Soil testing to predict phosphorus leaching

Subsurface pathways can play an important role in agricultural phosphorus (P) losses that can decrease surface water quality. This study evaluated agronomic and environmental soil tests for predicting P losses in water leaching from undisturbed soils. Intact soil columns were collected for five soil types that a wide range in soil test P. The columns were leached with deionized water, the leachate analyzed for dissolved reactive phosphorus (DRP), and the soils analyzed for water-soluble phosphorus (WSP), 0.01 M CaCl2 P (CaCl2-P), iron-strip phosphorus (FeO-P), and Mehlich-1 and Mehlich-3 extractable P, Al, and Fe. The Mehlich-3 P saturation ratio (M3-PSR) was calculated as the molar ratio of Mehlich-3 extractable P/[Al + Fe]. Leachate DRP was frequently above concentrations associated with eutrophication. For the relationship between DRP in leachate and all of the soil tests used, a change point was determined, below which leachate DRP increased slowly per unit increase in soil test P, and above which leachate DRP increased rapidly. Environmental soil tests (WSP, CaCl2-P, and FeO-P) were slightly better at predicting leachate DRP than agronomic soil tests (Mehlich-1 P, Mehlich-3 P, and the M3-PSR), although the M3-PSR was as good as the environmental soil tests if two outliers were omitted. Our results support the development of Mehlich-3 P and M3-PSR categories for profitable agriculture and environmental protection; however, to most accurately characterize the risk of P loss from soil to water by leaching, soil P testing must be fully integrated with other site properties and P management practices.     

Relationships between biosolids treatment process and soil phosphorus availability

Laws mandating phosphorus (P)-based nutrient management plans have been passed in several U.S. Mid-Atlantic states. Biosolids (sewage sludge) are frequently applied to agricultural land and in this study we evaluated how biosolids treatment processes and biosolids P tests were related to P behavior in biosolids-amended soils. Eight biosolids generated by different treatment processes, with respect to digestion and iron (Fe), aluminum (Al), and lime addition, and a poultry litter (PL), were incubated with an Elkton silt loam (fine-silty, mixed, active, mesic Typic Endoaquult) and a Suffolk sandy loam (fine-loamy, siliceous, semiactive, thermic Typic Hapludult) for 51 d. The amended soils were analyzed at 1 and 51 d for water-soluble phosphorus (WSP), iron-oxide strip--extractable phosphorus (FeO-P), Mehlich-1 P and pH. The biosolids and PL were analyzed for P, Fe, and Al by USEPA 3050 acid-peroxide digestion and acid ammonium oxalate, Mehlich-1, and Mehlich-3 extractions. Biosolids and PL amendments increased extractable P in the Suffolk sandy loam to a greater extent than in the Elkton silt loam throughout the 51 d of the incubation. The trend of extractable WSP, FeO-P, and Mehlich-1 P generally followed the pattern: [soils amended with biosolids produced without the use of Fe or Al] > [PL and biosolids produced using Fe or Al and lime] > [biosolids produced using only Fe and Al salts]. Mehlich-3 P and the molar ratio of P to [Al + Fe] by either the USEPA 3050 digestion or oxalate extraction of the biosolids were good predictors of changes in soil-extractable P following biosolids but not PL amendment. Therefore, the testing of biosolids for P availability, rather than total P, is a more appropriate tool for predicting extractable P from the biosolids-amended soils used in this study.     

