Measuring and modelling greenhouse gas fluxes between agricultural soils and the atmosphere

土壤是全球碳循环的主要组成部分，含有约1 500 Pg（1 Pg = 1 Gt = 1015 g）的有机碳（Batjes，1996年），约为植被中含量的三倍，大气中含量的两倍。通过光合作用，植物将二氧化碳（CO2）转化为有机形式的碳，并通过呼吸将一些返回大气。残留在植物组织中的碳通过它们的根和植物死亡和分解时的垃圾进入土壤。这些碳随后以土壤有机质的形式储存在土壤中。碳可以在土壤中储存数千年，也可以作为二氧化碳迅速释放回大气中。气候、植被类型、土壤质地和排水都影响碳在土壤中储存的数量和时间。因此，土壤在维持全球碳循环平衡方面发挥着重要作用。然而，由于农业的集约化和机械化，今天土壤的碳含量比几百年前要少。农业实践通过两种主要途径消耗土壤有机碳库：1。通过收割和移除作物减少凋落物中返回土壤的碳量。过度使用耕作方法会破坏土壤，增加土壤有机质的分解率，从而导致土壤中二氧化碳排放量增加。2019年6月，英国政府在法律上承诺到2050年实现温室气体（GHG）“净零”排放。农业部门约占英国温室气体排放量的10%。因此，实现净零排放将对农业和农业社区构成重大挑战。然而，土壤也可以通过吸收或“隔离”大气中的碳来帮助缓解气候变化。这可以通过改变管理做法来实现，例如减少耕作，缩短休耕期，提高动物粪便和作物残茬的使用效率，以及在主要经济作物之间种植覆盖作物。其他收益可以来自土地使用的变化，如种植树木和树篱，以及通过改变化肥施用率和方法来减少一氧化二氮（N2O）的排放。然而，需要改进土壤和大气之间碳、氮和温室气体通量变化的测量、监测和核实，以便进行定量经济和政策分析。目前，有关土壤碳、土地利用和气候的数据被结合起来，以建立模型，估计与农场管理做法变化有关的温室气体通量变化。然而，许多基于效率的温室气体缓解措施所提供的绝对缓解潜力仍然存在不确定性。因此，有必要增加和完善温室气体的测量范围内的耕地轮作更准确的项目旨在提高我们的理解的因素，控制温室气体通量的空间和时间的变化，从农业土壤（耕地，草地和户外猪）。特别是，根据您的特定研究兴趣，学生奖学金可以解决以下目标的组合：量化农业土壤中的有机碳和氮储量。测定作物残体、化肥和有机肥料对土壤的碳和氮输入。使用涡度协方差通量塔和静态箱量化水、碳和氮的陆气通量。通量塔还将允许量化作为温室气体的二氧化碳（CO2）通量。将在土地表面安装一系列颈圈，以允许直接测量N2O和甲烷通量。这将提供关于温室气体通量在土地利用之间以及在生长季节的时间内如何变化的信息。（四）在一系列耕作轮作和未来气候下的温室气体通量模型。

Soil is a major component in the global carbon cycle, containing about 1500 Pg (1 Pg = 1 Gt = 1015 g) of organic carbon (Batjes, 1996), which is about three times the amount in vegetation and twice the amount in the atmosphere. Through photosynthesis, plants convert carbon dioxide (CO2) into organic forms of carbon and return some to the atmosphere through respiration. The carbon that remains in plant tissue is added to the soil through their roots and as litter when plants die and decompose. This carbon is then stored in the soil as soil organic matter. Carbon can remain stored in the soil for millennia, or be quickly released back into the atmosphere as CO2. Climate, vegetation type, soil texture and drainage all influence the amount and length of time carbon is stored in the soil. Therefore, soils play a major role in maintaining a balanced global carbon cycle. However, the carbon content of soil is smaller today than a few hundred years ago owing to the intensification and mechanization of agriculture. Agricultural practices have depleted soil organic carbon pools by two main routes:1. Reducing the amount of carbon returned to the soil in litter by harvesting and removing the crop.2. Excessive use of tillage practices which breaks up the soil, increasing the decomposition rate of soil organic matter which leads to an increase in the release of CO2 from the soil.In June 2019, the Government legally committed the UK to reaching 'net-zero' greenhouse gas (GHG) emissions by 2050. The agriculture sector accounts for approximately 10% of the UK's GHG emissions. Therefore, achieving net-zero will pose significant challenges for farming and the farming communities. However, soils can also help mitigate climate change by absorbing or 'sequestering' carbon from the atmosphere. This can be achieved through changes in management practices, such as reduction in tillage, reducing fallow periods, improving efficiency of animal manure use and crop residue use, and planting cover crops between main cash crops. Additional gains can come from land use change, such as planting trees and hedges, and reducing nitrous oxide (N2O) emissions by modifying fertiliser application rates and methods. However, improvements in measuring, monitoring and verifying changes in carbon, nitrogen and GHG fluxes between the soil and atmosphere are needed for quantitative economic and policy analysis. Currently, data on soil carbon, land use and climate is combined to create models that estimate the change in GHG fluxes related to changes in farm management practices. However, uncertainty persists on the absolute mitigation potentials offered by many efficiency based GHG mitigation measures. Therefore there is a requirement to increase and refine GHG measurements from a range of arable rotations for greater accuracyThe project aims to improve our understanding of the factors that control the spatial and temporal variability in GHG fluxes from agricultural soils (arable, grassland and outdoor pigs). In particular, according to your particular research interests, the studentship could address a combination of the following objectives:i. Quantify soil organic carbon and nitrogen stocks within agricultural soilsii. Determine inputs of carbon and nitrogen to soil from crop residues and application of fertiliser and organic amendmentsiii. Quantify Land-Air fluxes of water, carbon and nitrogen using Eddy covariance flux towers and static chambers. The flux towers will also allow quantification of carbon dioxide (CO2) fluxes as greenhouse gases (GHGs). A series of collars at the land surface will be installed across the fields to allow direct chamber measurement of N2O and methane fluxes. This will provide information on how GHG fluxes vary between land uses and also through time during the growing season. iv Model GHG fluxes under a range of arable rotations and future climates.