Role of proteins and soluble peptides as limiting components during the co-composting of agro-industrial wastes.

The agri-food industry is at the centre of the circular economy, since the co-composting of its residual flows allows their management and adds value producing fertilisers. In this work, six composting piles were prepared combining agri-food sludge (AS), different fresh vegetable wastes (pepper waste (P), tomato waste (T), and leek waste (L), and, as bulking agents, vine shoot pruning (VS), garlic stalks (GS) and avocado leaves (AL)). Classical physico-chemical and chemical determinations and advanced instrumental methods (excitation-emission fluorescence (EEM) and gravimetric (TG, DTG and DTA) techniques) were used and compared to assess organic matter evolution and evaluate the quality of the composts obtained. The thermal profiles of the composting processes were viable to show the stabilization of the agri-food sludge with the different materials tested in the mixtures, reaching adequate levels of stabilization of organic matter. Preferential degradation of peptides and proteins was observed by fluorescence. This seemed to induce a limitation in the biodegradation of the remaining organic matter, indicating that these biomolecules are key in composting dynamics, acting as limiting components during the process. The results from thermogravimetric analysis indicated the degradation of labile compounds (e.g., carbohydrates and proteins), the most recalcitrant material becoming predominant at the maturity stage of the composting process. The rise in the thermogravimetric parameter R2 was associated with the increase in the concentration of more refracting compounds, which need more energy for their decomposition.

Comprehensive management of dog faeces: Composting versus anaerobic digestion.

The objective of this work was to study the possibilities to manage and recycle dog faeces (DF) using biological processes, using two approaches: composting (C) and anaerobic digestion (AD). Thus, different experiments have been carried out: i) two laboratory/pilot scale experiments (self-heating and composting tests) and one, on a commercial scale; ii) two AD experiments. In both approaches, municipal waste such as the organic fraction of municipal solid waste (OMSW) and urban pruning waste (GW) were used as co-substrates. The results obtained regarding the optimization of the composting process indicated that the best strategy was the use of a 1:2 ratio of DF, a 1:4 ratio of OMSW, and a 1:4 ratio of GW, according to the thermal parameters studied (temperature and cumulative quadratic exothermic index (EXI2)), and the quality of the compost obtained. A potentially limiting factor of the process was the high salinity of the DF waste. In addition, AD experiments were performed on DF, OMSW, and GW wastes in controlled anaerobic systems at a laboratory scale. In these experiments, the biogas production obtained was 229 mL biogas/g total solids for the DF residue, 248 mL biogas/g total solids for GW, and 263 mL biogas/g total solids for OMSW. The co-digestion yields a clear improvement in the efficiency of the process against the use of a single residue, increasing the production of biogas by up to 27% with respect to that of the DF waste alone during the first 25 days of AD. The results obtained with these procedures have shown the possibilities to add value to this waste in an urban context where the circular economy represents an increasingly favourable scenario, including the generation of fertilisers and/or energy at a local scale, provided that the collection of dog faeces is optimized.

Valorization of date palm (Phoenix dactylifera L.) pruning biomass by co-composting with urban and agri-food sludge.

In the Mediterranean countries, there is an increasing production of date palm wastes (Phoenix dactylifera L.), not only due to the raising production of date palm fruits, but also derived from the maintenance of urban and peri-urban green areas, especially in those affected by red palm weevil (Rhynchophorus ferrugineus). The management of this increasing volume of green wastes usually concludes with a controlled disposal that implies an important loss of resources, in terms of organic matter, nutrients and energy. In addition, the rise of wastewater generation and the incentive of the wastewater treatment processes have derived in an increase of the amount of the sludge produced, which makes difficult its management. This work studies the feasibility of co-composting palm wastes with sludge from the urban and agri-food sectors as alternative treatment to manage these organic waste streams and to obtain added-value compost. For this, four mixtures (P1, P2, P3 and P4) were prepared using as main component palm leave waste (PL) mixed with different types of sludge. In the piles P1, P2 and P3, sewage sludge (SS) was used as co-composting agent, while agri-food sludge (AS) was used in P4. Throughout composting, the thermal profile of the composting piles was assessed, as were physical, chemical, physico-chemical and maturity parameters. In addition, the changes in water-soluble organic matter were assessed using chemical analytical methods and the excitation-emission matrix (EEM) fluorescence spectroscopy. The results obtained showed the viability of the co-composting process to obtain end-products with adequate maturity degree and physical characteristics for their potential use as substrates, except for the salt contents that can limit their use in some agricultural sectors.

