Estimation of dairy pastures - the need for standardisation

Abstract

A study was undertaken to determine the reason for the differences in the estimation of pasture mass between dairying research centres in New Zealand and to define a common system of estimation that would overcome these differences and be able to describe the pasture situation on commercial dairy farms in different parts of New Zealand. Differences in the visual estimation of pasture between a standard observer and a local observer at the different dairying research centres in the order of 900 kg DM/ha were identified. This was attributed to a lack of regular visual calibration of persons who regularly assessed pasture, as differences between centres in the actual harvested DM yields of the visually assessed plots varied less (200-400 kg DM/ha). To achieve uniformity it is recommended that all centres measure total herbage mass (the amount of herbage above ground level) to regularly calibrate pasture assessment in dairy grazing management studies and on dairy farms. A reasonably consistent estimation of average farm cover, the ranking of paddocks (r2 > 0.9) for the purposes of determining grazing order and the estimation of pre- and post-grazing herbage mass was achieved using the rising plate meter and L'Huillier & Thomson's standard set of calibration equations published in 1988. With these recommendations, estimation of pasture will be more uniform. Standard calibration of the plate meter for the determination of rate of DM disappearance (pre-post grazing) achieved less consistency. Keywords: herbage mass, pasture assessment, pasture height, rising plate meter, visual pasture estimation