Soybean Irrigation Scheduling Using the Arkansas Tub Gauge.

The Arkansas Tub Gauge (ATG) uses an open-pan method of monitoring crop moisture use and a ‘checkbook' method for irrigation scheduling and is constructed from inexpensive materials available at most hardware stores.  Irrigation scheduling is based on observing the evaporative water loss in reference to a colored scale.  An adjustable reference point is set by the user based on the crop growth stage coefficient, pan coefficient, estimated soil moisture, and a target deficit.  The pan coefficient was determined to be 0.83 and the reference point adjusted from rainfall events less than 3 cm to within 5-11% of actual due to the tapered walls of the tub.   Field studies in 2011 and 2012 at three sites found no significant differences in furrow irrigated soybean yields between the ATG, atmometer, soil tensiometers, or the Arkansas Scheduler methods of irrigation scheduling.  Comparison demonstrations between the four scheduling methods were also conducted on eight grower fields in 2012 and 2013.  Irrigation timing between the four scheduling methods was generally within four days.  Cumulative potential evaporation of the ATG and the atmometer were very similar to values calculated from a nearby WatchDog^® 2900ET weather station.  The low cost, low maintenance, high visibility, and rainfall adjustment of the ATG provides an attractive alternative method of crop moisture monitoring.