Cover crop nutrient release — are you waiting on an inheritance?


The science supporting what we know and don’t know about soil health, nutrient cycling, and soil microbes builds every year. Not long ago, much of the soil management narrative focused on keeping soil covered (don’t farm naked!) to minimize erosion risk and build soil. Now we know that while preventing or at least decreasing erosion is important, it’s the living roots in the soil that have the greatest impact on biological processes, including nutrient retention and release.

Dr. Lee Briese, with North Dakota State University, presented on the topic of soil nutrient cycling and the gifts that cover crops impart to soil a Waterloo Soil and Crop Annual meeting earlier this month. The value is there, but what caught Johnson’s attention was Briese’s challenge of thinking about cover crop nutrient release as more of an inheritance (that you don’t really know when to expect) rather than a monthly or weekly allowance.

Peter “Wheat Pete” Johnson says there’s plenty more work to do on anticipating not just how much nitrogen or other nutrients will be released by the cover crop residue breakdown, but the when, as well.

For some crop rotations, we have a solid understanding of the anticipated N credit — such as when wheat is grown after peas, for example. But when it comes to a fall-terminated cover crop, when the N, P, or K becomes released back into the soil is still unclear, and certainly isn’t an “allowance” we can count on. Even in long-term cover crop research it takes five to seven years for that allowance to trickle in.

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