Do decomposing organic matter residues reduce phosphorus sorption in highly weathered soils?
Many studies have shown a reduction in phosphorus (P) sorption in highly weathered soils when organic matter (OM) is applied. To delineate the effects of OM addition on P availability through sorption competition and P addition, water leachate from incubated soybean (SB, Glycine max) and Rhodes grass (RG, Chloris gayana) was used in competitive P sorption studies. Addition of two rates of SB leachate to an Oxisol significantly increased P sorption at the higher rate, while a similar trend was observed following RG leachate addition at the same rates. Extending the range of highly weathered soils examined resulted in no observed decrease in P sorption following addition of OM leachate. The results provides further evidence contradicting the long held assumption that inhibition of P sorption by dissolved organic compounds, derived from decomposing OM, is responsible for increased P phytoavailability when P fertilizer and OM are applied together (A).
