Abstract
Environmental and economic considerations are currently driving a resurgence in interest in fertility-building crops. A literature review indicated red clover (Trifolium pratense) has the capacity to provide a large amount of nitrogen to subsequent crops, as well as a suite of ecosystem services. Available red clover varieties can be split into categories of early/late flowering, diploid/tetraploid and erect/prostrate. Many viable management and cultivation practices can be applied. A field trial focused on arable farming of six red clover varieties was carried out on clay soil in Cirencester UK from 2015-2017. Fertility-building was documented using dry matter (DM) and nitrogen (N) yields, extent of nodulation, soil mineral nitrogen (SMN) accumulation and morphological variation over two years. Treatments of one and two cuts were applied and all cuttings were removed. The experimental design in the fertility-building phase was two factorial (red clover variety and number of cuts) in completely randomized blocks. Soil fertility was then assessed using wheat (Triticum aestivum) and mustard (Sinapsis alba) as bioassay crops. The experimental design in the bioassay phase was a split-plot factorial design in completely randomized blocks with preceding variety and number of cuts as whole plot treatments and inclusion or omittance of herbicide as splits. The central hypothesis was that red clover variety selection, cutting management and use of herbicide significantly effect capacity to build soil-fertility.SMN accumulation was high in the first year, in which DM and N yields were low, but low in the second, in which DM and N yields were high. One cut and varieties Astred and Ruby were less susceptible to winter leaching of SMN. The early diploids Ruby and Astred were more resistant to clover rot (Sclerotina sp) and powdery mildew (Erysiphe sp) than other varieties and tetraploidy was not predictive of disease resistance. The late variety Amos provided most of its yield at the first cut and the early varieties the bulk of theirs at the second, but the intermediate variety Maro gave high yields at both cuts in both years. Morphology was highly variable, stem hair density may have effected disease resistance and mineralization rates and was correlated with growth habit. Nodulation and root biomass was assessed. All varieties were shown to be nodulated but Ruby had significantly fewer nodules than all other varieties and Ruby and Astred had significantly smaller root systems than all other varieties.
Herbicide (glyphosate) application and omission was included as a treatment in bioassay cultivation. The non-herbicide (NH) treatment failed to adequately terminate the clover crop and volunteering became problematic and hindered crop production in the herbicide (H) treatment. Number of cuts and variety selection were non-significant in almost all cases in wheat production, but this may have been caused by the increased variability incurred by the clover volunteering. Variety Ruby and 1 cut treatment produced higher mustard DM and N yields but only in the H treatment. The interaction of variety and cut was seen most prominently in Ruby, in which one cut was consistently higher than two. Herbicide application following red clover cultivation did significantly effect subsequent crop performance, but this was likely only due to the elimination of volunteers. One cut yielded significantly more total mustard DM and N than two cut, whilst Ruby yielded significantly more total mustard DM and N than all other varieties.
| Date of Award | 2017 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Nicola Cannon (Supervisor), John S. Conway (Supervisor) & John Dooley (Supervisor) |