“What are the right decisions for phosphorus management in crop production that reduce water quality impacts?” is a common question I have from farmers looking to improve yield yet are concerned about downstream water quality impacts of phosphorus.
A representative agronomic soil test has long been an essential tool for sound agronomic nutrient management decisions. That same agronomic test result can be a useful indicator for identifying fields where additional conservation practices might improve water quality. Fields with Soil Test Phosphorus (STP) levels two to three times higher than the agronomic need result in increased phosphorus losses measured on the edge of field water quality monitoring.
As soil test results are reviewed this fall, consider keeping a list of fields in three categories based on STP levels that define the risk of yield loss for the corn/soybean rotation and risk of increased water quality impacts.
- Less than 20 PPM Mehlich 3 STP (or 30 PPM if wheat/alfalfa in the rotation)
- Between 20-40 PPM (or 30-50 PPM if wheat/alfalfa are in the rotation)
- Greater than 50 PPM