EFFECTS OF SOIL DRYING AND HIGH ATMOSPHERIC EVAPORATIVE DEMAND ON LEAF PHOTOSYNTHESIS AND WATER STATUS OF MAIZE

Photosynthesis, stomatal conductance and water relations have been studied in response to witholding water in a maize crop under conditions of high atmospheric evaporative demand. The aim was to probe environmental stress by gas exchange measurements in the field. During the experiment severe soil dryness was attained at depth till 0.45 m in half the crop, the remaining half being irrigated as control. Furthermore for the majority of the experimental period air temperature and vapor pressure deficit peaked over 33 °C and around 35 mbar. In spite of the dried soil, leaves kept fully turgid in all plants while stomatal conductance and photosynthesis decreased greatly in unirrigated plants. Stomatal conductance measured after dawn is shown to integrate better than leaf water parameters long term stress with the possibility to distinguish daily stress effects of high transpiration. Its promising use in irrigation scheduling of crops with critical water supply in determining yield or production is hypothesized.