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The use of biochar has been revealed to have beneficial effects during the composting of manures and other N-rich materials by reducing N losses and enhancing the rate of the process. However, the impact of biochar has not been explored in other complex organic matrices with low N nitrogen that may hinder the composting process. The main novelty of this work was to study the impact of a small amount of biochar (4%) on the composting process of olive mill wastes, which are characterised by a recalcitrant lignocellulosic composition with reduced nitrogen (N) availability. Two treatments: (i) control (olive mill waste 46% + sheep manure 54%, dry weight) and (ii) the same mixture treated with biochar (4%), were composted during 31 weeks. The incorporation of a small amount of biochar improved N cycling by increasing NO3−-N content, indicating a higher nitrifying activity, and reducing N losses by 15% without affecting the amount of N2O released. The use of biochar as an additive for composting could improve the value of olive mill waste composts by reducing N losses and increasing N availability in lignocellulosic and N-poor materials., The authors wish to thank the Spanish Ministry of Economy and Competitiveness for supporting the research project PLANT-CHAR: Agronomical and environmental assessment of the use of biochar in organic waste composting (AGL2012-40143-C02-01) under which this work was financed. M.L. Cayuela is supported by a “Ramón y Cajal” research contract from the Spanish Ministry of Economy and Competitiveness.

This study was performed under the framework of the EU project FP7 KBBE.2011.1.2–02 FERTIPLUS co-funded by the European Commission, Directorate General for Research & Innovation, within the 7th Framework Programme of RTD, Theme 2-Biotechnologies, Agriculture & Food. ML Cayuela is supported by a “Ramón y Cajal” research contract from the Spanish Ministry of Economy and Competitiveness.

The use of biochar in organic waste composting has attracted interest in the last decade due to the environmental and agronomical benefits obtained during the process. Biochar presents favourable physicochemical properties, such as large porosity, surface area and high cation exchange capacity, enabling interaction with major nutrient cycles and favouring microbial growth in the composting pile. The enhanced environmental conditions can promote a change in the microbial communities that can affect important microbially mediated biogeochemical cycles: organic matter degradation and humification, nitrification, denitrification and methanogenesis. The main benefits of the use of biochar in composting are reviewed in this article, with special attention to those related to the process performance, compost microbiology, organic matter degradation and humification, reduction of N losses and greenhouse gas emissions and fate of heavy metals., The authors wish to thank the Spanish Ministry of Economy, Industry and Competitiveness for supporting research project CTM2015-67200-R (MINECO/FEDER) under which this work was financed.

Presentado en el II International Symposium on Organic Matter Management and Compost Use in Horticulture, celebrado en Santiago de Chile del 21 al 24 de octubre de 2013., The agricultural recycling of olive mill and winery wastes through composting and land application is reviewed in this manuscript in terms of the impact on greenhouse gas (GHG) emissions and the potential for soil C sequestration. The rich lignocellulosic composition and the low N availability of olive mill wastes have been revealed as the driving factors of the low degradation rate of these wastes during composting and after soil application. These peculiar characteristics minimise the emission of CH4 and N2O during composting and lead to an efficient and long-term C stabilisation when applied to the soil. These findings confirm the interest of the use of olive mill wastes in agriculture as a strategy to tackle the increasing CO2 concentrations in the atmosphere, which is further supported by the well-known favourable agronomical properties of these wastes. The suitability of this strategy is also examined for winery wastes, which share some similar physicochemical characteristics with olive mill wastes. The agricultural use of these organic wastes could have important environmental benefits in Mediterranean agroecosystems.

The presence of polycyclic aromatic hydrocarbons (PAHs) has been postulated as a mechanism by which biochar might mitigate N2O emissions. We studied whether and to what extent N2O emissions were influenced by the three most abundant PAHs in biochar: naphthalene, phenanthrene and pyrene. We hypothesised that biochars contaminated with PAHs would show a larger N2O mitigation capacity and that increasing PAH concentrations in biochar would lead to higher mitigation potentials. Our results demonstrate that the high-temperature biochar (550 °C) had a higher capacity to mitigate soil N2O emissions than the low-temperature biochar (350 °C). At low PAH concentrations, PAHs do not significantly contribute to the reductions in soil N2O emissions; while biochar stimulated soil N2O emissions when it was spiked with high concentrations of PAHs. This study suggests that the impact of biochar on soil N2O emissions is due to other compositional and/or structural properties of biochar rather than to PAH concentration., This study was performed under the framework of the EU project FP7 KBBE.2011.1.2–02 FERTIPLUS co-funded by the European Commission, Directorate General for Research & Innovation, within the 7th Framework Programme of RTD, Theme 2-Biotechnologies, Agriculture & Food. ML Cayuela is supported by a “Ramón y Cajal” research contract from the Spanish Ministry of Economy and Competitiveness.

Cation exchange capacity of manures has been found well correlationed with different parameters which define their humification grade. The CECCh and CEC/Ch ratios appear as suitable values to understand the humification state in these manures.

The use of appropriate amendments derived from two phase olive mill wastes (TPOMW) can represent a suitable option to maintain and restore C levels in agricultural soils under Mediterranean climates. We evaluated soil organic matter stabilisation pathways among different humic pools in a Calcaric Cambisol amended with 2% (40 Mg ha− 1) of TPOMW composting mixtures of different composition and at different degrees of stabilisation: starting mixture, after 14 weeks of composting (thermophilic stage) and after 30 weeks (mature compost). Non-humified soil organic C and two different fractions of humic acids (HA), namely free HA (biochemically stabilised) and bound HA (biochemically and chemically stabilised) were obtained by sequential extraction with NaOH and alkaline Na4P2O7 after 90 and 150-days incubation. HA were characterised by thermal analysis, size exclusion chromatography (HPLC-SEC), FTIR and 13C CPMAS-TOSS NMR. Amendments promoted incorporation of altered lignin structures, carbohydrate moieties and N-containing compounds into free HA and to a lesser extent into the bound HA, and increased the proportion of high MW fractions. There was an average increase of 40% for non-humic C in the free C fraction even after 90 days of incubation under optimum conditions for mineralisation. Augmentation of bound C resulted in an average increase of about 0.7 Mg ha− 1 of humic C in amended soils. This increase is important as it contributes to one of the more inert soil C pools and could represent a useful indicator for soil C stabilisation., This work was supported by the Spanish Ministry of Science and Innovation, research projects Ref. CTM2005-05324 and CTM2009-14073-C02-02.

Application of biochar (10% v/v) to a manure composting matrix was investigated to evaluate its effect on the chemical composition of humic substances during the composting process. The characteristics of the humic acid (HA) and fulvic acid (FA) fractions were analyzed in compost mixtures originating from two different manures (poultry manure (PM) and cow manure (CM)). The C contents of HA and FA from the manure compost/biochar blends (PM+B and CM+B) were higher than those from PM and CM, with an enhanced recalcitrant fraction, as determined by thermogravimetric analysis. Spectroscopic analysis showed that enrichment of aromatic-C and carboxylic-C occurred in the FA fractions of PM+B and CM+B to a greater extent than in PM and CM. Biochar addition into the composting mixture improved the final compost quality, especially for the light humified fraction (FA)., We are very grateful to the Japan Society for the Promotion of Science for their financial support as well as to the CSIC (Consejo Superior de Investigaciones Científicas) programs for supporting this bilateral project. The financial support from the Fundación Séneca (Murcia, Spain), the Spanish Ministry of Economy and Competitiveness (research project AGL2012-40143-C02-01) and the government agency Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) (Program “Atração de Jovens Talentos”) are also appreciated.

