An evaluation of the drop-disc technique for measurements of herbage production in ryegrass for silage

The drop-disc method of estimating herbage dry-matter production was evaluated for ryegrass from growth commencement to the silage stage; the latter typically corresponded to a maximum dry matter (DM) mass of almost 7 t ha⁻¹. A close linear relationship ( r ²= 0·829) was found between disc settlement height and DM mass up to 4–5 t ha⁻¹ for the period when growth was mainly vegetative rather than reproductive. During the latter stage, the presence of stems and the occurrence of lodging had a detrimental effect on the quality of disc calibration data. The technique was demonstrably useful in experiments as a cheap, rapid and trouble-free method for monitoring the initiation of grass production and rate of production during the vegetative stage.