Nitrogen efficiency of wheat cultivars in a Mediterranean environment

Experiments were conducted at 3 sites in Western Australia in 1993 using 33 wheat cultivars and crossbreds. Two rates of applied nitrogen fertiliser (0 and 40 kg/ha of nitrogen) were used to screen the lines for efficiency of nitrogen uptake, grain yield and grain protein production per unit of nitrogen applied, and nitrogen translocation to the grain. This information can be useful in determining nitrogen fertiliser strategies for wheat cultivars in the field. Nitrogen uptake in the plant tops was measured during the season and in the grain and straw at maturity. Grain yield, grain protein and nitrogen efficiency parameters were not markedly different between grain quality grades which are largely based on grain hardness. Yield efficient lines (high net yield increase per unit of applied nitrogen) were characterised by greater net uptake and net utilisation efficiencies but had similar yields and grain protein percentages as yield inefficient lines. Protein efficient lines (high net grain protein increase per unit of applied nitrogen) also had greater uptake efficiencies but lower utilisation efficiencies than protein inefficient lines. No lines were both yield and protein efficient suggesting that lines either use fertiliser nitrogen preferentially in yield production or in production of protein. The results indicate that in nitrogen-responsive situations it will be more profitable to use yield-efficient lines. Further investigation is needed to examine the suggestion that where soil nitrogen levels are higher (and yield responses to nitrogen are less) a greater economic return may come from using protein efficient lines. Some wheat lines had a high ability to recover fertiliser nitrogen applied to the crop. Others had a high ability to take up soil nitrogen. Tt is postulated that these differences may be due to differences in root systems. Some mid- and long-season lines that had high concentrations of nitrogen in the tops at anthesis metabolised that nitrogen poorly into grain yield or protein, This suggests that nitrogen efficiency may be partly related to maturity relative to length of growing season.