Recycling of Two-Phase Olive-Mill Cake “Alperujo” by Co-composting with Animal Manures

The use of poultry manure or goat/sheep manure in the co-composting of the two-phase olive-mill cake “alperujo” (ALP) with olive leaf (OL) is compared by studying organic-matter mineralization and humification processes during composting and the characteristics of the end products. For this, two different piles (P1 and P2) were prepared using ALP with OL mixed with poultry manure (PM) and goat/sheep manure (GSM), respectively, and composted by the turned windrow composting system. Throughout the composting process, a number of parameters were monitored, such as temperature, pH, electrical conductivity (EC), organic matter (OM), OM losses, total organic carbon (C_org), total nitrogen (N_t), C_org/N_t ratio, and the germination index (GI). In both piles, the temperature exceeded 55 °C for more than 2 weeks, which ensured maximum pathogen reduction. Organic-matter losses followed a first-order kinetic equation in both piles. The final composts presented a stabilized OM and absence of phytotoxins, as observed in the evolution and final values of the C_org/N_t ratio (C_org/N_t < 20) and the germination index (GI > 50 percent). Therefore, composting can be considered as an efficient treatment to recycle this type of waste, obtaining composts with suitable properties that can be safely used in agriculture.     

Optimization of Medlar Pruning Waste Composting Process by Cattle Manure Addition

In this study, medlar pruning waste (MPW) was composted with and without cattle manure (CM). Two piles were prepared: one contained only MPW (pile 1) and one contained MPW augmented with CM (pile 2). Both piles were composted in an enclosed composting vessel with passive aeration and aeration by turning. During the composting process, temperature, pH, electrical conductivity (EC), organic matter (OM), OM losses, total organic carbon (C_org), total nitrogen (N_T), C_org/N_T ratio, and germination index (GI) were measured. Pile 2 produced a faster increase of the temperature and had a longer thermophilic phase than pile 1. However, the rate of OM degradation was faster in pile 1 than in the pile containing CM (pile 2). The addition of CM also resulted in an increased pH and salt content. In both piles, C/N ratio decreased throughout the process, presumably as a result of the faster organic carbon degradation compared to N mineralization. However, only pile 2 had a final C/N ratio <20, the limit accepted for compost by the Spanish legislation on fertilizer. Also, both composts had GI > 50 percent, indicating an absence of phytotoxicity.     

Chemical and microbiological parameters for the characterization of maturity of composts made from farm and agro-industrial wastes

Bioconversion of farm wastes with agro-industrial wastes into enriched compost is an important possibility in need of research. In this article, changes in chemical and microbiological parameters were evaluated to determine the maturity of composts prepared from mixture of farm and agro-industrial wastes over a period of 150 days. Seven different composts were prepared by using a mixture of different farm wastes with or without enrichment with rock phosphate (RP), agro-industrial wastes and the inoculation of microorganisms. As composting proceeded, the organic C, water-soluble C (WSC), bacterial and fungal counts decreased, whereas total N, P, electrical conductivity (EC) and actinomycetes count increased gradually. Our results suggest that WSC <1%, C:N ratio < 20, neutral pH and a decrease in bacteria and fungal counts, along with an increase in actinomycetes count and stability at the end of composting, may be accepted as an indicator of compost maturity. Changes in organic C, EC, total N and P concentrations over time also proved to be reliable indicators of the progress of the composting process for establishing stability and compost maturity. Addition of RP, agro-industrial wastes and inoculation of microorganisms showed potential in improving the N and P contents of the composts.     

Evolution of organic matter and nitrogen during co-composting of olive mill wastewater with solid organic wastes

 Four olive mill wastewater (OMW) composts, prepared with three N-rich organic wastes and two different bulking agents, were studied in a pilot plant using the Rutgers system. Organic matter (OM) losses during composting followed a first-order kinetic equation in all the piles, the slowest being the OM mineralisation rate in the pile using maize straw (MS). The highest N losses through NH₃ volatilisation occurred in the mixtures which had a low initial C/N ratio and high pH values during the process. Such losses were reduced considerably when MS was used as the bulking agent instead of cotton waste (CW). N fixation activity increased during the bio-oxidative phase before falling during maturation. This N fixation capacity was higher in piles with a lower NH₄ ⁺-N concentration. Only the composts prepared with OMW, CW and poultry manure or sewage sludge reached water-soluble organic C (C_W) and NH₄ ⁺-N concentrations and C_W/N_org and NH₄ ⁺/NO₃ ^– ratios within the established limits which indicate a good degree of compost maturity. Increases in the cation-exchange capacity, the percentage of humic acid-like C and the polymerisation ratio revealed that the OM had been humified during composting. The germination index indicated the reduction of phytotoxicity during composting. Received: 14 June 1999     

