By Andi Anderson
Recent studies show that high soil test phosphorus (STP) levels contribute significantly to phosphorus loss, without improving crop yields. This makes overfertilization a costly and environmentally harmful practice.
Research by Byers et al. (2025) in the Western Lake Erie Basin found that fields with STP above 75 mg/kg contributed 34% of dissolved phosphorus loads, despite covering only 10% of the area. These fields lose more phosphorus per acre, making them a disproportionate source of water pollution.
Meanwhile, Kaiser et al. (2025) confirmed there’s no agronomic or economic benefit from maintaining high to very high STP levels for corn and soybean production. Fertilizing when STP is already high won’t improve yields and hurts your bottom line. In contrast, the best return on investment comes from fertilizing fields with low to medium STP.
Reducing high STP levels is possible but slow. According to Gatiboni et al. (2025), it may take up to 16 years to cut phosphorus levels in half through crop removal alone. This long-term process, called STP drawdown, is key to addressing legacy phosphorus—nutrients built up in soil over time that still fuel algal blooms like those in Lake Erie.
The Tri-State Fertilizer Recommendations remain the best strategy. They encourage phosphorus application only where necessary to maintain yield while protecting water. For high-STP fields, focus on drawdown and skip the fertilizer. For fields with lower STP, apply based on crop need.
Bottom line:
Apply phosphorus only when needed. Avoid fertilizing high-STP soils. Follow the Tri-State guidelines to save money, protect yields, and reduce water pollution.
Photo Credit: freepik
Categories: Michigan, Sustainable Agriculture