ARCHIVE: Fertiliser Manual (RB209)

Grazing of Grass/Clover Swards – Nitrogen


Generally little fertiliser nitrogen is needed on swards with an appreciable clover content. On average, a good grass/clover sward will give annual dry matter yields equivalent to that produced from about 180 kg N/ha applied to a pure grass sward. However newly sown grass clover leys may yield even more nitrogen depending on the percentage of clover. It is often difficult to decide how much nitrogen will be supplied from grass/clover as the clover content can be very changeable from year to year and within a given season. The following photographs indicate how to estimate clover content and assess nitrogen supply.

Assessing nitrogen supply from clover

Percentage ground cover from clover Potential nitrogen supply
180 kg/ha
240 kg/ha
300 kg/ha

 

These figures should be used as rough guides only as full clover development does not normally take place until late spring onwards. For this reason it is only possible to estimate nitrogen supply from clover retrospectively.

Applications of fertiliser nitrogen to purpose-sown grass/clover swards should be made with caution as any form of mineral nitrogen inhibits nitrogen fixation from the atmosphere by rhizobia in the clover nodules. However some nitrogen may need to be applied to grass/clover swards to encourage early spring or late autumn growth.

  • Apply up to 50 kg N/ha in mid February to early March if early grass growth is required
  • Apply up to 50 kg N/ha in late August to early September if autumn grass is required

Unnecessary use of nitrogen can significantly reduce the percentage of nitrogenfixing clover in the sward. Clover is particularly sensitive to nitrogen application during establishment. No nitrogen should be used during this period. However, some modern varieties of clover respond to fertiliser nitrogen and are grown in high yields as a source of protein. At high levels of fertiliser N, these clovers will fix little extra nitrogen.

ADLib logo Content provided by the Agricultural Document Library
© University of Hertfordshire, 2011