Soil Tests for Estimating Labile, Soluble, and Algae‐Available Phosphorus in Agricultural Soils

The relationships of three “quick” soil tests for P (Olsen, Bray‐1, and Mehlich I) with labile P, the equilibrium phosphorus concentration in the soil solution (EPC) and algae‐available P (as determined by 0.1 M NaOH extraction) were examined for a diverse group of noncalcareous agricultural soils. The soils were collected from 19 states in the southeast, north central, and northeast regions of the United States. In general, good relationships were obtained when soils were grouped according to geographic location. All soil tests were good predictors of labile P for the north central soils and for soils from Ohio and Pennsylvania ( r 2 ≥ 0.92). On the southeastern soils, the best relationships were found between labile P and the Olsen and Mehlich I soil test P measurements ( r 2 ≥ 0.90) after further separation of the soils into textural groups. Good relationships were found between EPC and the three soil test P measurements for the north central soils ( r 2 ≥ 0.80) and for the southeastern soils ( r 2 ≥ 0.71). For the soils from Pennsylvania and Ohio, Bray‐1 was the best predictor of EPC ( r 2 = 0.94). The relationships between algae‐available P and the soil test P and labile P measurements varied with the “active” Fe and Al content of the soils, although significant relationships between the parameters were developed for the north central soils ( r 2 ≥ 0.71) and for the southeastern soils separated into groups of low and high active Al contents ( r 2 ≥ 0.67).