Agriculture Reference
In-Depth Information
also compacted the soil. Most large commercial operations now use minimum or zero-
tillage systems. Herbicide is applied at the time of planting so that only one pass
through the field is needed. Under ideal conditions, this will control weeds until
harvest. If there is a heavy weed infestation, another pass through the field may be
needed for a second herbicide application. Witchweed (Striga helmonthica)isa
serious pest of sorghum in the Sahel region of Africa and maize in the sub-Saharan
regions of Africa. This is a parasitic weed that attaches to the roots to draw off nutrients
and, eventually, kills the plant. Large areas of Sudan and Niger have suffered major
losses because of this weed. Current efforts are underway to produce varieties resistant
to witchweed.
Insect management is normally done by selection of a variety. Modern maize and
sorghum hybrids have been genetically modified to discourage feeding by rootworms
and some leaf-feeding insects. In tropical areas, planting dates are often shifted to
avoid times of insect proliferation. Small commercial plantings of maize may utilize
chemicals for control of the leaf-feeding European corn borer or local preventive
measures may be used. One such method used in Mexico is to apply small amounts
of wood ash in the whorl of the young maize plant. Many transgenic temperate varieties
of maize and sorghum now utilize the Bt gene to discourage feeding by the corn borer
without application of toxic chemicals. There has been less success incorporating this
gene in tropical lines of maize and sorghum.
Disease management has been accomplished for hundreds of years by selection of
the most resistant plants. The seed of these plants are replanted to form new disease-
resistant, or tolerant, varieties. This is an especially effective way to put disease-
resistant varieties in the hands of small farmers.
3.2.9 Harvest and Storage
Harvesting of maize and sorghum varies according to the climate and type of farm
operation. The simplest is that of the commercial farmer. He takes a combine
through the field that removes the ear or panicle, runs it through a sheller, then separates
the grain from the cob, leaf, and stalks. Stopping when the combine grain bin is full, he
unloads the shelled grain into a waiting truck. When the truck is full, it drives directly
to the local grain elevator to deliver the harvested grain. In some large operations, the
farmer may store the grain in his own grain bins to await better market prices or to
use for livestock feed. A single hectare can be harvested in less than 30 minutes by
one person driving the combine.
Harvest of maize and sorghum by a small farmer in developing countries is often done
by hand, hiring day labor to twist off the ears of maize (as in Fig. 3.11) or cut off the
sorghum heads and collect them in a waiting wagon. If labor is scarce, he may cut the
stalks with a machete and form “shocks” (standing bunches of cut stalks) in the field.
When possible, he will pick off the ears and take them to his house for shelling and
later sale in the local market. Near large cities, truck drivers may pass by as the harvest
progresses and buy the grain directly from the farmer in the field. This has the advantage
of giving instant cash to the farmer and avoiding threshing, transport, and storage pro-
blems. Often, however, the price offered by the drivers is much below market price.
