Bioavailability of Phosphorus on Iron (Oxy)hydroxide Not Affected by Soil Amendment–Derived Organic Matter

Abstract

Numerous studies have demonstrated that synthetic organic acids can affect phosphorus (P) solubility in soils and uptake by plants. However, few studies have examined the effects of dissolved organic matter (DOM) derived from carbon (C)-rich soil amendments on P bioavailability. This study investigated how DOM extracted from crop residues, animal manures, and compost affected P adsorption onto iron (oxy)hydroxide (FeOOH) and its bioavailability using a plant bioassay. The results showed that pre-adsorbed DOM significantly decreased P adsorption by 19%. However, the pre-adsorbed DOM treatment did not significantly affect P uptake by tomato ( L. ‘German Johnson’) plants in a 5-wk agar-culture bioassay. The results of these laboratory-based studies suggest that the initial DOM leached from C-rich soil amendments such as crop residues and animal manures is unlikely to affect soil P bioavailability because orthophosphate forms strong inner-sphere bonds to the FeOOH and this DOM fraction does not.