Application of an Evaluating Method of Consumptive Use of Non-rice Crops in Consideration of Soil Moisture Movement to Paddy Based Land in Tropical Area

Study on diversified crop water requirements in the Philippines (III)

Abstract

The soil moisture depletion method will be the best suited for developing countries to obtain the real data of crop consumptive use (CU) due to the relative simpleness and low application costs. CU is the depletion amount in an effective soil layer (ESL). Resent studies suggest for the bottom depth of ESL to apply zero flux plane (ZFP) although the conventional method suggests to apply a depth at which moisture content hardly changes during an irrigation interval. The ZFP is a boundary between upward water movement by evapotranspiration and downward one by gravity, and identified with total potential gradients (TPGs). Applying ZFP for ESL can exclude gravitational water from the depletion amount. In order to prove the applicability and usefulness of ZFP for paddy based land, the authors evaluated CU amounts for 16 crops with ZFP. For verifying the usefulness of applying ZFP, the CU amounts evaluated with ZFP were compared with those with the conventional method, and the accuracy of CU amounts was evaluated with the existing evapotranspiration data and FAO data. The results indicated (1) increase of data utilization for determining CU, and (2) less error than the conventional method for estimating evapotranspiration due to less inclusion of gravitational water.