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GrassMaster Developments

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  • #16
    This evaluation of the latest Grassmaster Pro unit is courtesy of our development partner for the product, Roger Martyn, BAgSc.

    GrassMaster Pro developments: September 2015. By Roger Martyn, GrazeTech, Tasmania, Australia.

    A significant update to the GrassMaster Pro pasture probe operating system has been released in the last couple of months. This has been the culmination of over 3 years of ongoing R&D that has taken place since the 'Pro' series replaced the GrassMaster II series in 2012. It is in fact now 20 years since the introduction of the very first GrassMaster pasture probe, all of which use the capacitance technique.

    In essence, the new GrassMaster Pro operating system makes it a lot easier to use, and it now incorporates a very innovative means of recalibrating the unit as pasture dry matter content changes throughout a season.

    Trials I have carried out here in Tasmania show pasture dry matter percentage content (DM%) will range from as low as 10% in the very early flush of spring to up to 55% in late summer, when conditions are dry but pastures are still actively growing. The DM% differences over the season can result in up to two-fold variances between device readings and actual kg dry matter per hectare (kgDM/ha) content as measured by Cut Weigh and Dry (CWD) means.

    These DM% changes coupled with seasonal changes in pasture plant morphology - as pastures change from their vegetative to reproductive phases effect the accuracy of ALL types of pasture measurement devices currently commercially available, including plate meters. This is something few actually appreciate. While these differences are indeed very large, the good news is that for a good deal of a pasture's seasonal growth, the DM percentages tend to fall within the 18% to 25% range, the same band pasture measurement devices generally have default calibration equations set to.

    For the record, pasture growth beginning mid spring and into the summer and on until pastures start 'going to seed' typically fall within the 18% to 25% DM range. After that, DM%'s steadily climb to as high as 60%; the timing of which is determined by weather conditions and soil fertility. Early spring and early autumn conditions, however, can see DM percentages plummet to as low as even 8%, particularly in overcast weather and in nitrogen boosted conditions. Winter-time tends to see stable DM content of around 20%. The important thing to appreciate though is that the big swings in DM% content tend to coincide with critical animal feed management times, such as when dairy cows are commencing their lactation. In Autumn, after cows have been dried off, they often need extra DM allowance to improve their condition, just when farm pasture covers are lower. Getting this right at such times can greatly improve the success of the remaining season, in terms of animal production or the farm feed situation.

    This is why it is important to be able to easily recalibrate your pasture measurement device if needed. For most, this simply does not happen, due partly to a lack of really knowing which calibration equation to choose, even if the manufacturer's manual suggests one. Alternatively, you could do a more accurate CWD calibration, but for most this invariably ends up simply not happening. This is because CWDs can be time consuming, and for many are overly complicated and confusing to bother with.

    What the GrassMaster recalibration system does, is it allows the user to very easily and quickly recalibrate and improve the machine’s measurement accuracy, significantly. While the calibration will not to be as accurate as a full-blown CWD calibration, it will be much better than doing nothing at all, and for many surprisingly so. And here's why.

    The logic behind the new recalibration system is based on the following.
    Trials in dairy and sheep and beef research have repeatedly demonstrated that experienced pasture managers can assess pasture mass (kg DM/ha) to levels similar to those of actual CWD assessment.

    The GrassMaster Pro has very highly correlated machine readings against actual pasture mass i.e. the machine readings taken before the equation calibration converts them into kgDM/ha readings have a very tight relationship with CWDs on a given day in similar forage and nearby locations.

    By introducing a procedure into the GrassMaster Pro whereby an experienced pasture manager can sample a 'short' or low cover area of pasture, and scroll or key in his/her visual estimate of the same sample area, and repeat again for another 'long' or high cover pasture sample area, it is possible using the GrassMaster Pro's processing power to create a specific calibration equation. All the hard maths gets done behind the scenes. The operator simply has to scroll in how many kg DM/ha he/she thinks are present in each imaginary sample area.

    And this is what we've done. It is extremely quick to do, and dead easy. We refer to it as the 'Quadrat estimate option”.

    The net effect is that an experienced pasture manager can quickly visually calibrate the GrassMaster Pro, and then hand over the unit to a less experienced staff member to continue measuring the farm, confident the day’s data has good integrity, and certainly a whole lot better that what it might have been if no alterations were made. We believe this new feature to be a huge advance in modern pasture measurement technology.

    Since the GrassMaster Pro retains the raw data for each paddock reading, should an operator choose to do CWD's at the same time, the paddock readings can all be retrospectively changed after download. A future version will allow this to be done on the actual GrassMaster Pro as well.

    The GrassMaster Pro offers the Quadrat estimate as a preferred option, or it offers a chosen equation option. The unit facilitates up to 9 different fixed equation selections, each of which is fully adjustable. This might be useful, for example, if a farm has several pasture types that justify different equations- say ryegrass in one paddock followed by pure chicory stand in the next and so on. However, the quadrat estimate technique can be used on any forage and during any conditions, so it is capable of generating hundreds of equations to suit the environment.

    The GrassMaster Pro also now incorporates 'accelerometer' measurement triggering technology. An accelerometer is that bit of technology present in modern smart phones and tablets that allow the screen to know when to flip from portrait to landscape. The technology is also used for apps, such as in games, or in recording the number of strides one walks in a day. The GrassMaster Pro utilises the same technology to sense when the probe has hit the ground, to trigger a measurement. This is facilitating much quicker measuring with less forced errors, allowing the device to be used, for example, off the side of a quad bike without outpacing itself. This is a real boon for large farms and trial areas.

    Another very significant development is that this latest version (V3.03) now facilitates system upgrades via the internet. This will accelerate product development in the future, and greatly extends the technological life of the purchase.
    Graham Lynch


    • #17
      Great Scott!

      Today, a standard model GrassMaster Pro drymatter instrument was calibrated on just two 0.2m2 quadrats (low and high cover), using averaged skilled eye assessments supplied for the "actual" by several trained agronomy professionals. There was still dew on the grass, largely rye and clover mix throughout the farm, the soil was damp. About 16 readings were taken in each quadrat, spaced apart and averaged. The resultant linear equation was used to follow behind two highly skilled whole paddock assessors, over 15-20 paddocks. Of the paddocks that were compared, the calibrated GM Pro gave very similar average covers, within 200kgDM/Ha of the average between the two assessors. Often the agreement was within less than 50kg. The paddocks ranged from an estimated cover of 1,300kg to over 4,000kg.

      The research establishment must not be mentioned, because we were just tagging along behind as we had requested. But I was very pleased with those results, especially since the conditions were not perfect for GrassMaster use. In some paddocks only 25-30 samples were taken towards an average, when more would have been preferred. An RPM unit was used on quadrat cuts, but not used on the paddocks.

      We'll make a few small improvements to the GM Pro code so that we are working at the same speed as the eye assessors (we weren't a great deal slower), and try out some ideas for cleaning the probe quickly during a farm walk.

      Summary: A very promising day. I don't think there has ever been a drymatter instrument used anywhere in NZ that has been as accurate as that, over a range of paddocks.
      Graham Lynch