Effect of amendment of bauxite processing sand with organic materials on its chemical,physical and microbial properties

The effects of addition of a range of organic amendments (biosolids, spent mushroom compost, green waste compost and green waste-derived biochar), at two rates, on some key chemical, physical and microbial properties of bauxite-processing residue sand were studied in a laboratory incubation study. Levels of exchangeable cations were not greatly affected by additions of amendments but extractable P was increased significantly by mushroom and green waste composts and massively (i.e. from 11.8 to 966 mg P kg^?1) by biosolids applications. Levels of extractable NO₃^?–N were also greatly elevated by biosolids additions and there was a concomitant decrease in pH. Addition of all amendments decreased bulk density and increased mesoporosity, available water holding capacity and water retention at field capacity (?10 kPa), with the higher rate having a greater effect. Addition of biosolids, mushroom compost and green waste compost all increased soluble organic C, microbial biomass C, basal respiration and the activities of β-glucosidase, L-asparaginase and alkali phosphatase enzymes. The germination index of watercress grown in the materials was greatly reduced by biosolids application and this was attributed to the combined effects of a high EC and high concentrations of extractable P and NO₃^?. It was concluded that the increases in water storage and retention and microbial activity induced by additions of the composts is likely to improve the properties of bauxite-processing residue sand as a growth medium but that allowing time for soluble salts, originating from the organic amendments, to leach out may be an important consideration before sowing seeds.     

Nitrogen, phosphorus, and potassium uptake by wheat and their distribution in soil following successive, annual compost applications

The overall objective of the present study was to determine the loading limits of composts that should be applied annually to irrigated wheat. We conducted a container experiment in a greenhouse during four years. It included eight treatments: sewage sludge compost (SSC) and cattle manure compost (CMC), each applied annually to a sandy soil, at rates equivalent to 3, 6, and 12 kg m(-2), and two controls, one fertilized and one unfertilized. Total dry matter (DM), grain production, and the amount of N, P, and K taken up by plants increased with increasing compost rate. Nitrogen uptake by the plants of the fertilized control was much higher than by the plants of the highest compost rate. Phosphorus and K uptake by the plants amended with the highest compost rate was much higher than by the fertilized control plants. Inorganic N quantity in the soil increased with increasing compost rate and with successive applications. The net N mineralization during the first year of wheat growth was very low, less than 3.5% of the applied organic N under all compost application rates. The contribution of the organic N mineralization increased during the second and third years. Most of the N increase in the compost treatment was found in the upper layer of 0 to 15 cm, whereas in the fertilized treatment N accumulated from the surface to the bottom of the container, 0 to 55 cm. The successive application of high rates of composts resulted in P and K accumulation in the soil profile.     

Cadmium binding by fractions of dissolved organic matter and humic substances from municipal solid waste compost

The agricultural practice of amending soils with composted municipal solid waste (MSW) adds significant amounts of organic matter and trace metals, including Cd. Under these conditions, soluble organic complexes of Cd formed in the compost may be more significant than previously thought, due to Cd bioavailability and mobility in the soil environment. To study the relative importance of different types of organic ligands in MSW compost for the binding of Cd, six fractions of the dissolved organic matter (DOM) in addition to humic acid (HA) and fulvic acid (FA) were extracted and their complexation of Cd quantified at pH 7 using an ion-selective electrode (ISE). The highest complexing capacities (CC) for Cd were found for the most humified ligands: HA (2386 micromol Cd g(-1) C of ligand), predialyzed FA (2468 micromol Cd g(-1) C), and HoA, a fulvic-type, easily soluble fraction (1042 micromol Cd g(-1) C). The differences in CC for Cd of the various organic ligands were not directly related to total acid-titratable or carboxylic groups, indicating the importance of sterical issues and other functional groups. The strength of association between Cd and the organic ligands was characterized by calculating stability constants for binding at the strongest sites (pK(int)) and modeling the distribution of binding site strengths. The pK(int) values of the DOM fractions ranged between 6.93 (HiN: polysaccharides) and 8.11 (HiB: proteins and aminosugars), compared with 10.05 for HA and 7.98 for FA. Hence, the highly complex and only partially soluble organic molecules from compost such as HA and FA demonstrated the highest capacity to sequester Cd. However, strong Cd binding of organic ligands containing N-functional groups (HiB) in addition to a high CC of soluble, humified ligands like HoA indicated the relevance of these fractions for the organic complexation of Cd in solution.     

