Comparative Studies on Dry Matter Production, Plant Type and Productivity in Soybean, Azuki Bean and Kidney Bean : III. Dry matter production of soybean plant at various population densities

Abstract

Two soybean cultivars, Tokachinagaha (determinate) and Harosoy (indeterminate), were grown in the equidistant square pattern at five population densities, and dry matter accumulation in plant community were analyzed. The main results obtained were summarized as follows: 1. The maximum dry matter production was 1, 205 g/m2 at 25 pls./m2 for Tokachinagaha and 1, 123 g/m2 at l6 pls./m2 for Harosoy at about 120 days after planting. 2. With increase in population density, dry weight of branches decreased more remarkably than that of main stem, and it resulted in varying branch-main stem ratio in the plant community. 3. Relative light intensity at the bottom of the canopy was associated with LAI in whole varietics and growth stages. However, the regression value became larger in the later stage and that of Tokachinagaha (narrow leaf type) was slightly smaller than that of Harosoy (round leaf type) in each stage. The LAI required for 95% light interception was in the range from 3 to 4. 4. The decrease in NAR with increase in LAI initiated from LAI 0.3. This fact was also confirmed in LAI 0.06 to 0.6 for Harosoy at the early growth stage. 5. The estimated value of LAIopt. and CGRmax. varyed with varieties and growth stages. 6. CGR was closely related to photosyntheticallyactive radiation(PAR) intercepted by the canopy. However, the efficiency of dry matter accumulation per unit PAR intercepted (EPAR=CGR/PAR intercepted, dry weight mg/kcal) changed with growth. EPAR attained to the maximum at the young pod stage (near the maximum leaf area stage), then decreased. 7. Significant simple correlation coefficients were recognized between LAIopt., CGRmax. and EPAR, but a partial correlation coefHcient was signiticant only between CGRmax. and EPAR. CGR showed highly positive correlations with EPAR throughout the stages of pod filling.