Quantifying soil moisture deficit effects on soybean yield and yield component distribution patterns

Abstract

Soil moisture stress is the major abiotic stress factor that causes extensive losses to soybean production worldwide. Quantitative relationships between soil moisture deficit and yield components are needed to improve algorithms of the existing soybean models predictability. The objective of this study was to quantify water stress effects on various plant growth and reproductive traits using two soybean cultivars with distinct growth habits, indeterminate type, Asgrow AG5332 and determinate type, Progeny P5333RY. Plants grown in pots outdoors were moved into sunlit controlled environment at flowering stage. Five water stress treatments, 100, 80, 60, 40, and 20% of daily evapotranspiration of the control, were imposed at flowering and continued until maturity. Plant height and node numbers were recorded at 7-day intervals. Plant component dry weights, pod distribution patterns, and pod and seed yield were measured at the final harvest. A quadratic function best described the relationship between soil moisture content and midday leaf water potential and − 1.0 MPa leaf water potential was achieved at optimum soil moisture content of 0.15 m3 m− 3 soil. The middle region of the canopy in both cultivars accounted for about 60% of final yield compared to top and bottom regions. Branch pod yield was about threefold as high as mainstem yield, and it was more sensitive to moisture stress than mainstem yield. Harvest index declined linearly with decreasing soil moisture levels in the cultivars, and rate of decline in Asgrow AG5332 was lower (slope = 1.68) than the decline of Progeny P5333RY (slope = 2.42) m3 m− 3. The functional relationships between soil moisture stress and yield components will be useful to aid farm managers in scheduling irrigation and to improve the functionality of soybean crop models under varying soil moisture conditions.