VEGETABLE SOYBEAN FOR SUSTAINABLE AGRICULTURE. S. Shanlnugasundaram, S. C. S. Tsou, and M. R. Yan' ABSTRACT

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1 379 VEGETABLE SOYBEAN FOR SUSTAINABLE AGRICULTURE S. Shanlnugasundaram, S. C. S. Tsou, and M. R. Yan' ABSTRACT Vegetable soybean is one of the most important vegetables in Japan, Taiwan, China and Korea. Its importance in human nutrition is increasingly recognized in many countries. Research on vegetable soybean at AVRDC was initially aimed at developing varieties suitable for export to Japan, the biggest market for vegetable soybean. Increasing demand for vegetable soybean research in other countries prompted AVRDC to broaden its research scope to cover the tropics and subtropics. Data from advanced yield trials of vegetable soybean selections conducted at AVRDC in spring and autumn were used to demonstrate the potential of vegetable soybeans in sustainable agriculture. Twenty-four selections were evaluated using four replications in a randomized complete block design. The minimum and maximum biomass yields were 13.4 t/ha in autumn and 33.2 t/ha in spring season. Direct returns to the farmers can be obtained from pods, graded standard pods and shelled beans. The yield of these components ranged from 6.2 to 15.9, 2.6 to 10.6, 4.8 to 6.4 t/ha, respectively. The residues are stem with leaves and roots ( t/ha) arid empty shells ( t/ha) when the pods are shelled to obtain the beans. While beans are nutritionally important to people, the root, stein, leaves and shells are nutritionally valuable to animals, or when returned to soil they enrich and sustain its productivity. AVRDC has developed improved vegetable soybean varieties adapted to the tropics and suitable for ricebased cropping systems. The pods can be used for the fresh market or processed for export, and the ungraded pods can be used in the domestic market. Vegetable soybeans can be harvested in days after sowing even during the rainy season when other vegetable are in short supply. INTRODUCTION To meet the food requirements of the growing population especially in the tropics food production must be increased. Since cultivable land is limited, an increase in food production could be achieved primarily through increased productivity and cropping intensity. This means intensive agriculture. In modgrn agriculture increasing productivity invariably depend on nonrenewable fossil-fuel energy sources. It is time to look again at the merit of promoting the use of inputs from the farm by suitably altering the cropping systems to achieve improved productivity, profitability, stability and sustainability of crop production systems. Soybean Breeder and Director, Biochemist and Deputy Director General, and Research Assistant, respectively, AVRDC, P.O. Box 42, Shanhua, Tainan 741, Taiwan, R.O.C.

2 Vegetable Soybean Vegetable soybean [ Glycine max (L.) Merrill] is soybean harvested after the R6 and before the R7 growth stage (Fehr at al., 1971) while the pod is still green and the seeds have developed to fill 80 to 90% of the pod width (Shanmugasundaram at al., 1991). The characteristics and uses of vegetable soybean for the Japanese market are fully described by Shanmugasundaram at al. (1989) and Lumpkin and Konovski (1991). As a legume, vegetable soybeans fix atmospheric nitrogen through rhizobium bacteria in their root nodules through symbiosis. Therefore, the need for applying additional nitrogen input is minimal and depends largely on soil fertility, yield and profit goal. Vegetable Soybean Research at AVRDC The initial research on vegetable soybean at AVRDC was a contract research project with Council of Agriculture in Taiwan aimed at developing varieties suitable for export to Japan. Increasing interest and demand for vegetable soybean in other countries encouraged AVRDC to broaden its research scope to cover adaptation of the crop in the tropics and subtropics. The objectives of vegetable soybean research at AVRDC are to: 1. Develop varieties suitable for the export market. 2. Obtain high marketable yield. 3. Improve consumer quality. 4. Incorporate disease resistance. 5. Develop adaptation to mechanization. Continuous Cropping vs Crop Rotations Research has clearly shown that maize grown after soybean results in 16 to 176% higher yield compared to continuous cropping of maize (Table 1). Similarly yields of sorghum were 7 to 47% higher when grown after soybean compared to continuous cropping of the same crops. Soybean after sorghum had a 23 % yield advantage over soybean after soybean (Table 2). Table 1. Grain yield of maize grown after soybean compared to continuous cropping of maize with no additional nitrogen fertilizer. Maize yield (kg/ha) Increase References Following maize Following soybean (%) Robinson, Higgs et al., Randall, Hesterman et al., Lesoing, 1988

