ABSTRACT Although agriculture and livestock systems represent important sources of N2O 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 N2O emissions from a tropical Oxisol under row-crop, livestock, forest monocultures, and an integrated crop-livestock-forest system in the Southern Amazon - Brazil. Soil N2O 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 N2O fluxes was 16.9, 12.2, and 15.4 µg N2O-N 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 N2O-N m-2 h-1, respectively, both lower than the agricultural systems. The largest soil N2O 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 N2O-N ha-1 yr-1, all different of the forest system and native forest fragment (0.33 and 0.52 kg N2O-N ha-1 yr-1, respectively). Nitrogen fertilization and soil moisture influenced soil N2O emissions of all systems assessed in the Southern Amazon. The N2O 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 N2O emissions from the soil than row-crop and livestock. Thus, CLF represents a good option for N2O mitigation for the edaphic and climatic conditions of the Southern Amazon.

Resumo O objetivo deste trabalho foi avaliar o potencial de mitigação de óxido nitroso (N2O) 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 N2O. O sistema de ILPF apresenta potencial promissor para mitigar as emissões de N2O, 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.

Abstract 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 N2O emissions. The ICLF system has promising potential to mitigate N2O 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.