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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #121035
Title: SOIL PHOSPHORUS FRACTIONS IN SOLUTION: INFLUENCE OF FERTILIZER AND MANURE, FILTRATION, AND METHOD OF DETERMINATION

Author
item MCDOWELL, RICHARD - PENN STATE UNIVERSITY
item Sharpley, Andrew

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2001
Publication Date: 11/20/2001
Citation: McDowell, R.W., Sharpley, A.N. 2001. Soil phosphorus fractions in solution: influence of fertiliser and manure,filtration, and method of determination. Chemosphere. 45(6):737-748.

Interpretive Summary: A significant proportion of phosphorus in soil, soil solution, overland flow, and subsurface drainage can be in organic forms. While dissolved inorganic phosphorus is important for plant and algal uptake, a proportion of dissolved organic phosphorus can also be utilized. Studies that have examined the importance of organic phosphorus movement from soils often quantify this fraction as the difference between orthophosphate as detecte by the colorimetric acid-molybdate method before and after digestion. Thus, we studied the effects of colloids on phosphorus dynamics and the potential for hydrolysis in solution, how this can be quantified by different analytical methods, and finally what the effect of small colloidal particles were on how much phosphorus is measured in solution. We found that in order to minimize these effects on phosphorus measurement, filtration through a fine filter is required.

Technical Abstract: This study investigated the forms of soil P released to solution, accuracy of their determination, and influence of colloids on P sorption/desorption dynamics. A Hagerstown silt loam, amended with dairy and poultry manure or superphosphate at 5 rates (0, 25, 50, 100, and 200 kg P/ha), was extracted at two soil:solution ratios (1:5 and 1:100) and filtered at 3 pore sizes (0.8, 0.45, and 0.22 um). Results showed that dissolved reactive P (DRP; determined colorimetrically) was the dominant fraction in all soil water extracts. However, the relative proportion of DRP to dissolved organic P (DOP; determined as the difference between total dissolved P [TDP] and P detected by ion chromatography) decreased as the rate of P amendment increased. Organic P extracted from manured soils was more recalcitrant than that extracted from soils amended with superphosphate, the later attributed to its accumulation in more labile pools. The sorption/ desorption of P by solutions was greatly affected by the rate of amendment and the soil to solution extraction ratio. More P was sorbed by superphosphate compared to dairy manure amended soil solutions and was attributed to the saturation of colloidal P sorption sites by organic matter. In order to minimize the effects of colloids on P dynamics and the potential for hydrolysis in solution, filtration to at least 0.45 um is required. However, soils with a lesser aggregate stability may require additional filtration.