Influence of N fertilization rates, rainfall, and temperature on nitrate leaching from a rainfed winter wheat field in Taihu watershed

Cropland derived nitrate leaching was a major reason for groundwater pollution. The objective of this study was to on-farm investigate the behavior of nitrate leaching affected by N fertilization rates, rainfall, and temperature in a rainfed winter wheat field in Taihu watershed. The experiment had five urea-N rates (0–360 kg N ha−1 in 90-kg increments), and nitrate-N in leachate was daily collected by wedge-shaped fiberglass wick lysimeters during four stages (seeding stage, SS; tillering stage, TS; booting stage, BS; harvesting stage, HS). Results showed that: (1) higher potential of leachate would be engendered when the rainfall intensity was over 5.9 mm d−1; (2) variations of nitrate concentrations in leachate were well responsed to three split fertilizations, which increased with the increase of urea-N applied rates. A similar variation pattern of nitrate concentrations was observed in −0.3 m and −0.6 m soil leachate. Besides, the nitrate concentrations in leachate could be raised with the sharply increase of air temperature, especially in the SS and TS stages; (3) the fluxes of nitrate leaching were significantly affected by N rates (P < 0.05) with the loss ratio varied from 4.0% to 8.5% for five treatments, and the fluxes in four wheat growing stages followed the order of TS > HS > BS > SS. The N application rate of 180 kg N ha−1 optimized wheat production, but N application over that rate greatly increased nitrate leaching potential. Therefore, options other than lowering the N application rate need to be considered to reduce environmental impacts while maintain winter wheat production.