Possible Solutions to Soluble Phosphorus Pollution in the Lake Erie Watershed and in Ohio.

To reduce soluble reactive P (SRP) and harmful algae blooms (HAB) in Lake Erie, Ohio has initiated mandatory fertilizer applicator training based on the 4 R’s (right source, rate, time, and place). Based on possible causes, additional management practices will be needed.  Phosphorus (P) tie up soil hierarchy is dominated by soil organic matter (SOM) > AL³⁺ > Fe³⁺ > Fe²⁺ > Ca.  With SOM levels decreasing 40 to 60%, AL³⁺ and Fe³⁺ are absorbing more SRP and under saturated anaerobic conditions, Fe³⁺ converts to Fe²⁺, releasing SRP.  Management practices that increase SOM, water infiltration, and improve soil structure by flowing slowly through the soil-water matrix should decrease SRP losses by surface runoff and decreased preferential flow to subsurface drains.  Cover crops and no-till increased macro-pores and aeration, resulting in less Fe³⁺ converting to Fe²⁺ and SRP release.  Preliminary results showed that cover crops increased absorption of soluble (SRP) and exchangeable P (ExP)on an Epiaqualf soil.  The ExP was 8.8x higher (1.23 ppm vs 0.14 ppm) where cover crops were utilized than the control, and the control had 4.2x higher SRP (1.42 ppm vs 0.34 ppm). Comparing six systems (forest, alfalfa, CSW, CC, CS, SS); forested and alfalfa treatments had significantly less FeP than the other cropping systems and significantly more ExP). Comparing an Epiaqualf by Bray P₁ soil test (forest, grass, <25, 25-49, 50-99, 100-150, 150+ ppm Bray P₁) and management, the FeP percent mean values were highest on the cropland sites (22.9-42%) and lowest on the grass and forested sites (6.8-9.9%).  As cropland loses organic matter and P soil tests increase, more of the P is tied up by the inorganic portion, especially FeP which can lose SRP under freezing-thawing and wetting-drying of soil.