Biochar impacts on nutrient dynamics in a subtropical grassland soil: 1. Nitrogen and phosphorus leaching.

Despite the numerous benefits of biosolids, concerns over nutrient losses restrict the extent to which biosolids can be beneficially reused. We evaluated the effectiveness of biochar in controlling the lability of nutrients in agricultural land. This study was designed to investigate the potential impacts of co-applying biochar with biosolids or inorganic fertilizer on N and P leaching losses. A companion paper focuses on greenhouse gas responses. Nutrients were surface applied as biosolids (aerobically digested Class B) and inorganic fertilizer (ammonium nitrate and triple superphosphate) to an established perennial pasture at equivalent annual rates typical of field practices. Biochar was applied at an annual rate of 20 Mg ha-1 . Leachate N and P were monitored using passive-capillary drainage lysimeters. Results demonstrated significant temporal variability in leachate N and P, with larger pulses generally occurring during periods of high water table levels or after intensive rainfall. Inorganic fertilizer generally resulted in greater leachate N and P losses than biosolids. No differences in leachate N and P losses between biosolids and control were observed. Approximately 1% of applied N was lost via leaching from biosolids treatments vs. 16% for inorganic fertilizer. Regardless of the P source, negligible (0.1-0.2% of applied P), cumulative P leaching occurred during the 3-yr study. Biochar had no effect on P leaching but reduced N leaching from treatments receiving inorganic fertilizer by 60%. Prudent nutrient management is possible even on biosolids-amended Spodosols with high water tables.

Biochar impacts on nutrient dynamics in a subtropical grassland soil: 2. Greenhouse gas emissions.

Land application of biochar reportedly provides many benefits, including reduced risk of nutrient transport, greenhouse gas (GHG) emission mitigation, and increased soil C storage, but additional field validation is needed. We evaluated the effectiveness of biochar in controlling the lability of nutrients in agricultural land. This study was designed to evaluate the impacts of biochar co-applied with various N and P sources on GHG fluxes from a subtropical grassland. Nutrients (inorganic fertilizer and aerobically digested Class B biosolids) were surface applied at a rate of 160 kg plant available N ha-1  yr-1 with or without biochar (applied at 20 Mg ha-1 ). Greenhouse gas (CO2 , CH4 , and N2 O) fluxes were assessed using static chambers and varied significantly, both temporally and with treatments. Greenhouse gas fluxes ranged from 1,247 to 23,160, -0.7 to 42, and -1.4 to 376 mg m-2 d-1 for CO2 , N2 O, and CH4 , respectively. Results of the 3-yr field study demonstrated strong seasonal variability associated with GHG emissions. Nutrient source had no effect on soil CO2 and CH4 emissions, but annual and cumulative (3-yr) N2 O emissions increased with biosolids (8 kg N2 O ha-1  yr-1 ) compared with inorganic fertilizer (5 kg N2 O ha-1  yr-1 ) application. Data suggested that environmental conditions played a more important role on GHG fluxes than nutrient additions. Biochar reduced CO2 emissions modestly (<9%) but had no effects on N2 O and CH4 emissions.

Pesticide Sorption to Soilless Media Components Used for Ornamental Plant Production and Aluminum Water Treatment Residuals.

Commercial producers of containerized ornamental plants almost exclusively use soilless media as the substrate for growing the plants. Soilless media are composed primarily of organic materials as opposed to mineral soils. Significant amounts of pesticides can leach from pots containing soilless media to which pesticides have been added as drenches or top-dressings. One of the goals of this project was to identify whether individual components comprising soilless media have differing affinities for the pesticides acephate, imidacloprid, metalaxyl, and plant growth regulator paclobutrazol. One-point 24 h equilibrium sorption assays were conducted to characterize sorption of the pesticides to sand, perlite, vermiculite, coir, peat, pine bark, and aluminum-water treatment residuals (Al-WTRs). Five-point isotherms were then constructed for the more sorptive peat and pine bark substrate components, and for the Al-WTRs. Results indicated significant differences in pesticide behavior with each substrate. Sorption of acephate to most of the substrate components was relatively low, comprising 21-31% of the initial amounts for soilless media components and 63% in Al-WTRs. Al-WTRs were highly sorptive for imidacloprid as evidenced by a partition coefficient of K F = 3275.4 L kg-1. Pine bark was the most sorptive for metalaxyl-M with a measured K F = 195.0 L kg-1. Peat had the highest affinity for paclobutrazol (K F = 398.4 L kg-1). These results indicate that none of component of soilless media has a universally high attraction for all of the pesticides studied.

