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Cutting Pasture Samples to Calibrate your Estimates of Herbage Weight
In the Help file for the GrazFeed program, under ‘Pasture Assessment/Calibration’, the following comment about the method of cutting the herbage is recorded.
“This can be done with hand shears or, where power is available, with a shearing handpiece. The cutting blades should be held as flat as possible on the soil surface, so that the height of the stubble is no more than the thickness of the cutting blades. Do not cut below the soil surface in an attempt to remove more herbage, because this was not the procedure used to calibrate the equations in GrazFeed for predicting herbage intake”.
If, for some reason, you prefer to use a different procedure, you should be aware that your estimates must be adjusted to account for the different amount of herbage removed. You should measure the difference between your procedure and the recommended procedure within a number of quadrats and adjust your subsequent estimates by the mean difference. To do this, cut the herbage first in the recommended way and then measure what further material you can remove by your preferred technique.
For example, we have found in a specific case that herbage estimates made by running the shearing handpiece into the soil surface, removed on average, an additional 250 kg dry matter/ha. In another case, in a very prostrate pasture, herbage was estimated by removing all green material with a scalpel, giving a weight that was about 400 kg DM/ha greater than if cut with a shearing handpiece. The estimates of mean herbage weight entered into GrazFeed in these cases would have to be reduced by 250 or 400 kg DM/ha, respectively.
On the other hand, if a less close system of cutting is used, such as a battery- operated edge trimmer, the estimates entered into GrazFeed must be increased by the difference that you measure between this method and the recommended procedure.