Article

Spent coffee grounds as organic amendment modify hydraulic properties in a sandy loam Brazilian soil

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Abstract

Soil physical and chemical properties can be amended by application of organic residues, such as spent coffee grounds (SCG). In this work we examined SCG effects on the modification of some soil physical-hydraulic properties, such as soil water retention and aeration, investigating beneficial uses for this waste product. Soil properties were evaluated using pots filled with a mixture of a sandy loam soil with the contents of 0, 5, 10, 15 and 20% of SCG. The most relevant soil properties to the purposes were the moisture at container capacity (θcc), readily available water capacity (RAWC) and drainable porosity (ϕD). Additionally, under the hypothesis that SCG can be used as soil conditioner, lettuce crop, cultivar “Mimosa Roxa Roxanne”, was transplanted to the pots where the leaf area index and the cumulative biomass throughout the growing cycle were examined. Comparing to the absence of SCG (0%), soil SCG contents of 5, 10, 15 and 20% presented larger values of θcc and consequently larger RAWC and smaller ϕD. Although the increase of soil water storage from 43.2 (0%) to 53.3 (20%) mm, crop development was prejudiced by the reduction on ϕD from 0.1595 (0%) to 0.0827 (20%) m3 m−3, which affected soil aeration. This greater water availability, obtained with the increase of θcc, was promoted by the residue addition pointing out for a possible use of SCG to increase water retention for other crops.

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... SCG, may be used as prime material for a number of valuable products such as nutrients and antioxidants (Murthy and Madhava Naidu, 2012), soil amendment (Turek et al., 2019), heavy metal absorbent (Iakovleva et al., 2017), and biofuels (Massaya et al., 2019). With respect to the latter, SCG has been successfully converted into biodiesel, bioethanol (García et al., 2018), bio-ethers, bio-oil and biochar (Kim et al., 2014), and biogas (Burniol-Figols et al., 2016;Kansai et al., 2018;Somnuk et al., 2017). ...
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The antioxidant activity and individual bioactive compounds of lettuce, cultivated with 2.5-30% (v/v) of fresh or composted espresso spent coffee grounds, were assessed. A progressive enhancement of lettuce's antioxidant capacity, evaluated by radical scavenging effect and reducing power, was exhibited with the increment of fresh spent coffee amounts, while this pattern was not so clear with composted treatments. Total reducing capacity also improved, particularly for low spent coffee concentrations. Additionally, very significant positive correlations were observed for all carotenoids in plants from fresh spent coffee treatments, particularly for violaxanthin, evaluated by HPLC. Furthermore, chlorophyll a was a good discriminating factor between control group and all spent coffee treated samples, while vitamin E was not significantly affected. Espresso spent coffee grounds are a recognised and valuable source of bioactive compounds, proving herein, for the first time, to potentiate the antioxidant pool and quality of the vegetables produced.
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Field-crop yields are below their genetic and climatic potentials on many fine-textured soils due to low organic carbon content (OC), high bulk density ( rho <sub>b</sub>), low hydraulic conductivity (K<sub>s</sub>), insufficient air capacity (AC) and low plant-available water capacity (PAWC). Although soil conditioners derived from municipal, agricultural and industrial wastes are frequently used to improve soils, their effects on overall soil physical quality are still poorly understood. A laboratory soil core study was conducted to determine for a Brookston clay loam (Orthic Humic Gleysol) the effectiveness of masonry sand, greenhouse rockwool waste, yard waste compost and swine manure compost for improving soil physical quality relative to "ideal" levels proposed in the literature, and relative to "benchmark" levels found in the soil under virgin conditions, long-term conventional tillage and long-term no-tillage. The virgin soil produced near-surface (0.05-0.15 m depth) values for rho <sub>b</sub> (0.88 t m<sup>-3</sup>), AC (0.19 m<sup>3</sup> m<sup>-3</sup>) and PAWC (0.22 m<sup>3</sup> m<sup>-3</sup>) that fell within the optimal ranges proposed in the literature, while OC (68.2 g C kg<sup>-1</sup>) was slightly above optimal. The soil collected at Woodslee, Ontario, Canada, under long-term conventional tillage and no-tillage (maize-soyabean rotation) produced below-optimal organic carbon content (21.9-22.5 g C kg<sup>-1</sup>), excessive rho <sub>b</sub> (1.45-1.47 t m<sup>-3</sup>), insufficient AC (0.06 m<sup>3</sup> m<sup>-3</sup>) and low PAWC (0.14-0.19 m<sup>3</sup> m<sup>-3</sup>). Conventional tillage also produced below-optimal K<sub>s</sub> (10<sup>-6</sup> m s<sup>-1</sup>). Each conditioner could improve one or more of the above parameters, but not all five. Adding sand at 20-100 wt. % improved AC, but caused excessive reductions in OC and PAWC, and excessive increases in rho <sub>b</sub> and K<sub>s</sub>. Greenhouse rockwool waste added at 2.5-10 wt. % improved AC and rho <sub>b</sub>, but did not improve OC and PAWC. Yard waste compost added at 3.8-20 wt. % improved OC, rho <sub>b</sub> and PAWC, but did not improve AC. Adding swine manure compost at 3.8-20 wt. % improved OC and rho <sub>b</sub>, but did not improve AC or PAWC, and decreased K<sub>s</sub>. As no single conditioner could optimize all soil physical quality parameters, future studies using combinations of conditioners are proposed.
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The production of energy from renewable and waste materials is an attractive alternative to the conventional agricultural feed stocks such as corn and soybean. This paper describes an approach to extract oil from spent coffee grounds and to further transesterify the processed oil to convert it into biodiesel. This process yields 10-15% oil depending on the coffee species (Arabica or Robusta). The biodiesel derived from the coffee grounds (100% conversion of oil to biodiesel) was found to be stable for more than 1 month under ambient conditions. It is projected that 340 million gallons of biodiesel can be produced from the waste coffee grounds around the world. The coffee grounds after oil extraction are ideal materials for garden fertilizer, feedstock for ethanol, and as fuel pellets.
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The effect of phenylmercuric acetate on transpiration and growth was measured on sunflowers growing outdoors and on tobacco growing in a greenhouse. There was a significant reduction in transpiration in both plants; no reduction in growth was observed in tobacco, whereas some damage was evident in the sunflowers. Phenylmercuric acetate reduced transpiration in tobacco equally whether the soil was wet or somewhat dry.
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