Soil chemical and fertilizer influences on soluble and medium-sized colloidal phosphorus in agricultural soils

Maëlle Fresne; Phil Jordan; Owen Fenton; Per-Erik Mellander; Karen Daly

doi:10.1016/j.scitotenv.2020.142112

Soil chemical and fertilizer influences on soluble and medium-sized colloidal phosphorus in agricultural soils

Sci Total Environ. 2021 Feb 1:754:142112. doi: 10.1016/j.scitotenv.2020.142112. Epub 2020 Sep 1.

Authors

Maëlle Fresne¹, Phil Jordan², Owen Fenton³, Per-Erik Mellander⁴, Karen Daly³

Affiliations

¹ Agricultural Catchments Programme, Teagasc, Johnstown Castle Environment Research Centre, Wexford, Ireland; Crops, Environment and Land Use Programme, Teagasc, Johnstown Castle Environment Research Centre, Wexford, Ireland; School of Geography and Environmental Sciences, Ulster University, Coleraine, UK. Electronic address: maelle.fresne@hotmail.fr.
² School of Geography and Environmental Sciences, Ulster University, Coleraine, UK.
³ Crops, Environment and Land Use Programme, Teagasc, Johnstown Castle Environment Research Centre, Wexford, Ireland.
⁴ Agricultural Catchments Programme, Teagasc, Johnstown Castle Environment Research Centre, Wexford, Ireland; Crops, Environment and Land Use Programme, Teagasc, Johnstown Castle Environment Research Centre, Wexford, Ireland.

PMID: 33254851
DOI: 10.1016/j.scitotenv.2020.142112

Abstract

Colloid-facilitated transport can be important for preferential transfer of phosphorus (P) through the soil profile to groundwater and may in part explain elevated P concentrations in surface water during baseflow and particularly high flow conditions. To investigate the potential for colloidal P (P_coll) mobilisation in soils, this study assessed the role of soil chemical properties and P fertilizer type on medium-sized soil P_coll (200-450 nm) and its association with soil solution soluble bioavailable P (<450 nm). Hillslope soils from three agricultural catchments were sampled and untreated and treated (cattle slurry and synthetic fertilizer) subsamples were incubated. Soil supernatants were analysed for P and soil Water Dispersible Colloids (WDC) were extracted for analysis of P and P-binding materials. Soils physicochemical properties including degree of P saturation (DPS) and P sorption properties were determined. Results indicated that medium-sized P_coll was mostly unreactive P associated to some extent to amorphous forms of Fe. Medium-sized P_coll concentrations correlated negatively with soil maximum P sorption capacity and soluble P concentrations increased with increasing DPS. In soil with low sorption properties, cattle slurry increased soluble P concentrations by 0.008-0.013 mg l^-1 and DPS but did not influence medium-sized P_coll. Synthetic fertilizer increased medium-sized reactive P_coll by 0.011 mg l^-1 (0.088 mg kg^-1 soil) and DPS in a soil with lower DPS whereas it decreased it by 0.005 mg l^-1 (0.040 mg kg^-1 soil) in a soil with higher DPS. Additional soil parameters (M3-Fe, M3-Al, M3-P, and DPS) should be included in soil testing, especially in Cambisol/Podzol soils, to identify critical areas where risks of P_coll mobilisation are important. Further research should include the roles of finer colloidal and nanoparticulate (<200 nm) soil P fractions and soluble P to inform understanding of plant uptake and assess environmental risk.

Keywords: Agriculture; Cattle slurry; Groundwater pollution; Mobilisation; Soil water dispersible colloids; Synthetic fertilizer.