TECHNICAL PAPER #8
UNDERSTANDING SOIL PREPARATION
Paul J. Abrahams
Dr. J.W. Fitts
Dr. Nail Ozerol
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
Tel: 703/276-1800 . Fax: 703/243-1865
Understanding Soil Preparation
[C]1984, Volunteers in Technical Assistance
This paper is one of a series published by Volunteers in
Assistance to provide an introduction to specific
technologies of interest to people in developing countries.
The papers are intended to be used as guidelines to help
people choose technologies that are suitable to their
They are not intended to provide construction or
details. People are
urged to contact VITA or a similar organization
for further information and technical assistance if they
find that a particular technology seems to meet their needs.
The papers in the series were written, reviewed, and
almost entirely by VITA Volunteer technical experts on a
Some 500 volunteers were involved in the production
of the first 100 titles issued, contributing approximately
5,000 hours of their time.
VITA staff included Leslie Gottschalk
and Maria Giannuzzi as editors, Julie Berman handling
and layout, and Margaret Crouch as project manager.
VITA Volunteer Paul J. Abrahams, the author of this paper,
chemist for the McElrath Poultry Company and also a
farmer who raises corn, clover, and sheep.
VITA Volunteer reviewers
Dr. J.W. Fitts, Dr. Nail Ozerol, and Richard Roosenberg are
also experts in the field of soil preparation.
Dr. J.W. Fitts is
an agronomist with Agro Services International, Inc., an
consulting firm. He
was the head of the Soil Department at
North Carolina State University, and Director of the
Soil Fertility Evaluation Program at North Carolina State
University for several years.
He has published widely in the
fields of agronomy and soil science.
Dr. Nail Ozerol is the
director of N.H. Ozerol & Associates, a health care and
consulting firm. He
has published widely in the fields of
agriculture and nutrition.
Richard Roosenberg is program director
of the Tillers Research Program at The Nature Center, which
reviews animal-powered farm technology for its adaptation to
present needs in the United States and developing countries.
VITA is a private, nonprofit organization that supports people
working on technical problems in developing countries.
information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to
maintains an international Inquiry Service, a
specialized documentation center, and a computerized roster
volunteer technical consultants; manages long-term field
and publishes a variety of technical manuals and papers.
UNDERSTANDING SOIL PREPARATION
by VITA Volunteer Paul J. Abrahams
The purpose of soil preparation is to develop a planting
that will foster the best possible growth of agricultural
while preventing the deterioration of the land through
destruction of soil structure, or nutrient loss.
preparation system used must be economical, since a large
the expense in raising a crop occurs before the seed is ever
placed in the ground.
OBJECTIVES OF SOIL PREPARATION
The immediate goals to be accomplished in soil preparation
destruction of weeds,
incorporation of organic material,
incorporation of fertilizers and lime, and
development of the proper seed bed.
Destruction of Weeds
Weeds compete with agricultural crops for moisture,
and sunlight. They
also hinder harvesting, particularly if they
are viney types.
Some weeds are poisonous to people and animals.
Proper soil preparation coupled with effective crop rotation
will prevent the emergence of weeds at the time of planting.
This allows crops at their most tender stage to grow without
soil preparation will also retard the growth
of weeds as the crops develop, making cultivation and
Incorporation of Organic Material
Organic matter has many beneficial qualities that aid plant
the ability to retain water for the use of
the improvement of soil tilth (structure);
the ability to hold nutrients in the soil
leached out by rain.
The natural coverings of soil are forests or grasses, which
yearly add organic matter to the soil as dead wood, leaves,
roots. Whenever soil
is made bare by the removal of its
vegetative cover the level of organic matter will be
addition, soil microbes, such as bacteria and fungi, and
animals, such as insects and worms, are constantly consuming
When the forest or grassland is destroyed to grow crops, the
natural additions must be replaced by the farmer's efforts.
