by protecting the crop from adverse shoot and root environmental conditions. Many tropical and sub tropical countries have entered in to this sub sector of agriculture because of its fascinating benefits. Agriculture under protected environment in Sri Lanka has expanded rapidly since its introduction through the Ag.Ent project in 1987. The technology was adopted mostly by the middle level growers, as initial establishment cost is high when compared to traditional open field agriculture. According to Niranjan et al. (2005), local extent under protected agriculture is 62 ha and tomato is 2 ha, which constitutes about 40% of the total vegetable production by 78 growers. One of the important factors, which greatly influence tomato yield, is plant density (number of plants/unit area). Although spacing has no effect on plant survival rate, it affects yield/plant and total yield significantly (Sajjapongse et al., 1988). Plant density is a crucial factor at all times particularly, as it competes for water, nutrients, air and sunlight, and hence the crop growth and development become limited. Under protected agriculture, water and nutrients do not affect as they are supplied according to individual plant requirements. However, the other resources may become limited. It will significantly affect the metabolic activities within the plant and in turn influence the flower initiation, fruit development and ultimately lead to a reduction in fruit yield. Siriwardhana (2001) found that when plants are widely spaced it encourages greater vegetative growth (more branching or tillering depending on resource availability throughout the vegetative growth period) and delaying reproductive growth. It also takes longer time to obtain harvest maturity than at the high density. Tomatoes grown at closer spacing produce smaller plants with low biomass. Plants under such condition produce low yield. However, on the basis of hectare, the yield is high. A closer canopy provides shade for the developing fruit which improve quality over those fruits which are exposed to
EFFECT OF SPACING ON GREENHOUSE TOMATOES 83
sun (Underhill, 1978). Diseases and insects are more difficult to control due to increased amount of foliage under close plant spacing. Wide spacing gave high yield/ plant than narrow spacing because of adequate resource availability. If plants are set at a wider spacing, the plants do not protect each other and are excessively exposed to the unfavourable weather conditions and thus leads to yield loss. The potential yield and recorded average yield of greenhouse tomatoes are140-160 t/ha and 84.2 t/ha respectively under local protected conditions. The retail price for tomato is Rs.90-100/kg. The average farm gate price is Rs.75-80/kg (Niranjan et al., 2005). Most of the farmers, who grow tomatoes under protected condition, are compelled to use agro-techniques developed by other countries, which are not properly suitable to local conditions. As a result, most cultivators could not achieve striking benefits of the protected agriculture. In this regard, generation of recommended agronomic practices are urgently needed with special concern to maximizing production and improve the product quality. There is no recommended plant density given by the Department of Agriculture, for tomato cultivation under protected condition. Therefore, this investigation was carried out to find the suitable plant density using different spacing for promising tomato cultivar “Volcano” under greenhouse conditions. MATERIALS AND METHODS Experimental design The experiment was conducted at the Horticultural Crops Research and Development Institute (HoRDI), Gannoruwa under controlled environment conditions. Dimensions of the greenhouse were 7.5 m width, 15 m length and 4m center height. Seven different spacing treatments, comprising two different double row spacing (150 cm, 180 cm) with three different intra-row spacing and a control as practiced in open field were compared using a popular tomato variety “Volcano”. The experimental design was a Randomized Complete Block Design (RCBD) with three replicates having eight plants/treatment as indicated below. Spacing between double rows 180 cm 180 cm 180 cm 150 cm 150 cm 150 cm
Spacing between plants 40cm 50cm 60cm 40cm 50cm 60cm
Treatment A B C D E F
84 KULARATHNE et al. 80 cm (single rows)
50cm
G