Olive mill wastewater-evaporation ponds long term stored: Integrated assessment of in situ bioremediation strategies based on composting and vermicomposting.

During the last two decades, the method most widely used to manage olive mill wastewater (OMW) derived from olive oil production has been its disposal in evaporation ponds. Long-term storage of OMW leads to the accumulation of toxic sediments (OMWS) rich in recalcitrant compounds with phytotoxic and antimicrobial properties, which limit their use for agronomic purpose. The aim of this study was to compare the effect of two in situ bioremediation strategies (composting and a combination of composting followed by vermicomposting) to remove the potential toxicity of the sediments derived from long-term stored OMW. The results obtained showed that the composting method assisted with the earthworms enhanced the depletion of phenolic compounds and OMWS ecotoxicity more than composting, especially during the maturation stage. Moreover, vermicomposting was more effective in the reduction of the OMWS salinity. However, a pre-composting process to the OMWS is necessary prior to vermicomposting to provide the suitable conditions for earthworms survival and activity. Furthermore, the final compost showed a phytostimulating effect. Therefore, these in situ bioremediation strategies can be considered potential tools for decontamination and recovery of long-term stored OMWS in evaporation ponds, which currently poses an unsolved environmental problem.

Salinity, organic content, micronutrients and heavy metals in pig slurries from South-eastern Spain.

The increase in commercial pig production is an opportunity to reuse animal manures in arid and semiarid soils as a source of nutrients and organic matter. However, there are components in pig slurry that are potentially dangerous for the environment. In this study, pig slurries of 36 pig farms in South-eastern Spain were evaluated for salt content (electrical conductivity, chloride and sodium), organic load (BOD5 and COD), micronutrients (Fe, Cu, Mn and Zn), and heavy metals (Cd, Co, Cr, Ni and Pb). Except for electrical conductivity, Cu and Zn, components in pig slurries did not vary considerably between animal production stages, indicating similar management of diverse animal types. Assuming an application rate based on the maximum input of nitrogen from animal manure (210 kg total N/ha/yr), the estimates for soil annual load of Cl and Na, 415 kg/ha, could be a significant salinisation risk. Cu and Zn seemed to be the metals that could be accumulated most in soils where application of pig slurries is common (4 and 15 kg/ha/yr, respectively). The estimated heavy metal (Cd, Co, Cr, Ni and Pb) input to soils would be 260 g/ha/yr, with a relative contribution of Cr>Ni>Pb>Co>Cd.

Agrochemical characterisation of the solid by-products and residues from the winery and distillery industry.

The winery and distillery industry produces a great quantity of residues, whose management and disposal are environmental problems due to their seasonal character and some polluting characteristics. The main solid by-products and residues generated are grape stalk, grape pomace or marc, wine lee, exhausted grape marc and winery sludge. In this study, 87 samples of winery and distillery residues were collected from different Spanish wineries and distilleries. Electrical conductivity, pH, total organic matter, organic carbon, polyphenols and contents of plant nutrients and heavy metals were determined. The purpose of this research was to study the composition of these wastes and to find relationships in order to use easily analysable parameters to estimate their composition. In general, the winery and distillery residues showed low pH (mean values ranged from 3.8 to 6.8) and electrical conductivity values (1.62-6.15 dS m(-1)) and high organic matter (669-920 g kg(-1)) and macronutrient contents, especially in K (11.9-72.8 g kg(-1)). However, a notable polyphenol concentration (1.2-19.0 g kg(-1)) and low micronutrient and heavy metal contents were also observed, some of these properties being incompatible with agricultural requirements. Therefore, conditioning treatments are necessary prior to possible use of these wastes. In all wastes, significant correlations were found between easily determined parameters, such as pH, electrical conductivity and total organic matter, and most of the parameters studied. The regression models obtained are also discussed.

Composting of the invasive species Arundo donax with sewage and agri-food sludge: Agronomic, economic and environmental aspects.

This work evaluates several co-composting scenarios based on the use of Arundo donax biomass (AD) as bulking agent for the co-composting of sewage sludge (MS) and agri-food sludge (AS), to manage these organic wastes and to produce balanced organic fertilizers by optimizing the process. For this, six piles were prepared in commercial composting conditions, using AD in a range of 40%-80% (on a dry weight basis). Physico-chemical and chemical parameters and the thermal behaviour were evaluated during the process, as were the physical and chemical parameters of the final composts. The proportion of AD in the mixtures has a significant effect on the development of the thermophilic stage of composting, showing the piles with higher proportion of AD a quicker organic matter degradation. In addition, the evolution of the thermal indices R1 and R2 was different depending on the origin of the sludge used, indicating an increase in the relative concentration of more recalcitrant materials in the piles prepared with AS. The estimation of the global warming potential showed that the use of higher proportion of AD in the composting mixture may be a strategy to mitigate the emission of greenhouse gases during the composting process. Moreover, the end-products obtained had an additional marketable value, with a balanced nutrient content and a good degree of maturity, which indicates the viability of the composting process as a method for the stabilization of these organic wastes.

