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A Path for Circular Economy in Agriculture: From Organic Waste to Sustainable Energy and Soil Fertility

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A special issue of Agronomy (ISSN 2073-4395). This special issue belongs to the section "Farming Sustainability".

Deadline for manuscript submissions: 15 August 2026 | Viewed by 12782

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Dr. Daniela Pezzolla

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Department of Civil and Environmental Engineering, University of Perugia, Via G. Duranti, 93, 06125 Perugia, Italy
Interests: soil organic matter; GHG emissions; biofertilizer; sustainable agriculture
Special Issues, Collections and Topics in MDPI journals

Dr. Nicolò Montegiove

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Department of Civil and Environmental Engineering, University of Perugia, 06125 Perugia, Italy
Interests: green chemistry; biochemistry; biotechnology; biology; circular economy; sustainability; natural resources; renewable energy

Dr. Alberto Maria Gambelli

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Guest Editor

Department of Civil and Environmental Engineering, University of Perugia, Via G. Duranti 93, 06125 Perugia, Italy
Interests: natural gas hydrates; carbon capture and storage; methanation; gas mixture separation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The transition to a circular economy in agriculture offers a promising way to handle organic waste more effectively, improving both sustainability and resource efficiency. Agricultural and municipal organic residues often contribute to inadequately managed environmental challenges, including greenhouse gas emissions and soil degradation. Increasing the efficacy of organic waste treatments, such as anaerobic digestion in producing biogas and digestate and composting in creating high-quality soil amendments, can improve the valorization and sustainability of organic resources. In particular, anaerobic digestion can convert these residues into renewable energy, reducing reliance on fossil fuels and mitigating greenhouse gas emissions. This Special Issue wants to explore innovative strategies for converting organic waste into sustainable energy and soil enrichment, highlighting new solutions and technological advancements in waste-to-energy and waste-to-soil systems. The objective is to advance knowledge of these processes, promoting a circular economy in agriculture that fosters environmental sustainability and improves soil health.

Dr. Daniela Pezzolla
Dr. Nicolò Montegiove
Dr. Alberto Maria Gambelli
Guest Editors

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Keywords

sustainable agriculture
anaerobic digestion
composting
soil enrichment
waste management
organic waste
organic fraction of municipal solid wastes
pollution
renewable energy
circular economy

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Published Papers (9 papers)

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Research

32 pages, 2352 KB

Open AccessArticle

Biochar–Compost as a Solution to Tackle Water Stress and Soil Degradation in Drylands

by Alban Echchelh and Felipe Guilayn

Agronomy 2026, 16(4), 444; https://doi.org/10.3390/agronomy16040444 - 13 Feb 2026

Viewed by 674

Abstract

Desertification in Mediterranean drylands threatens food security. This study evaluated biochar–compost amendments on drought-affected sandy–calcareous soils, focusing on carbon (C) and nitrogen (N) dynamics. Laboratory soil incubations revealed that biochar reduced C mineralization, aiding long-term storage, but also decreased N mineralization, signaling potential short-term immobilization. However, leaching experiments showed that incorporating 2%, 5%, 10%, and 20% biochar into compost significantly reduced C losses by 22, 26, 36, and 48%, respectively, and N losses by 37, 67%, 45%, and 65%, respectively. In water-stressed lettuce trials, the use of compost alone could only yield 30% of the yield obtained in unstressed lettuce treated with compost. While the addition of 2–5% biochar to compost enabled the conservation of 44–45% of the yield of unstressed lettuce, a 10% biochar amendment doubled this number (88%). Nonetheless, a higher dose of 20% biochar in the compost offered no additional benefit with 84% of the yield of unstressed lettuce amended with compost. These findings position biochar–compost as a key strategy to enhance soil fertility and water-use efficiency. To counteract short-term N immobilization, the study recommends further investigation of early application combined with supplemental fertilization or fractionated biochar supply (over 2–3 years). Ultimately, tailoring biochar formulations to specific local conditions is essential to balance immediate crop productivity with long-term soil health. Full article

(This article belongs to the Special Issue A Path for Circular Economy in Agriculture: From Organic Waste to Sustainable Energy and Soil Fertility)

