Carbon dioxide production in soils, under barley, subjected to a range of drought treatments

Soil air was sampled daily for a period of 3 months at depths of 10, 20, 30, 40 and 50 cm, in plots cropped with barley; samples were taken from capillary probes and analysed for carbon dioxide using gas chromatography. Changes in carbon dioxide concentration were closely related to the water status of the soil, and were attributed to root respiration. Respiratory response to irrigation occurred in two phases. Early in the season a steady increase coincided with increased leaf area and later transient increases occurred after irrigation. These phases were correlated with yields of straw and grain respectively, showing that root respiration is an important aspect of plant performance. The curves relating yield and carbon dioxide concentration were extrapolated to zero yield to give carbon dioxide values corresponding to microbial respiration.