Kinetics of N-15-labelled nitrogen from co-compost made from cattle manureand chemical fertilizer in a paddy field: Effect of mixing ratio of cattlefeces and ammonium sulfate

In order to produce an effective organic fertilizer for plant uptake and to examine the characteristics of a nitrogen fertilizer, cattle feces and (NH 4)(2)SO4 were co-composted, and the kinetics of nitrogen uptake by rice pla nts from the co-compost was traced by the use of N-15. Cattle feces and (NH 4)(2)SO4, either of which was labelled with N-15, were co-composted in a ra tio of 1:3 or 3:1 for nitrogen, and the nitrogen kinetics from cattle feces or (NH4)(2)SO4 was investigated. In addition, four non-co-composted plots and a chemical fertilizer plot were set up as a control experiment. A 1 : 3 or 3 : I mixture of cattle manure and (NH4)(2)SO4, either of which was lab elled with N-15, was applied in the non-co-composted plots. And only (NH4)( 2)SO4 without manure was applied as a nitrogen fertilizer in a plot. In add ition to the data on the 1:1 co-compost reported in our previous paper (Mat sushita et al. 2000: Soil Sci. Plant Nutr., 46, 355-363), the characteristi cs of these co-composts as nitrogen fertilizer were estimated. The 1 : 3 co -compost was an efficient nitrogen fertilizer for rice plant uptake. The ef fect was conspicuous, especially in the early period of rice growth. Howeve r, inorganic nitrogen was in short supply in the middle period, and became mineralized again in the latter period of rice growth. The co-compost may n ot be suitable as a slow-acting fertilizer but could be efficient as a quic k-acting fertilizer, in terms of organic matter content. When cattle feces and (NH4)(2)SO4 were co-composted in a ratio of 3 : 1, the dry weight of th e rice plants in the co-composted plots was significantly lower than that i n the non-co-composted plots on August 12 and afterwards. The least active growth was associated with a shortage of inorganic nitrogen. Especially, th e N-uptake ratio by rice plants from (NH4)(2)SO4 in the 3:1 co-compost decr eased by about 40% of the value in the non-co-composted plot. The results s uggested that (NH4)(2)SO4 was actively assimilated during the co-composting period in the 3:1 co-compost. The co-compost may not satisfy the plant req uirement for nitrogen. In contrast, this co-compost could be efficient as a n amendment material for soil with a low nutrient content, because the N-re sidual ratios in soil from (NH4)(2)SO4 were about 80%. On the other hand, t he N-uptake ratio from (NH4)(2)SO4 with cattle manure in the non-co-compost ed plot was lower than that without cattle manure in the early period, comp ared with that in the latter period of rice growth. The results indicated t hat the slow acting ability of nitrogen from (NH4)(2)SO4 increased by the a ddition of cattle manure. Considering the nitrogen loss through the compost ing process, the N-uptake ratios from cattle feces and (NH4)(2)SO4 were in the order of 1:3 non-co-composted plot>1:3 co-composted plot>3:1 non-co-com posted plot>(NH4)(2)SO4 only plot>3:1 co-composted plot. In summary, the 1: 3 co-compost made of cattle manure and (NH4)(2)SO4 may display a quick acti ng ability, the 3:1 co-compost could increase the soil nitrogen content, an d the mixture of cattle manure and (NH4)(2)SO4 may exhibit a slow acting ab ility for nitrogen. In taking account of nitrogen utilization, the simultaneous application of cattle manure and (NH4)(2)SO4 without co-composting appears to be an effici ent method compared with the co-composting method.