O objetivo do presente trabalho foi avaliar o efeito de diferentes enriquecimentos minerais na compostagem de resíduos provenientes da produção de biodiesel sobre características químicas do produto final. Foram utilizados os seguintes resíduos: bagaço de cana, cinza de bagaço de cana, esterco de galinha poedeira, torta de filtro e farelo de mamona. Estes materiais foram misturados e enriquecidos com fertilizante mineral NPK, pós de rochas de serpentinito + micaxisto e pó de gnaisse, obtendo-se oito compostos orgânicos distintos. Aos 0, 30, 90 e 120 dias de compostagem, essas misturas foram amostrados e realizadas análises de pH, condutividade elétrica, C, N, cinzas e na última amostragem foram determinados CTC e nutrientes totais. Apenas o composto enriquecido com NPK, sendo o N na forma de sulfato de amônio, atendeu a legislação pertinente a compostos orgânicos, enquanto os compostos contendo torta de filtro e mamona com e sem enriquecimento apresentaram pH abaixo do limite e os demais apresentaram teores de N ou C abaixo do mínimo estabelecido na legislação brasileira. A adição de pós de rochas de serpentinito + micaxisto contribuiu para elevação da CTC dos compostos.The aim of this work was to evaluate the effect of different mineral enrichments during composting of biodiesel production residues on chemical characteristics of the end product. The following materials were used: sugar cane bagasse, ashes of sugar cane bagasse, poultry manure, filter cake and castor oil cake. These materials were mixed and enriched with mineral nutrients NPK, serpentinite and micaxist powdered rocks and gneiss powdered rocks, to obtain eight different composts. At 0, 30, 90 and 120 days after starting composting, these materials were sampled to measure pH, electrical conductivity, C, N, ashes, and, at the last sampling, CEC and total nutrients. Only the compost enriched with NPK (with N as ammonium sulphate) comply with the legislation pertinent to compost, while the composts that received filter cake and castor oil cake, with and without, mineral addition presented pH below the accepted limit and had C and N concentrations below the minimum established in the Brazilian legislation. The addition of serpentinite and micaxist powdered rocks contributed to raise the CEC of composts.

[PT] O objetivo do presente trabalho foi avaliar o efeito de diferentes enriquecimentos minerais na compostagem de resíduos provenientes da produção de biodiesel sobre características químicas do produto final. Foram utilizados os seguintes resíduos: bagaço de cana, cinza de bagaço de cana, esterco de galinha poedeira, torta de filtro e farelo de mamona. Estes materiais foram misturados e enriquecidos com fertilizante mineral NPK, pós de rochas de serpentinito + micaxisto e pó de gnaisse, obtendo-se oito compostos orgânicos distintos. Aos 0, 30, 90 e 120 dias de compostagem, essas misturas foram amostrados e realizadas análises de pH, condutividade elétrica, C, N, cinzas e na última amostragem foram determinados CTC e nutrientes totais. Apenas o composto enriquecido com NPK, sendo o N na forma de sulfato de amônio, atendeu a legislação pertinente a compostos orgânicos, enquanto os compostos contendo torta de filtro e mamona com e sem enriquecimento apresentaram pH abaixo do limite e os demais apresentaram teores de N ou C abaixo do mínimo estabelecido na legislação brasileira. A adição de pós de rochas de serpentinito + micaxisto contribuiu para elevação da CTC dos compostos., [EN] The aim of this work was to evaluate the effect of different mineral enrichments during composting of biodiesel production residues on chemical characteristics of the end product. The following materials were used: sugar cane bagasse, ashes of sugar cane bagasse, poultry manure, filter cake and castor oil cake. These materials were mixed and enriched with mineral nutrients NPK, serpentinite and micaxist powdered rocks and gneiss powdered rocks, to obtain eight different composts. At 0, 30, 90 and 120 days after starting composting, these materials were sampled to measure pH, electrical conductivity, C, N, ashes, and, at the last sampling, CEC and total nutrients. Only the compost enriched with NPK (with N as ammonium sulphate) comply with the legislation pertinent to compost, while the composts that received filter cake and castor oil cake, with and without, mineral addition presented pH below the accepted limit and had C and N concentrations below the minimum established in the Brazilian legislation. The addition of serpentinite and micaxist powdered rocks contributed to raise the CEC of composts., Os autores agradecem ao CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) e a FAPEAL (Fundação de Amparo à Pesquisa do Estado de Alagoas) pelo suporte financeiro para realização desta pesquisa.

A composting study was performed to assess the impact of biochar addition to a mixture of poultry manure and barley straw. Two treatments: control (78% poultry manure + 22% barley straw, dry weight) and the same mixture amended with biochar (3% dry weight), were composted in duplicated windrows during 19 weeks. Typical monitoring parameters and gaseous emissions (CO2, CO, CH4, N2O and H2S) were evaluated during the process as well as the agronomical quality of the end-products. Biochar accelerated organic matter degradation and ammonium formation during the thermophilic phase and enhanced nitrification during the maturation phase. Our results suggest that biochar, as composting additive, improved the physical properties of the mixture by preventing the formation of clumps larger than 70 mm. It favoured microbiological activity without a relevant impact on N losses and gaseous emissions. It was estimated that biochar addition at 3% could reduce the composting time by 20%., The authors wish to thank the Spanish Ministry of Economy and Competitiveness for supporting the research project Ref. AGL2012-40143-C02-01 under which this work was financed and ML Cayuela’s “Ramón y Cajal” research contract.

There is actually a common consensus in using biological technologies for the treatment of organic wastes. For instance, composting is used for aerobic biological stabilisation of organic wastes. The amount of materials and the variety of wastes composted are increasing. However, composting is inherently a process generating gaseous emissions. Greenhouse gases (GHG) such as carbon dioxide, methane and nitrous oxide from compost are of special relevance for global warming. Although a part of these gases is inherent to the process, another important part can be abated by low-cost biological technologies such as biofiltration and its variations. This article reviews the emission of GHG from composting gases, from detection and measurement to minimisation and abatement. Special emphasis is given to the measurement of GHG to obtain reliable emission factors for the different composting technologies. These factors will help to compare different waste treatment options based on overall analysis tools such as life cycle assessment. A specific chapter is related to carbon and nitrogen dynamics in the composting matrix, and their consequences on the production of carbon and nitrogen gases. Finally, we present a review of the best available practices to minimise the GHG emissions from composting and the final treatment of composting off-gases., The authors wish to thank the financial support of the Spanish Ministerio de Economía y Competitividad (Project CTM2012-33663-TECNO).

