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There is a growing appreciation of the nutritional and health benefits of oats but little recent research has been conducted on the agronomy of oats. Experiments were conducted in Ireland over a two year period (2016–2017) to study the effect of nitrogen (N) timing and rate on radiation interception, yield and quality of autumn sown oats. Two experiments were conducted in each year. In the first experiment, a nitrogen response curve (0, 30, 60, 90, 120, 150 kg N/ha; split-plot factor) was applied at either GS21, GS30, GS32 or GS39 (main-plot factor). In the second experiment, N was applied at GS30 at rates of 0, 30, 60, 90 kg/ha (main-plot factor) and then at GS32 at rates of 0, 30, 60, 90, 120 and 150 kg/ha (split-plot factor). Measurements of radiation interception were made throughout the growing season in addition to flag leaf chlorophyll content and plant height. Grain yield and quality was quantified at harvest. The effect of N timing on radiation interception diminished as N application was delayed but the timing of N supply had no effect on the grain yield in autumn sown oats as long as the crop had received N by GS32. Grain numbers were strongly related to intercepted radiation, particularly in the period immediately before and during anthesis. Radiation interception increased as the overall rate of N application increased but grain yield reached a plateau at 150 kg N/ha. Increases in grain yield after N application were primarily the result of increases in the number of grains per panicle. Splitting N in different ways between GS30 and GS32 had no significant effect on grain yield and grain weight but, for overall N rates of 120 and 150 kg/ha, hectolitre weight increased as the proportion of N applied at GS30 was increased. Grain numbers in oat crops can be optimised by applying N to ensure that radiation interception is maximised in the period prior to and during anthesis.
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