Can I use MAP or DAP Diammonium phosphate or other amendments to improve my phosphorous levels on an organic cattle ranch?
Answer: The number-one driver of getting the soil microbes to cycle nutrients is soil organic matter. Organic matter can be increased, but it will take some time. The fastest way to do so is to no-till in multi-species cover crops (six to 10 species) and to graze them off, taking about one third and trampling in two thirds. I have read of farmers increasing their soil organic matter by 0.8% (i.e., from 3.0 to 3.8%) in one season by doing so. That is a lot.In addressing low phosphorus levels, I would start with the reported unit from your lab tests and convert it to ppm of P. Different soil testing labs report P in differing units. If your report says 16 pounds of elemental P per acre, then you would multiply the 16 by 0.5 and you have 8 ppm of P. If the reported P is in pounds of P2O5 per acre, to convert it to ppm you multiply first by 0.5 and then again by 0.4364. This would give you 16 X 0.5 X 0.4364 = 3.5 ppm. In general, you would like to see P levels up in the range of 15 to 20 ppm in your pastures.If your organic matter is more than 3.0 percent, I would consider running a Haney test on your soils. The Haney test takes into account the ability of the soil microbes to mineralize N and P from minerals that are not in the plant available form. I would try the Haney test on a pasture that you have already sampled with the conventional test. It is possible that you have more P than you think if your microbe population is in good enough shape. Learn more about the Haney test. The best way to improve P levels with an amendment is through the addition of composted animal manure. Manure from cattle, sheep or poultry will supply P and also afford the added benefit of microorganism culture with compost.Secondly, you can improve your soil’s ability to cycle P, N, and other nutrients by grazing tall grass and trampling in the residual. This requires stocking densities of 100,000 pounds or more of live animal weight per acre. You can find a good discussion of this in the ATTRA Managed Grazing tutorial. Specifically, check out slides 40 through 45 in the Grazing the Mature Stand lesson.I also recommend that you view the videos Intensive Grazing: One Farm’s Set Up, as well as Gabe Brown: Farming in Nature’s Image. You might also be interested in Soil Health and Livestock: ATTRA Resources, which provides a list ATTRA publications, videos, and webinars on soil health.I believe that these two methods are going to improve P levels and your general sol health, which will, in turn, increase pasture production and animal production over time. If you do decide to put on DAP, you will be ineligible for organic certification for three years. Also, if you do apply DAP, do so sparingly. For instance, you might apply enough to bring up the ppm of P in 5 ppm increments. This will be a little easier on your pocketbook and your soil biology.