Organic matter is added by working animal manure, compost,
or leaves into the soil, or by plowing under green manure
such as clovers, vetch, or rye.
Crop residues such as stalks,
vines, and leaves will add to the organic matter level.
Incorporation of Commercial Fertilizers and Lime
Unless green manure crops are used or large amounts of
manure can be added to the soil, commercial fertilizers must
used to maintain proper soil fertility.
As a general rule, one
must add plant nutrients in an amount equal to that removed
(See Table 1.) If this is not done, the fertility
of the soil will drop slowly, causing a decrease in
and potassium may not have to be replaced
at the same rate as nitrogen.
Soil tests to determine the
needed amounts of these nutrients can save on fertilizer
It would take the addition of approximately five tons of
manure per acre to replace the nutrients removed from the
the harvesting of 100 bushels of corn.
A 50-bushel wheat crop
would require four tons.
That is equivalent to the addition of
11,000 kg per hectare of manure on corn and 9,000 kg per
of manure on wheat.
It would be preferable if all nutrients could be added as
because this would greatly increase the organic matter
the soil. However,
the large amounts of manure needed may be
difficult to obtain.
In general, it may be more efficient to
manure the garden or speciality crops and use commercial
fertilizers on field crops.
Proper soil fertility helps prevent erosion.
Fertile land produces
more and bigger plants in a given area than nutrient-poor
Fertilizer Amounts Needed to Replace
by Harvesting Corn Grain and Wheat
Amount of Fertilizer
At 100 bushels per
acre 80 lb
At 6200 kilograms
At 50 bushels per
acre 70 lb
At 3400 kilograms
land. Growing crops
protect the soil against beating rains.
Crop residues incorporated into the soil increase the level
Lime must be added to most soils periodically to neutralize
acidifying effect of commercial fertilizers.
Even land that does
not need fertilizer usually requires lime because growing
roots cause the soil to become more acid.
If possible, a soil
testing laboratory should be consulted to determine the need
Development of the Proper Seed Bed
The development of a suitable seed bed will ensure good seed
germination, allow rapid root growth, and aid in mechanical
The best soil is loose, having a crumb structure that breaks
easily into small pieces approximately three to seven
in diameter when handled.
The deeper this crumb condition is
maintained in a soil the better.
Crumb-type soil fits snugly
around the young seed with no air gaps.
This allows the seed to
be bathed in moisture.
Roots will grow readily into this type of
soil. Crumb soil is
easy to cultivate with machinery or by hand.
Tractor or animal-drawn cultivators can gently roll the
to plants, easily killing weeds.
The worst type of soil is one full of hard clods, larger
three centimeters in diameter.
The larger the clods the more
difficult the soil is to work.
Seeds covered by clods are surrounded
by air pockets, causing them to dry out too soon.
young plant has a hard time breaking through clods and many
never get to the surface.
Roots have a similar problem.
Mechanical cultivators will push large clods toward the
growing plants, breaking many.
Moreover, clods contain many weed
seeds, which will still germinate if the clod is merely
around by the cultivator.
Young grass and other weeds will not
be killed unless their roots are broken free from the
soil. This cannot be
accomplished by rolling clods (Figure 1).
Clods are formed primarily by working (plowing, harrowing,
cultivating) soil when it is still wet.
They are particularly
noticeable when a moldboard plow is used on wet ground.
smooth-sided clods are turned up by the shearing action of
plow. When these
clods dry out, they are almost impossible to
break down--even with extra harrowing.
The less organic matter a
soil contains, the more likely it is to form clods when
Humus in the soil prevents soil particles from cementing
The simplest way to develop a good crumb structure in a
by growing thickly planted legume and grass sod crops in
with the field crop.
Over time, the roots of legumes and grasses
will crumble even a hard soil to a great depth.
The roots also
open up passages in the soil for the movement of air and
The beneficial effect of these sod crops will last several
after they have been turned under.
And livestock can graze on
the growing grasses.
