Phosphorus source coefficient determination for quantifying phosphorus loss risk of various animal manures

• P source coefficients (PSC) were determined to quantify availability of manure P.
• Mehlich-3 P gave the most consistent PSC across soils and incubation durations.
• Mehlich-3 P gave laboratory PSC better reflecting field conditions.
• Two week incubation yielded the most consistent PSC across different soils.
• A 2-week incubation along with Mehlich-3 P can be recommended to measure manure PSC.

Quantification of phosphorus (P) loss risk of animal manures is essential to scientifically sound P risk assessment and environmental friendly nutrient management, but has faced significant challenges due to the shortage of appropriate techniques. This study was conducted to determine P source coefficients (PSC) for quantifying differential P loss risk of various manures relative to soluble chemical fertilizer. After 2-d, 2-week, 8-week, and 26-week soil incubations with various manures, P-amended soils were analyzed for Olsen P (Ol), Mehlich-3 P (M3), water extractable P (WEP), and Fe-oxide coated filter paper strip P (FeO), each of which was then used to calculate manure PSC. Manure PSCM3 had the strongest linear relationships (r2 = 0.95–0.97) among different incubation durations, compared with PSCWEP (r2 = 0.79–0.91), PSCOl (r2 = 0.85–0.94), and PSCFeO (r2 = 0.88–0.91). The 2 week incubation yielded PSCM3which had the strongest linear relationships (r2 = 0.87–0.97 with a mean of 0.95) among the tested soils, compared with those from 2-d, 8-week, and 26-week incubations. In addition, laboratory PSCM3 had the strongest linear relationships with those PSCM3 measured under field conditions, relative to PSCOl, PSCFeO, and PSCWEP. Hence, the 2-week incubation along with Mehlich-3 P yielded the most consistent PSCs for various manures across soil types, incubation durations, and soil conditions, and can be recommended as a common protocol for determining manure PSC. The recommended default PSC values are 110, 65, 46, and 43% for liquid swine, liquid dairy, solid poultry, and solid beef manures, respectively, for the new P index of Ontario.