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Green waste composts are obtained from agricultural production chains, their suppressive properties are increasingly being developed as a promising biological control option in the management of soil-borne phytopathogens. The wide variety of microbes harbored in the compost ecological niches may regulate suppressive functions through not yet fully known underlying mechanisms. This study investigates alpha- and beta-diversity of the compost microbial communities, as indicators of the biological features. Our green composts displayed a differential pattern of suppressiveness over the two assayed pathosystems. Fungal and bacterial densities, as well as catabolic and enzyme functionalities did not correlate with the compost control efficacy on cress disease. Differences in the suppressive potential of composts can be better predicted by the variations in the community levels of physiological profiles indicating that functional alpha-diversity is more predictive than that which is calculated on terminal restriction fragments length polymorphisms (T-RFLPs) targeting the 16S rRNA gene. However, beta-diversity described by nMDS analysis of the Bray&ndash, Curtis dissimilarity allowed for separating compost samples into distinct functionally meaningful clusters and indicated that suppressiveness could be regulated by selected groups of microorganisms as major deterministic mechanisms. This study contributes to individuating new suitable characterization procedures applicable to the suppressive green compost chain.

While the control of soil-borne phytopathogenic fungi becomes increasingly difficult without using chemicals, concern over the intensive use of pesticides in agriculture is driving more environmentally sound crop protection managements. Among these approaches, the use of compost to suppress fungal diseases could have great potential. In this study, a multidisciplinary approach has been applied to characterize microbiota composition of two on-farm composts and assess their suppress and biostimulant activities. The on-farm composting system used in this study was able to produce two composts characterized by an antagonistic microbiota community able to suppress plant pathogens and biostimulate plant growth. Our results suggest a potential role for Nocardiopsis and Pseudomonas genera in suppression, while Flavobacterium and Streptomyces genera seem to be potentially involved in plant biostimulation. In conclusion, this study combines different techniques to characterize composts, giving a unique overview on the microbial communities and their role in suppressiveness, helping to unravel their complexity.

In the present study, 133 bacterial isolates from 11 composted aromatic plant wastes were selected for their ability to inhibit the mycelial growth of the soil-borne phytopathogenic fungi Sclerotinia minor and Rhizoctonia solani. Successively, a subset of 35 from them were further characterized for their ability to control, in vivo, rocket damping-off caused by the two fungi. Moreover, the isolates were characterized for morphology of the colonies, Gram reaction, siderophore production, P-solubilization and for the presence of antimicrobial lipopeptide genes in the genome. The screening for the in vitro antagonisms showed a mycelial growth reduction ranging between 31.7% and 56.1% for R. solani and 34.4% and 59.4% for S. minor. All the isolates were not able to produce siderophores and some of them were able to solubilize P. The isolates contained two or more of the five lipoproteins coding genes investigated in this study. The most promising isolates were identified at species level by 16S-rRNA partial gene sequence analysis and were grouped in two main clusters related to Bacillus subtilis and Bacillus amyloliquefaciens reference strains. Results indicated that Bacillus isolates from compost are good candidates for application in the biocontrol of cultivated plants.

Summary Intensive agricultural systems negatively affect soil quality principally because of a reduction in soil organic matter (OM). Sustainable practices providing organic amendments could be useful to maintain or increase OM content in agricultural soils, preserving and improving soil fertility. In this study, biomass with a large C:N ratio was applied to intensively farmed agricultural soils to maximize the increase of soil OM and hence chemical and biochemical fertility. In particular, 30 and 60 t ha−1 of two mixtures of compost and scraps from poplar pruning, A1 and A2, with different C:N ratios (15 and 25, respectively), were applied to soils of two farms (F1 and F2) in a Mediterranean area (southern Italy) on an annual basis for two consecutive years. An effective, long-lasting increase of soil OM, on average of 60 and 55% in F1 and F2 soils, respectively, was reached at the end of the experiment. As well as a progressive increase in the C:N ratio, total N and available P also increased with organic amendments, with positive effects on soil microbial activity as demonstrated by the enhancement of the seven studied enzymatic activities. Principal component analysis demonstrated different responses to various organic amendments between F1 and F2 soils because of their geopedological diversity. The results indicate that the C:N ratio of the mixture is an important factor, but what is the best rate of addition to use is still not obvious. The use of a smaller amount (30 t ha−1) of the A1 mixture (10:1 compost:wood) appears, in these types of soils, to be the most suitable strategy to produce significant benefits.

