Managing grass surpluses

Grass growth rates were below average for mid-May in many parts of Northern Ireland, however high temperatures in late May caused a surge in growth across the country. It is vital to regularly monitor grass supply in these growing conditions as a short burst of growth at this stage of the season can create a surplus of grass and a rapid decline in sward quality if the surplus is not managed correctly.

To manage surpluses effectively it is essential that they firstly be identified, and this can only be done by assessing grass covers regularly. Targets for most herds at this time of the year should be an 18-21 day rotation, with cows grazing swards with grass covers of between 3,000 and 3,300 kg dry matter per hectare (third of the way up a wellington boot). The best way to identify potential grass surpluses across the grazing area is by producing a ‘grass wedge.’ For example, in the grass wedge shown (Figure 1) it is clear that the grass covers in the two fields that are due for grazing next (black bars) have increased above target. These fields should be removed immediately from the grazing rotation, and this decision can be made confidently as the grass covers on the next two fields (grey bars) are close to the pre-grazing target. If your cows are grazing swards that have covers that are higher than 3,500 kg DM/ha, you will be forced to slow down the rotation, and this will lead to further grass surpluses. To keep rotation length and grass covers on target, skip the fields with the heaviest covers or ‘surplus’ covers, as grass utilisation with these is likely to be poor.

The options to deal with this surplus grass include harvesting the grass for either clamp or round bale silage, or bringing additional stock onto the grazing platform to graze the surplus grass. Round baling has the advantage of being much more flexible compared to traditional silage harvesting, as smaller areas can be taken out of the rotation when necessary. Location of the fields, weather conditions and timing are all factors to consider when deciding on the most appropriate action.

Figure 1. A ‘grass wedge’ for a farm with surplus grass within the grazing area

Once a surplus is identified it is essential to react quickly.  Ideally these paddocks should be cut immediately so as to maintain their position within the grazing cycle, and allow them to be grazed next time round. If harvested immediately, when the base of the sward is still green, grass regrowth will start almost immediately. However, if fields with surplus grass are allowed to ‘bulk up’ before they are cut, they will fall out of ‘sequence’ within the grazing cycle, and recovery will be much slower following the harvest of a heavier crop of grass. Thus a surplus can easily result in a deficit if not dealt with immediately. Alternatively, if dry stock are used to remove the surplus, care must be taken that they do not take too long, as this will also slow grass regrowth and limit supply for the next rotation.

On most farms removing a surplus is likely to require contractor assistance, and as such, will incur a cost. However, failing to remove excess grass will lead to poorer sward quality, lower grass growth, lower animal performance and a poorer response to applied nitrogen fertiliser throughout the remainder of the 2010 grazing season. Consideration must also be given to the appropriate storage of the resulting bales/clamped silage, and the disposal of waste plastic. However, this surplus grass, if cut at a young leafy stage, represents a high quality feed that can be fed back to the herd as a buffer feed during periods of unsettled weather or during a grass deficit.

Only by assessing the grass supply on your grazing platform and checking that rotation length and pre/post grazing sward covers are on target, will surpluses be identified. Once identified, surpluses should be removed quickly to ensure that grass supply is not compromised for the next rotation. Although removing surpluses will incur a cost in most cases, this will be a small price to pay to ensure a continuing supply of quality grass for the dairy herd throughout the grazing season.

To maintain sward quality within the grazing area, grass surpluses must be identified and removed quickly