基于土壤水势变化的灌溉节水机理与调控阈值

大量试验结果表明,在农田灌溉过程中,土壤含水率及水势变化具有入渗排气、渗吸增能、吸脱水减能和缓慢脱水减能的阶段性特征。当土壤处于水分亏缺状态急需补充水分(土壤吸水)时,土壤水势梯度大于1.0 cmH2O/cm;当土壤水分得到充分补给达到过水(土壤含水率不变,且水通量不为零)状态时,土壤水势梯度等于1.0 cmH2O/cm;当土壤中水分过剩而处于脱水(流出大于流入水量)状态时,土壤水势梯度小于1 cmH2O/cm。由此,根据上述特征指导农田灌溉调控节水,其中土壤层下部(深度15~60 cm)的水势梯度等于或小于1.0 cmH2O/cm可作为监测及预警节水灌溉的阈值。

Mechanism and forecasting threshold of saving water from irrigation in farmland on the basis of soil moisture potential variation

It is indicated by a great deal of field test data that there are four phases in irrigation process of the farmland.The first phase is that the soil moisture potential value decreases but the soil moisture content is invariable.The second phase is that the soil moisture potential value decreases while the soil moisture content increases.The third phase is that the soil moisture potential value increases less while the soil moisture content decreases.The last phase is that the soil moisture potential value increases markedly while the soil moisture content decreases.The soil moisture potential gradient is greater than 1.0 cmH2O/cm if soil moisture is deficient.The soil moisture potential gradient is equal to 1.0 cmH2O/cm if soil moisture is invariable while water flux is present in the soil.The soil moisture potential gradient is less than 1.0 cmH2O/cm if soil moisture is surplus.Therefore,the soil moisture potential gradient equal to 1.0 cmH2O/cm could be used as the threshold of forecast to save water from farmland irrigation.