Addition of an organic amendment and/or residue mud to bauxite residue sand in order to improve its properties as a growth medium

The effects of addition of carbonated residue mud (RMC) or seawater neutralized residue mud (RMS), at two rates, in the presence or absence of added green waste compost, on the chemical, physical and microbial properties of gypsum-treated bauxite residue sand were studied in a laboratory incubation study. The growth of two species commonly used in revegetation of residue sand (Lolium rigidum and Acacia saligna) in the treatments was then studied in a 18-week greenhouse study. Addition of green waste-based compost increased ammonium acetate-extractable (exchangeable) Mg, K and Na. Addition of residue mud at 5 and 10% w/w reduced exchangeable Ca but increased that of Mg and Na (and K for RMS). Concentrations of K, Na, Mg and level of EC in saturation paste extracts were increased by residue mud additions. Concentrations of cations in water extracts were considerably higher than those in saturation paste extracts but trends with treatment were broadly similar. Addition of both compost and residue mud caused a significant decrease in macroporosity with a concomitant increase in mesoporosity and microporosity, available water holding capacity and the quantity of water held at field capacity. Increasing rates of added residue mud reduced the percentage of sample present as discrete sand particles and increased that in aggregated form (particularly in the 1-2 and >10mm diameter ranges). Organic C content, C/N ratio, soluble organic C, microbial biomass C and basal respiration were increased by compost additions. Where compost was added, residue mud additions caused a substantial increase in microbial biomass and basal respiration. L.?rigidum grew satisfactorily in all treatments although yields tended to be reduced by additions of mud (especially RMC) particularly in the absence of added compost. Growth of A.?saligna was poor in sand alone and mud-amended sand and was greatly promoted by additions of compost. However, in the presence of compost, addition of carbonated mud had a marked depressive effect on both top and root growth. The significant positive effect of compost was attributed to substantial inputs of K and marked reductions in the Na/K ratio in soil solution while the depressive effect of RMC was attributed to its greater alkalinity and consequently higher concentrations of HCO(3)(-) in solution.     

Estimating the Unknown Components of Nutrient Mass Balances for Forestry Plantations in Mine Rehabilitation, Upper Hunter Valley, New South Wales, Australia

Commercial forestry plantations as a postmining land use in the Upper Hunter Valley of New South Wales, Australia are restricted by both the poor nutrient availability of mining substrates and low regional rainfall. An experiment was conducted to investigate whether municipal waste products and saline groundwater from coal mining operations could improve early tree growth without impacting on the environment through salt accumulation and/or nutrient enrichment and changes in groundwater quality. Potential impacts were investigated by quantifying the nutrient cycling dynamics within the plantation using an input–output mass balance approach for exchangeable calcium (Ca²⁺), exchangeable magnesium (Mg²⁺), exchangeable potassium (K⁺), exchangeable sodium (Na⁺), nitrogen (N), and phosphorus (P). Measured inputs to and outputs from the available nutrient pool in the 0–30 cm of the overburden subsystem were used to estimate the net effect of unmeasured inputs and outputs (termed “residuals”). Residual values in the mass balance of the irrigated treatments demonstrated large leaching losses of exchangeable Ca, Mg, K, and Na. Between 96% and 103% of Na applied in saline mine-water irrigation was leached below the 0–30-cm soil profile zone. The fate of these salts beyond 30 cm is unknown, but results suggest that irrigation with saline mine water had minimal impact on the substrate to 30 cm over the first 2 years since plantation establishment. Accumulations of N and P were detected for the substrate amendments, suggesting that organic amendments (particularly compost) retained the applied nutrients with very little associated losses, particularly through leaching.     

Composting and compost application in China

The current situation of municipal solid waste (MSW) and sewage sludge production (in terms of volume as well as composition) in China is introduced. Composting and compost application in China are reviewed. In China, the production of municipal solid waste and sewage sludge is changing rapidly along with economic development. Composting is mainly applied for treating MSW, about 20% of the total amount of MSW being disposed. MSW composting is mainly co-composted with night soil or sewage sludge. Compost is used in agriculture, forestry and horticulture. Compost application is the key factor influencing the composting development in China. To promote composting and compost application in China, a state-wide survey on the production, composition and physical and chemical properties of MSW and sewage sludge should be carried out. More effort should be made to develop low cost and high efficient composting technologies according to China's conditions. The environmental impact of compost application should also be given more attention.     