3 Table 2. Influence of previous crop on non-irrigated maize, sorghum and soybean yields. AVRDC Mead (data from A. D. Flower day). (Penas 1982). 381 Crop yield (kg/ha) Maize Previous cro Sorghum Soybean Maize yield 3315 Sorghum yield 5590 Soybean yield 2015 (19 %) a/ (23 %) 4875 (47 %) 5980 (7 %) 1690 a/ Values in parenthesis are percent increase over monocrop yield. In the past, farmers in developing countries in Asia used a rice-legume cropping pattern. However, in recent years improved high yielding rice varieties, availability of market and assured water supply encouraged them to plant rice twice or even three times a year using non-renewable energy sources. To avoid monocropping, alternative agriculture should assure a market and an equitable return from the chosen crop. Vegetable soybeans can be such a crop. Experimental Details Advanced yield trials of vegetable soybean were conducted at AVRDC in Shanhua, Taiwan in spring and autumn. Twenty-one breeding lines developed at AVRDC and three check varieties were used. The experimental design consisted of a randomized complete block with four replications. The plot size was 5 m x 2 m. Each plot consisted of two raised beds and two rows of plants on each bed. Between-row spacing was 50 cm and within-row-between-hill spacing was 10 cm. Each hill had two or three seedlings in the spring to give a plant population density of 500,000/ha. In the autumn the plant population density was 350,000/ha. Seedlings were thinned in autumn but not in spring. AVRDC's suggested cultural practices were followed. The whole plot was harvested by cutting the plants at the ground level, and observations were recorded. From seedling emergence observations were made on a total of 29 characters. In this paper data on total biomass yield, total pod weight, graded pod yield, yield of stem and leaves, shelled bean weight and shell weight are discussed. Data were analyzed using the SAS program. RESULTS AND DISCUSSION In Taiwan vegetable soybeans are harvested by cutting or uprooting the whole plant. The pods from individual plants are then stripped. Stems with leaves are either returned to the field or fed to cattle. Initial sorting is done by selecting two- and three- seeded good quality pods called graded pods. Single-seeded, malformed or other rejected pods are normally shelled and the beans are marketed domestically. The graded pods are transported to the factory where they are further sorted and processed for export.

4 382 The total biomass yield varied from a low of 13.4 t/ha in autumn to a maximum of 33.2 t/ha in spring (see Table 3). On the average, of the total biomass 48.0% in spring and 49.3% in autumn are total pod by weight. The total pod yield could be as high as 15.9 t/ha in spring and 9.9 t/ha in autumn. However, the maximum graded pod yield was 10.6 t/ha in spring and 6.0 t/ha in autumn (Table 3). Therefore 67% and 61% of the total pods are exported in spring and autumn, respectively. in the domestic market. The remaining 33 % in spring and 39% in autumn are sold as shelled bean Table 3. The total biomass yield, total pod weight, and standard (graded) pod yield of vegetable soybean (kg/ha). Parameter Total biomass yield Total pod weight Standard (graded) pod yield S a/ F a/ Combined S F Combined S F Combined Minimum 26,200 13,400 20,600 12,950 6,180 9,570 6,450 2,560 5,055 Maximum 33,200 20,900 26,900 15,950 9,950 12,760 10,590 5,970 8,280 Mean 29,624 17,675 23,649 14,242 8,718 11,480 8,619 4,833 6,725 C.V. (%) a/ S: Spring season, F: Autumn season. Combined data from spring and autumn seasons indicated that 9.1 t/ha to a maximum of 15.0 t/ha of stems and leaves (average of 12.2 t/ha) are returned to the soil (seasons combined) depending upon variety. Grain soybean is harvested at the R8 growth stage. Research results from AVRDC clearly showed that the percent nitrogen in the shoot was higher at growth stage R6 than at R8. Percent nitrogen was higher in the shoot at growth stage R6 in autumn than in spring (Table 4). Examination of two different varieties, Kaohsiung No. 8 (KS 8) and KS 10 at growth stages R6 and R8 confirmed that at R6 the nitrogen content of the shoot was 17.5% to 25.6% higher than at R8 (Table 5). Therefore, by growing vegetable soybeans and returning the stem, leaves and shells to the soil approximately 79 to 115 kg N/ha are added to the soil. In the case of grain soybean the amount of N returned to the soil is about 36 to 56 kg/ha (Tables 4 and 5). Trikha (1986) reported that in India the contribution of residual nitrogen from soybean to the succeeding wheat crop is about 45 to 60 kg N/ha.

