Treatments
Six water deficit treatments were imposed with a drip
irrigation system (described by Martin et al., 1990). A
mobile rainshelter (12 x 55 m) covered the plots
automatically whenever rainfall occurred. The treatments
were fully randomised in two blocks and were designed
to subject the crop to varying degrees of stress at
different stages of crop development:
Fl: fully irrigated - weekly irrigation to replace
the previous week's water loss
FD: severe drought - no irrigation
MED: moderate early drought- no irrigation until 16
days pre-silking, then full irrigation
SED: severe early drought - no irrigation until
silking, then full irrigation
MLD: moderate late drought - full irrigation until 19
days post-silking, then no irrigation
SLD: severe late drought- full irrigation until 21
days pre-silking, then no irrigation
Drip irrigation was supplied weekly to each plot via
emitters spaced 300 x 450 mm apart, and irrigation
volume was measured using a flow meter connected tothe main line. The previous week's water loss or actual
evapotranspiration (E) was defined as :
E=l+.6.SM,
where I was the amount of irrigation applied in the
previous week and .6.SM was the change in soil moisture
content of the profile over the week, assuming runoff and
drainage were negligible. As defined here the term E
was identical to actual weekly water use defined below.