Crop management Nursery was established in styrifoam seedling trays inside the plant house. Seeds were sown in disinfected coir dust in these trays. When the seedlings were at the two true leaf stage, application of Albert solution commenced at the rate of 1 g/l daily. Four week old vigorously grown seedlings were transplanted in black polythene bags (30 x 35 cm), which were filled with coir dust and partially burnt paddy husk (2:1) potting medium. Before transplanting, bags were treated with fungicide Homai at a rate of 1 g/l and kept for two days for sterilization. Silver coloured polythene film was laid on the ground as a mulch to prevent emergence of weeds and contamination of soil borne diseases, before the bags were arranged. Plants were arranged in a double row system. Spaces between two double rows were180 and 150 cm and space between two rows of the double rows was 50 cm. Plants were arranged at 40, 50 and 60 cm distances within each double row. In the control treatment, plants were arranged in single rows where space between rows was 80 cm and 50 cm between the plants. Fertilizer application was done manually at daily intervals. The following concentrations of Albert’s fertilizer mixture was dissolved in water and applied according to the growth stage (Table 1). Irrigation was also done manually twice a day. Table 1. Albert’s solution concentration and volume of dissolved water according to growth stage. Growth stage
Albert’s fertilizer (g/l)
Amount (ml/plant/day)
2 days after transplanting Vegetative stage Flowering stage Fruit development
2 2 3 4
100 250 250 250
Foliar application of 1 g/l concentrated Ca(NO3)2 solution was commenced at the flowering stage and was repeated at weekly intervals throughout the growing period to prevent blossom end rot. Plants were trained as single stems. This was done by pruning lateral shoots when they were about 5 cm in length, by using a disinfected secateur (dipped in a Homai solution). Training was initiated two weeks after transplanting. A polythene string was tied at the base of each plant using a plastic ring, and the string was tied vertically to the overhead horizontal supporting wire to hold the plants. When the plants were grown, the main
EFFECT OF SPACING ON GREENHOUSE TOMATOES 85
stem was trained along the string to maintain a working height. This was done by moving the pots and keeping the plant spacing constant according to the treatments. The old leaves at the base of plants were removed at regular intervals to avoid damages caused by pathogens and to reserve food for growing parts. Manual shaking of overhead horizontal supporting wire was done every day in the morning (9-11 a.m.) to facilitate and enhance self pollination. Measurements and data collection Growth and yield parameters were collected from four plants from the middle portion of each treatment. Vegetative growth parameters; plant height, total number of leaves/plant, canopy diameter, length and width of the leaf at 1st cluster, total leaf area at 4 weeks and 6 weeks after transplanting and stem height to 1st flower cluster were measured. Total leaf area was measured using a 1 cm grid. Reproductive growth parameters measured were days to flowering, number of flowers/cluster, number of flowers aborted/cluster, number of total inflorescence/plant, days to harvesting maturity, number of fruits/truss, average fruit weight, fruit circumference, fruit height, total number of marketable fruits, total marketable yield/plant, total number of non-marketable fruits, total non- marketable yield per plant. All measured and calculated data were analyzed using a SAS package through ANOVA procedure. RESULTS AND DISCUSSION Vegetative growth parameters Plant height Mean plant height among treatments was not significantly affected by different plant densities (Fig. 1). This may be due to the adequate availability of solar radiation for plants in each treatment. That effect may be due to pruning of side shoots, basal leaves and training of plants at correct time and method. This result revealed that inter plant competition for light had not taken place between plants within the selected plant densities.
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300
Plant height (cm)
250 200 150 100 50 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Weeks after transplanting A F
B G
C
D
E
Figure 1. Variation of plant height in weeks after transplanting. (A-180 x 40 cm, B-180 x 50 cm, C-180 x 60 cm, D-150 x 40 cm, E-150 x 50 cm, F-150 x 60 cm, G-80 x 50 cm).
Total number of fully opened leaves Total leaf number during the growing period in the seven treatments was not significantly different (Fig. 2). This result indicated that rate of leaf development was not influenced by the plant densities.
45 40
Number of leaves
35 30 25 20 15 10 5 0 1
2
3
4
5
6
7
8
9 10
11 12 13 14 15 16 17 18
Weeks after transplanting A
B
C
D
E
F
G
Figure 2. Variation of total leaf number with time in relation to plant density. (A-180 x 40 cm, B-180 x 50 cm, C-180 x 60 cm, D-150 x 40 cm, E-150 x 50 cm, F-150 x 60 cm, G-80 x 50 cm).