Phosphorus forms in biosolids-amended soils and losses in runoff: effects of wastewater treatment process

Continuous addition of municipal biosolids to soils based on plant nitrogen (N) requirements can cause buildup of soil phosphorus (P) in excess of crop requirements; runoff from these soils can potentially contribute to nonpoint P pollution of surface waters. However, because biosolids are often produced using lime and/or metal salts, the potential for biosolids P to cause runoff P losses can vary with wastewater treatment plant (WWTP) process. This study was conducted to determine the effect of wastewater treatment process on the forms and amounts of P in biosolids, biosolids-amended soils, and in runoff from biosolids-amended soils. We amended two soil types with eight biosolids and a poultry litter (PL) at equal rates of total P (200 kg ha(-1); unamended soils were used as controls. All biosolids and amended soils were analyzed for various types of extractable P, inorganic P fractions, and the degree of P saturation (acid ammonium oxalate method). Amended soils were placed under a simulated rainfall and all runoff was collected and analyzed for dissolved reactive phosphorus (DRP), iron-oxide-coated filter paper strip-extractable phosphorus (FeO-P), and total phosphorus (EPA3050 P). Results showed that biosolids produced with a biological nutrient removal (BNR) process caused the highest increases in extractable soil P and runoff DRP. Alternatively, biosolids produced with iron only consistently had the lowest extractable P and caused the lowest increases in extractable soil P and runoff DRP when added to soils. Differences in soil and biosolids extractable P levels as well as P runoff losses were related to the inorganic P forms of the biosolids.     

Runoff phosphorus losses from surface-applied biosolids

Runoff losses of dissolved and particulate phosphorus (P) may occur when rainfall interacts with manures and biosolids spread on the soil surface. This study compared P levels in runoff losses from soils amended with several P sources, including 10 different biosolids and dairy manure (untreated and treated with Fe or Al salts). Simulated rainfall (71 mm h(-1)) was applied until 30 min of runoff was collected from soil boxes (100 x 20 x 5 cm) to which the P sources were surfaced applied. Materials were applied to achieve a common plant available nitrogen (PAN) rate of 134 kg PAN ha(-1), resulting in total P loading rates from 122 (dairy manure) to 555 (Syracuse N-Viro biosolids) kg P ha(-1). Two biosolids produced via biological phosphorus removal (BPR) wastewater treatment resulted in the highest total dissolved phosphorus (13-21.5 mg TDP L(-1)) and total phosphorus (18-27.5 mg TP L(-1)) concentrations in runoff, followed by untreated dairy manure that had statistically (p = 0.05) higher TDP (8.5 mg L(-1)) and TP (10.9 mg L(-1)) than seven of the eight other biosolids. The TDP and TP in runoff from six biosolids did not differ significantly from unamended control (0.03 mg TDP L(-1); 0.95 mg TP L(-1)). Highest runoff TDP was associated with P sources low in Al and Fe. Amending dairy manure with Al and Fe salts at 1:1 metal-to-P molar ratio reduced runoff TP to control levels. Runoff TDP and TP were not positively correlated to TP application rate unless modified by a weighting factor reflecting the relative solubility of the P source. This suggests site assessment indices should account for the differential solubility of the applied P source to accurately predict the risk of P loss from the wide variety of biosolids materials routinely land applied.     

Laboratory characterization of phosphorus in fresh and oven-dried organic amendments

This study was performed to determine the forms of P and to examine the influence of oven-drying on P forms in different organic amendments. Samples of biosolids, beef and dairy cattle manures, and hog manures from sow and nursery barns were used in this study. Both fresh and oven-dried amendments were analyzed for inorganic (Pi), organic (Po), and total phosphorus using a modified Hedley fractionation technique. Water extracted about 10% of total biosolids P and 30 to 40% of total hog and cattle manure P. The amount of P extracted by NaHCO3 ranged from 21 to 32% of total P in all organic amendments except in the dairy cattle manure with 45% of total P. The labile P fraction (sum of H2O- and NaHCO3-extractable P) was 24% of biosolids P, 60% of hog manure P, and 70% of dairy cattle manure P. The residual P was about 10% in biosolids and cattle manures and 5 to 8% in hog manures. Oven-drying caused a transformation in forms of P in the organic amendments. In hog manures, H2O-extractable Po was transformed to Pi, while in the dairy manure NaHCO3-extractable P was converted to H2O-extractable Pi with oven-drying. Therefore, caution should be exercised in using oven-drying for studies that evaluate forms of P in organic amendments. Overall, these results indicate that biosolids P may be less susceptible to loss by water when added to agricultural land.     