To ensure a good crumb structure as well as a good seed bed:
Rotate sod crops with field crops.
Add as much manure and other organic
Wait until wet soil is no longer sticky
squeezing a handful of soil in your hand.
that is too
wet will pack together in a sticky lump and
hand wet. Soil that is dry enough to
again easily when pressure is released.
II. SOIL PREPARATION
OF AGRICULTURAL LAND
CATEGORIES OF AGRICULTURAL LAND
Several factors affect the method of soil preparation:
length of growing season
annual distribution of rainfall
slope of the land
type of crops to be produced
size of farm
level of technology
Given the large variation in geographical conditions and
practices encountered in food-growing, it is easiest to
agricultural lands into three basic categories:
Large-scale agriculture on fertile, level
Intermediate-scale agriculture on erodible
Much of the world's best crop land is located along the
of major rivers.
Other highly productive areas include
lands that lie on the beds of ancient lakes and oceans,
have dried up or moved.
These lands are flat and highly fertile.
In many countries, such areas have been divided into large
and soybean farms that require high levels of technology.
Because these lands are level, erosion is relatively
The lands are also often wet, discouraging livestock
Even where livestock can be raised in most areas, such land
too valuable to be used as pasture; crops bring a better
per acre. All these
factors have often led to a mono cropping
system, with fields left fallow, between the yearly
the short run, it is more economical under these conditions
add commercial fertilizer than to use green manure
the long term, however, such practices may not be wise, as
can wear out the soil, increase erosion, and foster the
diseases and pests.
The method of farming hilly lands is very different.
case, erosion is the farmer's greatest enemy.
cannot be cropped every year, so it is best to use a system
routinely rotates crops with sod pasture.
machinery must be suited to deal with thick sod.
The garden is a special case for soil preparation because
kinds of vegetables with different growing habits are
a small area of land.
Since the land is worked very frequently,
it is usually not possible to set aside areas for sod
Gardens thus need large amounts of organic matter added
keep the soil from becoming exhausted.
The size of a garden
should be no larger than one's supply of manure or compost
SOIL PREPARATION OF FERTILE LOWLANDS
This method of soil preparation is used on large level
where erosion is at a minimum.
The main crops are corn, wheat,
rice, millet, sorghum, and soybeans.
Comparative advantages and
disadvantages include the following:
Large tractors are used to prepare the
the following steps:
Commercial fertilizer and lime are spread by
tractor-drawn wagon. Fertilizer may be
Land is chisel-plowed six to eight inches
Land is then smoothed out by disk harrow or
after plowing (with very large
it is possible to plow and smooth in one
using a large disk harrow).
Right before planting, a second smoothing
using disk or spike tooth harrow should
undertaken if needed.
The seeds of row crops such as corn are
ground if irrigation is not used; on ridges
irrigation is used; or on the side of ridges
if land is
salty. Row crops are planted with row
planters. Small grains such as wheat
with a grain drill.
Labor requirements are low, which is an
Energy use is very high.
Maintenance requirements for machinery are
The cost of the equipment is very high, but
good yearly yields and where labor costs are
type of farming will return more per acre
other, particularly if many acres are planted
is used to the fullest extent. This
work if one person has many acres of level
cultivate, particularly if crop yields can be
through irrigation. However, this
not work if
existing loan interest rates for machinery
are high or
if grain prices fluctuate widely.
If herbicides are used, one or more of the
steps may be left out. Fields may not
to be plowed
or harrowed, for example. No-till
plant directly in unplowed land by opening
up a furrow
with the disks and spraying the middle to
weeds. However, every few years the
land must be
bury excessive crop residues that can clog
harbor plant diseases.
SOIL PREPARATION ON ERODIBLE UPLAND SOILS
These soils need a sod cover crop for at least half the year
keep erosion to a minimum and rebuild soil structure.
on the farm is divided into two, three, or four segments
portion cultivated each year.
