COMPARATIVE STUDIES ON DRY-MATTER PRODUCTION, PLANT TYPE AND PRODUCTIVITY IN SOYBEAN, AZUKI BEAN AND KIDNEY BEAN .4. DRY-MATTER PRODUCTION OF AZUKI BEAN AT VARIOUS POPULATION-DENSITIES

Two azuki bean cultivars, Takarashozu (medium) and Akatsukidainagon (late), were grown in the equidistant square pattern at 5 population densities, and dry matter accumulation in the plant communities were analyzed. The maximum dry matter production did not differ in densities over 16 pls./m2, irrespectively of variety, and was about 620 g/m2. With increase in population density, dry weight of branches decreased remarkably and disappeared at the highest density. CGR (crop growth rate) and LAI (leaf area index) during growing season shifted higher with higher densities for ''Takarashozu'', but were relatively constant for density for ''Akatsukidainagon''. NAR (net assimilation rate) dropped temporarily in late July in the higher densities for ''Akatsukidainagon''. Relative light intensity at the bottom of the canopy was associated with LAI. The regression value (Ks) differed between varieties, and the LAI required for 95% light interception was 5.0 and 3.3 for ''Takarashozu'' and ''Akatsukidainagon'', respectively. The decrease in NAR with the increase of LAI initiated about 0.3 from LAI. The estimated values of LAIopt (optimum) and CGRmax (maximum) varied with varieties and stages. The maximum values of LAIopt and CGRmax were 4.1 and 14.7 g/m2 per day, and 3.7 and 16.7 g/m2 per day for ''Takarashozu'' and ''Akatsukidainagon'', respectively. The efficiency of dry matter accumulation per unit of photosynthetically-active radiation (PAR) intercepted (EPAR, dry weight mg/kcal) attained the maximum near the maximum leaf area stage, then decreased. Significant simple correlation coefficients were recognized between LAIopt, CGRmax and EPAR (mean value of each stage), suggesting that the variations in LAIopt and CGRmax. were partially due to photosynthetic activity changing with growth.