Size and composition of colloidal phosphorus across agricultural soils amended with biochar, manure and biogas slurry
Kamel Mohamed Eltohamy, Paul J. Milham, Mostafa Gouda, Daniel Menezes‐Blackburn, Sangar Khan, Boyi Liu, Junwei Jin, Ye Ye, Xinqiang Liang
Abstract
Abstract The long-term application of organic amendments like manure, biochar and biogas slurry can increase phosphorus (P) levels in agricultural soils; however, at present, it's not clear how this affects the P association with different mobile water-dispersible colloidal particles (P coll ). Thus, this study aimed to assess the effects of the long-term application of different organic amendments on the abundance, size and compositional characteristics of P coll . For this purpose, a total of 12 soils amended with the above three organic amendments were sampled from the Zhejiang Province, China, and P coll were fractionated into nano-sized (NC; 1–20 nm), fine-sized (FC; 20–220 nm), and medium-sized (MC; 220–450 nm) by a combination of differential centrifugation and ultrafiltration steps. These three P coll forms together accounted for 74 ± 14% of the total soil solution dissolved P content, indicating that P coll release was a key process in the overland P transport from these soils. Soils treated with biochar showed lower P coll contents than those treated with manure or slurry alone; this effect should be further explored in a controlled inductive research approach. Compositional analysis showed that inorganic P was the predominant P coll form in the NC (54 ± 20%) and FC (63 ± 28%) fractions, but not in the MC (42 ± 26%) fraction. Among the three fractions, the organic carbon (OC)–calcium (Ca) complex was the major carrier of NC-bound P coll , MC-bound P coll was better correlated with OC–manganese/iron/aluminium colloids than with OC–Ca colloids, and both of these phenomena co-occurred in the FC fraction. The current study provides novel insights into the impact of various carbon amendments on the propensity for P loss associated with different soil mobile colloidal fractions, and will therefore, inform future agronomic and environmental-related policies and studies.