Short-term carbon and nitrogen mineralisation in soil amended with winery and distillery organic wastes.

The aim of this work was to study the influence of the organic wastes derived from the winery and distillery industry (grape stalk (GS), grape marc (GM), wine lees (WL) and exhausted grape marc (EG)) and the soil type (clayey-loam (S1), loam (S2) and sandy textured (S3)) on different soil characteristics, especially the carbon and nitrogen mineralisation. The evolution of C mineralisation fitted a first-order kinetic for all amended soils. An initial increase was observed in the specific respiration (qCO(2)) at the beginning of the experiment. However, afterwards, the evolution in the qCO(2) was to tend towards the values of the control soil due to the pattern of the soil to recover its initial equilibrium status. The addition of these materials in the soils produced a slight increase of the inorganic nitrogen content, except in the case of GS and EG in most of the studied soils. The use of GS as amendment produced an inhibition in the N mineralisation in the three types of soils studied. Organic matter mineralisation was probably influenced by soil type, the sandy soil favouring more the N and C mineralisation processes than the clayey-loam and loam soils.

Dissolved organic matter fractions formed during composting of winery and distillery residues: evaluation of the process by fluorescence excitation-emission matrix.

The aim of the present paper is to assess the maturity degree reached by different samples of several mixtures from winery and distillery residues composted using the Rutgers composting system, by means of excitation-emission matrix (EEM) fluorescence spectroscopy. The composts were sampled once a week for about 200d. EEM spectra indicate the presence of different fluorophores. The fluorescence intensities of these peaks show trends related to the maturity of the composting samples selected. The "contour density" of EEM maps is strongly modified through time. We have used the quantitative method of fluorescence regional integration (FRI). The EEMs were delineated into five excitation-emission regions. The degree of compost maturity could be correlated with the percentage of the volumetric integration under the EEM within each region. Further refinement of these techniques should provide a relatively rapid method for assessing the suitability of the compost to soil application.

Co-composting of distillery and winery wastes with sewage sludge.

The winery and distillery wastes (grape stalk and marc (GS and GM, respectively), wine lees (WL) and exhausted grape marc (EGM)) are produced in great amounts in the Mediterranean countries, where their treatment and disposal are becoming an important environmental problem, mainly due to their seasonal character and some characteristics that make their management difficult and which are not optimised yet. Composting is a treatment widely used for organic wastes, which could be a feasible option to treat and recycle the winery and distillery wastes. In this experiment, two different piles (pile 1 and 2) were prepared with mixtures of GS, GM, EG and sewage sludge (SS) and composted in a pilot plant by the Rutgers static pile composting system. Initially, GS, GM and EGM were mixed, the pile 1 being watered with fresh collected vinasse (V). After 17 days, SS was added to both piles as a nitrogen and microorganisms source. During composting, the evolution of temperature, pH, electrical conductivity, total organic C, total N, humic acid-like C and fulvic acid-like C contents, C/N ratio, cation exchange capacity and germination index of the mixtures were studied. The addition of V in pile 1 produced higher values of temperature, a greater degradation of the total organic C, higher electrical conductivity values and similar pH values and total N contents than in pile 2. The addition of this effluent also increased the cation exchange capacity and produced a longer persistence of phytotoxicity. However, both piles showed a stabilised organic matter and a reduction of the phytotoxicity at the end of the composting process.

Development of organic fertilizers from food market waste and urban gardening by composting in Ecuador.