EFFECT OF SPACING ON GREENHOUSE TOMATOES 87
Ground cover %, width and length of leaf at 1 st cluster and canopy diameter Difference of ground cover % (visual observation) at 50% flowering (4weeks after transplanting) was not significant between treatments (Table 2). The reason may be due to the difference between lowest and the highest plant density, which may not be enough to make the difference between leaf area development. Width and length of the leaf at 1 st cluster and canopy diameter at 6 weeks after transplanting were not significantly different among treatments. Table 2. Effect of spacing on variation of ground cover %, leaf length (cm), leaf width (cm), canopy diameter (cm). Spacing 180 x 40 cm 180 x 50 cm 180 x 60 cm 150 x 40 cm 150 x 50 cm 150 x 60 cm 80 x 50 cm CV (%)
Ground cover % (at 50% flowering) 65.00 61.67 60.00 70.00 68.33 63.33 61.67 11.84
Leaf length (cm) 50.04 49.41 49.96 50.42 51.17 51.08 51.79 3.61
Leaf width (cm) 38.03 37.37 37.79 35.87 38.00 37.79 37.87 3.55
Canopy diameter (cm) 107.54 107.12 106.37 107.04 108.67 108.37 110.29 9.14
Leaf area per plant The leaf area per plant at 50% flowering stage (four weeks after transplanting) and 6 weeks after transplanting were not significantly different (Table 3). Temperature and Photosynthetically Active Radiation (PAR) are important climate factors affecting crop leaf growth. These results revealed that plant densities tested have not influenced total leaf area development, due to the availability of these two factors at satisfactory levels. Table 3.
Effect of spacing on variation of leaf area per plant at 50% flowering and 6 weeks after transplanting. Spacing 180 x 40 cm 180 x 50 cm 180 x 60 cm 150 x 40 cm 150 x 50 cm 150 x 60 cm 80 x 50 cm CV (%)
Leaf area (cm2) -50% flowering 1126.0 1172.0 1081.7 1456.0 1238.0 1473.7 1630.0 17.471
Leaf area (cm2) - 6 WAP 2800.3 3186.7 2857.7 3353.7 2924.0 3167.7 3135.3 12.210
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Leaf area index The total leaf area was not significantly different (Table 3). However, when the total leaf area is related to the land area at 4 and 6 weeks after transplanting, the significant effect was observed (Fig. 3). The treatment D (150 x 40 cm) showed the significantly higher Leaf Area Index (LAI) at 50% flowering and 6 weeks after transplanting. Heuvelink (2005) evaluated the influence of leaf area on tomato yield and showed that yield increased up to LAI of 4 without any negative effects on yield. Therefore, there is a potential of further increasing the plant density in order to achieve optimum LAI. High LAI also helps to decrease greenhouse air temperature through enhancing transpiration. 1.2
A
1
B
Leaf area index
0.8
B
B BC
BC
0.6
C a ab
0.4
bc
bc
bc
cd d 0.2
0 A
B
C
D 4WAP
6WAP
E
F
G
Treatments
Figure 3. Effect of spacing on variation of leaf area index with treatments. (A-180 x 40cm, B-180 x 50cm, C-180 x 60cm, D-150 x 40cm, E-150 x 50cm, F150 x 60cm, G-80 x 50cm). Letters on bars denote significant differences among treatments LSD at p=0.05. Simple letters – 4WAP, Capital letters – 6WAP).
Stem height to 1st flower cluster Stem height up to first inflorescence at 50% flowering stage did not show significant differences between different plant densities (Table 4). The reason may be due to low inter plant competition for light during the vegetative growth period.