Estimating source coefficients for phosphorus site indices

Phosphorus release to runoff varies widely for different land-applied organic P sources even when spread at equivalent total P rates. To address this variability, some P site indices include tabulated P source coefficients (PSCs) for differential weighting of applied P materials based on their runoff enrichment potential. Because runoff P can vary widely even within source categories depending on composition, storage, and treatment differences, this study explored a method for estimating PSCs based on the water-extractable P (WEP) content of the applied amendment. Using seven published rainfall-runoff studies that followed National Phosphorus Research Project protocols, runoff dissolved P (RDP) was correlated (r(2) = 0.80) with WEP for multiple surface-applied manures and biosolids. Assuming amendments with WEP >/= 10 g kg(-1) behave as highly soluble P sources and have a maximum PSC of 1.0, an empirical equation was developed for computing source-specific PSCs from laboratory-determined WEP values [PSC = 0.102 x WEP(0.99)]. For two independent runoff experiments, correlations between RDP loss and P source loading rate were improved when loading rates were multiplied by the computed (r(2) = 0.73-0.86) versus generic (r(2) = 0.45-0.48) PSCs. Source-specific PSCs should enhance the ability of assessment tools to identify vulnerable sites and P loss management alternatives, although the exact inclusion process depends on index scaling and conceptual framework.     

Biosolids effects on phosphorus retention and release in some sandy Florida soils

The soil solid phase components most responsible for P sorption in Florida soils are Fe and Al oxides. Thus, we hypothesized that land application of biosolids would significantly increase a soil's P retention by increasing its content of P-sorbing solids, especially when biosolids with high Fe and Al concentrations are applied to soils that sorb P poorly. Biosolids effects were quantified by a series of single-point isotherms on soils from two field studies sampled for up to 4 yr after initial biosolids application. Biosolids additions had little effect on P retention in a soil with abundant oxalate-extractable Fe and Al and a correspondingly large native P-sorbing capacity. However, biosolids significantly increased P retention in a soil with low oxalate-extractable Fe and Al content and low native P-sorbing capacity. Biosolids effects on P retention lasted 1 to 3 yr after application, depending on biosolids source and rate of application, and generally mimicked persistence of increased extractable Fe and Al concentrations in the poorly P-sorbing soil. Disappearance of added Fe and Al (and, hence, P retention capacity) from the surface horizons over time was relatively rapid, perhaps due to abundant organic acid production associated with biosolids degradation. Phosphorus in biosolids containing (or tailored to contain) abundant Fe and/or Al can be expected to behave as a slowly available P source, and to be less subject to leaching losses than completely soluble P sources.     

Effect of mineral and manure phosphorus sources on runoff phosphorus

Concern over nonpoint-source phosphorus (P) losses from agricultural lands to surface waters has resulted in scrutiny of factors affecting P loss potential. A rainfall simulation study was conducted to quantify the effects of alternative P sources (dairy manure, poultry manure, swine slurry, and diammonium phosphate), application methods, and initial soil P concentrations on runoff P losses from three acidic soils (Buchanan-Hartleton, Hagerstown, and Lewbeach). Low P (12 to 26 mg kg(-1) Mehlich-3 P) and high P (396 to 415 mg kg(-1) Mehlich-3 P) members of each soil were amended with 100 kg total P ha(-1) from each of the four P sources either by surface application or mixing, and subjected to simulated rainfall (70 mm h(-1) to produce 30 min runoff). Phosphorus losses from fertilizer and manure applied to the soil surface differed significantly by source, with dissolved reactive phosphorus (DRP) accounting for 64% of total phosphorus (TP) (versus 9% for the unamended soils). For manure amended soils, these losses were linearly related to water-soluble P concentration of manure (r2 = 0.86 for DRP, r2 = 0.78 for TP). Mixing the P sources into the soil significantly decreased P losses relative to surface P application, such that DRP losses from amended, mixed soils were not significantly different from the unamended soil. Results of this study can be applied to site assessment indices to quantify the potential for P loss from recently manured soils.     

