The economics of soil testing

Soil testing is the only tool we have to evaluate the pH, phosphorus (P), and potassium (K) status of the soil. Knowing this information allows growers to make economically optimum applications of lime and phosphorus and potash fertilizer. In these times of economic uncertainty, managing input costs is an important component of farm sustainability. Many growers have opted to cut costs by eliminating soil testing as part of their management program. This is not a recommended strategy. There are two main misconceptions about soil testing:

MISCONCEPTION #1: Soil testing is expensive.
FACT: Routine soil testing costs less than 40 cents per acre. University of Wisconsin soil testing recommendations are to analyze one composite sample per 5 acres and to soil test at least once every four years. Using a standard rate of $7.00 per analysis, this averages out to $0.35 per acre per year. Most, if not all, certified laboratories will also provide fertilizer recommendations based on University of Wisconsin recommendations along with the soil test values.  Some laboratories may have slightly higher prices or may charge shipping costs.

MISCONCEPTION #2: Maintenance applications of P and K are good enough.
FACT: Soils testing in the very low to low range for P and K require additional inputs beyond removal rates to optimize yield.
FACT: Soils testing in the high to excessive range require less than removal rates to optimize yield.
In either case, money is lost from either reduced yields or over application of P and K. When soils tests indicate the soil is in the very low to low category, this suggests that there is a very high likelihood that yields will increase due to application of fertilizer. However, it also indicates that the crop would benefit from building the “fertility” of the soil through additional P and K inputs over time.

For more information on soil testing, please visit our website www.soils.wisc.edu/extension/soilsampling.php.

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