Post-Flood Soil Impacts-What to Expect

Flooding destroys many acres of cropland each year, leaving fields dead or unplanted for up to a year. Crops often exhibit purpling, light green color and poor vigor when planted in fields which have been fallowed for a year or more. Mutually beneficial fungi called vasicular-arbuscular mycorrhizae (VAM) enhance nutrient uptake in plants, especially phosphorus. Fallowed fields have reduced levels of VAM and may delay nutrient uptake and plant growth. Growers facing the potential of post flood or fallow syndrome should consider establishing a cover crop in portions of fields that were not planted or were drowned-out due to excessive water. In many instances this will be difficult because persistent rains may not allow enough soil drying to permit planting, ponded portions of some fields are not easily accessible, and herbicides applied earlier in the growing season will result in rotational crop restrictions. Weed growth will support mycorrhizae populations, but may provide less consistent ground cover, more erosion risk, and increased future weed pressure than cover crops. Application of 60 to 80 lbs P/acre of starter fertilizer the year after flood and fallow will help offset mycorrhizal loss. Broadcast applications of P fertilizer have not been effective in preventing fallow syndrome, particularly in soils with high soil test P. High soil test P will lessen the fallow syndrome problem, but not eliminate it. Using VAM fungal inoculant as a way of restoring a mycorrhizal population is not readily available and too expensive to apply for field crops. Soybeans may be affected by fallow syndrome, but researchers and growers have generally experienced less growth retardation than for corn.

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Michael Rupert Michael Rupert
Pioneer
michael.rupert@pioneer.com


Michael Rupert is Agronomy Research Manager for the Eastern Business Unit of Pioneer Hybrid. Before that he spent 9 years in Hawaii as a Parent Seed Agronomist for Pioneer and a Production Researcher for Holden’s Foundation Seeds. Michael received an MS in Agronomy and Plant Breeding from UC Davis and grew up on a horse ranch in California. He also worked with alfalfa, rice, and fruit trees before beginning work with corn in 1997.