Blog > May 2020 > Determining Your Phosphorus Needs

Determining Your Phosphorus Needs

May 14, 2020

5.14.20 | Phosphorus Recommendations from Central Valley Ag on Vimeo.

In the recent Agronomy Focus articles and videos, we have reviewed Nitrogen and Sulfur recommendations. For both N and S, we deal with nutrients that are mobile in the soil, with a primary focus on feeding the plant for the growing season. This week we switch gears and focus on phosphorus. For phosphorus, we will focus more on building and feeding the soil so that the soil can feed the plant.

There are a few reasons why we focus on long term soil fertility when looking at Phosphorus. First, Phosphorus is not mobile in the soil, so we can count on it sticking around for the long term. Second, when compared to other nutrients such as Nitrogen, Sulfur, and Potassium, the uptake curve is much flatter without as high of daily plant accumulation as Nitrogen and Potassium.

We focus a lot on the soil test level when we go to make a Phosphorus application. We generally have a target range that we want of around 20-30 ppm. If we fall below this range, we will try to build soil test P. If we are in this range, we will replace crop removal. But, if we are above this range, we will apply less than crop removal and let the harvested crop mine the soil test level of Phosphorus a little.

Crop removal becomes a critical component of the recommendation, and we focus a lot on the 0.37 lbs /bu of P in harvested corn and the 0.8 lbs/bu in harvested soybeans. Multiplying those numbers times a grower’s expected yield becomes the main component in their P recommendation.

We also want to consider the product we are going to use. If you are going to use a higher rate of a liquid product as a starter, or 2x2 application, we can take that off the top of the recommendation. We have a choice of MicroEssentials SZ or MAP for the balance. We like the Sulfur and Zinc with their nice and even application from MESZ. The benefit of MAP is the higher analysis of P in that product if the soil test levels are low and need a large application of phosphorus. Sometimes we will blend the two products to get a little of the benefits of each product.

Similar to our other nutrients, we want to build a fertility program that works in your system, not just try to sell you fertilizer. The best way to do that for Phosphorus is an excellent soil sampling program to tell us what your fertility needs are. Follow that up with a sit-down visit with your Field Sales Agronomist to understand the goals you have for each field and how these fertilizer products work into your fertility plan and farm goals.

By Tim Mundorf, CVA Nutrient Management Lead

Posted: 5/14/2020 2:38:22 PM by Kelli Reznicek | with 0 comments


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