Spring barley (Hordeum vulgare L. cv. Lindwall) was sown in 2 experiments in 1995 and 1 experiment in 1996 in the eastern wheatbelt of Western Australia to examine the effect of varying moisture supply during grain filling on grain and malting quality. Drip irrigation (T-tape) to the soil surface was used to simulate rainfall. Plots were sown without rainout shelters and no rain fell during the linear phase of grain filling in all 3 experiments. The control plot received no irrigation. Irrigation treatments in 1995 were a once only 25 mm application at either 80, 185, 270, or 460 growing degree-days after awn emergence. Irrigation treatments in 1996 were a once-only 25-mm application at either 185 or 460 growing degree-days after awn emergence or a weekly irrigation treatment of 25 mm (total application of 75 mm over 3 irrigations). No attempt was made to compensate for evaporation or to match plant demand.

This study demonstrated improvements in grain plumpness, grain quality, and malting quality with a single 25-mm irrigation during the early linear stages of grain filling (20–40% complete as percentage of final grain weight) in water stressed plants. The irrigation resulted in increased average grain weight, grain yield, amount of maltable grain, and malt extract and decreased the amount of grain passing through a 2.5-mm slotted sieve, grain protein concentration and diastase. This single irrigation, however, was not sufficient to change screening levels to meet receival standards for malting barley and demonstrated the effect of moisture stress on narrow-grained cultivars such as Lindwall.

A single irrigation earlier than 20% grain fill completed had a smaller effect on grain plumpness, grain quality, and malting quality. A single irrigation during the latter part of grain filling (>90% grain fill completed) had little or no effect on grain plumpness, grain quality, or malting quality.

Weekly irrigation in 1996 had a bigger effect than a single irrigation and demonstrated the environmental limitation to quality in that season. Weekly irrigation increased average grain weight by 10 mg relative to control plots, reduced screenings from 88% to 18% through a 2.5-mm sieve, increased grain yields by 88%, increased malt extract by 3%, and decreased diastase by 116 pabah. There was no effect on grain modification or wort viscosity. Viscometric analysis of the barley flour showed a higher time to peak viscosity of the control, which suggests that gelatinisation temperatures were being decreased by irrigation in 1996.