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12 pages, 2366 KB

Open AccessCommunication

Spent Mushroom Substrate After Sieving Can Improve Its Conditioning Effect in Cow Manure Composting

by Yingrong Zhao, Yueni Song, Yun Yun and Yuan Luo

Agronomy 2026, 16(2), 164; https://doi.org/10.3390/agronomy16020164 - 8 Jan 2026

Viewed by 429

Abstract

Spent mushroom substrate (SMS) is an excellent conditioner for livestock manure composting. However, existing studies have confirmed that it is difficult to achieve the desired effect by directly mixing SMS with manure. Coarse (≥2 mm) and fine (<2 mm) of SMS particles from an edible fungus (Auricularia auricula) were obtained after sieving and used for cow manure composting. In our study, the appropriate ratio of coarse SMS to fine SMS particles added to the manure was explored. Four treatments were designed, adding 20% coarse SMS (T1), 15% coarse SMS + 5% fine SMS (T2), 5% coarse SMS + 15% fine SMS (T3), and 20% fine SMS (T4) to cow manure for composting, respectively. The physicochemical properties, maturity, and nutrient content of the composts were analyzed in a 35-day composting trial. The optimal treatment was determined through a comprehensive evaluation using the entropy-weighted TOPSIS method. The results showed that the highest composting temperature reached 65.13 °C in T3, and the duration of the thermophilic phase of T2 was the longest. The relative germination rate was not affected, and the relative radicle growth (RRG) reflected the variation in phytotoxicity during composting. After composting, the pH of the finished composts was between 8.78 and 9.05. The electric conductivity was between 2207 and 2513 μS cm⁻¹. The ammonium nitrogen content was less than 150 mg kg⁻¹, which was at the level found in mature compost. The RRG was no less than 80%, indicating the compost was mature and had no phytotoxicity. The available phosphorus and potassium contents increased by 4.8% to 59.1% compared with that before composting. The comprehensive evaluation showed that the treatment supplemented with 15% coarse SMS and 5% fine SMS was optimal. Full article

(This article belongs to the Special Issue A Path for Circular Economy in Agriculture: From Organic Waste to Sustainable Energy and Soil Fertility)

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21 pages, 2363 KB

Open AccessArticle

Linking Soil Carbon Fractions to Tea Antioxidant and Quality: Impact of Biochar and Biogas Slurry Applications

by Shaohua Wang, Bingqin Fang, Kai Jiang, Meng Mi, Zewen Jin, Ming Hung Wong, Shengdao Shan and Lifeng Ping

Agronomy 2026, 16(2), 144; https://doi.org/10.3390/agronomy16020144 - 6 Jan 2026

Viewed by 344

Abstract

The effects of soil organic carbon fractions and tea enzyme activities on the antioxidant quality of tea leaves were determined. The experiment set up single biogas slurry application and co-application of biochar and biogas slurry (50%, 100%, 150%, 200% slurry substitution for nitrogen fertilizer, 350 °C pig manure biochar at 1% and 2% application rates and 500 °C rice straw biochar at 1% and 2% application rates). The results showed that, compared with the control (CK), the combined application of biochar and biogas slurry had a synergistic effect, with the most significant effect observed when 350 °C pig manure was combined with biogas slurry at a ratio of 2%. This treatment resulted in peak levels of readily oxidizable organic carbon (ROC) and dissolved organic carbon (DOC) in the soil, significantly increasing by 8.43 g/kg and 0.23 mg/kg, respectively, compared to the CK, and significantly enhancing the activity of key carbon cycle enzymes such as β-glucosidase (S-β-GC). These improvements in soil biochemical properties directly translated into improved tea quality: the tea leaves treated under this treatment had the highest content of tea polyphenols and amino acids, and the ABTS and DPPH free radical scavenging rates increased by 3.25% and 5.97%, respectively, compared to the CK, while the malondialdehyde (MDA) content was the lowest. Mantel test and multivariate regression analysis further confirmed that particulate organic carbon (POC) and dissolved organic carbon (DOC) were the main carbon components driving the accumulation of tea polyphenols, while catalase (CAT) and other enzymes were key co-regulatory enzymes. The optimal application ratio of biochar and biogas slurry not only improved tea leaf quality but also resulted in increased SOC content within the study period, providing preliminary evidence for promoting SOC accumulation in the short term. Full article