Recycling of spent mushroom compost using earthworms Eisenia foetida and Eisenia andrei

A 90-day study conducted to explore the potential of epigeic earthworms Eisenia foetida and Eisenia andrei to transform the different types of agricultural wastes and spent mushroom compost into value-added product, i.e., vermicompost. Vermicomposting resulted in significant reduction in C:N ratio, pH, electrical conductivity, total organic carbon, TK; and increase in total Kajeldahl nitrogen, TP, and various micro and macronutrients compared to those in the worm feed. Our trials demonstrated that the vermicomposting could be considered as an alternate technology for recycling and environmentally safe disposal/management of the mushroom cultivation complexes’ residues mixed with different types of agricultural waste using epigeic earthworms E. foetida and E. andrei.     

Compost, manure, and gypsum application to timothy/red clover forage

Some of the most fertile agricultural land in Atlantic Canada includes dykelands, which were developed from rich salt marshes along the Bay of Fundy through the construction of dykes. A 2-yr field experiment was conducted on dykeland soil to evaluate the effect of fertility treatments: source-separated municipal solid waste (SS-MSW) compost, solid manure, commercial fertilizer, and gypsum on (1) timothy/red clover forage productivity, (2) N, S, and other nutrients uptake, and (3) residual NO(3)-N and NH(4)-N in the soil profile. All fertility treatments increased dry matter yields from the two cuts each year relative to the control. Residual soil NO(3)-N and NH(4)-N concentrations in the fall of the second year decreased with depth, and beyond 20-cm depth were lower than 1 mg kg(-1). Gypsum application equivalent to 40 kg S ha(-1) increased dry matter yields and N uptake by forage, and increased soil Mehlich 3-extractable S, tissue S, and uptake of S, Ca, P, Cu, Fe, and Mn relative to the control. High rates of compost can provide sufficient N, S, and perhaps other nutrients to a perennial forage system under the cool wet climate of Atlantic Canada with no heavy metal enrichment of forage. However, the chemical N provided greater total N uptake than organic sources, except the high rate of compost, suggesting that the N availability from organic sources was not well synchronized with forage N demand. Municipal solid waste compost may also increase soil and forage tissue Na, which might be of concern.     

Nitrogen management considerations for landspreading municipal solid waste compost

Many municipalities have examined composting as an alternative to landfilling for the management of organic solid waste materials. Ultimately these materials will be land-applied and therefore some knowledge of nutrient availability will be necessary to optimize crop yield and minimize environmental risk. Field studies were conducted in 1993 and 1994 on a silt loam and a loamy sand soil in Wisconsin to determine the effect of municipal solid waste compost (MSWC) on corn (Zea mays L.) yield, plant nutrient concentration, and soil nitrate N content. Municipal solid waste composts with ages of 7, 36, and 270 d were applied at rates of 22.5, 45, and 90 Mg ha(-1) to small plots. Rates of commercial nitrogen (N) fertilizer, ranging from 0 to 179 kg N ha(-1), were applied to separate plots to determine the N availability from the MSWC. Treatments were applied in the spring and incorporated before planting corn. The 270-d MSWC increased corn whole-plant dry matter and grain yield at each location in both years above the 7- and 36-d MSWC. Rate of MSWC only affected grain yield at the loamy sand site in 1994. Municipal solid waste compost had minimal effect on the levels of plant nutrients in the whole-plant tissue measured at physiological maturity. Nitrate N measured in the top 90 cm of soil was higher throughout the growing season in treatments receiving recommended N fertilizer when compared with any of the MSWC treatments. It was estimated that 6 to 17% of the total N in the 270-d MSWC became available in the first year. The land-application of mature MSWC at the tested rates would be an agronomically and environmentally admissible practice.     

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.     

