Fertilisers and Quality of Wheat and Barley

Keywords: wheat, barley, baking, malting, fertilisers, plant physiology.

Cereal quality is becoming of increasing importance in Europe as the supply of grain exceeds the demand. The most important quality markets are, for wheat, the baking and pasta industries and, for barley, the malting, brewing and distilling industries. Many attributes of quality depend strongly on genotype or environment. However, nitrogen, or protein, concentration in the grain, protein composition and specific weight can all be influenced by the level and timing of fertilisation to a greater or lesser extent depending on the growing conditions. Recommended levels and timing of nitrogen fertilisers are generally related to those for high yielding feed wheats and barleys and are subject to the same uncertainty.

In many parts of Europe the effects of weather, especially after ear emergence, are such as to make it impossible to guarantee that the recommended rates will produce grain of the desired nitrogen concentration even when adjustments are made to take account of local conditions. For malting barley a low nitrogen concentration in the grain is needed and timing of nitrogen application is of great importance to ensure that sufficiently high yields are attained without compromising the quality standard. In wheat, on the other hand, protein concentration must exceed a threshold value and the amount and timing of fertilisers must be adjusted to maximise the protein concentration without suffering the deleterious effects of excessive nitrogen.

The composition of the protein in wheat grain influences the baking quality of flour. Genotype has the largest effect on the composition but in certain circumstances levels of sulphur and copper in the soil are sufficiently low to affect the protein quality adversely. In these circumstances, however, these elements would probably be already applied to improve yields. Foliar application of urea during the milky ripe stage of grain development can increase the nitrogen concentration in the grain but may affect the protein composition adversely.

Specific weight is an indicator of how well the individual grains are filled. Poor grain fill is not usually associated with inadequate fertilisation but can occur when excessive levels of nitrogen applied early in the crops’ development permit the survival of more grain sites than can be filled adequately or when the uptake of copper is too low.

Achievement of quality standards in wheat and barley depends much more on site, season, variety, good husbandry and appropriate post-harvest treatment than on fertiliser policy. However, even quite small improvements in quality can make the difference between acceptance and rejection of a grain sample and so quality targets must be considered when planning a fertiliser programme.

Dr G Russell, Edinburgh School of Agriculture, Edinburgh, UK.

23 Pages, 1 Figure, 1 Table, 64 References.