Properties of slate mining wastes incubated with grape marc compost under laboratory conditions

The effect of the addition of spent grape marc compost (GMC) and vermicompost (GMV) as amendments to slate mining wastes was evaluated in a laboratory incubation experiment. Mixtures of slate processing fines (SPF), with three doses of each amendment (4%, 8% and 16% compost, dry weight), plus a control were incubated at 25 degrees C in the laboratory for 90 days. The changes in the chemical and biological properties of the mixtures (pH, total C, total N, inorganic N, available nutrients, microbial biomass carbon and dehydrogenase activity) were investigated during the incubation period, and once it was finished, the phytotoxicity of the mixtures was determined by the germination of Lolium multiflorum Lam. seeds. The addition of the amendments significantly increased the nutrient concentrations of the SPF and enhanced biological activity by increasing microbial biomass and enzymatic activity. Results improved with higher doses; within the composts, GMV showed a better performance than GMC. These results prove the suitability of grape marc-derived amendments for the biochemical amelioration of mining wastes, and highlight the benefits of organic amendment in restoration projects.     

Composting of a solid olive-mill by-product ("alperujo") and the potential of the resulting compost for cultivating pepper under commercial conditions

A pollutant solid material called "alperujo" (AL), which is the main by-product from the Spanish olive oil industry, was composted with a cotton waste as bulking agent, and the compost obtained (ALC) was compared with a cattle manure (CM) and a sewage sludge compost (SSC) for use as organic amendment on a calcareous soil. The experiment was conducted with a commercial pepper crop in a greenhouse using fertigation. Composting AL involved a relatively low level of organic matter biodegradation, an increase in pH and clear decreases in the C/N and the fat, water-soluble organic carbon and phenol contents. The resulting compost, which was rich in organic matter and free of phytotoxicity, had a high potassium and organic nitrogen content but was low in phosphorus and micronutrients. The marketable yields of pepper obtained with all three organic amendments were similar, thus confirming the composting performance of the raw AL. When CM and SSC were used for soil amendment, the soil organic matter content was significantly reduced after cultivation, while it remained almost unchanged in the ALC-amended plots.     

Effects of municipal solid waste compost application on the microbial biomass of cultivated and non-cultivated soil in a semi-arid zone.

The aim of this study was to assess whether soil microbial biomass could be used as an indicator of environmental changes following the application of organic residue (compost of municipal solid waste and farmyard manure) or mineral fertilizers (N and P) into cultivated or uncultivated loam-clayey soil, for three consecutive years. The carbon and nitrogen of the microbial biomass (B(C) and B(N) were studied using the fumigation-extraction method. For the two cultivated and uncultivated plots, B(N) and B(C) were more important in the superficial profile (0-20 cm) than in the deep one (20-40 cm). In the uncultivated soil, we observed a good linear relation between B(C) and B(N) at the level of upper soil horizon during the wet season with r coefficients of 0.95, 0.71 and 0.80 for the consecutive years 2000, 2001 and 2002, respectively. Microbial biomasses C and N increased during the rainy season and decreased during the dry season. Microbial biomass C and N showed the higher content with compost and farmyard manure at 40 tonnes ha(-1). Moreover, the results showed that at the beginning of the experiment, the microbial biomass was higher in the ploughed wheat-cultivated plot than in the uncultivated one. Microbial biomass C and N in the cultivated plot amended with compost at 40 tonnes ha(-1) were significantly different in comparison with the soil microbial biomass amended with farmyard manure. The combining of chemical fertilizer with the organic fertilizer, such as compost at 40 or 80 tonnes ha(-1) and farmyard manure, increased the microbial biomasses C and N after 1 and 2 years. In the cultivated or uncultivated plots the results revealed that the best application rate of the compost was 40 tonnes ha(-1) and when the compost rate was increased from 40 to 80 tonnes ha(-1) both B(C) and B(N) decreased significantly.     