Relating Compost Measures of Stability And Maturity to Plant Growth

Assessment of compost maturity is important for successful use of composts in agricultural and horticultural production. We assessed the “maturity” of four different sawdust-based composts. We composted sawdust with either cannery waste (CW), duck manure (DM), dairy (heifer) manure (HM) or potato culls (PC) for approximately one year. Windrows were turned weekly for the first 60 days of composting, covered for four winter months and then turned monthly for six more months. We measured compost microbial respiration (CO₂ loss), total C and N, C:N ratio, water soluble NO₃-N and NH₄-N, dissolved organic carbon (DOC), pH and electrical conductivity at selected dates over 370 days. Compost effects on ryegrass biomass and N uptake were evaluated in a greenhouse study. We related compost variables to ryegrass growth and N uptake using regression analysis. All composts maintained high respiration rates during the first 60 days of composting. Ammonium-N concentrations declined within the first 60 days of composting, while NO₃-N concentrations did not increase until 200+ days. After 250+ days, DM and PC composts produced significantly more ryegrass biomass than either CW or HM composts. Total C, microbial respiration and water-extractable NO₃-N were good predictors of compost stability/maturity, or compost resistance to change, while dissolved organic carbon, C:N ratio and EC were not. The compost NO₃-N/CO₂-C ratio was calculated as a parameter reflecting the increase in net N mineralization and the decrease in respiration rate. At ratio values >8 mg NO₃-N/mg CO₂-C/day, ryegrass growth and N uptake were at their maximum for three of the four composts, suggesting the ratio has potential as a useful index of compost maturity.     

The Effects of Goat Manure,Sewage Sludge And Effective Microorganisms on the Composting of Pine Bark

This study investigated the cocomposting of pine bark with goat manure or sewage sludge, with or without inoculated effective microorganisms (EM). Composting was done for 90 days and parameters monitored over this period included temperature, pH, electrical conductivity (EC), C/N ratio, inorganic N, as well as tannin content. Changes in temperature, pH and EC during composting were consistent with those generally observed with other composting systems. The parameters were influenced by the feedstock materials used but were not affected by inoculation with effective microorganisms. The highest temperature measured from pine bark-goat manure composts was 60°C but much lower maximum temperatures of 40°C and 30°C were observed for pine bark sewage sludge and pine bark alone composts, respectively. The C/N ratios of the composts decreased with composting time. Ammonium levels decreased while nitrate levels increased with composting time. Tannin levels generally decreased with composting time but the extent of decrease depended on the contents of the composting mixtures. The trends observed showed that temperature, pH, EC, C/N ratio, tannin levels, and inorganic NH₄-N and NO₃-N were reliable parameters for monitoring the co-composting of pine bark with goat manure or sewage sludge. The pine bark-goat manure compost had more desirable nutritional properties than the pine bark and pine bark-sewage sludge composts. It had high CEC, near neutral pH, low C/N ratio, and high amounts of inorganic N and bases (K, Ca, and Mg) while pine bark compost had the least amounts of nutrients, was acidic, and had high C/N ratio and low CEC. The final tannin content of the pine bark-goat manure compost was below the 20 g/kg upper threshold level for horticultural potting media, implying that its use as a growing medium would not cause toxicity to plants.     

