Abstract
Sorghum (Sorghum bicolor (L) Moench), Soybean (Glycine max L. cv. Kurosengoku) and Siratro (Macroptilium atropurpureum cv. Siratro) were grown in the field of which soil is derived from granite residual under mono- or mix-cropping system with or without application of fertilizer nitrogen (N). Their dry weights, dinitrogen fixations and N contents in various parts at their successive growth stages were examined to assess the dry matter production in relating with the nitrogen supply status and transference of fixed-N from legumes to sorghum in the mixture cropping. The following results were obtained. 1) The total dry matter yield was not necessaril greater in the mixing cropping. Sorghum was leading species to increase the total dry matter yield the mixing culture regardless of nitrogen application. 2) The dinitrogen fixing activity was consistently higher in soybean than in siratro. That of soybean was remarkably higher under mono- than mix-cropping system during its grain filling period, in contrast, that of siratro was rather slightly higher under the mixthan monoculture cropping system during its corresponding period due to the difference of light condition between them. 3) Total N amount in the plant was the greatest in the mono-culture of legumes regardless of fertilizer-N application. Without fertilizer-N, the total N amount in the mix-cropping was remarkably larger than that of sorghum in the mono-cropping but there was no difference between them with fertilizer-N. 4) The amount of N derived from dinitrogen fixation estimated by the difference method in using N amount of sorghum grown without application of fertilizer-N as a none N_2-fixing system was greater in soybean than in siratro. Proportions of fixed-N transferred to sorghum from soybean or siratro to their whole amount of fixed N were approximately 18 and 15%, respectively.