8 pages, 3 figures, 4 tables., The suitability of olive mill wastewater (OMW) for composting was studied by the addition of this liquid waste to a mixture of cotton gin waste and sewage sludge, and its composting was compared with that of another pile of similar composition, but without olive mill wastewater. Both piles were composted by the Rutgers static pile system in a pilot plant. To study the effects of both composts on plant yield and soil properties, a plot experiment was carried out with Swiss chard (Beta vulgaris L. var. cicla). Five treatments were applied: mineral fertiliser and two doses (30 and 60 tonnes ha−1) of both composts. The olive mill wastewater addition produced a compost with lower organic matter and nitrate concentrations, higher electrical conductivity, and a stabilised and humified organic matter similar to that of the compost produced without olive mill wastewater. The olive mill wastewater compost application to soil did not injure plants, producing a similar plant yield to both compost without olive mill wastewater and inorganic fertiliser. Also, the accumulation of potentially toxic heavy metals in plants cultivated with organic or mineral fertilisers did not reveal significant differences. The olive mill wastewater compost application to soil also improved the chemical and physicochemical properties of the soil., This research was carried out in the EU framework contract No. EVWA-CT 92-0006.

8 pages, 2 figures, 1 table., 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., This research was supported by a grant from the Italian Ministry for Agricultural and Forestry Policies (MiPAF), Project PARSIFAL, General Series, Paper No. 7.

A field experiment, lasting 14 months, was carried out in order to assess the effect of organic amendment and lime addition on the bioavailability of heavy metals in contaminated soils. The experiment took place in a soil affected by acid, highly toxic pyritic waste from the Aznalcollar mine (Seville, Spain) in April 1998. The following treatments were applied (3 plots per treatment): cow manure, a mature compost, lime (to plots having pH < 4), and control without amendment. During the study two crops of Brassica juncea were grown, with two additions of each organic amendment. Throughout the study, the evolution of soil pH, total and available (DTPA-extractable) heavy metals content (Zn, Cu, Mn, Fe, Pb and Cd), electrical conductivity (EC), soluble sulphates and plant growth and heavy metal uptake were followed. The study indicates that: (1) soil acidification, due to the oxidation of metallic sulphides in the soil, increased heavy metal bioavailability; (2) liming succeeded in controlling the soil acidification; and (3) the organic materials generally promoted fixation of heavy metals in non-available soil fractions, with Cu bioavailability being particularly affected by the organic treatments.

We thank the Spanish Comision Interministerial de Ciencia y Tecnologia (CICYT) for supporting PETRI project reference 95-0234-OP-02-02 under which this work was financed. We also thank Dr Louise Fletcher for her help with the editing.

The composting of spent mushroom substrate yields a product that is valuable for agricultural utilization and soil reclamation. Experiments were conducted to determine if the inclusion of rock dust, a mineral waste, could accelerate the composting process. The composting model system consisted of a reactor with an integrated control system that controlled the temperature and oxygen concentration of the composting mass. The addition of rock dust increased indicators of microbial activity in the start-up period of the composting process, the mesophilic phase, resulting in increased temperature and protein, and higher oxygen requirements.

The effects of the composting process on the chemical and structural properties of humic acids have been studied in seven different organic waste mixtures from different origin. Only slight changes in elemental composition have been found in the humic acids after the composting process pointing to a more aromatic structure with higher proportions of oxygen and nitrogen. Functional groups were the most sensitive to the changes caused by the composting process showing a marked increase in the total acidity and phenolic, carboxyl and carbonyl groups. Gel permeation chromatography showed a slight increase in the average molecular weight of the humic acids. Infrared spectroscopy did not show important differences in humic acid structure but a clear decrease in the intensity of the bands in the region 3000-2850 cm(-1) corresponding to the aliphatic fractions. As a general result, the composting process yields humic acids in which the elemental and functional composition are closer to that of the more humified soil humic acids.

In spite of the numerous studies reporting a decrease in soil nitrous oxide (N2O) emissions after biochar amendment, there is still a lack of understanding of the processes involved. Hence the subject remains controversial, with a number of studies showing no changes or even an increase in N2O emissions after biochar soil application. Unraveling the exact causes of these changes, and in which circumstances biochar decreases or increases emissions, is vital to developing and applying successful mitigation strategies. With this objective, we studied two soils (Haplic Phaeozem (HP) and Haplic Calcisol (HC)), which showed opposed responses to biochar amendment. Under the same experimental conditions, the addition of biochar to soil HP decreased N2O emissions by 76%; whereas it increased emissions by 54% in soil HC. We combined microcosm experiments adding different nitrogen fertilizers, stable isotope techniques and the use of a nitrification inhibitor (dicyciandiamide) with the aim of improving our understanding of the mechanisms involved in the formation of N2O in these two soils. Evidence suggests that denitrification is the main pathway leading to N2O emissions in soil HP, and ammonia oxidation and nitrifier-denitrification being the major processes generating N2O in soil HC. Biochar systematically stimulated nitrification in soil HC, which was probably the cause of the increased N2O emissions. Here we demonstrate that the effectiveness of using biochar for reducing N2O emissions from a particular soil is linked to its dominant N2O formation pathway.

In spite of the numerous studies reporting a decrease in soil nitrous oxide (N2O) emissions after biochar amendment, there is still a lack of understanding of the processes involved. Hence the subject remains controversial, with a number of studies showing no changes or even an increase in N2O emissions after biochar soil application. Unraveling the exact causes of these changes, and in which circumstances biochar decreases or increases emissions, is vital to developing and applying successful mitigation strategies. With this objective, we studied two soils (Haplic Phaeozem (HP) and Haplic Calcisol (HC)), which showed opposed responses to biochar amendment. Under the same experimental conditions, the addition of biochar to soil HP decreased N2O emissions by 76%; whereas it increased emissions by 54% in soil HC. We combined microcosm experiments adding different nitrogen fertilizers, stable isotope techniques and the use of a nitrification inhibitor (dicyandiamide)with the aim of improving our understanding of the mechanisms involved in the formation of N2O in these two soils. Evidence suggests that denitrification is the main pathway leading to N2O emissions in soil HP, and ammonia oxidation and nitrifier-denitrification being the major processes generating N2O in soil HC. Biochar systematically stimulated nitrification in soil HC, which was probably the cause of the increased N2O emissions. Here we demonstrate that the effectiveness of using biochar for reducing N2O emissions from a particular soil is linked to its dominant N2O formation pathway., European Community Marie Curie Fellowship (FP7PEOPLE-2010-MC-European Reintegration Grants (ERG) #277069)