Use of drinking water treatment residuals as a potential best management practice to reduce phosphorus risk index scores

The P risk index system has been developed to identify agricultural fields vulnerable to P loss as a step toward protecting surface water. Because of their high Langmuir phosphorus adsorption maxima (P(max)), use of drinking water treatment residuals (WTRs) should be considered as a best management practice (BMP) to lower P risk index scores. This work discusses three WTR application methods that can be used to reduce P risk scores: (i) enhanced buffer strip, (ii) incorporation into a high soil test phosphorus (STP) soil, and (iii) co-blending with manure or biosolids. The relationship between WTR P(max) and reduction in P extractability and runoff P was investigated. In a simulated rainfall experiment, using a buffer strip enhanced with 20 Mg WTR ha(-1), runoff P was reduced by from 66.8 to 86.2% and reductions were related to the WTR P(max). When 25 g kg(-1) WTR was incorporated into a high STP soil of 315 mg kg(-1) determined using Mehlich-3 extraction, 0.01 M calcium chloride-extractable phosphorus (CaCl(2)-P) reductions ranged from 60.9 to 96.0% and were strongly (P < 0.01) related to WTR P(max). At a 100 g kg(-1) WTR addition, Mehlich 3-extractable P reductions ranged from 41.1 to 86.7% and were strongly (P < 0.01) related to WTR P(max). Co-blending WTR at 250 g kg(-1) to manure or biosolids reduced CaCl(2)-P by >75%. The WTR P(max) normalized across WTR application rates (P(max) x WTR application) was significantly related to reductions in CaCl(2)-P or STP. Using WTR as a P risk index modifying factor will promote effective use of WTR as a BMP to reduce P loss from agricultural land.     

Phosphorus extractability of soils amended with stockpiled and composted cattle manure

Managing fertilizer applications to maintain soil P below environmentally unacceptable levels should consider the contribution of manure and synthetic fertilizer sources to soluble and extractable forms of P. Our objective was to evaluate soil and manure characteristics and application rates on P extractability in recently amended soils. Five soils of the U.S. southern High Plains were amended with beef cattle manures, composted beef manure, and inorganic fertilizers [Ca(H(2)PO(4))(2) or KH(2)PO(4)] at five rates and incubated under controlled conditions. Mehlich 3-, Olsen (NaHCO(3))-, Texas A&M extractant (TAM)-, and water-extractable P were determined for the soils after selected incubation periods. Except for TAM and some water extractions, P extractability as a function of total P applied was linear (P < 0.001) for a wide range of application rates. Mehlich-3, NaHCO(3), and water P extraction efficiencies of KH(2)PO(4)-amended soils averaged 22, 34, and 115% greater (P < or = 0.036), respectively, than efficiencies of soils amended with manures except for the Texline (calcareous) loam and Pullman clay loam soils. Phosphorus extraction efficiencies decreased with time for KH(2)PO(4)-amended soils (P < 0.05) but remained stable or increased for manure-amended soils during the 8-wk incubation period. Across all soils and manure sources, changes in water-extractable P per unit increase in Mehlich 3-, NaHCO(3)-, and TAM-extractable P averaged 100, 85, and 125% greater, respectively, for inorganic as compared with manure-amended soils. These source-dependent relationships limit the use of agronomic soil extractants to make correct inferences about water-extractable P and dissolved P in runoff.     

