Fallow Syndrome: Coming Soon to a Corn Field Near You?

The 2019 growing season is mostly in the history books, and for many of us, is one that we are thankful to have behind us. However, 2019 might have one more final shot to take. With the significant acreage that was prevent plant in 2019, some farmers and agronomists are beginning to consider the potential for fallow syndrome in 2020.

Fallow syndrome is not a condition that we routinely encounter in the eastern corn belt. In essence, fallow syndrome is a condition that can occur in fields where a crop was not planted the prior year, and is primarily a problem in grass crops, such as corn or wheat. It manifests as symptoms of a nutrient deficiency, particularly phosphorus, in a field where fertility is adequate. The reason for this condition is a decline in the population of beneficial microorganisms in the soil, such as mycorrhizal fungi. These microorganisms form a symbiotic relationship with the crop plant and enhance the crops ability to uptake nutrients from the soil in exchange for exudates from the roots that feed the microorganisms. In the absence of a suitable host, these microorganism populations decline, and the crop does not become as quickly inoculated as in a year following a crop.

The effects of fallow syndrome will generally be expressed more in fields that were kept clean for most of the prior season, as many weed species are suitable hosts for these microorganisms and will help to preserve their populations. Therefore, if a field was kept sprayed or tilled to limit weed populations, there is more of a risk of fallow syndrome than fields that had weed populations that were not managed or those that were managed by mowing during the season. Also, if a cover crop was planted on a field, fallow syndrome chances are reduced as many cover crop species are suitable hosts for these organisms. One exception to this are brassica species, such as radishes, turnips, or rapeseed, which are not suitable hosts for these microorganisms.

If planning to plant corn in fields that were fallow in 2019, a starter fertilizer application of phosphorus and zinc should be considered, particularly on fields where fertility levels are marginally low. As the root system of the corn plant develops and expands in size, the crop is better able to take in nutrients and the likelihood of these symptoms declines. In addition, microorganism populations will also increase and reestablish the symbiotic relationships within the crop. It is also important to remember that corn plants often exhibit purpling similar to a P deficiency early in the growing season due to the bright, sunny days and cool nights that often occur in the region during the spring.

While fallow syndrome is a real condition, it is unlikely that it will be a major concern for many growers during the 2020 season. As always, sound management is the best tool that we have to deal with this parting shot of 2019.