Currently, the management of urban waste streams in developing countries is not optimized yet, and in many cases these wastes are disposed untreated in open dumps. This fact causes serious environmental and health problems due to the presence of contaminants and pathogens. Frequently, the use of specific low-cost strategies reduces the total amount of wastes. These strategies are mainly associated to the identification, separate collection and composting of specific organic waste streams, such as vegetable and fruit refuses from food markets and urban gardening activities. Concretely, in the Chimborazo Region (Ecuador), more than 80% of municipal solid waste is dumped into environment due to the lack of an efficient waste management strategy. Therefore, the aim of this study was to develop a demonstration project at field scale in this region to evaluate the feasibility of implanting the composting technology not only for the management of the organic waste fluxes from food market and gardening activities to be scaled-up in other developing regions, but also to obtain an end-product with a commercial value as organic fertilizer. Three co-composting mixtures were prepared using market wastes mixed with pruning of trees and ornamental palms as bulking agents. Two piles were created using different proportions of market waste and prunings of trees and ornamental palms: pile 1 (50:33:17) with a C/N ratio 25; pile 2: (60:30:10) with C/N ratio 24 and pile 3 (75:0:25) with C/N ratio 33), prepared with market waste and prunings of ornamental palm. Throughout the process, the temperature of the mixtures was monitored and organic matter evolution was determined using thermogravimetric and chemical techniques. Additionally, physico-chemical, chemical and agronomic parameters were determined to evaluate compost quality. The results obtained indicated that all the piles showed a suitable development of the composting process, with a significant organic matter decomposition, reached in a shorter period of time in pile 3. At the end of the process, all the composts showed absence of phytotoxicity and suitable agronomic properties for their use as organic fertilizers. This reflects the viability of the proposed alternative to be scaled-up in developing areas, not only to manage and recycle urban waste fluxes, but also to obtain organic fertilizers, including added value in economic terms related to nutrient contents.

Use of composted sewage sludge in growth media for broccoli.

In this study, the use of composted sewage sludge (CSS) as a binary component with peat (P) in growth media for a horticultural crop, broccoli (Brassica oleracea var. Botryti cv. Marathon), was evaluated. Four treatments were established, based on the addition of increasing quantities of composted sewage sludge to peat (0%, 15%, 30% and 50%, v/v). Physical, physico-chemical and chemical analyses of the different mixtures of CSS and P were made. Plant growth, biomass production and macronutrient (N, P, K, Ca, Mg), micronutrient (Fe, Cu, Mn, Zn) and heavy metal (Pb, Ni, Cd, Cr) contents of plants were determined. The addition of CSS to P increased plant nutrient and heavy metal contents of plants and electrical conductivity (EC) and bulk density values of the substrates. The use of CSS did not affect the germination rate, even at 50% compost. For broccoli growth, the highest yield was obtained with the medium prepared by mixing the peat with 30% of compost; however, the mixture with the most sewage sludge compost (50%) had the greatest contents of macro and micronutrients.

Co phytoavailability for tomato in amended calcareous soils.

A plot study was conducted to assess changes in Co phytoavailability for a tomato cultivar grown on an agricultural soil (a Calcic Petrocalcid) amended with sewage sludge, under controlled conditions in South-eastern Spain. The experiment consisted of three main treatment blocks: (A) without organic fertilisation, (B) with addition of 60 tha(-1) and (C) 120 tha(-1) of sewage sludge. For each block (A, B, and C), four levels of Co (0, 50, 100 and 200 mgkg(-1)) were added, as CoCl2. Diethylenetriaminepentaacetic acid, DTPA (0.005 M plus triethanolamine), ammonium acetate (1 N at pH 7), and water extractable fractions of the soils were analysed for all the plots. The time dependent Co accumulation in different parts (roots, stems, leaves, and fruits) of the tomato plants was studied. Soil Co seemed to be mainly in non-available forms, according to the low concentrations found in the water and ammonium acetate extracts, compared to DTPA. The gradient of Co accumulation in tomato plants was root > leaf > stem + branches > fruit, with a concentration in the edible parts ranging between 4 and 25 mg kg(-1). The organic amendment enhanced the plant extraction of Co, this effect being more significant with time. Plant extraction efficiency decreased with increasing Co concentration in the soils. Co in fruit showed the best correlation with all the Co extraction pools in the soil.

Characterisation of the organic matter pool in manures.

