Soil Moisture Stress Effects on Root Architecture and Vegetative Growth of Soybean.

Due to the need of greater amounts of water for irrigation to support agriculture, the Mississippi Alluvial River Valley aquifer is being depleted at a higher rate. With the rapid rate of water removal and because of the uneven distribution of rainfall, the replenishment of the aquifer is hindered. Because of this limited water availability, soil moisture stress is becoming a severe environmental constraint to soybean productivity. To quantify soil moisture deficit effects on the soybean growth and development including root traits an experiment was conducted in sunlit growth chambers by seeding two soybean cultivars. Five soil moisture stress treatments, 100, 80, 60, 40, and 20% of daily evapotranspiration of the control were imposed after emergence and continued 18 DAP. Soybean growth and development parameters were taken at the harvest along with root parameters which were measured using winRhizo. Gas exchange and fluorescence parameters were taken at 15 DAP. Soybean shoot, root, and physiological growth decreased with increasing soil moisture stress, and the decrease was linear for most of the traits. Both cultivars showed a decrease of photosynthesis and stomatal conductance suggesting that reduction of net photosynthesis is mainly due to stomatal limitations. The decrease of total dry matter, leaf area, and net photosynthesis were steeper in Progeny 5333 confirming that it is the most drought sensitive cultivar than AG 5332. Leaf area among the shoot traits, net photosynthesis among physiological traits, and crossings among root traits were the most responsive to soil moisture stress, whereas least were node no., Ci/Ca, and root tips. The identified soil moisture and plant processes-dependent functional algorithms will be useful to improve the existing soybean simulation models which could be used for field management. Further, information would be helpful for producers to schedule irrigation and for optimum plant growth during early canopy development.