Farming After the Flood-Soil Fertility and Management Considerations
By Jac J. Varco, Ph.D.
Endowed Triplett Chair
Professor of Agronomy
Dept. of Plant and Soil Sciences
Mississippi State University
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This presentation discusses the residual effects on soil properties from extended flooded conditions, as was the case in the Southern Delta Region of Mississippi during the summer of 2019. Flood inundation effects include changes in soil chemistry from a mostly aerobic state to an aerobic state. Changes in nutrient availability occur because of losses of nitrogen through leaching and denitrification, and while soil-test phosphorus levels increase, subsequent crops, such as corn, can show phosphorus deficiencies because of the loss of vesicular arbuscular mycorrhizal (VAM) fungi. Soil-related concerns following a flood include avoiding damage to soil structure by tilling when the underlying soil is too wet and sampling the soil for testing purposes as near as possible to planting the next crop, so as to evaluate the fertility status after conditions have recovered back to near normal. Planting a cover crop in the fall can help remediate soil chemical, physical, and biological properties. Another recommendation is to avoid planting corn the first year; if doing so is necessary, then the grower should consider starter phosphorus or application of fertilizer phosphorus at a higher rate to avoid a deficiency. In some cases, zinc may be needed due to reduced availability from lack of VAM fungi, similar to phosphorus. Lastly, the grower should monitor crop tissue nitrogen levels and make side-dress nitrogen applications accordingly.