Need-to-know: Nutrient Management

Whats your P risk?

PHOSPHORUS LEVELS 101

Farmers have been adding inorganic nutrients (fertilizer N, P, & K) to the soil for better production for over a century. In recent years the amount applied per acre has increased considerably in order to meet the needs of the soil and to keep up with increasing yields. Over time, we have started to see evidence of these nutrients in our lakes and streams from runoff, leading to fine tuning this whole process of applying nutrients to cropland. Part of this fine tuning has lead to farmers having a planned Comprehensive Nutrient Management Plan (CNMP) that includes the 4Rs: right rate, right source, right placement, and right timing.

Since P2o5 levels are a key component of a CNMP, here are some simple soil test levels to keep in mind on each field:

• Below 50 PPM - Low risk - If you have these levels in any of your crop fields you are probably not contributing to a nutrient problem. Continue to apply P2O5 according to Tri-State-Fertility Guidelines or your local agronomist.

• Between 50 PPM and 150 - Medium Risk - You should consider soil loss BMPs such as Minimum till or no-till if not already implemented to reduce runoff potential. Monitor soil tests annually and consider a grid sampling program with Variable Rate Technology. Apply P2O5 according to Tri-State.

• 150 PPM and above - High Risk - When high rainfall events occur, you are probably losing nutrients though tile or surface runoff. Apply no more P2O5 and develope a draw down strategy to bring these levels down. Continue to monitor and soil test - consider buffers or other BMPS to protect any adjacent water courses.