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Fall Considerations for Soil Health
by LuAnn Rolling, District Conservationist

There are several things that producers can do this fall when considering trying to improve their overall soil health. A dry fall and early harvest takes some of the pressure off emptying manure storage structures before winter. It’s tempting to want to apply as soon as possible. However, it pays to postpone land application until soil temperatures drop below 50 degrees. Cooler soils maximize nitrogen availability and minimize its loss - whether applying anhydrous ammonia or ammonia-laden manure. That saves money.

It is not too late to plant cover crops. In addition to using any excess nutrients present in the soil the cover will provide additional soil surface coverage to prevent erosion and provide valuable root channels to provide for more water infiltration. Cover crop roots contribute to the 50% pore space goal. Roots build and maintain those channels over time. These root channels also allow cash crop roots to go down deeper into profile early in season so in dry conditions (like we had last spring) crops can tap into moisture.  

Fall is an excellent time to evaluate how your earthworm and insect populations are doing. Now is the time to get out a shovel and go look. You should see 2 to 3 earthworms in every shovel, and if your soils are very healthy 8 to 10. If you see very few you may be experiencing excessive rain runoff and crusting in your fields. Earthworms assist in water infiltration by creating burrows and increasing soil aggregation. As earthworms consume soil it passes through their guts and mixes with organic matter. In one study a healthy population of earthworms consumed 4 to 10 percent of the top 5 inches of soil annually.  

Another temptation with an early harvest may be to do some fall tillage. The major killer of earthworms is tillage. One study showed earthworm counts per acre went from 1.2 million to 60,000 after one disc pass. Some studies have shown up to 10 times more earthworms present in no-till systems vs. tilled systems.

Tillage degrades soil structure, causes erosion and compaction, and destroys the soil ecosystem. Tilling the soil is the equivalent of an earthquake, hurricane, tornado, and forest fire occurring simultaneously to the world of soil organisms. Simply stated, tillage is bad for the soil.

There is a common belief among many farmers and agronomists that tillage can accelerate residue breakdown by the cutting of crop residue into small pieces or burying residue in the soil profile. Also, there is the belief that the application of nitrogen fertilizer on crop residue after harvest can speed up the process of residue breakdown. Both assertions are not correct.

According to Mahdi Al-Kaisi, Professor of Soil Management/Environment, at Iowa State University, tillage can contribute to soil health and water quality deterioration by increasing soil erosion potential, sediment loss, and fall N applications result in water quality risks. Residue decomposition is controlled by biological processes that are influenced by environmental and soil conditions. His research, and many other studies, do not support these practices regardless of the justification or claims that propose tillage equipment can manage residue. Disturbing the soil does not constitute an improvement in soil health nor increase in residue decomposition.

So this fall, enjoy the weather. Do some field shovel tests and plant cover crops. Avoid manure or nitrogen application until the soil is below 50 degrees and DO NOT TILL.