Simple weighing lysimeters for measuring evapotranspiration and developing crop coefficients

Abstract

Knowledge of cotton crop evapotranspiration (ET) is important in scheduling irrigations, optimizing crop production, and modeling ET and crop growth. The ability to measure, estimate, and predict ET and cotton crop water requirements can result in better satisfying the crop' s water needs and improving water use efficiency. Weighing lysimeters have been used for many years to measure and study water use, and to develop crop-coefficient functions necessary in estimating ET. Electronic weighing lysimeters, consisting of a steel outer tank and inner tank, electronic loadcell assemblies, and a PVC drain system, were designed, constructed, and installed. Each lysimeter cost approximately US$1700 (in 2001) in materials, required two people and 40 hours of labor to construct, and were installed by two people using minimal excavation and hand tools. Daily ET data for cotton were collected from 2003 to 2006 to quantify cotton water-use and to develop crop coefficient functions. Seasonal water use ranged generally from 2 to 8 mm/d. Seasonal water-use patterns varied considerably among growing seasons due to variable environmental and crop-growth conditions, making determination of an average crop-coefficient