Parameterizing the FAO-56 Penman Monteith Evapotranspiration Calculation for Alluvial Soils of the Lower Mississippi River Alluvial Flood Plain.

The FAO-56 method is the standard method of calculating evapotranspiration from weather data. The reference ET calculated with the FAO-56 is then adjusted for local conditions using either a single coefficient to account for crop characteristics, or a dual coefficient to account for soil variability. Row crop production in the lower Mississippi River alluvial flood plain, a region commonly referred to as the Delta, is primarily cotton, corn and soybeans. The soils of the Delta are highly variable alluvial soils that range from rapidly draining sandy loams to poorly draining heavy clays. We are developing an irrigation scheduler based on estimating crop water use from weather conditions and calculating total available soil moisture. A water balance is then determined as the initial water in the soil, plus water from rainfall or irrigation, minus water used by the crop or evaporated from the soil. Here, we present results from field studies measuring soil available water from soils throughout the Delta for corn, cotton and soybeans during the growing season.