Grass measuring on Irish farms
What is measuring grass and why would anyone want to measure the grass growing in the field? Agricultural consultant and DoneDeal farming blogger Mark McConnell will discuss benefits of measuring grass and how it can save you money.
For us that are not of the farming disposition this will seem insane to be measuring grass.
Within the current economic climate we are faced with in the agricultural world measuring grass has never being more important and it could mean the difference between a farmer getting through this bad period and not surviving. In this feature we will discuss how to measure grass and the tools that are needed to do this.
One thing that we can do in Ireland is grow grass and the climate we have lends to the capacity to grow tons of grass.
Irish pastures have the potential to grow between 11 and 16 tonnes of DM per hectare per annum and grass growth is virtually year round facilitating a long grazing season. Recent advancements in grassland technology have the potential to significantly increase farm profitability through an extended grazing season and higher performance from pasture. Measuring and budgeting grass has the potential to significantly reduce variable and fixed costs and keep your business profitable in the times of volatile milk and beef prices. Measuring means putting a figure on how much grass is on your farm. Budgeting means making decisions to manage the amount of grass on your farm. Measuring alone is no good. You need to make decisions and targets each week in which your farm is going to meet.
The cheapest feed we have is grass and we need to get as much grass as possible into the cow. This is one added advantage that we have over our competitors is to be able to produce milk from grass.
In recent years we have gone too much to a concentrate based diet and we need to get back to grass. One great way to get as much grass in the cow’s diet is by measuring what we are growing in the fields.
Every day we can get cows out early to grass is worth a saving of €2.70 per cow per day and by maintaining the correct grazing yield and sward heights during the peak grass periods can earn a farmer an extra €150 per ha in milk receipts.
This can amount to a massive amount of money and mean the difference of a farmer making a profit and not breaking even.
There are two ways of measuring grass;
Quadrat method: (The quadrant and grass clippers which are very inexpensive)
This is a 0.5m × 0.5m quadrat which is placed in an area that is representative of the amount of grass in the paddock. The water is then knocked of the grass; the grass in the quadrat is then cut to between 3.5 and 4cm.
This is the equation to calculate the DM yield in a paddock:
Weight of grass (kg) × DM% × 40,000 = kg DM/ha in the paddock.
Grass cut within the quadrat weighs 200g (0.200 kg)
Grass DM% = 16% (0.16) 0.200 kg x 0.16 x 40,000 (there are 40,000 quadrats in a hectare) = 1,280 kg DM/ha
Plate Meter: (The plate meter which is a more expensive method)
This is like a steel stick with a plate on the bottom, in which the plate rests on top of the grass as it is very light and the stick pushes on down to the soil, recording the height of the grass. Then take heights across the entire paddock in a ‘W’ or ‘X’ pattern to ensure the quantity of grass in the paddock is accurately represented and measured. Subtract the ideal post grazing height/residual (e.g. 4cm) from the height of the grass in the paddock. Multiply the figure you get by 250 as there is 250 kg DM/cm.
Paddock height was 8.8cm
4cm is the desired post-grazing residual
(8.8cm – 4cm) x 250 kg DM/cm
= 1,200 kg DM/ha
Either method will give the same results or it is up to the individual to choose the method of choice.
Checking Farm Cover
Measure/estimate the quantity of grass in each paddock — DM yield e.g. 1,400 kg DM/ha
Multiply the DM yield of each paddock by the area of the paddock in ha 1,400 x 1.8 ha = 2,520 kg DM in the whole paddock
Repeat this for all the paddocks on the farm
Sum all the paddock DM yields together
Sum all the paddock areas together (i.e. get total area of grazing platform) in hectares
To calculate farm cover: Divide the sum of the quantity of grass on the farm by the total area
E.g. 10,000 kg (grass on the farm) / 20 ha = 500 kg DM/ha.
- Firstly record the date on a grass measuring recorder page
- Measure the grass in the paddock and write down the value beside the paddock name
- Complete this in each paddock
- When finished the walk you will see that the paddocks are ranked highest to lowest
- Then record all this information in the same way on the grass wedge page
- Shade in the squares up to the dry matter yield of the paddock
- The on the manual grass wedge page, write in the stocking rate (cows/ha) on the grazing platform
- Write in the allocation per cow and the rotation length
- Record how much grass you want left in each paddock when its grazed
- Calculate target pre-grazing yield by multiplying stocking rate, allocation per cow and rotation length and then adding on post grazing residual
- In the first column, mark your target pre-grazing yield with an X
- In the last highlighted column mark your target residual with another X
- Draw a line from one X to the other and your wedge is complete
- Any grasses above this line is all surplus grass
The line on the wedge graph is drawn from the target pre-grazing yield to the post-grazing residual.
Target pre-grazing yield equation: Stocking Rate (cows/ha) × Allocation (kg DM/cow/day) × Rotation length (days) + Residual (what will be left in the paddock after grazing) = Target pre-grazing yield (kg DM/ha).
Thanks for reading. You can see more of my Farming blogs for DoneDeal.ie here.