Purpose of land preparation.
Group Discussion: Why do we need to prepare & conserve
Preparing the land for crop production serves many
purposes, including: a) the creation of a seedbed, where
planted seeds are in contact with the soil moisture
so they will germinate to become established quickly
(#3-4). b) Weed control. Removal of weeds is necessary
because they successfully compete with crops for moisture,
nutrients and light. In addition, some weeds secrete
chemicals from their roots into the soil that inhibit
crop seeds from germinating. c) The incorporation of
crop residues and fertilizer materials into the soil,
when plowed into the soil, helps buildup organic matter
and nutrients for the crop (#5). d) Also, plowing breaks
the soil crust and hardpans, improving water penetration
and aeration. e) Shapes the soil for irrigation and
Because of the possible damage to soil structure from
overworking the soil, one modern approach to soil conservation
is to use only as much tillage as is required to produce
a good crop. The kind and amount of tillage is determined
according to crop, soil and field conditions. No one
set of guiding standards is appropriate for all situations.
Tillage must be done in a way that will assure adequate
protection of soil and water resources. A good soil
surface will prevent crust formation and allow rapid
Other management practices such as contouring, strip
planting, cover cropping, alley cropping,reduced tillage,
terracing and leaving some crop residue on the land
help to eliminate or minimize the loss of soil from
water and wind erosion (#6). Using good erosion control
practices not only preserves the soil, but also many
nutritional elements needed for plant growth. In addition
to these practices, a good fertilizer program promotes
greater crop growth. Crops, in turn, contribute to soil
improvement by protecting the soil against the impact
of falling rain, by holding the soil in place with extensive
plant root systems, and by providing soil nutrients
from organic matter of decomposing plant residues. (For
more ideas on fertilizer program, refer to lesson 1.5)
Methods of Land Preparation.
Equipment: Tractor and plowing implements, animal traction
and hand operations.
There are things that need to be considered, other
than weed control, in selecting the right tillage practices
(#7-9). Farmers probably already know that plowing is
the most effective method for weed control. Before planting,
plowing completely cuts off perennial weed shoots and
exposes many root stocks to sunlight so they dry out
and die. Also,the plow leaves the surface rough and
porous, increasing the amount of water that enters the
soil and helping to control erosion. Soil runoff can
also be reduced if furrows are plowed opposite to the
way water would flow. Good contact between the seed
and soil is needed in order for the seed to take on
enough water to swell and germinate.
A soil with good tilth can be described as one that
has good aeration, takes water readily, drains well,
and works down to a good, loose, seedbed. This is one
of the functions of tillage seedbed preparation (#10).
Tillage to prepare a seedbed after the land has been
plowed is accomplished with disks, harrows or field
cultivators. The best depth to plow is a much-discussed
subject. Although research shows that 8 inches (20 centimeters)
is usually deep enough, deeper plowing has sometimes
produced slightly higher yields. Disk plows should be
used in soils that have been plowed and left with rough
surfaces, in preparation of a good seedbed. There is
little reason why disking should not replace completely
plowing in soils that have relatively little or fine
crop residues. If you go once over with a disk plow
it nearly completes seedbed preparation. At this time,
most of the trash and residues are worked into the soil.
Overworking a field with a disk can be disastrous as
it leaves the soil surface fine, and loose. Overworked
soil easily looses moisture and the lower half of the
plowed soil layer may end up as hard as before it was
plowed because it gets compacted with the machinery.
It needs to be considered that the disk does not function
well in fields with large stones, it could be damaged.
While tillage of some kind is desirable, there are
many small farmers who, because of steep land and/or
lack of access to equipment, plant without tilling the
soil first. In these cases the farmer clears the land
with a machete (may do manual plowing, as well) and
plants using a planting stick (#11).
Group Discussion: How should land be prepared?
Best time for Seedbed preparation.
Marginal moisture supply is critical at plowing time
because the soil must be dry enough for tillage without
causing excessive compaction or creating clods in fine-textured
soils (#12-15). As soon as the crop has been taken out,
the land can be tilled and preparations can be started
for next cropping season. In areas where there are more
than one cropping season per year, land can be prepared
once a year, using the same crop furrows for subsequent
crops. The best time to work the land will be just before
planting time making sure the land is not too wet or
too dry. Under most conditions, a smooth, finely pulverized
seedbed should not be prepared until just before a crop
is to be planted.
Group Discussion: When should we start
preparing our production unit?
Activity: Participants decide if their
production units meet the criteria just discussed. What
can be done to better prepared their land.