Soil Field Capacity Calculation Using the Van Genuchten Model for Irrigation Scheduling and Drought Resilience.

Climate change is expected to cause changes in the distribution of regional precipitation.  Available water for irrigation should therefore be utilized more effectively and efficiently. An efficient irrigation system requires information on soil water status to determine irrigation application amounts and timing. Knowledge of the boundary of lower and upper limits of soil water content is necessary to avoid crop drought stress and leaching. However, in situ measurements of soil water characteristics needed to establish these boundaries are labor and time intensive. It is thus imperative to find alternative methods to develop the boundaries. The objective of this research was to propose a new method of calculating field capacity (FC) from the van Guenchten Model considering the process of soil water release. FC and soil matric potential (Ψm) at FC obtained from the proposed method in the current study were consistent with those from previous research in soils with similar textures. Soil volumetric water content (VWC) at different Ψm could be used for irrigation scheduling, e.g. the irrigation amount to bring the soil profile either to FC or to predetermined soil VWC levels. The proposed method is reliable in calculating soil properties related to soil water status in specific soils which may improve the accuracy of estimating soil water status and thus irrigation management.