Reclamation of high-elevation,acidic mine waste with organic amendments and topsoil

The Summitville Mine was a high-elevation (3500 m) gold mine in southwestern Colorado. The mine was abandoned in 1992, leaving approximately 200 ha of disturbance comprised partially of an open pit, a cyanide heap leach pad, and two large waste rock piles. Reclamation of these mine facilities is challenging due to extreme climatic conditions in conjunction with high acid-production potential and low organic matter content of waste materials on site. In addition, stockpiled topsoil at the site is acidic and biologically inactive due to long-term storage, and may not be suitable for plant growth. The purpose of this study was to evaluate the effects of organic amendments (mushroom compost vs. biosolids) and topsoil (stockpiled vs. nonstockpiled) on aboveground biomass and plant trace element uptake. An on-site field study was established in 1995 to identify the most effective combination of treatments for successful reclamation of on-site waste rock materials. Incorporation of organic matter significantly increased aboveground biomass, with mushroom compost being more effective than biosolids, but did not significantly influence trace element uptake. Conversely, the use of topsoil did not affect aboveground biomass, but did influence trace element uptake. Treatments that received topsoil supported plant growth with significantly higher trace element tissue concentrations than treatments that did not receive topsoil. In general, it was found that waste rock could be directly revegetated when properly neutralized, fertilized, and amended with organic matter. Additionally, stockpiled topsoil, when neutralized with lime, supported plant growth equivalent to that on nonstockpiled topsoil.     

Does municipal solid waste composting make economic sense?

Currently there is widespread interest on the part of local Governments in incorporating municipal solid waste (MSW) composting into their integrated solid waste management systems. However, there is little information on the costs of MSW composting and how those costs compare with the costs of alternative forms of waste disposal (especially traditional land disposal). This article begins to fill this information gap by reporting the results of a survey of 19 MSW composting facilities around the United States. Results indicate that MSW composting generally costs around $50 per ton, and that very few facilities receive any revenues from the sale of compost to offset operating costs. Additional economic analysis indicates that, at present, MSW composting cannot be justified on financial grounds in most parts of the US, but may be competitive with land disposal where the cost of landfilling is high (such as the north-east).1998 Academic Press     

Improvement of soil quality after "alperujo" compost application to two contaminated soils characterised by differing heavy metal solubility

Reclamation of trace element polluted soils often requires the improvement of the soil quality by using appropriate organic amendments. Low quality compost from municipal solid waste has been tested for reclamation of soils, but these materials can provide high amounts of heavy metals. Therefore, a high-quality compost, with low levels of heavy metals, produced from the main by-product of the Spanish olive oil extraction industry ("alperujo") was evaluated for remediation of soils affected by a pyritic mine sludge. Two contaminated soils were selected from the same area: they were characterised by differing pH values (4.6 and 7.3) and total metal concentrations, which greatly affected the fractionation of the metals. Compost was applied to soil at two rates (equivalent to 48 and 72 Tm ha(-1)) and compared with an inorganic fertiliser treatment. Compost acted as an available nutrient source (C, N and P) and showed a low mineralisation rate, suggesting a slow release of nutrients and thus favouring long term soil fertility. In addition, the liming effect of the compost led to a significant reduction of toxicity for soil microorganisms in the acidic soil and immobilisation of soil heavy metals (especially Mn and Zn), resulting in a clear increase in both soil microbial biomass and nitrification. Such positive effects were clearly greater than those provoked by the mineral fertiliser even at the lowest compost application rate, which indicates that this type of compost can be very useful for bioremediation programmes (reclamation and revegetation of polluted soils) based on phytostabilisation strategies.     

Evaluation of extracted organic carbon and microbial biomass as stability parameters in ligno-cellulosic waste composts

Extracted organic C and microbial biomass were evaluated as stability parameters in 3 different ligno-cellulosic waste composts. Organic C was extracted by both water and alkali and further separated in humic-like carbon (HLC) and nonhumic carbon (NHC). Conventional humification parameters, such as humification index and degree of humification were calculated from NHC and HLC. Microbial biomass carbon (B(C)) was determined as an indicator of the degree of biochemical transformation, whereas ninhydrin reactive N (B(NIN)) was measured to obtain the stability parameter B(NIN)/N(TOT) (N(TOT), total N). The water-extracted organic C did not provide reliable information on the transformations underwent by the ligno-cellulosic wastes during composting, since its content remained almost unaltered during the whole process. In contrast, parameters based on the alkali-extracted organic C and microbial biomass clearly reflected organic matter (OM) changes during the process. There was an increase in the net amount of HLC in the alkali extracts throughout composting, especially in the first 7 to 12 wk of the process, as well as a relative enrichment of HLC with respect to NHC. Values of humification index and degree of humification in end products were consistent with an adequate level of compost stability. The stability parameter B(NIN)/N(TOT) showed to be a reliable indicator of stability in ligno-cellulosic wastes. Parameters based on the alkali-extracted C and microbial biomass clearly reflected the transformation of the OM during composting and can be used as stability parameters in ligno-cellulosic waste composts.     

