Study shows how conventional tillage
has degraded soil organic matter

By Whitney Prestby, natural resource educator, UW-Extension

Building soil organic matter is often thought of as the “gold standard” for soil health benefits; yet for many, it feels like an elusive goal. In 2018, Barry Bubolz with the Natural Resources Conservation Service (NRCS) and Jamie Patton with University of Wisconsin-Madison conducted a study to better understand historical levels of organic matter and the changes in soil organic matter after decades of conventional agriculture. The study showed that over time, intensive tillage has drastically decreased our soil’s organic matter.
So why does it really matter? Soil organic matter is vital to building productive soils and growing healthy plants. Building and maintaining soil organic matter helps to improve the quality of soil by reducing compaction, increasing infiltration and increasing the soil’s water holding capacity. Soils with high organic matter create a habitat for beneficial insects and microbes that fight plant pests and diseases. Soil organic matter stores and supplies nutrients necessary for plant growth, which can reduce the need for commercial fertilizer and reduce a farm’s input costs.1 But as studies have shown, we can quickly deplete our soil’s organic matter, and the processes for rebuilding soil organic matter takes time and a serious commitment to conservation practices. Is rebuilding soil organic matter a tangible goal? Let’s dig into what we are seeing on the Door-Kewaunee Demo Farms.

When the project began in 2017, 22 field sites were selected and baseline values were collected for a variety of soil health parameters, including soil organic matter. The four demonstration farms showed tremendous dedication to the program and commitment to adopting conservation practices. Over the five years, these fields saw drastic changes in management, which included diverse cover crop mixes, increased biomass and minimal or no-tillage practices that kept the soil intact. In the fall of 2021, when these fields were retested, the results showed that the farmers’ hard work was beginning to pay off.

After completing the fifth year of the project, samples were collected at each of the 22 fields to compare how conservation practices impacted the soil’s health. All samples were sent to and completed at AgSource Laboratories. The initial findings (Table 1), suggest that conservation practices are helping maintain current soil organic matter and, in some cases, we may be seeing a trend upward. It’s important to recognize that these tests were not conducted using scientific protocols, and therefore, we cannot say these findings are statistically significant. However, the trends do suggest that conservation practices may help right the ship when it comes to the loss of soil organic matter.

“The recent soil tests indicated that soil organic matter levels are trending up, confirming the positive soil health changes the farms are seeing in their fields, informing them and others of the potential improvements that can be made on the landscape,” Barry Bubolz said.

Cover crops that increase biodiversity and biomass, combined with minimal or no-till practices, are key to building a healthy agricultural system.

1 Cooperband, Leslie. “Building soil organic matter with Organic Amendments”. 2002. University of Wisconsin – Madison

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