Conventional Compost Research Articles

Exploration of Agronomic Efficacy and Drought Amelioration Ability of Municipal Solid-Waste-Derived Co-Compost on Lettuce and Maize

Organic soil amendments, such as composts, mitigate the negative impacts on the environment that are caused by poor waste management practices. However, in the sub-Saharan African region, and Malawi in particular, studies investigating the agronomical efficacy and their ability to ameliorate drought stress when used as a soil amendment are minimal. This study aimed to evaluate the efficacy of sewage sludge and municipal solid waste (MSW) co-compost to ameliorate drought stress and improve crop productivity. Three experiments were conducted (i) to determine optimal application rate for co-compost, (ii) to evaluate yield response of maize and lettuce to co-compost application under contrasting soils, and (iii) to assess the effect of co-compost under water-limited conditions. Our results indicate that an application rate of 350 g co-compost per station was the most effective. This rate is 50% and 37% lower than the currently recommended rate for applying conventional compost to green vegetables and maize, respectively. In addition, under drought conditions, the co-compost application enhanced growth in lettuce, with less wilting, increased biomass and yield, approximately 130% greater leaf yield, and a 138% improvement in root growth. Furthermore, the relative root mass ratio (RRMR) was enhanced with the co-compost application by 103% under drought stress. This suggests that the co-compost amendment resulted in a greater allocation of biomass to the roots, which is a crucial morphological attribute for adapting to drought conditions. The concentration of K in the leaves and roots of plants treated with co-compost was significantly increased by 44% and 61%, respectively, under drought conditions, which may have contributed to osmotic adjustment, resulting in a significant increase in leaf relative water content (RWC) by a magnitude of 11 times. Therefore, in light of the rising inorganic fertilizer costs and the limited availability of water resources, these results demonstrate the potential of MSW and sludge co-composting in ameliorating the drastic effects of water- and nutrient-deficient conditions and optimizing growth and yield under these constraining environments.

Evaluation of the Fertilizer Potential of Black Soldier Fly Larval Frass Obtained by the Processing of Multiple Organic Wastes in Agriculture in Cameroon: Effects on Plant Growth Parameters and Maize Kernel Nutrient Composition

The growing utilization of inorganic fertilizers results in the depletion of a minimal quantity of essential elements, including phosphorus, nitrogen, and potassium. The residual fraction is discharged into the environment as organic waste, posing a threat to the ecosystem.The black soldier fly larvae (BSFL) have been acknowledged as a solution for the increasing problem of organic waste. BSFL provides numerous benefits, including their current use of waste material, known as frass, as an organic fertilizer. The aim of this study is to examine the fertilizing properties of frass and its effects on plant growth parameters and nutrient concentration in maize kernels when consumed. This will be compared to other cultivation methods including synthetic fertilizers, conventional compost, and no compost. Following a 90-day timeframe, a comprehensive analysis was performed to assess the growth characteristics and nutrient composition within the kennels. The results of this study indicate that frass positively affects plant growth and has a favorable blend of nutrients, as previously demonstrated by studies investigating the nutrient levels in maize. This study showcased the capacity of utilizing frass as a carrier to boost agricultural output and enhance the accessibility of particular nutrients in plants. Further investigation is required to substantiate these conclusions. The widespread use of black soldier fly larvae in the agricultural sector in poor countries, particularly in Sub-Saharan Africa, has the capacity to have a beneficial effect on integrated sustainable agriculture and the achievement of Sustainable Development Goals 2, 11, and 12.

Efficient elimination of antibiotics and antibiotic resistance genes in hyperthermophilic sludge composting

Composting is widely applied in recycling ever-increasing sewage sludge. However, the insufficient elimination of antibiotics and antibiotic resistance genes (ARGs) in conventional compost fertilizer poses considerable threat to agriculture safety and human health. Here we investigated the efficacy and potential mechanisms in the removal of antibiotics and ARGs from sludge in hyperthermophilic composting (HTC) plant. Our results demonstrated that the HTC product was of high maturity. HTC led to complete elimination of antibiotics and potential pathogens, as well as removal of 98.8 % of ARGs and 88.1 % of mobile genetic elements (MGEs). The enrichment of antibiotic-degrading candidates and related metabolic functions during HTC suggested that biodegradation played a crucial role in antibiotic removal. Redundancy analysis (RDA) and structural equation modelling (SEM) revealed that the reduction of ARGs was attributed to the decline of ARG-associated bacteria, mainly due to the high-temperature selection. These findings highlight the feasibility of HTC in sludge recycling and provide a deeper understanding of its mechanism in simultaneous removal of antibiotics and ARGs.

