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

Abstract

The effect of different nitrogen (N) management strategies (i.e. N rate; 0, 25, 50, 100 kg ha–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 (eCO2; 550 µmol mol–1) of wheat (cv. Yitpi) using the Australian Grains Free Air CO2 Enrichment facility. GPC did not increase significantly under eCO2 for most of the N management strategies assessed when compared with ambient CO2 (aCO2; 390 µmol mol–1). Grain yield of cv. Yitpi under aCO2 increased by 43% (P < 0.001) with application of 100 kg N ha–1 when compared with 0 kg N ha–1 at sowing; this response was approximately double (82%) when 100 kg N ha–1 was applied under eCO2 conditions. Under aCO2 conditions, by adding 100 kg N ha–1 at sowing, the GPC increased by 37% compared with the GPC at N0; whereas under eCO2 conditions, by adding the same quantity of N fertiliser, the GPC increased by only 28%. The highest level of N applied (100 kg ha–1), chosen for economic and practical reasons in a low-rainfall, yield-limiting environment, was lower than that reported in other global studies (250–350 kg ha–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.