Here’s how Eileen Kladivco put it: Even with well-managed corn and soybean production, there is always some leaching of nitrate that originates either from residual fertilizer N or from the natural decomposition of soil organic matter. Our annual cropping systems are “leaky” because there are long fallow periods between crop maturity in September and the active growth of the next cash crop in May. Most of the net downward flow of water to the drains occurs precisely during this long fallow period, when there is nothing to take up the nitrate. 

Eileen is an agronomy department professor at Purdue University, a well-regarded researcher and teacher about soil and making agriculture more profitable. She goes on to say that, Non-legume cover crops will scavenge or “trap” soil nitrate that would otherwise move out of the rootzone into tile drains or groundwater. Cover crops actively take up nitrate during a portion of that fallow season, reducing the losses that occur to tile drains and recycling the nitrogen for later use. To read her Full article – click here.

In another publication, the author talked about the biomass of cover crops. Basically, he said that more biomass generally means more nutrients and organic matter returned to the soil.

The “plant available nitrogen” (PAN) released from a cover crop depends on what cover crop you’re growing and when you terminate the cover crop. As the cover crop plant matures, more nitrogen gets stored in the stems, so in general it’s best to terminate the cover crop before it reaches that stage. With annual ryegrass, terminating it before it reaches 6 or so inches in the spring is important…both to take advantage of the nitrogen available but also to keep the plant from reaching the joint stage.

As soil organisms decompose cover crop residues, part of cover crop is released as carbon dioxide. The rest decomposes and contributes to the soil organic matter…as well as giving up the stored nitrogen for the corn or beans maturing in the same soil.

The high price of nitrogen has growers looking for way to be more efficient. Using annual ryegrass may provide 60-80 lbs of nitrogen per acre. This alone could more than pay for the cost of the seed and planting the cover crop. For more information on annual ryegrass and its capacity as a nitrogen sink, click here.