Biosolids Rates Research Articles

Analysis of effects and factors linked to soil microbial populations and nitrogen cycling under long-term biosolids application

Information about impacts of long-term biosolids application on soil microbial populations and functional groups and N cycling is important for evaluating soil health and agroecosystem sustainability under long-term biosolids application. Mine spoil plots received annual biosolids application from 1973 to 2010 at low (16.8 Mg ha−1 yr−1), medium (33.6 Mg ha−1 yr−1), and high rates (67.2 Mg ha−1 yr−1). A no-biosolids control received chemical fertilizer at the agronomic rate. Soil samples were collected in three seasons per year spanning 2003–2005 for measuring soil moisture, pH, soil organic C (SOC), total and extractable heavy metals (Cd, Cu, Ni, Zn), NO3−, N mineralization potential (NMP), microbial biomass C (MBC), and populations of three N-cycling bacteria (NCB) groups: ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and denitrifying bacteria (DNB). Soil samples were collected again in 2008 and 2010 for quantifying total and extractable heavy metals, and in 2018 (eight years after biosolids applications ended) for measuring SOC, MBC, NMP, and microbial respiration. During 2003–2005, mean MBC was 315, 554, 794, and 1001 mg kg−1 in the control, low, medium, and high biosolids treatments, respectively. Populations of NCB did not differ among treatments. Biosolids application increased total and extractable metal concentrations but the effect of biosolids rates were much lower on extractable than total concentrations. Soil extractable Cd and Cu concentrations decreased from medium to high applications, likely due to complexing with biosolids organic matter. Partial least squares regression analysis identified a strong positive effect on MBC of SOC and a weak negative effect of Cu, explaining the strong net positive effect of biosolids on MBC. In 2018, the medium and high biosolids treatments maintained higher SOC, MBC, NMP, and microbial respiration than the control. This study provided further evidence that long-term biosolids application has positive effects on soil microbes that persist for years after ending application.

Agronomic impacts of new regulations governing land application of Class B biosolids in Florida

AbstractAlthough land application of biosolids is an attractive option for beneficial reuse, it represents a complex challenge for government and private organizations. This 3‐year field study evaluated the agronomic impacts of reduced biosolids rates imposed by new regulations in Florida on bahiagrass (Paspalum notatum Flugge) herbage accumulation and nutritive value. Treatments consisted of a factorial combination of two phosphorus (P) sources (triple superphosphate and biosolids) applied at 0 (control), 20 (low), 40 (intermediate), and 60 kg total P ha−1 (high). Triple superphosphate plots received the same nitrogen (N) load (from ammonium nitrate) as the corresponding biosolids treatments. Bahiagrass herbage accumulation increased with increasing P and associated N rates. Bahiagrass annual herbage accumulation ranged from 2120 kg ha−1 in 2022 to 6970 kg ha−1 in 2020 and was 33%–80% less than previously published data. This was likely due to the reduced biosolids rates that did not supply sufficient N and P to sustain adequate forage production. Lesser herbage accumulation will likely lead to greater application of inorganic fertilizers, which generally have greater environmental footprint than biosolids. Biosolids generally resulted in either similar or greater bahiagrass crude protein, in vitro digestible organic matter, and tissue mineral concentrations than inorganic fertilizer. Similarly, no differences in bahiagrass N and P recovery between biosolids and inorganic fertilizer were observed. This study, along with a significant body of literature, demonstrated that biosolids have considerable fertilizer value and can be an effective alternative to commercial inorganic fertilizer while also providing environmental and economic benefits.

Effects of drinking water treatment residual amendments to biosolids on plant uptake of per- and polyfluoroalkyl substances.

