Assessing the use of composts from multiple sources based on the characteristics of carbon mineralization in soil

Impact of cellulolytic nitrogen-fixing composite inoculants on humification pathways and nitrogen cycling in kitchen waste composting

Low humification and nitrogen loss pose substantial challenges to the resource utilization in kitchen waste composting. This study investigated the effects of brown-rot fungi (BRF), cellulolytic nitrogen fixing bacteria (CNFB), and their composite microbial inoculants (CMI) during composting. Results indicated that microbial inoculants extended the thermophilic phase and enhanced cellulose degradation. Compared with the control, the degree of polymerization (HA/FA) in BRF, CNFB, and CMI was 2.28, 1.85, and 2.68 times higher, respectively, while increasing total nitrogen by 11.15%, 15.50%, and 19.73%. BRF and CMI primarily enhanced the Maillard humification pathway, while CNFB promoted the polyphenol humification pathway. Additionally, BRF enhanced nitrification and reduced denitrification, whereas CNFB and CMI improved nitrification, nitrogen fixation, and ammonification while reducing denitrification. Overall, BRF primarily promoted humification, while CNFB excelled in nitrogen retention. The CMI achieved optimal humification and nitrogen retention, indicating a potential sustainable solution for kitchen waste composting.

Insights into the critical roles of water-soluble organic matter and humic acid within kitchen compost in influencing cadmium bioavailability

Compost has demonstrated potential as a cadmium (Cd) remediation agent, while it still remains unclear about the core components in driving the bioactive transformation of Cd. To address this issue, this study isolated three components-kitchen compost powder (KC), humic acid (HA), and water-soluble organic matter (DOM)-from kitchen compost to regulate soil properties, bacterial community structures and functions, and Cd migration risks. The results revealed that the addition of 20% KC and HA reduced the bioavailability factor of Cd by 47.20% and 16.74%, respectively, with HA contributing 35.47% of the total reduction achieved with KC. Conversely, the application of DOM increased the Cd risk through a reduction in soil pH and an increase in the abundance of Cd-activating bacteria, which adversely affected the stability of Cd complexes. However, the porous structure and organic matter in KC and HA provided adsorption sites for Cd passivation and promoted the growth of Cd-fixing bacteria. This study effectively identifies both the positive and negative effects of key compost components on Cd migration and provides scientific guidance for applying kitchen compost in soil management.

Effects of two types nitrogen sources on humification processes and phosphorus dynamics during the aerobic composting of spent mushroom substrate

Aerobic composting is increasingly regarded as a promising technology for the recycling of spent mushroom substrate (SMS), and an applicable nitrogen source is necessary to improve the process. This study is the first to investigate the effects of protein-like N source (chicken manure, CM) and high-N source (urea, UR) on humification process and P dynamics during SMS composting. The effect of different N sources on microbial succession was also studied. Results showed that CM addition achieved a longer thermophilic phase (16 d vs 9 d), greater germination indices (131.6% vs 106.3%), and higher total phosphorus content (13.1 g/kg vs 6.56 g/kg) in the end products, as compared to UR. The addition of CM showed beneficial effects on humification and stabilization, including decreased weight loss and fluctuations in the level of functional groups. The P produced in the compost was interconverted and leached in the P pool. In this case, the P detected in the compost was in the form of orthophosphate and MgNH₄PO₄⋅6H₂O crystal as inorganic P and orthophosphate monoester as organic P. The most abundant microorganisms at the phylum level mainly include Firmicutes, Actinobacteria, and Proteobacteria, accounting for more than 88% of the total microorganisms. The addition of CM to SMS compost resulted in higher organic matter degradation rates. This work clarified the role of various N sources in SMS composting and presented an appropriate waste management method beneficial to bioresource technology and sustainable development of the edible fungi business.

