Assessment of the application of a cover crop and conservation tillage on soil and water properties dissolved nitrous oxide in an arable system

Hama-Aziz, Zanist Qader (2016) Assessment of the application of a cover crop and conservation tillage on soil and water properties dissolved nitrous oxide in an arable system. Doctoral thesis, University of East Anglia.

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Abstract

Agriculture is a major contributor to environmental pollution. About quarter of water bodies in
England are classified as being good ecological and chemical status. To tackle agricultural
pollution, a range of on-farm mitigation measures are recommended. The overall aim of this
study was to assess the effectiveness of cover cropping and reduced cultivation methods as infield
mitigation measures to reduce diffuse water pollution, improve soil quality and reduce
nitrous oxide greenhouse gas emissions. These mitigation measures were applied to seven
fields within the intensive arable River Wensum catchment, eastern England, with a further
two fields kept under conventional cultivation as a control. Soil and water chemistry,
principally water discharging from subsurface agricultural field drains, were regularly sampled
and analysed from these fields over a two-year period.
The results revealed the mitigation measures had no positive impact on soil quality. The soil
chemical condition, including soil organic carbon, phosphorus, magnesium and sulphate
concentrations were not improved by the use of a cover crop or reduced cultivation, whilst soil
physical condition deteriorated through increased compaction, as highlighted by increased bulk
density, penetration resistance and lower infiltration rates. Conversely, field drain water quality
improved markedly. The presence of a winter cover crop significantly reduced mean dissolved
nitrate concentrations from 13.9 mg N L-1 to 2.5 mg N L-1, an 82% reduction. Different
inversion intensity of the soil tended to have no effect on nitrate concentrations. Regarding
dissolved N2O, a slightly higher N2O concentration was recorded in field drains under a cover
crop than without cover crop. This finding suggests that whilst the use of a winter cover crop
is highly effective at reducing soil nitrate losses to rivers, it does not represent an effective
strategy for reducing N2O emissions. Indirect nitrous oxide emission factors (EF5g and EF5r)
were calculated using two approaches (IPCC 2006 and the N2O-N/NO3̄-N ratio) for both field
drain and stream water samples. Values for these two EFs obtained were found to be below the
IPCC default value of 0.0025. If the IPCC were to revise EF5 values in future then, regardless
of soil type, crop type, and land use practices, a value of 0.0009 (about one third of the current
value) for EF5g and a value of 0.0002 (one order of magnitude lower than the current value) for
EF5r may be a more reasonable estimates. Such radical downward revision would at least halve
the current estimates of N2O emissions associated with N leaching and runoff from agriculture
for both the UK and globally.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Vailele Chittock
Date Deposited: 23 Aug 2016 10:40
Last Modified: 23 Aug 2016 10:40
URI: https://ueaeprints.uea.ac.uk/id/eprint/59671
DOI:

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