NITROGEN TRANSFER FROM NODULATING SOYBEAN TO MAIZE OR TO NONNODULATING SOYBEAN IN INTERCROPS - THE N-14 DILUTION METHOD

In 1985, 1986 and 1988, maize (Zea mays L.) was monocropped or intercropped with nodulating or nonnodulating soybean (Glycine max [L.] Merr.). In addition, nodulating soybean and nonnodulating soybean were each monocropped and grown as a mixture. In 1985 and 1986, treatments were grown at 0 nad 60 kg N ha-1 and in 1988, the treatments were grown without N fertilizer, on N-depeted soil and on non-N-depleted soil. N-15 enriched N was applied to soil in all the aforementional treatments to test for N transfer from nodulating soybean to non-N2-fixing crops by the N-15 dilution method. The N-15 dilution method did not show the occurrence of N transfer in 1985 and 1986, but the N sparing effect was evident from the total N uptake of nonnodulating soybean, dwarf maize and tall maize, in 1986. In 1988, maize and nonnodulating soybean seed yields and seed N yields were higher on non-N-depleted soil than on N-depleted soil. On N-depleted soil, the N-15 dilution method indicated N transfer from nodulating soybean to maize and to nonndulating soybean. At a population ratio of 67% nodulating soybean to 33% nonnodulating soybean, N transfer was also seen on non-N-depleted soil in 1988.