The responses of sweet corn biomass and yield to timing and severity of water
deficit were determined in an experiment using a mobile rainshelter. Six
irrigation treatments were applied such that plots experienced: (1) no water
deficit; (2) full water deficit; (3) moderate pre-silking deficit; (4) severe
pre-silking deficit; (5) moderate post-silking deficit; or (6) severe
post-silking deficit. Drought was quantified using the concept of potential
soil moisture deficit, which was calculated from climatic data. Potential soil
moisture deficit can be related simply to a wide range of plant performance
variables, making it possible to compare the relative importance of variables
in determining the overall response of the crop to drought. For all
treatments, yield was related strongly to biomass, especially that accumulated
after silking. Biomass, in turn, was reduced by water deficit, mainly because
of reduced radiation use efficiency, but also because of reduced total
radiation interception, particularly in early deficit treatments. Both water
use efficiency and transpiration efficiency increased with water deficit, even
though soil evaporation as a proportion of total water use also increased with
deficit. There was no stage of crop development at which yield was
particularly sensitive to water deficit, although yield components changed
with timing of deficit. Importantly, measures of potential soil moisture
deficit integrated the effects of timing and severity of drought, making it
possible to simply and mechanistically account for the effects of water
deficit on biomass and particularly yield.