不同轮作模式对太湖地区大棚菜地土壤氮淋失的影响

为控制太湖地区设施菜地氮素淋失，减小地下水污染风险，本研究选取2种轮作模式，即芹菜-番茄-莴苣（模式1）和金花菜-番茄-莴苣（模式2），2种轮作模式下分别设置2个施氮量水平，即习惯施氮（N1）和减量施氮（N2），研究不同轮作模式和施氮水平对设施菜地全年氮素淋洗的影响，并观测了不同轮作模式下土壤硝态氮含量、 电导率和pH的变化。结果表明，与模式1 相比，模式2可分别使N1和N2处理的淋洗液中的 NO-3-N 平均浓度降低了36%和38%，进而使全年总氮淋洗量减少了41% 和38%，但淋洗液体积不变。模式2 结合减量施氮（N2）对设施菜地氮素淋失阻控效果最佳，全年总氮淋失量为63.0 kg/hm2，而年经济效益最高，可达 51.9104 Yuan/hm2，最大经济效益提高29%。一年三季蔬菜收获后，N1处理下模式2的土壤硝态氮含量（020 cm）为189.2 mg/kg，而模式1的高达269.3 mg/kg。因此模式2可分别使N1和N2水平下的土壤硝态氮含量减少30% 和 26%，同时也显著降低了土壤pH和电导率（P＜0.05）。在太湖地区，选择需氮量较少的作物进行合理优化轮作（如金花菜-番茄-莴苣轮作模式），是减少设施菜地氮素流失的有效手段，且具有较好的经济效益。

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.