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Title: Strategies to optimise white clover (Trifolium repens L.) content in grass white clover swards to consistently replace inorganic nitrogen in grazing systems
Author: Enríquez Hidalgo, Daniel
ISNI:       0000 0004 5369 6670
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2014
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Mixed perennial ryegrass white clover (WC) swards (GWc) provide a sustainable nitrogen source for grazing systems and improve herbage quality, but sward WC content and nitrogen fixation can be suppressed by fertiliser nitrogen application. Differences in structural characteristics between the species can affect dairy cow digestion process and performance. In this thesis aspects related to the effect of nitrogen fertilizer application on intensively grazed GWc and grass only swards (GO) and the effects of grazing both swards on dairy cow feeding behaviour, herbage depletion rate, rumen function, methane emissions and milk production were investigated. Regardless of nitrogen rate applied (rates up to 240 kg N/ha we applied), WC inclusion into grass wards increased herbage production, quality and nitrogen yield. These effects declined as nitrogen rate increased, due to a reduction in WC content and fixation, but less so below 120 kg N/ha. When cows rotationally grazed either a GO or GWc, both swards had similar herbage production, but GWc had slightly greater herbage quality. Sward WC contents were approximately 20%, yet cows had similar milk production and composition. Cow daily and per unit of output methane emissions were similar, but cows grazing GWc had lower methane emissions per unit of feed intake. Although cows in both groups grazed for similar times, the cows on GWc spent less time ruminating, especially in summer and autumn. Rumen volatile fatty acids were similar on both swards but isoacids and D-lactic acid percentages, ammonia content and rumen pH were higher in autumn for cows grazing GWc. Similar sward depletion rates were observed. Overall, WC related effects were more likely to occur from June onwards, when sward WC content was greatest.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available