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

Summer 1999, No. 7


The cornerstone of profitable crop production is a sound soil fertility program. Such programs require forethought and planning. One of the most useful tools in soil fertility planning is soil testing. Factors to consider in planning an efficient fertility program are fertilizer application rates, placement, and timing.

Planning winter wheat fertilization without soil test data is largely guesswork. Soil test information is only as good as the sample collected. If samples are not representative of the area in question, the value of the resulting test data and recommendations is compromised. Intensive (grid) sampling has in some cases been adopted to address within-field variability. Where more conventional composite sampling is used, care should be taken to assure that enough samples are collected to provide a sample that is representative of the entire area or field. Also, a reasonable yield goal should be established.

Nitrogen performs many vital functions in the wheat plant. Wheat requires 2 to 2.5 pounds of nitrogen per bushel of grain, or, if grazed, 1 pound per acre for each 3 pounds per acre animal gain. Shortages of nitrogen may cause reduced tillering, reduction in head size, poor grain fill, and low protein content. Adequate nitrogen must be available to the wheat plant at all phases of development. Splitting nitrogen applications generally improves use efficiency, minimizes risk to investment, and safeguards the environment. Topdress applications should be made early, prior to jointing, to maximize production efficiency. Timing, placement, and nitrogen source should be managed to fit climatic conditions, soil type, and tillage system.

Adequate phosphorus fertility is associated with increased tillering and grain head numbers, reduced winter kill, maximum water use efficiency, hastened maturity, and lower grain moisture at harvest. Winter wheat requires about 0.6 to 0.7 pounds phosphate per bushel of grain. Because phosphorous is relatively immobile in soils, banded or starter applications are often most effective in soils testing low to medium. Even in high testing soils, starter applications help plants get established more quickly. Banded phosphorous also helps young plants overcome the adverse effects of soil acidity. Broadcast phosphorous should be incorporated to improve positional availability. Soil test phosphorous should be increased to high levels and maintained for optimum long-term fertility.

Potassium in wheat production is associated with increased moisture and nitrogen use efficiency and decreased incidence of disease and lodging. The requirement for potash is approximately equal to that of nitrogen. Placement is not as critical as phosphorus since potassium is more mobile in soils. Split applications should be made on deep sandy soils in high rainfall areas to increase use efficiency.

Don’t overlook the importance of secondary and micronutrients. Applications should be based on soil tests and plant analysis.

Profitable and efficient wheat production involves supplying adequate amounts of plant nutrients when and where the crop needs them. Fertilizer application rates are of little meaning if nutrients are not in the proper place at the proper time. Effective fertility management strategies vary from region to region, but a characteristic of all good soil fertility management programs is early planning.


For more information, contact Dr. W.M. (Mike) Stewart, Great Plains Director, PPI, P.O. Box 6827, Lubbock, TX 79493. Phone: (806) 795-3252. E-mail:
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