More than two thirds of global nitrous oxide (N2O) emissions originate from soil, mainly associated with the extensive use of nitrogen (N) fertilizers in agriculture. Although the interaction of black carbon with the N cycle has been long recognized, the impact of biochar on N2O emissions has only recently been studied. Herein we reflect on proposed hypotheses to explain N2O decrease with biochar, linking them to specific mechanisms for N2O formation and consumption in soil. Moreover, to assist in elucidating key mechanisms in which biochar may act in mitigating emissions of N2O, we undertook a meta-analysis using published literature from 2007 to 2013. This quantitative analysis used 30 studies with 261 experimental treatments. Overall, we found that biochar reduced soil N2O emissions by 54% in laboratory and field studies. The biochar feedstock, pyrolysis conditions and C/N ratio were shown to be key factors influencing emissions of N2O while a direct correlation was found between the biochar application rate and N2O emission reductions. Interactions between soil texture and biochar and the chemical form of N fertilizer applied with biochar were also found to have a major influence on soil N2O emissions. While there is clear evidence that, in many cases, emissions of N2O are reduced, there is still a significant lack in understanding of the key mechanisms which result in these changed emissions. As such, we have guided readers with suggestions to address specific research gaps, which we anticipate will enhance our knowledge and understanding of biochar's N2O emission mitigation potential., This study was performed under the framework of the EU project FP7 KBBE.2011.1.2-02 FERTIPLUS “Reducing mineral fertilisers and agro-chemicals by recycling treated organic waste as compost and bio-char” project nr. 289853 co-funded by the European Commission, Directorate General for Research & Innovation, within the 7th Framework Programme of RTD, Theme 2 – Biotechnologies, Agriculture & Food. The European Social Fund is acknowledged for co-financing MLC's JAE-Doc contract at CSIC.

In order to study the suitability of olive mill wastewater (OMW) for composting, thisliquid waste was added to two different mixtures of agroindustrial and urban wastesand the composting process was compared with two other piles of similar composition,but without OMW. These four piles were studied in a pilot plant using the Rutgers staticpile system. The addition of OMW produced a greater proportion of degradable organic matter or a higher degradation rate, higher electrical conductivity values, greater losses of total N and lower nitrification than in piles without OMW. Its addition also restricted the increase of the cation exchange capacity and provoked the appearance of phytotoxicity or a longer persistence of phytotoxicity. However, in general, all the composts showed increases in the cation exchange capacity, the percentage of humic acid-like carbon, the polymerisation ratio of these humic substances (which revealed that the organic matter had been humified during composting) and the germination index, the latter indicating the reduction of phytotoxicity during the process.

The decomposition of seven different organic waste mixtures prepared with sewage sludges, animal manures, city refuse and industrial and plant residues, was studied during their aerobic incubation with soil. The waste mixtures were composted by the Rutgers static pile system, and four samples of each mixture were collected at various composting stages: the initial mixture, and samples taken during the thermophilic phase, at the end of the active phase and after maturation. These samples were added to a calcareous silt loam soil at a rate of 200 mg per 10 g soil, and the CO2–C evolution was determined during 70 days of aerobic incubation at 28°C. Carbon mineralization decreased as the composting time lengthened. The lowest values of C mineralization were found for the mature samples, and only a compost which had not attained an advanced degree of maturation gave results higher than 25% of TOC. Carbon mineralization followed a combined first- and zero-order kinetic model in most of the samples, suggesting that the organic C of the composting wastes was made up of two organic pools of differing degrees of stability. However, the differences in the slow C mineralization pool at the end of the active phase and after maturation were very small, indicating that the organic matter at both stages was of a similar microbial stability. Comparing the C mineralization which takes place in soil and during composting, it can be concluded that composting is the best way of obtaining maximum C stabilization, which is an important factor in soil conservation and reclamation., The authors wish to thank Dr. J.L. Gonzalez-Andujar for his statistical advice, and Mr. P. Thomas for the English revision. Research was carried out in the framework of EC contract N° EVWA-CT 92-0006.

Incubation experiments with soil were made to study C and N mineralization in a sewage sludge–cotton waste mixture at different stages of the composting process performed by the Rutgers static pile system. Three composting samples were selected: initial mixture (I); the end of the active phase (E); and the mature compost (M). The CO2-C evolved (as % of added C) from the composting samples after 70 d decreased in the order: I (62.3%)>E (22.3%)>M (19.8%). The course of C mineralization fitted a combined first- and zero-order kinetic for I and a first-order kinetic for E and M. Potentially mineralizable C was very similar in E and M, whereas a mineralization rate constant (K) lower than 0.033 d−1 may be taken as characteristic of a mature compost. N was immobilized in soil treated with sample I, although it only lasted for 3 d in soil treated with sample E, followed by a mineralization phase. In soil treated with sample M the phase of N mineralization started the first day, which means that immature compost leads to an initial N immobilization in the soil. Potentially mineralizable N, calculated from the first-order kinetic function, was low, increasing from E (5.45%) to M (9.12%), the opposite occurring with the rate constant, leading to very close values of mineralization rate (No×K). An experiment with perennial ryegrass (Lolium perenne) in which the same composting samples were applied to the soil, confirmed the results of N mineralization. Addition of I to soil caused an initial deficiency of N in plants due to N immobilization and competition between plants and microorganisms for inorganic N. However, further re-mineralization of immobilized N provided similar N to plants as that in the unfertilized soil. The initial waste mixture may require a long safety period after addition to soil before sowing, and it would release inorganic N in the soil later in the cropping season. The compost which had not undergone a maturation phase had similar nutritional N value as the mineral fertilizer, but the greatest N fertilizer efficiency was found in the mature compost, because of its high concentration of NO3-N and to a lesser extent also to its mineralizable N. The mature compost can even be added to the soil when the crop is growing.

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., The authors wish to thank the Spanish Ministry of Science and Innovation for supporting research projects Ref. CTM2005-05324 and CTM2009-1473-C02-02 under which this work was financed. A. Fernández-Hernández wishes to thank for the contract grant funded by the Agricultural Research Institute of Spain (INIA) and the European Social Fund.

Agricultural soils represent the main source of anthropogenic N2O emissions. Recently, interactions of black carbon with the nitrogen cycle have been recognized and the use of biochar is being investigated as a means to reduce N2O emissions. However, the mechanisms of reduction remain unclear. Here we demonstrate the significant impact of biochar on denitrification, with a consistent decrease in N2O emissions by 10–90% in 14 different agricultural soils. Using the 15N gas-flux method we observed a consistent reduction of the N2O/(N2 + N2O) ratio, which demonstrates that biochar facilitates the last step of denitrification. Biochar acid buffer capacity was identified as an important aspect for mitigation that was not primarily caused by a pH shift in soil. We propose the function of biochar as an “electron shuttle” that facilitates the transfer of electrons to soil denitrifying microorganisms, which together with its liming effect would promote the reduction of N2O to N2., This work was possible thanks to the OECD Cooperative Research Program that funded MLC's stay at Cornell University and to a European Community Marie Curie Fellowship (FP7-PEOPLE-2010-MC-European Re-integration Grants (ERG) #277069). We acknowledge additional funding by USDA Hatch, by the National Science Foundation's Basic Research for Enabling Agricultural Development (NSF-BREAD grant number IOS-0965336) and the Fondation des Fondateurs.