Runoff phosphorus losses as related to phosphorus source, application method, and application rate on a Piedmont soil

Land application of animal manures and fertilizers has resulted in an increased potential for excessive P losses in runoff to nutrient-sensitive surface waters. The purpose of this research was to measure P losses in runoff from a bare Piedmont soil in the southeastern United States receiving broiler litter or inorganic P fertilizer either incorporated or surface-applied at varying P application rates (inorganic P, 0-110 kg P ha(-1); broiler litter, 0-82 kg P ha(-1)). Rainfall simulation was applied at a rate of 76 mm h(-1). Runoff samples were collected at 5-min intervals for 30 min and analyzed for reactive phosphorus (RP), algal-available phosphorus (AAP), and total phosphorus (TP). Incorporation of both P sources resulted in P losses not significantly different than the unfertilized control at all application rates. Incorporation of broiler litter decreased flow-weighted concentration of RP in runoff by 97% and mass loss of TP in runoff by 88% compared with surface application. Surface application of broiler litter resulted in runoff containing between 2.3 and 21.8 mg RP L(-1) for application rates of 8 to 82 kg P ha(-1), respectively. Mass loss of TP in runoff from surface-applied broiler litter ranged from 1.3 to 8.5 kg P ha(-1) over the same application rates. Flow-weighted concentrations of RP and mass losses of TP in runoff were not related to application rate when inorganic P fertilizer was applied to the soil surface. Results for this study can be used by P loss assessment tools to fine-tune P source, application rate, and application method site factors, and to estimate extreme-case P loss from cropland receiving broiler litter and inorganic P fertilizers.     

Chemical fractionation of phosphorus in stabilized biosolids

Three chemicals-ferrous sulfate (FeSul), calcium oxide (CaO), and aluminum sulfate (alum)-were applied at different rates to stabilize P in fresh, anaerobically digested biosolids (FBS) obtained from an activated sewage treatment plant. A modified Hedley fractionation procedure was used to assess P forms in these sludge-borne materials and in a biosolids compost (BSC) prepared from the same FBS. Each biosolids material exhibited a unique pattern of P distribution among fractions. The most available P forms, namely: (i) water-soluble P (WSP); (ii) membrane-P; and (iii) NaHCO(3)-P, were stabilized by small rates of each of the chemicals; but the P transformation into more stable forms depended on the type of chemical added. The stabilized P forms were enhanced by high rates of CaO and FeSul, but were reduced by high rates of alum. The organic P (P(o)) in the first three fractions of the FeSul- and alum-stabilized biosolids was enhanced by the chemical addition, and P(o) transformation from NaOH-P(o) into NaHCO(3)-P(o) was found in calcium-stabilized biosolids. A positive relationship was found between NaHCO(3)-P(o) and the NaHCO(3)-extracted organic C in all chemically stabilized biosolids. One-step extraction by NaHCO(3) or NaOH underestimated P extraction compared to the stepwise extraction. The reported results are consistent with solid-state P speciation reported earlier and contribute important information for optimizing biosolids stabilization to reduce P loss after incorporation in soils and for maximizing soil capacity to safely store pre-stabilized biosolids.     

Characterization of phosphorus species in biosolids and manures using XANES spectroscopy

Identification of the chemical P species in biosolids or manures will improve our understanding of the long-term potential for P loss when these materials are land applied. The objectives of this study were to determine the P species in dairy manures, poultry litters, and biosolids using X-ray absorption near-edge structure (XANES) spectroscopy and to determine if chemical fractionation techniques can provide useful information when interpreted based on the results of more definitive P speciation studies. Our XANES fitting results indicated that the predominant forms of P in organic P sources included hydroxylapatite, PO(4) sorbed to Al hydroxides, and phytic acid in lime-stabilized biosolids and manures; hydroxylapatite, PO(4) sorbed on ferrihydrite, and phytic acid in lime- and Fe-treated biosolids; and PO(4) sorbed on ferrihydrite, hydroxylapatite, beta-tricalcium phosphate (beta-TCP), and often PO(4) sorbed to Al hydroxides in Fe-treated and digested biosolids. Strong relationships existed between the proportions of XANES PO(4) sorbed to Al hydroxides and NH(4)Cl- + NH(4)F-extractable P, XANES PO(4) sorbed to ferrihydrite + phytic acid and NaOH-extractable P, and XANES hydroxylapatite + beta-TCP and dithionite-citrate-bicarbonate (DCB)- + H(2)SO(4)-extractable P (r(2) = 0.67 [P = 0.01], 0.78 [P = 0.01], and 0.89 [P = 0.001], respectively). Our XANES fitting results can be used to make predictions about long-term solubility of P when biosolids and manures are land applied. Fractionation techniques indicate that there are differences in the forms of P in these materials but should be interpreted based on P speciation data obtained using more advanced analytical tools.     