Drinking water treatment residuals (DWTRs), solid by-products of drinking water treatment, are dominated by calcium (Ca), iron (Fe), or aluminum (Al), depending on the coagulant used. DWTRs are often landfilled, but current research is exploring options for beneficial reuse. Previous studies have shown that Al- and Fe-rich materials have potential to reduce the mobility of per- and polyfluoroalkyl substances (PFAS). Here, we investigated how amending biosolids with 5%wt/wt DWTRs affected plant bioavailable PFAS in two different simulated scenarios: (1) agricultural scenario with Solanum lycopersicum (tomato) grown in soil amended with an agronomically relevant rate of DWTR-amended biosolids (0.9% w/w, resulting in 0.045% w/w DWTR in the biosolids-amended soil) and (2) mine reclamation scenario examining PFAS uptake by Lolium perenne (perennial ryegrass) grown in soil that received DWTR-amended biosolids amendment at a rate consistent with the mine remediation (13% w/w, resulting in 0.65% w/w DWTR in the biosolids-amended soil). Amending biosolids with Ca-DWTR significantly reduced perfluorobutanoic acid (PFBA) uptake in ryegrass and perfluorohexanoic acid uptake in tomatoes, possibly due to DWTR-induced pH elevation, while Fe-DWTR amendment reduced PFBA bioaccumulation in ryegrass. The Al-DWTR did not induce a significant reduction in accumulated PFAS compared to controls. Although the reasons for this finding are unclear, the relatively low PFAS concentrations in the biosolids and relatively high Al content in the biosolids and soil may be partially responsible.

Assessment of availability of trace elements in turf soil after biosolids application

AbstractSoil amendments rich in organic matter and micronutrients can benefit plants by increasing the availability of micronutrients. To evaluate changes in the availability of trace elements in biosolids‐amended soil, soil and plant samples were collected from six managed turfgrass locations across the Chicago metropolitan area that received air‐dried biosolids topdressing at two rates: 2.2 Mg ha–1 per application (low biosolids rate), 11 Mg ha–1 per application (high biosolids rate), and urea 48.8 kg ha–1 total N per application (control). The low and high rates refer to biosolids total N and plant‐available N, respectively, considered for meeting the turfgrass N recommendation. Biosolids and urea application was conducted for each year of 2006–2008 with multiple applications per year. For micronutrients tested, biosolids application increased concentrations of soil‐available (Mehlich‐3 extraction) Zn (29.5 ± 2.9 mg kg–1, mean ± SE) and Cu (9.0 ± 0.6 mg kg–1) for the high rate vs. the control (10.4 ± 2.9 mg kg–1 for Zn and 6.1 ± 0.7 mg kg–1 for Cu). Soil‐available Mn, Fe, and Mo in the biosolids treatments did not differ from the control. Application of biosolids increased turf plant Cu, Zn, Mn, and Mo concentrations for both 2007 and 2008 and Fe for 2007 vs. the control with statistical significance at the high rate of biosolids. Topdressing with a plant‐available N‐based application rate for biosolids increased turfgrass nutrition of micronutrients without a concern of heavy metals.

The Clean Water Act and biosolids: A 45‐year chronological review of biosolids land application research in Colorado