Solid phase microextraction (SPME) is a fast, cheap and solvent free methodology widely used for environmental analysis. A SPME methodology has been optimized for the analysis of VOCs in a range of matrices covering different soils of varying textures, organic matrices from manures and composts from different origins, and biochars. The performance of the technique was compared for the different matrices spiked with a multicomponent VOC mixture, selected to cover different VOC groups of environmental relevance (ketone, terpene, alcohol, aliphatic hydrocarbons and alkylbenzenes). VOC recovery was dependent on the nature itself of the VOC and the matrix characteristics. The SPME analysis of non-polar compounds, such as alkylbenzenes, terpenes and aliphatic hydrocarbons, was markedly affected by the type of matrix as a consequence of the competition for the adsorption sites in the SPME fiber. These non-polar compounds were strongly retained in the biochar surfaces limiting the use of SPME for this type of matrices. However, this adsorption capacity was not evident when biochar had undergone a weathering/aging process through composting. Polar compounds (alcohol and ketone) showed a similar behavior in all matrices, as a consequence of the hydrophilic characteristics, affected by water content in the matrix. SPME showed a good performance for soils and organic matrices especially for non-polar compounds, achieving a limit of detection (LD) and limit of quantification (LQ) of 0.02 and 0.03 ng g−1 for non-polar compounds and poor extraction for more hydrophilic and polar compounds (LD and LQ higher 310 and 490 ng g−1). The characteristics of the matrix, especially pH and organic matter, had a marked impact on SPME, due to the competition of the analytes for active sites in the fiber, but VOC biodegradation should not be discarded in matrices with active microbial biomass., The authors thank Fundação de Amparo à Pesquisa do Estado de Minas Gerais – FAPEMIG (Process: CAG 20008-09) for financing the predoctoral stay of Mr. Fábio Satoshi Higashikawa at CEBAS-CSIC (Spain). This research was financed by a grant from the Spanish Ministry of Science and Innovation, research projects CTM2009-14073-C02-02 and AGL2012-40143-C02-01.

Five different piles were prepared by mixing olive mill wastewater (alpechin) and alpechin sludge with two bulking agents (cotton waste and maize straw) and two organic wastes with high content of nitrogen (sewage sludge and poultry manure), which were composted by the Rutgers static pile composting system in a pilot plant. The aim of this work was to study the evolution of total nitrogen and different forms of organic matter and evaluate the variation in the aerobic bacterial microbiota present and biotoxicity during the composting process. In piles prepared with alpechin, the use of the maize straw as a bulking agent reduced the nitrogen losses whereas the use of sewage sludge, instead of poultry manure, with cotton waste originated the highest degradation of organic matter. In piles prepared with alpechin sludge a similar evolution of the composting process was observed. There were not great variations during composting in the aerobic bacterial microbiota present in the mixtures. However, the pile prepared with alpechin sludge and maize straw was only one to present bacteria capable of growing in alpechin, and the toxicity study showed that this was only present in the starting mixtures., This research was supported by the EU Contract No. EVWA-CT92-0006 Bioremediation of Olive Mill Wasters for Use as Fertilizer.

Solutions of 0·1m and 0·25m potassium hydroxide were employed to extract a humic fertilizer from lignite at 20, 50 and 80°C. The effects of the temperature on the yields of humic and fulvic acids and on the characteristics of the former were investigated. Higher extraction temperatures did not significantly enhance yield in either case, and neither were the ratios between humic and fulvic acids significantly affected. Humic acids released by hot 0·25M KOH solutions held less N-rich material and exhibited a lower content of functional groups than those obtained at 20°C. When 0·1M KOH was employed at 50 and 80°C, changes in the molecular structure of humic acids were less apparent but there were fewer functional groups than in the humic acids obtained at 20°C. Increasing extraction temperatures were matched by the larger molecular size of humic acids extracted with both KOH solutions.

The low degradation rate of two-phase olive mill wastes (TPOMW) during composting and after soil application is a characteristic feature of these materials. The aim of this work was to evaluate the relationship between the lignocellulosic fraction of TPOMW and the organic matter (OM) degradation rate in three agricultural soils amended with four TPOMW composting mixtures at different degree of stabilisation and prepared with different bulking agents and N sources. The mineralisation kinetics of TPOMW composting mixtures in soil reflected a large amount of slowly mineralisable C even in the starting mixtures (I and T1) where this fraction represented up to 85% of the total potentially mineralisable C pool. The effect of rich lignocellulosic composition was confirmed by the study of the DTS (50% dry TPOMW + 50% sheep manure) mixtures prepared with dry TPOMW, which had undergone partial degradation in a storage pond for one year before composting. These DTS samples showed a more similar kinetic behaviour in soil than the more transformed composting mixtures as reflected in the principal component analysis (PCA) diagram, where they were grouped in the same quadrant dominated by the lignin/holocellulose ratio. Soils amended with mature composts evolved very low amounts of C (between 2 and 6% of the added C) after two months of incubation, which highlights the suitability of these materials as a suitable C source for the soil to promote long term soil C stabilisation., This work was supported by the Spanish Ministry of Science and Innovation, research projects Ref. CTM2005-05324 and CTM2009-1473-C02-02.

The oxidable carbon content of 46 calcareous soils from the South‐East of Spain was determined by the Walkley and Black method and compared with the total organic carbon (C) content obtained by an automatic microanalysis method. The results were fitted to linear, curvilinear, and exponential equations which permit the conversion of the oxidable C values into those of total organic C when no direct means of analysis of the latter is available. A conversion factor of 1.26 is recommended.

Changes in amounts of macro-(N, P, K) and micro-nutrients (Fe, Mn, Zn and Cu) were determined in two calcareous soils amended over an eight-month period with pig slurry applications ranging from 0 to 500 m3/ha, and planted in containers with green pepper (Capsicum annuum). Total N and exchangeable K increased after slurry applications of 300 m3/ha or more, and available P increased after the smallest application rate (100m3/ha). Maximum crop nutrient uptakes of 41, 40 and 91% for N, P and K occurred with the smallest dose of slurry. Large losses of N, ranging from 27 to 74% (mean 55%) of N added to soil, occurred with all slurry treatments. From 41 to 71% (mean 55%) of the total P added in pig slurry was fixed in non-assimilable forms. Most of the K from the pig slurry was available to the plants. Most of the micro-nutrients (Fe, Mn, Zn and Cu) from the slurry were immobilized in the soil, probably because of the high pH and the small amounts of organic matter in both the slurries and soils tested.

The mineralization and nitrification processes in pig slurry were investigated in Spain in 1990 in three calcareous soils, differing mainly in content and type of clay, two classified as Typic Calciorthids and one as a Xerollic Calciorthid. Two different amounts of slurry were mixed with the soils, one equivalent to 273 mg N/kg soil and the other equivalent to 546 mg N/kg soil. The mixtures of soil and slurry were aerobically incubated for 16 weeks at 28 °C. A mean initial immobilization of 22·19% of the total-N added was detected in soils treated with the lower rate of slurry. The amount of mineralized N after 112 days of incubation was between 36 and 47% of the total-N added with the lower slurry application to the three soils. The net amount of N mineralized throughout the experiment was therefore within the range 14–23% of the total-N added. The nitrification of the NH4-N added to the soil began after 7 days of incubation, and followed a first-order kinetic model. The mean values of potential nitrate formation were 61 and 51% of the total-N added in soils amended with 273 and 546 mg N as pig slurry per kg soil respectively. The rate constants were higher in the treatments with the lower slurry application (0·043–0·083 per day). Therefore, in these treatments, the nitrification process was faster and total nitrate levels were higher than in soils receiving double that amount of slurry. The NO3-N evolution was parallel to the total-N evolution from the 14th day of incubation onwards. The N-mineralization process was limited by the transformation of the organic-N into ammonium (ammonification).

