April- June 2002
Brian J. Lang , ISU Extension Field Specialist/Crops
Most farmers who conduct soil tests on a regular basis apply fertilizer according to the soil test recommendations. While this sounds practical, profitable, and environmentally sound, unfortunately it usually is not. Most soil test laboratories certified according to Iowa testing standards do not provide sound fertilizer recommendations. To meet certified standards, laboratories are only required to conduct the chemical analysis a certain way, however, they can provide whatever they desire for fertilizer recommendations. Iowa State University fertilizer recommendations are based on maximum economic returns to fertilizer applied, and are often found to be about half the amounts that many testing laboratories recommend.
Through the efforts of various watershed projects, ISU Extension teaches farmers how to read and interpret soil tests. With this understanding, farmers are not at the mercy of a testing laboratory's recommendations. The farmer can use the soil test analysis from the certified laboratory, but with Iowa State University interpretations and recommendations.
Most farmers who participate in this program reduce their fertilizer expenses by $10 to $15 per acre. One particular farmer with soil tests from a well known laboratory in northeast Iowa found their laboratory's recommendations to run $46 per acre higher than for that of ISU's recommendations. Farmers of a typical 15,000 acre watershed project usually see an average economic advantage of $200,000, with at least a 50% reduction in phosphorous fertilizer applied.
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July 11, 2006
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