Gaseous emissions of N2O and CH4 from subtropical Brazilian soil under integrated cropping-livestock and crop-livestock-forestry production systems

Agriculture and land use changes are two of the most important sources of greenhouse gases (GHGs) and in Brazil particularly they account for about two-thirds of the national emissions. However, expectations are that improved farming systems, like the integrated cropping-livestock system (ICLS), can combine food production with reduced GHG emissions. In this sense, we assessed the potential of ICLS for curbing soil nitrous oxide (N2O) and methane (CH4) emissions and sequestering soil organic carbon (SOC). The study was based on four field experiments conducted in east Paraná, Southern Brazil. Soil N2O and CH4 fluxes were measured in three experiments (static chamber method) and soil carbon accumulation to 1 m depth was assessed in two experiments. ICLS was characterized by winter pasture (oats plus ryegrass) under open grazing followed by a summer cash crop (soybean or maize). In the 3 year measurements in experiment 1, soil N2O emission was reduced by almost one-half in ICLS compared to continuous cropping (1.1 vs. 2.0 kg N ha-1 yr-1), but did not affect CH4 fluxes and SOC stocks (107–109 t ha -1 to 1 m depth). In experiment 2, the N2O emission factors for dairy cattle urine (0.34%) and dung (0.11%) were much lower than the default 2% of the Intergovernmental Panel on Climate Change (IPCC); and that the nitrification inhibitor dicyandiamide (DCD) reduced the N2O emission by 60–80% in autumn-winter when dissolved into urine, and by 45% in autumn when sprayed over a urine patch. In experiment 3, where the Ferralsol originally had a higher SOC stock (ca. 200 t ha-1), SOC increments with ICLS were not observed, but at least there was no decrease, which is also relevant. In experiment 4, the soil N2O emissions were reduced by 40% in ICLS relative to a continuous perennial pasture of guineagrass (14 vs. 23 kg N ha-1 in 1.5 years), and indicated a trend to increase soil CH4 consumption by about 80%. Overall, ICLS showed a potential to reduce soil N2O emissions relative to continuous cropping or perennial pasture, but did not change SOC stocks when the initial stocks were high, and the N2O emission factors for urine and dung were lower compared to the IPCC’s 2%, which suggests that this default value could be revised for subtropical Brazil.