[EN] The contribution of humic substances of different composts to the synthesis of humin in a tropical soil was evaluated. Increasing doses (0, 13, 26, 52, and 104 Mg ha-1) of five different composts consisting of agroinpowderrial residues were applied to a Red-Yellow Latosol. These composts were chemically characterized and 13C NMR determined and the quantity of the functional alkyl groups of humic acids applied to the soil as compost was estimated. Thirty days after application of the treatments, organic matter samples were collected for fractionation of humic acids (HA), fulvic acids (FA) and humin (HU), from which the ratios HA/FA and (HA + FA)/HU were calculated. The application of the composts based on castor cake resulted in the highest HU levels in the soil; alkyl groups of the HA fraction of the composts were predominant in the organic components added to the HU soil fraction., [PT] Avaliou-se a contribuição de substâncias húmicas provenientes de diferentes compostos orgânicos na síntese de humina em um solo tropical. Para isso, foram adicionadas doses crescentes (0, 13, 26, 52 e 104 Mg ha-1) de cinco diferentes compostos orgânicos formulados com resíduos orgânicos agroindustriais em um Latossolo Vermelho-Amarelo. As substâncias húmicas desses compostos foram caracterizadas quimicamente e por ressonância nuclear magnética do 13C, sendo estimados os quantitativos dos grupos funcionais alquil dos ácidos húmicos aplicados no solo via composto. Trinta dias após aplicação dos tratamentos, coletaram-se amostras de solo para fracionamento da matéria orgânica em ácidos húmicos (AH), ácidos fúlvicos (FA) e humina (HU), a partir dos quais foram calculadas as relações AH/FA e (AH + FA)/HU. A aplicação do composto à base de torta de mamona contribuiu para obtenção de teores mais elevados de HU no solo; a incorporação de componentes orgânicos à fração HU do solo foi regida pelo conteúdo de grupos alquil da fração AH dos compostos., The authors wish to thank the CNPq and FAPEAL for the financial support for this research, as well as Dr. Ana de Godos de Francisco and Diego Martínez Pérez of SACE – Universidad de Murcia – Spain, for their help with the 13C NMR spectroscopy.

The evolution of CO2, CH4 and N2O were monitored in five composting mixtures prepared from two-phase olive mill waste (TPOMW) and different agroindustrial by-products in order to assess the effect of the initial composition and the N source on greenhouse gas emission. Surface gas fluxes were measured using a closed static chamber and compared to the changes in different organic matter fractions (organic and watersoluble C) and N forms (NH4+ and NO3-). CH4 emissions depended on the organic matter mineralisation dynamics and the incorporation of manure in the starting mixture. The highest CH4 fluxes were registered during the intense degradation at early stages of the process (up to 100 g C m−2 d−1). The emission of N2O (0–0.9 g N m−2 d−1) occurred from 6th to 10th wk of composting (bioxidative phase), coinciding with an intense nitrification in the pile. The use of urea enhanced the N2O emission up to 3.7 g N m−2 d−1, due to an increase in available mineral N in the pile. Even though well managed TPOMW composting piles only represent a minor source of CH4 and N2O emissions, the addition of urea and easily available C fractions to the starting mixtures can significantly increase the environmental impact of TPOMW composting as far as greenhouse gas emissions are concerned., The authors wish to thank the Spanish Ministry of Science and Innovation for supporting research projects Ref. CTM2005-05324 and CTM2009-1473-C02-02 under which this work was financed.

Two-phase olive mill waste (TPOMW) is a semisolid sludge generated by the olive oil industry. Its recycling as a soil amendment, either unprocessed or composted, is being promoted as a beneficial agricultural practice in the Mediterranean area. One of the major difficulties when composting TPOMW is the compaction of the material due to its dough-like texture, which leads to an inadequate aeration. For this reason, the addition of bulking agents is particularly important to attain a proper composting process. In this study we followed the evolution of two composting mixtures (A and B) prepared by mixing equal amounts of TPOMW and sheep litter (SL) (in a dry weight basis). In pile B grape stalks (GS) were added (10% dry weight) as bulking agent to study their effect on the development of the composting process and the final compost quality. The incorporation of grape stalks to the composting mixture changed the organic matter (OM) degradation dynamics and notably reduced the total amount of lixiviates. The evolution of several maturation indices (C/N, germination index, water soluble carbon, humification indices, C/N in the leachates) showed a faster and improved composting process when GS were added. Moreover, chemical (NH4 +, NO3 −, cation exchange capacity, macro and micronutrients, heavy metals) and physical properties (bulk and real densities, air content, total water holding capacity, porosity) of the final composts were analysed and confirmed the superior quality of the compost where GS were added., This work was possible thanks to Fundación Séneca (Agencia Regional de Ciencia y Tecnologia. Región de Murcia) that financed the research project ref. 03062PI/05. Mari Luz Cayuela thanks Fundación Séneca for financing her postdoctoral contract Saavedra-Fajardo in CEBAS-CSIC.

The aim of this study was to evaluate the use of biochar (produced by slow pyrolysis of Eucalyptus grandis biomass) as bulking agent for the composting of poultry manure. Three composting mixtures were prepared by the turned-pile system by mixing poultry manure with different organic wastes used as bulking agent (biochar, coffee husk and sawdust) in a proportion of 1:1 (fresh weight). Despite the inert nature of biochar, the composting mixture prepared with biochar underwent an organic matter degradation of 70% of the initial content. The organic matter of the poultry manure–biochar mixture was characterised by a high polymerisation degree of the humic-like substances, with a relative high proportion of humic acids in relation to fulvic acids. At the end of the composting process, the humic acid fraction represented more than 90% of the alkali extractable fraction, reflecting the intense humification of this material. Enrichment of poultry manure with biochar reduced the losses of nitrogen in the mature composts, although the use of sawdust would be more efficient in preserving the organic matter and nitrogen in the mature compost., The authors thank CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for financing the predoctoral stay of Mr. Bruno Dias at CEBAS-CSIC (Spain). This research was partially financed by a grant from the Spanish Ministry of Science and Innovation (Intramural CSIC ref: 200840I060) and a grant from the Fundação de Amparo à Pesquisa do Estado de Minas Gerais – Fapemig (Process: CAG-APQ – 5362 – 3.08/07).