Application of compost of two-phase olive mill waste on olive grove: Effects on soil,olive fruit and olive oil quality

Composting is a method for preparing organic fertilizers that represents a suitable management option for the recycling of two-phase olive mill waste (TPOMW) in agriculture. Four different composts were prepared by mixing TPOMW with different agro-industrial by-products (olive pruning, sheep manure and horse manure), which were used either as bulking agents or as N sources. The mature composts were added during six consecutive years to a typical “Picual” olive tree grove in the Jaén province (Spain). The effects of compost addition on soil characteristics, crop yield and nutritional status and also the quality of the olive oil were evaluated at the end of the experiment and compared to a control treated only with mineral fertilization. The most important effects on soil characteristics included a significant increase in the availability of N, P, K and an increase of soil organic matter content. The application of TPOMW compost produced a significant increase in olive oil content in the fruit. The compost amended plots had a 15% higher olive oil content than those treatment with inorganic fertilization. These organics amendments maintained the composition and quality of the olive oil.     

Effect of fresh green waste and green waste compost on mineral nitrogen, nitrous oxide and carbon dioxide from a Vertisol

Incorporation of organic waste amendments to a horticultural soil, prior to expected risk periods, could immobilise mineral N, ultimately reducing nitrogen (N) losses as nitrous oxide (N₂O) and leaching. Two organic waste amendments were selected, a fresh green waste (FGW) and green waste compost (GWC) as they had suitable biochemical attributes to initiate N immobilisation into the microbial biomass and organic N forms. These characteristics include a high C:N ratio (FGW 44:1, GWC 35:1), low total N (<1%), and high lignin content (>14%). Both products were applied at 3 t C/ha to a high N (plus N fertiliser) or low N (no fertiliser addition) Vertisol soil in PVC columns. Cumulative N₂O production over the 28 day incubation from the control soil was 1.5 mg/N₂O/m², and 11 mg/N₂O/m² from the control + N. The N₂O emission decreased with GWC addition (P < 0.05) for the high N soil, reducing cumulative N₂O emissions by 38% by the conclusion of the incubation. Analysis of mineral N concentrations at 7, 14 and 28 days identified that both FGW and GWC induced microbial immobilisation of N in the first 7 days of incubation regardless of whether the soil environment was initially high or low in N; with the FGW immobilising up to 30% of available N. It is likely that the reduced mineral N due to N immobilisation led to a reduced substrate for N₂O production during the first week of the trial, when soil N₂O emissions peaked. An additional finding was that FGW + N did not decrease cumulative N₂O emissions compared to the control + N, potentially due to the fact that it stimulated microbial respiration resulting in anaerobic micro sites in the soil and ultimately N₂O production via denitrification. Therefore, both materials could be used as post harvest amendments in horticulture to minimise N loss through nitrate-N leaching in the risk periods between crop rotations. The mature GWC has potential to reduce N₂O, an important greenhouse gas.     

Use of thermal analysis techniques (TG-DSC) for the characterization of diverse organic municipal waste streams to predict biological stability prior to land application

The use of organic municipal wastes as soil amendments is an increasing practice that can divert significant amounts of waste from landfill, and provides a potential source of nutrients and organic matter to ameliorate degraded soils. Due to the high heterogeneity of organic municipal waste streams, it is difficult to rapidly and cost-effectively establish their suitability as soil amendments using a single method. Thermal analysis has been proposed as an evolving technique to assess the stability and composition of the organic matter present in these wastes. In this study, three different organic municipal waste streams (i.e., a municipal waste compost (MC), a composted sewage sludge (CS) and a thermally dried sewage sludge (TS)) were characterized using conventional and thermal methods. The conventional methods used to test organic matter stability included laboratory incubation with measurement of respired C, and spectroscopic methods to characterize chemical composition. Carbon mineralization was measured during a 90-day incubation, and samples before and after incubation were analyzed by chemical (elemental analysis) and spectroscopic (infrared and nuclear magnetic resonance) methods. Results were compared with those obtained by thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. Total amounts of CO₂ respired indicated that the organic matter in the TS was the least stable, while that in the CS was the most stable. This was confirmed by changes detected with the spectroscopic methods in the composition of the organic wastes due to C mineralization. Differences were especially pronounced for TS, which showed a remarkable loss of aliphatic and proteinaceous compounds during the incubation process. TG, and especially DSC analysis, clearly reflected these differences between the three organic wastes before and after the incubation. Furthermore, the calculated energy density, which represents the energy available per unit of organic matter, showed a strong correlation with cumulative respiration. Results obtained support the hypothesis of a potential link between the thermal and biological stability of the studied organic materials, and consequently the ability of thermal analysis to characterize the maturity of municipal organic wastes and composts.     

