垂直线源灌土壤湿润体尺寸预测模型研究

Empirical Model for Predicting Wetted Soil Dimensions under Vertical Line Source Irrigation

基于HYDRUS-2D模型建立了垂直线源灌土壤水分运动数学模型,设置81种情景,模拟获得不同土壤质地、初始含水率以及线源长度、线源直径和埋深条件下的湿润体变化过程。湿润体尺寸主要受土壤质地影响,土壤质地越粗,湿润锋运移越快,线源长度、线源直径和埋深对其影响较小。土壤湿润锋运移过程符合幂函数关系,幂函数指数在水平和垂直向上方向上变化较小,而在垂直向下方向上随饱和导水率(Ks)的增大而增大;幂函数系数随Ks的增大而增大。提出了包含Ks在内的垂直线源灌土壤湿润体尺寸预测模型,试验验证了所建模型的可靠性,MAE和RMSE接近0,PBIAS在-4%~9%之间,NSE不小于0.929,说明预测效果良好。所建模型仅需Ks即可推求,试验设计简单,初步实现了由土壤物理参数预测垂直线源灌土壤湿润锋运移距离的可能。

The wetting pattern is difficult to observe during the vertical line source irrigation.Knowledge of the dimensions of wetted soil around the emitter under irrigation is essential to design of cost-effective and efficient vertical line source irrigation systems.Based on the HYDRUS 2D model,a mathematical model of soil water movement in vertical line source irrigation was established.And 81 scenarios were set up to simulate the changing process of wetted soil under different soil textures,initial water content,line source length,diameter and depth conditions.The dimensions of wetted soil were mainly affected by soil texture,the thicker the soil texture was,the faster the wetted front was moved,and the length,diameter and buried depth of line source had little influence on it.The migration process of soil wetting front was in accordance with the power function relationship.The power function index was changed little in the horizontal and vertical upward directions,but it was increased with the saturated hydraulic conductivity(K s)in the vertical downward direction.The power function coefficient was increased with the increase of K s.An empirical model for predicting the wetted soil dimensions under vertical line source irrigation containing K s was proposed,the model reliability was verified by using experimental data.MAE and RMSE were close to 0,PBIAS was between-4%and 9%,and NSE was not less than 0.929,indicating that the prediction effect was good.The model can be estimated only by K s,and the experimental design was simple.The possibility of predicting the soil wetting front migration distance under vertical line source irrigation by soil physical parameters was initially realized.