CH4, CO2 and N2O emissions from grasslands and bovine excreta in two intensive tropical dairy production systems

摘要

The production of beef and milk has a significant impact on climate change, as these activities are responsible for a large proportion of the greenhouse gases emitted in agriculture. We used the static closed chamber technique to measure the rate of CH4-C, N2O-N and CO2-C emissions from pastures (102days) and bovine excretions (27days) in an intensive pasture monoculture (PM) and an intensive silvopastoral system (ISS) in the Cauca Valley of Colombia. Mean soil CO2-C (mgm(2)h(-1)), CH4-C and N2O-N emissions (gm(-2)h(-1)) were 236.7 versus 113.4; 46.7 versus 1.01 and 344.7 versus 40.1 for the PM and ISS, respectively. The accumulated flows for PM and ISS during the evaluation period were 751.6 and 424.3; 4.39 and -0.41; and 12.75 and 1.55 (kgha(-1)) for CO2-C, CH4-C and N2O-N, respectively. Regarding manure, the PM had lower CO2-C and CH4-C emissions (498.6 vs. 981.2mgm(-2)h(-1), and 1.9 vs. 4.7gm(2)h(-1); p>0.05), and higher N2O-N emissions (2967.3 vs. 1179.8gm(-2)h(-1); p=0.02) than the ISS, respectively. For the urine patches, the ISS emitted only 47.9, 2.2 and 11.6% of the CO2-C, CH4-C and N2O-N emissions observed in the PM, respectively. Moreover, comparing both systems with a forest, CH4-C and N2O-N emissions from the ISS were not different (p>0.05), but the PM presented higher emissions for the three gases (p0.0001). The emissions reported in the present study differ from the emission factors suggested by the IPCC and other authors for manure and urine. PM presented higher N losses than the ISS from both manure (1.77 vs. 1.37%) and urine (3.47 vs. 0.3%) (p0.05). The ISS might contribute to the reduction of GHG emissions from grasslands in contrast to traditional grazing systems, despite the high stocking rates and legume densities, producing emissions similar to those of a forest.