Land application of biosolids. Soil response to different stabilization degree of the treated organic matter

The effect of land application of biosolids on an agricultural soil was studied in a 2-month incubation experiment. The soil microbial biomass and the availability of heavy metals in the soil was monitored after the application of four different composting mixtures of sewage sludge and cotton waste, at different stages of composting. Land application caused an increase of both size and activity of soil microbial biomass that was related to the stabilization degree of the composting mixture. Sewage sludge stabilization through composting reduced the perturbance of the soil microbial biomass. At the end of the experiment, the size and the activity of the soil microbial biomass following the addition of untreated sewage sludge were twice those developed with mature compost. For the mature compost, the soil microbial biomass recovered its original equilibrium status (defined as the specific respiration activity, qCO2) after 18 days of incubation, whereas the soil amended with less stabilized materials did not recover equilibrium even after the two-month incubation period. The stabilization degree of the added materials did not affect the availability of Zn, Ni, Pb, Cu, Cr and Cd in the soil in the low heavy metal content of the sewage sludge studied. Stabilization of organic wastes before soil application is advisable for the lower perturbation of soil equilibria status and the more efficient C mineralization.     

Microbial biomass in a soil amended with different types of organic wastes.

Application of different types of organic wastes may have a marked effect on soil microbial biomass and its activity. The objective of this study was to quantify the amount of microbial biomass in a loamy-clayey soil, amended with different types of organic waste residues (composts of municipal solid waste of different ages, sewage sludge and farmyard manure) and incubated for 8 weeks at 25 degrees C and two-thirds of field capacity, using the fumigation-extraction method. Both microbial biomass-C and -N (BC and BN, respectively) appeared to be dependent on the type of organic waste residues, on their degree of stability, and on their chemical characteristics. In general, organic wastes increased the microbial biomass-C content in the soil and the microbial BC was positively correlated with the organic C content, the C/N, neutral detergent fibre/N (NDF/N) and acid detergent fibre/N (ADF/ N) ratios. The microbial biomass content decreased according to the period of incubation, especially when the compost used was immature. The microbial biomass-N was positively correlated with the total N and percentage of hemicellulose. The microbial biomass-C was linearly related with the microbial biomass-N and the ratio BC/BN was exponentially related with the BC.     

Sulphur mineralization kinetics of cattle manure and green waste compost in soils.

Sulphur mineralization of cattle manure (CM) and green waste compost (GWC) added to six agricultural soils with different chemical properties was monitored over 10 weeks in a laboratory incubation experiment. Although the amount of sulphur was higher in CM than in GWC, the cumulative SO4(2-)-S values in GWC-treated soils were higher than in soil amended with CM. The percentages of mineralized S were always higher in GWC-treated soil (in the range 1.3-8.5%) than in CM-treated soil (in the range 0.9-3.8%). In three of the six soils, particularly for CM, an immobilization of sulphur was observed. Three kinetic models were evaluated for their suitability to describe the mineralization process. The first-order model best described S mineralization for both amended and control soils. The GWC substantially increased the amount of potentially mineralizable S (S0) relative to the controls. In GWC-treated soils, the rates of S mineralization (k) were higher than rates in the controls. The k of CM-amended soils was often lower than the k of control soils. Parameters derived from the model were tested as indices for assessing the relationships between S mineralization and soil characteristics. The S0 was positively correlated to the amount of cumulative SO4(2-)-S and also to the content of organic C, N and S in soil.     