Table 2 below shows the relationships
between the slope of a field and the ideal rotation periods
for planting. These
are averages for all soil types. Soils
a thin topsoil, particularly when the subsoil is clay,
cultivated less often.
This type of agriculture is highly suited
for small tractors (20 to 40 horsepower) or for animal-drawn
Number of Times During a Four-Year Period
That Land May Be Cultivated
(*) Percent slope is
found by measuring the number of feet (or
meters) the land
falls every 100 feet (or meters).
The method of soil preparation is as follows:
Apply lime if needed.
If the cover crop is thick and viney, turn
land with a
plow with a colter. In the second and
years of cropping, implements other than the
plow may be more efficient and better for the
These include the chisel plow, depending on
Smooth soil with harrow immediately after
Wait approximately three to four weeks for
Smooth with disk or spike tooth harrow with
Plant seed with a row crop planter or grain
rows that run
across the slope of the land. This will
the topsoil from being washed away.
rainfall is always plentiful during the growing
season, it is
best to plant row crops such as corn in a
furrow two to
four inches (five to ten cm deep). This
moister soil for germination; make
easier (soil can be pushed into furrow to
and, in the case of heavy downpours, tend
erosion. In areas of heavy rainfall,
time of planting.
The amount of labor needed to cultivate a particular area of
sloping land is higher than on the level lowland farm
small equipment is used.
However, since the land is only
cultivated a portion of the time, the total amount of labor
needed for the whole farm on the average can be low.
animals are used, the labor requirement is higher; it takes
longer to cultivate the same amount of land with animals
with tractors, and the animals must be fed and housed.
Energy use is moderate since smaller equipment is used.
Moreover, land in the sod part of the rotation will require
little energy use, and if legumes are grown, the nitrogen
fertilizer cost will be lower.
The maintenance requirements of
the machinery used will be proportional to its size.
also be a periodic upkeep required on any fencing used.
The cost of such a system is lower than that for the lowland
farming technique since smaller equipment is used.
because fencing and animals will have to be purchased in the
beginning, initial costs can be high.
Also, a mower might be
necessary if the stock cannot control all the weeds in the
control during the sod or pasture phase of rotation
becomes very important during the periods when field crops
cultivated. In the
long run, the cost per acre of land will be
lower and the animals will provide additional income that is
often steadier than the marketing of grain.
The main advantage of this system is that the sod crop does
of the soil preparation itself.
The roots "plow" and "subsoil"
the ground and legumes capture nitrogen from the atmosphere
help save on fertilizer expense.
The root action helps
distribute organic matter and nutrients to a great depth in
soil, thus fostering the root growth of the cultivated crop
follows. While the
field is in a sod crop, erosion will be virtually
halted and when the soil is exposed during the cropping
year it will be less likely to erode because of its higher
organic matter content and water-holding ability.
of sod between row crops will help catch eroding soil on
Many weeds that hinder cultivation in continually cropped
are smothered out during the sod portion of the
leaf weeds are hardest hit.
Either the weed seed is killed
before germination or it is consumed by livestock before it
The only disadvantage to this system is in the time lost in
spring during the month-long decomposition period.
a sod crop may be somewhat more difficult than plowing bare
In general, it is best to use a moldboard plow to turn sod.
However, it may be advantageous on large acreage to use the
practice for as many years as possible.
With this practice,
a herbicide is used to kill the foliage of the sod.
Seed is then
planted into narrow furrows opened by disks.
are used to kill subsequent sod and weed growth.
SOIL PREPARATION IN GARDENS
This third category of farming is confined largely to small
of intensively cultivated land where large amounts of
material are added regularly.
The main crops produced are
many different kinds of vegetables are produced
within the garden and many successive plantings and
harvestings take place during the growing season.
The two main methods of soil preparation are clear
and mulch gardening.
In deciding which techniques to use, the
gardener should consider the soil structure, the amount of
available for tending the garden, and what type of tools and
machinery are available.
