Irrigation Management Effects On Soil Water Dynamics and Soybean Yield.

Increasing applied irrigation efficiency is essential for maximizing soybean yields in irrigated cropping systems.  A study was conducted in 2011 and 2012 near Scandia, KS to determine the effect of various irrigation rates and application timings on soil water and soybean yields in North Central KS.  Three irrigation timing treatments were evaluated: 1) full-season irrigation strategy, 2) deferring all irrigation to soybean growth stage R3 (begin-pod), and 3) irrigation timing based on actual soil water depletion. The first two treatments followed the SoyWater irrigation system simulated soil water depletion at 50%, whereas the irrigation trigger used for the third treatment was 50% measured depletion prior to growth stage R3 and 35% depletion between R3 and R6. Three different irrigation amounts of 17, 24, and 32 mm were applied within each treatment to determine the interaction between irrigation rate and timing.  Soil Water was measured weekly by neutron probe attenuation to measure the actual soil water amounts with irrigation rate and timing. Plant height and number of nodes were measured prior to harvest. Yield data were collected and water productivity (yield per water applied) was evaluated.  In 2011, there was a significant yield response to the highest (32mm) irrigation rate across all timing methods.  The 17mm and 24mm irrigation rates did not show a significant yield increase over the dryland check treatment.  When averaged across all irrigation rates in 2011, there were no significant yield differences between all three irrigation timing treatments.