The 1972 U.S. Clean Water Act set forth the generation of biosolids. In Colorado, biosolids land application research began in 1976 and continues today. Pastureland research suggested that sewage effluent could effectively be land applied to benefit aboveground plant growth and to polish water prior to reaching receiving waters. Forest wildfire-affected ecosystems can also benefit from biosolids applications; application rates of up to 80 Mg ha-1 can lead to greater plant establishment, soil microbial activity, and nutrient turnover and reduced nutrient and heavy metal concentrations in runoff below livestock and USEPA drinking water standards. Long-term (24-yr) observations in oil shale-mined lands showed that biosolids (up to 224 Mg ha-1 ) can have a positive effect on microbial-mediated nutrient cycling and, in turn, on aboveground plant community structure. Biosolids applications of up to 40 Mg ha-1 in high-elevation shrubland ecosystems, dominated by Mo-containing shale deposits, can aid in reducing imbalances between Mo and Cu in soils and plants; excessive plant Mo, when consumed by ruminants, can lead to molybdenosis. Biosolids and lime applications (both at 224 Mg ha-1 ) have been shown to improve long-term reclamation success on acid-generating, heavy metal-containing fluvial mine tailings. Thirty years of grazing land research, focused on soil and aboveground plant benefits, illustrate that soil health and plant productivity can be improved to the greatest extent at biosolids application rates close to 10 Mg ha-1 . Finally, 40 yr of dryland agroecosystem research (a) have helped identify biosolids N fertilizer equivalency (∼8kg N Mg-1 ) and thus dryland winter wheat application rates (e.g., 4.5-6.7 dry Mg ha-1 ); (b) have identified first-year mineralization rates of 25-32%; (c) dispute the "time bomb" theory by showing that plant metal uptake follows an exponential rise to a maximum; (d) showcase economic return to producers via increased wheat grain protein content; (e) suggest that biosolids-borne proteins and their degradation products are labile C and N sources; (f) have led to long-term tracking of micronutrients and heavy metals in soils and revealed that plants-soil concentrations will not lead to groundwater degradation and that plants are safe for human consumption; and (g) have shown that biosolids provide Zn, helping to overcome soil deficiencies and enhancing Zn biofortification in wheat grain. This latter point is important because ∼2 billion people globally suffer from Zn deficiencies. Forty-five years of research in Colorado have proven that biosolids can enhance environmental quality, improve soil health, and produce healthy food products.

Short-term amendment of biosolid on agricultural soil: effects on C and N mineralization and microbial activity

Adding biosolids to agricultural soils can improve its quality through increased storage of C and N. A study to analyze the short-term impact of the addition of biosolids on the release of nutrients and the microbial activity in agricultural soil was carried out. The microbial biomass C (MB-C), urease activity (UA), and mineralization of N and C at different application rates of biosolids were evaluated (0 mg, 100mg and 200 mg of N-NH4+ kg-1). In addition, a biosolid-only treatment was tested. It was observed an increase in C and N mineralization, NH3 volatilization, and MB-C content, according to the application rate of biosolids. In biosolid treatments, UA increased 100% on average in the first seven days of incubation. These results suggest that the nutrient content in the soil is improved and microbial activity is positively stimulated.

Impact of nitrogen input from biosolids application on carbon sequestration in a Pinus radiata forest

Forest management practices (e.g. choice of stand density, fertilisation) are just as important in carbon (C) forestry as in other types of forestry and will affect the level of C sequestration and profitability. Because C stored in wood is approximately proportional to the product of its volume and density, it is necessary to account for both volume growth and wood density when assessing the effects of fertilisation on C sequestration in pine forests. The effects of nitrogen (N) input from biosolids application on forest C sequestration were quantified from an intensively monitored biosolids field trial in a Pinus radiata plantation on a sandy soil in New Zealand. The field trial tested the application of three biosolids rates: Control (no application), Standard (300 ​kg ​N·ha −1 applied every three years), and High (600 ​kg ​N·ha −1 applied every three years), across three levels of stand density: 300, 450, and 600 stems·ha −1 . Carbon sequestration was estimated using the C-Change model from annual plot measurements of stand density, stem height and diameter, and annual breast height wood densities obtained from increment cores. By age 24 years, N-fertilised trees had sequestered 40 ​t ​C·ha −1 more than unfertilised trees, an increase of 18%. Fertilisation increased stem volume by 23% but reduced stem wood density by 2.5%. Most of the increased C sequestration occurred between age 6 and age 17 years and the Standard rate gave the same increase in C sequestration as the High rate. On average, there was no significant difference in growth rate between fertilised and unfertilised trees after the 17th growth year, but the increased growth ceased earlier at higher stand densities, and later at lower stand densities. This study indicates that 2–3 applications of the Standard rate would have been sufficient to achieve the increased C sequestration, with an applied N to C conversion ratio of 43–65 ​kg ​C·kg −1 N. Our results highlight that N fertilisation will become more widespread under greenhouse gas emissions trading schemes which encourages forest management practices that improve C sequestration in young forests in New Zealand in particular and other countries in general.

