施用尿素和控释氮肥的双季稻田表层水氮素动态及其径流损失规律

【目的】通过比较研究洞庭湖区双季稻田施用尿素（CF）和控释氮肥（CRNF）的表层水pH、电导率（EC）、总氮（TN）、NH4+-N和NO3--N浓度变化动态及TN径流损失规律，寻找有效控制氮素流失的最佳施肥管理措施。【方法】在渗漏池中按河沙泥（ASP）和紫潮泥（PCP）土壤的剖面层次填装土壤，对天然降雨引起的稻田氮素径流损失进行模拟试验。【结果】稻田土壤施用尿素后，表层水TN、NH4+浓度分别在第1、3天达到高峰，然后随着时间的延长而迅速下降；早稻表层水pH在施用尿素后15 d内（晚稻3 d）逐渐升高，EC表现与NH4+的变化同步。与施用尿素相比，施用CRNF能显著降低稻田表层水TN、NH4+浓度峰值，pH、EC峰值也有明显下降。氮素径流损失监测结果显示，洞庭湖区双季稻田施用尿素TN径流损失量为7.47 kg?ha-1，占施氮量的2.49%；施用CRNF、70%CRNF的TN损失量比施用CF的分别减少了24.5%和27.2%。早稻施肥后20 d内发生的2次降雨径流事件，施用尿素、CRNF和70%CRNF处理的2次TN径流损失量分别占全生育期径流损失总量的72%、70%和58%。其中，早稻施肥后第10天发生的第1次径流的2个控释肥处理的TN损失比施用尿素分别降低了42.9%和44.2%。【结论】双季稻田施用尿素后15 d内表层水氮素浓度高，是氮素流失的关键时期；控释氮肥能显著降低这个时期的表层水和所发生的径流液中的氮素浓度，从而显著削减水稻全生育期内的TN径流损失量。

Dynamics of Floodwater Nitrogen and Its Runoff Loss, Urea and Controlled Release Nitrogen Fertilizer Application Regulation in Rice

This study quantified the effect of controlled release nitrogen fertilizer (CRNF) on dynamics of electrical conductivity (EC), pH, TN、NH4+-N and NO3--N concentration in rice surface water and TN losses from runoff in alluvial sandy loamy paddy soil (ASP) and Purple calcareous clayed paddy soil (PCP). After applying urea, the surface water TN and NH4+-N concentration reached peak at the 1st day and the 3rd day respectively, then it went down rapidly; though the floodwater NO3--N in PCP at the 3rd to 7th arose to some extent, it showed very low level as a whole; The surface water pH from early rice within 15d (late rice within 3d) after receiving urea rose gradually, and EC kept the pace with dynamics of NH4+. Compared with urea application, the peak of floodwater TN、NH4+ concentration fallen significantly after applying CRNF, and the peak of EC and pH also fallen distinctly, but NO3- concentration raised a little. The effect of raining event occurred within 20d after applying fertilizer on TN losses from runoff was significant. Compared with applying urea, the TN concentration in runoff water caused by raining event within 10d after receiving CRNF declined significantly, as result, the TN losses from runoff in rice field during whole rice growing season decreased significantly.