Studies on the characteristics of dry matter production and seed yield of soybean [Glycine max] plant, 1: Characteristics of dry matter production of soybean grown under rotational upland field

In order to clarify the characteristics of the dry matter production and the yield of soybean and to obtain basic data for stabilizing and improving the yield of soybean, the characteristics of the dry matter production of soybeans grown under the rotational upland fields converted from rice paddy fields and those grown under common upland fields were compared. On the first year of the conversion, the growth of soybeans would be largely affected by meteorological factors because of the less developed physical conditions of the soil. It is therefore pointed out that the soil should be physically improved immediately after the conversion. Now the characteristics of the dry matter production of soybean grown under the rotational upland fields will be described mainly based on the results obtained in 1990. Although the growth of the soybeans under the rotational upland fields was inferior to that of the ones grown under the upland fields at the early stage, the former became comparable, or even exceeded, the latter as the growth proceeded. The soybeans under the rotational upland fields showed a large maximum LAI, a long period of time for maintaining leaf area and a large yield of the dry matter production. Further, they contained a large amount of nitrogen in leaves which contributed to an increase in net assimilation rate (NAR). The crop growth rate (CGR) and LAI of the soybeans grown under the rotational upland fields largely depended on NAR from the former half of the growth, compared with the soybeans grown under the upland fields. These results indicate that the former soybeans had a high assimilation efficiency. Similarly the soybeans grown under the rotational upland fields kept the leaf area by the latter half of the growth in reproductive phase, which suggests that these soybeans had excellent characteristics of the dry matter production from a morphological viewpoint