Six different wastewater treatment plants were monitored in order to identify the main bioaerosol sources and to evaluate the effect of the aeration system used in the biological treatment (air diffusion, horizontal rotors and surface turbine aerators) on the airborne microorganism levels to which workers may be exposed. Air samples were collected by using a single stage impactor. Total count of mesophilic bacteria was used as the monitoring parameter to compare the impact of the aeration system on generic bacterial bioaerosols rather than a quantitative estimation for pathogens or fecal indicator microbes. In this study, pre-treatment, biological treatment and sludge thickening were the processes that generated the highest amount of bioaerosols. Aeration systems involving mechanical agitation of the wastewater, such as horizontal rotors and surface turbines, generated a larger amount of bioaerosols (between 450 and 4580 CFU/m3) than air diffuser aerators (between 22 and 57 CFU/m3). The levels of airborne bacteria generated by air diffusers were very similar to those registered at the background locations (lower than 50 CFU/m3), unaffected by the activities taking place in the wastewater treatment plant. The use of air diffusers as an aeration system for the biological treatment would significantly minimise the potential biological hazard that wastewater treatment plant workers may be exposed to., This research was supported through a European Community Marie Curie Fellowship.

The hydrolysis of the fluorescein diacetate (FDA), related to several soil hydrolases, has been utilised to estimate the potential microbial activity of soil freshly amended with a wide range of organic amendments and compared to the size and activity of soil microflora, measured by the microbial biomass C (B C) and CO2 evolution, respectively. Three different composting mixtures at different phases of the composting process were added to a semi-arid soil and incubated for 2 months under laboratory conditions. The addition of the organic amendment immediately increased B C and both measures of microbial activity (FDA and CO2 evolution). Highly significant correlations were found between FDA hydrolysis and B C for soil amended with the three composting mixtures (r = 0.81–0.96; P, This research was supported by a grant from the Italian Ministry for Agricultural, Food and Forestry Policies (MiPAAF), Finalized Project PANDA and the research project Ref. CTM2005-05324 financed by the Spanish Comisión Interministerial de Ciencia y Tecnología (CICYT).

The present work deals with the potential of olive mill wastes as a C source for soil C sequestration strategy, which is based on the high lignocellulosic content that makes these wastes to degrade slowly during composting and after land application. A C balance was performed during the whole life cycle of two different two-phase olive mill wastes (TPOMW): C losses were calculated during the composting process and after soil application of the composting mixtures under laboratory conditions. The effect of the degree of stabilization of TPOMW on the overall C waste conservation efficiency was also evaluated. C losses after 34 weeks of TPOMW composting ranged from 40.58% to 45.19% of the initial C, whereas the amount of C evolved as CO2 after 8 months of incubation of soil amended with mature composts only represented between 20.6% and 21.9% of the added C. The total C losses considering the whole life cycle of the TPOMW showed lower losses compared to composts prepared with organic residues of different origin. Conversely to the typical behaviour of other organic wastes, the stabilisation degree of the TPOMW composting mixtures did not show any significant effect on the total C losses measured during composting and later land application. The low rate of degradation of TPOMW both during composting and after soil application makes the use of TPOMW as a C source an attractive strategy for soil C sequestration., The authors wish to thank the Spanish Comisión Interministerial de Ciencia y Tecnología (CICYT) for supporting the research project Ref. CTM2005-05324 under which this work was partially financed. Special thanks to Fundación Séneca (Agencia Regional de Ciencia y Tecnología, Región de Murcia) for financing the postdoctoral grant 02534/PD/05.

The phytotoxic and antimicrobial properties of olive mill wastes have been widely investigated and demonstrated over the past decade. However, their potential utilization as biodegradable pesticides against plant pathogens is still poorly understood. In this study, a series of laboratory bioassays was designed to test the inhibitory effects of sterile water extracts of two-phase olive mill waste (TPOMW) and TPOMW composts with different degrees of stabilization on several different plant pathogens. Fungicidal properties of TPOMW extracts, assayed in a microwell assay format, showed that the growth of Phytophthora capsici was consistently and strongly inhibited by all TPOMW extracts diluted 1:10 (w:v). In contrast, suppression of Pythium ultimum and Botrytis cinerea by the extracts was not as strong and depended on the specific TPOMW sample. Mature compost inhibited P. capsici and B. cinerea at dilutions as great as 1:50, w:v. Neither TPOMW nor TPOMW compost extracts were able to inhibit the growth of the basidiomycete root rot agent Rhizoctonia solani. In addition, studies were conducted on the allelopathic effects of TPOMW extracts on seed germination of four highly invasive and globally distributed weeds (Amaranthus retroflexus, Solanum nigrum, Chenopodium album and Sorghum halepense). Both the TPOMW and immature TPOMW compost extracts substantially inhibited germination of A. retroflexus and S. nigrum, whereas mature composts extracts only partially reduced the germination of S. nigrum. Finally, TPOMW extracts strongly inhibited egg hatch and second-stage juvenile (J2) motility of the root-knot nematode Meloidogyne incognita. However, only higher concentrations of stage-one and stage-two TPOMW compost extracts exerted a suppressive effect on both J2 motility and on egg hatch. The study shows the high potential of naturally occurring chemicals present in TPOMW and TPOMW composts that should be further investigated as bio-pesticides for their use in sustainable agricultural systems.

7 pages, 4 tables, 1 figure., Two-phase olive mill waste (TPOMW) is considered the main problem confronting the modern oil extraction and processing industry. Composting has been recently proposed as a suitable method to treat TPOMW so that it is suitable for use in agriculture. In the work reported here, the Lemna gibba bioassay was tested to assess the toxicity of TPOMW before and during the composting process. The method was compared with the Lepidium sativum bioassay and with other chemical maturity indices traditionally reported in the literature. The L. gibba test proved to be a simple, sensitive, and accurate method to evaluate toxicity before and during the composting of TPOMW. Plant growth response was measured by two methods: counting the number of fronds (leaves) and measuring total frond area (TFA) with image analysis software. Compared to the counting of fronds (L. gibba) or seeds (L. sativum), the use of area-measuring software permitted a very rapid, unbiased and easy way of analysing the toxicity of TPOMW before and during composting. Although the accuracy of the frond count method was similar to the traditional cress seed test, data analysis showed that the TFA measurement method was statistically more accurate (significantly lower variance) than the frond count approach. Highly significant correlations were found between TFA and some important maturation indices commonly reported in literature indicating that the L. gibba bioassay can be a useful tool to determine the degree of maturity of TPOMW composts., The authors are giving special thanks to the International Institute in Spain and the Fulbright Commission for financing the Ruth Lee Kennedy grant that has allowed M.L.C. to accomplish this work and to Fundación Séneca for financing the research project (ref 03062PI/05).

