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What’s in a Grass Mixture?

20 July 2023

This article is produced as a part of the FAS Crops & Soils Bulletin. Subscribe now to receive the full report in your inbox monthly.

Unlike cereals, grass swards are established from a range of species and varieties. In any one bag from the seed merchant there may be four or five grass species with four or five varieties of each. In addition there may be two or three white clover varieties.

The make up of the seed mixture is determined by its planned use ie grazing, silage, hay, cover crop, biodiversity rich; and the planned duration of  the sward. This may range from a one year green cover crop, through a three year ley, to over 10 years in permanent pasture.

So which species are most suited to what?

Perennial ryegrass is the principal grass used for livestock production and has been cultivated since the 17th century. It is popular because of its palatability to livestock, perennial nature and high productivity. Through breeding programmes since the 1940s its yielding ability has increased year on year. Its highest productivity is in the two to three years after sowing but will continue its productivity for a number of years if well maintained. A major attribute of Perennial ryegrass is its large growth response to increasing rates nitrogen fertiliser.

The varieties of Perennial ryegrass used within a seed mix are dependent on flowering date. The period of highest quality herbage production is determined by flowering date. if the grass is to be used principally for silage then it is desirable to use varieties with close flowering dates so that productivity is maximised around the date of cutting.

If the grass is cut significantly later than flowering date then the yield is greater, but quality in terms of carbohydrate and protein content will diminish.

However, for season-long grazing a greater range of flowering dates is required to maximise good quality growth over a longer period. In Scotland flowering dates run from the last week of May up until the first week of July. In grazing situations the grass won’t reach actual flower, but its growth habit is still determined by the variety’s normal time of flowering.

Greater productivity is achieved by using tetraploid Perennial ryegrass varieties, although persistency is lower than diploids. One particular advantage of tetraploid varieties is that they have greater cold tolerance than diploids.

Italian ryegrass is more productive than Perennial ryegrass but over a shorter period. Indeed significant productivity is only likely to last for two years. It is particularly productive early in the season and for that reason is often included in silage mixtures to obtain a highly productive first cut at the middle or end of June.  It was first introduced for agricultural production in the 1830s.

Hybrid ryegrass has been developed to take advantage of the high early season productivity of Italian with the longer duration of Perennial ryegrasses.

There are a number of grasses which may also be included to hedge against particular soil or climatic conditions where the ryegrasses may be at a disadvantage. They are not so productive, and less responsive to N fertiliser, but can provide herbage in poorer soils :-

Timothy is a species which can provide good yields over a number of years and is highly tolerant of wet soil conditions. Moreover it provides early spring growth. Indeed there can be significant growth during milder winter conditions. However, it is slow to establish. It was first introduced to Britain in the early 18th century, and named after Timothy Hanson who had cultivated the species in North America.

Cocksfoot grows well in drier conditions and is used in mixtures for drier soils. It is native to Britain but seed was also introduced from North America in the 18th century. The herbage produced is fibrous and tends to be low in quality.

These two species along with others such as Meadow fescue, Crested dogstail, Smooth Stalked Meadow Grass, Red fescue and Common bent are much less productive than the ryegrasses and don’t respond to nitrogen application to the same extent. However, they are more commonly being used in multi species swards where their more modest growth allows broadleaved forb and herb species to establish. The resultant pasture can be grazed or used for hay and,   at the same time, provide biodiversity.

White clover is included in most seed mixtures in order to reduce the need for nitrogen fertiliser and increase the protein concentration in the sward herbage.  The atmospheric nitrogen fixed by the clover raises the soil nitrogen levels, which in turn provide a greater nitrogen supply for the grass. Therefore the benefit to grass growth from the clover is a cumulative effect and is only likely to be obtained after the first year of establishment.

If the sward is to be primarily grazed then small leaved varieties should be used. They have greater tolerance of close grazing.  Larger leaved varieties are less tolerant of grazing, but are more suitable for silage or hay and are more able to compete with the growing grass.

Because of rising nitrogen fertiliser prices grass/clover swards are being used more frequently as a green manure break for cereal crops. The annual amount of nitrogen fixed by the clover is likely to be in the range of 80 to100 kg/ha of N.

Whatever the end use of the grass or clover it is important to check that it is listed in Recommended Grass and Clover Varieties published by SRDP, Farm Advisory Service. Only varieties that perform well under Scottish conditions achieve listed status.

Further detail on grass and clover variety choice recommended for use in Scotland is available here:

David Lawson, SRUC

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