Resumo -O objetivo deste trabalho foi avaliar o potencial de mitigação de óxido nitroso (N 2 O) em sistema de integração lavoura-pecuária-floresta (ILPF), em comparação ao monocultivo, e identificar os principais fatores que regulam as emissões deste gás. O experimento foi realizado em Sinop, MT, entre as safras 2012/2013 e 2013/2014, e avaliou os seguintes tratamentos: floresta, lavoura e pastagem, além do ILPF. Durante a realização do experimento, não houve presença de bovinos nas áreas com pastagem. Amostras de óxido nitroso foram coletadas semanalmente, com uso de câmaras estáticas, modelo topo-base. As concentrações do gás foram determinadas por meio de cromatografia gasosa. A precipitação pluvial e a disponibilidade de N foram os principais fatores reguladores das emissões de N 2 O. O sistema de ILPF apresenta potencial promissor para mitigar as emissões de N 2 O, com emissão acumulada de 0,367 kg ha -1 de N, em comparação a de 1,401 kg ha -1 emitidas pela lavoura; de 0,298 kg ha -1 , pela pastagem; e de 0,165 kg ha -1 , pela floresta.Termos para indexação: gases de efeito estufa, mudança do clima, sistemas integrados de produção. Nitrous oxide fluxes in an integrated crop-livestock-forestry systemAbstract -The objective of this work was to evaluate the mitigation potential of nitrous oxide in an integrated crop-livestock-forestry system (ICLF), compared with monocultures, and to identify the main factors that regulate the emissions of this gas. The experiment was conducted in the municipality of Sinop, in the state of Mato Grosso, Brazil, between the 2012/2013 and 2013/2014 crop seasons, with the evaluation of the following treatments: forest, crop and pasture, besides ICLF. During the experiment, no cattle were present in the pasture areas. Nitrous oxide samples were collected weekly using top-down static chambers. Gas concentrations were determined with gas chromatography. Rainfall and N availability were main factors regulating N 2 O emissions. The ICLF system has promising potential to mitigate N 2 O emissions, with 0.367 kg ha -1 N accumulated emission, compared with 1.401 kg ha -1 from cropland, 0.298 kg ha -1 from pasture, and 0.165 kg ha -1 from forest.

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Agriculture, forestry and other land uses are currently the second highest source of anthropogenic greenhouse gases (GHGs) emissions. In soil, these gases derive from microbial activity, during carbon (C) and nitrogen (N) cycling. To investigate how Eucalyptus land use and growth period impact the microbial community, GHG fluxes and inorganic N levels, and if there is a link among these variables, we monitored three adjacent areas for 9 months: a recently planted Eucalyptus area, fully developed Eucalyptus forest (final of rotation) and native forest. We assessed the microbial community using 16S rRNA gene sequencing and qPCR of key genes involved in C and N cycles. No considerable differences in GHG flux were evident among the areas, but logging considerably increased inorganic N levels. Eucalyptus areas displayed richer and more diverse communities, with selection for specific groups. Land use influenced communities more extensively than the time of sampling or growth phase, although all were significant modulators. Several microbial groups and genes shifted temporally, and inorganic N levels shaped several of these changes. No correlations among microbial groups or genes and GHG were found, suggesting no link among these variables in this short-rotation Eucalyptus study.

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Although agriculture and livestock systems represent important sources of N 2 O from the soil, they may also aid in emissions mitigation, mainly when integrated systems are taken into account, such as crop-livestock-forest, for food production. This work assessed the soil N 2 O emissions from a tropical Oxisol under row-crop, livestock, forest monocultures, and an integrated crop-livestock-forest system in the Southern Amazon-Brazil. Soil N 2 O emissions were measured using static chambers from November 2014 to October 2016 in four soil use systems [row-crop, livestock, forest, and integrated crop-livestock-forest (CLF)], and in a reference area under native forest fragment. For the whole period, the average of soil N 2 O fluxes was 16.9, 12.2, and 15.4 µg N 2 ON m-2 h-1 , to row-crop, livestock, and CLF systems, respectively, all with a similar average among them. The lowest fluxes were observed in the forest system and native forest fragment, with average fluxes of 4.0 and 6.3 µg N 2 ON m-2 h-1 , respectively, both lower than the agricultural systems. The largest soil N 2 O fluxes were observed throughout the rainy seasons in the row-crop, livestock, and CLF, mostly after N-fertilizer application to the soil surface or in the planted row. As a consequence, the cumulative emissions were greater in row-crop, livestock, and CLF systems, which in the averages of two cycles emitted respectively 1.40, 1.15, and 1.27 kg N 2 ON ha-1 yr-1 , all different of the forest system and native forest fragment (0.33 and 0.52 kg N 2 ON ha-1 yr-1 , respectively). Nitrogen fertilization and soil moisture influenced soil N 2 O emissions of all systems assessed in the Southern Amazon. The N 2 O emissions took place after both factors were met, corroborating the hole-in-the-pipe model. Even with more soil use intensification, once in the same area there were three cultures in succession during a year and perennial trees, CLF did not lead to greater N 2 O emissions from the soil than row-crop and livestock. Thus, CLF represents a good option for N 2 O mitigation for the edaphic and climatic conditions of the Southern Amazon.

The Brazilian agricultural sector is largely responsible for nitrous oxide (N2O) soil emissions, mainly due to beef cattle and the use of synthetic nitrogen fertilizers. Therefore, Brazil is looking for measures, such as integrated crop–livestock– forest (ICLF), to increase productivity and reduce greenhouse gas emissions in this sector. The forest component within this system plays a positive role in the context of climate change, soil conservation, carbon dioxide (CO2) sequestration, and biodiversity protection. The aim of this study was to evaluate the effect of management and rainfall on N2O emissions in eucalypt monoculture soils and eucalypt soils in ICLF systems. Manual static chambers were used to collect gas samples, from November 2013 to October 2014, in four treatments, i.e., one eucalypt monoculture (F) and three modalities of ICLF (livestock–forest [LF], livestock–crop–forest [LCF], and integrated crop–livestock–forest [ICLF]). A gas chromatograph with an electron capture detector was used to measure the N2O concentrations. The results showed that rainfall considerably affected N2O fluxes across all the treatments, indicating that rainfall is the main factor in increasing emissions. During the wet season, the N2O levels ranged from 0.158 to 0.482 kg N-N2O ha-1 across all treatments. During the dry season, all treatments behaved like sinks of N2O. Moreover, N2O flux did not differ between the soils in the eucalypt monoculture and ICLF systems. This indicates that the forestry component in the ICLF systems did not affect N2O soil fluxes.