Concurrent Response of Soybean to Fixed (Full and Limited) and Variable Rate Irrigation Management in Three Soil Types: II. Growth, Yield, Evapotranspiration and Water Productivity

Soybean growth, yield, crop evapotranspiration (ETc) and crop water use efficiency (CWUE or crop water productivity, CWP) under different irrigation levels in three different soil types in the same field were investigated concurrently. Treatments in each soil type were: (i) variable rate irrigation (VRI), (ii) fixed rate full irrigation (FR-1″) and (iii) fixed rate limited irrigation (FR-0.75″). There was not enough evidence suggesting the superiority of VRI over FRI-1″ or FRI-0.75″ in terms of improving yield or CWUE. Leaf area index (LAI) and plant height were stronger functions of soil types than irrigation treatments. Growing season cumulative grass-reference evapotranspiration (ETo) and cumulative precipitation were 629 and 489 mm, respectively, in 2018; and 589 and 551 mm, respectively, in 2019. Variations in yield among irrigation treatments for both seasons were not significant (p > 0.05). Soil type, rather than irrigation treatments, explained variation in yield with statistical significance (p < 0.05). Soil types had substantial impact on ETc and CWUE. Since spatial variability in soil properties has a profound impact on soybean growth, yield, ETc and CWUE, soil variability in horizontal and vertical domain must be considered for developing accurate management zones and prescriptions for VRI, and for in-season VRI, FRI and limited irrigation management for successful and effective operations.