Conventional agriculture that uses extensive tillage without organic inputs to soils can cause a degradation in soil quality. The improvement of soil organic matter (SOM) content can be achieved through the use of organic amendments. Application of organic amendments, such as compost, is a reliable tool to improve soil quality. On-farm composting is an ecological technology and can be used to recycle agricultural waste materials, such as animal manure or crop residues, that can be incorporated into the soil to improve soil quality. Therefore, the objective of this work was to characterize, by CPMAS-NMR spectroscopy and chemical properties, a commercial organic waste compost and an on-farm compost and, then, to compare their use as organic amendments on soil quality. A greenhouse study on intensive agricultural soils of Southern Italy was done. The following amendments, as soil treatment, were used: a municipal compost (MC), with C:N 13.3, and an on-farm compost (OF), with C:N 17.1, applied at the rate of 8.5 and 6.0 Mg DM ha−1, respectively. After one, four, eight, twelve and fifteen months soil samples were collected and analyzed for chemical (pH, electrical conductivity, limestone, CEC, available phosphorus, organic carbon, total nitrogen and exchangeable bases) and microbial (urease, phosphomonoesterase, β-glucosidase, total hydrolytic activity and Biolog Ecoplate™) properties. MC compost was characterized by larger electrical conductivity and exchangeable Na+ content with respect to OF compost, while this latter was characterized by about twice of organic carbon (470 g kg−1). As showed by CPMAS-NMR spectroscopy, OF compost was characterized not only by cellulosic polysaccharides, but also significant amounts of both alkyl components and lignin derivatives. An effective increase of soil organic carbon (SOC) in plots under MC (+36%) and OF (+25%) composts, respectively, was reached at the end of the experiment. Soil amendments improved soil biological functions as revealed by a general trend of positive effects on hydrolase activity, phosphomonoesterase, β-glucosidase as well as urease. EC and exchangeable Na+ were considerably larger only in the plots under MC compost (25% and 19%, respectively), with respect to control plot. The possible increase of soil salinity after compost amendment may negatively affect soil quality in the long-term. In conclusion, our results demonstrated that the supply of compost produced on-farm, can enhance soil biological and biochemical properties, without the drawbacks of municipal composts, representing a promising alternative to the latter and an important way to reuse wastes produced by cultivation and processing of vegetables.

In the Mediterranean region, difficult climate conditions and inadequate land management have led to a reduction of the organic matter content of soils. As a solution, municipal solid waste (MSW) compost and sewage (S) sludge were investigated for their effectiveness in maintaining soil fertility. Clayey-loamy soil was amended with 0, 40, and 80 t ha -1 of MSW compost or S sludge and cultivated with Triticum durum. Soil was sampled 15 and 70 days after sowing, and the activities of arylsulphatase, phosphatase, dehydrogenase (DH), β-glucosidase (β-GLU), urease, and catalase (CAT) were assayed. The wheat was harvested after 68 days, then soil properties as well as plant growth and K + and Na + contents were determined. Almost all soil enzymatic activities were significantly (P < 0.01) affected by amendment dose, sampling time, and their interaction. At 15 days, MSW compost had a moderate effect on DH, β-GLU, and CAT activities under both applied doses. A significant increase of all the measured activities was observed after 70 days at either 40 t ha -1 or 80 t ha -1 (ranged between 16%-160% and 10%-81%, respectively), likely providing a long-term nutrient release. The activities of arylsulphatase, phosphatase, DH, CAT, and β-flu (only with the lower dose) were strongly enhanced at 15 days after S sludge treatment. After 70 days, an increase of the enzymatic activities occurred with S sludge, although its beneficial effect was reduced mainly at 80 t ha -1 presumably because of the presence of micropollutants in the sludge. Plant growth was significantly improved by 40 and 80 t ha -1 of compost (93% and 126%, respectively); however, less impact was observed with S sludge. Overall, the results suggest that addition of MSW compost could enhance the fertility of degraded soils and promote plant growth.