EFFECT OF SPACING ON GREENHOUSE TOMATOES 89
Reproductive growth parameters Days to 50% flowering There was no significant difference among treatments in terms of days to reach 50% flowering (Table 4). Leaf number below the 1st inflorescence may be under genetic control and also be affected by environmental conditions such as light intensity and temperature. In this experiment the rate of leaf initiation was not affected throughout the growing period. The height of 1st flower cluster at 50% flowering was not significantly different. Therefore, number of days to 50% flowering was not affected by plant density. Number of inflorescence per plant and number of flowers per cluster Total number of inflorescences per plant was not significantly different among treatments (Table 4). This may be due to the plant density which does not influence the total biomass production per plant and dry matter partitioning on development of generative organs. Kleinhenz et al. (2006) also found that plant density 2.1 plants/m2 in single rows vs. 4.2 plants/m2 in double rows had no meaningful effect on biomass production and partitioning on a per-plant basis. There was no significant difference of number of flowers per cluster up to 8 flower clusters in each treatment (Table 4). Table 4. . Effect of spacing on variation of days to 50% flowering, plant height up to 1 st cluster, number of inflorescence per plant. Spacing
Days to 50% flowering
Height (cm)
Total number of inflorescence /plant
180 x 40 cm 180 x 50 cm 180 x 60 cm 150 x 40 cm 150 x 50 cm 150 x 60 cm 80 x 50 cm CV (%)
61 63 62 61 61 61 64 2.66
63.41 61.41 55.46 68.37 67.83 63.08 73.41 8.54
11 11 11 11 11 11 11 6.45
Number of flowers /cluster 8 8 7 7 7 7 7 3.95
Number of fruits set/cluste r 7 7 5 5 5 5 5 6.19
Number of fruits set per cluster The effect of pant densities on fruit setting was not significantly different. One to two flowers aborted due to the failure of the pollination process. This indicates that there are no source limitation under given plant densities to make a difference of fruit setting among treatments.
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Days to 50% fruit maturity The variation of plant density did not exert a significant effect on days to 50% fruit maturity (Table 5). Reasons may be due to non significant effects on the following parameters: days to 50% flowering, number of inflorescence/plant, number of florets/cluster, number of fruits set/cluster (Table 4) and same amount of leaf mass production in all treatments (Fig. 2). Average fruit weight and number of fruits per plant The average fruit weight and number of fruits per plant were not significantly different among treatments (Table 5). The competition between sinks was not a limiting factor for assimilate distribution, even in the lowest plant density treatment. It showed that there is a potential of increasing plant density further up to a limit that will not affect the average fruit weight and number. Fruit size Table 5 presents the variation of fruit size in terms of fruit length and circumference. Both were not significantly different among treatments, thus indicating that treatments have no effect on fruit size. Fruit size and yield depend on the assimilate distribution within the plant which is controlled by the activity of both sources and sinks. When assimilate availability is lower than total demand, competition between sinks becomes the determinant factor for the control of assimilate distribution. Competition can exist between vegetative and reproductive structures, among inflorescences and among fruits on the same truss. In this experiment results indicated that the plant density did not influence assimilate partitioning among fruits, which affects fruit size. Table 5. Effect of spacing on variation of days to 50% fruit maturity, average fruit weight (g), number of marketable fruits /plant, fruit size. Spacing 180 x 40 cm 180 x 50 cm 180 x 60 cm 150 x 40 cm 150 x 50 cm 150 x 60 cm 80 x 50 cm CV (%)
