Development, growth, water-use and yield of a spring and a winter wheat in response to time of sowing

Abstract

The development, growth, water-use and yield of spring (Banks) and winter (Quarrion) cultivars of wheat were measured in response to time of sowing under rainfed conditions. Crop duration shortened in both cultivars (210 to 120 days) as sowing was delayed from May to August with Quarrion maintaining the longer cycle. The difference between cultivars was small (3 days) at the May sowing increasing to 21 days in August, but there were large differences in the relative durations of the component phenophases. Consistent with the shorter cycle, growth of both cultivars decreased as sowing was delayed from May to July (11.3 to 9.9 t ha-1). With August sowing, the pattern continued in Banks (6.7 t ha-1) but not in Quarrion. Seasonal evapotranspiration (ETa) of both cultivars was similar, declining from 306 to 262 mm as sowing was delayed from May to July. On average, Quarrion used more water (34%) of ETa than Banks (19%) during emergence to floral initiation (E-FI), and a corresponding smaller proportion during subsequent phenophases, floral initiation to anthesis (FI-A ) (31 v. 41%) and anthesis to maturity (A-M) (35 v. 41%). The differences between cultivars increased as sowing was delayed from May to August. Maximum evapotranspiration (ETm), estimated by the Penman equation, was evaluated against measurements made with weighed lysimeters. The ratio ETa/ETm fell progressively during the crop cycles and was always smaller for the later-developing Quarrion than for Banks. Crops of both cultivars had adequate water supply during E-FI, mean value of the ratio 0.93, but experienced water stress during FI-A and A-M. Stress was greater in Quarrion (ratios 0.71 and 0.56) than in Banks (0.88 and 0.62). In Quarrion, yield decreased progressively from 4.3 t ha-1 when sown in May to 1.6 t ha-1 in August. In contrast, yield of Banks increased from 3.7 t ha-1 in May to 4.5 t ha-1 in June and then decreased to 3.5 t ha-l in July and 2.6 t ha-1 in August. Crop water-use efficiencies are analysed for ETa (WUE) and for transpiration (TE). Excluding the August-sown crops, they ranged respectively over 11.9 to 14.8 and 25.0 to 32.5 for Quarrion and over 11.0 to 15.7 and 23.3 to 31.6 kg ha-1 mm-1 for Banks. Maximum efficiencies were not achieved by the crops of greatest yield.