Saving good-quality silage

TO produce high quality and high DMD silage the grass crop should be cut when the seed heads start to emerge from the grass and before the grass has headed.

The reason for this is that the grass will get stalky after heading, with the stalk being much less digestible than the leaf of the grass plant the quality of the silage will decline.

The silage crop should be monitored throughout May and June in order that the optimum time to cut is identified.

This is a much safer method than cutting simply by calendar date.

Cutting after heading will reduce silage quality though the yield of silage may be increased. Silage DMD declines by 2.5-3.0 units every week in late May/ mid June.

Silage is simply pickled grass and is preserved by reducing the pH to acid levels.

This can be done by one of two methods – adding acid or increasing sugar content.

Sugar is needed to allow bugs to produce acid to preserve the grass. The sugar content can be increased by adding sugar in the form of molasses or by wilting.

Wilting is the preferred method (and the cheapest) with the target being to dry out the crop to 30% dry matter.

This has the physical effect of concentrating the sugars in less moisture - the sugar percentage will rise. To achieve this it will be necessary to wilt for 24 hours after cutting.

Research has indicated that there is no benefit in wilting for longer periods than 24 hours. Sugar content of grass is at its highest on bright sunny days with cool nights with the highest levels in the afternoons which is the ideal time to harvest.

Dew will have evaporated at this stage as well which will also help to raise dry matter levels. Tedding gives the best results if possible but opening the mower gates wider will also improve drying if this is not practical.

Nitrogen levels in the grass at the time of harvesting are also important but not as critical as sugar levels. The normal uptake of nitrogen fertiliser is 2 units/ day/acre so after applying 80 units of nitrogen/acre the crop can be cut after 40 days. If sugar levels are greater than 3% good preservation should be achieved. Both sugar and nitrogen levels can be assessed prior to cutting by your local Teagasc office.

The full process of preservation normally takes about 3 weeks. Round bales should be removed from the field immediately to prevent crow damage to the plastic. Also ensure effluent tanks are empty and to comply with nitrates regulations and Cross Compliance that new bales are not stored within 20 metres of watercourses.