(This article belongs to the Special Issue A Path for Circular Economy in Agriculture: From Organic Waste to Sustainable Energy and Soil Fertility)

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29 pages, 4768 KB

Open AccessArticle

Enhancing the Valorization of Spent Pleurotus Substrate Through Anaerobic Digestion by Extracted Enzymes

by Diana Constantinescu-Aruxandei, Alexandru Vlaicu, Daria Gabriela Popa, Ștefan-Ovidiu Dima, Mălina Deșliu-Avram, Alin Cristian Nicolae Vintilă, Marius Ghiurea, Mihaela Cilțea-Udrescu, Ioana Popa-Tudor, Naomi Tritean, Georgeta Ramona Ivan, Cristian-Andi Nicolae, Mihaela Ganciarov, Gabriel Vasilievici and Florin Oancea

Agronomy 2025, 15(11), 2663; https://doi.org/10.3390/agronomy15112663 - 20 Nov 2025

Viewed by 852

Abstract

Spent mushroom substrate (SMS) could be used as a substrate in anaerobic digestion (AD), but some studies have reported modest production and yield of methane. Several solutions have been proposed to mitigate this issue, such as co-digestion with other substrates, various pretreatments, and the use of additives. In this study we report for the first time the possibility of enhancing the process of methane production from spent Pleurotus substrate (SPS) using a pretreatment with enzymes recovered by a simple aqueous extraction from SPS. This represents an alternative to harsher chemical and physical pretreatment methods. The pretreatment increased the methane production from SPS by 16% at saturation, and a 25% faster anaerobic digestion process was obtained. After 2 days of AD, the methane volume for SPS + enzyme was 287 ± 9 NmL, approaching the maximum of 295 ± 14 NmL obtained for this variant, and was 39% more than SPS without pretreatment (207 ± 16 NmL). Pleurotus cultivation, AD, and the enzymes increased the crystallinity of the substrate. The enzymes increased the chemical oxygen demand, total carbon, and the concentration of pentanoic acid and 2-methyl-butanoic acid and decreased the concentration of hexanoic acid in the liquid digestate. The pretreatment increased, in general, the P and K content in the liquid and solid digestates. All data were compared with the hay used for Pleurotus cultivation. Full article

(This article belongs to the Special Issue A Path for Circular Economy in Agriculture: From Organic Waste to Sustainable Energy and Soil Fertility)

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13 pages, 3383 KB

Open AccessArticle

Impact of Artificial Humic Acid on the Migration and Transformation of Soil Phosphorus

by Lin Zhao, Yun Hao, Markus Antonietti, Ying Zhao, Fan Yang and Zhuqing Liu

Agronomy 2025, 15(11), 2482; https://doi.org/10.3390/agronomy15112482 - 25 Oct 2025

Viewed by 896

Abstract

Phosphorus (P) is a critical factor in enhancing agricultural yield improvement, but the over-application of P fertilizers has led to the widespread accumulation of ineffective P in soils worldwide. Artificial humic acid (AHA) has gained recognition as a new method for enhancing P effectiveness in soils. This study aims to explore the patterns and mechanisms underlying the effect of AHA on P effectiveness. A 60-day indoor incubation experiment was conducted using a soil column system, in which the soil was fractionated into five distinct particle size classes: 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm. Findings revealed that AHA effectively promoted the accumulation of Olsen-P in fine-textured soils. Following the application of AHA, the fraction of particles with a size of 2 mm exhibited the highest increase in Olsen-P, at 15.4%, whereas the fraction with a size of 8 mm showed the lowest increase, at 0.2% relative to the control, at the 60th day. Additionally, AHA promoted the migration of HCl-P while enhancing the immobilization of Olsen-P. During the initial cultivation phase, the concentrations of HCl-P in the topsoil (0 cm) differed little from those in the deeper soil (40 cm). As cultivation progressed, the concentrations of NaOH-P and HCl-P in the 0 cm soil decreased more markedly than those at the 40 cm depth by the later cultivation stage. Finally, the structural equation modeling results indicated that among NaHCO₃-P, NaOH-P, and HCl-P, NaOH-P had the most significant effect on Olsen-P. These findings offer valuable insights into how AHA could be used to improve the effectiveness of P in soils. Full article

