Effects of precipitation and soil moisture on N2O emissions from upland soils in Guizhou Potential effect of fertilising and tilling on N2O emission from upland soils analyzed by DNDC model Potential effect of fertilising and tilling on N2O emission from upland soils analyzed by DNDC model A meta-analysis of field experiment data for characterizing the topsoil organic carbon changes under different fertilization treatments in uplands of China