Measuring grass may seem like an obvious thing to do but it’s really important. AHDB Beef & Lamb has produced a sward stick and some really useful tools for producers so they can use the information gathered.
The sward stick uses sward heights developed decades ago that provide a balance between what is good for animals and for the grass plant. The heights are higher for cattle due to the fact that they need to wrap their tongues around the grass to feed, while sheep nibble.
The height is measured to where the highest leaf touches the stick – do not straighten it. Ideally 40 leaf top measurements should be taken across the field to get an average. A standard sward height can be used to ensure stocking rates are appropriate for set stocked systems and can help plan rotations.
See the charts below for the sward height targets for sheep and cattle.
Sward height targets – sheep
Sward height targets – cattle
These numbers can be used to monitor grass growth, e.g. if a field is measured once animals are removed and then again two weeks later, the difference divided by the number of days will be estimate of grass growth.
The movement from the standard sward stick to the compressed sward stick should only happen when the kg DM per ha figures are going to be used to estimate grass growth or to plan rotations based on supply and demand.
When grass is growing rapidly it should be measured every two weeks at a minimum, this can be decreased to monthly when it is growing slowly.
If using standard sward heights or kg DM/ha figures to plan rotations, the fields in front should be monitored to see what is happening. If fields are not recovering then the rotation can be slowed or adjusted accordingly. And if grass is growing quickly the rotations can be speeded up or fields removed from the rotation for silage.
If 50 per cent of the grazing fields are measured every month with the compressed sward stick and kg DM/ha figures produced, an average farm cover measurement can be calculated. This allows a long-term plan for grass and is important, especially when planning for all grass wintering. For example, the target farm cover for a mixed farm should not go above 2,200 kg DM/ha during late spring and it shouldn‘t go below 1,500 kg DM/ ha in late winter.
Targets for kg DM/ha
What can be done with the figures?
Using the compressed sward stick to get an estimate of kg DM/ha is important if producers are using intakes to predict grass demand. The key figures to know are the weight of the stock and their potential intakes – 2.5 per cent of bodyweight, dry stock – less than 2.5 per cent, high performing stock – more than 2.5 per cent.
For example, a 400 kg growing beef animal predicted to eat 3 per cent of bodyweight will be allocated 12 kg DM per ha, therefore a group of 30 will need 360 kg DM per day. This information plus the area available, the total kg DM per ha measured and target residue (the amount left) can be used to plan stocking rates.
Email the BRP team to request the sward stick