Immobilization of lead by amendments in a mine-waste impacted soil: Assessing Pb retention with desorption kinetic, sequential extraction and XANES spectroscopy

Chemical stabilization is an in-situ remediation that uses amendments to reduce contaminant availability in polluted soils. Rates of phosphate, lime, biochar, and biosolids were evaluated as affecting Pb speciation and mobility in soil samples of a mining area located in Vazante, state of Minas Gerais, Brazil. Chemical and mineralogical characterization, desorption kinetics, sequential extraction, leaching evaluation in columns and speciation using X-ray absorption near edge structure were performed. Pb adsorbed on bentonite and on anglesite were the predominant species in the unamended soil. The treatments with phosphate and lime transformed part of the Pb species to pyromorphite. Conversely, part of Pb species was transformed to Pb adsorbed on citrate in the soil amended with biochar, while PbCl2 was formed in soil samples amended with biosolids. Phosphate and lime increased the Pb extracted in the residual fraction, thus showing that more recalcitrant species, such as pyromorphite, were formed. Biosolids and biochar treatments decreased the Pb in the residual fraction, and the fraction associated to organic matter increased after the addition of biosolids. Phosphate and lime were effective to immobilize Pb and to decrease Pb desorption kinetics, but the organic amendments increased the desorption kinetics of Pb in all rates applied. The soil amended with phosphate decreased the Pb leached in the experiment with leaching columns.

Soil carbon response to long-term biosolids application.

Astudy was conducted in three agroecosystems in California (Sacramento, Solano, and Merced counties) that received biosolids applications for 20 yr. Management varied in application rates and frequencies, resulting in average cumulative amount of biosolids applied of 74 (Solano), 105 (Merced), and 359 (Sacramento) Mg biosolidsdry ha-1 , resulting in the addition of 26 (Solano), 36 (Merced), and 125 (Sacramento) Mg biosolids-C ha-1 . Measurements included soil organic carbon (SOC) and total nitrogen (N) concentrations from 0 to 100 cm and microbial biomass C (MBC) and microbial biomass N (MBN) from 0 to 30 cm in biosolids-amended and control sites. Biosolids treatments had greater amounts of SOC and total N at all sites, and MBC and MBN were greatest at Sacramento and Solano. The largest increases in SOC were at the site that received the lowest cumulative loading rate of biosolids (Solano), where SOC content to 100 cm was 50% greater in amended soils (p<.001). Net changes in soil C stocks to 30 cm were 0.4±0.1 (Solano), -0.04±0.1 (Merced), and 0.3±0.2 (Sacramento) Mg C ha-1 yr-1 . These values change when considering deeper soil depths (0-100 cm) to 0.5±0.1 (Solano), 0.2±0.2 (Merced), and 0.216±0.2 (Sacramento) Mg C ha-1 yr-1 , reflecting differences in C stocks changes in surface and subsurface soils across sites. Rates of C storage per dry Mg of biosolids per year applied were 1±0.2 (Solano), 0.5±0.4 (Merced), and 0.04±0.1 (Sacramento). Our results suggest that local controls on soil C stabilization are more important than amendment application amount at predicting climate benefits and that accounting for soil C changes below 30 cm can provide insight for sequestering C in agroecosystems.

