The Ag Climatise policy document highlighted the need to decrease chemical nitrogen (N) fertiliser use on Irish dairy farms, and thereby reduce the environmental impact of dairy farming – both in terms of greenhouse gas (GHG) emissions and water quality. Five key practices can be used to reduce N fertiliser use on all farms:

1 Replace N fertiliser in early spring on up to two-thirds of the milking platform by using low-emission slurry spreading (LESS) equipment.

2 Measure farm cover weekly to see how much grass is on the farm. Use this information with the grass growth prediction available from the Moorepark St Gilles (MoSt) grass growth model to predict grass supply for the week ahead. If growth is surplus to demand, N fertiliser application could be reduced.

3 Soil fertility – ensure that soil pH is >6.2 and both P and K are index 3. Nitrogen use efficiency is greater in soils with optimum fertility.

4 Are you making baled silage in every rotation, particularly in July and August? If you are, then grass growth exceeds demand and N fertiliser application can be reduced.

5 Swards dominated by perennial ryegrass are more productive and have greater N use efficiency. Consider reseeding poorly-performing swards.

Teagasc research indicates that N fertiliser application can be reduced in grass-white clover swards with clover content =20%, while maintaining herbage production, and increasing animal production (Table 1).

Establishing white clover requires a combination of reseeding and over-sowing.

A full reseed is the most reliable method of establishment as it gives white clover a better chance to establish and provides the best opportunity for weed control.

Over-sowing is a simple and low-cost method, but success is dependent on weather conditions around the time of sowing, soil moisture, post-sowing grazing management and competition from the existing sward. Some key points when using both methods include:

  • Ensure optimum soil fertility (ie pH > 6.3, index 3 for P and K).
  • Reseed/oversow in spring/early summer.
  • Graze swards at a low pre-grazing herbage mass (<1,100 kg DM/ha) and graze tight (=4cm) for at least the first three grazings post-sowing/over-sowing.
  • Avoid over sowing old swards with a low perennial ryegrass content – a full reseed is best in these conditions.