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Tips to prevent fallow syndrome where crops have drowned out

WORTHINGTON -- If you are a crop producer in southern Minnesota, odds are you have had your share of drowned out spots in fields this year. Depending on field drainage and the rainfall received, there are still areas in fields across the region that have not been successfully replanted to a crop. Although options become more limited as the season progresses, establishing a crop in bare or drowned out spots will help avoid the issue called "fallow syndrome" in 2013.

Fallow syndrome can severely limit the growth of a crop in soils where no crop or weed growth occurred the previous year. When there is no plant growth in an area for an extended period of time, populations of "good fungi," called active arbuscular mycorrhizae, are dramatically reduced because these fungi need actively growing roots to survive. These fungi assist in the uptake of phosphorus and other nutrients with limited mobility in the soil, such as zinc. Corn and small grains tend to be more affected by this syndrome, although it has been reported as an issue in soybean as well. Replanting drowned out or bare spots to some kind of crop can help maintain levels of these fungi in the soil.

At this point, drowned out or bare spots may still be replanted to soybeans, although a variety with an earlier relative maturity than what was originally used would be recommended as planting is delayed into late June.

Another economical option would be to plant a cover crop of oats in these areas. George Rehm, retired University of Minnesota Extension soil scientist, recommends a seeding rate of about 1 bushel per acre ( Planting soybeans or a cover crop will also help reduce weed growth and help manage weed seedbank levels.

Replanting to corn for grain would not be recommended at this late planting date, as the crop would likely not reach maturity before a killing frost, grain moisture could be high at harvest, and yield potential would be greatly reduced.

If it is not feasible to plant a crop in a bare spot yet this year and corn or small grains will be planted next year, a banded application of phosphorus at planting next year may help alleviate the effects of fallow syndrome. This is recommended even if soil test values for phosphorus are high. Note that broadcast applications of phosphorus have not been shown to be as effective as banded applications. It is also recommended to sample the soil for zinc and to include zinc in the banded fertilizer application if test levels are low or marginal.

If soybeans will be planted in 2013, information from Iowa State University states that a high rate of banded or broadcast phosphorus should be applied to help reduce potential issues with this syndrome. It is not recommended, however, to place phosphorus with the soybean seed due to injury potential.

Lizabeth Stahl and Dave Nicolai are Extension Educators in Crops with University of Minnesota Extension.