The use of clover in grassland to replace nitrogen (N) can substantially lower greenhouse gas and ammonia emissions from pasture-based production.

Averaged over 12 years at Solohead Research Farm, we have found similar pasture production from grass-clover swards receiving of 95kg/ha of N applied in spring compared with swards receiving 245kg/ha applied across the growing season.

Clover has a higher temperature requirement for growth than grass and therefore we apply N in February, March and April to compensate for this.

Clover is a shallow-rooted species

Most of the N fixation by clover takes place during the summer and autumn and we have found little or no benefit from applying N to well-managed grass-clover swards from May onwards.

Stopping applying N can mean that P and K can be neglected during the summer and autumn.

James Humphreys and Daniel Barrett at Solohead.

Clover is a shallow-rooted species with around 15% of the root density of perennial ryegrass, making it much less competitive for soil nutrients.

Regular applications of a P and K compound fertiliser throughout the growing season are necessary for high levels of clover productivity and biological N fixation.

This can be achieved by applying an N-containing compound fertiliser in spring, such as 24:2.5:10 or 18:6:12.

Sulphur should be included in these compounds in sulphur-deficient areas, particularly in April.

Small, regular applications of a non-N compound fertiliser are beneficial from May onwards; for example, a half bag of 0:7:30 per acre after every second grazing is very cost-effective.

Nitrogen fixation is a biological process that is regulated by soil pH (lime status).

We aim to keep soil pH levels at around 6.5 at Solohead

Optimum soil pH for biological N fixation is in the range 6.5 to 7.0, which is higher than is typically recommended for grassland (6.2 to 6.5).

We aim to keep soil pH levels at around 6.5 at Solohead. This is achieved by regular soil testing and application of ground limestone.

It is important to be aware that soil pH levels of greater than 6.2 are not recommended for high-molybdenum soils.

This does not mean that clover should not be grown on such soils; it means being careful about applying lime and ensuring livestock are adequately supplemented with copper.

Your soil test results should indicate if you are in a high-molybdenum area.