Comments on “Amounts, Forms, and Solubility of Phosphorus in Soils Receiving Manure”

Abstract

Groundwater discharge areas in boreal forest ecosystems can potentially be areas where Fe and Al accumulate in the forest floor and affect the solubility of P. This study was conducted to determine phosphate sorption properties using humus soils containing high native amounts of Al and Fe. Humus soils were collected from two different forested groundwater discharge areas varying in pH and amount and distribution of At and Fe species. The phosphate sorption capacities were 265 and 216 mmol P kg(-1) dry wt. soil, respectively, for the two humus soils. Pyrophosphate extractable Al and Fe dominated in the first soil, 738 mmol kg(-1) dry wt. The concentration of pyrophosphate extractable Al and Fe in the second soil was 317 mmol kg(-1) dry wt.. whereas citrate-dithionite (CD) extracted 548 mmol Al and Fe kg(-1) dry wt. Using 0.1 mol dm(-3) NaCl as ionic medium gave a higher phosphate sorption compared with deionized water at the midrange additions, but no difference at the highest addition. Phosphate sorption was pH independent when 0.1 mol dm(-3) NaCl was used, whereas deionized water gave a sorption minimum at approximately pH 6. Dissolved organic carbon (DOC) release in solution was positively correlated with phosphate sorption, especially in 0.1 mol dm(-3) NaCl ionic medium. However, dissolved organic P (DOP) was unaffected by the phosphate sorption. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) indicated that precipitation of Al and Fe phosphates dominated at higher phosphate additions in the soil with mainly organically bound At and Fe, whereas both surface sorption and precipitation occurs in the soil with a larger amount of CD-extractable Fe.