Two-phase olive mill waste (TPOMW) is a semisolid sludge generated during the extraction of olive oil by the two-phase centrifugation system. Among all the available disposal options, composting is gaining interest as a sustainable strategy to recycle TPOMW for agricultural purposes. The quality of compost for agronomical use depends on the degree of organic matter stabilization, but despite several studies on the topic, there is not a single method available which alone can give a certain indication of compost stability. In addition, information on the biological and biochemical properties, including the enzymatic activity (EA) of compost, is rare. The aim of this work was to investigate the suitability of some enzymatic activities (β-glucosidase, arylsulphatase, acid-phosphatase, alkaline-phosphatase, urease and fluorescein diacetate hydrolysis (FDA)) as parameters to evaluate organic matter stability during the composting of TPOMW. These enzymatic indices were also compared to conventional stability indices. For this purpose two composting piles were prepared by mixing TPOMW with sheep manure and grape stalks in different proportions, with forced aeration and occasional turnings. The composting of TPOMW followed the common pattern reported previously for this kind of material with a reduction of 40–50% of organic matter, a gradual increase in pH, disappearance of phytotoxicity and formation of humic-like C. All EA increased during composting except acid-phosphatase. Significant correlations were found between EA and some important conventional stability indices indicating that EA can be a simple and reliable tool to determine the degree of stability of TPOMW composts., The authors wish to thank to Fundación Séneca for financing the postdoctoral grant (Ref. 02534/PD/05) and the research project (Ref. 03062PI/05).

9 pages, 4 figures, 2 tables., Soil sequestration of atmospheric CO2 through land application of organic residues may have beneficial effects as a strategy to offset the increase in the concentration of greenhouse gases (GHG) in the atmosphere. The significance of different variables on GHG production and soil C sink capacity was investigated by monitoring CO2 and N2O fluxes from amended soils under laboratory conditions. In the first experiment, the effects of the chemical composition and complexity of three N-rich organic fertilisers (blood meal, hydrolysed leather, and hoof and horn meal) on the CO2 and N2O productions were studied. A second experiment was aimed at evaluating the effects of the degree of transformation of composts prepared from two-phase olive mill waste on soil C sink capacity. The three N-rich organic fertilisers caused different CO2 and N2O evolution patterns in the amended soils, despite their similar elemental composition. The total amount of added C that was mineralised in the soil ranged from 10.4% to 15.5%, while N2O–N originating from horn and hoof meal was 6 and 13 times higher than that coming from hydrolysed leather and blood meal, respectively. Mineralisation of the C added to the soil was inversely correlated to the degree of stabilisation of the composting mixtures. Soils amended with the initial composting mixture evolved from 2 to 7.3 times more CO2–C than the soil amended with the more stabilised compost. However, the C conservation efficiency of organic residues, calculated by the combined losses during composting, and after land application, was higher for the less transformed organic materials. Both studies showed the key importance of the variables studied on the GHG emissions and C sink efficiency of amended soils under controlled conditions. Laboratory experiments could be a useful tool to assist in the designing of field scale experiments for an effective quantification and monitoring of the overall changes in soil C and N pools., This research was supported by a grant from the Italian Ministry for Agricultural and Forestry Policies (MiPAF), Project PARSIFAL, General Series, Paper No. 18. The authors wish to thank the Spanish Comisión Interministerial de Ciencia y Tecnologia (CICYT) for supporting the research project under which this work was partially financed.

8 pages, 3 figures, 1 table., The soil microbial biomass survives as a largely dormant population for long periods without fresh substrates, depending for growth upon a rapid uptake of substrates when they become available. Currently, little investigation has been made into the mechanisms involved in the transition from dormancy to activity. We found that additions of trace amounts of different simple and complex substrates (glutamic acid, amino acids mixture, glucose, protein hydrolysates, carbohydrates, compost extract), even at very low application rates (5-μg C g−1 soil), caused an immediate and significant activation (measured as increased CO2-C evolved) of the soil microbial biomass. The different substrates caused different intensities of respiration response, which were related to the substrates’ composition, complexity, and degradability. The difference between the CO2-C evolved from the amended soil minus that evolved from a similarly incubated but non-amended soil ranged from 80 to 160% of the humified carbon C added as substrate, with most of the substrates causing a positive priming effect, in agreement with previous findings. The activation ended after 5–70 h, depending on the substrate, but the microbial biomass could be reactivated with further additions. It seems that the microbial biomass first responds to traces of substrate by increasing its metabolic activity in anticipation of a larger ‘food event’. Overall, these results indicate that soil micro-organisms have evolved metabolic and physiological strategies that allow them to survive and growth in the generally poor-substrate soil environment., This research was supported by a grant from the Italian Ministry for Agricultural and Forestry Policies (MiPAF), Project PARSIFAL, General Series, Paper No. 16. Rothamsted Research receives grant-aided support from the Biological and Biotechnological Sciences Research Council.

8 pages, 3 tables, 3 figures., Composting of two-phase olive mill waste (TPOMW) mixed with sheep litter and grape stalks was performed using two different aeration systems: forced aeration and windrow turning. The aim was to find out which of these technologies was the most appropriate for the composting of these materials. The efficiency of each aeration method was evaluated by monitoring the evolution of parameters such as temperature, biodegradation of organic matter fractions (carbohydrates, lipids, phenols, lignin, cellulose and hemicellulose) and nitrogen loss. Besides, the quality of the final composts was compared in terms of their main chemical characteristics (total N, N-NH4+, N-NO3−, P2O5, K2O, pH, electrical conductivity, polymerisation degree, humification degree and germination index) and their hygienisation degree (faecal coliforms and faecal streptococci). The study revealed that forced aeration of static pile presents several drawbacks for the composting of two-phase olive mill waste due to its physical properties. Several windrow turnings were required to avoid the formation of preferential air path-flows, the compaction and heterogeneous drying of the material. Piles elaborated by windrow turning showed a longer thermophile phase which lead to a higher degradation of fibres and a greater loss of nitrogen. The quality of the end products obtained by both methods was quite similar, although the organic matter of composts prepared by windrow turning had a higher humification degree. Turnings of TPOMW composting piles are necessary for the normal development of the process and the high investment necessary to implement the forced aeration could be avoided. The benefits that forced aeration introduces by means of the control of temperature can be obtained by optimising pile size and turning frequency., The authors wish to thank the Spanish Comisión Interministerial de Ciencia y Tecnología (CICYT) for supporting the research project Ref.PTR1995-0458-OP under which this work was financed.

10 pages, 2 tables, 2 figures., Olive mill wastes represent an important environmental problem in Mediterranean areas where they are generated in huge quantities in short periods of time. Their high phenol, lipid and organic acid concentrations turn them into phytotoxic materials, but these wastes also contain valuable resources such as a large proportion of organic matter and a wide range of nutrients that could be recycled. In this article, recent research studies for the valorisation of olive mill wastes performed by several authors were reviewed: second oil extraction, combustion, gasification, anaerobic digestion, composting and solid fermentation are some of the methods proposed. Special attention was paid to the new solid waste generated during the extraction of olive oil by the two-phase system. The peculiar physicochemical properties of the new solid waste, called two-phase olive mill waste, caused specific management problems in the olive mills that have led to the adaptation and transformation of the traditional valorisation strategies. The selection of the most suitable or appropriate valorisation strategy will depend on the social, agricultural or industrial environment of the olive mill. Although some methods are strongly consolidated in this sector, other options, more respectful with the environment, should also be considered, The authors thank the Spanish Comisio´n Interministerial de Ciencia y Tecnología (CICYT) for financing this work through the PETRI project n ref PTR1995-0458-OP.