Proposed by: James Hoorman

Presenter: Hoorman, J., Cover Crops, Ohio State University Extension, Ottawa, OH 45875

A phosphorus (P) speciation study (N=50 soil samples) was conducted on a Hoytville clay soil (Wood County, Ohio) to address P runoff. Phosphorus speciation fractionizes the P into plant available soluble reactive phosphorus (SRP), exchangeable organic P (ExP), and non-plant available inorganic P (calcium P (CaP), iron oxide P (FeP), and aluminum oxide P (AlP)). SRP is causing major harmful algae blooms in Lake Erie. SRP levels varied by management and was significantly lower (P<.05) on conventional tillage (0.69a) versus no-till fields (0.93b) and by manure type (dairy =0.56a and poultry =1.37b). Significant differences (P<.05) were also found in the inorganic forms (CaP, FeP, AlP) related to management. Lake Erie soils are high in iron content (20-30%). FeP is unstable under saturated soil conditions, releasing SRP when Fe3+ (ferric state) is reduced to Fe2+ (ferrous state). Keeping soils well drained reduces the amount of SRP in surface water by keeping the FeP tied up in the ferric state. SRP was significantly less (P<.05) with a red clover cover crop (0.34a) than fields with no cover (1.42b). Cover crops had significantly (P<.05) more organic ExP (1.23b) than no covers (0.14a) or 8.8X higher ExP. ExP (organic) and SRP (inorganic) are plant available forms of P but the ExP is a larger stable molecular form of P. Ongoing research is quantifying how this affects P runoff. Cover crops had significantly higher levels of P in an organic form which is both plant available P and more stable than fields without any covers.

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