Leachability and phytoavailability of nitrogen, phosphorus, and potassium from different bio-composts under chloride- and sulfate-dominated irrigation water

Concerns over increased phosphorus (P) application with nitrogen (N)-based compost application have shifted the trend to P-based composed application, but focusing on one or two nutritional elements does not serve the goals of sustainable agriculture. The need to understand the nutrient release and uptake from different composts has been further aggravated by the use of saline irrigation water in the recent scenario of fresh water shortage. Therefore, we evaluated the leachability and phytoavailability of P, N, and K from a sandy loam soil amended with animal, poultry, and sludge composts when applied on a total P-equivalent basis (200 kg ha(-1)) under Cl(-) (NaCl)- and SO4(2-) (Na2SO4)-dominated irrigation water. Our results showed that the concentration of dissolved reactive P (DRP) was higher in leachates under SO(4)(2-) than Cl(-) treatments. Compost amendments differed for DRP leaching in the following pattern: sludge > animal > poultry > control. Maize (Zea mays L.) growth and P uptake were severely suppressed under Cl(-) irrigation compared with SO4(2-) and non-saline treatments. All composts were applied on a total P-equivalent basis, but maximum plant (shoot + root) P uptake was observed under sludge compost amendment (73.4 mg DW(-1)), followed by poultry (39.3 mg DW(-1)), animal (15.0 mg DW(-1)), and control (1.2 mg DW(-1)) treatment. Results of this study reveal that irrigation water dominated by SO4(2-) has greater ability to replace/leach P, other anions (NO3(-)), and cations (K+). Variability in P release from different bio-composts applied on a total P-equivalent basis suggested that P availability is highly dependent on compost source.     

Fertilizer source effect on ground and surface water quality in drainage from turfgrass

Nutrients in surface and ground water can affect human and aquatic organisms that rely on water for consumption and habitat. A mass-balance field study was conducted over two years (July 2000-May 2001) to determine the effect of nutrient source on turfgrass runoff and leachate. Treatments were arranged in an incomplete randomized block design on a slope of 7 to 9% of Arkport sandy loam (coarseloamy, mixed, active, mesic Lamellic Hapludalf) and seeded with Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.). Three natural organic (dairy and swine compost and a biosolid) and two synthetic organic nutrient sources (readily available urea and controlled-release N source sulfur-coated urea) were applied at rates of 50 and 100 kg N ha(-1) per application (200 kg ha(-1) yr(-1)). Runoff water collected from 33 storms and composite monthly leachate samples collected with ion exchange resins were analyzed for nitrate (NO3- -N), phosphate (PO4(3-) -P), and ammonium (NH4+ -N). Nutrient concentrations and losses in both runoff and leachate were highest for the 20-wk period following turfgrass seeding. The NO3- -N and NH4+ -N losses declined significantly once turfgrass cover was established, but PO4(3-) -P levels increased in Year 2. Turf's ability to reduce nutrient runoff and leachate was related to overall plant growth and shoot density. The use of natural organics resulted in greater P loss on a percent applied P basis, while the more soluble synthetic organics resulted in greater N loss.     

Municipal solid waste management in China: Status,problems and challenges

This paper presents an examination of MSW generation and composition in China, providing an overview of the current state of MSW management, an analysis of existing problems in MSW collection, separation, recycling and disposal, and some suggestions for improving MSW systems in the future. In China, along with urbanization, population growth and industrialization, the quantity of municipal solid waste (MSW) generation has been increasing rapidly. The total MSW amount increased from 31.3 million tonnes in 1980 to 212 million tonnes in 2006, and the waste generation rate increased from 0.50 kg/capita/day in 1980 to 0.98 kg/capita/year in 2006. Currently, waste composition in China is dominated by a high organic and moisture content, since the concentration of kitchen waste in urban solid waste makes up the highest proportion (at approximately 60%) of the waste stream. The total amount of MSW collected and transported was 148 million tonnes in 2006, of which 91.4% was landfilled, 6.4% was incinerated and 2.2% was composted. The overall MSW treatment rate in China was approximately 62% in 2007. In 2007, there were 460 facilities, including 366 landfill sites, 17 composing plants, and 66 incineration plants. This paper also considers the challenges faced and opportunities for MSW management in China, and a number of recommendations are made aimed at improving the MSW management system.     

