Soil test P levels greater than 150 PPM or P Risk Index of High to Very High.

Soil test phophorus (STP) is a good indicator for the potential of phosphorus movement off site, though other mangement and soil conditions can result in higher or lower actual measured losses. As STP values increase, the elevated soil solution levels are exposed to loss through tile or surface water with water movement. Fields at 150 PPM (300 lbs/A) Bray P1 or higher tend to have annual edge of-field losses of 2 to 5 lbs of DRP per acre. As STP values increase, the elevated soil solution levels are exposed to loss through tile or surface water with water movement. Tile water concentrations will be 0.08 to 1.5 PPM of DRP. These fields likely have a past history of manure application or were planted to high-value crops such as vegetables that resulted in higher fertilizer recommendations.

No additional phosphorus should be applied and a drawdown strategy should be used to reduce STP levels on these fields.

Farmers and other professionals should closely watch soil test reports for elevated STP levels. STP is highly buffered by soil phosphorus reserves, and STP levels do not change quickly. If elevated phosphorus levels exist, the field should be evaluated for potential phosphorus contributions through tools such as the Ohio P Risk Index to see if further use of BMPs would benefit water quality.

Fertilizer rate determination and application practices

  • Apply no additional applications of P until soil test reach 50 PPM or less. Recognize that the reduction in STP happen slowly. At current crop yields, nutrient removed will only be expected to move 2-4 PPM annually. Any additional reductions above this crop removal are losses to water.  Developing Phosphorus and Potassium Recommendations for Field CropsTri State Fertilizer Recommendations
  • Soil test once per rotation or at least every four years. A single sample should not represent more than 25 acres. Where past practices or inherent soil characteristics can lead to variable nutrient levels across a field, using precision soil sampling. Soil Sampling to Develop Nutrient Recommendations Developing a Strategy for Precision Soil Sampling
  • Identify lower testing field for application of organic nutrients.
  • Use variable rate application where spatial variation results in a range of suggested nutrient application rates to avoid applications if only areas of the field are at these elevated soil test levels.
  • Monitor beginning and ending soil test levels, production and fertilizer added for adaptive fertilizer management.

Before planning manure or other organic nutrient sources are applied

NRCS 590 NRCS 590 Criteria on rate should be applied and are outlined below:

STP Bray P1

Application Criteria

>150 PPM

No added P2O5. Use draw down strategies.

 

Best Management Pratices