Heads-up on variety choice
When choosing a grass variety mix, the objective must be to combine three to four grasses of differing traits to obtain good seasonal DM production (spring/autumn) and high sward density.
In choosing a silage mix, high overall DM production and density will be the underlining traits. Silage mixes should not be used where swards are used mainly for grazing. When considering heading date it is better to use a small range in heading dates (e.g. seven to 10 days), a wider range in heading dates used will be reflected in a longer heading period. All varieties will head but some have a greater tendency to head and continue to re-head, which is not desirable in a grazing sward.
There are two recommended lists available in Ireland, from DAFF (www.agriculture.gov.ie) and AFBI (www.darni.gov.uk). See the table below for varieties documented in the DAFF 2010 recommended list. No single grass variety has all the desired agronomic traits.
Teagasc currently have a number of studies investigating the merits of mixtures and monocultures. Some varieties have better characteristics than others. However, within the first 11 months of sowing the cultivar hierarchy will be established. There is little to be gained from sowing less than 3kg of individual varieties within seed mixes. Within a grass seed mix, varieties with different traits are combined to address this. With fertiliser prices volatile, clover is emerging as a venue of reducing nitrogen fertiliser input mid-season. Clover should be incorporated into grazing swards and left out of swards designed for intensive silage harvests. At low stocking rates clover has a major role to play.
Grass cultivars which have been tested on recommended lists (DAFF or AFBI) should only be used in mixes. The following guidelines should be used when choosing a seed mixture:
- Spring and autumn production, mid-season DM production is consistent across varieties, a more flattened grass supply is advantageous (more grass in spring and autumn and less surplus mid-season).
- Sward quality -- consistent with the mean value.
- Choose varieties with a narrow range in heading dates.
- Adequate ground cover -- this is a major parameter for wetter soils.
Varieties for grazing
Grazing mixes should be dominated by late heading diploids but should also have a proportion of tetraploid varieties. Tetraploid varieties have the highest DM yields and large leaf area, even though their tiller density is lower than diploids. In general terms they have an average 1t DM/ha higher yield than diploids.
Tetraploids should be combined with high ground cover, highly digestible diploids. There are some excellent late heading tetraploids available with high early spring/autumn growth.