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Soil Fertility Considerations and Fallow Syndrome

By Daniel Kaiser, Extension Nutrient Management Specialist

The increased number of corn acres managed with prevented planting in 2013 has resulted in numerous questions about management in 2014. One major question that arises is the effect of fallow syndrome.  Fallow syndrome is a result of reduced colonization of plant roots by vesicular arbuscular mycorrhizae (abbreviated VAM).  Since VAM are important in the uptake of elements such as phosphorus and zinc, questions arise as to proper management for the following years crops.  However, fallow syndrome does not affect all crops nor will it likely be an issue for all prevented planting acres

Boersma starter.jpg
Jim Boersma, Pioneer Hi-Bred International

Corn will likely show the greatest potential impact on grain yield from fallow syndrome and the effects can be clearly seen as small purple plants early in the growing season (see included picture).  The potential risk for other crops such as soybean is low and special management will not be required.  For corn, the best way to mitigate potential negative impacts of fallow syndrome is the use of small rates of banded phosphorus and chelated zinc applied directly on the seed as a starter fertilizer.  It is not well known as to the exact rate to use for all circumstances but a normal application of 5 gallons per acre of 10-34-0 may be enough.  Under fallow syndrome banding is important.  Broadcasting extra phosphorus and zinc previously has not been shown to effectively treat the problem.

The greatest risk for fallow syndrome will be in fields that remained clear (fallowed) throughout the growing season.  Fallow syndrome is not uncommon in Minnesota and has been found to occur when corn is grown following sugar beet since Sugar beet is not a host crop for VAM.  Other crops which are not hosts include Brassicas.  Forage radish would be a crop that falls within the Brassica family than has been seeded on prevented planting acres.  However, research has not identified that forage radish would necessarily induce fallow syndrome, but the potential risk may be higher.  In the cases where oat or other small grain crops were seeded there should be a very low risk of fallow syndrome since oat is a host for VAM.  Remember, even though the potential risk may be higher there is no guarantee that treatment is needed or will be economical.

Specialty fertilizer products are available that are marketed to increase root growth and potentially help with VAM colonization.  However, I have not seen any clear wonder product that would work as well as a small rate of "pop-up" starter fertilizer when the use of starter fertilizer is possible.  A concentrated band of nutrients near the roots is important when managing fields prone to fallow syndrome and is the best management strategy.  Make sure if starter is used to not apply too high of a rate.  Even if conditions are right for a higher chance of a economic return to starter over application still may result in a high risk for root damage to corn and especially to soybean where fertilizer application directly on the seed is not recommended.

Additional Information

Additional information on specialty fertilizer product can be found in the compendium of non-traditional products.  The compendium is managed by soil fertility extension faculty at several Land Grant Universities in the North Central region.  Due to the number of products sold not all may be included in research.  Further information can be found by using the link below.

--Compendium of non-traditional products

Potential 2014 research

The greater than normal number of acres in prevented planting does off an opportunity for research to study the impacts of starter use on corn following fallow or cover crops.  I am potentially looking for a number of field sites in southeast and south-central currently either in fallow or following forage radish to study the impacts of starter fertilizer use on corn since very little data is available on economics and the need for starter following forage (tillage) radish.  The size of the studies would be less than one acre and would be fertilized and planted with research plot equipment.  A fee for land use would be available for those cooperating

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  1. Dan: Good article! I would concur that 10-34-0 with Zn is a must starter for corn following sugarbeet. We routinely recommend 5-10 gal as a starter with the seed. If this isn't done, you can guarantee the purple corn syndrome will develop, atleast in the RR Valley soils.
    Craig Edwards
    West Central Ag services
    Ada, Mn

  2. Thanks for the comment Craig, I was also wondering what would happen with some of the cover crops used in the south this year. May have some similarities to problems faced by sugar beet growers when using turnips or radish.


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