Small grains that pass through a 2-mm slotted screen (sievings or screenings) are one of the most important causes of price dockages of wheat in Australia because grain size variation greatly affects flour yield and commercial value. The aims of this study were to examine the effects of season, time of sowing, plant population, and applied nitrogen, and their interactions with cultivars, on small grain screenings. Twenty-one field experiments involving 16 new cultivars and elite crossbreds, and various management variables, were conducted in the medium (annual rainfall 325–450 mm) and low (annual rainfall <325 mm) rainfall zones of the Northern Agricultural Region of Western Australia over 3 diverse cropping seasons (1999–2001).
Rainfall events towards the end of the season were critical to the level of screenings. Screenings were higher in season 2000 with terminal drought stress, but were low in 2001 despite severe drought stress during early growth. Delayed seeding caused higher screenings in 1999 (average rainfall with even distribution) and in 2000 (terminal drought) but not consistently in 2001 when early drought stress restricted tillering and spike size thereby constraining the yield level. Strong varietal and time of sowing interactions were evident but the relationship between maturity group and the level of screenings was not consistent. Rather, the ability of cultivars to adjust yield components was more important; 82% of the total variance in small grain screenings was accounted for by a regression model based on variety-specific kernel weight, post-heading rainfall (from about 2 weeks before anthesis), and location factors.
The effect of increasing plant population on screenings was mostly negative, with some minor exceptions for a few cultivars in the low-rainfall zone. As applied nitrogen was increased, screenings generally increased and cultivar influenced this trend more than rainfall zone. It is postulated that for a cultivar to be unaffected by applied nitrogen, it should have inherently higher grain weight as well as high stability of grain weight across nitrogen levels. Applied nitrogen had a significant effect on screenings only at higher plant populations.
In experiments where the level of screenings exceeded 5%, the yield components that were significantly associated with screenings, in order of relative importance, were grain weight > grain number/area > grain number/head > grain yield. Cultivars differed in production of screenings in response to plant population, nitrogen fertiliser and sowing time. Harrismith was the most sensitive cultivar and Wyalkatchem was overall the most tolerant cultivar. Delayed seeding had the least effect on the screenings of cultivars Westonia, Carnamah, and Wyalkatchem. Carnamah was the most stable cultivar against higher levels of applied nitrogen, whereas Westonia required high plant numbers to contain screenings. It is concluded that cultivars can be classified according to specific sensitivities, and appropriate management practices may be suggested to growers.
Abiotic Stress Response of Near-Isogenic Spring Durum Wheat Lines under Different Sowing Densities
