19 April 1996

Why miss benefits of buffer


30 cattle x 300kg x 12kg of nitrogen

100kg liveweight

= 1080kg of N a year

BUFFER grazing is a cheap, simple and low risk way to improve production of both grass and cattle, says Dr Basil Lowman in Signets April issue of Beef and Sheep Notes.

The cost is minimal – just the time to put up an electric fence. Theres no risk because normal grazing areas are still available if required, and the benefits are twofold, he says. These are improved liveweight gains at grass and the chance to produce more home-grown forage for cattle next winter.

To buffer graze, normal numbers of stock are allocated to each grazing field. But before cattle are turned out a temporary electric fence is put up to reduce the size of the initial grazing area.

Target stocking weight at this stage should be about 3000kg of beef/ha (1214kg/acre). That is about 10 x 300kg store cattle/ha (4 x 300kg/acre) at turnout.

The height of the grass in the reduced grazing area is them monitored weekly, says Dr Lowman. When grazed grass meets targets, the clean grass behind the electric fence can be cut as a bonus crop. This is the excess grass which otherwise would have become stemmy and would have had to have been topped in late June.

However, when the grass height falls below target then the electric fence can be moved back to supplement the original grazing area, he says. When the grazing area falls below target, but the grass in the buffer area is too long to graze efficiently, it should be cut and grazed. Mow two or three swaths parallel to the electric fence, says Dr Lowman.

The fence is then moved, one swath at a time, and placed in the centre of the swath. This then acts as a feed barrier with the cattle quickly consuming the mown grass with little waste. It also leaves a uniform mown sward to secure a quick and uniform regrowth.

When the buffer area is conserved the electric fence is normally removed to provide the animals with a mini-aftermath before the main silage aftermaths become available.

Dr Lowman recognises that in many situations more fertiliser may have to be applied due to the higher initial stocking rate of buffer grazing area. But on a per animal basis fertiliser applications will often be reduced, he says. Target annual nitrogen application is 12kg N per 100kg of liveweight at turnout. For example, if a 5ha (2-acre) field normally carries 30 store cattle at an initial liveweight of 300kg then the annual nitrogen dressing to the field would be:

With the whole field normally grazed this would come to 216kg of N/ha. However, under a buffer grazing system, only 3ha (1.2 acres) would initially be grazed, and the 1080kg of nitrogen would be put on to the 3ha (1.2 acres) of grazing, equivalent to 360kg of N/ha. The buffer area of 2ha (0.8 acres) would need extra fertiliser, similar to that required for a silage crop.

The annual nitrogen application should be put on in five dressings, 25% at T-sum, 20% in mid-May, mid-June and mid-July, with the final 15% being applied in mid-August. Assuming the buffer area is conserved then the mid-July dressing would be applied across the entire 5ha (2 acres). &#42