Field Studies of Cereal Leaf Growth

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Abstract
A mechanical auxanometer, suitable for measuring hourly rates of leaf extension of grass and cereal crops, is described. Several of these instruments were used to monitor leaf extension rates (RE) of a spring barley crop. RE of main stem and first leaf tillers responded similarly to environmental factors. During May, when soil water deficits were less than 50 mm, and on dull days later in the season, RE was directly related to meristem temperature with night and day measurements responding similarly. During the central 10 h of bright days in late May and June, RE was unrelated to temperature but slowed during bright sunshine and accelerated at the start of cloudy periods. Pressure chamber measurements of total leaf water potential (Ψ) showed that bright sun caused Ψ to decrease rapidly and that this was associated with slow RE. Analysis of 2 h mean values of Ψ and RE indicated that, at any given temperature, RE slowed in direct proportion to decrease of Ψ.