Evaluation of N environmental risks on Andosols from an intensive dairy farming watershed using DNDC

Abstract

Manure nitrogen (N) in the livestock sector has become a key driver of environmental change. The denitrification–decomposition (DNDC) model was used to evaluate N pollution strengths on Andosols with intensive dairy manure application in Upper Naka River Watershed, Japan. The calibrated model was capable of predicting Andosol N flows because the simulated soil mineral N content, soil nitrogen oxide (N2O) fluxes, denitrification rate, and crop N uptake matched the patterns and magnitudes of the field observations from a wide range of soil textures, as well as manure management and cropping systems. The simulations showed that current intensive manure application systems caused low crop N use efficiency and a large amount of NO3−-N leaching and N2O emission. The crop N use efficiency was 27%–42% and 37%–55% of input N for uplands and paddy rice, respectively. The uplands showed much more serious N environmental pollution risks with N leaching 123–362kgNha−1yr−1 and N2O emissions 6.53–11.8kgNha−1yr−1 than that in the lowland paddy rice with N leaching 17.4–103kgNha−1yr−1 and N2O emissions 0.59–2.77kgNha−1yr−1. Forage rice/barley crop systems have high N cleaning capability due to the greater crop N uptake which reached to 304kgNha−1yr−1. High precipitation stimulated more NO3−-N leaching. Sandy soil also showed higher N leaching and was unsuitable for paddy rice. Slurry application stimulated more N2O emission than compost manure. To mitigate the current high N pollution, the critical N application rate was recommended to be approximately 380, 470, 640, and 390kgNha−1yr−1 for loam sand planted with maize/grass, loam soil with maize/grass, forage rice/barley, and rice/fallow with winter manure application, respectively.