Evapotranspiration-based irrigation scheduling tools for use in eastern Colorado

his study has one main focus, the testing of tools for use in evapotranspiration (ET)-based irrigation scheduling. The purpose of the first part of this study was to develop and test two irrigation scheduling tools, one for use with annual crops (Colorado Irrigation Scheduler: Annual (CIS-A)) and the other for use with forage crops (Colorado Irrigation Scheduler: Forage (CIS-F)). The tools use ET information calculated using the ASCE Standardized Reference ET equation to track the daily soil water balance in a crop's root zone and make recommendations on irrigation timings and amount of water to be applied. The second part of this study tested the accuracy of a Model E atmometer (ET gage Company, Loveland, CO, USA) in providing estimates of reference ET in southeastern Colorado.;In the first part of the study the CIS-A was tested at two sites (north and south) during the 2010–2012 growing season in a corn (Zea mays L.) field located near Greeley, Colorado. The results of the study indicated that the performance of the tool was acceptable based on the relatively small magnitude of errors in the estimated deficits compared to total available water (TAW) in the soil profile. RMSE was at most 15.3% of TAW, as was the case in 2012 at the north site, and was as low as 8.6% of TAW in 2011 at the north site. The CIS-A tended to overestimate the observed deficit during all years of the study and across all sites. Overall average error indicated that the CIS-A was within 15.92 mm (root mean square error, RMSE) and 12.61 mm (mean absolute error, MAE) of the observed deficit for the entire study. Satisfactory performance of the CIS-A was observed in all years and across all sites with the exception of 2012 at the north site. In 2012 the performance of the CIS-A was less than acceptable. Evaluations of the CIS-F during the 2010 and 2011 growing seasons showed mixed results. The CIS-F was tested on two weighing lysimeters in two different alfalfa ( Medicago sativa L.) fields located at the Arkansas Valley Research Center (AVRC) near Rocky Ford, Colorado. During both years of the study the CIS-F tended to overestimate the observed deficit. The CIS-F performed best in 2011with a RMSE within 6.6% of TAW. In 2010 poorer results were obtained. However, in 2010 RMSE was still within 11.5% of TAW. Upon further analysis it was found that much of the error encountered during the evaluation of the CIS-F occurred early in each growing season. ETc was found to be significantly higher than lysimeter measured ET during the initial part of the alfalfa growing season causing the CIS-F to estimate a deficit greater than what was observed.;The objective of the second part of this study was to determine if an ETgage Model E atmometer, equipped with a canvas...