Deep Nitrogen and Cover Crop Nutrient Recycling: Part II

We saw that radish can capture deep soil nitrate in fall and store the nitrogen in its biomass. After the radish dies, when does the nitrogen become available for subsequent cash crops?

One of the concerns with some traditional cover crops is that they capture nutrients, but they don’t release them in a timely manner; sometimes they even force the application of additional fertilizer because they immobilize nutrients.

Nitrogen from forage radish is mineralized early in spring, making it available for cash crops, and reducing the need for fertilizer. In Maryland, the increased nitrogen availability from radish coincides with the earliest vegetable plantings in late March through April and into May in finer textured soils (in sandy soils, much of the mineralized nitrogen can leach deep into the profile by May). Data will be posted here as soon as we get it published.

I talk/write a lot about radish, but I’m always careful to note that however amazing it is, radish is not a cure-all, one-size-fits-all cover crop silver bullet!

The early mineralization of nitrogen following a radish cover crop means that a pure radish cover crop may not be the best choice as a cover crop before later season crops like tomatoes or squash. And spring weed suppression by radish doesn’t last forever, so once that weed-free planting zone in early spring is gone, tillage or herbicides are necessary. For later-planted crops, a cover crop mixture (including radish?) might be best to delay nitrogen mineralization. One mixture some colleagues have worked with is crimson clover, radish, and rye. I will try to get a guest post about that in the future.

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