日光温室深埋秸秆不同灌水下限对土壤热扩散率的影响

Effects of Different Lower Limits of Irrigation on Soil Thermal Diffusivity under Straw Deep Burying in a Greenhouse

通过温室小区试验,探讨深埋秸秆条件下不同灌水下限对土壤热扩散率的影响。利用Matlab数学软件对地表及距垄台表面深度为15 cm处实测地温数据进行拟合,标定正弦函数温度曲线。同时,利用常规方法计算振幅并拟合相位,得到正弦函数温度曲线。计算两种方法得到的模拟地温与实测地温误差,并比较两种方法的拟合度,选择适宜的深埋秸秆条件下正弦函数温度曲线。根据正弦函数温度曲线得到的振幅和相位分别计算相应的土壤热扩散率。结果表明:深埋秸秆条件下,两种方法在深层土壤处的温度曲线拟合度皆较高,深层土壤温度波动规律更加稳定。用标定法得到的模拟地温与实测地温间误差皆小于常规法误差,基于标定法计算出的土壤热扩散率精度更高。振幅法和相位法计算的土壤热扩散率存在一定差异,由振幅法计算的土壤热扩散率小于由相位法计算的土壤热扩散率,但两种方法计算的土壤热扩散率与不同灌水下限的关系是一致的,即在深埋秸秆条件下土壤热扩散率随土壤含水量的增加而增加,但当土壤含水量达到一定水平后,土壤热扩散率不再随含水量增加,甚至会随含水量的增加而减小。这说明不同灌水下限对土壤热扩散率的影响是非线性的。

A greenhouse plot experiment was set to explore the effect of different lower limits of irrigation on soil thermal diffusivity under straw deep burying. The Matlab software was used to fit the measured data of soil temperature at the ground surface and at the depth of 15 cm from the ridge and then to calibrate the sine function temperature curve. At the same time, the temperature curve of sinusoidal function was obtained by calculating the amplitude and fitting the phase with the conventional method. The error between simulated and measured ground temperatures was obtained by two methods, and their r-squared values were compared to select the appropriate sine function temperature curve under the straw deep burying. Then the soil thermal diffusivity was calculated according to the amplitude and phase obtained from the sine function temperature curve. The results showed that the fitting degrees of temperature curves by calibration and conventional methods were both relatively high at deep soil under straw deep burying, and the deep soil temperature was more stable. The error between simulated and measured ground temperatures obtained by calibration method was less than that by conventional method. Therefore, the soil thermal diffusivity calculated by calibration method had a high accuracy. The soil thermal diffusivity calculated by amplitude method was less than that by phase method. The soil thermal diffusivity under the straw deep burying increased with the increase of soil moisture content. However, when the soil moisture content reached a certain level, the soil thermal diffusivity decreased with the increase of soil moisture content. It was clear that the effects of different lower limits of irrigation on soil thermal diffusivity were nonlinear.