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Agricultural soils are the primary source of nitrous oxide emissions due to management practices including fertiliser application. While fertiliser rates are one of the main drivers of nitrous oxide emissions, emissions are also dependent on other variables such as climate and soil properties. To understand the spatial and inter-annual variations in emission rate, simulations of N 2 O emissions were made from 2000 to 2010 for UK grass and croplands. In addition, the sensitivity of these emissions to soil and climate inputs was also tested. Emissions of between 0.3 to 3.5 kg N ha −1 yr −1 and 0.7–7 kg N ha −1 yr −1 were simulated across UK croplands and grasslands, respectively. While inter-annual variations can be attributed to climate influences, the primary driver of spatial variations in emissions was soil clay content. However, when the sensitivity of nitrous oxide emissions to soil clay content alone was tested, it was not always the best predictor of emissions, when soil texture is altered outside of the normal range used as inputs to the model from different databases. [ABSTRACT FROM AUTHOR]

• Sandy soil under a drier climate emitted less N 2 O than clay soil under a wetter climate. • Nitrification inhibitor reduced emissions from compacted soils. • Nitrification inhibitor decreased soil nitrate concentrations especially in compacted soils. • Extreme rainfall was a strong driver of spring N 2 O emissions. 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 (N 2 O). Soil compaction can result in impeded water movement and the development of anaerobic conditions that favour N 2 O 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 N 2 O 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 N 2 O 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 N 2 O emissions. The use of DCD decreased cumulative N 2 O 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 (NO 3 −) concentrations and decreased potential NO 3 − 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 N 2 O emissions of between 0.10 and 0.78 Mt of N 2 O, 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, N 2 O emissions were reduced. [ABSTRACT FROM AUTHOR]

• Soil compaction reduced grass silage dry matter yield under both tractor and animal trampling. • Bulk density of the soil was significantly increased by compaction for the heavier soil. • Visual evaluation of soil structure was useful in assessing compaction from grassland management. • Poor growing conditions enhanced the reduction of dry matter yields from compaction. Soil compaction has been estimated to be responsible for 33 million ha of soil degradation in Europe, reducing crop yields, however there is limited data on grassland silage yields loss. Extended grazing periods, increased size and weight of farm vehicles and more extreme weather have fostered concern over the consequences of grassland management on reduced grass yield and soil quality. This work aimed at studying the effect of increased animal trampling and mechanical (tractor) soil compaction on grassland silage mean dry matter (DM) yields and soil structure over a three year period at two UK sites. These sites were on two established perennial ryegrass fields with contrasting soil textures; an imperfectly drained silty clay loam in SW Scotland and a well drained sandy loam from central England. Results showed trampling and tractor compaction decreased mean DM yields over three years and by the third year DM yield for the trampled area was 11.4% less on the soil with greater clay content soil and 12.0% less on the more sandier soil than the no compaction control. DM yield for the tractor compaction, by the third year, was 14.5% less than no compaction DM yield, on both soil types. Compaction treatments gave the greatest reductions for the first silage cut DM yields annually, for both soil types. The largest reductions (19.0% for trampling and 37.7% for tractor) were on the soil with the greater clay content in the second year, with the coolest start to the growing season. Compaction reduced N uptake, decreased drainage and increased water filled pore spaces (WFPS). Linear regression of visual evaluation of soil structure (VESS) scores and bulk densities provided evidence that VESS is an effective tool for detecting grassland compaction and would assist with the management of moderately compacted soils where deteriorate soil conditions may result in yield loss. [ABSTRACT FROM AUTHOR]