Evaluating phosphorus loss from a Florida spodosol as affected by phosphorus-source application methods

Incorporating applied phosphorus (P) sources can reduce P runoff losses and is a recommended best management practice. However, in soils with low P retention capacities, leaching can be a major mechanism for off-site P loss, and the P-source application method (surface or incorporation) may not significantly affect the total amount of off-site P loss. We utilized simulated rainfall protocols to investigate effects of P-source characteristics and application methods on the forms and amounts of P losses from six P sources, including five biosolids materials produced and/or marketed in Florida, and one inorganic fertilizer (triple superphosphate). A typical Florida Spodosol (Immokalee fine sand; sandy, siliceous, hyperthermic Arenic Alaquods) was used for the study, to which the P sources were each applied at a rate of 224 kg P ha(-1) (approximately the P rate associated with N-based biosolids applications). The P sources were either surface-applied to the soil or incorporated into the soil to a depth of 5 cm. Amended soils were subjected to three simulated rainfall events, at 1-d intervals. Runoff and leachate were collected after each rainfall event and analyzed for P losses in the form of soluble reactive P (SRP), total dissolved P (TDP), total P (TP), and bioavailable P (BAP) (in runoff only). Cumulative masses (runoff + leachate for the three rainfall events) of P losses from all the P sources were similar, whether the amendments were surface-applied or incorporated into the soil. The solubility of the amendment, rather than application method, largely determines the P loss potential in poorly P-sorbing Florida Spodosols.     

An alum-based water treatment residual can reduce extractable phosphorus concentrations in three phosphorus-enriched coastal plain soils

The accumulation of excess soil phosphorus (P) in watersheds under intensive animal production has been linked to increases in dissolved P concentrations in rivers and streams draining these watersheds. Reductions in water dissolved P concentrations through very strong P sorption reactions may be obtainable after land application of alum-based drinking water treatment residuals (WTRs). Our objectives were to (i) evaluate the ability of an alum-based WTR to reduce Mehlich-3 phosphorus (M3P) and water-soluble phosphorus (WSP) concentrations in three P-enriched Coastal Plain soils, (ii) estimate WTR application rates necessary to lower soil M3P levels to a target 150 mg kg(-1) soil M3P concentration threshold level, and (iii) determine the effects on soil pH and electrical conductivity (EC). Three soils containing elevated M3P (145-371 mg kg(-1)) and WSP (12.3-23.5 mg kg(-1)) concentrations were laboratory incubated with between 0 and 6% WTR (w w(-1)) for 84 d. Incorporation of WTR into the three soils caused a near linear and significant reduction in soil M3P and WSP concentrations. In two soils, 6% WTR application caused a soil M3P concentration decrease to below the soil P threshold level. An additional incubation on the third soil using higher WTR to soil treatments (10-15%) was required to reduce the mean soil M3P concentration to 178 mg kg(-1). After incubation, most treatments had less than a half pH unit decline and a slight increase in soil EC values suggesting a minimal impact on soil quality properties. The results showed that WTR incorporation into soils with high P concentrations caused larger relative reductions in extractable WSP than M3P concentrations. The larger relative reductions in the extractable WSP fraction suggest that WTR can be more effective at reducing potential runoff P losses than usage as an amendment to lower M3P concentrations.     

