Effects Of Biochar On Nitrogen Leaching In Anthropogenic-alluvial Soil In Ningxia Irrigation Region

Excessive nitrogen (N) application to farmlands in the Yellow River Irrigated Region of Ningxiaresults in severe non-point source water pollution through N leaching. Improved fertilizer Nuseefficiency and reduced N leaching are important for sustainable high yielding production and waterquality. Anthropogenic-alluvial soil, a special soil type in the Yellow River Irrigated Region of Ningxia,is formed under the joint action of long-term irrigation and fertilizer application. Anthropogenic-alluvial soil has low nutrient retention ability with specific N transformation processes. Biochar hasbeen widely used in improving soil condition, reducing nutrient loss and increasing crop yield. Thisresearch investigated the effect of biochar on N leaching and soil physical and chemical properties ofAnthropogenic-alluvial rice field in Ningxia. The study comprised two experiments: A fieldexperiment and a soil column simulation experiment in a laboratory. The objectives of the studywere to (i) investigate the feasibility of biochar application in improving fertilizer N use efficiencyand reducing Nloss, and (ii)provide technical advice on reducing agricultural non-pointsource pollution in the region. The main findings are as follows:(1) Addition of biochar to Anthropogenic-alluvial soils decreased the concentration of total Nand nitrate. The differences were not significant in the field experiment but significant in the soilcolumn experiment. Soil column simulation experiment indicated that biochar applicationsignificantly reduced the concentration and leaching of nitrate.2%biochar addition reduced the nitrateleaching by49%. The peak of ammonium N leaching was delayed with the increase in biocharaddition. The significant decrease in ammonium leaching (18%) was observed only under10%biochar addition. The field experiment showed that, when no fertilizer N was added, biocharapplication had no significant effect on N concentration in surface water. When fertilizer N wasapplied, addition of biochar decreased the concentration of N and nitrate, but increased theconcentration of ammonium, although the effects were not significant. The leaching of total Ndecreased with the amount of biochar application, but the decrease was not significant.(2) Application of biochar significantly increased soil nutrient availability but had nosignificant effect on soil pH. Soil column simulation experiment indicated that biochar application didnot significantly affect the contents of total salt and phosphorus, but significantly increased total N,available phosphorus and available potassium. In the field experiment, biochar applicationsignificantly increased total N and phosphorus, and available potassium in soil, but had nosignificant effect on soil water content and available phosphorus.(3)Biochar application significantly increased rice yield under fertilizer N application. Theamount of biochar was positively correlated with rice yield（r=0.962，P=0.038<0.05）. Addition ofbiochar increased rice yield when no fertilizer was applied, but the increase was not significant. Biocharapplication increased rice N uptake and utilization rate.