Evaluation of nitrogen use efficiency (NUE) in wheat.

Nitrogen fertilizers are a major input required for cereal crop production worldwide. The management of this resource is a significant challenge to most agricultural systems as it can have significant impacts on yield and the environment. The use of applied nitrogen fertilisers in cereals is poor, where only 30-40% is actually used by cereals and the remainder lost to the environment by surface runoff, soil denitrification and volatilization (Ehdaie et al., 2010; Butterbach-Bahl and Dannenmann 2011). Improving cereal nitrogen use efficiency (NUE) is imperative to achieve yield and quality with less direct N inputs. In this study, experiments were conducted in 2010 to evaluate the effect of N fertilizer application (0, 50, 100, 150 kg urea/ha) on the growth and yield of wheat varieties at specific locations across South Australia while a small pilot glasshouse study was conducted at the Waite Campus, Adelaide University. The field experiments were designed as a randomised split-plot with three replications for each wheat cultivar and N treatment. Plant response to N treatment was measured through estimates of plant height, leaf chlorophyll content (SPAD meter), plant spike number, grain yield, 1000 grain weight, shoot biomass weight, grain N % and final grain protein content, harvest index (HI) and NUE. Restrictions in space and large growing pots limited the controlled glasshouse study to a technical study. The results found little variability between the three field sites in Grain %N in response to increasing N provision. There was a trend of increasing grain %N at both Mintaro and Pinnaroo, which was broadly in evidence across the individual lines. Grain yield was highest at Mintaro and was double of that achieved at both Pinnaroo and Tuckey. Whereas, in the glasshouse experimental results show that there was a strong response in grain %N to increasing N provision when plants were grown over the spring/summer season but not during the autumn/winter. Nitrogen use efficiency (NUE) was found to be greater at low nitrogen treatment (N1) in all experiments and decreased roughly with increased N application. In general, the results indicated that wheat cultivars responded well to nitrogen application with the medium rate of application within experiments, while beyond this rate caused no significant improvements in plant growth and yield.Thesis (M.Ag.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 201