Abstract
Soybean is dependent upon N fixed by nodule bacteria (Rhizobium japonicum) as well as combined N from soil and fertilizer in order to produce seeds. P and K applications promote the nodulation or the nodule activity of soybean. Our study was conducted to determine the responses of seed yield and nodulation in wild and cultivated soybeans (Glycine soja Sieb. et Zucc. and G. max (L.) Merrill) to P and K application. The plastic pots which contain 4.0 kg paddy field soils on dry basis were fertilized by three levels of P and K before planting (Table 2). Ten early cultivated varieties were planted on 13 May in 1980 and 1981, and ten late cultivated ones and a wild line on 27 July in 1980 and 9 July in 1981. (Tables 1 and 4). The following results were obtained. 1. Norin No. 2, Orihime and Lincoln in early varieties, Akiyoshi, Oshokuakidaizu and Akisengoku in late ones responded better in seed yield to P and K application than the other ones for two years. K-01 line (a wild line) responded a little in 1980 and didn't in 1981 (Table 5). 2. Most early and late varieties responded the better in a year when the seed yield level was the lower (Table 5). 3. Leaf and nodule dry weights per plant increased in response to P and K application in cultivated varieties. But K-01 line showed a small increase in these characters in 1980 and no increase in 1981 (Table 6). 4. There were varietal difference in the increased rate of nodule dry weight by P and K application in cultivated soybean. The more the varieties increased their nodule dry weight, the better they tended to respond to P and K application (Tables 5 and 7). 5. Nodule dry weight per plant was significantly correlated with the amount of accumulated N per plant at early pod filling stage in early and late varieties in 1980 and 1981 (Fig. 1).
