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21.11: Making Adjustments to Fertilizer Application Rates

  • Page ID
    25251
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    If information about cropping history, cover crops and manure use is not provided to the soil testing laboratory, the report containing the fertilizer recommendation cannot take those factors into account. The “Worksheet for Adjusting Fertilizer Recommendations” is an example of how you can modify the report’s recommendations. New computer models have been developed that integrate this type of information—soil test results, manure applications, previous rotation and cover crops, and enhanced efficiency products—with other soil, management and weather data to better estimate the combined dynamic impacts of various N sources and to fine-tune fertilizer applications.

    Worksheet for Adjusting Fertilizer Recommendations

    Note: This sample worksheet is based on the following scenario:
    Past crop = corn; Cover crop = crimson clover, but small to medium amount of growth; Manure = 10 tons of dairy manure that tested at 10 pounds of N, 3 pounds of P2O5 and 9 pounds of K2O per ton. (A decision to apply manure was made after the soil sample was sent, so the recommendation could not take those nutrients into account.)
    Soil test recommendation (lbs/acre) N
    120
    P2O5
    40
    K2O
    140
    Accounts for contributions from the soil.
    Accounts for nutrients contributed from manure and previous crop only if information is included on form sent with soil sample.
    Credits
    (Use only if not taken into account in
    recommendation received from lab.)
    Previous crop (already taken into account)
    Manure (10 tons @ 6 lbs N, 2.4 lbs P2O5, 9 lbs K2O per ton, assuming that 60% of the nitrogen, 80% of the phosphorus and 100% of the potassium in the manure will be available this year)
    Cover crop (medium-growth crimson clover)

    0


    -60


    -50
    -24 -90
    Total nutrients needed from fertilizer 10 16 50

    This page titled 21.11: Making Adjustments to Fertilizer Application Rates is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Fred Magdoff & Harold van Es (Sustainable Agriculture Research and Education (SARE) program) via source content that was edited to the style and standards of the LibreTexts platform.