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Consider Fall Cover Crops Now!
Submitted by LuAnn Rolling, District Conservationist

According to Dr. Jerry Hatfield, formerly with the USDA Agricultural Research Service in Iowa, we’ve lost half of our topsoil. We’ve lost half of the carbon in the remaining soil leaving us with 25% of our original “filter”. We’ve also lost 50% of the inherent Nitrogen fertility in our soil. Due to climate change and loss of aggregation (soil structure) we are projected to lose the rest of our topsoil in 80 to 100 years.

You just need to drive around after a rain, and not even a significant rain, to see the dirty water pouring off of fields and the immediate change to brown streams in Allamakee County. Every where you look there are gullies in fields. It’s due in part to increased rainfall, but even more to poor soil health. 

Our soils have lost their “resilience” or their ability to withstand weather events.  They have lost their structure so they immediately crust and do not allow water to infiltrate. We have reduced our earthworms which make large channels for air and water to infiltrate into the soil. 

It takes more nitrogen to produce a bushel of corn today than it did in 1960.  This is wholly due to the loss of soil microorganisms.  A plant root alone can only “take up” about 20% of the fertilizer that is applied.  All the rest of the nutrients have to be broken down by soil microorganism to be available to the plant. Healthy soil will form a fungal relationship with plant roots to form vast “webs” that can extend for miles under the soil to increase the area for a plant to capture nutrients.  Due to tillage, herbicides and only planting one or two crops we have lost the ability to form the relationship with fungi to make this happen.

This damage can be repaired, but it takes some management changes. The first would be no tillage, as it tears up the fungi and opens the soil up allowing bacteria to bloom, consume vast amounts of soil carbon and then die. 

The second thing would be cover crops, as one of the keys to healthy soil is keeping a living root in the soil for as long as possible.  As we approach August and potentially new crop rental agreements I would strongly encourage landowners to require cover crops. Many landlords are now sharing in the expense of the cover crop as they realize the long term viability of their farm hinges on the soil being maintained.

The third thing to do is increase crop diversity.  Growing the same crop every year or every other year leads to less diversity in the soil organisms and the general decline of soil health.  As we raise those same one or two crops we are seeing increased weed pressure leading to increased herbicide use which also leads to soil decline.

Science supports the theory that soil can be repaired. A recent review of 56 studies published in the journal PLoS One found that soil from farms that didn’t till or use synthetic chemicals and used cover crops and crop rotation contained 32% to 84% more microbial mass than conventional farms.  This soil bacteria and fungi work in tandem to make minerals in the ground water-soluble - a form that a plant can readily take into their roots.

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