Can nitrogen fertiliser maintain wheat (Triticum aestivum) grain protein concentration in an elevated CO2 environment?

The effect of different nitrogen (N) management strategies (i.e. N rate; 0, 25, 50, 100kgha(-1), split N application, foliar N application, legume precropping) were assessed for how they may reverse the reduction of grain protein concentration (GPC) under elevated CO2 (eCO(2); 550 mu molmol(-1)) of wheat (cv. Yitpi) using the Australian Grains Free Air CO2 Enrichment facility. GPC did not increase significantly under eCO(2) for most of the N management strategies assessed when compared with ambient CO2 (aCO(2); 390 mu molmol(-1)). Grain yield of cv. Yitpi under aCO(2) increased by 43% (P<0.001) with application of 100kgNha(-1) when compared with 0kgNha(-1) at sowing; this response was approximately double (82%) when 100kgNha(-1) was applied under eCO(2) conditions. Under aCO(2) conditions, by adding 100kgNha(-1) at sowing, the GPC increased by 37% compared with the GPC at N0; whereas under eCO(2) conditions, by adding the same quantity of N fertiliser, the GPC increased by only 28%. The highest level of N applied (100kgha(-1)), chosen for economic and practical reasons in a low-rainfall, yield-limiting environment, was lower than that reported in other global studies (250-350kgha(-1)). In a low-rainfall, yield-limiting environment, it is not practical to increase GPC by applying N alone; new cultivars may be required if grain growers are to maintain grain protein (and functionality) in the future as CO2 levels continue to increase.