不同降雨强度下旱地农田氮磷流失规律

为阐明旱地农田径流氮磷流失规律，以种植空心菜的旱地为研究对象，采用人工模拟降雨方式，设计10、15、25 mm·h^-1三个降雨强度，研究不同雨强下旱地氮磷流失特征和径流拦截效果。结果表明：在相同降雨量条件下，旱地径流量随降雨强度的增大而增加，10、15、25 mm·h^-1雨强下产生的径流总量分别为197.07、381.92、649.45 m³·hm^-2，对应的径流系数分别为0.20、0.38、0.65。总氮（TN）浓度变化随产流时长呈现出先上升后下降的趋势，峰值明显，氮的流失形态以硝酸盐氮（NO₃^--N）为主；TN流失量随着降雨强度的增大而增加，10、15、25 mm·h^-1雨强下分别为0.67、2.48、9.74 kg·hm^-2。总磷（TP）流失浓度随降雨强度的增大而降低，流失过程相对平缓，磷的流失形态以颗粒态磷（PP）为主；10、15、25 mm·h^-1雨强下TP流失量分别为0.061、0.050、0.030 kg·hm^-2。通过田间沟渠水位的管控，可有效减少TN的径流排放，不同雨强下减少比例分别为100.00%、63.56%、33.98%。研究表明，氮的拦截是控制旱地面源污染的重点，在拦截能力有限的情况下，选择污染负荷较高的时段可有效提高面源污染拦截效果。

The loss of nitrogen and phosphorus from dryland farmland under different rainfall intensities

To investigate the loss pattern of N and P in dryland farmland runoff, artificial simulated rainfall runoff experiments were carried out on a dryland farmland that grew spinach. The experiments was conducted under rainfall intensities of 10, 15 and 25 mm·h^-1 in order to analyze N and P loss characteristics and runoff interception effective for dryland under different rainfall intensities. The results indicated that the runoff yield of dryland farmland increased with the increasing rainfall intensity under the same rainfall. The runoff yields under the 10, 15, and 25 mm·h^-1 rainfall intensities were 197.07, 381.92 m³·hm^-2 and 649.45 m³·hm^-2, respectively, with the corresponding runoff coefficients of 0.20, 0.38 and 0.65. The concentrations of TN and NO₃^--N first increased and then decreased with the time of runoff production, distinct peak values could be observed from the change of concentrations. The nitrogen loss was primarily in the form of NO₃^--N. The loss of concentration of TN rose with increasing rainfall intensity, the losses were 0.67, 2.48 kg·hm^-2 and 9.74 kg·hm^-2 under 10, 15 and 25 mm·h^-1 rainfall intensities, respectively. However, the loss of concentration of TP decreased gradually with the increasing rainfall intensity. Particulate phosphorus was the main form in the phosphorus loss. The TP loss were 0.061, 0.050 kg·hm^-2 and 0.030 kg·hm^-2 under 10, 15 and 25 mm·h^-1 rainfall intensities. TN discharge could be effectively reduced by controlling the field ditch water level. The reduction rates under 10, 15 and 25 mm·h^-1 rainfall intensities were 100.00%, 63.56% and 33.98%, respectively. The results indicate that nitrogen interception is the key element of the dryland farmland runoff control. When the effectiveness of the interception is limited, the interception effect of non-point source pollution can be improved by choosing to intercept the period with high pollution load.