Nitrogen Cycling in Pastures

I was recently asked about the copious amounts of white clover in a pasture as the farmers were concerned about bloat risk with their sheep. She and her family had done some research and came up with differing opinions regarding management. I was asked to give the definitive answer. We talked through some scenarios and came to a manageable conclusion for their operation. I did some research of my own and provided some suggestions. What intrigued me was around nutrient cycling, particularly nitrogen, and how we take it for granted and make assumptions. Pasture systems are complex cycles of nutrients. This article will focus on nitrogen (N), the most-limiting nutrient for pasture production. (Other macro- and micronutrients are needed for N uptake, but due to space it all can’t be addressed in this article.) Adequate N supports forage growth or dry matter (DM) production. Nitrogen also affects protein content of the grass. Adequate nitrogen helps provides nice, green, color to pastures and will provide quality forage for milk, meat, and fiber production. Plants take up N via their root systems in the form of nitrates and ammonia. This can come from nitrogen fertilizers and mineralization (decomposition) of manure and organic matter. Soil bacteria do the work using carbon as energy and nitrogen to facilitate g

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4 thoughts on “Nitrogen Cycling in Pastures

  1. Re: “Generally, alfalfa is the highest ‘fixer’, followed by white clover, red clover, and trefoil.”

    Not that I’d plant it for sheep to graze. . . but isn’t sweet clover somewhere near the top of the list?

  2. This is an excellent treatment of a complex subject. The new Soil Health tests, developed by Drs. Roy Haney and Will Brinton for on-farm measurement of biological inputs capture several aspects of the N cycling described here, and then some. A whole new world has been opened up for the farmer to get a better understanding of the fascinating and important goings on in his/her soil, but these tests take work and thought to fully comprehend and apply. Nancy’s contribution here and the link she provides to Bellows review will be very helpful in this regard.

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