Effect of rotation patterns on nitrogen leaching loss from protected vegetable soil in Tai Lake region

To control nitrogen (N) leaching loss from protected vegetable production fields and minimize the risk of N pollution of groundwater in the Tai Lake region, China, a field experiment was conducted to evaluate the effects of different rotation patterns and fertilizer application rates on nitrogen leaching loss using lysimeters. Soil NO-3-N concentration, electrical conductivity and pH values were also analyzed. There were two types of rotation patterns, pattern 1 (celery-tomato-lettuce) and pattern 2 (burclover-tomato-lettuce), and two N levels, the conventional N application rate (N1) and reduced N application rate (N2). Comparison with the rotation pattern 1, the averageNO-3-N concentrations in the leachate of the rotation pattern 2 are decreased by 36% (N1) and 38% (N2), and the total N leaching under the two N treatments decreased by 41% and 38% respectively, although the leachate volumes are not affected by the rotation pattern or N application rates. The optimum way to control the N leaching loss is a combination of the rotation pattern 2 and the reduced N application rate (N2). For example, the total annual N leaching loss is 63.0 kg/ha under the combined treatment, and an economic return (up to 519 thousand Yuan/ha) is achieved, which is an increase of 29%. After growing three vegetable crops in a year, soilNO-3-N concentration in the topsoil (0-20 cm) is 189.2 mg/kg in the N1/rotation pattern 2 combination, whereas it is 269.3 mg/kg in the N1/rotation pattern 1 combination. In addition, the rotation pattern 2 reduces soilNO-3-N content by 30% (N1) and 26% (N2) respectively, and soil pH and electrical conductivity are reduced significantly (P＜0.05). In the Tai Lake region, rotation patterns requiring less N input (e.g., bur clover-tomato-lettuce) could be practiced to reduce N leaching loss and achieve greater economic return.