Evaluation of Parameters During Composting of Two Contrasting Raw Materials

The aims of this work were: i) to evaluate, during a composting process, some parameters in two contrasting raw materials: one a ligneous material (C1) and the other (C2) a mixture of horse and poultry manure with a low straw percentage and ii) to compare results from microbiological and chemical analyses of both composting material during the process. Total carbon, total nitrogen, C: N ratio, ash, organic matter, organic matter destroyed, CEC, soluble organic carbon, soluble ammonium and nitrate, ammonium: nitrate ratio and respiration rate were evaluated during 18 weeks. C1 material showed a lower rate of organic matter mineralization probably due to the high proportion of ligneous material. This material reached a greater CEC during the experiment. Increase in CEC during composting is due to conversion of the remaining organic material into humic substances. These results would imply that C1 presented a greater humification level and consequently, a better quality. On the other hand, the greater decrease in soluble organic carbon and NH₄⁺-N values in C2 is in accordance with greater organic matter mineralization. A high decrease in soluble fractions, especially the more degradable ones (water soluble components) indicates a high mineralization of the organic matter during composting and a lower humification level. According to the data obtained in our experiment, some parameters such as CEC, soluble organic carbon and soluble NH₄⁺-N seem to achieve the stability level for both studied materials, while those parameters or indices such as C: N ratio, NH₄⁺-N: NO₃^?-N ratio indicated stability/maturity only in C2 material during the experimental time.     

Composting Olive Mill Waste and Sheep Manure For Orchard Use

An industrial-scale composting plant has been designed for producing organic fertilizers from olive mill waste using the windrow pile system. Materials to be composted, two phase olive mill waste (TPOMW) and sheep litter (SL), were characterized and made into three piles consisting of different proportions of each. Throughout the composting process, temperature (T), moisture (M), organic matter (OM), total organic carbon (C_org), total nitrogen (NT), germination index (GI), pH and electrical conductivity (EC) were monitored. The potential agronomic value of the final composts was ascertained by analyzing the bulk density, OM and Corg concentration, pH, EC, macro and micronutrient content (N, P, K, Ca, Mg, Fe, Cu, Mn, Zn, B), the concentration of humic and fulvic acids and inorganic nitrogen (NH₄⁺,NO₂^?,NO₃^?). Each compost was applied to an area of one hectare within a six year-old olive plantation. Four months after application, the soils showed an increased OM concentration and cationic exchange capacity (CEC).     

Transformations of carbon and nitrogen during composting of animal manure and shredded paper

Composts produced from animal manures and shredded paper were characterized in terms of their carbon (C) and nitrogen (N) forms and C mineralization. Total, water-soluble, acid-hydrolyzable and non-hydrolyzable C and N contents were determined on composts sampled on days 0, 11, 18, 26, 33, 40 and 59 after composting was initiated. Water-soluble and acid-hydrolyzable C and N decreased during composting, whereas non-hydrolyzable C remained relatively constant, and non-hydrolyzable N greatly increased during composting. The water-soluble forms of N were characterized by a decrease of ammomium (NH₄ ⁺-N) at the beginning of composting, followed by an increase of nitrate (NO₃ ^–-N) towards the end of composting. The mineralization of C in composted materials was generally higher at the beginning than at the end of composting, whereas no differences were observed for mineralization of C in non-hydrolyzable materials. The addition of N inhibited C mineralization in composts except in samples collected on days 40 and 59, while C mineralization was strongly stimulated by adding N to the non-hydrolyzable materials. The data suggest that the N forms in the non-hydrolyzable materials were chemically similar and not readily available to microbes, indicating that the C/N ratios often used to assess the biodegradability of organic matter and to develop compost formulations should be based on biologically available N and C and not on total N and C. Received: 12 May 1997     

Cocomposting of Beet Vinasse and Grape Marc In Windrows and Static Pile Systems

Two composts were obtained by cocomposting a concentrated depotassified beet vinasse and grape marc using an aerated static pile and a windrow system. The composting mixtures comprised grape marc (83%) and vinasse (17%) for the aerated static pile system and grape marc (77%), vinasse (20%) and phosphate rock (3%) for the windrow. Changes in temperature followed a similar path for both mixtures, however the thermophilic phase was longer in the aerated static pile (25 days) than in the windrow (10 days). This fact caused differences in both organic matter degradation, weight losses (21% for static pile and 10% for windrow) and gas losses during the process. Nevertheless, the composts obtained by the two systems had a high fertilizer nutrient value (18.2 g kg^?1 N; 3.1 g kg^?1 P; 13.6 g kg^?1 K, C/N 16.1 for compost obtained in static pile and 20.6 g kg^?1 N; 13.7 g kg^?1 P; 13.1 g kg^?1 K; C/N 18 for compost obtained in windrow). A high degree of stability was reached in both composting systems (124 cmol_c kg^?1 CEC for static pile and 153 cmolc kg^?1 CEC for windrow at 80 days of composting). The chemical and physical properties of both vinasse composts suggest their possible use as soil conditioner.     