In this research, different types of animal manure were evaluated with respect to organic matter (OM), total organic carbon (C(ot)), total N (N(t)), C(ot)/N(t) ratio, water-soluble organic carbon (C(w)), organic N (N(org)), carbohydrates, C(w)/N(org) ratio, humic acid-like carbon (C(ha)), fulvic acid-like carbon (C(fa)), humification index ((C(ha)/C(ot))x100) (HI) and the C(ha)/C(fa) and NH(4)(+)-N/NO(3)(-)-N ratios. In comparison with the limits set by the Spanish legislation for organic fertilisers, most of the manures had high OM contents, moderate N(org) concentrations (except in the case of the chicken and pig manures where this parameter was high) and C(ot)/N(t) ratios above the value stated in the legislation. The study of the different fractions of organic matter showed that the horse, pig and rabbit manures had the greatest content of C(ot). However, the fraction of easily-biodegradable organic compounds (C(w)) was significantly higher in the horse, goat and chicken manures. The study also showed that, in most cases, the percentage of fulvic acid-like C was greater than that of the humic acid-like C, indicating that the organic matter of these wastes is not completely humified. Values of HI ((C(ha)/C(ot))x100) and C(ha)/C(fa) ratio in the studied manures were not significantly different. Regarding the parameters related to the organic matter stability such as C(w), carbohydrates and the C(ot)/N(t), C(w)/N(org) and NH(4)(+)-N/NO(3)(-)-N ratios, it has been determined that the organic matter of these materials was not completely stabilised. The heterogeneity in OM composition of the studied manures did not allow the formulation of simple equations for evaluation of the composition of these wastes from easily-determined parameters.

Estimation of nutrient values of pig slurries in Southeast Spain using easily determined properties.

The contents of available nutrients in pig slurries are not easy to quantify in situ without laboratory facilities, but chemical analyses using standard laboratory methods also take time and are costly and not practical for most farms. Thus, when animal slurries are applied to land, their fertiliser potential is often unknown. In addition, in the last years, the changes in the management of industrial piggeries has changed the nature of the pig slurries vg. decrease of the dry matter content, and consequently the methods and equations used for estimating the nutrient contents in these residues must be checked. In our study, slurry samples were collected from the storage tanks of 36 commercial farms in Southeast Spain. Samples were analysed for pH, electrical conductivity (EC), redox potential (RP), specific density (D), total solids (TS), sedimentable solids (SS), biological oxygen demand (BOD(5)), chemical oxygen demand (COD), total nitrogen (TKN), ammonium nitrogen (AN), organic nitrogen (ON), and total contents of phosphorus, potassium, calcium and magnesium. Relationships between major nutrient levels of pig slurries and a range of physical and chemical properties were investigated. We also analysed the variability of pig slurries according to the production stage. TKN, AN and K were closely related to EC. The P content in slurries was related more closely to solids-derived parameters such as D. The use of multiple properties to estimate nutrient contents in pig slurries, especially for AN and K, seemed unnecessary due to the limited improvement achieved with an additional property. Therefore, electrical conductivity seemed to be the most appropriate single, easily determined parameter for estimation of total and ammonium nitrogen and potassium in pig slurries, with more than 83% of the variance explained. P seemed to be the worst key nutrient for estimation using any easily determined parameter.

Uses of winery and distillery effluents in agriculture: characterisation of nutrient and hazardous components.

Twenty-one samples of winery and distillery effluents were collected from different Spanish winery and distillery industries. Electrical conductivity, pH, redox potential, density, organic charge (chemical oxygen demand, biological oxygen demand, total, volatile and suspended solids, oxidisable organic C and polyphenols) and contents of plant nutrients and heavy metals were analysed. The aim of this work was to study the composition of these effluents and to find relationships which would make it possible to use easily determined parameters to estimate their composition. The winery wastewater (WW) and vinasse (V) showed an acidic pH, a high organic load and notable polyphenol, macronutrient, micronutrient and heavy metal contents. Some of these properties are not compatible with agricultural requirements; therefore, conditioning treatment of these liquid wastes is necessary to produce a safe, stable and easily manageable end product. Generally, in both effluent types, significant correlations were found between easily analysable parameters, such as suspended, volatile and total solids, pH, electrical conductivity, density and redox potential, and most of the parameters studied. The linear regression equations obtained permitted an immediate characterisation of the WW and V samples using these parameters.

Chemical, Thermal and Spectroscopic Methods to Assess Biodegradation of Winery-Distillery Wastes during Composting.

