Changes to soil quality indicators following conversion to organic vegetable production (OF0401)

This is the final report of Defra project OF0401. The attached report document starts with an Executive Summary, from which this text is extracted. The aim of this 1 year study was to examine how key functional indicators of soil quality are affected by contrasting organic and conventional management regimes. In particular, the project investigated the impact of contrasting fertility building regimes on soil quality, focussing on the initial 5-year period following conversion from conventional to organic production. Five 0.8 ha areas at HRI-Wellesbourne were selected for study. These were: two organic vegetable rotations supporting contrasting fertility building regimes, an organic arable rotation, a grass-clover ley, and a conventionally managed cereal rotation. The organic areas had been converted from conventional cereal production 5 years prior to the start of the study. The conventional area was adjacent. A range of chemical, biological and physical attributes were determined. There were differences between the organic and conventional management regimes in most chemical, biological and physical soil quality parameters. Contrasting organic management regimes had different effects on soil quality. Relative to organic vegetable and conventional arable management, the organic arable management rotation enhanced amounts of light fraction organic matter and labile N, with beneficial implications for long term nutrient retention and soil organic matter development. There was little difference in chemical quality between the organic vegetable and the conventional arable areas. There was evidence that organic management promoted a microbial community that was distinct in composition and functional attributes to that in conventional soil. Relative to conventional management, areas under organic management had greatly increased inoculum of arbuscular mycorrhizal fungi, a larger proportion of 'active' relative to 'resting' biomass within the microbiota, increased metabolic diversity and a distinct microbial community metabolism. However, there was evidence that the productivity of newly converted organic systems could be limited by low inoculum and diversity of arbuscular mycorrhizal fungi inherited following conventional management. The clearest effect on soil structure was with regard to the detrimental effects of vegetable production rather than to any benefit associated with organic management. Wheeling lines caused compaction that resulted in poor growth of subsequent cereal crops. However, it is likely that increased levels of organic matter may result in a soil better able to cope with damaging operations. There were differences in the susceptibility of the chemical and biological quality parameters to change. These differences provide possibilities to use selected parameters as early indicators of the effects of management on soil quality. Furthermore, the results highlight the need, when investigating soil quality, to consider a wide variety of 'quality' analyses. Limited data sets, focussing on traditional measures of soil quality (e.g. total SOM and biomass-N), could lead to unsound conclusions regarding the effects of management on other functional aspects of soil quality. There are opportunities to conduct further statistical analysis of our comprehensive data set in order to develop an index suitable for quantifying soil quality in organic systems. Such an index would be of generic value to rate soil quality in diverse agricultural systems. Further work is needed to determine the applicability and conclusions of our study to other soil types and organic management regimes. The work has highlighted fundamental shifts in microbial community structure and functioning following conversion from conventional to organic management. There is a need to characterise and quantify these changes. This will provide new groups of 'indicator' organisms which could be suitable for assessing changes to soil quality, and could also provide opportunities to manage soil microbial communities to improve the sustainability of organic and conventional farming

Incorporation of nitrogen from crop residues into light fraction organic matter in soils with contrasting management histories

The proportion of N from crop residues entering the light-fraction organic matter (LFOM) pool was investigated in soils with contrasting soil organic matter and microbial characteristics arising from different management histories. A laboratory experiment was conducted in which 15N-labelled sugar beet, Brussels sprout or ryegrass shoots, which possessed a range of C/N contents, and hence different biochemical qualities, were incorporated into a sandy–loam soil collected from within a field (FC) or from the field margin (FM). Amounts of C and N incorporated into LFOM were determined after 112 days. The FC and FM soils had organic C contents of 0.9% and 2.5%, respectively. Addition of crop residues increased total LFOM N content and reduced its C/N in FC soil but had no effect on total LFOM N or its C/N in FM soil. Ryegrass incorporation into FC was the only treatment in which there was a net increase in LFOM C. Isotopic analysis indicated that more crop-residue-derived N became incorporated into the LFOM N pool in FM relative to FC soil, with per cent crop residue N incorporated ranging from 25.9% to 35.3% in FC and between 38.9 and 68.5 in FM. Incorporation of crop residues had a positive priming effect on pre-existing LFOM N in FM but not FC soil. We conclude that the characteristics of plant material, together with differences in soil organic matter and microbiology resulting from contrasting management, determined the amount of crop residue C and N incorporated into both HFOM and LFOM

