Flooding of Soybeans During Early Reproductive Development
Occasionally, flooding of soybeans will occur during the growing season in the Midsouth. Soybean stress from flooding is thought to be most pronounced when plants are in the early reproductive phase, the time when irrigation of soybeans is normally initiated in the region. A recent study was conducted in Arkansas to determine the effect of flooding soybeans in the early reproductive phase on yield and seed composition. Results are reported in an article titled “Impact of flooding at the early reproductive growth stage on yield and seed composition”. Major points about that research and its results follow.
• The study was conducted on a silt loam soil in a zero-graded field near Stuttgart, Arkansas [34°27N lat.] in 2019 and 2020.
• Flooding treatment consisted of a 4-day submergence of soil [10-16 cm water depth] at R1/R2. The non-flooded treatment was furrow-irrigated according to standard practices for the region.
• 31 soybean genotypes [9, 13, and 9 classified as susceptible, moderately susceptible, and tolerant to flooding damage, respectively] were evaluated in the experiment.
• Visual damage to genotypes was scored on a 1-4 scale 7 days after flood removal, with 1 = ≤10% damaged plants, 2 = 10% to ≤30% damaged plants, 3 = 30% to ≤50% damaged plants, and 4 = >50% damaged plants.
• Grain yield of each genotype was determined at maturity, and seed protein and oil content were measured in a subsample of harvested seeds from each genotype in each treatment.
• 9 genotypes were visually rated as tolerant, 13 as moderate, and 9 as susceptible, but genotype ratings did not necessarily correlate to seed yield of the genotypes. This emphasizes the need to develop improved methods to accurately classify genotypic response to flooding.
• Overall, tolerant genotypes yielded more than those rated moderate and susceptible. However, all genotypes yielded less when flooded for the 4 days in this study.
• Flooding in this study did not significantly affect seed protein and oil content.
• The authors concluded from their results that visual phenotyping of flooding damage to soybeans may not fully reflect flood tolerance in terms of seed yield. This limitation of subjective visual scoring for flood tolerance emphasizes that the identification and incorporation of flood-tolerant alleles through plant breeding is needed to potentially reduce soybean yield losses attributed to flood damage.
It is interesting to note that flooding of soybeans for 4 days as done in the above study resulted in significantly reduced yields of even genotypes that were rated as tolerant to flooding. These results confirm that prolonged flooding of any soybean variety during reproductive development should be avoided when possible. This means that flood irrigation that is used on soybean acreage in the region as well as field drainage should be managed to ensure that the flood period is of the shortest duration. Also, producers who use flooding as an irrigation method should ensure that they use soybean varieties that have been proven to best tolerate the saturated soil conditions that will result from this practice.
Click here to access a White Paper that contains information about the effects of flood irrigating soybeans, and here for the Miss. Soybean Irrigation Guide.
Composed by Larry G. Heatherly, Mar. 2025, larryh91746@gmail.com