Phosphorus accumulation and leaching risk of greenhouse vegetable soils in Southeast China

Over-fertilization has caused significant phosphorus (P) accumulation in Chinese greenhouse vegetable production (GVP) soils. This study, for the first time, quantified profile P accumulation directly from soil P measurements, as well as subsoil P immobilization, in three alkaline coarse-textured GVP soil profiles with 5 (S5), 15 (S15), and 30 (S30) years of cultivation in Tongshan, Southeast China. For each profile, soil samples were collected at depths of 0–10 (topsoil), 10–20, 20–40, 40–60, 60–80, and 80–100 cm. Phosphorus accumulation was estimated from the difference in P contents between topsoil and parent material (60–100 cm subsoil). Phosphorus mobility was assessed from measurements of water-soluble P concentration (P_Sol). Finally, P sorption isotherms were produced using a batch sorption experiment and fitted using a modified Langmuir model. High total P contents of 1 980 (S5), 3 190 (S15), and 2 330 (S30) mg kg^?1 were measured in the topsoils versus lower total P content of approximately 600 mg kg^?1 in the 80–100 cm subsoils. Likewise, topsoil P_Sol values were very high, varying from 6.4 to 17.0 mg L^?1. The estimated annual P accumulations in the topsoils were 397 (S5), 212 (S15), and 78 (S30) kg ha^?1 year^?1. Sorption isotherms demonstrated the dominance of P desorption in highly P-saturated topsoils, whereas the amount of adsorbed P increased in the 80–100 cm subsoils with slightly larger P adsorption capacity. The total P adsorption capacity of the 80–100 cm subsoils at a solution P concentration of 0.5 mg L^?1 was 15.7 (S5), 8.7 (S15), and 6.5 (S30) kg ha^?1, demonstrating that subsoils were unable to secure P concentrations in leaching water below 0.5 mg L^?1 because of their insufficient P-binding capacity.