Kinetics of N-15-labelled nitrogen from co-compost made from cattle manureand chemical fertilizer in a paddy field

In order to produce an effect;ive organic fertilizer, cattle manure was co- composted with chemical fertilizer. And the kinetics of nitrogen uptake by rice plants from the co-compost was investigated using the N-15 labelled co -composts on either cattle manure or chemical fertilizer. As a control, nit rogen kinetics from the mixture of cattle manure and chemical fertilizer wi thout co-composting was investigated. At the early stage, rice growth may h ave been promoted by co-composting, while, it may have been promoted by the larger N-content of cattle manure at the harvesting stage. The ratios of n itrogen uptake by rice plants and residual nitrogen in soil from the cattle manure and chemical fertilizer were determined by measuring N-15-atom%. Th e N-uptake ratios by rice plants from the cattle manure in the co-composted plot were about 2-4 times higher than those from the cattle manure without co-composting. However, the N-uptake ratios from the chemical fertilizer i n the co-composted plot were lower than those from the chemical fertilizer without co-composting. The N-content of the rice plants derived from chemic al fertilizer without co-composting decreased consistently after 28 d. The nitrogen from chemical fertilizer in the co-compost was absorbed again in t he latter period of rice growth. The total nitrogen uptake by rice plants f rom cattle manure and chemical fertilizer was similar regardless of co-comp osting. However, co-composting would be advantageous at least in terms of t he following aspects: increase of the N-uptake by rice plants from cattle m anure, slow-release ability of nitrogen from chemical fertilizer, decrease of nitrogen loss by denitrification.