Crop Water Use in the Ogallala Aquifer Regioin.

As the Ogallala Aquifer levels continue to decline, information regarding irrigation use and improved irrigation efficiency is needed.  Daily weather data has been recorded throughout the region for decades and can provide a historic background and aid in future decisions.  Our objectives were to use daily weather data and the crop coefficient approach to estimating crop water use to estimate daily evapotranspiration (ET), crop water use and the ET:precipitation ratio for the entire region overlying the Ogallala Aquifer.  Daily maximum and minimum air temperatures and rainfall data from 1970 through 2000 from over 200 stations across seven states were used to estimate potential ET using the FAO-56 methods.  Crop water use was estimated from four planting dates using crop coefficients determined based on crop heat unit accumulation from planting.  Water use for corn, grain sorghum and cotton were estimated for every day during the growing season every year.  Cumulative water use and precipitation were also estimated on a daily basis to calculate the ET:precipitation ratio which is often used to identify irrigation needs in a region.  As growing season length declined from south to north, water use also declined.  Crop water use varied among the crops and planting dates. These results will be useful in educating producers on crop water use by a given crop and may help improve irrigation use efficiency.