Use of a nitrification inhibitor reduces nitrous oxide (N2O) emissions from compacted grassland with different soil textures and climatic conditions

Grassland accounts for 70% of the global agricultural area. Grassland amended with N fertiliser, although increasing productivity, encourages the emission of the greenhouse gas nitrous oxide (N2O). Soil compaction can result in impeded water movement and the development of anaerobic conditions that favour N2O production and emissions from denitrification. Soil compaction has become more prevalent in grassland with the use of increasingly heavy machinery and the extension of seasonal animal grazing periods, especially when soil moisture is high; close to field capacity. The effect of a nitrification inhibitor - dicyandiamide (DCD) on emissions of N2O from grassland moderately compacted from animal trampling or a tractor were investigated at two experimental field sites in the UK; a silt clay loam soil in a wet climate (SRUC) and a sandy loam in a drier climate (HAU). Compaction treatments repeated annually over three years (2011-2013) gave an overall increase in soil bulk density for the tractor compaction and animal trampling at both sites but to different degrees related to soil texture. Cumulative N2O emissions from tractor compaction for both SRUC and HAU were significantly greater than from the uncompacted control over the three years, with changing climate, soil texture and soil pH influencing the magnitude of N2O emissions. The use of DCD decreased cumulative N2O emissions at both sites, with the reduction greatest under tractor compaction, especially for the drier, sandier soil with the greater porosity. DCD appeared to decrease soil nitrate (NO3-) concentrations and decreased potential NO3- losses from leaching and run-off. Extrapolating from these data, the presence of moderate compaction, as identified in grasslands in England and Wales, could result in an estimated annual increase in N2O emissions of between 0.10 and 0.78 Mt of N2O, but these emissions could be reduced by up to 16% and 51% through the use of DCD, depending on compaction depth and soil texture. Although no yield increases were seen from the use of the DCD at both sites, N2O emissions were reduced.