Plant, Soil, and Weather Based Cues for Irrigation Timing in Soybean Production.

With declining water tables, expanded use of irrigation management tools is needed to improve irrigation efficiency in Arkansas soybean production. This study was conducted in 2014 and 2015 to examine irrigation initiation timing on a sandy loam soil in a furrow irrigated commercial field in Mississippi County. A major research objective was to develop, validate, and expand use of irrigation timing cues, incorporating information from weather stations, atmometers, and soil moisture measurements. Cues for irrigation initiation were based on plant maturity measures and evapotranspiration (ET). Four irrigation initiation timing treatments were evaluated: initiation occurred when ET deficits reached 1.5 in (early start), 2.4 in (standard), and 3 in (late start), and rainfed. Although the classified soil type was a sandy loam, the field was variable with areas of coarse sand (sand blows) present. The experimental design was a randomized complete block with 4 replications and comprised approximately 16 hectares. Pest response to irrigation timing was shown to be similar among treatments during both years, while height varied directly with the amount of irrigations received. With above average rainfall in 2014, results from the study showed that delayed initiation of irrigation actually increased yield. Analysis of yield monitor data on sandy loam soil indicated 6106 kg/ha in late initiated plots and an average of 5817 kg/ha in all other treatments. Severe yield penalties only occurred in areas of the field characterized as sand blows within rainfed strips. This shows that groundwater could be saved by delaying irrigation without yield loss.