Grassland research at Moorepark

Published 2 August 13

With rising fertiliser prices and N applications being restricted in Ireland under the Nitrates Directive, there has been some resurgence of interest in the role of white clover in dairy pastures. Poor clover persistency in swards receiving high rates of fertiliser N is one of the reasons why clover is not more widely used.  However, researchers from Moorepark estimate that good grazing management (4 – 4.5cm residuals) and selection of small-medium sized clovers are likely to benefit clover persistence.

In light of this, two studies were undertaken at Moorepark to examine the potential of white clover in dairy grazing pastures.

Study 1: Including white clover in fertilised grass swards

A three-year plot experiment was undertaken to assess the performance of grass-clover swards (approximately 27% clover content). Grass-only swards had different levels of fertiliser application: 0, 60, 120, 180 and 240kg N/ha. Over the course of the three years , plots were grazed 29 times and herbage mass and clover content measured prior to each grazing.

Key Results

  • Over the course of the three years , herbage production was on average 2t DM/ha greater from the grass-clover plots than the grass only plots, regardless of fertiliser rate (Figure 1).
  • At lower levels of fertiliser N input, the increase in herbage production was greater with clover inclusion. For example, at 60kg N/ha there was approximately 3t DM/ha more herbage on the grass-clover plots compared to the grass-only plots. However, even at high N inputs (240kg N/ha) DM yield was still 1.1t DM/ha greater with the inclusion of clover in the sward.

Figure 1 Annual Herbage Production 

Figure 1: Average annual herbage production (kg DM/ha) on grass only and grass clover swards receiving 0, 60, 120, 180 or 240kg N/ha/annum (from Hennessy et al. 2013).

Study 2: Influence of clover inclusion in grass swards on milk and herbage production

Researchers at Moorepark also compared milk and herbage production from a grass only sward and a grass-clover sward over two grazing seasons. The grass-only sward comprised of a 50:50 diploid-tetraploid mix (two varieties) sown at 37kg/ha, while the grass-clover sward consisted of the same grass varieties sown at 37kg/ha plus 5kg/ha of white clover. Both swards received 250kg N fertiliser per annum.

Key Results

  • Herbage production was greater from the grass-clover sward (14.7t DM/ha) compared with the grass-only sward (13.6t DM/ha) in the second year; there was no difference in herbage production between swards in the first year.
  • In addition, there was little difference in milk production per cow during the first year. However, in the second year milk production was on average 1.6 litres/cow/day higher (17.0 vs. 18.6) from the grass clover sward than the grass-only sward.
  • This increase was evident from mid-June onwards as clover content increased in the sward and digestibility of the grass declined with heading.
  • The lack of a difference between treatments in the first year may have been due to a lower clover content (18%) compared with year 2 (23%).