Estimating Soil Phosphorus Requirements and Limits from Oxalate Extract Data

Abstract

Excessive fertilizer and manure phosphorus (P) inputs to soils elevates P in soil solution and surface runoff, which can lead to freshwater eutrophication. Runoff P can be related to soil test P and P sorption saturation, but these approaches are restricted to a limited range of soil types or are difficult to determine on a routine basis. The purpose of this study was to determine whether easily measurable soil characteristics were related to the soil phosphorus requirements (P(req), the amount of P sorbed at a particular solution P level). The P(req) was determined for 18 chemically diverse soils from sorption isotherm data (corrected for native sorbed P) and was found to be highly correlated to the sum of oxalate-extractable Al and Fe (R2 > 0.90). Native sorbed P, also determined from oxalate extraction, was subtracted from the P(req) to determine soil phosphorus limits (PL, the amount of P that can be added to soil to reach P(req)). Using this approach, the PL to reach 0.2 mg P L(-1) in solution ranged between -92 and 253 mg P kg(-1). Negative values identified soils with surplus P, while positive values showed soils with P deficiency. The results showed that P, Al, and Fe in oxalate extracts of soils held promise for determining PL to reach up to 10 mg P L(-1) in solution (leading to potential runoff from many soils). The soil oxalate extraction test could be integrated into existing best management practices for improving soil fertility and protecting water quality.

The Use of Phosphorus Sorption Parameters in the Monitoring of Potential Emissions of this Component from the Arable Lands

“…Similar relationships in the effectiveness of these two solutions have also been observed by other researchers [Dangelo 2003;Ige et al 2007;Maguire and Sims 2002;Zhang et al 2005] Relying solely on soil tests that determine the amount of phosphorus available to plants as an indicator of soil susceptibility to leaching of phosphorus compounds is of little use. The Al M3 / Al ox ratio was 0.82 on average, 0.3 in the case of Fe M3 / Fe ox , and 0.4 for P M3 /P ox .…”

Phosphate sorption indices as affected by the calcareousness of soils

“…On the other hand, the amount of fertilizer applied often exceeds the uptake by plants, and this results in a build-up of P in the soil. A fraction of applied P is lost through surface runoff and leaching processes and the lost P constitute the major nonpoint source of phosphorus in water bodies (3) . Elevated levels of P in freshwater systems leads to eutrophication, which results in the depletion of oxygen leading to fish death as well as affecting other aquatic life forms in an adverse manner.…”

Sorption of Phosphorus from Swine, Dairy, and Poultry Manures

“…After equilibration, the concentration remaining in solution is measured and used to calculate the concentration sorbed to the soil. In most cases, sorption studies are conducted by adding known concentrations of inorganic P in a predefined medium such as calcium chloride (CaCl 2 ) or potassium chloride (KCl) (Borling, Otabbong, and Barberis 2001;D'Angelo et al 2003;Kleinman and Sharpley 2002;Nair et al 1984;Reddy et al 1980;Sharpley 1995;Siddique and Robinson 2003). A potential limitation to this approach, however, is that in many regions the application of P to agricultural fields is in the form of animal manure.…”