松针覆盖土壤的水分动态及其HYDRUS模拟

Soil moisture dynamics under pine needle mulch and its HYDRUS simulation

为准确还原松针覆盖条件下的土壤水分动态变化规律,设置0.29、0.58、0.87g/cm^(2)共3个不同的松针覆盖水平(分别记为F_(1)、F_(2)、F_(3))和不覆盖松针处理(F_(0))进行一维土柱垂直入渗试验,以van Genuchten模型为基础,针对松针覆盖层的特性设置相应的水力特征参数,并使用HYDRUS-1D对土柱入渗和蒸发过程进行模拟。结果表明:与F_(0)相比,松针覆盖处理F_(1)、F_(2)、F_(3)的土壤蒸发量随松针覆盖层厚度增加而逐渐减少,松针覆盖处理能明显降低土壤蒸发量;松针覆盖土壤会优先蒸发松针覆盖层内部的水分,F_(3)在0~300 min时段内始终保持着3种覆盖处理中最高的时段蒸发量和累计蒸发量,且时段蒸发量呈现出随时间逐渐减小的趋势;4种处理的土壤含水量空间分布主要在5 cm以上的浅层土壤中表现出较大的区别,试验截止时,F_(1)、F_(2)、F_(3)在该深度下的地表土壤含水量较F_(0)提升比例分别为67.3%、94.9%、110.2%;7.5~17.5 cm深度下,F_(1)、F_(2)、F_(3)的土壤含水量相比F_(0)的均有提升,但相互之间差距不明显;4种处理在20cm以下的深层土壤含水量虽然较为接近,但湿润锋深度随覆盖量增长呈现逐渐增加的趋势;HYDRUS-1D模型的模拟值同实测值间的均方根误差低于0.025,相关系数高于0.6,拟合程度较好。

In order to accurately reappear the dynamic changes of soil moisture covered by pine needle,one-dimensional soil column vertical infiltration experiments were performed with 3 different pine needle coverage levels(0.29,0.58,0.87 g/cm^(2) denoted as F_(1),F_(2),F_(3))and 1 bare soil control group(F_(0)).The simulation of the infiltration process was based on the van Genuchten model,and the corresponding hydraulic characteristic parameters of the model were set according to the characteristics of the pine needle layers,and the infiltration and evaporation process of the soil column was simulated using HYDRUS-1 D software.The experimental results showed that compared with F_(0),the soil evaporation of pine needle mulch treatments F_(1),F_(2) and F_(3) decreased with the increase of the thickness of the pine needle mulch.The pine needle mulch treatments showed a strong inhibitory effect on the reduction of soil moisture.The water inside the pine needle mulch was preferentially evaporated,therefore F_(3) maintained the highest period evaporation and cumulative evaporation of the 3 coverage treatments and the period evaporation showed a trend of gradually decreasing over time in the period of 0-300 min.The spatial distribution of soil water contents were mainly different in the shallow soil above 5 cm.At the end of the experiment,as compared with F_(0),the soil surface water contents of F_(1),F_(2) and F_(3) increased by 67.3%,94.9%and 110.2%,respectively.At a depth from 7.5 to 17.5 cm,compared with F_(0),the soil water contents of F_(1),F_(2) and F_(3) were higher,but the difference among them were not signifcant.Although the soil water contents were similar for the four treatments under 20 cm,the depth of the wetting front showed a gradual increase over the coverage increase.The root mean squared errors between the simulated values of the HYDRUS-1D model and the measured values were lower than 0.025,and their correlation coefficients were higher than 0.6,which indicated the simulation fitted well.