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The effect of defoliation for winter forage on recovery and grain yield of barley and oats in Tasmania
thesisposted on 2023-05-27, 08:37 authored by Abdul-Rahman, MS
Experiments were carried out between 1983 and 1987 at the University Farm in Southern Tasmania to compare the winter oats cultivar, Esk (prostrate, dual-purpose), with a range of barley cultivars: Shannon (spring, erect habit of growth, two-row grain type), Malebo (erect, six-row forage type), Triumph (spring, semi-prostrate, two-row grain type), and WU3072 (winter, prostrate, two-row grain type). In a preliminary experiment on Esk oats, nitrogen fertilizer promoted recovery after grazing by increasing tillering, leaf area and radiation interception, and by delaying leaf senescence. The rapid winter growth of erect barley cultivars provided substantial amounts of dry matter (1.5 - 2.3 t/ha) for winter grazing. However, the shoot apices on the mainstems of these cultivars developed rapidly below the soil surface and emerged above ground level as much as 6-8 weeks before those of the prostrate cultivars, thus curtailing the \safe\" period for grazing. Malebo exceeded Triumph in yield of digestible dry matter prior to winter grazing. The lowest level of crude protein at grazing was found in Esk oats. Although tiller numbers were increased following defoliation leaf production was more important for recovery. Faster regrowth after defoliation better radiation interception greater efficiency of crop regrowth and higher final forage and grain yields were achieved by Malebo and WU3072 compared to Shannon and Triumph. The erect Malebo replaced leaf area rapidly after defoliation through the production of longer wider and thicker leaves. The prostrate WU3072 retained considerable leaf area after defoliation. In glasshouse experiments the rate of movement and development of the mainstem apex was less sensitive to high temperature in Malebo than in Shannon and Triumph. Esk oats was shown to respond strongly to vernalization and photoperiod resulting in both stability in flowering time and late flowering after the time when frosts were likely to occur. The barleys to vernalization however varied in their responses 4 from moderate in WU3072 to weak or nil in the spring cultivars and hence ear emergence even after early defoliation occurred several weeks earlier than in Esk oats. In the field experiments differences between cultivars in total dry matter at the dough stage of development were not large. Esk generally gave the highest yield of dry matter when undefoliated but following early defoliation Malebo produced over 2 t/ha more than Esk. The lowest grain yield and harvest index was in Esk. Early defoliation did not significantly reduce grain production in any cultivar whereas a single defoliation in late winter or two defoliations (early and late) drastically reduced grain yield because of the removal of growing points on the mainstems and primary tillers. WU3072 was more tolerant of late defoliation than other barley cultivars because of its residual leaf area and delayed reproductive development. Its advantage in grain yield came from 2 more ears per m and more grains per ear."
Rights statementThesis (Ph.D.)--University of Tasmania, 1989. Bibliography: p. 233-251