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Chlormequat can be applied to winter barley for growth manipulation with a view to increasing ear number per m<SUP>2</SUP> and hence grain yield, but, reviewing the literature on field trials showed the effects were not consistent. Previous work showed that the grain yield per m<SUP>2</SUP> of winter barley was strongly correlated with the number of grains per m<SUP>2</SUP> which itself was shown to be mostly influenced by the number of ears per m<SUP>2</SUP>. Three agronomic factors, cultivar, sowing date and nitrogen fertiliser, were identified from the literature as important influences on ear production in winter barley. These were therefore considered to have the potential to modify plant response to chlormequat, in terms of ear production, and might thus account for some of the inconsistency of the effect of chlormequat on grain yield in field trials. The intention of these studies was to move towards a description of winter barley production systems into which chlormequat may be integrated to consistently increase grain yield. Because little information was available on the growth, development and grain yield components of field grown modern winter barley cultivars, these attributes were monitored and analysed in detail for a range of modern cultivars grown at two sites in north-east Scotland in the harvest years 1984 and 1985. Tipper and Maris Otter were identified as strongly contrasting cultivars, being good examples of the extremes of the range of growth parameters found. In addition, the analyses identified the extreme importance of high cultivar biomass per plant for the attainment of high cultivar grain yield per plant. Evidence that increases in biomass have already contributed to the higher grain yields of modern cultivars of both spring barley and winter wheat was also found within the literature. The effect of chlormequat at a range of application times in the spring on early and late sowings of Igri, Tipper (low ear production) and Maris Otter (high ear production) was tested. When averaged over all cultivars and sowing dates chlormequat applied prior to stem extension significantly increased the number of ears per m<SUP>2</SUP> in 1983--4 which led to increases in grain yield. In 1984--5 chlormequat applied at the start of stem extension significantly increased the number of grains per ear and significantly increased grain yield; within-plant uniformity, in terms of shoot contribution to grain yield, was also increased. Chlormequat had no consistent effect on the grain yield of the cultivars Igri and Tipper, but did increase the grain yield of both early and late sown Maris Otter by increasing the number of grains per m<SUP>2</SUP>. These higher grain numbers were achieved through consistent increases in the number of ears per m<SUP>2</SUP> which were nearly always associated with increases in the number of grains per ear on the main stem and early primary tillers. These larger sink sizes of Maris Otter followed temporary reductions in shoot height which were offset by compensatory increases in shoot growth. The growth, development and grain yield components of Maris Otter were described in detail with a view to enabling cultivars with similar growth characteristics to be identified. Application of nitrogen fertiliser did not modify the effect of chlormequat on shoot height or shoot dry weight. In these experiments chlormequat increased neither ear number per m<SUP>2</SUP> nor grain number per ear; therefore, the effect of nitrogen application strategy on the ability of chlormequat to increase in sink size could not be evaluated. It was suggested that application of chlormequat to Igri winter barley receiving more than 100 kg N/ha is unlikely to reduce grain yield. These investigations confirmed the extreme importance of high crop biomass for the attainment of high grain yield. The findings of these investigations together with the findings of a re-analysis of advisory service field trial data on the effect of chlormequat on winter barley are discussed in relation to commercial winter barley production. Finally, it is suggested that more consistent increases in grain yield may be achieved by restricting the use of chlormequat for tiller manipulation to cultivars of the Maris Otter type such as Halcyon and Pipkin which are slow developing, produce relatively large numbers of tillers and eventually many ears per plant.

Master of Science / Department of Agronomy / P.V. Vara Prasad / Sorghum (Sorghum bicolor L. Moench) is cultivated as an important food grain in the semi-arid regions of Africa. Processed grain sorghum is traditionally consumed as porridge, couscous, traditional tô or beer. The quality of such foods is highly dependent upon grain characteristics. Sorghum grain quality traits mainly include kernel hardness, kernel weight, kernel size, protein content and kernel color. Grain quality traits are often influenced by environment, genotypes, fertilizer management and their interaction. The objective of this study was to determine the impact of different levels of nitrogen application (0, 45, and 90 kg ha[superscript]-1) on grain quality of selected sorghum genotypes. The field experiment was conducted at three locations in 2010 (Manhattan, Ottawa, and Hays) and at two locations in 2011 (Manhattan and Ottawa). The experiment was laid in split plot randomized complete bloc design and replicated four times. The main plots were assigned to three N regimes: control (0 kg N ha[superscript]-1), half recommended rate (45 kg N ha[superscript]-1) and recommended rate (90 kg N ha[superscript]-1). The subplots were assigned to twelve genotypes (six hybrids and six inbred lines). Plot size was 6.1 m x 3.0 m with a row spacing of 0.75 m. After harvest, grain quality traits (hardness, weight, diameter and protein content) were evaluated using standard procedures and the data subjected to statistical design using SAS. There were significant effects of genotype for most grain quality traits across both locations in Manhattan. Inbred lines SC35 and SC599 had maximum hardness at all locations while hybrid 95207, had the lowest hardness for all locations. Also, Inbred lines SC35 and Tx340 had maximum protein content at all the locations. While hybrids 95207, 26056, 23012 had the lowest protein content. Genotypes Tx430, SC35, had higher hardness and with higher protein content were classified as high quality. We conclude that application of N (45 or 90 kg ha[superscript]-1) significantly improved grain protein, but not other quality traits. There are opportunities to improve grain protein through fertilizer management and plant breeding.

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Call number: LD2668 .T4 1951 O8 / Master of Science