Days to 50% fruit maturity 40 40 40 40 39 40 39 2.290
Average fruit weight (g) 100.83 100.33 105.40 97.03 102.40 104.40 101.23 4.58
Number of fruits /plant 31.33 31.00 31.00 29.33 30.00 31.33 27.00 5.90
Fruit size Average fruit width (cm) 18.27 18.17 18.57 18.00 18.40 18.50 18.13 1.93
Average fruit length (cm) 9.40 9.43 9.53 9.33 9.50 9.43 9.2 1.82
EFFECT OF SPACING ON GREENHOUSE TOMATOES 91
Number of fruits/m2 Number of fruits/m2 was highly significant among the treatments (Table 6). Even though number of fruits/plant was not significantly different (Table 5), the unit area production was significantly changed due to differences in plant densities. Therefore, higher plant densities gave higher production compared to lower densities. Increment in the number of fruits/m 2 was 41 as the plant density increased from 1.85 plants/m2 to 3.33 plants/m2. Other plant densities gave in-between values. It is a beneficial situation to gain higher number of fruits/m2 while maintaining the average fruit weight and number of fruits at a non significant level from the highest plant density treatment. Yield per plant and unit area Fruit yield/plant was not significantly different between treatments but per unit area production was significantly different (Table 6). In all treatments per plant production was approximately 3 kg. When considering the productivity, treatment 150 x 40 cm gave the highest value as 9.83 kg/m2. It was significantly different from the lowest yield, in treatment 150 x 60 cm, 5.99 kg/m2. Other treatments, 180 x 40, 150 x 50 cm, 80 x 50 cm, 150 x 60 and 180 x 50 cm, gave the values of 8.89 kg/m2 ,8.43, kg/m2 7.42 kg/m2, 7.42 kg/m2 and 7.21 kg/m2 respectively. Treatments with higher number of plants per unit area intercept more light when compared to lower plant densities even though the leaf are was same. The significantly higher LAI in denser plant population (Fig. 3) maximized assimilation availability and helped to keep the fruit biomass in these treatments at higher levels when compared to lower plant density treatments. Table 6. Effect of spacing on number of fruits per m2 and yield. Spacing
Number of fruits/ m2
Yield (kg) Per plant Per m2 180 x 40cm 87 b 3.20 8.89 ab 180 x 50cm 69 c 3.24 7.21 d 180 x 60cm 57 d 3.23 5.99 e 150 x 40cm 98 a 2.95 9.83 a 150 x 50cm 80 b 3.16 8.43 bc 150 x 60cm 70 c 3.34 7.42 cd 80 x 50cm 68 c 2.97 7.42 cd CV (%) 6.50 7.08 7.91 LSD 8.7 NS 1.1 Means in each column followed by the same letter are not significantly different at p = 0.05
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Quality analysis of fruits Brix value, pH, moisture %, peel thickness and % of titratable acidity (as anhydrous citric acid) were not significantly different (Table 7). This study was done for plants grown in a pot system. Fertilizer management and water management were done individually for all the plants. This may be the reason for the uniformity in all fruit quality parameters. Table 7. Effect of spacing on quality parameters of tomato fruits after fully ripening. Spacing 180 x 40cm 180 x 50cm 180 x 60cm 150 x 40cm 150 x 50cm 150 x 60cm 80 x 50cm CV (%)
Brix value 4.13 4.13 4.44 4.70 4.50 4.53 4.87 10.96
pH
Moisture %
4.38 4.41 4.47 4.39 4.48 4.39 4.40 2.37
95.96 96.33 96.29 96.39 96.29 96.15 95.62 0.47
Peel thickness (cm) 0.66 0.70 0.63 0.50 0.66 0.70 0.66 19.35
% of anhydrous citric acid 0.31 0.28 0.26 0.29 0.28 0.27 0.29 8.57
Co-relation of LAI and yield/ m2 There was a correlation between LAI and yield/m 2 (Fig. 4). 2 The R value was 0.61 for two variables. Total yield/unit area increased with the increase of LAI. Optimum LAI did not reach a value to provide maximum yield under the given spacing in this experiment. 12.00
R2 = 0.6131
10.00
Yield/m2
8.00
6.00
4.00
2.00
0.00 0.20
0.40 Series1
0.60
0.80
1.00
1.20
1.40
LAI (6 weeks after transplanting ) Linear (Series1) Linear (Series1)
Figure 4. Co-relation of LAI and yield/m2.
