From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335

Winter 1997, No. 8


Some unique and interesting nutrient management challenges have come with the freedom-to-farm. Where many fields were previously planted to cotton year after year, corn and soybeans are now being considered for planting. A clear understanding is needed about the nutrient uptake and removal by each crop, to plan for optimum flexibility and potential economic returns.

    Without question, fertilization rates and strategies should begin with a sound soil testing program, with research-based recommendations developed from scientific correlation and calibration studies. Regrettably, not all crop rotations have been thoroughly researched, especially with inclusion of new high-yielding crop varieties with improved pest management traits (glyphosate tolerance, insect resistance, etc.) World markets often dictate open-minded planning since the decision to plant a certain crop may be delayed until very near the recommended planting deadline. These situations and challenges require that we consider a fertilization plan to provide optimum nutrient supplies for the most demanding crop that may be planted.

    For example, while soybeans yielding 55 bushels per acre do not take up as much phosphorus and potassium as a 180 bushel per acre corn crop, soybeans will remove more K2O than corn. In fact, 55 bushel per acre soybeans will remove more phosphorus and potassium than a 2-bale per acre cotton crop. Although rice does not remove large amounts of phosphorus and potassium, it has a high uptake demand for these two nutrients in making a 7,000 pound per acre yield: almost equal to the uptake demand of a 55 bushel per acre soybean crop.

    Research has shown that while good responses to annual phosphorus and potassium inputs may be achieved on soils testing low in these nutrients, yields are frequently higher on soils which have had fertility built to high soil test levels. Utilization of soil moisture is optimized, disease avoidance is improved, nitrogen use efficiency is frequently increased, and protective ground and canopy cover is enhanced, which helps to maximize photosynthetic efficiency.

    Plan to provide optimum fertility levels for the 1998 crop to include phosphorus and potassium rates for top yields in each part of each field. Plan to meet the nutrient requirements of the most demanding crop in the rotation.

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For more information, contact Dr. Cliff S. Snyder, Midsouth Director, PPI, P.O. Drawer 2440, Conway, AR 72033-2440. Phone (501) 336-8110. E-mail:
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