Runoff and Leachate Phosphorus and Nitrogen Losses from Grass-Vegetated Soil Boxes Amended with Biosolids and Fertilizer.

Recent evidence suggests an upward trend in surface water phosphorus (P) concentrations in many segments of Florida, including the upper basin of the St. Johns River, a region that currently receives about two-thirds of the state Class B biosolids land application. Concerns about water quality in this area are encouraging reexamination of the regulations governing biosolids programs. The objectives of this study were (i) to identify and thoroughly characterize the main biosolids sources routinely applied in the region, and (ii) to evaluate runoff and leachate N and P losses from a typical Florida Spodosol amended with biosolids or commercial inorganic fertilizer. Biosolids and inorganic fertilizer were surface applied uniformly at a rate equivalent to ∼114 kg P ha, which corresponded to a typical P load associated with nitrogen (N)-based biosolids application. Soluble reactive P (SRP) was the predominant form of P lost in runoff and leachate. Inorganic P fertilizer increased flow-weighted runoff total P concentrations nearly 60-fold relative to control treatment (0.4 vs. 22 mg P L for control and fertilizer treatments, respectively). With exception of biological P removal (BPR) biosolids, all other tested biosolids yielded flow-weighted runoff P concentrations similar to untreated soils. Cumulative P and N losses (as a percentage of P and N applied) were greater from commercial inorganic fertilizer (∼38% of P and 46% of N) than any biosolids source (3% of P and 6% of N). Results demonstrate the value of water-extractable P (WEP) as an indicator of biosolids P loss potential.

Endocrine-disrupting compounds in reclaimed water and residential ponds and exposure potential for dislodgeable residues in turf irrigated with reclaimed water.

Endocrine-disrupting chemicals (EDCs) occur in reclaimed water (RW), which may serve as an exposure source for humans. The presence of EDCs in RW used to irrigate turf and in nearby water-retention ponds was determined. In addition, the total dislodgeable mass of each EDC was determined after irrigation (using RW) to simulate exposure of a 3-year-child playing in turf grass recently irrigated with RW. Five EDCs (estrone, 17ß-estradiol, 17α-ethynylestradiol, bisphenol A, and 4-n-nonylphenol) were quantified in 28 samples of RWs (wastewater-treatment plant effluents) and 88 samples from residential surface water-retention ponds. St. Augustine variety of turf grass was irrigated with spiked RW to study dislodgement of the five EDCs overtime using a drag-sled method. Grass clippings were analyzed to relate masses of EDC on grass with masses dislodged. EDCs were detected in both RW and ponds at ng/L concentrations. Maximum EDC masses were dislodged immediately after irrigation. Dislodged masses of estrone and 17ß-estradiol are two separate EDCs, 17ß-estradiol and 17α-ethynylestradiol decreased rapidly and were lower than detection limits 4 h after application. Dislodged bisphenol-A and nonylphenol decreased more slowly but were not detected 6 h after application. Avoiding contact with recently irrigated turf grass should decrease the risks of exposure to these EDCs.

Orthophosphate Leaching in St. Augustinegrass and Zoysiagrass Grown in Sandy Soil under Field Conditions.