Phytase supplementation and reduced-phosphorus turkey diets reduce phosphorus loss in runoff following litter application

Concerns about regional surpluses of manure phosphorus (P) leading to increased P losses in runoff have led to interest in diet modification to reduce P concentrations in diets. The objectives of this study were to investigate how dietary P amendment affected P concentrations in litters and P losses in runoff following land application. We grew two flocks of turkeys on the same bed of litter using diets with two levels of non-phytate phosphorus (NPP), with and without phytase. The litters were incorporated into three soils in runoff boxes at a plant-available nitrogen (PAN) rate of 168 kg PAN/ha, with runoff generated on Days 1 and 7 under simulated rainfall and analyzed for dissolved reactive phosphorus (DRP) and total P. Litters were analyzed for water-soluble phosphorus (WSP) and total P, while soils in the runoff boxes were analyzed for WSP and Mehlich-3 phosphorus (M3-P). Formulating diets with lower NPP and phytase both decreased litter total P. Phytase had no significant effect on litter WSP at a 1:200 litter to water extraction ratio, but decreased WSP at a 1:10 extraction ratio. Using a combination of reducing NPP fed and phytase decreased the total P application rate by up to 38% and the P in surplus of crop removal by approximately 48%. Reducing the NPP fed reduced DRP in runoff from litter-amended soils at Day 1, while phytase had no effect on DRP concentrations. Increase in soil M3-P was dependent on total P applied, irrespective of diet. Reducing overfeeding of NPP and utilizing phytase in diets for turkeys should decrease the buildup of P in soils in areas of intensive poultry production, without increasing short-term concerns about dissolved P losses.     

Runoff and leachate losses of phosphorus in a sandy Spodosol amended with biosolids

Florida Spodosols are sandy, inherently low in Fe- and Al-based minerals, and sorb phosphorus (P) poorly. We evaluated runoff and leachate P losses from a typical Florida Spodosol amended with biosolids and triple superphosphate (TSP). Phosphorus losses were evaluated with traditional indoor rainfall simulations but used a double-deck box arrangement that allowed leaching and runoff to be determined simultaneously. Biosolids (Lakeland, OCUD, Milorganite, and Disney) represented contrasting values of total P, percent water-extractable P (PWEP), and percentage of solids. All P sources were surface applied at 224 kg P ha(-1), representing a soil P rate typical of N-based biosolids application. All biosolids-P sources lost less P than TSP, and leachate-P losses generally dominated. For Lakeland-amended soil, bioavailable P (BAP) was mainly lost by runoff (81% of total BAP losses). This behavior was due to surface sealing and drying after application of the slurry (31 g kg(-1) solids) material. For all other P sources, BAP losses in leachate were much greater than in runoff, representing 94% of total BAP losses for TSP, 80% for Milorganite, 72% for Disney, and 69% for OCUD treatments. Phosphorus leaching can be extreme and represents a great concern in many coarse-textured Florida Spodosols and other coastal plain soils with low P-sorption capacities. The PWEP values of P sources were significantly correlated with total P and BAP losses in runoff and leachate. The PWEP of a source can serve as a good indicator of potential P loss when amended to sandy soils with low P-retention capacities.     

