A healthy soil system: building organic matter

MADISON – Northeast Wisconsin’s Door-Kewaunee Watershed is home to a network of farmers demonstrating innovative conservation practices to protect water quality in the Great Lakes.

In partnership with the USDA Natural Resources Conservation Service (NRCS), Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) and Peninsula Pride Farms, the Door-Kewaunee Demonstration Farms Network (DK Demo Farms) is working to implement best management practices to reduce soil erosion and phosphorus runoff, increase soil organic matter and improve soil health.

Jamie Patton was the guest speaker for the DK Demo Farms’ Spring Field Day hosted by Heim’s Hillcrest Dairy in Casco. Patton, a senior outreach specialist with the University of Wisconsin‒Madison & Extension Nutrient and Pest Management Program, discussed the importance of promoting soil health in improving farm sustainability and water quality in the region, as well as the relevant agronomic practices farmers can use to improve the biological, chemical and physical properties key to a healthy soil.

Speaking from the bottom of a soil pit dug across a field with different land use histories, Patton highlighted how soil characteristics can change with management over time and how these soil characteristics can impact plant growth, rainwater infiltration and soil erosion.

One of the primary indicators of a healthy soil system is its organic matter content.

Jason Nemecek, Wisconsin NRCS State Soil Scientist, explains, "Organic matter is one of the major keys to soil health. It can help aggregate stability, water infiltration, soil aeration and fertility. It may also help bind environmental pollutants, such as heavy metals and pesticides."

So, how might farmers increase the organic matter of their soils? The key is to increase the amount of organic material being deposited in the soil system, while simultaneously decreasing its loss through erosion and decomposition.

One practice to increase the amount of organic matter being added is through the use of cover crops. In northeast Wisconsin, cover crops are typically planted in the fall after the farm’s cash crop (the crop grown primarily for grain or forage) is harvested. Often, the cover crop is not harvested, but rather, grown solely to protect and enrich the soil. In some situations, the farmer may harvest the cover crop as feed prior to establishing the next cash crop.

The cover crop’s contribution to soil organic matter is two-fold. First, the crops’ aboveground plant matter helps protect the soil from raindrop impact, runoff and erosion, while also providing a habitat for beneficial insects and contributing to the soil organic matter content as it decomposes.

Second, the cover crop’s roots create pore channels as they penetrate the soil, helping to reduce compaction and improving water and air movement into the soil. As the cover crop roots grow, and as they die and decompose, they add various organic materials to the soil, materials that increase the soil’s organic matter content, as well as serve as a key food source to the soil microbial population, a population that helps maintain soil fertility, soil porosity and water quality.

The four farms participating in the DK Demo Farms project are enhancing their knowledge of utilizing cover crops within their rotations and are experimenting with new opportunities to establish cover crops earlier in the growing season, including interseeding cover crops into growing corn.  

To reduce soil organic matter loss through erosion and decomposition, many farmers are turning to no-till systems, leaving “the tillage work” to the plants and soil biology. In a no-till system, farmers do not use tillage equipment to turn under crop residues and prepare a seedbed for planting. Instead, planting operations are carried out in the residue remaining from the prior year’s cash crop and/or cover crops.

By not tilling the soil, remaining plant residue protects the soil surface from raindrop impact and reduces runoff, thereby increasing water infiltration and reducing erosion. Additionally, reducing tillage helps preserve soil organic matter by limiting unnatural introductions of oxygen into the system, introductions that can overstimulate the decomposition process.

Soils managed under no-till also often benefit from increased soil biological activity, increasing the overall health of the soil. The DK Demo Farms are utilizing no-till practices, identifying key management strategies that make the practice successful in northeast Wisconsin.

The DK Demo Farm field day, attended by more than 40 local farmers and agri-business professionals, also included discussions about manure setback regulations, manure applications, and research work by UW-Extension’s Discovery Farms on nitrogen use efficiency.