Co-amendment of dicyandiamide with waste carbonization products into composting: Enhanced fertility, reduced gas emission and increased economic benefits

Dicyandiamide (DCD) could reduce composting nitrogen (N) losses, but the decomposes at high temperatures limited its efficacy, which might be mitigated by co-application with biochar (BC) and wood vinegar (WV). Our study revealed that DCD alone or co-applied with BC and WV did not reduce N2O emissions during the composting of chicken manure and wheat straw. However, it significantly decreased NH3 and CH4 emissions by 22.6–45.6% and 53.8–85.6%, respectively, equivalent to a 24.1–44.8% reduction in GWP compared to the control. Furthermore, the combined use of DCD with BC and WV enhanced total N content by 5.6–36.6%, increased the compost accumulation temperature by 3.8–6.1%. DCD alone addition increased the compost dissolved organic matter (DOM) content by 12.2%, and when coupled with BC and WV, it enhances the biological index value to promote new DOM generation. DCD combined with BC could increase the final humus content of compost, thereby enhancing its quality, which approach also produced greater economic benefits (266.3 CNY t−1), compared to conventional composting. In conclusion, co-application of DCD with BC and WV in composting not only reduces the emission of NH3, N2O and CH4, but also increases the compost fertility and provides more economic benefits.

Effects of multi-component passivator on heavy metal passivation, compost quality and plant growth

Direct land application of conventional compost may cause ecological risks due to the presence of heavy metals. To effectively reduce heavy metal bioavailability in compost, a multi-component passivator comprising Candida utilis, sodium humate, zeolite and attapulgite was developed, which showed passivation rates of 59.28%, 86.93% and 38.95% for zinc (Zn), copper (Cu), and ferrum (Fe), respectively, in compost. The addition of customized multi-component passivator in compost not only reduced the mobility of heavy metals, but also improved the quality of the compost and further increased the abundance of lignocellulose-degrading beneficial microorganisms in compost. Subsequent fertilization results showed that the compost product fermented with customized multi-component passivator greatly improved the growth of Chinese cabbage, with significant increases in height, weight, root length, and total chlorophyll contents of 97.63%, 210.13%, 20.42%, and 40.38%, respectively. It can be concluded that the custom-made multi-component passivator is expected to be a good additive for heavy metal passivation, high-quality compost, and plant growth.

Effect of Vermicompost on Soil Fertility and Crop Productivity in the Drylands of Ethiopia

The nutrient type and amount contributed from vermicompost varies depending on the source material, earthworm type used, agro-ecology and farmers’ management. These call for crop, soil and site specific study. This study, therefore, aimed at determining: (i) the optimal vermicompost application rate/s for wheat and maize production; and (ii) the role of vermicompost on soil fertility improvements. Field experiments in three agro-climatic zones (highland, midland and lowlands) were established on wheat and maize crops following a randomized complete block design. The treatments were vermicompost (2.5, 5.0, 7.5 and 10 t ha−1), conventional compost (10 t ha−1), and recommended rates of Nitrogen and Phosphorus (NP = 100 kg DAP and 50 kg Urea) fertilizers. Our results revealed that the studied soil chemical properties, primarily, organic carbon (OC %), N (%) and available P (mg kg−1) increased with increasing vermicompost rate. The 10 t ha−1 vermicompost treated plots had 157-210%, 64-81% and 100-242% higher soil total nitrogen content as compared to the control, 10 t ha−1 conventional compost and NP fertilizer treatments, respectively. Application of 10 t ha−1 vermicompost also resulted in a 1.5-fold and 43-63% grain yield increment of both tested crops compared to the control and NP treated plots, respectively. However, the highest net benefit was obtained from 5 t ha−1 vermicompost for maize (86% increase) and 10 t ha−1 of vermicompost for wheat (152% increase compared to the control). In conclusion, vermicompost at 5 t ha−1 for maize and 10 t ha−1 for wheat can be recommended to sustainably manage farm productivity.

