Nitrogen use efficiency and recovery from N fertilizer under rice-based cropping systems

Abstract

Broad bean-rice, hairy vetch-rice, naked barley-rice and fallow-rice cropping systems was investigated at Kyoto University Farm, Takatsuki, Japan during 2001-2002 and 2002-2003 to determine the effects of broad bean and hairy vetch on seasonal crop N accumulation, fertilizer N use efficiency (FNUE) and N recovery from rice-based cropping systems using 15N-labeled fertilizer. Cropping systems used as main plot treatments and N fertilizer at rates of 0, 40, 80 and 120 kg ha-1 as subplot treatments. Hairy vetch added 6.4 to 13.1 g N m-2 of which 1.4 to 5.4 g fixed N m-2 while broad bean added 32.0 to 35.2 g N m-2 of which 18.1 to 27.5 g fixed N m-2 to the soil when incorporated as green manure. Broad bean-rice accumulated 19.4 to 20.4 and 21.4 to 22.6 g N m-2 and hairy vetch-rice accumulated 12.9 to 18.7 and 13.2 to 16.4 g N m-2 in 2002 and 2003, respectively. In 2002, FNUE was highest in hairy vetch-rice with N 40 kg ha-1 while in 2003 FNUE was highest in naked barley-rice with N 40 kg ha-1. In broad bean-rice, plant nitrogen accumulation at maturity always increased and FNUE decreased in spite of increased grain yield of rice. The highest (94 %) recovery of 15N-labeled fertilizer was achieved in rice after broad bean with N 40 kg ha-1 and the recoveries of 15N-labeled fertilizer were higher in the first year than the second year.