Minimizing Confounding Factors in Phosphorus Leaching Assessment for Dairy‐and Poultry‐Manure‐Amended Soils

Soil phosphorus (P) concentrations have increased over the years, increasing P losses to surface waters. Phosphorus saturation ratios (PSR), used as environmental soil tests, have different relationships with conventional water‐soluble‐P (WSP) determinations for dairy and poultry‐manure‐amended soils. Objective was to develop a WSP procedure to characterize P leaching from manure‐amended soils. Soil samples were collected from dairy and poultry sites. WSP was determined using 1∶10 and 5∶1 soil–water ratios. Soils in columns were leached using unsaturated flow. Results showed that relationships between PSR and WSP 5∶1 were consistent for all soils. The 5∶1 ratio, closer to field moisture conditions, could be a good indicator of P leaching. There was good correlation between the WSP 1∶10, 5∶1, and column leachate, and a paired t test showed no difference between the last two. Thus, a single 5:1 extraction could be as useful in P leaching assessments as laborious column studies.