Laboratory and greenhouse assessment of plant-available N in organic materials

Laboratory indices (KCl extraction, thermal fractionation, pepsin extraction, C:N ratio and N mineralization) of organic materials were compared with plant availability of mineral-N produced from organic-N in a greenhouse experiment. Six types of organic materials [farmyard manure (FYM), pig manure (PG), poultry manure (PL), sewage sludge (SS), pressmud (PM) and compost (CP)] were compared with urea as a chemical reference fertilizer. Relative effectiveness of organic N (RE_o) was used to compare the fraction of N extracted with different N availability laboratory indices. RE_o values of organic materials ranged from 0.14 to 0.77 and decreased in the following order: PL > PG > SS > PM > CP > FYM. The KCl-extracted inorganic N, pepsin-extracted organic N and N mineralized during 42 days gave a positive relationship with RE_o, and the C:N ratio a negative relationship with RE_o. Among the different N availability laboratory indices, pepsin extraction of organic N, C:N ratio and N mineralization can be recommended for determining mineralizable organic N in organic materials. KCl-extracted inorganic N proved to be a useful index for organic materials having a low inorganic N fraction. Thermal fractionation did not provide a suitable index of plant-available N in organic materials.     

The Effect of Different C/N Ratios on the Composting of Pig Manure and Edible Fungus Residue with Rice Bran

The aim of this study was to determine the effects of initial C/N ratio (16.3, 19.1, 24.1, and 29.6) on decomposition rate and nitrogen loss during the composting of pig manure and edible fungus residue with rice bran. The results showed that all composting piles reached a temperature greater than 55°C for at least 7 days (which meets the requirements for destroying pathogens), and the maturity times of composts with low initial C/N ratios were shorter than in composts with high initial C/N ratios. The nitrogen loss in the composting pile with initial C/N of 16.3 was significantly higher than the other treatments. Furthermore, the statistics analysis showed that the initial C/N ratios of the composts, which varied from 16.3 to 29.6, had a significant negative linear correlation with the loss of total organic matter (R = ?0.9661) and loss of total nitrogen (R = ?0.9365). Therefore, for treating more agricultural wastes and achieving high-quality final product as well as the reduction of nitrogen losses, this study recommends that initial C/N ratios ranging from 20 to 25 are suitable for composting pig manure and edible fungus residue.

Highlight:

Various agricultural wastes can be successfully composted with initial C/N ratios 16:1–30:1.

Nitrogen loss had a significant linear negative correlation with the initial C/N ratio.

Compost with a low C/N ratio was beneficial to dispose of more pig manure since reducing the addition of carbon materials.     

Mass and Nutrient Losses During the Composting Of Dairy Manure Amended with Sawdust or Straw

Composting has become an increasingly popular manure management method for dairy farmers. However, the design of composting systems for farmers has been hindered by the limited amount of information on the quantities and volumes of compost produced relative to farm size and manure generated, and the impact of amendments on water, dry matter, volume and nitrogen losses during the composting process. Amendment type can affect the free air space, decomposition rate, temperature, C:N ratio and oxygen levels during composting. Amendments also initially increase the amount of material that must be handled. A better understanding of amendment effects should help farmers optimize, and potentially reduce costs associated with composting. In this study, freestall dairy manure (83% moisture) was amended with either hardwood sawdust or straw and composted for 110-155 days in turned windrows in four replicated trials that began on different dates. Initial C:N ratios of the windrows ranged from 25:1 to 50:1 due to variations in the source and N-content of the manure. Results showed that starting windrow volume for straw amended composts was 2.1 to 2.6 times greater than for sawdust amendment. Straw amended composts had low initial bulk densities with high free air space values of 75-93%. This led to lower temperatures and near ambient interstitial oxygen concentrations during composting. While all sawdust-amended composts self-heated to temperatures >55°C within 10 days, maintained these levels for more than 60 days and met EPA and USDA pathogen reduction guidelines, only two of the four straw amended windrows reached 55°C and none met the guidelines. In addition, sawdust amendment resulted in much lower windrow oxygen concentrations (< 5%) during the first 60 days. Both types of compost were stable after 100 days as indicated by CO₂ evolution rates <0.5 mg CO₂-C/g VS/d. Both types of amendments also led to extensive manure volume and weight reductions even after the weight of the added amendments were considered. However, moisture management proved critical in attaining reductions in manure weight during composting. Straw amendment resulted in greater volume decreases than sawdust amendment due to greater changes in bulk density and free air space. Through composting, farmers can reduce the volume and weights of material to be hauled by 50 to 80% based on equivalent nitrogen values of the stabilized compost as compared to unamended, uncomposted dairy manure. The initial total manure nitrogen lost during composting ranged from 7% to 38%. P and K losses were from 14 to 39% and from 1 to 38%, respectively. There was a significant negative correlation between C:N ratio and nitrogen loss (R₂=0.78) and carbon loss (R₂=0.86) during composting. An initial C:N ratio of greater than 40 is recommended to minimize nitrogen loss during dairy manure composting with sawdust or straw amendments.     

