Cow manure greatly improves soil health

In a new study from the American Society of Agronomy, experts have discovered that excess cow manure leads to healthier soils that have improved microbial communities. This is not easy to achieve in dry areas like the Southern High Plains of Texas.

“We know that planting perennial grasslands for cattle production can help protect and restore soil in semi-arid lands that are likely to erode and degrade from intense farming. But producers need additional ways to increase soil carbon and nutrient stores,” said study lead author Lindsey Slaughter.

She describes soil health as the ability of a living soil ecosystem to perform a variety of important functions, such as nutrient cycling and storing and purifying water.

The “living” part of the soil is made up of a community of microorganisms that help maintain its health. For example, they help break down materials like manure so that its nutrients become part of the soil.

“Improving the soil’s ability to perform these roles and support plant and animal life is our target for soil health,” said Slaughter. “Adding the manure can provide a boost of material that can be incorporated into soil organic matter. This helps provide a stronger foundation for more microbial activity and nutrient cycling.”

To investigate, the experts applied a low level of manure to two types of pastures. These pastures consisted of either grass that was fertilized occasionally or a mix of grass and legumes that was not fertilized.

Overall, manure helped increase soil organic carbon and the number of microbes in the soil. It took almost a year and a half to see these changes, but the researchers said this is not totally surprising.

“This tells us that it can take a long time for even a little added compost to become incorporated into the soil organic matter of semi-arid grasslands, but it definitely helps,” said Slaughter.

“We think this is mostly due to the dry climate at our study site,” says Slaughter. “We commonly get little rainfall per year. The microbial community was not able to work quickly or efficiently to decompose the manure without water.”

The experts found that the pastures which had received fertilizer responded better to the manure. This is likely because the nitrogen in the fertilizer helped the microbes decompose the manure better.

“Microbes help directly with releasing nutrients from organic material in a form that plants can use, as well as decomposing those residues to build soil organic matter,” said Slaughter. “A lot of work has been done on how this can help improve cropping systems. However, we wanted to also test this on forage pastures.”

According to Slaughter, the next steps in the research are to determine whether more manure or multiple applications would get faster results. They also plan to investigate if irrigation or fertilizer would help incorporate the manure faster.

“We need more research along these lines to help us design strategies that quickly and effectively increase soil health and productivity in these grasslands,” said Slaughter. 

“This helps farmers save money on nutrients and amendments while building soil organic matter and nutrient cycling capacity. This also saves them water and protects against soil degradation.”

The study is published in the Soil Science Society of America Journal.

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By Chrissy Sexton, Earth.com Staff Writer