SOYBEAN DEVELOPMENT, YIELD AND YIELD COMPONENT RESPONSES TO SHADE LEVEL AND TIME OF SHADING (LIGHT)

Net light radiation received by plants is less in the Tropic than Temperate regions. The reduction of incident radiation is further reduced when mixed or relay intercropping systems are used. Soybean experiments were conducted in 1982 and 1983 to determine the effect of different degrees and time of shading on various soybean growth and physiological parameters. Treatments consisted of three varieties (Williams, Pella and Sprite), three degrees of shading (no shade, 33% and 67% shade) and three times of shading in 1982 (R2 through maturity, R2 through R5 and R5 through maturity) but only two times of shading in 1983 (R2 through maturity and R5 through maturity).;Pod number and seeds per plant decreased at the R2 stage shading treatment. The R2 through R5 stage and the R5 stage shading treatments did not effect total pods or seeds per plant. Pods and seeds per plant decreased with increased shading levels. In general, soybean grain yield decreased with increased shading levels, but grain yield was not affected by shading when the shading treatments were applied at the R2 through R5 stage. However, grain yield for the Sprite variety at the R5 stage was not affected by shading. On the other hand, seed weight for the Sprite variety increased with increased shading levels.;Results of these experiments suggest that determinate varieties are potentially better suited for Indonesian conditions. The data further suggest that in mixed or relay intercropping systems the potentially reduced incident radiation during early flowering stages (prior to R5) appears to be less detrimental than during the seed development stages (post R5).;Temperature within the crop canopy was not affected by the shading treatments. Specific leaf weight of the soybean leaves was not affected by shading, but chlorophyll and nitrogen content increased with increased shading levels. Leaf abscission, measured as dropped leaves, increased when the plants were shaded at the R5 stage in 1982 and increased with increased shading levels in 1983. Dropped flowers (or flower abortion) was not affected by shading. However, dropped pods increased when 33% shade was applied at the R2 stage but decreased when shaded at the R5 stage.