Recommendations Services

The basic philosophy of soil test fertilizer recommendations is:

• Base them on soil test results;
• Recommend that lower-testing soils be built up to higher test levels by adding extra fertilizer;
• Apply maintenance amounts of plant nutrients to higher-testing soils to keep them there and to keep productivity high; and
• Do not apply specific nutrients to soils testing very high in these nutrients.

Individualized fertilizer recommendations use site- and grower-specific information, rather than laboratory-generated recommendations based on assumptions and generalizations. Computer programs are available that help personalize recommendations by considering the following:

SOIL TEST CALIBRATION RELEVANCY

How appropriate is the calibration used in the standard recommendation for the field in question? Unusual soil types, a different climate, no-till or ridge-till culture, crop variety, cropping history and field variability are examples of factors that could cause differences.

YIELD POTENTIAL

Yield potential determines the economic value of each percentage change in relative yield and may influence the shape of the calibration curve.

FERTILIZER PLACEMENT

Band placement often reduces lost yield as sub-optimal soil test levels are built to optimum levels because the short-term recovery of applied fertilizer by crop plants is improved. Some recommendation systems reduce the rate recommended when banding is used, compared to broadcast. However, rate studies have shown the optimum rate when banding is sometimes equal to or greater than the optimum broadcast rate. It is wise to build soil test levels to optimum regardless of placement method used.

FARMER FINANCIAL CIRCUMSTANCES

The financial objective of farmers, like other investors with limited capital, is to maximize the return on the last dollar invested after considering all possible investment alternatives and their associated risks. Therefore, cash flow influences fertility management decisions.

UNIFORM AND BALANCED NUTRIENT DISTRIBUTION

Balance recommendations to ensure each nutrient is used efficiently.

LAND TENURE (PERIOD OF TIME THE GROWER WILL FARM THE FIELD)

Soil test phosphate and potassium are capital investments, and buildup costs should be amortized over the expected time of ownership or operation. The longer the period of time benefits will be accrued from buildup, the lower the cost of buildup becomes and the higher the optimum soil test level becomes. Landowners and operators, as well as the environment, benefit from the development of agreements in which the costs and returns of soil test buildup are equitably shared. Such agreements can help avoid the loss of productivity and accelerated erosion typical of run-down farms having impoverished soil fertility.

SOIL TEST BUFFER POTENTIAL

Soil test buffer potential is the quantity of fertilizer required to change the soil test level, and is usually expressed as pounds of P2O5 or K2O required per ppm of soil test level change. Some low-pH and some high-pH soils fix applied phosphate readily, and increasing soil test phosphate is more costly, decreasing the optimum soil test level. Soil test phosphate and potassium levels are usually easier to change in sandier soils than on medium or fine-textured soils, except with very sandy soils, where potassium leaching becomes significant.