滴灌系统运行方式对砂壤土水氮分布影响的试验研究

以一种砂粒含量高达95%的砂土为对象，开展了滴灌施肥灌溉条件下，灌水器流量、灌水量和系统运行方式对水分、硝态氮和铵态氮分布影响的室内试验。灌水器流量的变化范围为0.5～2.0L/h，灌水量为6～7.7L；系统运行方式包括不同灌水和施肥次序组成的4种方案。研究结果表明，径向和垂直湿润距离随灌水量的增加呈幂函数关系增加；灌水量相同时，随灌水器流量的增大，灌水器周围的土壤含水率增加，垂直湿润距离减小，而径向湿润距离变化不大；灌水器流量一定时，垂直湿润距离随灌水量的增大而明显增加。对氮素分布的测试结果表明，硝态氮在湿润体边界存在累积现象；铵态氮在灌水器附近出现浓度高峰，且铵态氮集中在灌水器周围15cm范围内。滴灌施肥灌溉系统运行方式对硝态氮在土壤中的分布影响明显，建议采用最初用灌水施肥总时间的1/4灌水，再用1/2时间施肥，最后用1/4时间冲洗管道的运行方式，以便将施入土壤的氮素最大限度地保留在作物根区内，防止硝态氮淋失。

Effect of drip irrigation system operation on water and nitrate distribution in soil

Laboratory experiments were conducted to study the effects of fertigation strategies on water and nitrogen distribution from a surface point source of ammonium nitrate. A sandy soil with sand content of 95% was used. In the experiments, discharge rate varied from 0.2 to 2.0L/h and applied volume varied from 6.0 to 7.7L. Four fertigation strategies were tested. The results demon strated that the surface wetted radius and vertical wetted depth were exponentially proportional to the applied water volume. The increase in rate resulted in the decrease in vertical wetted depth and the in crease of soil water content around the source as well as the insignificant change of wetted horizontal area. Vertical wetted depth increased significantly as the volume applied increased. The measurements of nitrate distribution showed that nitrate accumulated at the boundary of the wetted volume for all fertigation strategies tested. There existed an extremely high ammonium concentration in the proximity of the point source and most of ammonium applied through fertigation was absorbed in a range of 15cm from the source. Fertigation strategies significantly effect the nitrate distribution in soil. The strategy of applying water at first for one-fourth of the total irrigation time, then applying fertilizer solution for one-half of the total irrigation time, followed by applying water for the remaining one-fourth of the total irrigation time made the most nitrate close to the source.