Agriculture Reference
In-Depth Information
use. The rapid growth of the maize plant, plus its ability to produce up to 1000 kernels
for every seed planted, led to its rapid spread and adoption by most cultures.
Early movement of sorghum from its origin in Africa was most probably along
trade routes established between East Africa and the western coast of India. Overland
trade was also a means for movement into the Fertile Crescent and along the Silk Road
into China. Introduction in the United States was most probably a result of the slave
trade from west Africa. A syrup-type variety was the first deliberate introduction in
1857. Since then, varieties have been introduced from South Africa, India, Sudan,
and China.
3.2.6 Soil Preparation and Planting
In many developed countries, maize and sorghum production is a mechanized system.
One of two systems of soil preparation may be used: conventional tillage or minimum/
zero tillage.
Under the conventional tillage system, the field is plowed with a moldboard plow
that lifts and turns over the upper 7 inches of soil. This acts to bury weeds and loosen the
soil, permitting easier root penetration by seedlings. This is an energy-intensive
procedure requiring a tractor, several types of heavy equipment, and two to three
trips over the same field before planting.
Minimum or zero-tillage systems reduce preplant tillage to a minimum or to none
at all. Specialized planters are able to till a narrow strip or to plant in soil undisturbed
since the previous year. This method reduces costs of planting but permits weeds to
grow unchecked. A necessary component of the zero- or minimum tillage system is
the use of chemical herbicides. When applied before, or during planting, these will
kill competing weeds, permitting the crop to germinate and grow for several weeks
without weed competition.
In less developed countries and in subsistence agriculture, farmers have been using
minimum or zero tillage for hundreds of years. Often only a pointed stick is used to
make a 2- to 3-inch hole into which two to three seeds are dropped. The hole is
covered and the seeds left to germinate. True zero tillage requires use of a chemical
herbicide to control weeds. When maize is a commercial crop, the additional cost of
herbicides is repaid by better yields and lowered field preparation costs. Sometimes
farmers will use a stick plow to till the soil before planting, but the depth is often
only 3 to 5 inches. This acts to kill growing weeds and gives the crop a chance to
develop before the weeds catch up. As can be seen in Figure 3.10, the tillage is some-
times less than desirable.
3.2.7 Fertilization
Maize and sorghum are nutrient-hungry crops. Each produces a heavy stalk and a large
number of leaves in a short period to form nutrient-dense grains. Every kilogram of
maize harvested from a field carries off 16 g of nitrogen, 7 g of phosphate, and 5 g
of potash.