Evaluation of the Use of Sewage Sludge Biochar as a Soil Amendment—A Review

In recent decades, minimization and recycling/reuse policies were introduced to reduce the quantities of generated waste and for alternative waste recovery. Organic wastes represent 46% of total global solid waste. Possible uses of organic wastes include using it as fertilizer and amendment for soil, for energy recovery and for the production of chemical substances. Sewage sludge disposal and reuse are identified as future problems concerning waste. The total amount of sludge generated in the entire world has increased dramatically, and this tendency is expected to increase significantly in the years to come. In most developed countries, special attention is given to sewage sludge treatment in order to improve the quality and safety of using it on the ground surface. Sewage sludge pyrolysis is considered an acceptable method, from an economic and ecological perspective, for the beneficial reuse of sewage sludge. This method has many advantages because, during the pyrolysis process, the sludge volume is reduced by 80%, pathogenic agents and hazardous compounds from sewage sludge are eliminated, metals are immobilized in solid residue and organic and inorganic fractions are immobilized in a stabilized form of pyrolytic residues (biochar). The biochar generated by sewage sludge pyrolysis does not contain pathogenic agents and is rich in carbon and nutrients.

Two types nitrogen source supply adjusted interaction patterns of bacterial community to affect humifaction process of rice straw composting

This study investigated effects of high-nitrogen source (urea) (R_UR) and protein-like nitrogen source (chicken manure) (R_CM) on humification process during lignocellulose biomass composting. It demonstrated that decreasing ratio of crude fiber (CF), polysaccharide (PS) and amino acids (AAs) in R_CM (29.75%, 53.93% and 73.73%, respectively) was higher than that in R_UR (14.73%, 28.74% and 51.92%, respectively). Humic substance (HS) concentration increased by 7.51% and 73.05% during R_UR and R_CM composting, respectively. The lower total links, more independent modularization and higher proportion of positive correlations between functional bacteria and organic components was observed with R_CM network than R_UR, indicating that protein-like nitrogen source supply may alleviate competition within bacterial community. Moreover, chicken manure supply favorably selects greater special functional bacterial taxa (Pusillimonas, Pedomicrobium, Romboustia and other 24 genus) related to AAs and stimulates the collaborative division of bacterial community. This is significance for strengthening effective transformation of organic components.

Effects of Garden Amendments on Soil Available Lead and Plant Uptake in a Contaminated Calcareous Soil

Gardeners use organic and inorganic substances to enhance plant growth, which can inadvertently impact soil solubility and plant uptake of unknown contaminants. Consequently, human exposure can increase through gardening and consumption of produce grown in potentially contaminated soils. A greenhouse experiment was established to examine the effects of biochar, compost, and common inorganic fertilizer on soil lead (Pb) availability for radish (Raphanus sativus, L.) and lettuce (Lactuca sativa, L.) grown in a calcareous soil containing excessively high lead (Pb), along with Pb accumulation in radish tissue. Results indicate that soil amended with biochar and planted to radish saw an 18% reduction in available Pb and an 11% decrease in plant tissue content when compared to the control. Compost showed an 8% reduction in available Pb, but a 19% increase in tissue content. In contrast, soil with inorganic fertilizer planted to radish increased in both soil Pb availability by 11% and Pb tissue content by 40%. Adding water-soluble inorganic fertilizers to contaminated calcareous soils without added organic matter enhances soil Pb availability and often asymptomatic plant Pb bioaccumulation. In conclusion, gardeners are encouraged to test their soils for contamination and apply biochar in combination with compost, as this combination is recommended to improve soil health and aid in overcoming initial N deficiencies induced by biochar.

Untangling the response of fungal community structure, composition and function in soil aggregate fractions to food waste compost addition

Soil fungi are key drivers in regulating the ecosystem function, playing a vital role in protecting the plant from phytopathogens and other biotic and abiotic pressures. However, the potential impact of compost addition and soil aggregate size on the fungal community and functional ecological guild remains uncertain. This study investigated the structure, composition, and function of soil fungal communities across aggregate fractions under food waste compost addition using Miseq sequencing and FUNGuild. Compost addition exerted a negative impact on fungal α-diversity, and shifted the structure and changed the composition of fungal community. Compost addition rates exhibited more contributions to fungal α-diversity variations (R = 0.609, 0.895, and 0.501 for Sobs, Shannon, and Chao indices, respectively, P = 0.001) and the separation of community structure than soil aggregate size (R = 0.952, P = 0.001). Biomarkers, including Chaetomiaceae, Ascobolaceae, and Sordariomycete, displayed significant superiority in compost-added soils, whereas the populations of Nectriaceae and Clavicipitaceae were significantly decreased. The relative abundances of animal and plant pathogens were significantly decreased, whereas that of saprotrophs were increased. The abundances of pathogens correlated positively with pH and negatively with nutrients (soil organic matter, dissolved organic carbon, total nitrigen, NH₄⁺, and NO₃^-), whereas those of saprotrophs showed an opposite trend. The dose of compost was the major driver for fungal functional guild variation, whereas carbon and nitrogen source exhibited more contributions to function variation than pH value. These results provide a reference for sustainable ecological agriculture by applying compost rationally under the conditions of soil health and agricultural performance.

