By Lizabeth Stahl and Jill Sackett, University of Minnesota Extension Educators
The challenging spring of 2013 resulted in wide-spread planting delays across the state and a significant amount of acres that remain unplanted at this time. If the decision has been made to take the "prevented planting" option for insurance purposes, the question remains about what to do with these acres. Leaving the ground bare greatly increases the risk of not only soil erosion, but also the risk of "Fallow Syndrome" the following year.
"Fallow Syndrome" can severely limit crop growth 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 (AM), are dramatically reduced because AM fungi need actively growing roots to survive. AM 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. Drowned-out spots in fields are also at risk of "Fallow Syndrome". Planting some kind of an annual crop on prevented planting acres or on drowned-out spots in the field can help maintain levels of AM fungi in the soil.
From a biological perspective, weeds could serve as a "cover crop" to help prevent "Fallow Syndrome", but the resulting seed production and contributions to the weed seedbank would lead to increased weed management issues in the future.
Planting a cover crop on prevented plant acres or drowned-out spots in the field can provide multiple benefits beyond addressing the issue of "Fallow Syndrome". For example, if nitrogen was applied but corn was not able to be planted, a cover crop that helps scavenge nitrogen might be a good choice. Cover crops can also help supply nitrogen, and vary in their effectiveness at erosion prevention, fighting weeds, alleviation of compaction, and forage value.
The U of MN Fact Sheet "Prevented Plant Cover Crop Options" (CC.for.PP.factsheet.June.2013 (5).pdf) lists suggested planting dates and seeding rates for cover crops, and also compares a number of cover crops in their effectiveness at providing various benefits. A list of cover crop seed sources and pilots for aerial seeding has been compiled by the U of MN (MN.Cover.Crop.Business.Directory.July.2013 (3).pdf).
Further details about using a cover crop for prevented plant acres (i.e. seeding date considerations, using the cover crop for hay or forage, etc.) are discussed on the U of MN Late Planting Website at http://z.umn.edu/lateplanting. Note, be sure to check with your local FSA and crop insurance representative to ensure you are in compliance with rules and regulations related to cover crop use on prevented plant acres.
If it is not feasible to plant any crop 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. If corn will be planted in 2014, it is also recommended to soil sample for zinc and to include zinc in the banded fertilizer application if soil test levels are low or marginal.
If soybeans will be planted in 2014, information from Iowa State University states that a high rate of banded or broadcast phosphorus should be applied to help reduce potential issues with "Fallow Syndrome". It is not recommended, however, to place phosphorus with the soybean seed due to a high risk for injury.