Search

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]

Cultivated agricultural soils are the largest anthropogenic source of nitrous oxide (N 2 O), a greenhouse gas approx . 298 times stronger than carbon dioxide. As agricultural land covers 40–50% of the earth’s surface agricultural N 2 O emissions could significantly influence future climate. The timing, amount and form of manufactured nitrogen (N) fertiliser applied to soils are major controls on N 2 O emission magnitude, and various methods are being investigated to quantify and reduce these emissions. A lack of measured N 2 O emission factors (EFs) means that most countries report N 2 O emissions using the IPCC’s Tier 1 methodology, where an EF of 1% is applied to mineral soils, regardless of soil type, climate, or location. The aim of this research was to generate evidence from experiments to contribute to improving the UK’s N 2 O agricultural inventory, by determining whether N 2 O EFs should vary across soil types and agroclimatic zones. Mitigation methods were also investigated, including assessing the impact of the nitrification inhibitor (NI) dicyandiamide (DCD), the application of more frequent smaller doses of fertiliser, and the impact of different rates and forms of manufactured N fertiliser. Nitrous oxide emissions were measured at one cropland site in Scotland and two in England for 12 months in 2011/2012, along with soil and environmental variables. Crop yield was also measured, and emission intensities were calculated for the contrasting fertiliser treatments. The greatest mean annual cumulative emissions from a range of ammonium nitrate (AN) fertiliser rates were measured at the Scottish site (2301 g N 2 O-N ha −1 ), which experienced 822 mm rainfall compared to 418 mm and 472 mm at the English sites, where cumulative annual emissions were lower (929 and 1152 g N 2 O-N ha −1 , respectively). Climate and soil mineral N influenced N 2 O emissions, with a combination of factors required to occur simultaneously to generate the greatest fluxes. Emissions were related to fertiliser N rate; however the trend was not linear. EFs for AN treatments varied between sites, but at both English sites were much lower than the 1% value used by the IPCC, and as low as 0.20%. DCD reduced AN- and urea-generated N 2 O emissions and yield-scaled emissions at all sites. AN application in more frequent smaller doses reduced emissions at all sites, however, the type of fertiliser (AN or urea) had no impact. A significant difference in mean annual cumulative emissions between sites reflected differences in rainfall, and suggests that location specific or rainfall driven emission estimates could be considered. [ABSTRACT FROM AUTHOR]

Dung and urine excreted onto grasslands are a major source of nitrous oxide (N 2 O). These N 2 O emissions stem from inefficient utilisation of nitrogen (N) ingested by ruminants, and the inability of pasture to utilise the deposited N. Predicted growth in dairy and meat consumption means that there is a requirement to quantify N 2 O emissions, and investigate emission reduction mechanisms. Three 12 month ‘seasonal’ experiments were undertaken at Crichton, SW Scotland, where N 2 O emissions were measured from applications of cattle urine, dung, artificial urine and urine + a nitrification inhibitor (NI), dicyandiamide (DCD). The three application timings were ‘spring’, ‘summer’ and ‘autumn’, representative of early-, mid- and late grazing seasons. N 2 O emissions were measured from static chambers for 12 months. The aim was to quantify emissions from cattle excreta, and determine their dependence on the season of application, and the respective contribution of dung and urine to total excreta emissions. Measurement from NI amended urine was made to assess DCD's potential as an emission mitigation tool. Emissions were compared to the IPCC's default emission factor (EF) of 2% for cattle excreted N. Mean annual cumulative emissions from urine were the highest when applied in summer (5034 g N 2 O-N ha − 1 ), with lower emissions from spring (1903 g N 2 O-N ha − 1 ) and autumn (2014 g N 2 O-N ha − 1 ) application, most likely due to higher temperatures and soil moisture conducive to both nitrification and denitrification in the summer months. Calculated EFs were significantly greater from urine (1.1%) than dung (0.2%) when excreta was applied in summer, and EFs varied with season of application, but in all experiments were lower than the IPCC default of 2%. These results support both lowering and disaggregating this EF into individual EFs for dung and urine. Addition of DCD to urine caused no significant reduction in emissions, suggesting that more research is required into its use as a mitigation option. [ABSTRACT FROM AUTHOR]

A recent paper by Miszczak et al. (2020) examines metal contamination of mires in Poland and Norway. The authors conclude that lead (Pb) records in ombrotrophic peatlands cannot be used to reconstruct the chronological history of anthropogenic activities due to post-depositional mobility of the metal. We contest this general conclusion which stands in contrast with a significant body of literature demonstrating that Pb is largely immobile in the vast majority of ombrotrophic peatlands. Our aim is to reaffirm the crucial contribution that peat records have made to our knowledge of atmospheric Pb contamination. In addition, we reiterate the necessity of following established protocols to produce reliable records of anthropogenic Pb contamination in environmental archives. [ABSTRACT FROM AUTHOR]

Abstract: The well characterised temporal trend in the 206Pb/207Pb atom ratio of atmospheric lead deposition in Scotland during the 20th century was used to investigate the surface integrity of several cores collected by different methods from Flanders Moss ombrotrophic peat bog, central Scotland, during 1996–2001. Based on 206Pb/207Pb profile comparisons, in conjunction with identified 210Pb radionuclide inventory deficits for two of the cores, it was deduced that 25±7 yrs worth of material was missing from the more seriously affected core. After allowing for an appropriate vertical offset based on 206Pb/207Pb profile matching, the subsequent matching of profiles of titanium, lead, sulfur, arsenic, iron, phosphorus and manganese in three cores for which total concentration data were available was excellent. Without such offset correction, erroneous conclusions could have been drawn concerning the recent historical record of anthropogenic lead and arsenic deposition, the position of the redox boundary, which controls geochemical cycling and enrichment of iron, and the nutrient recycling status of manganese and phosphorus in the near-surface vegetation. Topographic, vegetative and coring (both device and operator) influences may have been responsible, thus endorsing the use of reliable, multiple core sampling and the use of lead isotope ratio profiles, supplemented by appropriate radionuclide data, in both assessing and ensuring the surface integrity of peat cores. [Copyright &y& Elsevier]

• 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]