聚丙烯酰胺应用对黄土复合坡面降雨产流的影响

Effects of polyacrylamide application on rainfall runoff in composite slopes of loessial soil

复合坡是自然界常见的主要坡型。通过室内人工降雨模拟试验，研究了复合坡面降雨产流规律以及聚丙烯酰胺（polyacrylamide，PAM）应用对其的影响。试验采用2种复合坡型（凹型坡和凸型坡）的12个坡度组合和4个PAM施用量，共48个试验处理。结果显示，PAM应用显著缩短了初始降雨产流时间，初始产流时间平均比对照处理提前63.7%～71.6%。PAM应用明显改变了坡面径流随降雨历时的变化规律。PAM应用后，除了大坡度（≥10°）、小量PAM应用（0.5 g/m2）的凸型坡外，降雨径流系数在整个降雨过程中基本维持稳定。PAM应用增大了降雨径流系数和径流量，且径流系数和径流量随着 PAM 施用量的增大而增大。凸型坡的径流量平均比凹型坡的大14.7%～31.8%。当PAM施用量为0.5、1.0和2.0 g/m2时，凹型坡和凸型坡的径流量分别比对照处理增加55.7%、100.2%、147.3%和16.6%、69.3%、108.9%。在黄土坡地上大剂量（≥1.0 g/m2）应用PAM可明显增大坡面径流量，实际应用中应制定合理的PAM施用量。

Soil and water loss from sloped lands in a loess plateau is the most serious region problem in China, and a composite slope is one of the main slope types in nature. Soil infiltration and runoff studies on composite slopes during rainfall processes and the effects of polyacrylamide （PAM） application rate on them were carried out by simulated rainfall experiments in the laboratory. The experimental treatments included two slope types （concave and convex slopes） with 12 combinations of slope gradients, and four PAM application rates of 0 （control）, 0.5, 1.0, and 2.0 g/m2 （0, 5, 10, and 20 kg/ha）. The concave slopes were composed of upslope gradients of 20 deg and 25 deg and down slope gradients of 5 deg, 10 deg, and 15 deg. The convex slopes were upslope gradients of 5 deg, 10 deg, and 15 deg and down slope gradients of 20 deg and 25 deg, respectively. The total number of experimental treatments was 48. Results indicated that PAM application significantly shortened the time of initial runoff initiation after an average rainfall by 63.7%-71.6%, as compared with the control treatment. After PAM application, the effects of slope type and the combination of different slope gradients on the time of initial runoff initiation were not obvious. Compared with the control treatment, the slope runoff pattern during the rainfall process was significantly changed after PAM application. Without PAM application, the runoff coefficient on concave slopes increased progressively with the rainfall process and then tended to be steady; the runoff coefficient on convex slopes was similar to that on concave slopes at the slope gradient of 5 deg, but it increased persistently with the rainfall process at the slope gradient greater than 10 deg. After PAM application, the runoff coefficient was generally steady during the majority period of the rainfall process, except for convex slopes when the upslope gradient was equal to or greater than 10 deg under a PAM application rate of 0.5 g/m2. Polyacrylamide application increased runoff coefficient as compared with control treatment. Runoff coefficient and total runoff volume increased with the increase of the PAM application rate. When PAM application rates were 0.5, 1.0, and 2.0 g/m2, total runoff volume increased by 55.7%, 100.2%, and 147.3%on concave slopes and 16.6%, 69.3%, and 108.9%on convex slopes, respectively. Under experimental conditions, total runoff volume on convex slopes was generally greater than that on concave slopes by 14.7%-31.8%. Polyacrylamide application at a rate greater than 0.5 g/m2 on loessial sloped land may increase runoff rate and total runoff volume significantly, which is favorable to rainfall runoff collection and its reutilization, but is disadvantageous to soil and water loss control. Therefore, a suitable PAM application rate should be determined comprehensively according to soil type, PAM property, and the PAM application purpose in practice.