土壤水动力状态的标识特征及其应用

Specific characteristics of soil hydrodynamic field state and its applicationto irrigational infiltration

通过土壤水动力状态变化与土壤含水量和水势梯度之间关系试验研究,发现在降水或灌溉入渗过程中,土壤水系统将经历"吸水"(土壤含水量增大)、"过水"(含水量不变,且水通量不等于零)和"脱水"(含水量变小)过程,其总水势梯度大于、等于和小于1.0cmH2O/cm是重要标识特征。上述土壤水动力状态变化特征,在指导农田节水灌溉中具有独特作用。灌溉初期的水势梯度愈大,表明土壤水分亏缺愈严重,需要加大灌溉水量或延长灌溉时间;灌溉初期的水势梯度愈趋近1.0cmH2O/cm,表明土壤水亏缺愈少,应注意调控灌溉水量或限控灌溉时间,避免较多无效灌溉水量的发生。水势梯度等于1.0cmH2O/cm是降水或灌溉入渗过程中土壤含水量饱和的征兆,可作为灌溉节水调控的关键阈值,即当被监测土壤层的水势梯度趋近1.0cmH2O/cm时应结束该次灌溉。

It is indicated by a great deal of test data that soil moisture potential gradient is greater than 1.0 cm H2O/cm during soil moisture absorption in unsaturated infiltration if soil moisture is in wane.Soil moisture potential gradient is equal to 1.0 cm H2O/cm during soil moisture transfers in unsaturated infiltration if soil moisture is in invariable that water flux is in existence.The soil moisture potential gradient is less than 1.0 cm H2O/cm during soil moisture dehydration in unsaturated infiltration if water from surface-ground is in end.Therefore,the soil moisture potential gradient 1.0 cm H2O/cm is the threshold of forecasting for water saving of farmland irrigation.The greater is soil moisture potential gradient in initial stage of irrigation,the more is the wane of soil moisture content which result in more irrigation is needed.Soil moisture is less in wane if soil moisture potential gradient is 1.0 cm H2O/cm in initial stage of irrigation,so that less irrigation is necessary to avoid the waste of water resources.