Abstract
Background Colloid-facilitated phosphorus (P) transport is a recognized important pathway for soil P loss in agricultural systems, but limited information is available on the soil aggregate-associated colloidal P. To elucidate the effects of aggregate size on the loss potential of colloidal P (P coll ) in agricultural systems, soils (0-20 cm depth) from six land use types were sampled in Zhejiang province in the Yangtz river delta region, China. The aggregate size fractions (2–8 mm, 0.26–2 mm, 0.053–0.26 mm and <0.053 mm) separated by wet-sieving method were analyzed.Results Results showed that the 0.26–2 mm small macroaggregates had the highest total P (TP) content. For acidic soils, the highest P coll content was also found in the 0.26–2 mm aggregate size, while the lowest was found in the <0.053 mm (silt+clay)-sized particles, the opposite of that found in alkaline soils. Paddy soils contained less P coll than other land use types. The P coll in total dissolved P (TDP) was dominated by <0.053 mm (silt+clay)-sized particles. Aggregate size did strongly influence the loss potential of P coll in paddy soils, where P coll contributed up to 83% TDP in the silt+clay sized particles. The P coll content was positively correlated with TP, Al, Fe and mean weight diameter (MWD). Aggregate associated total carbon (TC), total nitrogen (TN), C/P, and C/N had significant, but negative effects on the contribution of P coll to potential soil P losses. The P coll content of the aggregates was controlled by aggregate associated TP and Al content as well as soil pH value, with P coll loss potential from aggregates being controlled by its organic matter content.Conclusion Therefore, we conclude that management practices that increase soil aggregate stability or its organic carbon content will limit P coll loss from agricultural systems.
GLOMALIN, CARBON, NITROGEN AND SOIL AGGREGATE STABILITY AS AFFECTED BY LAND USE CHANGES IN THE HUMID FOREST ZONE IN SOUTH CAMEROON
