Barley and its environment. I. Theory and practice

This paper outlines the historical aspects and basic philosophy of an experimental programme to investigate the relation between weather and the growth of barley. The approach depends on the calculation of the exchange of CO2and water vapour between the crop and the atmosphere using the Bowen ratio and aerodynamic methods. The basic transfer equations, used in both methods, were extended to exploit measurements at a set of levels above the canopy rather than the more traditional method of using two levels only. The sensing and recording instruments used in the experiment are fully described, together with details of the site and crops on which the measurements were made. Data analysis depended on the use of a large computer because measurements were made continuously throughout the growing season. Programming methods are outlined and illustrated by samples of the output. Good agreement is demonstrated between fluxes of CO2calculated by the Bowen ratio and aerodynamic methods, and the advantages of using multipoint profiles clearly demonstrated.