At this time of year many people will be thinking of reseeding. They will be considering which field to reseed, which varieties to use and what type of mix.

When deciding which field to reseed it is always best to make an inspection of the grasses in the existing sward. Swards that contain lower proportions of perennial will inevitably have much lower yields. Yorkshire fog will yield about 20% less than perennial ryegrass with creeping bent yielding only half that of perennial at first cut. This has a significant impact on production and takes no account of the loss in quality (D-Value). If we take perennial ryegrass at a D-Value of 73, Yorkshire fog will be 68 and creeping bent 58.

Response of the various weed grasses to nitrogen is also equally poor. The fields with the lowest proportion of perennial should therefore be given priority in a reseeding programme. It is estimated that the costs of reseeding can be in excess of £200.00 per acre, but this will be more than recouped in the first year of the new sward by extra milk or LWG.

When considering what mixture to purchase it is important to think about the end use  In the short term,  hybrids and Italian are often effective, as they give extra yields over a shorter period of time. These species are popular in rejuvenation mixtures where a short term boost is required to keep a worn out sward going for another two to three years.

If the grass is to be used for grazing, silage or both the most commonly used species in Northern Ireland is perennial ryegrass, and there are a range of varieties available. The main split is heading date and polyploidy (diploid v tetraploid). Diploid varieties are the main component of mixtures used locally. They give quality, high yields and good density and will last for many years if managed correctly. Tetraploid perennial varieties are more upright and open growing. They tend to have higher sugar content - although this is often equalled by High Sugar Grass diploid varieties. Due to their open character Tetraploids should, at most, only represent 35-40% of a mixture.

The quality of chosen varieties is also very important as this has a significant impact on output. The difference in D-Value between the top and bottom varieties on the local recommended list is four units. (AberWolf 77 v Boyne 73, others at this level). This can result in between 1-2 litres extra milk per day depending on dry matter intakes.

Further information can be found on the local AFBI Variety Recommended List. This covers perennials, hybrid and Italian ryegrasses, timothy and clover. Another good source of information is the Pasture Profit Index developed by researchers in Teagasc, Moorepark which ranks grass varieties on traits of economic importance. Choosing varieties recommended by either of these credible sources is a must when looking to reseed.

The above described measures are very important, but their benefits will be undermined if proper attention is not paid to soil structure, fertility and weed problems in the old sward. These need to be rectified in advance to ensure a long term productive sward

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