Budgeting grass to meet demand

Information on grass growth, grass cover (supply) and stock grass intake (demand) may then be used to prepare a grass budget. A grass budget is simply a statement of grass supply and grass demand for the grazing stock.

Grass growth predictions such as those from GrassCheck can also be incorporated to allow you to forward budget grass supply. These variations in grass growth during the year require seasonal adjustment in stocking rates to ensure efficient grassland utilisation.

Grass budgeting is particularly useful over a two to three month period in spring and autumn when grass growth rates are increasing or declining quite rapidly, or at any period when stock demand is changing significantly.

Developing a grass wedge through rotationally grazing around a number of paddocks or fields is a useful grassland management system. The grass wedge illustrates the quantity of grass available across the grazing platform. Areas are rested between grazings, allowing grass time to regrow.

Those grazing areas with the longest rest periods can be assessed weekly to identify when in the rotation grass surpluses or deficits are likely to occur. A line drawn from the target pre-grazing cover to the target post-grazing cover gives a guide to surpluses and deficits.

Establishing a grass wedge by mid-April through turn-out from early March onwards will provide a breakdown of the grass available in each paddock on the farm. To build the wedge the fields due to be grazed first in the spring should be the first to be closed off in the autumn.

The three grass wedge charts below, (Figures 10 – 12) illustrate various scenarios on farm and outline the action that could be taken to correct the problem.

In the three scenarios paddock 1 is the first field to be grazed in the rotation at a pre-grazing target cover of 3,000 KG DM/ha and paddock 20 is the last field in the rotation with a post-grazing cover of 1,600 KG DM/ha.

In this scenario pre-grazing covers are too high and well above target as are post-grazing covers. Action is required immediately. In most instances grass surplus to grazing requirements should be conserved for silage, possibly as round bales.

Other stock such as replacement heifers could be introduced into the rotation to reduce covers. Higher covers are more difficult to graze off cleanly and will have a detrimental effect on spring grass growth due to the presence of dead material at the base of the sward.

In this scenario there is a serious deficit of grass on the farm.

Supplementation with concentrate or silage (possibly from round bales made during a grass surplus) will ensure dietary requirements are met. The grazing area could be increased by bringing in silage aftermath or removing some stock from the grazing platform.

In this scenario there is no surplus or deficit of grass and no action is required.

However it is important to continue to monitor grass covers regularly as changes can occur quickly due to rainfall or temperature fluctuations.