Water deficit effects on sweet corn. II. Canopy development

The response of sweet corn canopy development to timing and severity of wat er deficit was determined in an experiment using a mobile rainshelter. Six irrigation treatments were applied such that plots experienced: (1) no wate r deficit; (2) full water deficit; (3) moderate pre-silking deficit; (4) se vere pre-silking deficit; (5) moderate post-silking deficit; or (6) severe post-silking deficit. Soil moisture content profiles were measured using ne utron moisture probes and water deficit was quantified using the concept of 'potential soil moisture deficit' (Dp), which was calculated from climatic data. Water deficit reduced leaf area, and the effect varied depending on its timing and severity. Early water deficit reduced the rate of leaf expan sion (but not duration of expansion) and, consequently, the maximum area of individual leaves; it therefore reduced the maximum leaf area index (LAI). Moderate post-silking water deficit did not significantly reduce maximum L AI, but it hastened leaf senescence. Severe water deficit late in crop grow th reduced canopy development by decreasing maximum LAI and advancing leaf senescence. A model was developed which accounted for these effects. Two me asures of Dp were defined which related to both short-term transient respon ses and those integrated over longer times. The model made it possible to s imply and mechanistically describe the effects of water deficit on canopy d evelopment.