5 383 Table 4. Nitrogen yield from soybean Kaohsiung No. 8 at different growth stages and seasons. Stage Season Seed Shoot (kg/ha) (%) (kg/ha) ( %) R6 Spring R6 Autumn R8 Spring R8 Autumn (Data source: Dept. of Soil Science, AVRDC) Table 5. Nitrogen yield from soybean at different growth stages. Variety Stage Shoot Pod (kg/ha) (%) (kg/ha) ( %) KS 8 R KS 8 R KS 10 R KS 10 R '/ egetable soybeans are also sold either as fresh or frozen shelled beans. Thus, the yield of shelled bean was also determined. The green bean yield varied from 4.8 t to 6.4 t/ha with a mean of 5.6 t/ha (spring and autumn). Shell weight varied from 4.6 to 6.7 t/ha with a mean of 5.8 t/ha. The results suggested that the whole pod consists of approximately 50% shell and 50% beans by weight. Normally the shells are fed to the cattle. By combining the data from the spring and autumn seasons it is estimated that about 76 % of the total biomass from vegetable soybean is either returned to the soil or used as animal feed or utilized for both purposes. About 24% of the total biomass is used for human nutrition. According to Swaminathan (1987), "the farmer's decision on technology choice and adoption will always be based on the net return per hectare as well as security of that return and not by gross yield per hectare". The popularity of vegetable soybean cultivation supports this. The price of grain soybean is US$ 0.60/kg or a gross return of US$ 1,200 for 2,000 kg/ha. The cost of production is about US$ 1,696. The net return is minus US$ 496. However, the price of vegetable soybean pod is US$ 0.32/kg. For an average yield of 8,000 kg/ha the gross return is US$ 2,560 and the net return is US$ 884/ha. Thus it is not surprising that the grain soybean area in Taiwan has gradually declined over the years while that for vegetable soybean has gradually increased from an insignificant area in 1980 to about 10,000 ha in 1990.

