Photosynthesis, respiration and evaporation of a field‐grown potato crop

SUMMARY Measurements are reported of the effects of irradiance, air temperature and water stress on the photosynthesis, respiration and transpiration of a field‐grown potato crop. The measurements, relating to one season (1974) only, were made using a field enclosure system on plots of irrigated (I) and non‐irrigated (NI) potatoes. In the moist summer of 1974, soil moisture deficits differed little between I and NI plots, and water stress had no significant effect on the NI plants. Results show that maximum rates of net CO2 uptake (whole plants) were about 6 g h‐1 m‐2 ground area, and rates of respiration, for above‐ground and for below‐ground plant parts, were essentially constant, at about 0·3 g h‐1 m‐2 ground area, throughout the 3 months of measurement. The dependence on irradiance of the whole plants gross photosynthesis was for each measurement day adequately represented by a rectangular hyperbola relation. The season's accumulations of dry matter as calculated from these hyperbolae and from the season's measured irradiance agreed well with values derived from plant weighings.