Sulfur bentonite-organic-based fertilizers as tool for improving bio-compounds with antioxidant activities in red onion.

BACKGROUND: Red onion is popular in cuisines worldwide and is valued for its potential medicinal properties. Red onion is an important source of several phytonutrients such as flavonoids, thiosulfinates and other sulfur compounds, recognized as important elements of the diet. Nowadays, there is the need of producing food enriched in health benefit compounds. In this study, pads of sulfur bentonite (SB) with the addition of orange residue (OR) or olive pomace (OP) were used to improve the quality of red onion. The experiment was conducted for 3 months in the field to evaluate the phytochemicals of differently amended red onion. RESULTS: Treated plants were better in quality than controls. Antioxidant activity, detected as DPPH, ORAC and ABTS, was highest in plants grown in the presence of SB enriched with agricultural wastes, particularly SB-OR. Polyphenols increased in all treated plants. The volatile fraction was clearly dominated by sulfur compounds that are strictly related to the concentration of the aroma precursors S-alkenyl cysteine sulfoxides. The greater amount of thiosulfinates in treated compared with untreated onion evidenced that SB pelletized with agricultural wastes can represent a new formulation of organic fertilizer able to improve the beneficial properties of onion. The results highlighted that the best red onion quality was obtained using SB-OR pads. CONCLUSION: The use of SB bound with agricultural wastes represents a novel strategy to increase bio-compounds with beneficial effects on human health, to enhance the medical and economic values of sulfur-loving crops, with important consequences on the bio and green economy. © 2019 Society of Chemical Industry.

Three different methods for turning olive pomace in resource: Benefits of the end products for agricultural purpose.

In Mediterranean countries the olive oil industry produces, yearly, a huge quantity of pollutant wastes in a short time that are phytotoxic for their high content of phenols and wax that affect soil and groundwater quality. With the use of biological processes, we can transform these wastes into fertilizers for a sustainable agriculture. We used three different methods anaerobic digestion, aerobic digestion, and crude agricultural waste management system to produce organic fertilizers. The obtained compounds were chemically analysed to verify if their characteristics fell into the marketability limits permitted by the current Italian regulation. Their effects on soil were subsequently assessed. Results evidenced that all the by-products obtained were suitable as fertilizers. They were able to increase soil organic matter, microbial biomass, and nutrients with beneficial effects on soil fertility, but at different extent. The best effects were in the order: compost, olive pomace-sulphur-bentonite pelletized and digestate. Considering that the three different methodologies dispose different amounts of olive pomace (90% in aerobic digestion, 12% in anaerobic digestion and 5% in sulphur bentonite pelletized) in different time (4months for compost, 1month for anaerobic digestion and 1day for sulphur-bentonite pelletized) and processing set-up, each method can be differently competitive for environment and/or agriculture. Aerobic digestion has economic advantage over other alternatives and has the greatest fertilizer effect even if the production time is longer than the other two. Digestate, coming from anaerobic digestion, reduces the environmental impact of greenhouse gas emissions it is rich in nutrients and can be obtained in a shorter time than compost. Olive pomace-sulphur-bentonite pelletized represents a crude waste management systems that reduce greenhouse gas emission in the atmosphere producing fertilizers able to generate, mainly in alkaline soils, a soluble zone of nutrients while minimizing leaching losses to the environment.

Anaerobic co-digestion of recalcitrant agricultural wastes: Characterizing of biochemical parameters of digestate and its impacts on soil ecosystem.

Anaerobic digestion (AD) of organic wastes is a promising alternative to landfilling for reducing Greenhouse Gas Emission (GHG) and it is encouraged by current regulation in Europe. Biogas-AD produced, represents a useful source of green energy, while its by-product (digestate) is a waste, that needs to be safely disposal. The sustainability of anaerobic digestion plants partly depends on the management of their digestion residues. This study has been focused on the environmental and economic benefits of co-digest recalcitrant agricultural wastes such olive wastes and citrus pulp, in combination with livestock wastes, straw and cheese whey for biogas production. The aim of this work was to investigate the effects of two different bioenergy by-products on soil carbon stock, enzymes involved in nutrient cycling and microbial content. The two digestates were obtained from two plants differently fed: the first plant (Uliva) was powered with 60% of recalcitrant agricultural wastes, and 40% of livestock manure milk serum and maize silage. The second one (Fattoria) was fed with 40% of recalcitrant agricultural wastes and 60% of livestock manure, milk serum and maize silage. Each digestate, separated in liquid and solid fractions, was added to the soil at different concentrations. Our results evidenced that mixing and type of input feedstock affected the composition of digestates. Three months after treatments, our results showed that changes in soil chemical and biochemical characteristics depended on the source of digestate, the type of fraction and the concentration used. The mainly affected soil parameters were: Soil Organic Matter (SOM), Microbial Biomass Carbon (MBC), Fluorescein Diacetate Hydrolysis (FDA), Water Soluble Phenol (WSP) and Catalase (CAT) that can be used to assess the digestate agronomical feasibility. These results show that the agronomic quality of a digestate is strictly dependent on percentage and type of feedstocks that will be used to power the digester.