Phosphorus (P) is required to maintain healthy, high-quality, warm-season turf. However, excessive P applications to soils with poor P retention capabilities may lead to leaching losses to groundwater. This field study was conducted to determine the maximum P fertilizer application rate to (Walt.) [Kuntze] 'Floratam' St. Augustinegrass (St. Augustinegrass) and 'Empire' zoysiagrass (zoysiagrass) below which P leaching is minimized. Five P levels ranging from 0 to 5.0 g P m yr were surface applied as triple superphosphate. Turf was established on an uncoated, low-P sand with negligible P retention capacity. Leaf and root growth, tissue P concentration, soil P concentration, soil P saturation, leachate volume, and orthophosphate (P) concentration in leachates were measured. Mehlich 1-extractable soil P (M1-P) and soil P saturation ratio (PSR) increased with time as the P rate increased. Lower M1-P and PSR values were measured with St. Augustinegrass, which absorbed more P than did zoysiagrass. The root system of St. Augustinegrass was larger and deeper compared with zoysiagrass, promoting greater P uptake and less P leaching. If tissue analysis indicates that P fertilization is required and the soil has the capacity to retain additional P, application of 0.8 g P m yr to zoysiagrass and 1.07 g P m yr to St. Augustinegrass is appropriate and does not result in increased P leaching.

Risk assessment of land-applied biosolids-borne triclocarban (TCC).

Triclocarban (TCC) is monitored under the USEPA High Production Volume (HPV) chemical program and is predominantly used as the active ingredient in select antibacterial bar soaps and other personal care products. The compound commonly occurs at parts-per-million concentrations in processed wastewater treatment residuals (i.e. biosolids), which are frequently land-applied as fertilizers and soil conditioners. Human and ecological risk assessment parameters measured by the authors in previous studies were integrated with existing data to perform a two-tiered human health and ecological risk assessment of land-applied biosolids-borne TCC. The 14 exposure pathways identified in the Part 503 Biosolids Rule were expanded, and conservative screening-level hazard quotients (HQ values) were first calculated to estimate risk to humans and a variety of terrestrial and aquatic organisms (Tier 1). The majority of biosolids-borne TCC exposure pathways resulted in no screening-level HQ values indicative of significant risks to exposed organisms (including humans), even under worst-case land application scenarios. The two pathways for which the conservative screening-level HQ values exceeded one (i.e. Pathway 10: biosolids➔soil➔soil organism➔predator, and Pathway 16: biosolids➔soil➔surface water➔aquatic organism) were then reexamined using modified parameters and scenarios (Tier 2). Adjusted HQ values remained greater than one for Exposure Pathway 10, with the exception of the final adjusted HQ values under a one-time 5 Mg ha(-1) (agronomic) biosolids loading rate scenario for the American woodcock (Scolopax minor) and short-tailed shrew (Blarina brevicauda). Results were used to prioritize recommendations for future biosolids-borne TCC research, which include additional measurements of toxicological effects and TCC concentrations in environmental matrices at the field level.

Toxicity and bioaccumulation of biosolids-borne triclosan in food crops.

Triclosan (TCS) is an antimicrobial compound commonly found in biosolids. Thus, plants grown in biosolids-amended soil may be exposed to TCS. We evaluated the plant toxicity and accumulation potential of biosolids-borne TCS in two vegetables (lettuce and radish) and a pasture grass (bahia grass). Vegetables were grown in growth chambers and grass in a greenhouse. Biosolids-amended soil had TCS concentrations of 0.99, 5.9, and 11 mg/kg amended soil. These TCS concentrations represent typical biosolids containing concentrations of 16 mg TCS/kg applied at agronomic rates for 6 to 70 consecutive years, assuming no TCS loss. Plant yields (dry wt) were not reduced at any TCS concentration and the no observed effect concentration was 11 mg TCS/kg soil for all plants. Significantly greater TCS accumulated in the below-ground biomass than in the above-ground biomass. The average bioaccumulation factors (BAFs) were 0.43 ± 0.38 in radish root, 0.04 ± 0.04 in lettuce leaves, 0.004 ± 0.002 in radish leaves, and <0.001 in bahia grass. Soybean (grain) and corn (leaves) grown in our previous field study where soil TCS concentrations were lower (0.04-0.1 mg/kg) had BAF values of 0.06 to 0.16. Based on the data, we suggest a conservative first approximate BAF value of 0.4 for risk assessment in plants.

Toxicity and bioaccumulation of biosolids-borne triclosan in terrestrial organisms.

