Nano
and colloidal particles (1–1000 nm) play important
roles in phosphorus (P) migration and loss from agricultural soils;
however, little is known about their relative distribution in arable
crop soils under varying agricultural geolandscapes at the regional
scale. Surface soils (0–20 cm depth) were collected from 15
agricultural fields, including two sites with different carbon input
strategies, in Zhejiang Province, China, and water-dispersible nanocolloids
(0.6–25 nm), fine colloids (25–160 nm), and medium colloids
(160–500 nm) were separated and analyzed using the asymmetrical
flow field flow fractionation technique. Three levels of fine-colloidal
P content (3583–6142, 859–2612, and 514–653 μg
kg–1) were identified at the regional scale. The
nanocolloidal fraction correlated with organic carbon (Corg) and calcium (Ca), and the fine colloidal fraction with Corg, silicon (Si), aluminum (Al), and iron (Fe). Significant linear
relationships existed between colloidal P and Corg, Si,
Al, Fe, and Ca and for nanocolloidal P with Ca. The organic carbon
controlled colloidal P saturation, which in turn affected the P carrier
ability of colloids. Field-scale organic carbon inputs did not change
the overall morphological trends in size fractions of water-dispersible
colloids. However, they significantly affected the peak concentration
in each of the nano-, fine-, and medium-colloidal P fractions. Application
of chemical fertilizer with carbon-based solid manure and/or modified
biochar reduced the soil nano-, fine-, and medium-colloidal P content
by 30–40%; however,the application of chemical fertilizer with
biogas slurry boosted colloidal P formation. This study provides a
deep and novel understanding of the forms and composition of colloidal
P in agricultural soils and highlights their spatial regulation by
soil characteristics and carbon inputs.