Soil is a highly complex system in which bacteria play a dominant role. Soil microorganism biodiversity is extremely important for sustaining the nutrient cycles of soil ecosystems. The diversity of soil bacterial and fungal communities can be influenced by agricultural management. The use of amendments, such as the incorporation of compost into the soil, strongly affects soil microbial communities directly or indirectly. The use of compost can be an important tool to control soil-borne pathogens. Certain groups of microorganisms (bacteria and fungi) present in compost produce metabolites, such as siderophores and antibiotics, with specific suppressive activity against soil-borne pathogens: among these compost bacteria, species of Pseudomonas and Bacillus are very important. In this study, we investigated the effects of increasing doses of compost on the density of several cultivable soil microbial groups in an agricultural system of Southern Italy. The number of total bacteria, total fungi, siderophore-producing bacteria (principally Pseudomonas spp.) and spore-forming bacteria (principally Bacillus spp.) was evaluated over a period of five months. Moreover, we analyzed the ability of spore-forming bacteria isolated from soil and compost to inhibit, in vitro, five soil-borne phytopathogenic fungi (Rhizoctonia solani, Fusarium oxysporum, Sclerotinia minor, Fusarium solani, Pyrenochaeta lycopersici). The number of total bacteria and siderophore-producing bacteria was greater in the soil treated with compost than in soils treated with mineral fertilization or not manured, with an increase related to the dose of compost applied. Moreover, the compost used in this study produced a substantial increase in the number of spore-forming bacteria in the soil. Approximately 80% of these bacteria were able to inhibit the soil-borne phytopathogenic fungi Rhizoctonia solani, Fusarium oxysporum, Sclerotinia minor, Fusarium solani and Pyrenochaeta lycopersici. These results show that compost from the organic fraction of municipal solid wastes furnishes a high number of spore-forming bacteria exhibiting antibiotic activity against phytopathogenic fungi. The application of compost can change the composition of the soil microbial community, modifying the relationships among microorganisms, both competitive and/or antagonistic, producing a decrease in the activity of plant pathogens. These results were in agreement with the decrease in the symptoms of disease on tomato plants cultivated in the soils treated in this study.

The effectiveness of compost supply at several doses (0, 50, 100, and 150 t/ha) to a saline soil was studied using municipal solid waste (MSW) and palm waste (PW) composts. The experiment was carried out in pots under cultivation of Polypogon monspeliensis (halophyte forage species) and Hordeum vulgare (common forage species) and lasted three months. The investigation focused on some selected soil physico-chemical properties, soil microbial biomass, and ten soil enzymatic activities; Arylsulfatase (ARY), dehydrogenase (DEH), β-glycosidase (β-GLU), protease (PRO), urease (URE), invertase (INV), Fluorescein diacetate hydrolase (FDAH), catalase (CAT), acid and alkaline phosphatases (PHO). Both amendments improve markedly the saline soil quality. They ameliorate the physico-chemical properties. The increase of soil pH is regarded as an interesting fact and is usually proportional to the compost application rate. Electrical conductivity increased proportionally to the applied rates. Soil carbon and nitrogen amounts were also improved and the highest raise (7.5-folds) was noted for carbon. According to the substantial increase of the organic matter, levels of measured microbial biomass and several enzyme activities in saline soil were improved. DEH activity which proposed as a measure of overall microbial activity exhibited a significant increase only at dose 2 (100 t/ha). Consequently, One hundred tones of composts per hectare, under which some enzymes exhibited an optimal of activity and metal accumulation can be minimized, appeared an interesting rate for saline soil amendment.

Intensive agriculture is a farming system characterised by a large use of inputs, causing a large pressure on the environment. As peculiar and efficient example of intensive agriculture cultivation under plastic tunnels provides several advantages for farmers due to improvement of microclimatic conditions coupled with a relatively low investment costs. In the Mediterranean Basin such cultivation systems reach about 200,000 ha mainly in Spain, Turkey, Italy, and Morocco. As downside, intensive agriculture negatively affects soil fertility principally because of a loss in soil organic matter. Sustainable practices providing organic amendments could be a useful tool to maintain or increase organic matter content in agricultural soils, preserving and improving soil fertility. An improved knowledge of management factors affecting soil quality is crucial to plan farming systems that effectively maintain soil fertility. Therefore, this review focuses on the potential value of organic amendments in the recovery of soil fertility, in particular in sites under plastic cover intensive farming system. Following a brief overview of the effects of intensive agriculture on soil, the review describes various organic amendments used in agriculture and their benefits on soil fertility, to conclude with the need, in the future researches, to identify organic amendments able to maximize a recovery of soil fertility.