Integrated Analysis of Growth and Light Interception in Winter Lettuce I. Analytical Methods and Environmental Influences

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Abstract
Measurements on protected lettuce crops have been used to assess two new procedures for analysing the rate of dry-matter production in crops or plant stands. ‘Integrated growth analysis’ brings together two traditionally distinct treatments of growth analysis by resolving crop growth rate (CGR) into stand biomass and the relative growth rate of individual plants. ‘Light conversion analysis’ resolves CGR as the product of incident light receipt, efficiency of light interception by leaves, and efficiency of utilization of intercepted light in dry-matter production. Observations from winter lettuce trials were used to fit statistical progressions to the primary data and to obtain instantaneously-derived estimates of all of the analytical components. Trials in three successive years yielded similar patterns in time for the components of each of the analytical procedures, giving confidence in their validity. In light conversion analysis, changes in CGR were due mainly to incident light, which varied threefold, and to intercepting efficiency, which rose from a low initial value to full interception at hearting; the efficiency of utilization of light varied less dramatically, with the value at hearting being about twice that at planting. In integrated growth analysis a 30 per cent increase in CGR due to CO2 enrichment, and a 5 per cent increase due to lower daily minimum temperature, could each be coherently resolved into variations in biomass, leaf area ratio and net assimilation rate. In different ways it is concluded that both of these approaches can assist in analysing growth and in identifying the options available for improving crop yield.