Environmental Impacts of Using Municipal Biosolids on Soil, Plant and Groundwater Qualities

This study was conducted to evaluate the effect of three different rates of municipal biosolids produced in Qatar on plant characteristics and soil texture and its potential impacts on groundwater. Petunia atkinsiana, was used in this study. The experiment took place in a greenhouse in pots with soil mixed with 0, 3, 5, and 7 kg/m2 biosolids. Pelletized class A biosolids from the Doha North Sewage Treatment Plant were used. Results revealed significant differences in all measured parameters, which were affected by biosolid treatments compared to the control treatment. Electrical conductivity, pH, macro and micronutrients and heavy metals were significantly affected by biosolid treatments. The comparison of the discovered levels against the international acceptable ceilings of pollutants indicated the advantages of utilizing class A biosolids, as they were well below the international acceptable levels and showed the best test rates, indicating that the product is a sustainable and efficient organic fertilizer for ornamental plants. Furthermore, the results highlight no potential significant impacts on groundwater due to trace presence of heavy metals, owing to the nature of deep groundwater in Qatar and the usage of modern irrigation devices that fulfil the exact needs of plants in a harsh climate and high evaporation rate.

Zero-Valent Iron Nanoparticles Remediate Nickel-Contaminated Aqueous Solutions and Biosolids-Amended Agricultural Soil.

Nickel (Ni+2) accumulation in wastewater treatment sludge poses a potential environmental risk with biosolids-land application. An incubation experiment was conducted to evaluate the effect of nanoparticles of zero-valent iron (nZVI) on Ni+2 sorption in biosolids-treated agricultural soils. Two application rates of biosolids (0, 5%, w/w) and four treatment levels (0, 1, 5, and 10 g/kg) of nZVI were examined, either separately or interactively. The results of this study showed significant differences in Ni+2 sorption capacity between different nZVI treatments. The initial Ni+2 concentration in biosolids-amended soil significantly affected Ni sorption in the soil treated with nZVI. The “H-shape” of sorption isotherm in nZVI-treated soil reflects strong interaction between the Ni concentration and the nZVI treatment, while the C-shape of sorption isotherm in biosolids-amended soil without the nZVI treatment indicates intermediate affinity for Ni+2 sorption. Nickel retention in soil was increased with the increase of nZVI levels. The removal efficiency of Ni+2 by nZVI from solution was increased with the increase of pH from 5 to 11 and reached a maximum of 99.56% at pH 11 and nZVI treatment of 10 g/kg. The Ni+2 desorption rate decreased from 92 to 7, 4, and 1% with increasing nZVI treatment levels from 0 to 1, 5, and 10 g/kg, respectively, with a soil Ni+2 concentration of 50 mg/L. The maximum adsorption capacity (𝑞max) of 10 g/kg nZVI-treated soil was 333.3 mg/g, which was much higher than those from the other treatments of 0 (5 mg/g), 1 (25 mg/g), and 5 g/kg (125 mg/g). The underlying mechanism for Ni+2 immobilization using nZVI in an aquatic environment is controlled by a sorption process, reduction of metal ion to zero-valent metal, as well as (co)precipitation. Moreover, increasing the nZVI treatment level in biosolids-amended soil significantly decreased bioavailable Ni+2 concentrations in the soil.

Enhanced Mesophilic Anaerobic Digestion of Primary Sewage Sludge

Processing of the produced primary and secondary sludge during sewage treatment is demanding and requires considerable resources. Most common practices suggest the cotreatment of primary and secondary sludge starting with thickening and anaerobic digestion. The aim of this study is to investigate the anaerobic digestion of the primary sludge only and estimate its impact on sludge treatment and energy recovery. Within this context, the performance of the anaerobic digestion of primary sludge is explored and focused on practices to further enhance the methane production by using additives, e.g., a cationic polyelectrolyte and attapulgite. The results showed that the overall yield in methane production during anaerobic digestion of primary sludge alone was higher than that obtained by the anaerobic digestion of mixed primary and secondary sludge (up to 40%), while the addition of both organic polyelectrolyte and attapulgite enhanced further the production of methane (up to 170%). Attapulgite increased the hydrolysis rate of biosolids and produced relatively stabilized digestate, though of lower dewaterability. Moreover, the results suggest that single digestion of primary sludge may accomplish higher methane production capacities at lower digestors’ volume increasing their overall efficiency and productivity, while the produced digestates are of adequate quality for further utilization mainly in agricultural or energy sectors.