Preparation of high-temperature and low-temperature-resistant solid microbial agent for cattle manure fermentation and effect on composting.

We used microbiology and molecular biology techniques to screen out high-temperature and low-temperature-resistant saprobiotics for compost and prepared a compound fermentation bacteria agent to rapidly ferment cattle manure into high-quality organic fertilizer in low-temperature season. Conventional composting and high-throughput techniques were used to analyze the changes of physical and chemical indexes and biodiversity in the process of composting, from which high and low-temperature-resistant strains were obtained, and high-temperature and low-temperature-resistant solid composite bactericides were prepared and added to composting to verify the effects of composite bactericides on composting. The conventional composting cycle took 22days, and the diversity of microflora increased first and then decreased. Composting temperature and microbial population were the key factors for the success or failure of composting. Two strains of high-temperature-resistant bacteria and six strains of low-temperature-resistant bacteria were screened out, and they were efficient in degrading starch, cellulose, and protein. The high-temperature and low-temperature-resistant solid bacterial agent was successfully prepared with adjuvant. The preparation could make the compost temperature rise quickly at low temperature, the high temperature lasted for a long time, the water content, C/N, and organic matter fell quickly, the contents of total phosphorus and total potassium were increased, and the seed germination index was significantly improved. Improve the composting effect. The solid composite bacterial agent can shorten the composting time at low temperature and improve the composting efficiency and quality.

Evaluation of different fertilizer sources for sustainable carrot production in Tehuledere district, northern Ethiopia

The demand for organic agriculture has been growing due to concerns about the environmental and health impacts of chemical-intensive farming. The study aimed to investigate the effects organic fertilizers on carrot (Nantes) growth and yield in Tehuledere district. The experiment was conducted at two sites (Gobeya and Libannos) using four fertilizer types (vermicompost, conventional compost, mixture of the two, and inorganic fertilizer) and a control. The experiment was laid out in randomized complete block design with three replications, and data were analyzed using R-software. The study analyzed various growth (emergence percentage, plant height, leaf number, fresh weight, and dry weight of leaves), and yield (root length, root diameter, fresh weight of roots, marketable root yield, unmarketable root yield, and total root yield) parameters. Generally, fertilizer application improved (p < 0.001) growth and yield compared to the control. Vermicompost and inorganic fertilizer (NPSB) showed similar results (p > 0.001) but the highest values (p < 0.001) for most of the parameters (marketable yield was 41.7 t/ha±0.76 for vermicompost and 42.5 t/ha±1.14 for NPSB). However, NPSB could pose negative environmental impact that could not result in sustainability if used in excess and inappropriate (method and time) in particular. Therefore, carrot production using vermicompost is recommended for farmers of Tehuledere district and similar agroecological areas to enhance productivity while contributing to sustainable agriculture. The results have implications for policy makers, researchers, and farmers interested in promoting environmentally friendly and sustainable carrot production.

Local circular economy: BSF insect rearing in the Italian Agri-Food Industry

With a growing population, both food and waste production will increase. There is an urgent need for innovative ways of valorizing waste. The black soldier fly (Hermetia illucens L.) efficiently converts agri-food by-products (BPs) into high-quality materials; its rearing process yields larvae (BSFL) rich in fat and protein for feed purposes, with “frass” acting as organic fertilizer. While the insect rearing sector is expanding, few producers use BPs. Therefore, a case study approach was adopted to evaluate the potential for establishing an Italian BSFL production plant on BPs available on the territory. After contacting more than 115 agri-food companies (maximum 100 km from the BSFL plant), they were classified based on sector, distance, size, and BPs (quantity, seasonality, management). BPs with a low value (fruit and vegetable residues) were treated as waste, associated with costs and low valorization. By merging the available BPs on the territory and following the literature on BSFL nutritional needs’ two diets (Scenario BSFL) were created, assessing their suitability comparing them to the current full-scale plant diet (Scenario 0). The exploitation of BPs for BSFL rearing reduced local waste production by 52 % compared to conventional composting (Scenario 0). In addition, integrating BPs into the larval feed formulation increased BSFL production value (+47 times). These results highlight the potential of locally-based insect rearing to valorize BPs and create a network of sustainable actors within the agri-food industry. Further investigations are needed to improve the connection between agri-food and insect industrial activities, expanding this framework to other regions.

