Emissões de N2O em diferentes sucessões de cultura em dois sistemas de preparo do solo para produção de soja

Abstract

The greenhouse effect is a natural process essential to life on Earth. However, the concentration of the gases responsible for the global warming has increased in the atmosphere. Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are among the most important greenhouse gases (GHG). Agriculture is the main economic activity in Brazil, however, it is the main N2O producer, so, it is one of the targeted sectors to implement mitigation plans for GHG emissions. One of the mitigation procedures for agriculture taken by Brazil is the expansion of the No tillage (NT) area. NT system is able to accumulate carbon in soil, notwithstanding, the alterations caused in soil by the adoption of this system can increase the N2O emissions. The work objective was to evaluate the influence of soil tillage and nitrogen fertilization on N2O emissions in two succession systems for soybean production. Two experiments were carried out at Embrapa soybean experimental station in Londrina-PR. The experiments were divided in four huge areas, each one received a treatment. The treatments were: conventional tillage (CT) and without nitrogen fertilization, no tillage and without nitrogen fertilization. In each treatment were used six static closed chambers to monitor the N2O fluxes. The first experiment started in 2013 with the wheat seedling followed by the soybean seedling. The second started in 2014 with corn seedling followed by soybean seedling. Wheat experiment was conducted for two years and corn experiment for one year. The areas are being maintained with the tillage preparation and crops for 33 years for wheat – soybean succession and for 21 years for corn – soybean succession. Through the whole year samples of N2O emissions and soil samples to determine moisture, nitrate (NO3-), ammonium (NH4+) and soluble carbon (C) were taken. Productivity of soybeans responded to soil preparation. After wheat, in NT, the average was 2.6 Mg ha-1 and in CT, 1.3 Mg ha-1, after corn, in NT 2.0 Mg ha-1, and 0.7 Mg ha-1 in CT. In winter there was not difference, for wheat, the average was 2.7 Mg ha-1, and to corn was 4.2 Mg ha-1.N2O emissions were similar between CT and NT in the two years of wheat succession, and in the corn succession. On wheat – soybean succession, N2O emissions in CT vary between -14.8 to 156.5 µg N-N2O m-2 h-1, and in NT, -14.6 to 214.0 µg N-N2O m-2 h-1. In corn – soybean succession between -10.2 to 486.3 µg N-N2O m-2 h-1 for CT and -11,1 to 364,4 µg N-N2O m-2 h-1 for NT. The highest emissions occurred in treatments that received nitrogen fertilization. However, the differences became limited to the wheat and corn cycles, soybean emissions were similar, regardless of treatment applied. Soluble C did not showed significant correlation with N2O emissions, N-Mineral showed correlation in the wheat cycle, on the second year of the succession, and in the corn cycle. %WFPS showed correlation in the soybean cycle in the first year of the wheat succession. Calculated emission factors were lesser than 1%.