A Protocol to Determine Phosphorus Source Coefficients for Various Animal Manures Using Laboratory Incubation Studies.

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 (SCF). We applied solid beef (SB), liquid dairy (LD), liquid swine (LS), and solid poultry (SP) manures and SCF P, respectively, to six representative agricultural soils in Ontario. After 2 d, 2 wk, 8 wk, and 26 wk incubations, manure PSC was calculated using the measures of soil Olsen P (PSC_Ol), Mehlich-3 P (PSC_M3), water extractable P (PSC_WEP), and Fe-oxide coated filter paper strip P (PSC_FeO), respectively. Manure PSC_M3 had the strongest linear relationships (r² = 0.95-0.97) among different incubation durations, compared with PSC_WEP (r² = 0.79-0.91), PSC_Ol (r² = 0.85-0.94), and PSC_FeO (r² = 0.88-0.91).The 2 wk incubation yielded PSC_M3values which 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 wk, and 26 wk incubations. Hence, the 2 wk incubation along with Mehlich-3 P yielded the most consistent PSCs for various manures across soil types and incubation durations, and can be recommended as a common protocol for determining manure PSC. The recommended default PSC values are110, 65, 46, and 43% for LS, LD, SP, and SB, respectively, for the new P index of Ontario.