Agriculture Reference
In-Depth Information
3.3.7 Fertilization
Fertilization must at least supply an amount equal to the nutrients removed in the grain
plus an allowance for losses in the field. For a harvest of 4400 kg wheat grain taken
from 1 ha, 90 kg of nitrogen, 43 kg phosphate, and 27 kg of potash fertilizer are
removed.
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This amount must be replaced before planting just to supply the crop
with needed nutrients and avoid depletion of soil fertility. The source of the nutrients
for commercial farmers is usually chemical fertilizers, though this is often sup-
plemented by manure from farm animals. The amount of fertilizer needed by wheat
depends also on the type of grain being produced. Durum wheat is marketed by
protein content, which is affected by nitrogen levels in the soil. The farmer must care-
fully balance the soil nutrient status against desired yield levels to obtain a quality
product and maximize profit.
Fertility levels in developing countries are often less than desirable, which negatively
affects grain yields. Chemical fertilizers are frequently expensive. This means they are
reserved for high-value cash crops such as vegetables. Fertilization of wheat is often
done only with animal manure, which is available in limited quantities. Even though
the grain is the most important commercial product of most wheat and barley fields,
the straw is used as fodder for animals during the dry season. The net effect is that all
of the plant above ground is removed with all the nutrients it contains. This further
reduces soil fertility since these residues are not left to decompose and replenish the soil.
Fertilization of barley is a problem because it is grown in areas of low rainfall.
With lower rainfall comes the risk of irregular rainfall patterns and the risk of low
yields. As a result, barley is even less likely to receive adequate fertilization for
maximum yields. In commercial farming enterprises, barley is usually given a
minimal application of fertilizer because of this risk. In small or subsistence farms, it
often receives no fertilization.
3.3.8 Weeds, Insects, and Diseases
Weed control in wheat and barley is more difficult than maize or other crops planted in
wide rows. When wheat and barley are planted in very narrow rows, tractors or
animals cannot move between the rows for cultivation operations. When they are
planted by broadcasting the seed, the plants are randomly spaced and weed control
is even more difficult. While the plants are in the rosette growth stage, it is possible
to carry out some field operations such as herbicide application or hand weeding.
As soon as the stalks begin to form, any field operations will injure plants and
reduce yield.
Many insect species feed on wheat and barley plants in the field. They can affect
plants at all growth stages such as seedling, at tillering, and stem elongation. In most
cases the damage is not severe enough to warrant application of insecticides. By
using specific cultural practices, it is possible to avoid damage by specific insects.
Pupae of the Hessian fly will attack the stem of wheat plants causing stunted growth
and death of the seedlings. The most common control practice in the U.S. Midwest
is to delay planting until after the “fly-free date” in the fall. Crop rotation, resistant