Effects of an assistive electric field on heavy metal passivation during manure composting

Composting is one of main technologies for treating and thus utilizing livestock manure and sludge. However, heavy metals are major concerns in compost utilization due to their potential environmental hazards and health risks. This study aimed to investigate the effects of electric field-assisted composting on the variations of heavy metals and the affecting factors. The results showed that electric field significantly reduced the contents of bioavailable heavy metals including Mn, Zn, Cu, Ni, and Cd, with their bioavailable concentrations decreasing by 61.7, 63.8, 64.9, 83.7, and 63.8 %, respectively. The heavy metals being transformed into stable states were increased, indicating that the electric field also passivated these heavy metals and reduced their biological toxicity and stabilized their forms. Spearman's correlation analysis revealed that the changes in substances, temperature, and organic matter were the dominant environmental factors affecting the forms of heavy metals. Microbial community analysis indicated an increase in the abundance of metal-resistant bacteria such as Pseudomonas and Bacillus during electric field-assisted composting, with their relative abundances being increased to 2.66 % and 15.63 % in the pile of electric field-assisted composting, respectively, compared to the values of 1.88 % and 4.36 % respectively in the conventional composting. The current study suggests that electric field-assisted composting can significantly reduce the availability of heavy metals in the compost, and thus mitigate the health risks associated with its application.

Exploring the humification process of municipal sludge in hyperthermophilic composting through metagenomic and untargeted metabolomic

Hyperthermophilic composting (HC) has been widely recognized for the advantage of high treatment efficiency for organic wastes. However, the humification process is still unclear. In this study, the humification process of HC was investigated, compared to conventional composting (CK). The results showed that the highest composting temperature, organic matter degradation rate, and humification index in HC were 92.62 °C, 23.98%, and 1.59, while those in CK were 70.23 °C, 14.49 %, and 1.04, indicating HC accelerated humification process. Moreover, the results of metagenomic and untargeted metabolomic showed that the genes and metabolisms related to carbohydrate, lipid, amino acid, fatty acid, and nucleotide were more abundant in HC. Consequently, the metabolic pathways regarding organic matter degradation and microbial reproduction were enhanced in the high temperature stage of HC, further accelerating the humification reaction in the low temperature stage. This work contributes to the comprehension of the humification mechanism in HC.

Adjusting pH of the Secondary Composting Materials to Further Enhance the Lignocellulose Degradation and Promote the Humification Process

Straw waste has a large amount of lignocellulose, which shows a strong resistance to biodegradation in the composting process and hinders the formation of humic substances. Therefore, the effects of pH adjustment and inoculation of degradation bacteria on the composting process, lignocellulose degradation and humus formation in secondary fermentation were explored through aerobic composting experiments. The experiment was designed with four treatment groups: CK (conventional composting), T1 (adjusting pH), T2 (inoculating P. chrysosporium), and T3 (adjusting pH and inoculating P. chrysosporium), respectively. Results showed that except for treatment CK, all other treatments met the maturation standards at the end of composting. Adjustment of the pH value and the inoculation of Phanerochaete chrysosporium (P. chrysosporium) can significantly shorten the fermentation time. Among them, the lignin content of treatment T3 was reduced significantly by 14.28% compared to treatment T2; the content of humic acid in T3 increased significantly by 51.32% and 14.04% compared with T1 (adjusting pH) and T2 (p &lt; 0.05), respectively. In terms of key enzyme activity and precursor substance changes, the pH adjustment treatment was superior to other treatments after composting. This study confirmed that the change of pH conditions is an important environmental factor for microorganisms to enhance the humification process; degrading enzymes were used as a “bridge” to enhance the continuous degradation of lignocellulose by microorganisms and increase the supplementation of precursors and the synthesis of humic acid, which is the mechanism to enhance the humification process. Our findings provided a new method to enhance the humification process, which is a valuable and economical technical approach to improve organic fertilizer quality.

