Drought and Heat Stress on Corn
Potential yield loss during grain fill can occur due to stand loss, incomplete kernel set, reduced kernel weight and premature plant death. 1 Because kernel fill takes priority over all other plant processes, moisture stress during kernel fill increases the chance for potential leaf death, stalk rot and lodging, kernel weight reduction, and grain fill period. Corn is most sensitive to drought stress during the pollination process; however, yield loss during grain fill may still be 3.0 percent to 5.8 percent per day of stress. 2,3 Kernel abortion and reduced dry weight accumulation in the kernels can occur after pollination. Developing kernels, especially those near the tip of the ear, can be prone to abortion if temperatures are high and moisture is limited during the two weeks following pollination.
Cell division that occurs in the endosperm during the first seven to 10 days after pollination determines the potential number of cells that accumulate starch. 2 Dry weight accumulation is the yield component that is affected after the kernels have reached the dough stage. Severe stress that causes premature death of leaves can result in yield losses because theproduction of photosynthates is greatly reduced. Limited amounts of photosynthates to nourish the developing kernels can cause kernels to be smaller and lighter, or “shallow kernels.” Additionally, severe stress during the grain fill period can cause premature kernel black layer formation, which can also reduce grain fill because further kernel development is terminated.
Drought and Heat Stress on Soybean
Because flowering occurs over a wider window of time compared to corn, soybean plants can typically withstand drought stress reasonably well. However, plants are most sensitive to intense and prolonged stress during the flowering and early pod fill growth stages. Drought stress can cause floral abortion, reduced pod number, fewer seeds per pod and reduced seed size. A moderate drought stress can significantly reduce or irreversibly stop nitrogen fixation, disrupting seed development. 4 Drought stress during R4 through R6 (full pod through full seed) can have a devastating effect on yield potential because flowering stops and plants cannot compensate for lost pods. 5 Specifically, drought stress during early seed fill can reduce the number of seeds per pod. Later drought stress (after abortion limit stage) can reduce seed weight. 6
Management Tips for Managing Drought-Stressed Soybean Fields
As mentioned earlier, effects from drought are expected to be less on soybean plants than on corn plants. If soybean leaves begin to curl or drop, it is time to decide whether to leave the plants in the field and hope for the best or cut them for hay. This decision depends on the stage of growth and the condition of the crop.8 Monitor fields that have great amounts of dead or dying soybean areas. Severe drought during the early filling stage, followed by rainfall at the R5 to R6 growth stage can cause pods to become prone to shattering; therefore, harvesting at higher moisture levels should be considered.
1 Nielsen, R.L. 2013. Effects of stress during grain filling in corn. Purdue University. https://www.agry.purdue.edu/
2 Lauer, J. 2006. Concerns about drought as corn pollination begins. University of Wisconsin. Field Crops 28.493-42. http://corn.agronomy.wisc.edu/
3 Wright, J., Hicks, D., and Naeve, S. 2006. Predicting the last irrigation for corn and soybeans in central Minnesota. University of Minnesota Extension. https://www.extension.umn.edu/
4Lenssen, A. 2012. Soybean response to drought. Iowa State University. https://crops.extension.iastate.edu/
5Rosenberg, M., Hall, R.C., and Twidell, E.K. 2012. Effects of drought stress on soybean production. South Dakota State University Extension. 03-2009-2012. https://igrow.org/
6Desclaux, D., Huynh, T.T., and Roumet, P. 2000. Identification of soybean plant characteristics that indicate the timing of drought stress. Crop Science. Vol. 40:716-722.
7Wright, D.L., Mayo, D.E., and Jowers, H.E. Using drought-stressed corn for silage, hay, or grazing. University of Florida. Publication #SS-AGR-274 http://edis.ifas.ufl.edu/
8Roozeboom, K. 2011. Drought-stressed soybeans means decisions for producers. Kansas State University. http://www.ksre.ksu.edu/
Web sources verified 08/21/18.