Grass measuring has become very popular on Irish dairy farms as a tool to ensure that dairy cows are receiving the best quality grass possible.
The weather and grass growth over the last number of weeks in most parts of the country has been exceptional, considering the conditions experienced earlier in the spring and into May.
With the weather expected to continue to hold, the issue of grass growth slowing down due to drought conditions is now becoming a real possibility.
Most farms have by now, completed first-cut silage, and some have even managed to remove surplus paddocks as bale silage.
Maintain average farm cover
It is important to maintain an average farm cover of above 550kg/DM (dry matter)/ha, with grazing of some paddocks closed for second-cut silage required if the weather continues and the average farm cover drops below this figure.
If this option is taken it is important to ensure that enough silage is harvested later in the year, for feeding over the winter period.
If you are in the position where you have leftover bales from last year, these could also be used to slow down or lengthen the rotation.
Other options include increasing concentrate supplementation – which can be expensive – but these options should only be taken if grass growth continues to slow and rain does not come.
The only way you will know that these management decisions need to be made is if you are measuring your grass regularly.
Grass measuring
To avoid a scenario where you run out of grass, it is important to ensure that you are measuring grass growth on your farm.
Teagasc recommends walking the farm 30- 40 times in the year to get the most out of grass measuring.
During high growth periods, a farm walk should be completed every five days, or up to twice per week.
There are several methods that can be used when you are measuring grass on your farm.
Plate meter
Plate meters are used to measure the quantity of grass DM in a sward, it does this by measuring the height of the sward (not kg of DM).
Because of this, the operators need to be consistent, with adverse conditions leading to inaccurate measurements.
Gateways, troughs, fence lines and areas that have been damaged should be avoided; ensure that you are also measuring a fair representation of the paddock.
It is recommended that operators should walk in a ”W” or ”X” shape when measuring swards.
Once you have obtained your measurement you can then subtract the post grazing height/residual you are aiming to achieve (3.5cm – 4cm).
The figure which is left should then be multiplied by 250 for a cattle sward (this figure is 300 for sheep).
For example: 6cm (total height) – 3.5cm (desired residual) x 300kg/DM/cm = 750kg DM/ha.
Cut and weigh
The cut and weigh method is also used to obtain the quantity of grass DM in a sward.
This method uses a quadrant (0.5m x 0.5m), a plastic bag, a scale and shears to cut the grass.
Similarly to the plate meter method areas around gateways, troughs, fence lines and damaged areas should be avoided to obtain the most accurate measurement.
One important thing to note is when using the cut and weigh method, once you have placed the quadrant in your selected area – you should knock-off excess water on the sward.
To calculate the DM of the sward using the cut and weigh method, first cut the sward in the quadrant to the desired residual. This grass is then collected and placed into a plastic bag.
To then calculate the amount of grass present, weigh the grass sample and minus the bag weight.
This is then multiplied by DM% of grass (varies from day to day and location of farm).
The figure obtained is then multiplied by 4,000 (the number of quadrats in a hectare) with this figure then multiplied by the number of hectares in the paddock.
For example: 0.08kg (grass weight) x 0.18 (18% DM) x 40,000 (the number of quadrats/ha) = 576DM/ha x 1.2ha (paddock size) = 691.2 DM/ha in paddock.
