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Coffee waste-derived biochar was found to immobilize heavy metals in contaminated soil, although there are few studies involving these materials. Given the large amount of waste generated in the coffee industry, this presents a relevant opportunity to contribute to the circular economy and environmental sustainability. Therefore, the objective of this study was to evaluate the effects of the application of biochars derived from coffee grounds and coffee parchment in the remediation of a Cd, Zn and Pb contaminated soil and at the development of jack beans (Canavalia ensiformis) in this area's revegetation. The biochars were pyrolyzed at 700 °C, and the treatments were: contaminated soil (CT); contaminated soil + calcium carbonate (CaCO3); contaminated soil + 5% (weight (w)/weitght (w)) coffee ground biochar and contaminated soil + 5% (w/w) coffee parchment biochar. These treatments were incubated for 90 days, followed by the cultivation of jack beans for 60 days. Soil samples, soil solution and plants were analyzed for nutrients and heavy metals. The addition of coffee grounds and coffee parchment biochars significantly reduced the contents of heavy metals in the soil compared to the Control (32.13 and 42.95%, respectively, for Zn; 26.28 and 33.06%, respectively, for Cd and 28.63 and 29.67%, respectively, for Pb), all of which had a superior performance than the CaCO3 treatment. Thus, following the observed reduction in the soil soluble fraction of metals, its uptake by the plants was also reduced, especially limiting Cd and Pb accumulation in plant dry matter. In addition, coffee parchment biochar promoted a greater accumulation of nutrients in the shoots, i.e., for K and P (1450 and 21.5 mg pot−1, respectively, dry matter basis) compared to the control (54.4 and 9.3 mg pot−1, respectively). Therefore, coffee parchment biochar use in association with jack beans may represent a viable tool for the remediation of metal contamination concomitantly with revegetation of the contaminated area. [ABSTRACT FROM AUTHOR]

Increasing N use efficiency is an important strategy to intensify sustainable agriculture, optimize nutrient use, and reduce N loss to the environment via different routes. Owing to its physicochemical properties, biochar can be used as an additive to produce biochar-based fertilizers (BFs) with increased efficiency. We investigated N availability and ammonia loss from 17 BFs (3%–38% N). N availability and release from BFs were evaluated by water extraction experiments and soil column leaching. BFs (5%–10% N) had an average of 64% solubilized N after five extractions, whereas urea had 98% solubilized N. However, BFs produced with urea released N more slowly in soil, with the release rate 60% less than that of urea. Ammonia volatilization was evaluated using a 22-d experiment, where N was applied to soil surface (pH = 4.4). We compared urea, BF granulated with urea, and BF produced by coating urea granules with acidified or unacidified biochar. Compared to urea, biochar-based fertilizers granulated with urea and urea granules coated with acidified biochar significantly reduced (t-test at 5%) ammonia volatilization by 14%. The results demonstrated the potential of BFs as enhanced efficiency fertilizers. Therefore, BFs might be a good option to mitigate N loss. [ABSTRACT FROM AUTHOR]

Biochar is a promising tool for an efficient and low environmental impact agriculture since can offer both soil carbon (C) sequestration and mitigation of nitrous oxide (N 2 O) emissions. The extent of biochar C stability after soil amendment and efficiency in reducing N 2 O emissions from an external nitrogen (N) source were accessed through laboratory incubations. A clay loam soil was amended with chicken manure (CM), sewage sludge (SS), eucalyptus sawdust (ES) and filter cake (FC) feedstocks and corresponding slow-pyrolysis (400 °C) biochars at 5 g C kg − 1 soil in combination with two N fertilizer rates (0 and 140 mg N kg − 1 soil). Carbon dioxide (CO 2 ) and N 2 O emissions were measured during 60 days. Biochars and feedstocks CO 2 emissions were described by an exponential first order kinetics model. For C mineralization an interaction effect was observed for feedstock source and organic amendment. Lower values of mineralizable C was found for biochars than corresponding feedstocks, except for ES. Carbon losses in 60 days of incubation totaled between 0.8 and 9.4% and 2.4 and 32% for biochars and feedstocks, respectively. Regarding to N 2 O emissions, only CM-biochar impacted emissions with a two-fold increase in non-fertilized soil. When NH 4 NO 3 was co-applied, biochars reduced fertilizer induced N 2 O emissions, reaching a seven-fold reduction in SS-biochar treatment. The fertilizer emission factor (EF) decreased with biochar amendments as well, varying between 0.01 and 0.08% of the fertilizer N emitted as N 2 O, which shows the biochar potential to reduce fertilizer induced N 2 O emissions, with major reduction by SS-biochar mitigating 87% of the soil-fertilizer emissions. Such potential could be explored by designing biochars based on feedstock chemical and structural properties, including a mixed feedstock source biochar that promotes C sequestration and mitigates N 2 O emissions. [ABSTRACT FROM AUTHOR]

• BC-based fertilizers with 51% of BC had 21% higher maize yield than urea. • Grain N was 16% higher with BC-based fertilizers than with mineral sources. • BC-based fertilizers replacing urea result in more favorable carbon balances. • BN 51/10 use promoted soil C sequestration and helped mitigate net greenhouse gases. The sustainable development of agriculture depends on increasing N use efficiency (NUE) and consequently reducing N losses from different sources, such as NH 3 volatilization, NO 3 − leaching, and N 2 O emissions. While the chemical and physical properties of biochar (BC) in fertilizers have been evaluated to increase NUE, a lack of information exists regarding the effects of BC amendments in tropical soils. We performed a one-year field experiment with tropical soil to evaluate the effects of BC-based N fertilizers (BN) on maize yield and on greenhouse gas (GHG) emissions. The treatments consisted of five fertilizers: ammonium nitrate (AN), urea (U), BN 51/10 (51% BC, 10% N), BN 40/17 (40% BC, 17% N), BN 29/20 (29% BC, 20% N), and a control (without N fertilizer). The N fertilizers (80 kg N ha−1) were broadcast 20 days after sowing. Yield, grain N uptake, NUE, ammonia volatilization, and GHG emissions were measured. The results demonstrated the potential of BNs to enhance the efficiency of the fertilizers. BN 51/10 and BN 40/17 had an average maize yield that was 26% higher than that of U, and BN 51/10 resulted in a NUE that was 12% higher than what was observed for U. Both the effects on yield and NUE were attributed to lower N release rates of the BN-amended fertilizers compared to that of the conventional soluble N sources. The BC-based fertilizers presented better environmental performance, and BN 51/10 showed the lowest emission intensity when C sequestration by BC was not considered, with a value that was 14% lower than that of the U treatment. When considering C sequestration by BC, the emission intensity of the C equivalents demonstrated that all BNs presented C sequestration that differed from that of the mineral N sources. BC-based nitrogen fertilizers may have promising applications for sustainable agricultural development by mitigating N losses and increasing C stocks. [ABSTRACT FROM AUTHOR]