Decrease in water-soluble 17beta-Estradiol and testosterone in composted poultry manure with time

Little attention has been paid to the environmental fate of the hormones 17beta-estradiol and testosterone excreted in animal waste. Land application of manure has a considerable potential to affect the environment with these endocrine disrupting compounds (EDCs). Composting is known to decompose organic matter to a stable, humus-like material. The goal of the present study was to quantitatively assess levels of water-soluble 17beta-estradiol and testosterone in composting chicken manure with time. Chicken layer manure was mixed with hay, straw, decomposed leaves, and starter compost, adjusted to approximately 60% moisture, and placed into a windrow. A clay-amended windrow was also prepared. Windrows were turned weekly, and temperature, oxygen, and CO(2) in the composting mass were monitored for either 133 or 139 d. Commercial enzyme immunoassay kits were used to quantitate the levels of 17beta-estradiol and testosterone in aqueous sample extracts. Water-soluble quantities of both hormones diminished during composting. The decrease in 17beta-estradiol followed first-order kinetics, with a rate constant k = -0.010/d. Testosterone levels declined at a slightly higher rate than 17beta-estradiol (i.e., k = -0.015/d). Both hormones could still be measured in aqueous extracts of compost sampled at the conclusion of composting. The decline in water-soluble 17beta-estradiol and testosterone in extracts of clay-amended compost was not statistically different from normal compost. These data suggest that composting may be an environmentally friendly technology suitable for reducing, but not eliminating, the concentrations of these endocrine disrupting hormones at concentrated animal operation facilities.     

Evaluation of municipal solid waste composting kinetics

Most modern municipal solid waste (MSW) composting operations have emphasized the enhancement of decomposition of the organic fraction of the waste to comply with strict environmental regulations. This can be achieved once the composting process kinetics are well understood. This study examined process kinetics through experimentation with bench-scale reactors under controlled composting conditions to show the interdependence between biological, chemical and physical factors during composting of MSW. The effects of temperature, moisture content, waste particle size and carbon to nitrogen (C/N) ratio on process kinetics were evaluated. The results obtained revealed that these factors should be carefully controlled in order to achieve optimum process performance. It has been found that the organic matter degradation during composting follows a first-order kinetic model.     

Solubility of phosphorus and heavy metals in potting media amended with yard waste-biosolids compost

The potential risk of surface and ground water contamination by phosphorus (P) and heavy metals leached from compost-based containerized media has become an environmental concern. Solubility and fractionation of P and heavy metals were evaluated in media containing 0, 25, 50, 75, or 100% compost derived from biosolids and yard trimmings for potential impacts on the environment. As compost proportion in peat-based media increased from 0 to 100%, concentrations of total P, Cd, Cu, Ni, Pb, Zn, and Mn in the media increased whereas concentrations of total Co and Cr decreased. Except for Cu, all heavy metals in the water-soluble fraction decreased with increasing compost proportion in the media, because of higher Fe, Al, and Ca concentrations and pH values of the composts than the peat. When the media pH is controlled and maintained at normal range of plant growth (5.5-6.5), leaching of the heavy metals is minimal. Incorporation of compost to the peat-based media also decreased the proportion of total P that was water-soluble. However, concentrations of bioavailable inorganic phosphorus (NaHCO3-IP), readily mineralizable organic phosphorus (NaHCO3-OP), potentially bioavailable inorganic phosphorus (NaOH-IP), and potentially bioavailable organic phosphorus (NaOH-OP) were still higher in the media amended with compost because of higher total P concentration in the compost. Further study is needed to verify if less or no topdressing of chemical P fertilizer should be applied to the compost-amended media to minimize P effect on the environment when compost-amended potting media are used for nursery or greenhouse crop production systems.