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                              TECHNICAL PAPER #8
                               Paul J. Abrahams
                              Technical Reviewers
                                  Dr. J.W. Fitts
                                Dr. Nail Ozerol
                              Richard Roosenberg
                                 Published By
                       1600 Wilson Boulevard, Suite 500
                         Arlington, Virginia 22209 USA
                     Tel: 703/276-1800 . Fax: 703/243-1865
                        Understanding Soil Preparation
                               ISBN: 0-86619-208-5
                  [C]1984, Volunteers in Technical Assistance
This paper is one of a series published by Volunteers in Technical
Assistance to provide an introduction to specific state-of-the-art
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 situations.
They are not intended to provide construction or implementation
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 illustrated
almost entirely by VITA Volunteer technical experts on a purely
voluntary basis.  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 typesetting
and layout, and Margaret Crouch as project manager.
VITA Volunteer Paul J. Abrahams, the author of this paper, is a
chemist for the McElrath Poultry Company and also a full-time
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 agricultural
consulting firm.  He was the head of the Soil Department at
North Carolina State University, and Director of the International
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 nutrition
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.   VITA offers
information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to their
situations.  VITA maintains an international Inquiry Service, a
specialized documentation center, and a computerized roster of
volunteer technical consultants; manages long-term field projects;
and publishes a variety of technical manuals and papers.
             by VITA Volunteer Paul J. Abrahams
The purpose of soil preparation is to develop a planting medium
that will foster the best possible growth of agricultural crops
while preventing the deterioration of the land through erosion,
destruction of soil structure, or nutrient loss.   The soil
preparation system used must be economical, since a large part of
the expense in raising a crop occurs before the seed is ever
placed in the ground.
The immediate goals to be accomplished in soil preparation are:
     *   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, nutrients,
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
competition.  Careful soil preparation will also retard the growth
of weeds as the crops develop, making cultivation and harvesting
Incorporation of Organic Material
Organic matter has many beneficial qualities that aid plant
     (1)   the ability to retain water for the use of crops during
     (2)   the improvement of soil tilth (structure); and
     (3)   the ability to hold nutrients in the soil instead of
          being 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, and
roots.  Whenever soil is made bare by the removal of its
vegetative cover the level of organic matter will be reduced.  In
addition, soil microbes, such as bacteria and fungi, and larger
animals, such as insects and worms, are constantly consuming
organic material.
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, straw,
or leaves into the soil, or by plowing under green manure crops
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 animal
manure can be added to the soil, commercial fertilizers must be
used to maintain proper soil fertility.   As a general rule, one
must add plant nutrients in an amount equal to that removed in
harvested crops.  (See Table 1.) If this is not done, the fertility
of the soil will drop slowly, causing a decrease in subsequent
yields.  Phosphorus 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 expenses.
It would take the addition of approximately five tons of cattle
manure per acre to replace the nutrients removed from the soil by
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 hectare
of manure on wheat.
It would be preferable if all nutrients could be added as manure
because this would greatly increase the organic matter content of
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
   Table 1.   Fertilizer Amounts Needed to Replace Nutrients
             Removed by Harvesting Corn Grain and Wheat
             Grain at Good Yields
                                      Amount of Fertilizer
                             Nitrogen   Phosphorus               Potassium
                                        Pentoxide                 Oxide
                              (N)         ([P.sub.2][O.sub.5])     ([K.sub.2]O)
  At 100 bushels per acre    80 lb          35 lb                     21 lb
  At 6200 kilograms per
  hectare                     90 kg          39 kg                      24 kg
  At 50 bushels per acre     70 lb          26 lb                    13 lb
  At 3400 kilograms per
  hectare                     79 kg          29 kg                    15 kg
land.  Growing crops protect the soil against beating rains.
Crop residues incorporated into the soil increase the level of
organic material.
Lime must be added to most soils periodically to neutralize the
acidifying effect of commercial fertilizers.   Even land that does
not need fertilizer usually requires lime because growing plant
roots cause the soil to become more acid.   If possible, a soil
testing laboratory should be consulted to determine the need for
soil additives.
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 millimeters
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 crumbs up
to plants, easily killing weeds.
The worst type of soil is one full of hard clods, larger than
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.   The
young plant has a hard time breaking through clods and many will
never get to the surface.  Roots have a similar problem.
Mechanical cultivators will push large clods toward the young
growing plants, breaking many.   Moreover, clods contain many weed
seeds, which will still germinate if the clod is merely rolled
around by the cultivator.  Young grass and other weeds will not
be killed unless their roots are broken free from the surrounding
soil.  This cannot be accomplished by rolling clods (Figure 1).

usp1x4.gif (486x486)