Evaluation of Chemical Extraction Methods for Determining Plant-Available Potassium in Some Soils of West Bengal,India

The effectiveness of eight chemical extraction methods was evaluated on 15 Indian soils for the prediction of plant-available potassium (K⁺) to Sudan grass (Sorghum vulgare var. sudanensis) grown in modified Neubauer technique. Average amounts of soil K⁺ extracted were in descending order: Morgan’s reagent > 0.5 M sodium bicarbonate (NaHCO₃) > neutral 1N ammonium acetate (NH₄OAc) > 1N nitric acid (HNO₃) > 0.02 M calcium chloride (CaCl₂) > 0.1N HNO₃ > Bray and Kurtz No.1> distilled water. The highest simple correlation with plant K⁺ uptake was obtained with NH₄OAc-K⁺ (r = 0.866**) and the lowest with CaCl₂-K⁺ (r = 0.45*). To develop the predictive models using stepwise regression, plant K⁺ uptake was used as the dependent variable and the extractable soil K⁺, pH, sand, silt and organic carbon (C) contents as the independent variables. Based on the final R², the NH₄OAc model was found to be the best predictor of plant-available K⁺ in the soils when used along with sand and organic C.     

Characteristics of Composts Derived from Waxed Corrugated Cardboard

The characteristics of 12 composts containing, by volume, spent mushroom substrate (SMS, 50 percent), waste waxed corrugated cardboard (WCC, 0 percent, 25 percent or 50 percent), and/or pulverized wood wastes (WW, 50 percent, 25 percent or 0 percent) were measured during two separate windrow composting periods (12-16 weeks). Supplemental N was added to some of the composts in the form of poultry manure, and/or soybean processing wastes. During the first eight to 10 weeks, composts containing 50 percent WCC tended to reach and maintain the highest temperatures, but subsequently cooled most rapidly. Microbial activity (CO₂ evolution) also was initially highest in these composts but fell by the twelfth week to levels comparable to composts containing lower levels of WCC. The paraffin wax in WCC containing composts was almost completely degraded (>95 percent). After 12 weeks of composting N (1.2-1.6 percent DW), P (0.30-0.55 percent), and K (0.9-1.2 percent) concentrations were within typical ranges and N and P were highest in composts containing 50 percent WCC. KC1 extractable NH₄-N (494 mg-N kg^?1) and NO₃+NO₂-N (281 mg-N kg^?1) were highest and lowest, respectively, in composts containing 50 percent WCC. Electrical conductivity (4.5-8.5mS/cm) and pH (7.5-8.5) were high in all composts and highest in composts with 50 percent WCC. Concentrations of phenolic compounds were highest in composts containing 50 percent WCC, manure, and soybean wastes and were positively correlated with NH₄-N. C:N ratios of all composts were within an acceptable range (18-23:1).     

Evaluation of the maturity of municipal waste compost using simple chemical parameters

Abstract

Changes in different chemical parameters of the mixtures of several organic residues during composting were studied in order to establish simple parameters that can be useful as indices of compost maturity. Circular chromatography test and the study of the colour in solid samples of compost cannot be considered sufficiently reliable for determining the degree of maturity in composts. Similarly, parameters such as ash, C/N ratio, CEC, total organic carbon (TOC), and total nitrogen (TN) must be ruled out. Other parameters such as water soluble carbon (WSC), water soluble carbohydrates, the C/N ratio of the water soluble extract, and the ratios WSC/TN and CEC/TOC, can be used as indices of compost maturity.     

