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N 2 O emissions resulting from the application of nitrogen (N) fertilizers and vinasse represent the main sources of greenhouse gases (GHG) emissions in sugar-energy sector. Conversely, the application of biochar in soils has been worldwide recognized as an strategy to mitigate N 2 O emissions, although little is known about their effects on soils under energy cane production. The study aimed to evaluate the effects of biochar addition as a strategy to mitigate soil N 2 O emissions in soil under energy cane cultivation, as well as to quantify the abundance of N 2 O-producing and N 2 O-reducing microbial guilds. A greenhouse experiment was conducted in a completely randomized design, with five treatments and four replications. The treatments were: i) no N fertilization (control); ii) N fertilization; iii) N fertilization plus vinasse; iv) N fertilization plus biochar; v) N fertilization plus vinasse plus biochar. All treatments (except control) were balanced to receive the same amount of nutrients. Biochar was added at a rate of 5 g kg−1 of soil. Soil N 2 O emissions were quantified by static chambers for 78 days, and soil sampling were performed to determine chemical and microbiological attributes, including functional genes of the nitrogen cycle (AOA, AOB, nir K, nir S, nos ZI and nos ZII) by real-time PCR. Results indicated that vinasse addition increased N 2 O emissions. Conversely, the application of biochar reduced N 2 O emissions associated with the application of N fertilizer (56 %) and N fertilizer + vinasse (41 %). The high N 2 O emissions observed in vinasse treatment were directly correlated with nitrifier microorganisms (AOB and AOA), indicating that nitrification should be the main pathway of N 2 O emissions in this treatment. The production of energy cane biomass was similar between N fertilizer treatments. High N 2 O emission intensities (mg N 2 O g biomass−1) were obtained in treatments with vinasse application. This study concluded that biochar is an effficient strategy to mitigate N 2 O emissions, providing the first insights into how biochar affects the microbial community associated with N 2 O emissions from soil under energy cane cultivation. [Display omitted] • Organic residues are important drivers of N 2 O emissions in agricultural soils. • The application of vinasse increased N 2 O emissions by 86 %. • Highest N 2 O emissions correlated with nitrifier microorganisms (AOB, and AOA). • The addition of biochar reduced N 2 O emissions by rates ranging from 41 % to 54 %. • Energy cane biomass was not affected by N fertilization methods. [ABSTRACT FROM AUTHOR]

Pasturelands, often degraded, represent most of the converted lands globally. It is important to understand how different pasture management approaches can improve soil quality, increase feed production and farmer income. Here, the impact of different soil enhancers on soil quality and productivity of three cultivars of Brachiaria (Syn. Urochloa) forage grass is presented. Soil enhancers included: biochar - a carbon-rich product from biomass pyrolysis, moinha (local charcoal residue), traditional fertiliser containing nitrogen, phosphorus and potassium, lime, and forage peanut (Arachis pintoi cv. Amarillo). Considering the total biomass produced over the experiment (sum of four harvests), the highest dry biomass production was observed for Brachiaria brizantha cv. Piatã (14.1 Mg ha−1) and cv. Marandu (12.7 Mg ha−1), for biochar application of 30 Mg ha−1. Paiaguás had the highest dry matter production (12.4 Mg ha−1) for the treatment with forage peanut plus 15 Mg ha−1 of biochar. The increases in dry mass production translated to additional income, as compared with the control, of U$ 1 291, U$ 1 183 and U$ 991 per year for Marandu, Piatã and Paiaguás, respectively. The increases in forage grass productivity were reflected by positive changes in soil characteristics such as improvement in cation exchange capacity, pH and nutrient contents. Improved management of tropical pasturelands holds opportunity for more sustainable food production, and for ecosystem services protection and recuperation, for example, biodiversity net-gain, water regulation and carbon sequestration. [ABSTRACT FROM AUTHOR]