Effect of Soil Moisture Stress on Leaf Area Index, Evapotranspiration and Modeled Soil Evaporation and Transpiration

ABSTRACT -LEAF area index (L) development of a crop decreases with increased soil moisture stress. This affects the amount of soil evaporation that occurs through the growing season. Leaf area index of winter wheat (Triticum aestivum L.) and spring barley (Hordeum volgare L.) were measured during the growing season on plots receiving different irrigation levels to develop a functional model to predict L under soil moisture stress and non-soil-moisture-stress conditions based on measurement of evapotranspiration or modeled transpiration. The wheat study was conducted for 2 years on Pullman clay loam (fme-loamy, mixed, thermic Torrertic Paleustoll). The barley study was conducted for 1 year on a Wall sandy loam (Typic Camborthid, coarse, loamy, mixed, calcarous, Mesic family). Leaf area index was linearly related to cumulative evapotranspiration (Etcum) ^P t^ maximum L. The wheat and barley functions relating relative L (L/L^^J to relative cumulative evapotranspiration (Etcum/Etcumm where Etcumm = E^cum ^t L^) up to maximum L where statistically (P<0.05) the same. Relative L from the time maximum L occurred to harvest was linearly related to the relative cumulative evapotranspiration that occurred from maximum L to harvest time. The linear functions presented in this paper were used to model L in an irrigation scheduling model and thus in turn, model the evaporation process based on L. The irrigation scheduling model also modeled evaporation using crop coefficients. Modeling soil evaporation using modeled L improved the predictibility of the model in the low moisture range for barley. The model was insensitive as to the method of modeling evaporation when predicting wheat yield and evapotranspiration..