Incorporating white clover into intensive dairy production systems has the potential to increase their sustainability through increased milk output and reduced nitrogen (N) input. To support intensive stocking rates (<2.75 cows/ha) some inorganic N will still be required to support herbage production, particularly in the spring. However, sward white clover content, and hence N fixation has been shown to be suppressed by applications of inorganic N. In this thesis, the effects of varying N application rates on grass-clover swards as well as the effect of those swards on overall herbage production, dairy cow production, dairy cow rumen function and overall farm gate N balance were investigated. White clover inclusion increased herbage production at fertiliser application rates of up to and including 180 kg N/ha/year in the plotbased study described in chapter 4 of this thesis. The results from this demonstrated the negative relationship between increasing N fertiliser application rates and sward white clover content with sward white clover content decreasing as N application rate increased from 0 kg N/ha/year to 240 kg N/ha/year. Clover inclusion was found to increase milk solids production per cow and per hectare. There was no difference in cumulative herbage production between grass-clover swards receiving 150 kg N/ha/year and grass-only and grass-white clover swards receiving 250 kg N/ha/year. This indicated that the N fixing ability of the grass-white clover swards was supporting sward productivity at the lower N regime. Clover inclusion in the diet significantly altered the rumen function of the dairy cows with increased rumen ammonia and total VFA concentrations in the rumen of the grass-clover fed cows over those of the grass only and total mixed ration (TMR) fed cows.
The farm gate N balance outlined the environmental benefits of white clover inclusion in grazed swards resulting in improved overall N use efficiency (NUE) and reduced N surpluses in the grass-white clover swards compared to grass-only swards. Overall, this thesis provides evidence that white clover can be successfully incorporated into intensive dairy production systems with benefits in terms of farm output and improved on-farm sustainability, though with both positive and potentially some negative environmental implications. The overall outcome of the project was to provide evidence that it is possible to maintain and benefit from clover inclusion in grass swards that are intensively managed at high N fertilizer rates, if grazing management is of a high standard with good control of pre- and post-grazing heights. The project also identified some knowledge gaps, particularly around achieving good spring sward productivity, differing environmental implications and longer-term stability of the clover system, that provide clear objectives for future research in this area.
|Date of Award||Dec 2020|
- Queen's University Belfast
|Sponsors||Teagasc Walsh Scholarship|
|Supervisor||Trevor Gilliland (Supervisor) & Christopher Elliott (Supervisor)|
- White clover
- milk production
- nitrogen fixation
- volatile fatty acids
- rumen function