Adjusting nitrogen applications on white clover swards
When sufficient quantities of white clover are present within grassland swards, farmers can tailor their nitrogen application programmes to make full use of the clover plant’s ability to fix nitrogen from the atmosphere – thus reducing chemical nitrogen usage and saving on costs.
However, for such benefits to be realised, an understanding of how much clover is present within the sward must be obtained by getting boots on the ground and assessing the quantity and distribution of white clover within your paddocks – April is the perfect month to do this.
Through years of studies, researchers in Teagasc’s Grassland Science Department in Moorepark have developed a blueprint for nitrogen applications for grass-white clover swards. The recommended rates of chemical nitrogen presented in table 1 below are based on a number of key principals.
Firstly, the recommended application rates for chemical nitrogen are dictated by the level of white clover present within the sward. Fertiliser strategies for swards containing 0%, 5%, 10%, 15% and 20% of white clover are outlined.
Secondly, across the clover content categories, spring nitrogen applications are similar to those on grass-only swards. This is to encourage growth and development and to ensure pasture is available to feed animals in the early spring.
As the grazing season progresses, however, and due to the seasonal growth habit of the clover plant, its ability to capture and provide nitrogen to the companion grasses contained within the sward increases as we move from May through to August - thus providing farmers with the opportunity to reduce chemical nitrogen applications, provided sufficient levels of white clover are present.
Table 1: Nitrogen fertiliser application strategy for a dairy farm on a range of sward clover contents assessed in April
| 1April average sward clover content | Feb | March | April |
May (2 rotations) |
June (2 rotations) |
July (2 rotations) | Aug | Sept | Total |
|---|---|---|---|---|---|---|---|---|---|
| Kg N/ha | |||||||||
| Grass sward | 24 | 36 | 20 | 32 | 28 | 28 | 21 | 23 | 212 |
| 25% | 20 | 35 | 20 | 20 | 20 | 20 | 20 | 20 | 175 |
| 310% | 20 | 35 | 20 | 15 | 15 | 10 | 15 | 20 | 150 |
| 415% | 20 | 35 | 20 | 15 | 10 | Soiled water6 | 10 | 20 | 130 |
| 520% | 20 | 35 | 20 | 15 | Soiled water | Soiled water | Soiled water | 15 | 105 |
1April average sward clover content (%) – Clover content determined in April ; 25% clover content in April = 10% average annual sward clover content; 310% clover content in April = 20% average annual sward clover content; 415% clover content in April = 25% average annual sward clover content; 520% clover content in April = 30% average annual sward clover content; 6SW – soiled water – soiled water should be applied when chemical N fertiliser is not spread.
As part of a recent Grass10 Clover Spring Farm Walk, Teagasc Dairy Specialist, James Dunne discussed the nutrient management of clover swards, highlighting the importance of assessing clover content before adjusting your nitrogen strategy throughout that summer period.
James noted that a clover content of 20% is desired and this will allow a significant reduction in chemical nitrogen to be achieved. However, he added: “Where we don’t have enough clover content, we need to maintain a certain level of nitrogen on those swards throughout that mid-season to ensure we have adequate levels of growth across the farm.”
James concluded with his key points, adding: “Score your paddocks now as we head through mid-April for clover content and then adjust your nitrogen strategy throughout that summer period based on those results.”
Watch the video below where James Dunne discusses the nutrient management of clover swards: