Abstract
During routine field application of the disc pasture meter (DPM) in the tall-grass rangeland of the Kruger National Park (KNP), it was noticed that the instrument frequently settles above the bulk of the grass leaf mass, leading to the suspicion that the settling height is inflated and non-representative. Taking into consideration the relatively heterogeneous nature of the herbaceous layer in terms of its floristic and structural diversity, as well as the increasing tendency to use the instrument for research purposes where a greater degree of precision is desirable, it was decided to re-evaluate the calibration of this instrument. Field sampling was undertaken, and by means of double normal distribution and 'broken stick' regression analyses, two populations were identified, both with a non-linear relation between compressed DPM height and above-ground standing crop. Beyond a DPM height of 26cm, the correlation is poor, apparently being strongly influenced by the structure of the grass plant; tall grasses or grasses with highly lignified culms lead to a weaker correlation. Two equations for DPM height groups (≤26cm and >26cm) were produced: kg ha−1 = [31.7176 (0.32181/x) x0.2834]2 (r = 0.979; r2 = 0.951; P < 0.0005) and kg ha−1 = [17.3543 (0.9893x) x0.5413]2 (r = 0.948; r2 = 0.882; P < 0.0005) where x is the mean DPM height in cm of a site.
Published Version
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