UT Fertilizer Recommendations Profit Most

Several soil testing laboratories serve clients in Tennessee. Generally, soil-testing results are very similar among laboratories. Most laboratories participate in quality control programs that ensure accuracy of results. Fertilizer recommendations made from those results can, however, vary widely among laboratories. University laboratories historically have followed a "feed the crop" approach to making fertilizer recommendations, whereas many commercial laboratories tend to try and rapidly build soil test levels (maintenance approach) and add on many micronutrient recommendations. In many comparisons of fertilizer recommendations among laboratories (Lessman, 1986; Murdock, 1992; Williams, 1999), university recommendations have always proven to be the most profitable.

Farm trials were established at four sites (Lawrence, Lincoln, Smith, and Washington counties) during 2002 to demonstrate the economic advantage of University of Tennessee Soil Testing Laboratory recommendations over those given by commercial laboratories. The three treatments tested were (1) University of Tennessee fertilizer recommendations (2) fertilizer recommendations from a commercial lab operating within Tennessee, Lab A, and (3) fertilizer recommendations from a commercial lab operating in an adjacent state, Lab B. Each treatment was replicated three times at each location. Data were not obtained or presented from Washington County due to crop failure.

Fertilizer costs (not including lime) from commercial laboratories, in corn production systems, were as much as 1.75 greater than what was needed to maximize yield. In the tobacco production system, commercial laboratory fertilizer costs were as much as 2.25 times that needed to maximize production. Cost differences are due to both type and amount of nutrient recommended by the laboratories.

There were no differences in crop yields (averages of 3 replications) that could be attributed to the fertilizer recommendations with any degree of certainty. University of Tennessee recommendations provided yields that were as good as yields resulting from the more costly commercial laboratory recommendations. There was evidently no crop yield response to extra primary nutrients added or to minor elements in these three production fields. The University of Tennessee Soil Testing Laboratory provided producers in these county demonstrations with the most return on their fertilizer dollars spent in 2002.

Information on the soil testing program at the University of Tennessee and soil test information sheets are available at your local county Extension office, or online at http://bioengr.ag.utk.edu/soiltestlab .

Hugh Savoy, Associate Professor
Click here for a higher-resolution printable version

©Biosystems Engineering & Soil Science · bess@utk.edu · bioengr.ag.utk.edu · 865-974-7266