Monitoring operational and leachate characteristics of an aerobic simulated landfill bioreactor

Long-term biodegradation of MSW in an aerobic landfill bioreactor was monitored as a function of time during 510 days of operation. Operational characteristics such as air importation, temperature and leachate recirculation were monitored. The oxygen utilization rates and biodegradation of organic matter rates showed that aerobic biodegradation was feasible and appropriate to proceed in aerobic landfill bioreactor. Leachate analyses showed that the aerobic bioreactor could remove above 90% of chemical oxygen demand (COD) and close to 100% of biochemical oxygen demand (BOD5) from leachate. Ammonium (NH4+), nitrate (NO3-) and sulphate (SO4(2-)) concentrations of leachate samples were regularly measured. Results suggest that nitrification and denitrification occurred simultaneously, and the increase in nitrate did not reach the levels predicted stoichiometrically, suggesting that other processes were occurring. Leachate recirculation reduced the concentrations of heavy metals because of the effect of the high pH of the leachate, causing heavy metals to be retained by processes such as sorption on MSW, carbonate precipitation, and hydroxide precipitation. Furthermore, the compost derived from the aerobic biodegradation of the organic matter of MSW may be considered as soil improvement in the agricultural plant production. Bio-essays indicated that the ecotoxicity of leachate from the aerobic bioreactor was not toxic at the end of the experiment. Finally, after 510 days of degradation, waste settlement reached 26% mainly due to the compost of the organic matter.     

Managing compost stability and amendment to soil to enhance soil heating during soil solarization

Soil solarization is a method of soil heating used to eradicate plant pathogens and weeds that involves passive solar heating of moist soil mulched (covered) with clear plastic tarp. Various types of organic matter may be incorporated into soil prior to solarization to increase biocidal activity of the treatment process. Microbial activity associated with the decomposition of soil organic matter may increase temperatures during solarization, potentially enhancing solarization efficacy. However, the level of organic matter decomposition (stability) necessary for increasing soil temperature is not well characterized, nor is it known if various amendments render the soil phytotoxic to crops following solarization. Laboratory studies and a field trial were performed to determine heat generation in soil amended with compost during solarization. Respiration was measured in amended soil samples prior to and following solarization as a function of soil depth. Additionally, phytotoxicity was estimated through measurement of germination and early growth of lettuce seedlings in greenhouse assays. Amendment of soil with 10% (g/g) compost containing 16.9 mg CO₂/g dry weight organic carbon resulted in soil temperatures that were 2–4 °C higher than soil alone. Approximately 85% of total organic carbon within the amended soil was exhausted during 22 days of solarization. There was no significant difference in residual respiration with soil depth down to 17.4 cm. Although freshly amended soil proved highly inhibitory to lettuce seed germination and seedling growth, phytotoxicity was not detected in solarized amended soil after 22 days of field solarization.     

Reducing salinity and organic contaminants in the Pearl Harbor dredged material using soil amendments and plants