(This article belongs to the Special Issue A Path for Circular Economy in Agriculture: From Organic Waste to Sustainable Energy and Soil Fertility)

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17 pages, 989 KB

Open AccessArticle

Evaluation of Plant-Available Water in Degraded Alfisol Using Biomass Copyrolyzed with Plastic

by Jonathan Henríquez-Arevalo, Cristina Muñoz, Marco Sandoval and Winfred Espejo

Agronomy 2025, 15(8), 1985; https://doi.org/10.3390/agronomy15081985 - 19 Aug 2025

Viewed by 958

Abstract

The exponential increase in global plastic production, reaching over 380 million tons in recent years, has exacerbated environmental problems, particularly in agriculture. Agricultural residues, such as hazel (Corylus avellana L.) pruning and plastic wastes, are underutilized resources that can be transformed via pyrolysis into biochar. This study focuses on copyrolyzed biochar produced from hazel biomass and polyethylene and aims to evaluate its effect on the water retention properties of degraded Alfisol. Van Genuchten’s hydrological model was used to analyze parameters such as rapid drainage pores, plant-available water pores, and air capacity (AC) under varying particle sizes (small and large) and application rates (1% and 5% w/w). The results revealed that fine particles at higher doses (5%), especially in P-5%-large and P-5%-small, considerably improved plant-available water retention, particularly within micropores and mesopores. Microstructural modifications induced during pyrolysis enhanced the water retention capabilities of biochar copyrolyzed with plastic. However, its effects on AC and pore connectivity warrant further investigation to assess long-term soil functionality. By integrating waste valorization with improved agricultural practices, this study underscores the potential of biochar copyrolyzed with plastic as an amendment for degraded soil. However, the long-term stability of this amendment requires further study. Full article

(This article belongs to the Special Issue A Path for Circular Economy in Agriculture: From Organic Waste to Sustainable Energy and Soil Fertility)

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18 pages, 4367 KB

Open AccessArticle

Structure Optimization and Performance Simulation of a Double-Disc Fertilizer Spreader Based on EDEM-CFD

by Mingxiong Ou, Guanqun Wang, Ying Lu, Zhengji Zhang, Huijie Pan, Weidong Jia and Xiang Dong

Agronomy 2025, 15(5), 1025; https://doi.org/10.3390/agronomy15051025 - 24 Apr 2025

Cited by 5 | Viewed by 1777

Abstract

To address practical issues, such as uneven fertilizer distribution and poor particle dispersion, during the operation of a centrifugal double-disc fertilizer spreader, a discrete element method (DEM) simulation was initially performed. In this simulation, the blade inclination angle, fertilizer discharge offset angle, and spreading height were selected as experimental factors. The spreading width and the coefficient of variation (C_v) of fertilizer uniformity served as evaluation indicators. A quadratic orthogonal simulation experiment was designed to evaluate spreading performance. Subsequently, regression equations were established to optimize parameters and determine the optimal design configuration. Experimental results showed optimal performance with a blade inclination angle of −5°, fertilizer discharge offset angle of 45°, spreading height of 1050 mm, and disc rotational speed of 400 rpm. Considering that fertilizer spreaders are susceptible to air resistance and environmental wind during field operations, an EDEM-CFD coupling method was employed to simulate realistic operating conditions. Virtual simulation results demonstrated optimal fertilizer spreading performance at disc rotational speeds ranging from 350 to 400 rpm under tailwind conditions, and from 400 to 500 rpm under headwind conditions. Based on the simulation results, a prototype was built and tested. The experimental results closely matched the simulation predictions, thereby confirming the effectiveness of the simulation model. This study provides valuable insights and serves as a reference for designing and optimizing fertilizer spreader performance under practical operational conditions. Full article

