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Coventry, David Richard McDonald, Glenn Keith Hooper, Peter School of Agriculture, Food and Wine 2010 http://hdl.handle.net/2440/62681 In southern Australia a large proportion of crop nitrogen requirements are usually applied early in the season, either just before or at sowing, or during the first 6-8 weeks after sowing. However, the time of greatest demand for nitrogen by wheat crops is during the stem-elongation phase when the crop is growing fastest, while early demand for nitrogen is small. The study utilised two field sites in South Australia (Hart and Mintaro) over two seasons (2003-04) to examine the effect of delayed applications of nitrogen fertiliser on nitrogen use efficiency (NUE) to dryland wheat. Treatments were applied to manipulate the crop canopy and to measure the balance between canopy size and structure and crop nitrogen uptake. In both seasons and sites significant (P<0.05) grain yield increases were obtained by later nitrogen application times. Grain protein also increases with rate of applied nitrogen and delayed time of application, with the 1st node (GS31) treatment generally producing the highest values. Applying higher rates of nitrogen fertiliser reduced NUE, while later applications were able to increase NUE. Canopy manipulation was able to increase crop nitrogen uptake, coinciding with improved grain yield formation. Generally, the data suggest that the nitrogen taken up later in the season is used very efficiently by the crop. The experiments outlined in this thesis showed that there is potential to improve NUE in dryland wheat grown in southern Australia, using tactical applications of nitrogen fertiliser. Thesis (M.Ag.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 2010 nitrogen; use efficiency; wheat; application; timing; fertiliser Strategic applications of nitrogen fertiliser to increase the yield and nitrogen use efficiency of wheat. Thesis Copyright material removed from digital thesis. See print copy in University of Adelaide Library for full text.open.access