A comparison of spectral reflectance and sward surface height measurements to estimate herbage mass and leaf area index in continuously stocked ryegrass pastures

Abstract

AbstractMeasurements of sward surface height and of the ratio of light at 660 and 730 nm reflected from a pasture canopy were correlated with measurements of leaf area index (LAI) and herbage mass of two ryegrass dominant swards. Both pastures were continuously stocked by sheep to maintain a range of sward heights from 2 to 6 cm corresponding approximately to LAI 2 to 5.Sward height appeared to be linearly related to both LAI and herbage mass, whereas 660/730 reflectance displayed a non‐linear relationship with both parameters. The accuracy of prediction by the two methods over the range LAI 1 to 3 or herbage mass 700 to 1800 kg DM ha‐1 was very similar. However, reflectance measurements could not be used above about LAI 3–4 and to this extent were less useful. Nevertheless, reflectance measurements have a potential advantage in their ability to sample large areas of pasture very quickly.