麦田降雨入渗特征及其计算模型

Rainfall Infiltration Characteristics and Regression Models in Winter Wheat Field

为探讨多种因素对麦田降雨入渗特征的影响及其相应的定量关系,通过人工模拟降雨试验,研究麦田降雨强度(RI)、冠层覆盖度(LAI)及0-40cm土层土壤初始含水量(θ40)对降雨入渗规律的影响。结果表明:其他影响因素一定条件下,入渗率和累积入渗量与降雨历时分别具有显著的幂函数和对数函数关系(P<0.01);平均入渗率、稳定入渗率和入渗量随RI增大而增大,入渗率趋于稳定值的时间随RI增大而提前,降雨蓄积系数则随RI增大而减小;平均入渗率、稳定入渗率、入渗量和降雨蓄积系数随LAI增大而增大,入渗率趋于稳定值的时间则随LAI的增大而滞后,当降雨强度增大时,LAI对麦田入渗过程的影响减弱。在RI和LAI不变时,入渗率趋于稳定值的时间随θ40增大而提前,平均入渗率、入渗量和降雨蓄积系数随θ40增大而减小,但稳定入渗率基本相同。通过对模拟降雨实测数据统计分析,入渗率、累积入渗量可最终表示为t、RI、LAI和θ40的四因素函数关系,并建立降雨蓄积系数回归计算模型(P<0.01)。

A rainfall simulation experiment at Guangli Irrigation Experimental Station during March to June, 2011, was carried out to study the effects of rainfall intensity（RI）, canopy coverage（LAI）, and the initial water content in the 0-40 cm soil profile（θ40 ） on rainfall infiltration characteristics in a winter wheat （cv. Wenmai NO. 19） field, quantitative relationships between those impacting factors and rainfall infiltration were further explored. Five rainfall intensities, i.e. 1.00, 1.33, 1.67, 2.00, 2.33 mm/min, with the rain- fall duration for 60 min were arranged using a completely randomized block design with three replicates and were implemented at five growth stages of winter wheat（i, e. , green-turning, jointing, heading, flowering and filling stages）. Results showed that, keeping LAI and θ40 constant, a power function was best fit to describe the curve of infiltration rates against rainfall duration （Y = abx, P〈 0. 01）, and a logarithmic function of cumulative infiltration against rainfall duration was also significant to express the relationships between the two factors （Y=a＋bln X, P〈0. 01）. As the rainfall intensity（RI） intensified, mean infiltration rate, stable infiltration rate, and cumulative infiltration significantly increased and the time with infiltration rates stabilizing（t） advanced, while rainfall accumulation coefficient deceased with the RI intensifying. Mean infiltration rate, stable infiltration rate, cumulative infiltration, and rainfall accumulation coefficient increased, respectively, as the leaf area index（LAD increased while there was a time ag for infiltration rate stabilization when LAI continued to increase, which was probably attributable to the slowing in speed of rain drops by dense canopy coverage. Effect of LAI on rainfall infiltration weakened when RI intensified. This indicated that heavy rainfall brought significantly high penetration capacity of drops through crop canopy,and thereby, resulted in more damage for crops production. Keeping RI and LAI constant, it advanced the time of infiltration rate stabilization while reduced mean infiltration rate, cumulative infiltration, and rainfall accumulation coefficient as θ40 increased. This demonstrated that high initial soil water content at topsoil might reduce rainfall infiltration rate, and thus accelerate surface soil runoff and soil erosion while suitable moisture status mitigated negative influence of heavy rainfall. According to the statistical analysis based on measured artificial rainfall data, infiltration rate, cumulative infiltration, and rainfall accumulation coefficient could be eventually expressed as a combined function of t, RI, LAI, and θ40 using the Levenberg-Marquardt nonlinear regression metbod（P〈0.01）.