A thick layer of mulch:
shades out weeds,
helps soil retain moisture,
protects soil from traffic compaction,
keeps soil from splashing on plants, and
reduces the amount of equipment required,
on the other hand, may possibly harbor
insect pests and
allows use of mechanical tillage
works well against grass-type weeds
works well on large-scale cultivating.
In clear cultivation, a small tractor, animal-drawn
power tiller, or hoe is used to keep the areas between the
vegetable rows clear of weeds.
The soil in these areas, which
usually becomes hard due to heavy traffic, is loosened in
same process. In
mulch gardening, thick layers of straw, leaves,
bark, plastic film, or newspaper are placed between the rows
shade out most weeds.
The soil under the covering remains loose
and retains moisture.
This method makes cultivating machinery
impractical, but requires hand weeding to remove any pest
that may break through the mulch.
Both clear cultivation and mulch gardening require the
of large amounts of manure, compost, and/or fertilizer to
soil regularly; use as much manure as possible, up to 10
acre (2,000 kg per hectare).
The simplest method is to spread
fresh barn manure over the garden at the end of the growing
season and work this into the soil immediately by plowing it
under, mixing it with a tiller, or spading the ground deeply
a fork-type tool. By
planting time, the manure will have decomposed
enough so as not to harm the growing crop.
Note that in
tropical areas of relatively high year-round temperature and
seasons of very heavy rains, it may be better to spread aged
manure over the garden just before planting.
decays completely very quickly in the tropics, and humus and
nutrients may be washed away by the rains before they can be
use to the crop.
If tillage is to be employed, space the rows far enough
accommodate the kind of equipment used.
Three to four-foot
spacing (1-1.2 meters) for an animal-drawn cultivator and
spacing (1 meter) for a power tiller are recommended.
rows may be used with hand hoeing.
When mulch is used, the vegetables may be grown in beds
four feet wide with traffic paths in between.
is done on the paths so as not to compact the soil in the
Topsoil may also be dug from the paths and placed on the
increase rooting depth.
Although gardens are extremely labor intensive, cultivating
may be reduced by the use of machinery.
Manure spreading is the
Cultivating is much easier, however, if the manure
or compost is added in sufficient quantities, as the organic
matter will make the soil much easier to work.
The efficiency of
a garden can be greatly increased by irrigating during dry
periods. This will
ensure profitable yields in times when
drought might have made all the work a waste of time.
plantings may be irrigated simply by allowing water to flow
between the rows.
Irrigating mulched beds may require more care
and possibly special equipment such as drip irrigation
However, the mulch helps retain soil moisture and so less
irrigation is necessary.
The cost of a garden should be kept as low as possible.
garden is combined with a rotational system that includes
livestock, a steady supply of manure is available.
virtually eliminates fertilizer costs.
A heavily manured garden
will produce abundantly in a small area of space.
A small garden
will not require much machinery, keeping costs way down.
Maintenance requirements should also be low.
should be lubricated properly and the surfaces of iron,
and leather items oiled regularly.
Hoes should be kept sharp for
The best way to ensure a large supply of animal manure is to
keep livestock in a barn, corral, or other enclosure at
Bedding straw retains urine and keeps manure drier.
works exceptionally well with sheep or goats.
LAND USE SURVEY
All farmers should make a land use survey of their
farms are composed of both good and poor land, in one field
several distinct fields.
Each field must be rated according to
slope, size, and soil type.
These factors will determine how
often and what type of crops are to be grown in each field.
Many acres-along narrow rivers have fertile level fields
the river that can be cultivated every year.
As one moves away
from the river, a point is reached where the slope becomes
steeper and the land rises toward a hill.
These hillsides should
be used for livestock grazing and cultivated only at
Each of the three major types of agriculture can show up on
farm. Farmers will
choose the type of agriculture and soil preparation
needed for each part of their farm.