Phytoremediation is an emerging technique that can be used to economically remediate sites contaminated with trace elements and/or man‐made organic contaminants. This technique was used on Pearl Harbor (Oahu, Hawaii) dredged material (PHDM) containing polycyclic aromatic hydrocarbons (PAHs) and some heavy metals. The dredged material was first amended with a high‐calcium soil (Waialua Mollisol) and a biosolids‐based compost at different proportions to yield varying salinity levels. A mixture that yielded an electrical conductivity (EC, a measure of salinity) of the saturated paste extract of 15 to 20 dS/m was identified and used to evaluate the salt tolerance of five plant species. Relative germination and one‐month‐old biomass indicated that common bermuda grass (Cynodon dactylon), seashore paspalum (Paspalum vaginatum), beach pea (Vigna marina), and cow pea (Vigna unguiculata) can produce at least 40 percent of biomass of the control at an EC of approximately 18 dS/m, suggesting the four plants are relatively salt tolerant. In contrast, Desmodium intortum either did not germinate or died within two weeks after germination at the same salinity level. A subsequent greenhouse experiment, using mixtures of the PHDM (0 or 25 percent dry weight), organic amendments (10 percent leucaena green manure or biosolids‐based compost), and a Mollisol (65 or 90 percent dry weight) in 6‐liter pots containing 4 kilograms of material yielded the following results: (1) A combination of transplanted seashore paspalum, seeded bermuda grass, and seeded beach pea was effective in taking up sodium (Na), thereby reducing salinity and making the medium more amenable to diversified microbes and plants, which may be effective PAH degraders; (2) total PAH concentration was reduced by about 30 percent after three months of active plant growth, but degradation of individual PAH members varied significantly, however; (3) leguminous green manure, as a soil amendment, was more effective than compost for use in bio‐ and/or phytoremediations; and (4) soil amendments, when applicable, could supplement living plants in reducing organic contaminants, such as PAHs. © 2002 Wiley Periodicals, Inc.     

Effects of composted sewage sludge on microbial biomass, activity and pine seedlings in nursery forest

The investigation was carried out in a 2 year experiment to evaluate the benefits and hazards of the use of composted sewage sludge as a restoration agent for the soil of the nursery forest intended for growing Pinus sylvestris seedlings. The grey forest soil (Haplic Greyzem) was amended with compost at the 25, 50, 75, 100, 150 and 175 t ha(-1) application rates on a dry matter basis. The organic matter content increased with the increase in sludge amendment as well as the metal content. However, the concentrations of individual metals were below the current limits established for Russia and European countries. Sludge amendments enhanced the germination and decreased the mortality of the seedlings. The effects were more obvious for the soil with the highest sludge treatment. The beneficial effects on the biomass of seedlings and the height of the shoots as well as on the length of the roots of the pine seedlings were greater in plots with the highest rates of composted sludge. The application of composted sludge to soil was followed by an increase in microbial biomass and to a lesser extent in basal respiration. In the absence of any detrimental effect on microorganisms, this study lends support to using composted sewage sludge as the organo-mineral fertilizer for the soil of nursery forest.     

Effects of municipal solid waste compost and sewage sludge on chemical and spectroscopic properties of humic acids from a sandy Haplic Podzol and a clay loam Calcic Vertisol in Portugal

The effects of amendment with municipal solid waste compost (MSWC) and anaerobically digested sewage sludge (SS) on the compositional and structural features of soil humic acids (HAs) were investigated. For this purpose, HAs were isolated from MSWC, SS, and two different Portuguese soils, a sandy Haplic Podzol and a clay loam Calcic Vertisol, which were either unamended or amended with MSWC or SS at a rate of 60tha(-1). The isolated HAs were analyzed for elemental and acidic functional group composition, and by ultraviolet/visible, Fourier transform infrared (FT IR), and fluorescence spectroscopies. The application of MSWC and especially SS to soils determined an increase of C, N, H, and S contents and E(4)/E(6) ratios (i.e., ratios of absorbances at 465 and 665nm), and a decrease of O, COOH, and phenolic OH contents and C/N, C/H, and O/C ratios of soil HAs. The FT IR and fluorescence results showed that the organic amendments, especially SS, caused an increase of the aliphatic character and a decrease of the degrees of aromatic polycondensation, polymerization, and humification of amended soil HAs. Both MSWC and SS affected more markedly the clayey soil HAs than the sandy soil HAs, possibly due to less extended mineralization processes and the protective action of clay minerals on amended soil HAs.     