Triclosan (TCS) is a common constituent of personal care products and is frequently present in biosolids. Application of biosolids to land transfers significant amounts of TCS to soils. Because TCS is an antimicrobial and is toxic to some aquatic organisms, concern has arisen that TCS may adversely affect soil organisms. The objective of the present study was to investigate the toxicity and bioaccumulation potential of biosolids-borne TCS in terrestrial micro- and macro-organisms (earthworms). Studies were conducted in two biosolids-amended soils (sand, silty clay loam), following U.S. Environmental Protection Agency (U.S. EPA) guidelines. At the concentrations tested herein, microbial toxicity tests suggested no adverse effects of TCS on microbial respiration, ammonification, and nitrification. The no observed effect concentration for TCS for microbial processes was 10 mg/kg soil. Earthworm subchronic toxicity tests showed that biosolids-borne TCS was not toxic to earthworms at the concentrations tested herein. The estimated TCS earthworm lethal concentration (LC50) was greater than 1 mg/kg soil. Greater TCS accumulation was observed in earthworms incubated in a silty clay loam soil (bioaccumulation factor [BAF] = 12 ± 3.1) than in a sand (BAF = 6.5 ± 0.84). Field-collected earthworms had a significantly smaller BAF value (4.3 ± 0.7) than our laboratory values (6.5-12.0). The BAF values varied significantly with exposure conditions (e.g., soil characteristics, laboratory vs field conditions); however, a value of 10 represents a reasonable first approximation for risk assessment purposes.

Biodegradation of triclosan in biosolids-amended soils.

Land application of biosolids can constitute an important source of triclosan (TCS) input to soils, with uncertain effects. Several studies have investigated the degradation potential of TCS in biosolids-amended soils, but the results vary widely. We conducted a laboratory degradation study by mixing biosolids spiked with [¹4C]-TCS (final concentration = 40 mg/kg) with Immokalee fine sand and Ashkum silty clay loam soils at an agronomic application rate (22 Mg/ha). Biosolids-amended soils were aerobically incubated in biotic and inhibited conditions for 18 weeks. Subsamples removed at 0, 2, 4, 6, 9, 12, 15, and 18 weeks were sequentially extracted with an operationally defined extraction scheme to determine labile and nonlabile TCS fractions. Over the 18-week incubation, the proportion of [¹4C] in the nonlabile fraction increased and the labile fraction decreased, suggesting decreasing availability to biota. Partitioning of TCS into labile and nonlabile fractions depended on soil characteristics. Less than 0.5% of [¹4C]-TCS was mineralized to carbon dioxide (¹4CO2) in both soils and all treatments. A degradation metabolite, methyl triclosan (Me-TCS), was identified in both soils only in the biotic treatment, and increased in concentration over time. Even under biotic conditions, biosolids-borne TCS is persistent, with a primary degradation (TCS to Me-TCS) half-life of 78 d in the silty clay loam and 421 d in the fine sand. A half-life of approximately 100 d would be a conservative first approximation of TCS half-life in biosolids-amended soils for risk estimation.

Long-term reclaimed water application effects on phosphorus leaching potential in rapid infiltration basins.

Rapid infiltration basins (RIBs) are effective tools for wastewater treatment and groundwater recharge, but continuous application of wastewater can increase soil P concentrations and subsequently impact groundwater quality. The objectives of this study were to (1) investigate the effects of reclaimed water infiltration rate and "age" of RIBs on soil P concentrations at various depths, and (2) estimate the degree (percentage) of sorption equilibrium reached between effluent P and soil attained during reclaimed water application to different RIBs. The study was conducted in four contrasting cells of a RIB system with up to a 25 year history of secondary wastewater application. Soil samples were collected from 0 to 300 cm depth at 30 cm intervals and analyzed for water extractable phosphorus (WEP) and oxalate extractable P, Al, and Fe concentrations. Water extractable P and P saturation ratio (PSR) values were generally greater in the cells receiving reclaimed water compared to control soils, suggesting that reclaimed water P application can increase soil P concentrations and the risk of P movement to greater depths. Differences between treatment and control samples were more evident in cells with longer histories of reclaimed water application due to greater P loading. Data also indicated considerable spatial variability in WEP concentrations and PSR values, especially within cells from RIBs characterized by fast infiltration rates. This occurs because wastewater-P flows through surface soils much faster than the minimum time required for sorption equilibrium to occur. Studies should be conducted to investigate soil P saturation at deeper depths to assess possible groundwater contamination.