SOIL PREPARATION EQUIPMENT
Soil preparation technology has developed as people have
bigger and bigger machinery.
However, the greatest mistake a
farmer can make is to buy machinery that is larger than the
that needs to be done.
Most gardens should still be worked by hand.
It is the lack of
manure and compost that makes the soil hard and leads
think they need more equipment to work it.
Mixed livestock and
crop farming on sloping land needs no more than a small
or draft animals.
Only the huge farms and the most fertile,
level land can economically use today's large tractors.
The system of rotational agriculture was developed before
invention of the tractor and commercial fertilizer.
It is a
system in which plants and animals do most of the work of
preparing the soil for the production of crops.
Hence, it is
well suited to farmers who have little money to spend and
land will not produce the grain yields obtained by prime
land farms where farm technology is at its peak.
Rotational livestock grazing systems require less equipment
cropping. The more
land grazed, the more manure is available for
the portion of land that is cropped.
REPLACEMENT OF NUTRIENTS
Growing plants absorb nutrients from the soil.
must be replaced, or the soil will lose its ability to
healthy plant life.
The major nutrients that have to be replaced
regularly are nitrogen, phosphorus, potassium, and
can be bought as commercial fertilizers, but they are also
in all kinds of vegetable matter and animal waste products
Table 3). Many of
these resources can be obtained locally.
The best way to use plant wastes is to compost them.
breaks down fibrous vegetable matter and makes it easier to
with the soil.
Bacteria and fungi digest large vegetable parts,
turning the material into a nutrient-rich fertilizer.
piles are made by alternating layers of plant wastes,
a calcium source such as limestone or ash.
If the pile is kept
moist, the vegetable matter will be combined with manure and
calcium to form humus, a perfect source of plant nutrients.
Raw manure can be spread directly onto the field, but during
wet weather it should be worked quickly into the ground for
Manure has an unpleasant odor but if properly
handled, it should not smell strong.
It also contains large
amounts of nitrogen which will be lost to the atmosphere if
worked quickly into the soil.
Nutrients Found in Vegetable and Animal Wastes
Waste vegetable parts
Manure and fertilizer need to be spread evenly over a
allowed to remain in piles, it can burn plants, stunting
growth. It may also
produce growth that is too rapid, causing
lack of buds, or lodging, in grain and vegetable plants that
all vine. Lime
should also be spread evenly to be of greatest
III. FUTURE OF SOIL PREPARATION TECHNOLOGY
In the future, the mechanical processes used in agriculture
increasingly to be replaced by biological methods.
Over the past
10 years, the cost of machinery and replacement parts, fuel,
fertilizers, and other agricultural chemicals has doubled,
grain and livestock prices have remained stationary. Thus,
is an ever-increasing need for farmers to manufacture their
soil inputs. While
potassium and phosphorus may have to be purchased
or secured off the farm, the most important nutrient,
nitrogen, can be produced by the use of soil-saving legumes
More research is needed to develop new varieties of legumes
crop rotation or for companion cropping.
An ideal legume would
grow vigorously for a few months before the grain crop is
planted. Then the
legume would become dormant and act like a
mulch while the grain crop is growing, only to revive growth
after the grain is harvested.
Such a plant does not yet exist,
but legumes should be included in soil-building programs.
Properly suited legumes must be introduced to areas where
seed is difficult to purchase.
Legumes are also important to
soil conservation efforts.
Erosion is a world-wide problem, and
land too steep for continuous cropping should be placed in
Legumes such as alfalfa provide excellent pasture while
they enrich the soil.
Ensminger, M.E., and Olentine, C.G. Jr.
Feeds and Nutrition.
California: Ensminger Publishing Co.,
Forages. Ames, Iowa:
Iowa State University Press,
Russell, F. Walter.
Soil Conditions and Plant Growth. London,
Logmans Green and Co., Ltd., 1961.
Archer, Sellers G.
Soil Conservation. Norman,