Phytoavailability of Biosolids Phosphorus

Abstract

various biosolids to assure efficient agronomic utilization of biosolids P. Efficient utilization of biosolids P for agronomic purposes requiresWhen P considerations dictate biosolids application, accounting for differences in the phytoavailability of P in various biosolids. Greenhouse studies were conducted with a common pasture the 1995 USEPA design manual (USEPA, 1995) advises grass grown in two P-deficient soils amended with 12 biosolids and consideration of the "relative effectiveness" (50%) of a commercial fertilizer (triple superphosphate, TSP) to quantify P biosolids P compared with fertilizer P. No literature is uptake and to assess the relative phytoavailabilities of the P sources.cited to support the 50% value, but several researchers Biosolids were grouped into three general categories of phytoavaila-(e.g., de Haan, 1980; Hall and Williams, 1984; Coker bility relative to TSP: high (Ͼ75% of TSP), moderate (25-75% of and Carlton-Smith, 1986) report ranges from 10 to 100% TSP), and low (Ͻ25% of TSP). Two biosolids, produced via biological effectiveness relative to fertilizer P determined in greenphosphorus removal (BPR) processes, were in the high category, and house studies. Canadian regulators (Ontario Ministry mimicked fertilizer P with regard to P phytoavailability. Most biosolids of Environment and Energy and Ontario Ministry of produced by conventional wastewater and solids digestion and addi-

The Longer‐Term Phytoavailability of Biosolids‐Phosphorus

“…B iosolids are generally applied to meet crop N requirements. Applying biosolids at N‐based rates generally supplies P in excess of crop P removal, resulting in an accumulation of soil P (O'Connor et al, 2004). High‐P soils represent an increased risk for nonpoint pollution of surface waters (Sharpley et al, 1994, 1996).…”

“…If P‐based rates are mandated, accurate determinations of biosolids relative phosphorus phytoavailability (RPP; the plant availability of biosolids‐P compared to fertilizer P) are necessary to assure that biosolids‐P is applied at rates agronomically equivalent to fertilizer P (O'Connor et al, 2004). If the phytoavailability of biosolids‐P is less than inorganic fertilizer P, biosolids application rates based on inorganic fertilizer recommendations could be agronomically limiting.…”

“…The USEPA (1995) tacitly acknowledges that biosolids‐P is less phytoavailable than fertilizer P, and assigns a 50% agronomic “relative effectiveness” value to biosolids. Yet, studies suggest that P phytoavailability varies greatly among biosolids (de Haan, 1980; O'Connor et al, 2004, Elliott et al, 2005). O'Connor et al (2004) suggested grouping biosolids into three categories of phytoavailability relative to the inorganic fertilizer TSP): low (<25% of TSP), moderate (25–75% of TSP), and high (> 75% of TSP).…”

“…Yet, studies suggest that P phytoavailability varies greatly among biosolids (de Haan, 1980; O'Connor et al, 2004, Elliott et al, 2005). O'Connor et al (2004) suggested grouping biosolids into three categories of phytoavailability relative to the inorganic fertilizer TSP): low (<25% of TSP), moderate (25–75% of TSP), and high (> 75% of TSP). The O'Connor et al (2004) study identified biosolids produced with conventional wastewater and solids digestion (conventional biosolids) as being in the moderate category, biosolids produced via biological P removal processes (BPR biosolids) as being in the high category, and some biosolids with uniquely high total Fe+Al concentrations as being in the low category.…”

Are stabilized biosolids a eutrophication risk?

“…Smith et al (2002) reported variable effects of advanced-treated biosolids on Olsen-P accumulation in soils, but did not consider soluble P release. Reductions in P availability to crops, and in P release to runoff, have been reported elsewhere after application of iron (Fe)-rich, or thermally dried, biosolids, whilst biologically treated and lime-stabilized biosolids have shown greater P availability and P release (Frossard et al, 1996;Maguire et al, 2001;Penn & Sims, 2002;O'Connor et al, 2004;Krogstad et al, 2005). For example, Maguire et al (2000) found that the application of higher quantities of P-rich biosolid dosed with Fe and/or Al did not increase soluble reactive P (SRP) loss in runoff, because the percentage P saturation of the soil was not increased.…”