Co-occurrence pattern of ARGs and N-functional genes in the aerobic composting system with initial elevated temperature

Animal manure is known to harbor antibiotic resistance genes (ARGs). Aerobic composting is a prevalent cost-effective and sustainable method to treat animal waste. However, the effect of initially elevated temperature on antibiotic resistome during the composting process is unclear. In this study composting was subjected to initial external heating (EHC) for a period of 5 days compared to conventional composting (CC). After composting ARGs abundance was significantly reduced by 2.43 log in EHC and 1.95 log in CC. Mobile genetic elements (MGEs) also exhibited a reduction of 1.95 log in EHC and 1.49 log in CC. However, during the cooling phase, the genes resisting macrolide lincosamide and streptogramin B (MLSB) rebounded by 0.04 log in CC. The potential human pathogenic bacteria Pseudomonas (41.5–61.5%) and Actinobacteria (98.4–98.8%) were significantly reduced in both treatments and the bulk of targeted antibiotics were eliminated by 80.74% in EHC and 68.98% in CC. ARGs and N-functional genes (NFGs), mainly denitrification genes, were carried by the same microbial species, such as Corynebacterium sp. and Bacillus sp., of the dominant phylum. Redundancy analysis (RDA) revealed that CC microbial communities played a key role in the enrichment of ARGs while in EHC the variation of ARGs was attributed to the composting temperature. The number of high-risk ARGs was also lower in EHC (4) compared with CC (6) on day 30. These results provide insight into the effects of an initially enhanced temperature on ARGs removal and the relationship between ARGs and NFGs during the composting process.

Potassium-rich mining waste addition can shorten the composting period by increasing the abundance of thermophilic bacteria during high-temperature periods

Conventional compost sludge has a long fermentation period and is not nutrient rich. Potassium-rich mining waste was used as an additive for aerobic composting of activated sludge to make a new sludge product. The effects of different feeding ratios of potassium-rich mining waste and activated sludge on the physicochemical properties and thermophilic bacterial community structure during aerobic composting were investigated. The results showed that potassium-rich waste minerals contribute to the increase in mineral element contents; although the addition of potassium-rich waste minerals affected the peak temperature and duration of composting, the more sufficient oxygen content promoted the growth of thermophilic bacteria and thus shortened the overall composting period. Considering the requirements of composting temperature, it is recommended that the addition of potassium-rich waste minerals is less than or equal to 20%.

Amended compost alleviated the stress of heavy metals to pakchoi plants and affected the distribution of heavy metals in soil-plant system

With the development of the social economy, soil heavy metal pollution has become a common worldwide issue. Therefore, the remediation of soil heavy metal pollution is imminent. This study aimed to investigate the effect of amended compost on reducing heavy metal bioavailability in soil and relieving heavy metals stress on plants under Cu and Zn stress in a pot experiment. To model the restoration of heavy metal-polluted farming soil, conventional compost (CKw), activated carbon compost (ACw), modified biochar compost (BCw) and rhamnolipid compost (RLw) were utilized. The results showed that the application of amended compost could promote the growth and quality of pakchoi and enhance the stress ability of malondialdehyde and antioxidant enzymes to heavy metals. The distribution of Cu and Zn in different subcellular parts of pakchoi was also affected. The application of amended compost significantly reduced the heavy metals content in the shoot of pakchoi, among which the content of Cu and Zn in the shoot of pakchoi in RLw was significantly decreased by 57.29% and 60.07%, respectively. Our results can provide a new understanding for efficient remediation of contaminated farmland soil by multiple heavy metals.

