The effect of conventional tillage and associated grassland management on the emission of greenhouse gases (CO2, CH4 and N2O) and soil properties

Grasslands represent a large portion of agricultural land and are major contributors to the gas exchange between biosphere and atmosphere. Agricultural management can impede the ability of grasslands to act as carbon sinks. In this project, CO2, CH4 and N2O fluxes from two adjacent grasslands in the SE of Scotland were measured with closed static chambers from March to June 2014, in order to estimate the effect of ploughing and associated management on the emission of the aforementioned greenhouse gases (GHGs) and on soil properties. Environmental conditions and soil properties were measured simultaneously. One field was ploughed with a mouldboard plough in May 2012 and the other field in May 2014. Also, the two fields were continuously grazed and regularly received inorganic fertiliser. CO2 fluxes were mainly influenced by temperature and were neither strongly influenced by fertilisation nor ploughing, although CO2 emissions were smaller after the ploughing event in 2014. CH4 fluxes were high after the ploughing in 2014; highest fluxes reached 7355 μg CH4-C m-2 h-1 for individual chamber locations. N2O emissions were higher after the ploughing in 2014 (up to 2578 μg N2O-N m-2 h-1 individual chambers) compared to emissions after fertilisation (up to 710 μg N2O-N m-2 h-1 for individual chambers). Additionally, increased concentrations of NO3- were measured in the ploughed grassland in 2014. For the study period, a higher overall GHG budget was measured for the unploughed grassland (1.27 g CO2 eq m-2 h-1) compared to the ploughed grassland (1.13 g CO2 eq m-2 h-1), which was due to the higher portion of CO2 emitted by the unploughed grassland offsetting the higher CH4 and N2O emissions from the ploughed grassland. The importance of environmental factors in influencing GHG emissions from grasslands was highlighted by the comparison of datasets from 2012 and 2014, which showed very different responses to the ploughing