Organic phosphorus leaching risk from agricultural soils across China

Background: Leaching from agricultural land is one of the major pathways of phosphorus (P) loss from soils to waterbody and may induce adverse effect on territorial environment. Past studies usually focused on the loss of inorganic P (P-I) while ignored the role of organic P (P-O) in leaching process. A total of 63 agricultural soil samples were collected from across China with various soil types including 21 paddy soils, 13 chernozems, 11 red soils and other type soils (n = 18) to identify the potential risk of P-O and P-I leaching from agricultural lands and to explore their relationships with soil basic properties, Fe/Al oxides, and P status. Results: CaCl2-extractable organic P (CaCl2-P-O) accounted for 8-89% (35% on average) of CaCl2-extractable total P (CaCl2-P-T) and available organic P (AP(O)) accounted to over half of available total P (AP(T)) (57 +/- 25%). CaCl2-P-T was positively correlated with AP(T) under all soil types except paddy soils. CaCl2-extractable inorganic P (CaCl2-P-I) and available inorganic P (AP(I)) were strongly correlated for chernozem (r = 0.968), while CaCl2-P-O the was strongly correlated with AP(O) for red soils (r = 0.901). Conclusions: P-O greatly contributed to the potential P leaching risk and should be included in the risk assessment of total P leaching. The control of soil AP(T) excess accumulation in both P-O and P-I fractions in agricultural land is the key point to cut down P leaching. Mitigation measures to limit P-O leaching should be established based on the soil types.