By Mohammad Shamim
Water is essential for crop growth, but like many things in nature, too much can be just as damaging as too little. Recently, many areas in Kentucky received excessive rainfall that left fields flooded. Understanding how soybean responds to flooding can help explain why two fields only a few miles apart may have very different yield potential this fall.
While drought restricts water uptake, flooding creates the opposite problem. Excess water fills soil pores that normally contain air, drastically reducing oxygen availability around the roots. Within hours, soybean roots experience oxygen deficiency (hypoxia), and prolonged flooding can lead to complete oxygen deprivation (anoxia). Without oxygen, roots cannot efficiently produce the energy (ATP) required for nutrient uptake, root growth, and maintenance, leading to impaired water absorption even though water is abundant (Kozlowski, 1997; Bailey-Serres and Voesenek, 2008).
Flooding affects soybean at every level of biological organization. At the molecular level, genes associated with anaerobic metabolism and stress responses are activated while photosynthesis-related genes are downregulated. Physiologically, stomatal conductance, chlorophyll content, nitrogen fixation, and photosynthetic rates decline. Morphologically, plants often become stunted, root systems deteriorate, nodules lose activity, leaves may yellow prematurely, and pod set is reduced. The situation is most severe if the whole plant is submerged. In this scenario, the whole photosynthetic machinery stops working, gas exchange comes to a complete halt, growth ceases, and if flood water has soil particles on it, it will deposit on leaves surface and reduce both gas exchange and light capture.
Source : uky.edu