Revealing the Inner Dynamics of Fulvic Acid from Different Compost-Amended Soils through Microbial and Chemical Analyses

The formation of fulvic acid (FA), an aromatic compound, is affected by the compost amendment. This study aimed to assess the extent of the humification of FA in soil amended with seven different composts. Results showed that composts improved the FA concentration in soil. Parallel factor (PARAFAC) analysis, combined with hetero-two-dimensional correlation spectroscopy (hetero-2DCOS), indicated that the inner changes in FA components determined the evolution of mineralization. The diversity in the composts used and the dominant microbes present might be responsible for the evolution of different mechanisms of FA transformation. Structural equation models (SEMs) demonstrated that the FA components were transformed directly by microbes, or indirectly via changes in the total organic carbon (TOC) and total nitrogen (TN) contents, C:N ratio, humic substance (HS) levels, and humic acid (HA): FA ratio, which regulate the microbial community structure. Our results will be useful for improving the bioavailability of compost products and realizing sustainable utilization of the soil.

Organic fertilizer application and Mg fertilizer promote banana yield and quality in an Udic Ferralsol

Low soil fertility, high rates of fertilizer application and low yields and quality are major problems in intensive banana production in acid soils of south China. A field experiment was carried out for two years to determine the optimum management practices for maximizing soil health and banana yield and quality. The experiment consisted of an unamended control (CK) and lime (Lime), calcium magnesium phosphate fertilizer (CMP), organic fertilizer (OF), and organic fertilizer combined with calcium magnesium phosphate fertilizer (OFC) treatments. Soil nutrient concentrations and banana shoot biomass, nutrient uptake, yield and fruit quality were determined. Application of lime and CMP was found to increase soil pH and nutrient availability and increase banana yield. Yet, the banana biomass and yields in the Lime and CMP treatments were significantly lower than those in the OF and OFC treatments in which soil organic matter (SOM) content increased. Total soluble solids and soluble sugar contents increased in the CMP and organic fertilizer treatments. A consistent increase in Mg concentrations in banana leaves over the two years in the CMP and organic fertilizer treatments indicates that Mg is essential for banana production and quality. Short-term adding Mg from banana corms increased total soluble solids and soluble sugar content. The application of organic fertilizer combined with CMP or Mg solution is therefore recommended to increase soil health and promote the yield and quality of banana in intensively managed plantations in subtropical regions.

Effect of the combined application of fungal residue and chemical fertilizers on the mineralization of soil organic carbon in paddy fields

Improving soil quality, reducing waste, and mitigating climate change require an understanding of the balance between soil organic carbon (SOC) accumulation and depletion after the application of different quantities of fungal residue and chemical fertilizers. We evaluated the mineralized carbon (MC) content and mineralization rate (MR) after nine applications of chemical fertilizers (C) and fungal residue (F) in paddy fields, at rates of 0, 50, and 100%. A double exponential model was used to calculate the potential rates of MC and SOC turnover. The combined application of fungal residue and chemical fertilizers led to significantly higher MC and MR, by 24.97-100.05 and 24.36-98.07%, respectively, during 57 days of incubation than that of the control. The MC and MR values were highest with the C₅₀F₁₀₀ treatment. Simulations with the double exponential model showed that both the active SOC pools (C₁) and potential SOC mineralization flux C₁ + C₂ were highest with C₅₀F₁₀₀, and the MR constants, k₁ and k₂, were highest with C₁₀₀F₁₀₀. The potential SOC MR [(C₁ + C₂) / SOC] was highest with C₅₀F₁₀₀. The application of fungal residue and chemical fertilizers to paddy fields effectively alleviated soil acidification caused by chemical fertilizers and increased the nutrient content, MC, MR, C₁, and C₁ + C₂ of soils. However, the over-use of fungal residue or chemical fertilizers produces the reverse effects. Therefore, appropriate quantities of chemical fertilizers and fungal residue need to be applied to enhance the carbon sequestration capacity of soils while improving the MC and MR.

