Pasture assessment: getting it right

04 January 2016

In this opinion piece, John Francis of Holmes Sackett, NSW MBfP State Coordinator, discusses the key messages associated with pasture assessment.

In mid February, I conducted a Farm300 meeting at Adelong in the Riverina district of NSW. The aim of this meeting was to identify opportunities to better match feed supply with feed demand through feed budgeting. Once identified, the aim is to change practices to improve productivity, lower the intensity of greenhouse gas emissions and improve profitability.

One of the meeting sessions focused on pasture assessment.

Two improved perennial grass and clover based pastures were assessed with each being managed under a different stocking rate regime. Visual estimates of the amount of pasture yield in terms of kilograms of dry matter per hectare (kg DM/ha) were made before pasture cuts were taken to compare visual assessments with the actual pasture yield.

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 as shown in the image below. In winter, the gaps between grass will be filled with cover.

mbfp-apr-2015-01.jpg

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. See the pictures below of both pre and post cut.

mbfp-apr-2015-02.jpg

mbfp-apr-2015-03.jpg
The ‘eyes’ don’t have it

Visual estimates of pasture yield made by participants, including me, ranged from 1,350 to 2,000kg DM/ha for the first pasture and 2,500 to 3,000kg DM/ha for the second. This did not compare well with cut samples which revealed pasture yields of 1,900 and 5,500kg DM/ha for pastures one and two respectively.

Our visual assessments were well off the mark when compared with the more objective process of cutting, drying and weighing. This 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 and what was there to be measured.

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.

This variation and change in perception highlighted the importance of calibrating our eyes on an ongoing basis by taking pastures cuts more regularly throughout the season.

The participants concluded from the pasture assessment exercise that:

    Pasture assessment from late spring to summer is highly variable and pasture cuts are absolutely necessary for calibration of the eye.
    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 put in a low oven (120°C) for 30 to 60 minutes, or until dry. This was far more convenient and less problematic than microwaving samples, which requires constant supervision (drying may take longer in winter when pastures have a greater moisture content)
        the final weighing and calculation took another five to 10 minutes
        total time required was 15 minutes with 30 to 60 minutes of drying time
    Variations in the amount of moisture in pastures are one of the key reasons visual pasture assessment can differ significantly from cut sample assessments.

In the next MBfP eNewsletter we will discuss how these results can be analysed using the GrazFeed program to assess and predict livestock performance on these pastures.
Further information:

    Contact John Francis, NSW MBfP State Coordinator
    Module 2 and Module 3
    Tool 2.02 Assessing groundcover
    Tool 2.07 Field based pasture measurements
    Tool 3.01 Pasture rulers, sticks and meters
    Tool 3.03 Pasture growth estimates

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