Mehlich 3 as a generic soil test extractant for environmental phosphorus risk assessment across Alabama soil regions

Abstract

Abstract Individual states in the United States have adopted different soil test P (STP) methods for agronomic and environmental purposes. Working between soil regions and state borderlines can be complicated by using multiple STP methods. For example, Alabama uses Mehlich 1 (M1) for noncalcareous soils (Appalachian Plateau [AP], Coastal Plain [CP], Limestone Valley [LV], Piedmont Plateau [PP]) and Lancaster (La) for calcareous soils (Blackland Prairie [BP]). Mehlich 3 (M3) has been proposed as an efficient and possibly a generic extractant for a broader range of soils. The objective of this study was to evaluate whether M3 can be used as a common or generic extractant for environmental P loss risk assessment for both calcareous and noncalcareous soils. More than 769 soil samples were collected from 68 agricultural fields representing noncalcareous and calcareous soils, and their extraction efficiencies for M1, M3, and La were compared. Mehlich 1 extracted 13.8, 13.1, 6.3, and 6.2% of total P; whereas M3 extracted 29.8, 35.4, 10.5, and 14.8% of total P from AP, CP, LV, and PP, respectively. There was no significant difference between La and M3 extractable P for both acidic and alkaline soils of BP. The conversion factor of 1.42 (95% confidence interval [CI95%] = 1.36–1.47) was found suitable to convert M1‐P to M3‐P values for noncalcareous soils, and 0.92 (CI95% = 0.87–0.98) was suitable to convert La‐P to M3‐P values for calcareous soils. The linear relationship between water‐soluble P (WSP) and extractable P was stronger for M3 than for M1 and La for all soil regions, as indicated by a greater correlation coefficient. Results suggest that M3 can be adopted as a generic extractant for environmental P loss risk assessment for calcareous and noncalcareous soils.