Effect of Centibar Thresholds at Soybean Growth Stages on Yield and Irrigation Water Use Efficiency.

Effect of Centibar Thresholds at Soybean Growth Stages on Yield and Irrigation Water Use Efficiency Wilks Wood, L. J. Krutz, John Orlowski, J. T. Irby, L. Falconer, B. Henry, The Mississippi Alluvial River Valley aquifer is being depleted at distressing rates due to irrigation withdrawal for cotton, corn, soybeans and rice. Compounding this issue is that current irrigation practices adopted by producers typically result in overwatering crops at the VN to R2 and R6 to R7 growth stages. Also, the use of soil moisture sensors is relatively new to the Mid-South and knowledge of this technology is currently inadequate in our region. To determine the effect of differing centibar thresholds at separate growth stages on soybean grain yield and water use efficiency, an experiment was conducted at the Delta Research and Extension Center located in Stoneville, Mississippi in 2015 and 2016. Treatments were arranged in a split-plot design within a randomized complete block. The main plot factor were growth stages that consisted of VN to R2, R3 to R4, R5 to R6.5 and season long. The sub-plot factor was centibar (cbar) thresholds which were -50, -85 and -125. Irrometer Watermark moisture sensors were used to determine when irrigation events would be initiated. A season long threshold of -85 cbar yielded similar to a season long -50 cbar threshold, however, the -85 cbar threshold had 41% greater irrigation water use efficiency. Also, a 9% yield loss occurred when irrigations were delayed during the R5-R6.5 growth stage. Overall, -85 cbar is a safe threshold to utilize throughout the season, and irrigations should not be delayed during the R5-R6.5 growth stage. Results from this study provide valuable insight into improving soybean production and water conservation in the Mid-South.