(This article belongs to the Special Issue A Path for Circular Economy in Agriculture: From Organic Waste to Sustainable Energy and Soil Fertility)

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16 pages, 2318 KB

Open AccessArticle

Effect of Temperature on the Inocula Preservation, Mesophilic Anaerobic Digestion Start-Up, and Microbial Community Dynamics

by Jingwei Wu, Huan Zhang, Ye Zhao, Xufeng Yuan and Zongjun Cui

Agronomy 2024, 14(12), 2991; https://doi.org/10.3390/agronomy14122991 - 16 Dec 2024

Cited by 5 | Viewed by 2854

Abstract

Anaerobic digestion (AD) is a well-established technology for the sustainable conversion of agricultural organic by-products and waste into bioenergy. Temperature is crucial for optimizing methane production through inocula preservation and reactor start-up in AD. The preservation of inocula induced by temperature has rarely been assessed from an engineering perspective. There has also been limited exploration of the influence of high-to-moderate temperature transition on the initiation of AD. This study employed continuous mesophilic AD reactors with potential engineering applications to conduct revival tests. These tests evaluated the methane production activity of sludge stored at different temperatures and investigated the impact of high-temperature initiation on mesophilic AD. Additionally, we elucidated the correlation between these assessments and microbial diversity as well as composition. The results indicated that bacterial diversity was higher in the inoculum stored at 35 °C compared to 15 °C, ensuring a stable start-up operation of the mesophilic AD. The richness of the bacteria and diversity of the archaea remained stable during the transition from high to mesophilic temperatures. This was conducive to enhancing methanogenic activity of mesophilic AD initiated at 55 °C. The continuously operated AD system showed significant differences in microbial composition compared to its inoculum. Increased abundance of Coriobacteriaceae and Prevotellaceae led to propionate and butyrate accumulation, respectively, reducing AD operational capacity. Methanogenic archaea were less diverse in AD initiated with low-temperature preserved inoculum compared to that with a medium temperature. Streptococcaceae induced by high temperarure could promote AD stability. Hydrogenotrophic methanogens had a competitive advantage in mesophilic AD due to their prior exposure to high-temperature initiation, possibly influenced by Thermotogaceae. Full article

(This article belongs to the Special Issue A Path for Circular Economy in Agriculture: From Organic Waste to Sustainable Energy and Soil Fertility)

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18 pages, 1615 KB

Open AccessArticle

Effect of Biochar and Wood Distillate on Vegeto-Productive Performances of Tomato (Solanum lycopersicum L.) Plants, var. Solarino, Grown in Soilless Conditions

by Anna Agosti, Samreen Nazeer, Lorenzo Del Vecchio, Leandra Leto, Andrea Di Fazio, Jasmine Hadj-Saadoun, Alessia Levante, Massimiliano Rinaldi, Rohini Dhenge, Camilla Lazzi, Martina Cirlini and Benedetta Chiancone

Agronomy 2024, 14(11), 2725; https://doi.org/10.3390/agronomy14112725 - 19 Nov 2024

Cited by 4 | Viewed by 2320

Abstract

Nowadays, tomato, a commercially important crop, is increasingly cultivated in a soilless cultivation system to counteract climate change. Normally, this system uses cocopeat as a substrate, but its high cost and environmental impact have led to growing interest in alternatives like biochar (BC). In addition, biostimulants, such as wood distillate (WD), a pyrolysis by-product, are increasingly being used to improve fruit yield and quality. BC was used to partially replace (2% and 5%) cocopeat in growth bags for soilless tomato cultivation. Moreover, WD (3 mL/L) was distributed in the substrate every two weeks. The effect of BC and WD on tomato plant growth, fruit quality, and substrate microbial community was investigated. The integration of BC and WD into a soilless growing system for tomato cultivation can improve the fruit quality and influence the microbial activity of the substrate. Replacing part of the cocopeat in the substrate with BC and using an agri-waste-derived biostimulant represent a step forward in making agriculture more sustainable. Full article

(This article belongs to the Special Issue A Path for Circular Economy in Agriculture: From Organic Waste to Sustainable Energy and Soil Fertility)

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