Cutting Phosphorus Fertilizer Applications Without a Soil Test?

The current farm economy has driven a wide range of crop budget conversations. How to produce more with less is the key to the economics for 2025. But the key to that statement is twofold, we need to focus on maintaining and increasing yield while cutting costs. All crop inputs are in the cross hairs, but $800 per ton phosphorus products seem to have a bullseye painted on them.

Phosphorus is key in maintaining yield, so cuts to phosphorus inputs need to be made wisely. The idea of reducing phosphorus rates without a soil test is a recipe for problems, however there are producers looking to do just that. We have all heard of examples of producers getting good yields on soils testing low in phosphorus, so why fertilize? Why soil test?  The answer to this question is in data.

Often in publications, soil fertility data like this is summarized with the red line that leads the reader to think that as soil test phosphorus increases, yield increases. This can be misleading. When reviewing more detailed data, there are soils testing low in phosphorus (left side of the scatter plot) that are yielding near 100% of relative yield, and some at 60%. As soil test phosphorus levels increase (moving to the right), the top end yields do not change much (green line), but the low-end yields (yellow line) increase significantly.

Applications of phosphorus on low testing soils may not always increase yield but can mitigate the risk of low yields. This data also suggests that there is no value in building/maintaining a soil test above 40-50 ppm M3- ICP and soils testing less than 20-30 ppm M3- ICP are still potential candidates for phosphate applications.

A soil test can identify those fields that can forgo an application of phosphorus, and those fields that should have phosphorus applied to maintain yield potential, especially if the spring of 2025 soil conditions challenge early season root development. If you have any questions about phosphorus management, be sure to contact your ALGL agronomist.