Fallow- and flooded-soil syndromes: Effects on crop production

Fallow Soil Syndrome has been a problem for farmers in arid areas. The first observations were made in the 1940s when crops failed to produce as expected when planted to fallowed fields. Recent flooding in the midwestern U.S. states caused extensive crop damage and left many areas barren of plant growth. There was concern that crop production problems would develop when subsequent crops were planted to previously flooded areas. Like Fallow Soil Syndrome, the symptoms of Flooded Soil Syndrome are P deficiencies developing in crops even when adequate soil P concentrations are measured. Commonly used soil chemical extracts are not reliable when attempting to predict occurrence of the problem. Soil vesicular-arbuscular mycorrhizae (VAM) fungi have been shown to increase host plant uptake of relatively immobile nutrients like P. In studies of fallowed soils, VAM colonization rates are lower than similar unfallowed soils. Decreased VAM colonization rates appear to be a factor in development of the disorder. Corn (Zea mays L.) is probably the crop most susceptible to Fallow and Flooded Soil Syndromes. Phosphorus deficiencies have successfully been corrected using a starter P fertilizer applied in a band at planting. Broadcast fertilizer treatments have been ineffective on corn but effective for soybean [Glycine max (L.) Merr.].