Critical livestock densities and manure management for the typical paddy rice and corn cropping systems in an intensive livestock watershed, Japan

Intensive manure application is a significant source for environmental nitrogen fluxes. In this study, we evaluated the effect of intensive manure management on nitrogen(N) loading and recommended the critical livestock density for the typical paddy rice and corn cropping systems in a dairy farming watershed using a calibrated DNDC model. The results indicated that a significant amount of N was lost as N2O emission and NO3−-N leaching under current intensive manure application. As the number of dairy cattle increased, soil N2O emissions and NO3−-N leaching increased with a rate of 2.11kg N LU−1 yr-1 and 39.7kg N LU−1 yr-1, respectively. Changing manure to chemical fertilizer, NO3−-N leaching was trend to increased. If decreasing fertilizer rate too low, crop N decreased and the soil N was significantly deficit. Integrated all the analysis, we recommended that critical N application rate was approximately 150–300kg N ha−1 yr−1 for corn system and 100–250kg N ha−1 yr−1 for paddy rice system, respectively. The critical livestock density in these cropping systems is 0.7–3.0 LU ha−1 yr−1 for dairy cattle manure using. Based on these recommendations, the crop N use efficiency(NUE) could increase from 17 % to 65 % for corn cropping and from 59 % to 75 % for paddy rice cropping. To mitigation the significant environmental nitrogen, the current livestock densities need to decrease by 40–60 % in the studied region or the major crop system needs to be changed from one season rice to double rotation cropping system.