Sensitive response mechanism of ARGs and MGEs to initial designed temperature during swine manure and food waste co-composting

The rapid aerobic composting process has been used to reduce organic wastes, but the associated risks of antibiotic resistance genes (ARGs) need to evaluate in an efficient way. The primary objective of this work was to explore the underlying mechanism of initial adjustment in composting temperature on the variation of ARGs, mobile genetic elements (MGEs), and microbial composition during co-composting. The co-composting was initially externally heated (T2) for 5 days. The results showed that ARGs abundance in conventional composting (T1) was reduced by 49.36%, while multidrug was enriched by 86.16% after a period of 30 days. While in T2 ARGs were removed by 79.46% particularly the fraction of sulfonamide, multidrug, and vancomycin resistance genes were >90% without rebounding of any ARGs. Whereas, MGEs were reduced by 68.12% and 93.62% in T1 and T2, while the half-lives of ARGs and MGEs were lower in T2 compared to T1 (86.3%,86.7%). T2 also affected the metabolism function by regulating carbohydrate metabolism (9.62–10.39%) and amino acid metabolism (9.92–10.93%). Apart from this, the potential human pathogenic bacteria Pseudomonas was reduced by 90.6% in T2 and only 32.9% in T1 respectively. Network analysis showed that Ureibacillus, Weissella, Corynebacterium, Escherichia-Shigella, Acinetobacter were the main host of multiple genes. Structural equation models exhibited that bacterial communities were mainly responsible for the enrichment of ARGs in T1, whereas, it was directly affected by MGEs in T2. Similarly, ARGs variation was directly related to composting temperature. With this simple strategy, ARGs associated risk can be significantly reduced in composting.

Residues from black soldier fly (Hermetia illucens) larvae rearing influence the plant-associated soil microbiome in the short term.

The larvae of the black soldier fly (BSFL, Hermetia illucens) efficiently close resource cycles. Next to the nutrient-rich insect biomass used as animal feed, the residues from the process are promising plant fertilizers. Besides a high nutrient content, the residues contain a diverse microbial community and application to soil can potentially promote soil fertility and agricultural production through the introduction of beneficial microbes. This research assessed the application of the residues on plant-associated bacterial and fungal communities in the rhizosphere of a grass-clover mix in a 42-day greenhouse pot study. Potted soil was amended with BSFL residues (BR+) or conventional compost (CC+) produced by Rwandan waste management companies in parallel to residues and compost sterilized (BR-, CC-) by high-energy electron beam (HEEB) as abiotic controls. The fertilizers were applied at a rate of 150 kg N ha−1. Soil bacterial and fungal communities in both fertilizer and soil were assessed by high-throughput sequencing of ribosomal markers at different times after fertilizer application. Additionally, indicators for soil fertility such as basal respiration, plant yield and soil physicochemical properties were analyzed. Results showed that the application of BSFL residues influenced the soil microbial communities, and especially fungi, stronger than CC fertilizers. These effects on the microbial community structure could partly be attributed to a potential introduction of microbes to the soil by BSFL residues (e.g., members of genus Bacillus) since untreated and sterilized BSFL residues promoted different microbial communities. With respect to the abiotic effects, we emphasize a potential driving role of particular classes of organic matter like fiber and chitin. Indeed, especially taxa associated with decomposition of organic matter (e.g., members of the fungal genus Mortierella) were promoted by the application of BSFL residues. Soil fertility with respect to plant yield (+17% increase compared to unamended control) and basal respiration (+16% increase compared to unamended control) tended to be improved with the addition of BSFL residues. Findings underline the versatile opportunities for soil fertility arising from the application of BSFL residues in plant production and point to further research on quantification of the described effects.

Composting effect and antibiotic removal under a new temperature control strategy

