Fig. 2. Linear relationships between average runoff dissolved reactive phosphorus (DRP) concentrations and ratio of either bicarbonate-extractable inorganic phosphorus from furrow soil (Fur-P_i) or iron-oxide impregnated paper–extractable phosphorus from furrow soil (FeO-P_s) divided by phosphorus sorption index (PSI) (r² > 0.12 significant at 5% probability).