Abstract
Nitrous oxide (N2O) is the most important non-CO2 greenhouse gas and soil management systems should be evaluated for their N2O mitigation potential. This research evaluated a long-term (22 years) experiment testing the effect of soil management systems on N2O emissions in the postharvest period (autumn) from a subtropical Rhodic Hapludox at the research center FUNDACEP, in Cruz Alta, state of Rio Grande do Sul. Three treatments were evaluated, one under conventional tillage with soybean residues (CTsoybean) and two under no-tillage with soybean (NTsoybean) and maize residues (NTmaize). N2O emissions were measured eight times within 24 days (May 2007) using closed static chambers. Gas flows were obtained based on the relations between gas concentrations in the chamber at regular intervals (0, 15, 30, 45 min) analyzed by gas chromatography. After soybean harvest, accumulated N2O emissions in the period were approximately three times higher in the untilled soil (164 mg m-2 N) than under CT (51 mg m-2 N), with a short-lived N2O peak of 670 mg m-2 h-1 N. In contrast, soil N2O emissions in NT were lower after maize than after soybean, with a N2O peak of 127 g m-2 h-1 N. The multivariate analysis of N2O fluxes and soil variables, which were determined simultaneously with air sampling, demonstrated that the main driving variables of soil N2O emissions were soil microbial activity, temperature, water-filled pore space, and NO3- content. To replace soybean monoculture, crop rotation including maize must be considered as a strategy to decrease soil N2O emissions from NT soils in Southern Brazil in a Autumn.
Highlights
The atmospheric concentrations of the three main greenhouse gases (GHGs) – carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) – have increased rapidly in the last few decades, which is a phenomenon associated to anthropogenic activities (Mosier et al, 1991; 1998)
It is estimated that 75 % of CO2, 94 % of N2O, and 91 % of the CH4 emissions in Brazil come from agricultural activities (Embrapa, 2006)
The N2O emission from soil after soybean harvest is higher under no-tillage than under conventional tillage
Summary
The atmospheric concentrations of the three main greenhouse gases (GHGs) – carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) – have increased rapidly in the last few decades, which is a phenomenon associated to anthropogenic activities (Mosier et al, 1991; 1998). It is estimated that agriculture contributes with approximately 22 % to the total CO2 emissions, 80 % to the total N2O and 55 % to the total CH4 emissions (IPCC, 2007). Nitrification, which requires aerobic conditions, depends on NH4+ supply and is mediated by autotrophic bacteria, whereas denitrification is performed by anaerobic heterotrophic bacteria, which depend on the availability of labile organic C (Rice et al, 1988) and NO3-. Their activity is intensified in anaerobic environments or soil microsites with low O2 availability (Moreira & Siqueira, 2006; Aita & Giacomini, 2007). In addition to these soil variables, temperature, water-filled pore space (WFPS), and pH have been identified as N2O-production-controlling variables in agricultural soils, since they affect the activity of nitrifying and denitrifying bacteria as well (Maag & Vinther, 1996; Weitz et al, 2001; Dalal et al, 2003)
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