1.60
EFFECT OF SPACING ON GREENHOUSE TOMATOES 93
Co-relation between plant density and yield/m2 The correlation between plant density and yield/ m 2 was highly significant (R2 = 0.953) (Fig. 5). The yields had a positive linear relationship with increasing plant density. This relationship showed that optimum plant density required to have the optimum LAI in order to achieve maximum yield is yet to be determined. 12.00 R2 = 0.953 10.00
Yield/m 2 (kg)
2.67
2.78
3.33
2.22
8 .00
2.5
6 .00
1.85
2.22
4 .00 2 .00 0 .00 1 .5
2 2.5 3 Plant density ( Number of plants/m2 )
3.5
Figure 5. Co-relation of LAI and yield/ m2
Influence of plant density on net returns (for 112 m2 poly tunnel) Table 8. Return on investment (Rs) of greenhouse tomato production in 112 m 2 greenhouse per season. Spacing
Number of Yield (kg) Total Total cost* Net return plants income** 180 x 40 cm 296 888 71040 53395 17644 180 x 50 cm 240 720 57600 50159 7441 180 x 60 cm 200 600 48000 47846 154 150 x 40 cm 370 1110 88800 57677 31123 150 x 50 cm 300 900 72000 53629 18371 150 x 60 cm 250 750 60000 50737 9263 80 x 50 cm 270 810 64800 51894 12906 * Costs of plants is estimated at fixed cost of Rs.12280/112 m 2/season and variable costs including coir dust (Rs. 5.50/plant), Seeds (Rs. 1.00/plant), Polythene (Rs. 2.00/plant), Chemicals (Rs. 5.00/plant), fertilizer (Albert’s Fertilizer-Unipower;Rs. 310/kg ; 143g/plant) and Labour Cost (Rs. 24000/season) ** Income is calculated at average price of Rs. 80 /kg marketable fruits.
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The financial return on investment was calculated separately based on inputs and output of each plant density. Fixed cost and variable costs were considered for the analysis. The financial input depended on plant density and was subjected to the costs of plants and labour for working on the plants (including fertilizer application, picking, training and pruning). Table 8 shows that in the case of increasing plant populations, both inputs and gross returns were significantly higher. Maximum return on investment could be achieved from the highest plant density of 3.3 plants/m2. CONCLUSIONS The marketable yield per plant was not significantly affected by plant density. The highest plant density of, 3.3 plants/m2 produced a significantly high marketable yield and the highest number of fruits/m 2. There was a 3.84 kg increment compared to the lowest plant density (1.9 plants/m 2) and 3.5 fold higher productivity compared to open field tomato cultivation. Maximum economic returns can be achieved by greenhouse tomatoes by practicing 150 x 40 cm (3.3 plants/m2) double row planting system. The density of 3.3 plants/m2 treatment gave excellent results, and there is possibility of further decreasing inter-row spacing as it showed positive co-relation with LAI and yield/m2. ACKNOWLEDGEMENTS Authors wish to acknowledge Dr. I.J. de Soyza, the Director HoRDI, Mrs. Ranjani Pieris Head of the vegetable division, HoRDI, for their encouragement and Dr. K.H.Sarananda, Research Officer In-charge, and the staff of Fruit Research Unit, Gannoruwa for helping with fruit quality analysis. REFERENCES AgStat. 2007. Pocket Book of Agriculture Statistics, Vol: IV, pp.26. Socio- Economics and Planning Center, Department of Agriculture, Sri Lanka. Department of Agriculture. 2007. Tomato. http:/www.agridept.gov.lk FAOSTAT database. 2005. Tomato. http:/www. FAO org. Kallo, A. 1985. Tomato. Allied Publishers Private Limited. New Delhi. 121-136p. Heuvelink, E. 2005. Tomatoes. Crosswell press, UK. 88-89, 115,124p. Kleinhenz, V., K. Katroschan, F. Schuit and H. Stutzel. 2006. Biomass accumulation and partitioning of tomato under protected cultivation in the humid tropics. Horticultural Science 71:173-182. Niranjan, F., H.P.M Gunasena and M. B. Sakalasooriya. 2005. Controlled environmental agriculture in Sri Lanka. Council for Agricultural Research Policy, Colombo 7. Sri Lanka. 2p.
EFFECT OF SPACING ON GREENHOUSE TOMATOES 95 Sajjapongse, A., Y. Ota, Y.C. Roan and C.L.Wu.1988. Some aspects of cultural management at AVRDC. In Tomato and Pepper Production in Tropics, Eds. AVRDC publication No. 89 -317. Pp. 349-347. AVRDC Shanhua, Tainan, Thaiwan. Siriwardhana, K.P.D. 2001. Effect of genotype and plant density on seed quality in Pea (Pisum sativum L.). Annals of the Sri Lanka Department of Agriculture 3:255-263. Underhill, J.P. 1978. Tomato cultural and varietal investigations in the Sultanate of Oman. International research Institute. New York. 21-22 p.