Taking an environmentally sensitive approach to pest management


Integrated Pest & Crop Management



AUTHOR

John A. Lory
University of Missouri
Division of Plant Sciences
(573) 884-7815
loryj@missouri.edu

Peter C. Scharf
University of Missouri
Division of Plant Sciences
(573) 882-0777
scharfp@missouri.edu

Managing High Phosphorus Prices

John A. Lory
University of Missouri
(573) 884-7815
loryj@missouri.edu

Peter C. Scharf
University of Missouri
(573) 882-0777
scharfp@missouri.edu

Published: October 15, 2008

The remarkable, unprecedented rise in fertilizer phosphorus prices has farmers searching for ways to reduce phosphorus applications. How you proceed will depends on how you anticipate phosphorus prices will change over the next few years.

High prices currently are driven by higher worldwide demand for phosphorus than supply. Industry projections imply demand will continue to exceed supply for at least the next couple of years. This implies phosphorus prices will remain high. However the recent turmoil in the world economy may reduce global demand making the current estimate for demand over-stated.

Many farmers have used soil testing in a phosphorus soil fertility program to bring their soil test levels to an optimum level (approximately 22 ppm Bray-I P). Phosphorus application on these farms maintains optimum soil test levels by replacing phosphorus removed by the crop either annually or every other year. Taking one or even two years off from maintenance phosphorus applications on high yielding fields is unlikely to reduce yields. If you do not apply phosphorus fertilizer for too many years soil test levels will drop to a point that will reduce yield.

Postponing phosphorus applications on optimum testing fields may make sense if you expect phosphorus prices to fall significantly in the next year or two. By not applying now you avoid current high prices but will need to invest in extra phosphorus in the future to compensate for the missed applications. Using this approach you would save money if phosphorus prices fall because you would spend less for fertilizer bought at the lower price in the future.

If you predict phosphorus prices will stay the same or increase over the next few years there is no benefit to delaying phosphorus applications on fields with optimum soil test phosphorus levels. In this scenario, waiting to apply provides no opportunity of savings and may cost extra money if prices rise. Delaying applications under these conditions only makes sense if it helps you address short-term financial management goals for your farm.

Farmers who have low phosphorus testing soils that are trying to maximize yield will need to apply phosphorus fertilizer despite high prices. Low testing fields need annual applications to provide enough phosphorus in the soil to maintain high yields. Most fertilizer recommendations on low testing fields include phosphorus to raise soil test towards optimum (buildup phosphorus) plus fertilizer to replace phosphorus removed by the crop (maintenance phosphorus). Farmers with low testing fields may chose to reduce or eliminate buildup phosphorus to save money. For example, high fertilizer prices may favor an eight-year buildup strategy instead of a four-year buildup strategy. This will slow the pace of raising soil test phosphorus to optimum but is unlikely to negatively affect yields. On low testing soils maintenance phosphorus applications are needed if the objective is to maximize yield.

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REVISED: April 6, 2012