Long-term accumulation, depth distribution, and speciation of silver nanoparticles in biosolids-amended soils.

Biosolids can be a source of metals and metal nanoparticles. The objective of this study was to quantify and characterize the accumulation and transport of silver (Ag) in a natural soil that has received agronomically recommended rates of biosolids as fertilizer from 1994 to 2017. Total Ag concentrations were measured in biosolids and soil samples collected from 0 to 10cm between 1996 and 2017. The depth distribution of Ag in soil to 60-cm depth was measured in 2017. Electron microscopy, in combination with X-ray spectroscopy, and X-ray absorption spectroscopy were used to characterize the Ag. The Ag concentrations in the biosolids-amended soil increased steadily from 1996 until 2007, after which the concentrations leveled off at about 1.25mg Ag kg-1 soil. This corresponded with a decrease of Ag concentrations in biosolids over time. The majority of the Ag (82%) was confined to the top 10cm of the soil, small amounts (14%) were detected at 10-to-20-cm depth, and trace amounts (4%) were detected at 30-to-40-cm depth. The Ag in the biosolids was identified as S-containing nanoparticles (Ag2 S) with a diameter of 10-12nm; however, in soil, the Ag concentrations were too low to allow identification of Ag speciation. This study shows that in a real-world field scenario, biosolids applied at agronomic rates represent a long-term, economically viable source of crop nutrients without increasing the concentration of total Ag in soil above a maximum of 1.5mg Ag kg-1 . This concentration is below estimated ecotoxicity limits for Ag2 S in soil.

Nanosized water treatment residuals improve water retention and phytoavailability of P and Al in biosolids-amended soil

Two lysimeter experiments were conducted to evaluate the impacts of biosolids and drinking water treatment residual nanoparticles (nWTRs) on phosphorus and aluminum phytoavailability and yield of corn plants. Two consecutive experiments were conducted with different application rates of biosolids (0% and 3%) and nWTRs (0%, 0.1%, 0.2%, and 0.3%). The results revealed that the total biomass production (grain plus stover) increased significantly (p < .05) as a result of nWTRs application at 0.1% rate. Application of nWTRs to biosolids-treated soil slightly decreased yield at 0.2% and 0.3% application rates. The best combination ratio between nWTRs and biosolids at which high corn yield is 0.1% nWTRs to 3% biosolids. Application of 3% biosolids significantly increased bioavailable P in the studied soil, but application of 0.3% nWTRs significantly decreased the bioavailable P concentrations in soil in the two seasons of cultivation. Application of nWTRs at 0.1% and 0.2% rates decreased soil pH in the soil treated with 3% biosolids in first and second seasons of cultivation in comparison with control treatment. The application of nWTRs greatly and significantly (p < .05) increased the water-holding capacity of studied soil treated with and without biosolids.

Use of biosolids for sod production: Impact on the import/export of nutrients, heavy metals, and soil mineral matter

AbstractSod production has been criticized as being unsustainable because of the soil export that occurs at each harvest. Wastewater treatment residuals (biosolids) disposal is often limited by nutrient or metal accumulation in the soil. Biosolids‐based sod production may be a solution to minimize soil loss and land‐apply wastewater residuals. The objectives of this study were to assess biosolids‐based sod production impact on import and export of nutrients, heavy metals, carbon, and to quantify soil loss from sod harvest with and without biosolids. Anaerobically digested, dewatered sludge (Cake) and Cake mixed with sand and sawdust (MetroMix) were applied at three rates based on estimated plant available nitrogen (PAN). An additional treatment mimicked conventional sod production practices that rely on synthetic fertilizer. All biosolids rates and sources increased Mehlich‐3 extractable phosphorus (P) to &gt; 175 mg kg−1 in the harvested sod, which could contribute to P runoff or leaching at the site of establishment. Heavy metal concentrations from both biosolids sources were below EPA loading limits and would require over 200 years of regular application (22 Mg ha−1) to exceed EPA maximum cumulative loading limits. Biosolids at 22 Mg ha−1 did little to reduce soil mineral matter loss compared to conventionally grown sod. After two sod production cycles, soil carbon increased by 50% in the surface soil (0–10 cm), but was reduced at a depth of 20–30 cm. While high P concentrations in the biosolids limit repeated applications, moderate use of biosolids may alleviate reliance on synthetic fertilizers for N and P.