Arbuscular mycorrhizal fungi in organic systems

Arbuscular mycorrhizal fungi (AMF) are potential contributors to plant nutrition and pathogen suppression in low input agricultural systems, although individual species of AMF vary widely in their functional attributes. Recent studies at HRI and elsewhere have suggested that in some agricultural systems inoculum of AMF is substantially lower under conventional management relative to that under organic management. Further studies have suggested that conventional management selects AMF communities with limited benefits to their plant hosts relative to those in organic systems. There is a need to investigate the generality of these findings, and their implications for the productivity of organic systems, particularly during the period following conversion to organic management. The current project was designed to pull together existing understanding of the role, and potential role, of AMF in organic systems, and to identify sites and develop methods for use in a subsequent research programme. The project had three objectives: 01 To deliver a literature review covering current knowledge of the role of AMF in conventional and organic agricultural systems. The review considered the ways in which management influences the structure and functioning of AMF communities, including their contributions under conventional and organic management, and recommendations for future research needs. 02 To establish the extent of differences in AMF inoculum between organic and conventional systems, covering a range of management practices. Paired organic and conventional fields at 12 sites from across England were selected to investigate the relationships between management, AMF communities and soil chemistry. Organic and conventionally managed soils showed no significant difference in soil chemical properties (Organic C, total N, total P, extractable P, K, Mg). However, organically managed soils had greater AMF spore numbers and root colonisation potential, and therefore higher AMF inoculum potential, than conventionally managed soil. The relative difference in AMF spore numbers between organic and conventionally managed fields increased with time since conversion. Differences in AMF inoculum potential between organic and conventionally managed fields, and between farm sites, could not be related to differences in soil chemistry. 03 To develop a method suitable for characterising AM fungus communities in soil libraries, based on 18S rRNA terminal restriction fragment length polymorphism (T-RFLP) T-RFLP was shown to provide a rapid semi-quantitative method for analysis of AMF community diversity. However it was clear that primers currently used to amplify AMF are selective and do not allow diversity of the whole AMF community to be determined. Additionally these primers amplify contaminant fungi which need to be removed from the T-RFLP profile prior to analysis. However, contaminant diversity was shown to be low. The project has identified sites and techniques which could be valuable in future research to study the role of AMF under organic management. The study has also highlighted a number of key areas in which further research is needed in order to harness AMF to improve sustainability and productivity of organic and other agricultural systems. In particular, there is a need to determine the extent to which AMF diversity varies between organic and conventional management, the rate and mechanisms by which AMF diversity increases following conversion to organic production, the relationships between AMF diversity and crop nutrition/ pathogen control, and the soil factors controlling the effectiveness of AMF inoculum

Benchmark experiments with global climate models applicable to extra-solar gas giant planets in the shallow atmosphere approximation

The growing field of exoplanetary atmospheric modelling has seen little work on standardised benchmark tests for its models, limiting understanding of the dependence of results on specific models and conditions. With spatially resolved observations as yet difficult to obtain, such a test is invaluable. Although an intercomparison test for models of tidally locked gas giant planets has previously been suggested and carried out, the data provided were limited in terms of comparability. Here, the shallow PUMA model is subjected to such a test, and detailed statistics produced to facilitate comparison, with both time means and the associated standard deviations displayed, removing the time dependence and providing a measure of the variability. Model runs have been analysed to determine the variability between resolutions, and the effect of resolution on the energy spectra studied. Superrotation is a robust and reproducible feature at all resolutions

Anisotropic magnetoresistance contribution to measured domain wall resistances of in-plane magnetised (Ga,Mn)As