Modification of soil humic matter after 4 years of compost application

Two soil plots, 1 ha each, were amended yearly for 4 years, respectively, with 35.8 and 71.6 Mg ha(-1) yr(-1) of mature compost (CM) obtained from food and vegetable residues. The compost, amended soils, and a control soil plot after 4 years (S4), were analyzed for humin (HUC), humic acid (HAC), fulvic acid (FAC), and non-humic carbon (NHC) content. Compared to S4, the amended soil contained more humified C (HAC, FAC and HUC) and less NHC. Further evidence of the effect of compost on soil organic matter was obtained by the analysis of the humic acid (HA) fractions isolated from both the compost and the soils. These were characterized by elemental analyses and Diffuse Reflectance Infrared Fourier Transformed spectroscopy. The HAs isolated from CM and from S4 were significantly different. The HAs isolated from the amended plots were more similar to HA isolated from CM than to HA isolated from S4. The experimental data of this work indicate that the compost application may affect significantly the soil organic matter composition, and that the approach used in this work allows one to trace the fate of compost organic matter in soil.     

Recycling of waste biomass and mineral powder for preparation of potassium-enriched compost

An attempt was made to recycle waste biomass and mineral powder (waste mica) as an alternative source of potassium (K) through composting technology. Two different waste biomass, isabgol straw and palmarosa distillation waste along with two levels of waste mica (2 and 4% as K) were used for preparation of enriched composts. A notable decrease of C:N ratio was observed at the end of the composting (150 days) as an indicator of compost maturity. The mature composts were evaluated for K-supplying capacity through laboratory leaching and soil incubation study. Significantly higher water-soluble K released initially followed by a sharp decrease up to 21 days of leaching thereafter gradually decreased up to 35 days of leaching. Water-soluble K was released from K-enriched (mica charged) compost significantly higher than the ordinary compost throughout the leaching period. Soil incubation study also revealed that application of K-enriched compost greatly improved the available K (water soluble and exchangeable) pools in K-deficient soil which indicated that a considerable amount of K releases during composting. Therefore, K-enriched compost could be an effective alternative of costly commercial K fertilizer and eco-friendly approach to utilize low-cost waste mineral powder and plant residue.     

Assessment of chemical and biochemical stabilization of organic C in soils from the long-term experiments at Rothamsted (UK)

Biological and chemical stabilization of organic C was assessed in soils sampled from the long-term experiments at Rothamsted (UK), representing a wide range of carbon inputs and managements by extracting labile, non-humified organic matter (NH) and humic substances (HS). Four sequentially extracted humic substances fractions of soil organic matter (SOM) were extracted and characterized before and after a 215-day laboratory incubation at 25 degrees C from two arable soils, a woodland soil and an occasionally stubbed soil. The fractions corresponded to biochemically stabilised SOM extracted in 0.5M NaOH (free fulvic acids (FA) and humic acids (HA)) and chemically plus biochemically stabilised SOM extracted from the residue with 0.1M Na4P2O7 plus 0.1M NaOH (bound FA and HA). Our aim was to investigate the effects of chemical and biochemical stabilization on carbon sequestration. The non-humic to humic (NH/H) C ratio separated the soils into two distinct groups: arable soils (unless fertilised with farmyard manure) had an NH/H C ratio between 1.05 and 0.71, about twice that of the other soils (0.51-0.26). During incubation a slow, but detectable, decrease in the NH/H C ratio occurred in soils of C input equivalent or lower to 4Mgha(-1)y(-1), whereas the ratio remained practically constant in the other soils. Before incubation the free to bound humic C ratio increased linearly (R2=0.91) with C inputs in the soils from the Broadbalk experiment and decreased during incubation, showing that biochemical stabilization is less effective than chemical stabilization in preserving humic C. Changes in delta13C and delta15N after incubation were confined to the free FA fractions. The delta13C of free FA increased by 1.48 and 0.80 per thousand, respectively, in the stubbed and woodland soils, indicating a progressive biological transformation. On the contrary, a decrease was observed for the bound FA of both soils. Concomitantly, a Deltadelta15N of up to +3.52 per thousand was measured after incubation in the free FA fraction and a -2.58 Deltadelta15N in the bound FA. These changes, which occurred during soil incubation in the absence of C inputs, indicate that free FA fractions were utilised by soil microorganisms, and bound FA were decomposed and replaced, in part, by newly synthesized FA. The 13CPMAS-TOSS NMR spectra of free HA extracted before and after 215 days of incubation were mostly unchanged. In contrast, changes were evident in bound HA and showed an increase in aromatic C after incubation.     