The objective of this work was to study the co-composting process of wastes from the winery and distillery industry with animal manures, using the classical chemical methods traditionally used in composting studies together with advanced instrumental methods (thermal analysis, FT-IR and CPMAS 13C NMR techniques), to evaluate the development of the process and the quality of the end-products obtained. For this, three piles were elaborated by the turning composting system, using as raw materials winery-distillery wastes (grape marc and exhausted grape marc) and animal manures (cattle manure and poultry manure). The classical analytical methods showed a suitable development of the process in all the piles, but these techniques were ineffective to study the humification process during the composting of this type of materials. However, their combination with the advanced instrumental techniques clearly provided more information regarding the turnover of the organic matter pools during the composting process of these materials. Thermal analysis allowed to estimate the degradability of the remaining material and to assess qualitatively the rate of OM stabilization and recalcitrant C in the compost samples, based on the energy required to achieve the same mass losses. FT-IR spectra mainly showed variations between piles and time of sampling in the bands associated to complex organic compounds (mainly at 1420 and 1540 cm-1) and to nitrate and inorganic components (at 875 and 1384 cm-1, respectively), indicating composted material stability and maturity; while CPMAS 13C NMR provided semi-quantitatively partition of C compounds and structures during the process, being especially interesting their variation to evaluate the biotransformation of each C pool, especially in the comparison of recalcitrant C vs labile C pools, such as Alkyl /O-Alkyl ratio.

Nitrogen mineralisation potential in calcareous soils amended with sewage sludge.

Mineralisation of organic N is an important consideration when determining the annual amount of sewage sludge to be applied to agricultural soils. The mineralisation of sludge organic N was studied in two different textured soils (clayey and sandy soil) treated with aerobic and anaerobic sludge at two different rates (30 and 50 g sludge kg(-1) soil). The mineralisation of sludge organic N was determined during 20 weeks incubation period by analysis of inorganic N produced by a non-leached procedure. Sludge organic N mineralisation was influenced by soil type, organic N mineralisation being greater in the sandy soil (from 30% to 41%) than in the clayey soil (from 13% to 24%). Mineralisation rates decreased rapidly the first two weeks, followed by a slower decrease with time. Although total mineralisation increased with sludge addition rate, net mineralisation decreased with sludge addition rate, probably due to denitrificaton losses. The aerobically treated sludge gave higher mineralisation rates than the anaerobically treated one. The values of N0 and k for treated soils varied depending on the type of sludge and soil.

The potential of near infrared reflectance spectroscopy (NIRS) for the estimation of agroindustrial compost quality.

Composting is an environmentally friendly alternative for the recycling of organic wastes and its use is increasing in recent years. An exhaustive monitoring of the composting process and of the final compost characteristics is necessary to certify that the values of compost characteristics are within the limits established by the legislation in order to obtain a safe and marketable product. The analysis of these parameters on each composting batch in the commercial composting plant is time-consuming and expensive. So, their estimation in the composting facilities based on the use of near infrared reflectance spectroscopy (NIRS) could be an interesting approach in order to monitor compost quality. In this study, more than 300 samples from 20 different composting procedures were used to calibrate and validate the NIRS estimation of compost properties (pH, electrical conductivity (EC), total organic matter (TOM), total organic carbon (TOC), total nitrogen (TN) and C/N ratio, macronutrient contents (N, P, K) and potentially pollutant element concentrations (Fe, Cu, Mn and Zn)). The composts used were elaborated using different organic wastes from agroindustrial activities (GS: grape stalk; EGM: exhausted grape marc; GM: grape marc; V: vinasse; CJW: citrus juice waste; Alpeorujo: olive-oil waste; AS: almond skin; EP: exhausted peat; TSW: tomato soup waste; SMS: spent mushroom substrate) co-composted with manures (CM: cattle manure; PM: poultry manure) or urban wastes (SS: sewage sludge) The estimation results showed that the NIRS technique needs to be fitted to each element and property, using specific spectrum transformations, in order to achieve an acceptable accuracy in the prediction. However, excellent prediction results were obtained for TOM and TOC, successful calibrations for pH, EC, Fe and Mn, and moderately successful estimations for TN, C/N ratio, P, K, Cu and Zn.

Estimation of phosphorus content and dynamics during composting: use of near infrared spectroscopy.

The content and chemical forms of P in compost are essential variables for its proper management with an agricultural purpose, especially considering the increasing P over-fertilization in agrosystems. In this study, the estimation of P content and dynamics in different composting scenarios was developed using near infrared reflectance spectroscopy (NIRS) coupled with a statistical tool for calibration, a penalized signal regression. Samples were analyzed on total P and partitioned using NaOH-solution (31)P NMR spectroscopy quantifying pyrophosphate, orthophosphate, orthophosphate diesters, phospholipids, and orthophosphate monoesters pools. According to the results obtained, total P content (r(2)=0.99 and root mean square error of cross-validation=0.53) and P forms can be estimated during composting using NIRS, as well as in the mature product, orthophosphate and orthophosphate monoesters being the most abundant P forms throughout the experiment. Penalized signal regression allows detecting the significant wavenumbers in each composting period, and also with the different P pools in the composting pile depending on time.