Water quality impacts of converting to a poultry litter fertilization strategy

When improperly managed, land application of animal manures can harm the environment; however, limited watershed-scale runoff water quality data are available to research and address this issue. The water quality impacts of conversion to poultry litter fertilization on cultivated and pasture watersheds in the Texas Blackland Prairie were evaluated in this three-year study. Edge-of-field N and P concentrations and loads in surface runoff from new litter application sites were compared with losses under inorganic fertilization. The impact on downstream nutrient loss was also examined. In the fallow year with no fertilizer application, nutrient losses averaged 3 kg N ha(-1) and 0.9 kg P ha(-1) for the cultivated watersheds and were below 0.1 kg ha(-1) for the pasture watersheds. Following litter application, PO(4)-P concentrations in runoff were positively correlated to litter application rate and Mehlich-3 soil P levels. Following litter application, NO(3)-N and NH(4)-N concentrations in runoff were typically greater from cultivated watersheds, but PO(4)-P concentrations were greater for the pasture watersheds. Total N and P loads from the pasture watersheds (0.2 kg N ha(-1) and 0.7 kg P ha(-1)) were significantly lower than from the cultivated watersheds (32 kg N ha(-1) and 5 kg P ha(-1)) partly due to lower runoff volumes from the pasture watersheds. Downstream N and P concentrations and per-area loads were much lower than from edge-of-field watersheds. Results demonstrate that a properly managed annual litter application (4.5 Mg ha(-1) or less depending on litter N and P content) with supplemental N should supply necessary nutrients without detrimental water quality impacts.     

Repeated compost application effects on phosphorus runoff in the Virginia Piedmont

Increasing amounts of animal and municipal wastes are being composted before land application to improve handling and spreading characteristics, and to reduce odor and disease incidence. Repeated applications of composted biosolids and manure to cropland may increase the risk for P enrichment of agricultural runoff. We conducted field research in 2003 and 2004 on a Fauquier silty clay loam (Ultic Hapludalfs) to compare the effects of annual (since 1999) applications of composted and uncomposted organic residuals on P runoff characteristics. Biosolids compost (BSC), poultry litter-yard waste compost (PLC), and uncomposted poultry litter (PL) were applied based on estimated plant-available N. A commercial fertilizer treatment (CF) and an unamended control treatment (CTL) were also included. Corn (Zea mays L.) and a cereal rye (Secale cereal L.) cover crop were planted each year. We applied simulated rainfall in fall 2004 and analyzed runoff for dissolved reactive P (DRP), total dissolved P (TDP), total P (TP), total organic C (TOC), and total suspended solids (TSS). End of season soil samples were analyzed for Mehlich-3 P (M3P), EPA 3050 P (3050P), water soluble P (WSP), degree of P saturation (DPS), soil C, and bulk density. Compost treatments significantly increased soil C, decreased bulk density, and increased M3P, 3050P, WSP, and DPS. The concentration of DRP, TDP, and TP in runoff was highest in compost treatments, but the mass of DRP and TDP was not different among treatments because infiltration was higher and runoff lower in compost-amended soil. Improved soil physical properties associated with poultry litter-yard waste compost application decreased loss of TP and TSS.     

Biosolids-derived nitrogen mineralization and transformation in forest soils

Utilization of biosolids through land application is becoming increasingly popular among wastewater managers. To minimize the potential contamination of receiving waters from biosolids-derived nitrogen (N), it is important to understand the availability of N after land application of biosolids. In this study, four secondary biosolids (two municipal and two pulp and paper industrial biosolids) were used in a laboratory incubation experiment to simulate N mineralization and transformation after land application. Municipal biosolids were from either aerobically or anaerobically digested sources, while pulp and paper industrial biosolids were from aerated wastewater stabilization lagoons. These biosolids were mixed with two New Zealand forest soils (top 100 mm of a volcanic soil and a brown soil) and incubated at two temperatures (10 and 20 degrees C) for 26 wk. During incubation, mineralized N was periodically leached from the soil-biosolids mixture with 0.01 M CaCl2 solution and concentrations of NH4 and NO3 in leachate were determined. Mineralization of N from aerobically digested municipal biosolids (32.1%) was significantly more than that from anaerobically digested biosolids (15.2%). Among the two pulp and paper industrial biosolids, little N leached from one, while as much as 18.0% of total organic N was leached from the other. As expected, mineralization of N was significantly greater at 20 degrees C (average 22.8%) than at 10 degrees C (average 9.7%). It was observed that more N in municipal biosolids was mineralized in the brown soil, whereas more N in pulp and paper industrial biosolids mineralized in the volcanic soil. Transformation of NH4 to NO3 was affected by soil type and temperature.