Traceability of organic contaminants in the sludge line of wastewater treatment plants: A comparison study among schemes incorporating thermal hydrolysis treatment and the conventional anaerobic digestion

The traceability of conventional pollutants and 10 organic microcontaminants in the sludge line of a wastewater treatment plant (WWTP) was evaluated. The application of thermal hydrolysis (TH) as pre-treatment to anaerobic digestion (AD) or as inter-treatment (between two AD stages) was considered and compared with the conventional digestion scheme. TH scenarios reduced the mass flow rate of biosolids (40–60%) as well as the ratio of solids (50–100%), organic matter (5–26%) and nitrogen (8–13%) destined to biosolids. Micropollutants showed a strong tendency to accumulate in the solid phase (more than 90% were sorbed) in spite of thermal and dewatering processes, but TH scenarios exhibited greater removal efficiency (80%) in comparison to conventional AD (50%), reducing the ratio of micropollutants destined to biosolids from a conventional 48% to 7–8%. These findings reveal that TH could increase the value of biosolids from sewage sludge treatment because of greater removal of pollutants and dewaterability.

Responses of nematode, bacterial, and fungal populations to high frequency applications and increasing rates of biosolids in an agricultural soil

Responses of nematode, bacterial, and fungal populations to high frequency applications and increasing rates of biosolids in an agricultural soil

Nitrogen release and plant available nitrogen of composted and un-composted biosolids.

The nitrogen (N) release from composted and un-composted biosolids and plant available N (PAN) of the biosolids were quantified to evaluate if composting can contribute to stabilize biosolids N and reduce the nitrate ( ) leaching potential in biosolids-amended soil. Biosolids were composted at >55°C for 21days after mixing the biosolids with yard waste at 1:1 (w/w) ratio. In the N release study, we installed field lysimeters filled with soil (sand and clay) amended with composted and un-composted biosolids at two rates (30 and 150 dry Mg/ha) and measured the inorganic N in leachate after each rainfall and soil inorganic N monthly. The N released from composted biosolids during the two-year study period were lower (6% of organic N added for clay and 11% for sandy loam soil) as compared to un-composted biosolids (14% of organic N added for clay and 21% for sandy soils). Composted biosolids showed a lower N release rate constant k value of 0.0014 and 0.0027month-1 for clay and sandy soil, respectively, compared to corresponding values of 0.0035 and 0.0068month-1 for un-composted biosolids. We used greenhouse bioassay with corn (Zea mays), ryegrass (Lolium perenne), and Miscanthus (Miscanthus giganteus) as test plants grown for six months with reference to N chemical fertilizer ranging from 0, 75, 150 to 300kgN/ha to evaluate the PAN of the biosolids. Based on our study, plant growth was not affected by using either composted or un-composted biosolids but the PAN was lower in composted biosolids (4.0%-5.9%) than un-composted biosolids (11.4%-13.6%). Composting results in higher N-retention efficiency in biosolids and composted biosolids are a valuable source of N to support the plant growth with lower N released to the environment. Thus, the potential of N leaching would still be low in the situations where a high rate of biosolids needs to be applied for land reclamation or landscaping soil reconstruction. PRACTITIONER POINTS: Composting enhances N-retention efficiency in biosolids and composted biosolids are a valuable source of N to support the plant growth with lower N released to the environment. Potential of N leaching would still be low in the situations where a high rate of biosolids needs to be applied for land reclamation or landscaping soil reconstruction. N released from composted and un-composted biosolids can be adequately described by first-order kinetic model.