Aluminum water treatment residuals as permeable reactive barrier sorbents to reduce phosphorus losses.

Two aluminum water treatment residuals (Al-WTRs) from water treatment plants in Manatee County, FL and Punta Gorda, FL were evaluated as potential permeable reactive barrier (PRB) media to reduce groundwater phosphorus (P) losses. Short-term (<24h) P sorption kinetics and long-term P sorption capacity were determined using batch equilibration studies. Phosphorus desorption was characterized following P loadings of 10, 20, 30, 40 and >70 g kg(-1). Sorption and desorption studies were conducted on the <2.0mm material and three size fractions within the <2.0mm material. The effect of dissolved organic carbon (DOC) on P retention was determined by reacting Al-WTRs with P-spiked groundwater samples of varying initial DOC concentrations. Phosphorus sorption kinetics were rapid for all size fractions of both Al-WTRs (>98% P sorption effectiveness at shaking times ≥2 h). The effect of DOC was minimal at <150 mg DOCL(-1), but modest reductions (<22%) in P sorption effectiveness occurred at 587 mg DOC L(-1). The P sorption capacities of the Manatee and Punta Gorda Al-WTRs (<2.0mm) are ∼44 g kg(-1) and >75 g kg(-1), respectively, and the lifespan of an Al-WTR PRB is likely many decades. Desorption was minimal (<2% of the P sorbed) for cumulative P loadings <40 g kg(-l), but increased (<9% of the P sorbed) at cumulative P loads >70 g kg(-1). The <2.0mm Manatee and Punta Gorda Al-WTRs are regarded as ideal PRB media for P remediation.

Toxicity and bioaccumulation of biosolids-borne triclocarban (TCC) in terrestrial organisms.

Triclocarban (TCC) toxicity and bioaccumulation data are primarily limited to direct human and animal dermal exposures, animal ingestion exposures to neat and feed-spiked TCC, and/or aquatic organism exposures. Three non-human, terrestrial organism groups anticipated to be the most highly exposed to land-applied, biosolids-borne TCC are soil microbes, earthworms, and plants. The three ecological receptors are expected to be at particular risk due to unique modes of exposure (e.g. constant, direct contact with soil; uptake of amended soil and pore water), inherently greater sensitivity to environmental contaminants (e.g. increased body burdens, permeable membranes), and susceptibility to minute changes in the soil environment. The toxicities of biosolids-borne TCC to Eisenia fetida earthworms and soil microbial communities were characterized using adaptations of the USEPA Office of Prevention, Pesticides, and Toxic Substances (OPPTS) Guidelines 850.6200 (Earthworm Subchronic Toxicity Test) and 850.5100 (Soil Microbial Community Toxicity Test), respectively. The resultant calculated TCC LC50 value for E. fetida was 40 mg TCC kg amended fine sand(-1). Biosolids-borne TCC in an amended fine sand had no significant effect on soil microbial community respiration, ammonification, or nitrification. Bioaccumulation of biosolids-borne TCC by E. fetida and Paspulum notatum was measured to characterize potential biosolids-borne TCC movement through the food chain. Dry-weight TCC bioaccumulation factor (BAF) values in E. fetida and P. notatum ranged from 5.2-18 and 0.00041-0.007 (gsoil gtissue(-1)), respectively.

Retention-release characteristics of triclocarban and triclosan in biosolids, soils, and biosolids-amended soils.

