滴灌条件下核桃园土壤水分动态变化的数值模拟研究

为探究滴灌条件下核桃根系对土壤含水量的影响,试验以8 a生核桃树为研究对象,使用分层分段挖掘法分析核桃根系的空间形态分布,通过构建HYDRUS-2D模型,对有根系吸水下的土壤水分变化进行求解,并利用实测点数据校验2D模型的可用性。经过实际计算与理论分析,得出如下结论:在垂直二维剖面中,水平距树0~30 cm、垂直40~60 cm土层的细根根长密度分布最大,为1 618.216 m·m~(-3)。对比实测数据与模拟数据,结果显示RMSE均小于0.0186 cm~3·cm~(-3),ME绝对值小于0.0108 cm~3·cm~(-3),证明数值模拟效果较好,HYDRUS模型可应用于实际试验研究。将根系模块纳入模型模拟,并比照单独水流模块作用,结果显示根系对土壤含水量产生影响,使体积含水率曲线整体低于单独水作用下的含水率曲线,且两者关系差异性显著。模拟核桃生育前期土壤含水量变化,结果表明灌水后6 d至7 d内,土壤含水量存在明显减小现象,故可将生育前期灌水周期设定为6 d或7 d。

Study on numerical simulation of soil moisture dynamic variation for walnut orchard under drip irrigation

Eight-year-old walnut trees were used to study the effect of root system on soil water content in different soil layers under drip irrigation.The root system was sampled from different soil layers.HYDRUS-2D model was built with consideration of water uptake by root system and checked.The results are described as follows:in vertical 2D profile,the soil layer of 40 ～60 cm being 0～ 30 cm away from the tree had the maximal fine root density of 1 618.216 m · m-3.The RMSE value and ME of the measured and simulated values from HYDRUS-2D are less than 0.0186 cm3· cm-3 and 0.0108 cm3 ·cm-3,respectively,suggesting that HYDRUS model could be used in the actual experiment research.The simulated results were different according to whether the effect of root system was considered,and the volumetric water content with root system considered is significantly lower.According to the simulated value for early stage of walnut,the soil content decreased a lot 6 days and 7days after irrigation,indicating that the irrigation cycle in earlier growing stage could be set 6 days or 7 days.