Enhanced soil aggregate stability limits colloidal phosphorus loss potentials in agricultural systems

BACKGROUND: Colloid-facilitated phosphorus (P) transport is recognized as an important pathway for the loss of soil P in agricultural systems; however, information regarding soil aggregate-associated colloidal P (Pcₒₗₗ) is lacking. To elucidate the effects of aggregate size on the potential loss of Pcₒₗₗ in agricultural systems, soils (0–20 cm depth) from six land-use types were sampled in the Zhejiang Province in the Yangtze River Delta region, China. The aggregate size fractions (2–8 mm, 0.26–2 mm, 0.053–0.26 mm and < 0.053 mm) were separated using the wet sieving method. Colloidal P and other soil parameters in aggregates were analyzed. RESULTS: Our study demonstrated that 0.26–2 mm small macroaggregates had the highest total P (TP) content. In acidic soils, the highest Pcₒₗₗ content was observed in the 0.26- to 2-mm-sized aggregates, while the lowest was reported in the < 0.053 mm (silt + clay)-sized particles, the opposite of that revealed in alkaline and neutral soils. Paddy soils contained less Pcₒₗₗ than other land-use types. The proportion of Pcₒₗₗ in total dissolved P (TDP) was dominated by < 0.053 mm (silt + clay)-sized particles. Aggregate size strongly influenced the loss potential of Pcₒₗₗ in paddy soils, where Pcₒₗₗ contributed up to 83% TDP in the silt + clay-sized particles. The Pcₒₗₗ content was positively correlated with TP, Al, Fe, and the mean weight diameter. Aggregate-associated total carbon (TC), total nitrogen (TN), C/P, and C/N had significant negative effects on the contribution of Pcₒₗₗ to potential soil P loss. The Pcₒₗₗ content of the aggregates was controlled by the aggregate-associated TP and Al content, as well as the soil pH value. The potential loss of Pcₒₗₗ from aggregates was controlled by its organic matter content. CONCLUSION: We concluded that management practices that increase soil aggregate stability or its organic carbon content will limit Pcₒₗₗ loss in agricultural systems.