Transport models that incorporate retention/release characteristics of organic compounds in soils and sediments typically assume that organic-carbon normalized partition coefficients (K(OC)) apply to all solid matrices and that the partitioning process is completely reversible. Partition coefficients (K(d)) (from which the K(OC) was calculated), and retention/release characteristics of triclocarban (TCC) and triclosan (TCS) in biosolids, soils, and biosolids-amended soils were determined. Four soils of different physicochemical properties amended with biosolids at 10 g/kg, together with unamended soils, and several biosolids were separately spiked with either [(14)C]TCC or [(14)C]TCS for the various determinations. The hysteresis coefficient values of the two compounds were consistently <1 in all three solid matrices, suggesting strong hysteresis. Multiple desorption steps (24 h each) over several days revealed incomplete desorption of the two compounds from all three solid matrices. The K(d) values determined in biosolids (log K(d) 3.34 +/- 0.13 for TCC and 3.76 +/- 0.39 for TCS) were greater than those determined in soils (log K(d) 1.71 +/- 0.09 for TCC and 2.25 +/- 0.26 for TCS) and biosolids-amended soils (log K(d)1.90 +/- 0.16 for TCC and 2.31 +/- 0.19 for TCS), however, the K(OC) values of all three solid matrices were similar (log K(OC) of 3.82 +/- 0.16 for TCC and 4.26 +/- 0.31 for TCS). Thus, it was concluded that a single or a narrow range of K(OC) values for TCC and TCS may be appropriate to describe retention of the compounds in soils and sediments. However, models that assume complete reversibility of the retention/release processes of the compounds in soils and sediments may not adequately describe the retention/release characteristics of the compounds in soils and sediments, especially when the chemicals are biosolids borne.

Fate of 14C-triclocarban in biosolids-amended soils.

Triclocarban (TCC) is an antibacterial compound commonly detected in biosolids at parts-per-million concentrations. Approximately half of the biosolids produced in the United States are land-applied, resulting in a systematic release of TCC into the soil environment. The extent of biosolids-borne TCC environmental transport and potential human/ecological exposures will be greatly affected by its bioavailability and the rate of degradation in amended soils. To investigate these factors, radiolabeled TCC ((14)C-TCC) was incorporated into anaerobically digested biosolids, amended to two soils, and incubated under aerobic conditions. The evolution of (14)CO2 (biodegradation) and changes in chemical extractability (bioavailability) was measured over time. Water extractable TCC over the study period was low and significantly decreased over the first 3 weeks of the study (from 14% to 4% in a fine sand soil and from 3 to <1% in a silty clay loam soil). Mineralization (i.e. ultimate degradation), as measured by evolution of (14)CO(2), was <4% over 7.5 months. Methanol extracts of the amended soils were analyzed by radiolabel thin-layer chromatography (RAD-TLC), but no intermediate degradation products were detected. Approximately 20% and 50% of the radioactivity in the amended fine sand and silty clay loam soils, respectively, was converted to bound residue as measured by solids combustion. These results indicate that biosolids-borne TCC becomes less bioavailable over time and biodegrades at a very slow rate.

Measured physicochemical characteristics and biosolids-borne concentrations of the antimicrobial Triclocarban (TCC).

Triclocarban (TCC) is an active ingredient in antibacterial bar soaps, a common constituent of domestic wastewater, and the subject of recent criticism by consumer advocate groups and academic researchers alike. Activated sludge treatment readily removes TCC from the liquid waste stream and concentrates the antimicrobial in the solid fraction, which is often processed to produce biosolids intended for land application. Greater than half of the biosolids generated in the US are land-applied, resulting in a systematic release of biosolids-borne TCC into the terrestrial and, potentially, the aquatic environment. Multiple data gaps in the TCC literature (including basic physicochemical properties and biosolids concentrations) prevent an accurate, quantitative risk assessment of biosolids-borne TCC. We utilized the USEPA Office of Prevention, Pesticides, and Toxic Substances (OPPTS) harmonized test guidelines to measure TCC solubility and log K(ow) values as 0.045 mg L(-1) and 3.5, respectively. The measured physicochemical 2 properties differed from computer model predictions. The mean concentration of TCC in 23 biosolids representative of multiple sludge processing methods was 19+/-11 mg kg(-1).

Phosphorus release from a biosolids-amended sandy spodosol.

