How High Soil-Test P Increases Phosphorus Loss from Crop Residues
A study led by William R. Osterholz examined how soil phosphorus availability affects the amount of phosphorus remaining in corn and soybean residues after crop maturity and how readily that phosphorus can be released into water.
Why It Matters
Phosphorus is essential for crop production, but it can contribute to water-quality problems when it moves from agricultural fields into surface waters.
Although most of the phosphorus taken up by grain crops is removed during harvest, some remains in stalks, leaves, and other crop residues. As these residues decompose, the phosphorus can be recycled back into the soil. However, rainfall, irrigation, or standing water may also release phosphorus from the residues before it is incorporated into the soil.
This process is particularly important in fields with elevated soil-test phosphorus. Crops grown in these fields may leave behind residues containing more phosphorus, increasing the potential for dissolved phosphorus losses and phosphorus accumulation near the soil surface.
Key Takeaway
The amount of phosphorus supplied to the crop by the soil strongly influenced how much phosphorus remained in the residue after maturity. Crops grown in soils with higher soil-test phosphorus produced residues containing more phosphorus and, consequently, a greater amount that could potentially be released into water.
Crop residues provide important benefits, including erosion protection, moisture conservation, organic matter inputs, and nutrient recycling. The findings do not suggest that residues should be routinely removed. Instead, they reinforce the importance of preventing excessive phosphorus accumulation in the soil.
Soil-test phosphorus affects more than fertilizer recommendations. It can also influence how much phosphorus is stored in crop residues and potentially released during rainfall or drainage events.
In fields with high soil-test phosphorus, growers should avoid unnecessary phosphorus applications and consider how residue management, runoff, drainage, and phosphorus stratification may interact.
Reference: Osterholz, W. R., Ventouris, M., & LaBarge, G. A. (2026). Phosphorus content and leaching potential from crop residues increased with soil test P. Journal of Soil and Water Conservation, 81(2), 185–198. https://doi.org/10.1080/00224561.2026.2629204
