Yield and quality of milling wheat in response to water deficit and sowing date on a shallow soil

The yield and quality response of a spring-sown milling wheat ('Conquese) to four levels of irrigation and two sowing dates (27 August 2010 and 27 September 2010) was determined in a Canterbury shallow soil (<30 cm to gravel). Irrigation treatments were: full replacement of potential evapotranspiration (PET) weekly, half PET every week, half PET every 2 weeks and no irrigation. The full PET replacement irrigation significantly increased all measured yield components over the no irrigation treatment. The two PET replacement treatments had similar yields. The total amount of water applied had a greater effect on yield than did the frequency of its application. Grain yields were related to maximum potential soil moisture deficit and decreased by 1.4 t ha(-1) for each 100 mm increase. Grain yield was directly correlated to total aboveground biomass production (with a harvest index of 0.44) and the grain population (grains m(-2)) rather than to individual grain weight. Delaying the sowing date increased protein levels by an average of 0.93% over all irrigation treatments. Grain quality measured using rheological properties also improved with delayed sowing without any reduction in grain yield, but irrigation had no effect on grain quality. Overall, these results confirm that in order to maximise grain yields growers should irrigate their milling wheat crops to maximise crop biomass production by maintaining soil moisture above a critical deficit.