by Emily Oldfield, BLT Guest Writer
What is soil health?
Can you diagnose a soil as healthy or not? Recently, the concept of “soil health” has gained traction in policy, research, and farming circles. The generally agreed-upon definition of soil health, put out by the Soil Science Society of America, is “the continued capacity of the soil to function as a vital living ecosystem that sustains plants, animals, and humans.” The ability of a soil to function rests, in part, on the amount of organic matter in the soil (that is, anything that was alive and is now decomposing in the soil). Soil organic matter constitutes a small fraction of the total volume of soil (see figure), but it has an outsize influence on the overall health of soil. Soil organic matter contributes to soil fertility in several key ways: by providing increased aeration and water holding capacity; by providing habitat for soil organisms, which fuel nutrient cycling by decomposing organic matter; and by retaining and releasing nutrients critical to plant growth.
From the state level to the international arena, initiatives are launching that promote building up soil organic matter in agricultural soils. A few examples include the California Healthy Soils Initiative, which incentivizes growers and ranchers to enact management practices that improve soil health. Closer to home, Massachusetts is considering legislation to establish a healthy soils program within their Department of Agricultural Resources. This legislation was initiated in the aftermath of New England’s summer drought of 2016, which led to significant crop failures across the state (soil organic matter’s ability to absorb and retain water can help mitigate the impacts of drought). At the national level, the 2018 Farm Bill passed by Congress includes funding for agricultural practices that improve soil health. Finally, the 4 per mile Initiative, launched at the United Nations Climate Change Conference in 2015, promotes practices that boost organic matter concentrations in soils.
How to build soil health?
Practices to build soil health rest on increasing the amount of organic matter in the soil. Such practices include adding compost to farm beds, retaining plant residues on the soil surface, planting cover crops such as rye and vetch after fall harvest, and reducing or eliminating soil tillage to prevent the break-up of organic matter in the soil. These practices can have benefits beyond the immediate health of a particular field – they can actually impact the larger ecosystem as well. For instance, increasing soil organic matter helps retain soil nutrients, which helps prevent agricultural fertilizer run-off that can pollute local watersheds; it can reduce the need for inputs of mineral fertilizers by providing sufficient crop-available nutrients; and it can also help sequester carbon and therefore potentially help mitigate rising atmospheric carbon dioxide levels under climate change.
You can learn more about soil health and initiatives aimed at increasing soil organic matter concentrations with these online resources: www.nrcs.usda.gov/wps/portal/nrcs/main/soils/health, and www.4p1000.org.
Figure 2: Examples of farming practices that can increase soil organic matter concentrations. On the left, no-till practices prevent the breakdown of soil structure and loss of soil organic matter by minimizing disturbance to the soil; on the right, planting cover crops increases carbon inputs into the soil and protects soil from loss and erosion after cash crops have been harvested. Images courtesy of the National Resource Conservation Service (top) and the Yale Sustainable Food Program (bottom).
Emily Oldfield recently completed her PhD in soil ecology at the Yale School of Forestry and Environmental Studies. The big over-arching question of her dissertation research was how to continue feeding a growing population in a way that minimizes harm on the environment. In answering this question, she focused specifically on the role that soil organic matter plays in fostering soil fertility, crop productivity, and carbon sequestration.
