Cereals processing technology

20 Cereals processing technology
shrivelled grain with low specific weight. Manganese deficiency is most
frequently observed on light sandy, or chalk soils with high pH values. Low
availability of manganese results in grey-white lesions on the leaves.
Deficiencies of other trace elements are less common, although it is desirable
to monitor the trace element content of crops from time to time through plant
analysis. Maintaining the soil pH at an appropriate level will also be
beneficial.
Nitrogen is by far the most important nutrient, influencing both grain yield
and quality. With the exception of the high organic peat soils the levels of
available soil nitrogen in most arable soils is well below that which is required
for satisfactory growth and high yields of grain. Total soil nitrogen, on the other
hand, is often present well in excess of crop requirements but is present in the
organic matter fraction and is therefore dependent on microbial activity to
release the nitrogen into a mineral form, suitable for crop uptake. This process of
mineralisation is very dependent on soil environmental conditions, particularly
an adequate level of soil moisture, high temperature and aerobic soil conditions.
The release of nitrogen from this organic fraction will progress at a faster rate in
spring and autumn than at other times of the year. Nevertheless, it is difficult to
predict accurately rates of mineralisation throughout the growing season in such
a way that it would be possible to adjust fertiliser inputs accurately to meet the
precise nitrogen demand of crops. A significant proportion of the mineral
nitrogen fraction not used by the crop is leached into water courses, presenting a
potential environmental hazard.
The role of nitrogen in promoting grain yield has often been evaluated in
terms of its effect on single plant components such as leaf area, tiller
production and survival, grain weight and number. More recently, research
efforts have been directed at evaluating the effects of nitrogen on the whole
green crop canopy, in particular its role in manipulating the canopy size to
enable maximum radiation interception over as long a time interval as possible.
This approach, which has become known as canopy management, is currently
being evaluated in commercial wheat crops throughout the UK (Sylvester-
Bradley et al. 2000).
The amount of inorganic nitrogen fertiliser applied to cereals in the UK has
increased appreciably over the last thirty years. There have been a number of
agronomic reasons for this trend, but without question the driving force has been
the realisation by cereal producers that high nitrogen rates are associated with
high yields and hence higher financial returns. This has been made possible
through the introduction of high yielding varieties with improved lodging and
disease resistance, coupled with the adoption of highly effective fungicide
programmes to control foliar diseases and plant growth regulators to improve
further the crop’s standing ability.
The nitrogen requirements of winter cereals are significantly higher than
those of spring sown cereals on account of their longer growing season and
higher demand for biomass production. Additionally, the timing of N application
will vary according to their very different growth patterns. The results of