We demonstrate the presence of an important anisotropic magnetoresistance contribution to the domain wall resistance recently measured in thin-film (Ga,Mn)As with in-plane magnetic anisotropy. Analytic results for simple domain wall orientations supplemented by numerical results for more general cases show this previously omitted contribution can largely explain the observed negative resistance.Comment: 4 pages; submitted to Phys Rev

Measurement of 3-Flavour Neutrino Oscillation Parameters in the NOvA Experiment

NOvA is a long-baseline neutrino oscillation experiment consisting of two functionally identical tracking calorimeters, a Near and Far Detector, that measure neutrino interactions induced by the Fermi National Accelerator Laboratory’s NuMI beam at baselines of 1 km and 810 km, respectively. The NuMI beam can be configured to produce either a primary νµ neutrino or ¯νµ anti-neutrino beam. Neutrino oscillations are observed and measured by the analysis of νµ + ¯νµ disappearance and νe + ¯νe appearance in the beam, comparing the neutrino energy spectra in the Near and Far detectors means that neutrino oscillation parameters sin2 θ23, |∆m2 32|, and δCP can be constrained. This thesis presents the 2018 NOvA νµ+¯νµ disappearance, νe+¯νe appearance, and combined analyses using both neutrino and anti-neutrino data, where oscillation fits have been performed, where possible, on an event-by-event basis rather than on a bin-by-bin basis as has conventionally been used in NOvA oscillation analyses. This allows for better precision in applying both neutrino oscillation probabilities and systematic uncertainties. Furthermore, oscillation analyses for the disappearance, appearance, and combined channels are presented using an unbinned likelihood fit and compared with the equivalent binned χ 2 likelihood fit used in the standard analysis. The 14 ktonne detector equivalent beam exposures used for this thesis are 8.85 × 1020 and 6.91 × 1020 protons on target for neutrino and antineutrino data respectively, corresponding to 5 years of NOvA data taking. A combined νµ + ¯νµ disappearance and νe + ¯νe appearance fit to the Far Detector data, assuming normal mass ordering and using the event-by-event oscillation and unbinned fitting methodologies, produces oscillation parameter constraints of ∆m2 32 = (2.50+0.08 −0.06) × 10−3 eV2 , sin2 θ23 = 0.59+0.02 −0.04, and δCP = 0.72+0.5 −0.9 π

Dense Gas, Massive Stars, and Ionising Radiation: Simulating Stellar Feedback in Spiral-Arm Molecular Clouds

Star formation (SF) has been continuous since the Universe was 200 million years old. It occurs in the interstellar medium (ISM) – the gas and dust between stars within galaxies. The majority of SF occurs inside giant molecular clouds (GMCs) – the most massive agglomerations of dense gas within the ISM – typically the stars form in clusters. Initially the SF is governed solely by a GMC’s morphology, but, as stars form, the energy and momentum they inject into their surroundings – stellar feedback – affects ongoing star formation within the GMC. The effects of this feedback not only help to break up the cloud, but affect the wider ISM, and hence influence both neighbouring GMC evolution and future GMC formation. This thesis explores how two forms of stellar feedback – photoionisation and supernova (SN) – affect Milky Way-like spiral arm regions through the use of nu- merical hydrodynamic simulations. The numerical initial conditions are created by extracting a 500 pc2 region from simulations of whole galaxies. This means the simulations begin with a ‘realistic’ arrangement of neighbouring GMCs. The ISM is affected by the warm (104 K) HII regions that form and expand around massive photoionising stars and the hot (106 K) SNe ejecta that are emitted from the same stars at the end of their lifetimes. In these simulations photoionisation breaks GMCs and the denser clumps in their substructure up into a larger number of objects while, at the same time, increasing the total mass of dense ISM. This results in more rapid, and partially displaced, SF when compared with simulations without stellar feedback. The main cause of these effects is the compression of dense, but non-star forming, gas from multiple sides by HII regions. SNe have little effect on SF on spiral arm scales. However, SNe are able to heat large regions of the ISM to high temperatures, but only if the gas has already been exposed to photoionising feedback