Biowastes alone and combined with sulfur affect the phytoavailability of Cu and Zn to barnyard grass and sorghum in a fluvial alkaline soil under dry and wet conditions

Management of degraded soils (i.e., metal contaminated soils, salt affected soils, and soils with low organic matter content) by applying biowastes (e.g., biosolids and compost) and inorganic soil amendments such as sulfur is of great agro-environmental concern. Because Cu and Zn chemical behaviour may be altered with these additions, we aimed at studying the impact of mono- and co-application of different rates (1.25% and 2.5%) of biosolids, compost, and sulfur on the mobilization of Cu and Zn and their uptake in a fluvial soil contains low and high metal concentrations and under two distinct moisture regimes (wet, where we grew barnyard grass; dry, with sorghum). We measured metal fractions and potential availability, along with soil pH, as well as plant yield and metal content in both plants, in an attempt to identify differences in metal behaviour. We found that organic matter (OM) (increased with biosolids and compost application) and soil pH (dramatically reduced with added sulfur) highly affected Cu and Zn mobility. Plant yield increased with increasing soil OM content and decreased with decreasing soil pH, particularly in the 2.5% sulfur treatment. However, Cu absorption was different in the two studied moisture regimes, as it was higher in the wet soil (Cu-DOC complexes, encouraged under wet conditions, may explain this), while it was lower in the dry soil. The biosolid-added Cu was significantly more bioavailable to sorghum plants than the spiked Cu. Co-application of sulfur and biosolids showed significantly higher sorghum uptake of Cu than application of sulfur to the spiked soil with Cu. Zinc uptake decreased in the high compost application rate (2.5%). This behaviour can be explained with the altered geochemical metal fractionation: added metals were distributed mainly in the oxides and organic fraction, but in the wet soil the percentage was higher compared to the dry, possibly due to metal-DOC associations. Also the residual fraction was lower in the wet, denoting higher metal mobility. We conclude that the observed differences between wet and dry soil concerning the metal geochemical behaviour, as were induced by added OM (with biosolids and compost) and reduced pH (with sulfur), are mainly responsible for the markedly different metal uptake patterns. These results may be an aid for effective phyto-management of alkaline fluvial soils with low and high content of Cu and Zn under paddy- and upland cultivation systems.

Biosolids Improve Urban Soil Properties and Vegetable Production in Urban Agriculture

Exceptional quality (EQ) biosolids may be used to rehabilitate disturbed urban soils for vegetable production in urban gardens. The objectives of this study were to investigate the effects of various EQ biosolids products on urban soil properties and vegetable yield. Field research was conducted at Blacksburg, VA, in an urban subsoil fill from a nearby construction site. Three EQ biosolids products were applied biannually at agronomic nitrogen (N) rates (fall 2016–2017, and summer 2017–2018) and annually at land reclamation rates (5× agronomic N rate; fall 2016–2017). A heat‐dried and pelletized EQ biosolids product and inorganic fertilizer were applied biannually at agronomic N rate only. Biosolids increased soil C storage vs. the control by 37 to 84% after 2 yr. Soil N availability was less than expected based on previous greenhouse research even after cumulative biosolids rates. Lower N availability likely was due to low organic matter and high clay concentrations that reduced organic N mineralization. Cabbage [Brassica oleraceaL. var.capitataL.] (∼3.1 kg m–2) and Siberian kale [Brassica napusL. subsp.napusvar.pabularia(DC.) Alef.] (∼1.1 kg m–2) yields were greater with reclamation rates than with the inorganic fertilizer (1.0 kg m–2and 0.4 kg m–2, respectively) in fall 2017. Despite limiting soil physicochemical conditions, biosolids addition at reclamation rates showed greater potential to increase vegetable yield after 2 yr of application.