Abstract:Soil water deep leaching and nitrate(NO3--N)distribution in the soil profile and NO3--N leaching losses below the root zone were investigated in fields under a local traditionally managed wheat-maize crop rotation system in the North China Plain.Coupled with the soil water balance method,soil water deep leaching and NO3--N concentration in suction samples were determined.The results indicate that water leaching,NO3--N distribution and leaching losses exhibited pronounced spatial and temporal variability.Events of water leaching and NO3--N leaching loss were prone to occur during the summer maize growing season(rainy season),after each irrigation operation and significant rainfall.Annual soil water deep leaching reached 33~48 mm(averaged 39 mm)in 1998/1999 cropping year and 90~92 mm(averaged 90.7 mm)in 1999/2000,accounting for 10% and 19% of the total amount of irrigation plus rainfall,respectively.The amount of NO3--N leached below the root zone (including leaching loss of soil-and fertilizer-N)averaged NO3--N 12 kg hm-2 a-1(ranging from NO3--N 6 to 17 kg hm-2 a-1) in 1998/1999 and NO3--N 61 kg hm-2 a-1(ranging from NO3--N 30 to 84 kg hm-2 a-1)in 1999/2000,equivalent to 1.4%~4.1% and 7.3%~20.3% of the N fertilizer applied,respectively.The results indicate that during the summer maize growing season,potentials do exist of reducing water and fertilizer inputs,so as to improve water and fertilizer use efficiency in this region.