6 384 Grain soybean in Taiwan matures in 105, 95 and 85 days in spring, summer and autumn, respectively. However, vegetable soybeans are harvested in 80±2.3, 75.9±4.6, and 70.9±2.6 days in spring, summer and autumn, respectively (Tray et al., 1991). Vegetable soybean is a shorter duration crop. Vegetable soybeans can be included in a cropping system with other crops to enhance productivity and thus increase the income of the farmers. Farmers can try a number of different cropping patterns depending upon the market and environment as shown in Figure 1. Vegetable soybean is a high value crop. Therefore, it is important to choose the optimum environment to maximize income from growing the crop together with other selected crops. In recent years, the cost of labor in Taiwan has increased significantly. Labor cost comprises a big chunk of the production costs. Since land preparation, planting, harvesting and sorting are major labor intensive operations mechanization is being introduced into these areas. Land preparation, planting and covering of seeds is already being done in a single operation by machine. Pod sorting machines are also available. Pod harvesting machines are currently being experimented. Such mechanical harvesting of pods ensures that all the remaining residues from the vegetable soybean plant are returned to the soil. Returning the residue of vegetable soybean to the soil may have resulted in sustainability due to: 1) a positive shift in soil nutrient status; 2) modification of soil physico-chemical properties; 3) disruption of pathogen, insect, weed and nematode life cycles and population levels, thus reducing disease and insect damage and minimizing cost to control them; 4) changes in soil microbiological population; 5) modified rhizosphere dynamics; other factors may have been involved. All these need to be further investigated. CONCLUSION Vegetable soybean helps to increase soil nitrogen. Since it is from an organic source and produced in the farm it is a renewable form of energy. Organic nitrogen improves soil fertility and other properties of the soil. The short growth duration of vegetable soybean offers farmers a wider choice in a cropping system to enhance their income. The income from growing vegetable soybean is considerably higher than grain soybean and hence it is an attractive crop to farmers. Growing vegetable soybean provides employment opportunities to farm families since it is processed at different stages to produce a value added crop. For sustainable agriculture which can address human and soil nutrition and increase farmers' income simultaneously vegetable soybean represents an excellent crop for a rice-based cropping system in Taiwan and probably in other countries. REFERENCE Fehr, W. R., C. C. Caviness, D. T. Burmood, and J. S. Pennington Stages of development descriptions for soybeans, Glycine max (L.) Merrill. Crop Sci. 11:

7 Francis, C. A., M. D. Clegg, and S. C. Mason Alternatives to monoculture: sustainable systems for U.S. Crop Production. ASPAC. Food and Fertilizer Technology Center. Extension Bulletin No pp :-Iesterman, O. B., C. C. Schaeffer, D. K. Barnes, W. E. Lueschen, and J. H. Ford Alfalfa dry matter and N production and fertilizer and response in legume-corn rotations. Agron. J. 78: Higgs, R. L., W. H. Paulson, J. W. Pendleton, A. E. Peterson, J. A. Jackobs, and W. D. Schrader Crop rotations and nitrogen: Crop sequence comparisons on soils of the driftless area of southwestern Wisconsin, Research Div., Coll. Agriculture and Life Sci., Univ. Wisconsin, Madison, Res. Bull. R2761. Lesoing, G. W Progress report on research project Agricultural Research and Development Center, Mead, Nebraska. (unpublished). Lumpkin, T. A. and J. Konovsky A critical analysis of vegetable soybean-production, demand, and research in Japan. In: Vegetable Soybean: Research Needs for Production and Quality Improvement: proceedings of a workshop held at Kenting, Taiwan, April 29 May 2, Asian Vegetable Research and Development Center, Publication No , pp Penas, E. J Soybeans in rotation what's their worth? Soil Science News. Univ. Nebraska Cooperative Extension Service, vol. 4, No. 9. Randall, G. W Rotation nitrogen study, Waseca, Soil Series 109, Agr. Exper. Stat. Misc. Pub]. 2 (revised). Dept. Soil Science, Univ. Minnesota, St. Paul, p Robinson, R. G Allelopathy. Academic Press, New York. 353 pp. Shanmugasundaram, S., S. C. S. Tsou, and S. H. Cheng Vegetable soybeans in the East. In: World Soybean Research Conference. IV. A. T. Pascale. (ed). Buenos Aires, Argentina, Shanmugasundaram, S., S. T. Chang, M. T. Huang, and M. R. Yan Varietal improvement of vegetable soybean in Taiwan. In: Vegetable Soybean: Research Needs for Production and Quality Improvement: proceedings of a workshop held at Kenting, Taiwan, April 29 May 2, Asian Vegetable Research and Development Center, Publication No , pp Swaminathan, M. S Strategies for a new approach to agriculture in the tropics. Towards a second green revolution: proceedings of the international meeting held at Rome, Italy, 8-10 September, Elsevier Science Publishing Company Inc. pp Trikha, R. N The potential of soybean in Indian cropping systems. Shanmugasundaram, 385 S. (ed). Soybean in tropical and subtropical cropping systems: proceedings of a symposium held at Tsukuba, Japan, September October 1, Asian Vegetable Research and Development Center. Shanhua, Taiwan, R.O.C. pp