Soil Moisture Stress Effects on Yield Component Distribution in Soybean.

Soil moisture stress is the major abiotic stress factor that causes extensive losses to soybean production worldwide. The objectives of this study were to examine the soil moisture stress effects on two soybean cultivars reproductive growth and to quantify the yield component distribution on two cultivars, AG 5332 and PR 5333 with different growth habit. Plants grown in pots outdoors were moved into sunlit controlled environment at prior to flowering stage. Five soil moisture stress treatments, 100, 80, 60, 40, and 20% of daily evapotranspiration of the control were imposed at flowering and continued until maturity. Growth and development of plants were evaluated throughout the experiment at 7-day intervals. Final plant dry weights and pod and seed yield were determined. Midday leaf water potential (LWP), gas exchange, and fluorescence were measured weekly from 7 to 35 days after treatment. Midday LWP, plant height, and net photosynthesis of soybean declined linearly with decreasing soil moisture levels. The distribution of pods on the main stem and branches varied significantly in both the cultivars. The middle region of the canopy in both cultivars was responsible for approximately 55% of final yield compared to top and bottom regions. Approximately 45% and 64% reductions in seed number and seed weight were recorded under 20% moisture stress level compared to the control in Progeny 5333, while AG 5332 accounted 46 and 43% decline for those yield components. The information on the seed distribution patters across different soil moisture levels will be useful to optimize yield through proper management practices and scheduling irrigation during the growing season.