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Salute Soil Health: If your crops struggle following a prevented planting situation, consider adding cover crops.

May 26, 2020

3 Min Read
tilled, unplanted field
COVER CROP OPTION: If you suspect fallow field syndrome is impacting your crop, consider planting cover crops to help restore vitality to the soil. Tom J. Bechman

No one wants to revisit the 2019 crop year. However, decisions made during that year will influence your soils and crops for years to come. 2019 prevented planting fields were especially affected and should be closely monitored to help bring them back to productivity.

If you plant corn in a former prevent-plant field without starter fertilizer containing phosphorus, you may notice it struggling, emerging unevenly and turning purple. This is most likely because the field is suffering from fallow field syndrome.

This syndrome is caused by a lack of vesicular arbuscular mycorrhizae fungi. VAM form symbiotic relationships with plants, especially grass species like corn. The plant feeds VAM sugars through root exudates, and in turn, VAM collect nutrients, mainly phosphorus and zinc, for plants by gathering them from spaces the roots can’t access. Phosphorus isn’t as mobile in the soil as other nutrients, making VAM critical for plants to uptake enough P for healthy growth.

Prevent-plant fields managed with tillage or herbicide during the fallow period tend to be more susceptible to fallow syndrome due to the lack of living plants that provide a food source for VAM. Tillage also physically breaks up fungal strands, weakening fungi and causing a population downturn.

If fields still struggle in 2020, consider planting a cover crop to boost VAM populations and jump-start your soil biology. About 80% of plant families form VAM associations, making these fungi a critical part of healthy and productive crops.

Cover crops and VAM

Many common cover crops can form VAM associations. Small grain or grass cover crops, such as cereal rye, oats and annual ryegrass, encourage the most VAM growth. Including one of these species in a cover crop mix will provide even more benefit due to the diverse root structures and exudates promoting a variety of soil life.

Brassicas such as turnips, radishes, mustards and rape don’t form VAM associations. They can be included at low rates in a mix to add diversity but shouldn’t be planted alone. In the spring, crops in fields that were cover-cropped with VAM-supporting species form associations earlier in the season, due to cover crop roots keeping the population active and fed. This helps jump-start crop nutrient uptake during critical early growth stages.

Cover crops can also help to address soil compaction. Cover crop roots help loosen soil and break up compacted layers, increasing water infiltration and decreasing ponding. Cover crops will also help build organic matter by building soil carbon. In prevent-plant fields that were tilled, this is especially important. Carbon was released from the soil as carbon dioxide during tillage, causing a reduction in organic matter levels.

These are reasons why 2019 will continue to influence fields and crop yields for years to come. By keeping these effects in mind while planning crop rotation and management, you can rebuild your soil and help it return to a healthier and more productive state.

But why stop there? Consider taking additional steps, such as making cover crops a permanent part of your crop rotation, to make your soils even better than before.

Kautz is a district conservationist with the Natural Resources Conservation Service. She writes on behalf of the Indiana Conservation Partnership.

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