Cereals processing technology

Cereal production methods 21
numerous field trials have clearly demonstrated that there is very little benefit
from the application of autumn nitrogen to winter wheat or barley. Indeed there
may be an excess of nitrogen in seedbeds prepared by traditional ploughing
arising from the breakdown of organic matter. Applications of inorganic
nitrogen at this time only serves to increase the likelihood of nitrate leaching.
Winter cereals established by direct drilling have been shown to benefit from a
moderate application of nitrogen in the autumn.
The amount of spring and summer nitrogen required for optimum yields is
lower in winter barley than winter wheat, largely due to the former being more
prone to lodging than wheat. The rates of application can vary from as little as
50 kg/ha to over 250 kg/ha, depending on a range of agronomic and
environmental factors; the most important being the previous cropping, soil
type, expected grain yield and overwinter rainfall, while other variables such as
the variety’s standing ability, disease resistance and crop density must also be
taken into account.
The effectiveness of applied nitrogen in promoting crop growth and
ultimately grain yield is greatly improved by ensuring that adequate nitrogen
is made available according to the demands of the crop. If this objective is
achieved then the loss of soil nitrates through leaching will also be minimised.
Normal practice is to apply the spring nitrogen in two dressings, the first in late
February to early March and the second some time during the period late March
to late April. The first of these dressings, of approximately 40 kg/ha, will be
applied according to ground conditions and the likely demand for nitrogen by
the crop. The second or main application is generally considered to have the
greater effect on grain yield and is applied to coincide with the start of stem
extension. The window of application will therefore vary according to sowing
date, variety and spring temperatures. The timing of the main spring nitrogen to
winter sown malting barley is critical in achieving low grain nitrogen
concentrations and should be completed in March, irrespective of the crop’s
stage of growth.
Winter wheat grown for breadmaking requires an additional application of
late nitrogen to promote grain protein content. This can either be applied as a
solid fertiliser a few weeks after the main application, or as an urea-based
solution sprayed onto the crop during grain filling.
The demand for nitrogen by spring cereals is considerably lower than for
winter cereals due to the short growing season leading to reduced biomass
production. The risk of nitrate leaching is also greatly reduced and therefore the
benefits of splitting the application is considerably less than for winter cereals,
although with high rates of nitrogen in excess of 125 kg/ha, there may be some
practical benefits in splitting the application. To produce low grain nitrogen
spring barley it is desirable to apply all the nitrogen before the two leaf stage. In
contrast spring wheat for breadmaking would benefit from a late season
application of nitrogen to promote grain protein levels.