How to accurately assess pasture
28 May 2015
Think you can accurately assess pasture just by looking at it? Think again, says NSW More Beef from Pastures coordinator John Francis.
Visual assessment of pastures is often way off the mark, according to John and producers should use tools such as taking regular pasture cuts to "calibrate their eyes."
During the MLA Farm300 program, John ran an event at Adelong in southern NSW to identify opportunities to match feed supply with demand through budgeting.
At the event, producers were asked to visually assess two perennial grass and clover based pastures, which were then measured through cutting, drying and weighing.
The first pasture had been grazed by lambs at a high stocking rate. The pasture height was low (average of 4cm) and the clover density low, as expected during summer, but overall the pasture was of moderate density, with 100% ground cover and 50% green grass cover.
Visual estimates of pasture yield made by participants: ranged from 1,350-2,000kg DM/ha
Cut samples estimate of pasture yield: 1,900 DM/ha
The second pasture, also of improved perennial grass and clover, had not been grazed as heavily and therefore had a higher pasture height (average 7.5cm). Clover density was low, as with the first pasture, but there was significantly more standing and lodged dead material in this pasture compared with the first.
Visual estimates of pasture yield made by participants: ranged from 2,500-3,000kg DM/ha
Cut samples estimates of pasture yield: 5,500 DM/ha
“This (inaccuracy) can be explained in part by the significant variation in pasture growth in the Adelong district over the previous 100 days, which had significantly distorted participant perception of pasture performance.
"Pastures had ranged in height in the district by over 40cm and density and moisture content has been within a range of 50%. As these factors influence yield, it is not surprising that there is inconsistency with visual assessments given the recent variability in pasture production," said John.
The participants concluded from the pasture assessment exercise that:
1) Pasture assessment from late spring to summer is highly variable and pasture cuts are absolutely necessary for calibration of the eye.
2) Pasture cuts are not as time consuming as first thought:
- each cut was completed in well under five minutes
- pasture cuts were then weighed (five minutes) before being spread out on a baking tray and dried in an oven. The alternative is to microwave pasture samples, however, this requires constant supervision and handling. The drying time will depend on the moisture content of the sample
- the final weighing and calculation took another 5-10 minutes
- the total time required was 15 minutes plus drying time
"One of the constraints with pasture cuts is conducting enough to provide a representative sample across any paddock.
“There are two MLA-funded projects investigating new approaches in pasture assessment which will hopefully reduce time required for calibration and cutting,” John said.
John Francis, NSW MBfP State Coordinator E: firstname.lastname@example.org
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