EFFECTS OF SUBSTITUTION OF MINERAL NITROGEN WITH ORGANIC AMENDMENTS ON NITROGEN LOSS FROM SLOPING CROPLAND OF PURPLE SOIL

Nitrogen loss from purple soil can lead to large negative impacts to the environment considering the wide distribution of this soil type in the upper reaches of the Yangtze River.Therefore,nitrogen loss patterns from sloping cropland of purple soil in the Sichuan Basin with the following fertilization regimes were studied in a wheat-maize rotation system:100%organic fertilizer(OM),using pig manure to replace 30%of mineral N(OMNPK)and crop residue to replace 15%of the mineral N(CRNPK)plus standard mineral fertilization(NPK)and no fertilizer control.The cumulative hydrological N loss could be as high as 45 kg·ha^(−1) N.The interflow accounted for up to 90%of the total N loss followed by sediment and overland flow losses.The high N loss via interflow found in this study highlighting that sloping cropland of purple soil may be one of the hot spots of N leaching.Compared to the NPK regime,organic substitution regimes(i.e.,OM,OMNPK and CRNPK)decreased total hydrological N loss loadings by 30%−68%.In addition,they can maintain annual crop yields and decrease yield-scaled total hydrological N losses by 18%−71%.In conclusion,long-term substitution of mineral N with organic amendments can maintain high crop productivity and reduce environmental N loss loadings,and thereby recommended as good N management practices to minimize the risk of agricultural non-point source pollution in the purple soil region of China.