By Dean Kreager Published in Farm and Dairy 7/14/2022
Soil health is one of the hot topics in agriculture. I continue to receive an increasing number of questions and get involved in more conversations involving “soil health” and “regenerative agriculture”. Many universities and farmers are trying to define healthy soils and find ways to improve the health of the soil. We know that keeping soils covered with a growing crop reduces soil loss and improves water infiltration. We also know there may be a number of other benefits to soils by having livestock grazing over them. What more can be done to improve the soil health in our pastures and what will the benefits be?
What is soil health?
In this column, my colleagues and I have often stressed the importance of soil testing. A soil test will let us know the pH and the amount of some of the important nutrients that will be available to our plants. This is a great tool to help manage pasture productivity. Beyond our standard soil test results there are many additional properties in the soil that can greatly affect productivity and sustainability. “Soil health” takes into account a combination of many factors including chemical, physical, and biological properties. Soil aggregates, pore space, mycorrhizal fungi, biological activity, organic matter, carbon, and water infiltration are just a few of the terms that are often discussed when talking about soil health.
Pastures have benefits to soil health through continuous cover of the ground; however, there are options in managing the pasture that can further improve the health of the soil over time. Management can affect properties such as water infiltration, organic matter, carbon sequestration, and microbial health.
Water infiltration is the ability of water to enter the ground during rains and not be lost as runoff. Having a growing forage with deep penetrating roots helps provide channels for water to enter. This infiltration rate becomes extremely important when there are record rainfalls in a 24-hour period like what occurred in central Ohio in early July this year. The ability of large amounts of water to enter the ground instead of running off will both protect from erosion and increase soil moisture to help through those dry periods. The amount, size, and depth of roots in the pasture has been compared among grazing management systems. University studies spanning from Texas to North Dakota have reported similar results. Forages that are continuously grazed at a moderate to heavy rate often have a shallower root system and do not allow as much water to enter the ground in a short time. Forages that have been rotationally grazed appeared to have much deeper roots which leads to deeper channels and greater amounts of water that can be absorbed into the soil.
Organic matter is a very important part of the soil. It consists of plant or animal tissue that is being broken down. Some benefits of organic matter include increased water holding, increased nutrient holding, and support of beneficial microorganisms living in the soil. These microorganisms can help cycle nutrients back to growing plants. Manure and uneaten forages that are trampled into the ground become contributions to the organic matter. Organic matter does not accumulate quickly but grazing animals can help speed the process.
Pastures that have been well managed will often have higher rates of carbon sequestered into the soil than native fields that have not been grazed. This increase in carbon increases organic matter which increases the water holding capacity of the soil. At the same time, the sequestered carbon is part of reducing greenhouse gas levels. Once again, the rest periods with rotational grazing allow greater root development which places greater amounts of carbon deeper into the ground. Management practices can improve the carbon sequestration rate.
Another grazing benefit to the soil health comes from the stimulation of forage during grazing. Research has shown that the grazing signals the plant to pump out sugars from its roots. The sugars provide nutrition for the living microorganisms in the soil allowing them to do their jobs. One of their jobs involves breaking down dead materials and recycling those nutrients to growing plants. The more food that is available for the microorganisms, the more they reproduce and the quicker they do their job. Once again, a larger root system has a greater potential for feeding the microorganisms.
Improvements in grazing management can have positive effects on soil health. A few points to remember when trying to build soil health in your pasture include: use rotational grazing with appropriate rest periods, do not graze more than 50% of the growth, and avoid grazing wet areas which can cause compaction. Improvements in soil health can help with productivity and resilience of the pasture. I am not suggesting that you do away with soil testing. Proper pH adjustment and fertilizer applications are needed for healthy plants which are vital to improvements in soil health.