Effect of compost treatment of sewage sludge on nitrogen behavior in two soils

This work aims to evaluate the effects of compost treatment of digested sewage sludge on nitrogen behavior in two soils, a Spodosol and an Oxisol soil. Digested sewage sludge was composted with sawdust and woodchips, diluting the total nitrogen to one-fourth (dry mass basis) of its original value. Then, sludge and compost were added to the two soils on an equivalent dry weight basis to consider the risk of NO3- -N leaching. Compost treatment of sewage sludge has slowed down the release of mineral-N to half in the Spodosol and to one-third in Oxisol soil. As a result, NO3- -N concentrations in soils incubated with compost were less than half of the amounts found from soils incubated with digested sludge. Estimates were made of the maximum monthly nitrate to leach from the four combinations of soil and sludge treatment. Application of digested sludge, at a higher nitrogen application rate, resulted in a higher nitrate leaching potential than application of the compost product. Soil type also played an important role, with the Oxisol having slightly higher estimated leaching potential than the Spodosol. The higher nitrate release rate in the Oxisol is counterbalanced by its higher field capacity to lessen the expected difference between the two soils.     

Fertilization of maize with compost from cattle manure supplemented with additional mineral nutrients

An alternative approach for cattle manure management on intensive livestock farms is the composting process. An industrial-scale composting plant has been set up in northwest Spain for producing compost from cattle manure. Manure composting involved an increase in pH, electrical conductivity (EC), cation exchange capacity (CEC) and NO3(-)--N concentration, and a decrease in temperature, moisture content, organic matter (OM) content, NH4+--N concentration and C/N ratio. Cu, Zn and Ni concentrations increased due to the reduction of pile mass during the composting process. The resulting compost was applied to a field to study the viability of applying this compost combined with a nitrogen mineral fertilizer as a replacement for the mineral fertilization conventionally used for maize (Zea mays L.). The thermophilic phase of the composting process was very prolonged in the time, which may have slowed down the decomposition of the organic matter and reduced the nitrification process, leading to an over-short maturation phase. The humification and respirometric indexes, however, determined immediately after compost application to the soil, showed it to be stable. Compost application did not decrease the grain yield. A year later, soil pH, OM content and CEC were higher with the compost treatment. Total P, K, Ca and Na concentrations in compost-amended plots were higher than in mineral-fertilized ones, and no significant differences between treatments were found in soil concentrations of NH4+--N,NO3- --N, available P, Mg and B. Compost caused no heavy metal pollution into the soil. Therefore, this compost would be a good substitute for the mineral fertilizers generally used for basal dressing in maize growing.     

Phytostabilisation—A Sustainable Remediation Technique for Zinc in Soils

Two studies were conducted to determine a feasible and practical phytoremediation strategy for Zn-contaminated soils. The aim of the first study was to identify promising plant species capable of Zn remediation for the soils and climatic conditions of British Columbia. The purpose of the second study was to assess the effects of soil amendments in modifying the soil properties and providing the right conditions for the plants to immobilise Zn. Promising plants for phytostabilisation in the first study (Lolium perenne, Festuca rubra and Poa pratensis) were tested in the presence of soil amendments (lime, phosphate and compost, both individually and in combination) in the second study. The efficiency of treatments to stabilise Zn was based on Zn fractionation in the soil and on absorption and partitioning of Zn in plants. Maximum Zn immobilisation was achieved in the soil by a combination of lime, phosphate and compost, in conjunction with growth of P. pratensis.