Soil-Test P

Description
This practice involves not applying P on fields where the Soil-Test P (STP) values exceed the upper boundary of the optimum level for corn and soybean in Iowa. The practice continues until the STP level reaches the optimum level.

Benefits
Since a large portion of P loss is associated with erosion (sediment bound P or dissolved P in surface runoff), the amount of P applied to the soil and its effect on STP and total soil P has a significant impact on the total P loss from a field. Decreasing the total soil P concentration by limiting or stopping P application to high-testing soils until STP is lowered reduces P loss.