Soil test P levels less than 50 PPM (or P Risk Index of Low to Medium)

Soil test phosphorus (STP) can be used for both crop management and as an environmental loss indicator. In crop management, fields with an STP level of less than 15 PPM (30 lbs/A) Bray P1 are at the greatest risk of yield loss from a deficiency of phosphorus in a corn/soybean rotation. If the crop rotation includes wheat or alfalfa, the STP level with greatest risk of yield loss is STP less than 25 PPM (50 lbs/A) Bray P1. This STP level is defined as the “critical level,” with phosphorus application needed to maintain productivity. Information found in the Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa (Vitosh et al., 1995) should be used as a guide for developing phosphorus recommendations.

From an environmental perspective, STP is a useful initial indicator for the potential of phosphorus movement off-site, though other management practices or soil conditions can influence actual measured losses. As STP values increase, the elevated soil solution levels are exposed to loss through tile or surface water during rainfall events. Site evaluation tools such as the Ohio P Risk Index provide a more comprehensive evaluation of soil or nutrient loss and can be used to assess risk. Increased risk can define fields where additional conservation practices are needed.

Fields with STP below 50 PPM (100 lbs/A) Bray P1 will generally produce low levels of phosphorus runoff in water quality sampling. Acute losses of phosphorus levels leaving the site can occur at the time of fertilizer application, especially with surface applications. The suggested agronomic soil test level for no additional fertilizer application for crop production is greater than 50 PPM when all possible rotational agronomic crops are considered. A build/maintenance approach to fertilizer recommendations is used to maintain agronomic productivity in STP values less than 50 PPM.

Fertilizer rate determination and application practices

Use of manure

Best Management Practices