Manure and cover crops

For centuries, livestock manure has been a cost-effective fertilizer source for crops and increasing soil quality. Cover crops do the same thing and prevent nutrients from leaching. Pairing the two combines their benefits.

Dan Anderson is an assistant professor in the Ag and Biosystems Engineering department at Iowa State University. He says there are variables that can affect how well this works.

"Depending on what tillage implement, how are we injecting that manure into the soil, how does it disturb the cover crop, how does the cover crop recover? And then, things like what does that do for nutrient cycling? We know that normally we talk about cover crops scavenging for nitrogen, for residual nitrogen in the soil. But, if we’re putting manure on in the fall and still growing that cover crop, it’s a little bit different, it’s almost like a fertilized crop," says Anderson. "So, there’s just a few differences in how we want to understand that, think about, and use it in the system."

Should you plant the cover crop before or after you put manure on? He says either one can work. They do see a little bit better tie up of nitrogen if the cover crop is planted first, but the process should be based on how the farmer can integrate it into his system.

In terms of water supply, nitrogen from the manure tends to stay put rather than leaching away.

"What we’ve seen is, when we’ve had cover crops integrated in that system, we’ve reduced nitrogen losses by somewhere around 20%-30% with the cover crop so it’s actually a benefit. Certainly, you can think about cover crops as improving soil tilth and giving us some of that macro-pore maybe potential for flow. But we tend to see the opposite," he says. "We get better soil structure and that increases the water-holding capacity of that soil. So, when we put the manure on it actually stays in the topsoil."