Soil phosphorus availability as affected by root exudates of cover crop species

Plant species can modify the phosphorus (P) sorption in soils through the release of low molecular weight organic acids (LMWOA) in their root exudates. These LMWOAs compete with P for adsorption sites on soil minerals and induce dissolution of Fe and Al oxyhydroxides via complexation or ligand promoted dissolution, which could affect P availability for crops and P loss. This study examined the effect of plant species and P input on the P sorption dynamics with respect to LMWOA. A greenhouse study was conducted with ten different plant species, two P fertilizer treatments (0 and 70 kg P ha^{- 1}), and two-time intervals (35 and 70 days). All treatments were structured in a 10 × 2 × 2 complete factorial with two controls arranged in a randomized complete block design with five replicates (210 experimental units). Species from Poaceae and Fabaceae exhibited a consistent trend of increased LMWOA release in low P compared to high P conditions whereas Brassicaceae species consistently released higher concentrations of LMWOAs regardless of P. On average, LMWOA release followed the order: Brassicaceae > Fabaceae > Poaceae. In certain circumstances, P availability may be more closely related to specific LMWOAs, particularly oxalic and citric acids, rather than total LMWOA concentration. Their influence on P sorption and water-extractable P is dependent on plant species, growth stage and P status. Our findings suggest that certain cover crop species rye, triticale and crimson clover may have potential to enhance P availability as well as minimize P loss.