负压灌溉下土壤水分运移特性及氮素分布规律研究

[目的]揭示负压水肥一体化灌溉对红壤水分及氮素运移特征的影响。[方法]配置6种不同质量浓度硝酸铵溶液(0、10、15、20、25、30mg/L),设置无压(负水头高度为0)和负压(1/2极限负水头高度)2个水平进行红壤入渗试验,分析了其入渗特性及氮素分布规律。[结果]硝酸铵溶液促进水分入渗,无压和负压状态下,入渗溶液质量浓度为25mg/L和15mg/L时水平与垂直方向湿润锋运移均达到最大,与相应CK相比累积入渗量最大分别增长2.69倍和3.00倍,平均入渗率分别增长2.38倍和2.18倍;土壤硝态氮和铵态氮量显著增加(p<0.05),与相应CK相比无压和负压状态下硝态氮量最大分别增长8.05倍和7.75倍,铵态氮量最大分别增长13.37倍和10.42倍。停渗时刻,同一质量浓度入渗溶液无压状态下水平与垂直方向湿润锋运移距离、累积入渗量均显著高于负压状态,各处理最大分别高出2.01、2.148和4.69倍;距出水点相同的距离,无压状态下土壤含水率、硝态氮和铵态氮量均高于负压状态。[结论]负压灌溉显著缩短水平与垂直方向湿润锋运移距离,降低土壤累积入渗量、含水率、硝态氮和铵态氮量。2种入渗条件下,土壤硝态氮量随入渗距离增加而增加,而土壤铵态氮量随入渗距离增加则呈下降趋势。

Water Flow and Nitrogen Distribution in Soil under Negative-pressure Irrigation

【Objective】Negative-pressure irrigation is a new irrigation technology and in this paper, we investigate its impact on water flow and nitrogen distribution in red soil under different combinations of irrigation amount and nitrogen application.【Method】Ammonium nitrate was used in the experiment and we compared six concentrations: 0, 10, 15, 20, 25 and 30 mg/L, under two water pressure treatments: zero pressure and pressure at1/2 of the limit negative head height.【Result】Application of ammonium nitrate facilitated water infiltration. Under zero and negative-pressure irrigation, water movement in the horizontal and vertical direction reached maximum when the ammonium nitration concentration was 25 and 15 mg/L respectively, at which the maximum cumulative infiltration increased by 269% and 300% and the associated infiltration rate increased by 238% and218% respectively. Both nitrate and ammonium in soil increased significantly(p<0.05). Under zero and negative pressure, the maximum nitrate content in soil increased by 805% and 775% respectively, while the maximum ammonium content increased by 1 337% and 1 042% respectively. After the irrigation ceased, the distances the wetting front moved in the horizontal/vertical direction and the cumulative infiltration under zero pressure were more than that under negative pressure. At the same location, nitrate, ammonium and soil moisture under negative pressure were higher than those under zero pressure.【Conclusion】Negative-pressure irrigation significantly impedes water movement, thereby reducing cumulative infiltration, water content, nitrate and ammonium in soil. For the two pressures we examined, soil nitrate increased along the infiltration distance as opposed to soil ammonium that decreased along the infiltration distance.