Bioavailability Evaluation of Dissolved Organic Matter Derived from Compost-Amended Soils

In this study, hetero-two-dimensional correlation spectroscopy (hetero-2DCOS) combined with parallel factor analysis (PARAFAC) was employed to reveal the inner changes in the dissolved organic matter (DOM) components derived from soil amended with seven different composts. The dynamics of the four DOM components showed that the fluorescence peaks in each component varied in different directions during mineralization. Structural equation models (SEMs) demonstrated that the compost amendments changed the correlations of the total organic carbon (TOC), total nitrogen (TN), and bacterial community composition with DOM components and strengthened the cooperative function related to transformation of DOM components. The compost sources were further ranked as cabbage waste (CW) > chicken manure (CM), dairy cattle manure (DCM), tomato stem waste (TSW), peat (P) > municipal solid waste (MSW), sewage sludge (SS) by projection pursuit regression (PPR) analysis. It is helpful to improve the bioavailability of compost products to obtain composts with a particular function.

Effects of ambient temperature and aeration frequency on emissions of ammonia and greenhouse gases from a sewage sludge aerobic composting plant

This study analyzed emissions characteristics of NH₃ and greenhouse gases (i.e. N₂O, CH₄, and CO₂) from a municipal sewage sludge aerobic composting plant. Samples were collected during different seasons in which ambient temperatures and aeration frequencies varied. Results revealed (1) the maximum gas emissions occurred during the mesophilic phase for N₂O (22%-56%) and CH₄ (65%-95%), and in the thermophilic phase for NH₃ (84%-86%) and CO₂ (65%-74%); (2) raising ambient temperatures promoted emissions of NH₃ and greenhouse gases, while improved aeration frequency increased NH₃ but decreased greenhouse gas emissions; (3) CO₂ and N₂O were found to be the key greenhouse gases emitted during aerobic composting according to assessment of the CO₂ equivalent. The results obtained from this study suggest that adjusting ambient temperature to -3 to 5 °C and aeration frequency in composting workshops can be useful approaches for the reduction of NH₃ and greenhouse gas emissions from municipal sewage sludge composting plants.

Effective use of iron-aluminum rich laterite based soil mixture for treatment of landfill leachate

Landfill leachate poses environmental threats worldwide and causes severe issues on adjacent water bodies and soil by direct discharge. The primary objective of this study is to analyze the efficient use of compost and laterite mixtures (0, 10, 20, 30 and 40 wt% compost/laterite) on leachate treatment and to investigate the associated removal efficiencies under different sorption processes. Therefore, in the experimental design, laterite is used for providing adsorption characteristics, and compost for activating biological properties of the filter. The filtering process is continued until major physical changes occur in the filter at approximately 100 days. The raw leachate used for the experiment shows higher average values for many analyzed parameters. Parameters for the experiment are selected based on their availability in raw leachate in the Sri Lanka. During filtering, removal efficiencies of BOD (>90%), COD (>85%), phosphate (>90%) and nitrate (75-95%) show higher values for all filters. These removals are mainly associated with biodegradation, which is activated by the added compost. Perhaps the removal of nitrate steadily increases with time, which indicates in denitrification by the added excess carbon from the leachate. The removal of total suspended solids (TSS) is moderate to high, but conversely, the electric conductivity (EC) is unsteady, indicating an association between iron exchange and carbonate degradation. A very high removal efficiency is reported in Fe (90-100%), and wide ranges of efficiencies in Mn (30-90%), Cu (45-85%), Ni (30-93%), Cd (37-98%), Zn (15-98%), and Pb (35-98%) involve heterogeneous sorption processes. Furthermore, the normalization of raw leachate by the liquid filtrate has apparent improvements. The differences (p > .05) in removal efficiencies between the filters are significant. It can be concluded that the filter with laterite mixed with 20% of compost has the optimum conditions. Further, the Fourier-transforminfrared (FT-IR) models for filter media conclude multiple sorptions and reveal evidence on vacant sites. X-ray diffraction (XRD) analyses indicate secondary minerals gibbsite, hematite, goethite and kaolinite as the major minerals that involved on the sorption process.