Reducing the reliance on nitrogen fertilizer for wheat production

Abstract

All crops require nitrogen (N) for the production of a photosynthetically active canopy, whose functionality will strongly influence yield. Cereal crops also require N for storage proteins in the grain, an important quality attribute. Optimal efficiency is achieved by the controlled remobilization of canopy-N to the developing grain during crop maturation. Whilst N will always be required for crop production, targeting efficient capture and use will optimise consumption of this valuable macronutrient. Efficient management of N through agronomic practice and use of appropriate germplasm are essential for sustainability of agricultural production. Both the economic demands of agriculture and the need to avoid negative environmental impacts of N-pollutants, such as nitrate in water courses or release of N-containing greenhouse gases, are important drivers to seek the most efficient use of this critical agronomic input. New cultivars optimised for traits relating to N-use efficiency rather than yield alone will be required. Targets for genetic improvement involve maximising capture, partitioning and remobilization in the canopy and to the grain, and yield per se. Whilst there is existing genetic diversity amongst modern cultivars, substantial improvements may require exploitation of a wider germplasm pool, utilizing land races and ancestral germplasm.

Keywords: Cereals; GPD, grain protein deviation; HI, harvest index; NHI, nitrogen harvest index; NUE, nitrogen use efficiency; NUpE, nitrogen uptake efficiency; NUtE, nitrogen utilization efficiency; Nitrogen; SSA, sub-Saharan Africa; WGIN, Wheat Genetic Improvement Network; Wheat; Yield.

Fig. 1

Wheat yields (continuous line) since 1942 in Great Britain and available information on the pattern of N application rates for England and Wales (bar chart) to cereal crops over the same period. Data extracted from UK Department of Food and Rural Affairs, the Rothamsted archive and British Survey of Fertilizer Practice. Figure courtesy of Chris Dawson and Associates, UK.

Fig. 2

Illustration of impact of N fertilizer application on winter wheat yield (solid line, diamonds), N-losses due to leaching (bar chart) and estimated grain NUE (dashed line, squares). Data taken from the Broadbalk long-term experiment at Rothamsted, from 1990 to 1998 (cv. Apollo 1990–1995 and cv. Hereward 1996–1998). Modified from Hawkesford (2011) and used with permission (Wiley and Sons, Ltd: Chichester).

Fig. 3

Impact of N fertilizer application on grain yield and total N taken up by the crop at maturity. Data are from the Defra Wheat Genetic Improvement Network trials (2007–2010), analysed in accordance with Barraclough et al. (2010). Data are available on the WGIN website (http://www.wgin.org.uk/). N application rates are 0, 100, 200 and 350 kg N ha⁻¹ (open triangles, closed triangles, open squares, closed squares, respectively).

Fig. 4

Idealized major fluxes of N in a high yielding wheat crop. Fertilizer application of 180–200 kg/ha is representative of the UK and is likely to be applied in a 3-way split. Width of arrow is a qualitative indication of size of flux.

Fig. 5

Grain protein deviation. Grain N content and grain yields for 47 cultivars, mean data over a 9-year period (2004–2012) in the WGIN trials at Rothamsted. Analysis performed as previously described (Barraclough et al., 2010) with data published on the WGIN website (http://www.wgin.org.uk/).