The soil carbon saturation controls phosphate sorption and mobility in organically amended Ferralsols
Year: 2026
Type: article
Abstract: Phosphorus (P) fertilizer efficiency in highly weathered soils is constrained by phosphate sorption on iron (Fe) and aluminum (Al) oxides. Integrated soil fertility management promotes the combined use of P fertilizers and organic amendments (OAs), but the mechanisms underlying OA-P interactions remain unclear. This study evaluated how OA dose, OA quality, and time affect P mobility, assessed through phosphate sorption and diffusion from a fertilizer granule. Three Ferralsols were incubated with compost, farmyard manure (FYM), or straw at four doses (0–4 % w/w) in a full factorial design. Phosphate sorption strength (K D ) was quantified after 1 and 49 days of incubation and related to the soil’s degree of carbon saturation (DCS), an operational metric that is proportional to the molar ratio of organic C to the reactive Fe and Al oxides. Across all soils and treatments, K D decreased with increasing DCS (R 2 = 0.66) at 49 days after amendment, consistent with increasing competition of organic anions with phosphate for sorption sites. In contrast, the short-term (1-day) effects of amendments on K D were primarily related to soil pH. A diffusion experiment using Ferralsol samples from a field trial with three years of FYM application showed wider diffusion zones around fertilizer granules in FYM-amended than in control soils. Together, these findings suggest that OA-induced improvements in P fertilizer use efficiency observed in field trials are related to competition effects and that the effects of OA dose and quality can be predicted with a mechanistic model.
Source: Geoderma
Institution: KU Leuven
Language: English
Subfield: Soil Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: gold
Estimated APC paid: $3,320
Funder: European Research Council
Award: G251864292
OpenAlex ID: W7204788262