Temperature and moisture affect methane and nitrous oxide emission from bovine manure patches in tropical conditions

Résumé

Animal production systems are important sources of greenhouse gases (GHG), especially methane (CH4) and nitrous oxide (N2O). Brazilian beef production is almost exclusively (more than 90%) pasture-based. GHG emissions from faeces deposited in pastures have been extensively studied in temperate climates, but emissions under tropical conditions are unclear. The aim of this study was to examine the effects of tropical temperature and moisture conditions on GHG emission from manure. We hypothesized that periodical rainfall and high temperature on tropical climates would increase the GHG emission from faeces by maintaining an anaerobic environment within the faeces. We measured the emission of CH4 and N2O from cattle faeces in two different field sites in Brazil: São Paulo (subtropical) and Rondônia (tropical), as well as under controlled conditions, simulating summer conditions. Emissions of CH4 from faeces ranged from 117 to 1007 mg C–CH4 m-2 h-1. In the field, summer emissions were 2.9 (São Paulo) and 2.5 (Rondônia) times higher than winter (p <0.05). In controlled conditions, prolonged moisture conditions at high temperature (35 °C) resulted in higher emissions (p <0.05) than the no-rewetted treatment (2831 and 1781 mgCH4 m-2, respectively). Emission factors determined were 0.02 and 0.05 kg CH4 head-1 year-1 (winter and summer São Paulo, respectively) and 0.06 and 0.10 kg CH4 head-1 year-1 (winter and summer Rondônia, respectively), significantly lower than the IPCC default value of 1 kg CH4 head-1 year-1. CH4 emissions from faeces were slightly higher than from others studies in temperate climates. N2O emission from faeces was lower than the control at the Rondônia site during the summer, with net negative fluxes. We conclude that climate is a strong factor controlling GHG emission from faeces. Our study showed that in a continental-size country as Brazil, an average emission factor as proposed by the IPCC is not the best option.