The main objective of this study was to investigate the feasibility of a new temperature control strategy in the co-composting process to accelerate operation cycle and remove antibiotics from mixed organic wastes. The evaluation of the composting process showed that composting with temperature control (TC) was completed within 14 days. The final compost of TC exhibited a 10% higher degradation of organic matters, more humus formation and 11.25% lower heavy metals concentration than conventional composting (CC), which fully met the Chinese National Agricultural Organic Fertilizer Standard requirements. The degradation extent and kinetic of macrolides, tetracyclines, sulfonamides and fluoroquinolones showed that the removal efficiency of total antibiotics in TC was 23.58% higher than CC, with less half-life, which was significantly correlated with higher temperature. Particularly, the highest removal was observed for sulfonamides (87.45%) in TC, the half-life of which was reduced by 75.95% compared with CC. The higher degradation rate was attributed to enhanced decomposition of unstable antibiotics and degrading activity of microbes at high temperature. The microbiological analysis showed that the external heating led to a distinct composition and succession of bacterial community in TC. Firmicutes, Proteobacteria, Actinobacteriota and Bacteroidota were dominant and the emergence of Patescibacteria and Chloroflexi at cooling period in TC proved that the later composting environment was in an oligotrophic state. Current research provided a promising rapid composting approach for high-quality fertilizer production and antibiotic management in organic waste disposal.

Coupling effect of high temperature and thermophilic bacteria indirectly accelerates the humification process of municipal sludge in hyperthermophilic composting

Due to its high treatment efficiency and environmental friendliness when used to treat organic waste, hyperthermophilic composting (HC) has attracted extensive attention in recent years. However, it is still unclear how HC accelerates the degradation and humification process of organic matter. This study investigated the effects of high temperature and thermophilic bacteria on the degradation and humification of organic matter during HC. In the process of HC and conventional composting (CC), total organic carbon content decreased by 30.76 mg/g and 18.50 mg/g, while humic acid carbon content increased by 2.26 mg/g and 1.41 mg/g, respectively. These results showed that HC accelerated the humification process by enhancing the degradation of organic matter and the production of humic acid compared to CC. Redundancy analysis revealed that the rapid humification process of HC was related to high temperature and thermophilic bacteria. Thermophilic bacteria accelerated the degradation of organic matter in the high temperature stage, and the degradation products provided sufficient substances for the humification reaction in the low temperature stage, thereby accelerating the humification reaction. In conclusion, the coupling effect of high temperature and thermophilic bacteria indirectly accelerated the humification process. This work contributes to understanding the humification mechanism of HC.

Determination of the Application Rate of Conventional Compost Integrated with Chemical Fertilizer on Maize (Zia Maize) Yield in Dugda District of East Shoa Zone, Oromia

Integrated soil fertility management is the application of inorganic in combination with organic fertilizer to maintain soil fertility and improve crop yield. A study was conducted in East Shoa Zone, Dugda District on farmers' fields to determine the combined effects of conventional compost as organic fertilizer and NPS as inorganic fertilizer on soil chemical properties and maize production. There were five treatments: Recommended rate of inorganic fertilizer, 100, 75, 50 and 25% equivalent level of compost for nitrogen fertilizer. Recommended level of 69 P2O5/ha were equally applied at all treatments. The experiment was laid out in RCBD design with three replications. The analysis of variance showed no significant differences (P &gt; 0.05) in maize grain yield response. However, the highest maize grain yield (8728.20 kg ha-1) was obtained from treatment two that received 100% equivalent compost for nitrogen fertilizer and the lowest (8325 kg ha-1) was obtained from treatment one where recommended chemical fertilizer alone was applied. Composite Soil samples were also collected before compost application and after harvesting to evaluate the residual effect of compost on soil physiochemical properties. Accordingly, laboratory analysis showed no significance differences (P &gt; 0.05) in total N, available P, soil organic carbon and CEC. However, analysis of variance of post-harvest composite soil samples indicated significant differences on soil available P, OC, TN and CEC as compared to initial soil sample. On the other hand, partial budget analysis was done to determine economically optimum rate of compost integrated with chemical fertilizer. Accordingly, the highest net benefit (126527 Eth. Birr ha-1) was recorded for treatment two where 100% compost (4.6t/ha) plus 150kg/ha NPS fertilizers were applied. The highest marginal rate of return (146) was also obtained from the same treatment. Therefore, the present study showed that combined application of organic and NPS fertilizer enhanced maize productivity and soil fertility status in the study area. Hence combined fertilizer application of 4.6 t ha1 conventional compost integrated with 150 kg ha-1 NPS improved maize productivity and soil chemical properties, and recommended for the study area and similar agro-ecology.