Effects of aeration and moisture during windrow composting on the nitrogen fertilizer values of dairy waste composts

The objective of this work was to evaluate the effects of turning and moisture addition during windrow composting on the N fertilizer values of dairy waste composts. Composted-dairy wastes were sampled from windrow piles, which received four treatments in a 2×2 factorial of turning (turning vs. no turning) and moisture addition (watering vs. no watering) at two stages of maturity (mature vs. immature). Composts were characterized for their chemical properties. An 84-day laboratory incubation of soils with addition of the composts at two levels was conducted to evaluate the inorganic N accumulation patterns from the variously treated composts. Chemical analyses of variously treated composts did not differ between compost treatments or maturity. In contrast, the inorganic N accumulation patterns differed between soils that received immature versus mature turned composted-dairy wastes. The results suggested that turning was a more important factor than moisture addition affecting the composting process. There was no significant difference in inorganic N accumulation patterns among soils that received different immature composts, while the N accumulation patterns observed for soils that received different mature composts depended on compost treatments. Soils amended with mature composts treated by frequent turning had higher N mineralization potentials (N₀), mineralization rate constants (K), and initial potential rates (N₀K) in comparison to soils with composts that had not been turned. Soils with mature composts treated by watering had a higher N₀, lower K, and therefore similar N₀K when compared to soils with composts that had not been watered. Soils that received mature composts treated by watering and frequent turning had higher N mineralization potentials and N₀ to total organic N ratios than soil alone, which suggested that intensive management of composting would ensure positive N fertilizer values of dairy waste composts, if the appropriate composting duration is completed.     

Evaluation of Indian rock phosphates for predicting agronomic potential through chemical and biological methods

ABSTRACT

The chemical reactivity of Indian rock phosphates (RPs) was measured by five chemical extraction methods (i.e. water, neutral ammonium citrate (NCA), 2% citric acid (CA), 2% formic acid (FA) and absolute citrate solubility (ACS)). These measurements were assessed by agronomic response data obtained by growing ryegrass and palmarosa in two highly weathered acidic soils under pot culture experiment. The phosphorus (P) solubility value of RP measured by different methods followed the order: ACS > 2% CA > 2% FA > NAC > water. Considering triple superphosphate (TSP) as a standard reference P fertilizer, the agronomic response of RPs followed the order Udaipur RP > Jhabua RP ≥ Purulia RP > Mussorie RP. Methods based on citrate solubility (i.e. NAC, 2% CA and ACS) were significantly and positively correlated with agronomic response irrespective of the plant species and soil types. The best correlation value obtained with NCA indicated that P solubility in NAC solution may offer better prediction of agronomic effectiveness of RP in terms of biomass yield, relative agronomic efficiency (RAE) and P recovery efficiency. So, the present investigation will help to predict the agronomic effectiveness of low-grade RP based on chemical methods.     

Nitrogen Mineralization as Influenced by Different Organic Manures in an Inceptisol in the Foothill Himalayas

Nitrogen-use efficiency can be enhanced through an understanding of the nitrogen (N) mineralization behavior of organic sources. An incubation study was conducted to assess the impact of organic manures on N mineralization. The manures, farmyard manure (FYM), Leucaena leucocephala, and poultry manure, were applied to the soil alone or along with urea. There was a rapid increase in the amount of mineral N released with a peak appearing either at 14 days (+urea treatments) or 21 days (manure only) of aerobic incubation. Thereafter the net N mineralized decreased gradually and levelled off beyond day 56. Overall the cumulative net N mineralized after 98 days of incubation was in the order urea > Leucaena + urea > poultry manure + urea _> FYM + urea > Leucaena > poultry manure > FYM > zero N. The potentially mineralizable N (N₀) was lower in treatments where urea was not applied.     

Chemical,Physical and Biological Criteria for Maturity in Composts for Organic Farming

Properties of organic farming composts were examined during the composting process: pH, electrical conductivity, C/N ratio, total N content, NH₄₊ content, NO_3?content, ash content, and organic matter content. In addition to these properties the respiration rate, microbial population counts, hydrolysis of Fluorescein Diacetate (FDA) and the activity of the enzyme amidase were studied. Composts at several stages of maturity were incubated in soil, and their N mineralization rates were measured. The end of the thermophilic stage was characterized by irreversible decrease in pile temperature to under 55°C, followed by stabilization of the chemical properties. This stage in the composting process is also characterized by decrease in CO₂ evolution rate, changes in microbial populations and specific patterns in FDA hydrolysis and amidase activity. Based on this evidence, we suggest that biological parameters can be considered as indicators for compost maturity.