Most regulations governing biosolids land application do not consider that phosphorus (P) solubility can vary widely among biosolids. Current regulations typically group all biosolids together in one category or group biosolids together with manures. Research has shown that not all biosolids have the same potential to affect the environment when land applied, but the database is limited. The purpose of this study was to characterize P release from several biosolids produced and/or marketed in Florida. A small soil column dynamic laboratory incubation was conducted to assess P release potential. Eleven biosolids and a mineral fertilizer (triple super phosphate) were individually mixed with a typical low-P sorbing Florida soil (Immokalee fine sand) at 56 and 224 kg P ha(-1). Columns were periodically leached over 5.5 mo to attain 60 mL (1/2 pore volume) of drainage in each leaching. Soluble reactive P was determined and summed over the eight leachings to represent total P source release. Cumulative P release (as a percentage of P applied) was greatest from biological P removal (BPR) and BPR-like biosolids and least from heat-dried materials. Phosphorus release from biosolids depends on biosolids treatment type (digestion) and P chemistry, suggesting that biosolids regulations must account for differences in P lability to accurately gauge environmental risk.

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.

Surface applied water treatment residuals affect bioavailable phosphorus losses in Florida sands.

Water treatment residuals (WTR) can reduce runoff P loss and surface co-application of P-sources and WTR is a practical way of land applying the residuals. In a rainfall simulation study, we evaluated the effects of surface co-applied P-sources and an Al-WTR on runoff and leacheate bioavailable P (BAP) losses from a Florida sand. Four P-sources, namely poultry manure, Boca Raton biosolids (high water-soluble P), Pompano biosolids (moderate water-soluble P), and triple super phosphate (TSP) were surface applied at 56 and 224 kg P ha(-1) (by weight) to represent low and high soil P loads typical of P- and N-based amendments rates. The treatments further received surface applied WTR at 0 or 10 g WTR kg(-1) soil. BAP loss masses were greater in leachate (16.4-536 mg) than in runoff (0.91-46 mg), but were reduced in runoff and leachate by surface applied WTR. Masses of total BAP lost in the presence of surface applied WTR were less than approximately 75% of BAP losses in the absence of WTR. Total BAP losses from each of the organic sources applied at N-based rates were not greater than P loss from TSP applied at a P-based rate. The BAP loss at the N-based rate of moderate water-soluble P-source (Pompano biosolids) was not greater than BAP losses at the P-based rates of other organic sources tested. The hazards of excess P from applying organic P-sources at N-based rates are not greater than observed at P-based rates of mineral fertilizer. Results suggest that management of the environmental P hazards associated with N-based rates of organic materials in Florida sands is possible by either applying P-sources with WTR or using a moderate water-soluble P-source.

Controlled application rate of water treatment residual for agronomic and environmental benefits.

Water treatment residuals (WTR) are useful soil amendments to control excessive soluble phosphorus (P) in soils, but indiscriminate additions can result in inadequate control or excessive immobilization of soluble P, leading to crop deficiencies. We evaluated the influence of application rates of an Al-WTR and various P-sources on plant yields, tissue P concentrations, and P uptake and attempted to identify a basis for determining WTR application rates. Bahiagrass (paspalum notatum Fluggae) was grown in a P-deficient soil amended with four P-sources at two application levels (N- and P-based rates) and three WTR rates (0, 10, and 25 g kg(-1) oven dry basis) in a glasshouse pot experiment. The glasshouse results were compared with data from a 2-yr field experiment with similar treatments that were surface applied to an established bahiagrass. Soil P storage capacity (SPSC) values increased with application rate of WTR, and the increase varied with sources of P applied. Soil soluble P concentrations increased as SPSC was reduced, and a change point was identified at 0 mg kg(-1) SPSC in the glasshouse and the field studies. A change point was identified in the bahiagrass yields at a tissue P concentration of 2.0 g kg(-1), corresponding to zero SPSC. Zero SPSC was shown to be an agronomic threshold above which yields and P concentrations of plants declined and below which there is little or no yield response to increased plant P concentrations. Applying P-sources at N-based rates, along with WTR sufficient to give SPSC value of 0 mg kg(-1) SPSC, enhanced the environmental benefits (reduced P loss potential) without negative agronomic impacts.