Clods are formed primarily by working (plowing, harrowing, or
cultivating) soil when it is still wet.   They are particularly
noticeable when a moldboard plow is used on wet ground.   Large
smooth-sided clods are turned up by the shearing action of the
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 plowed.
Humus in the soil prevents soil particles from cementing into
The simplest way to develop a good crumb structure in a field is
by growing thickly planted legume and grass sod crops in rotation
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 water.
The beneficial effect of these sod crops will last several years
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:
     1.   Rotate sod crops with field crops.
     2.   Add as much manure and other organic material as
     3.   Wait until wet soil is no longer sticky before working.
         Check by squeezing a handful of soil in your hand.  Soil
         that is too wet will pack together in a sticky lump and
         leave your hand wet.  Soil that is dry enough to plow
         will crumble again easily when pressure is released.
Several factors affect the method of soil preparation:
     *   length of growing season
     *   annual distribution of rainfall
     *   soil type
     *   slope of the land
     *   type of crops to be produced
     *   size of farm
     *   level of technology
Given the large variation in geographical conditions and cultural
practices encountered in food-growing, it is easiest to assign
agricultural lands into three basic categories:
     1.   Large-scale agriculture on fertile, level low-lands
     2.   Intermediate-scale agriculture on erodible uplands of
         varying fertility
     3.   Gardens
Much of the world's best crop land is located along the flood-plains
of major rivers.  Other highly productive areas include
lands that lie on the beds of ancient lakes and oceans, which
have dried up or moved.  These lands are flat and highly fertile.
In many countries, such areas have been divided into large grain
and soybean farms that require high levels of technology.
Because these lands are level, erosion is relatively limited.
The lands are also often wet, discouraging livestock production.
Even where livestock can be raised in most areas, such land is
too valuable to be used as pasture; crops bring a better return
per acre.  All these factors have often led to a mono cropping
system, with fields left fallow, between the yearly cropping.  In
the short run, it is more economical under these conditions to
add commercial fertilizer than to use green manure crops.  Over
the long term, however, such practices may not be wise, as they
can wear out the soil, increase erosion, and foster the growth of
diseases and pests.
The method of farming hilly lands is very different.   In this
case, erosion is the farmer's greatest enemy.   Sloping land
cannot be cropped every year, so it is best to use a system that
routinely rotates crops with sod pasture.   Soil preparation
machinery must be suited to deal with thick sod.
The garden is a special case for soil preparation because many
kinds of vegetables with different growing habits are produced in
a small area of land.  Since the land is worked very frequently,
it is usually not possible to set aside areas for sod rotation.
Gardens thus need large amounts of organic matter added yearly to
keep the soil from becoming exhausted.   The size of a garden
should be no larger than one's supply of manure or compost can
This method of soil preparation is used on large level fields
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 ground for
        planting in the following steps:
        -   Commercial fertilizer and lime are spread by truck
           or tractor-drawn wagon.  Fertilizer may be applied
           by planters.
        -   Land is chisel-plowed six to eight inches deep.
        -   Land is then smoothed out by disk harrow or spike
           tooth harrow after plowing (with very large
           tractors, it is possible to plow and smooth in one
           operation using a large disk harrow).
        -   Right before planting, a second smoothing
           operation using disk or spike tooth harrow should
           be undertaken if needed.
        -   The seeds of row crops such as corn are planted on
           level ground if irrigation is not used; on ridges
           if irrigation is used; or on the side of ridges
           if land is salty.  Row crops are planted with row
           crop planters.  Small grains such as wheat are
           planted with a grain drill.
     *   Labor requirements are low, which is an advantage when
        labor costs are high.
     *   Energy use is very high.
     *   Maintenance requirements for machinery are extremely
     *   The cost of the equipment is very high, but on land
        that gives good yearly yields and where labor costs are
        high, this type of farming will return more per acre
        than any other, particularly if many acres are planted
        and machinery is used to the fullest extent.  This
        system can work if one person has many acres of level
        land to cultivate, particularly if crop yields can be
        assured through irrigation.  However, this system will
        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 soil
        preparation steps may be left out.  Fields may not need
        to be plowed or harrowed, for example.  No-till
        planters can plant directly in unplowed land by opening
        up a furrow with the disks and spraying the middle to
        kill weeds.  However, every few years the land must be
        plowed to bury excessive crop residues that can clog
        planters or harbor plant diseases.
These soils need a sod cover crop for at least half the year to
keep erosion to a minimum and rebuild soil structure.   The land
on the farm is divided into two, three, or four segments with one
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 with
a thin topsoil, particularly when the subsoil is clay, should be
cultivated less often.  This type of agriculture is highly suited
for small tractors (20 to 40 horsepower) or for animal-drawn
        Table 2.   Number of Times During a Four-Year Period
                  That Land May Be Cultivated
Percent Slope(*)                  Allowable                  Preferred

uspximg.gif (100x600)

0                                     4                          3
0-2                                   3                          2
2-6                                   2                          1
6-10                                  1                          0
Over 10                               0                          0
(*)  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
        moldboard plow with a colter.  In the second and
        subsequent years of cropping, implements other than the
        moldboard plow may be more efficient and better for the
        soil.   These include the chisel plow, depending on crop
        sequence and weeding techniques.
     *   Smooth soil with harrow immediately after plowing.
     *   Wait approximately three to four weeks for cover crop
        to decompose.
     *   Smooth with disk or spike tooth harrow with drag if
        needed before planting.
     *   Plant seed with a row crop planter or grain drill in
        rows that run across the slope of the land.  This will
        help prevent the topsoil from being washed away.  Except
        where 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
        will provide moister soil for germination; make
        cultivation easier (soil can be pushed into furrow to
        kill weeds); and, in the case of heavy downpours, tend
        to stop erosion.  In areas of heavy rainfall, apply
        fertilizer at time of planting.
The amount of labor needed to cultivate a particular area of
sloping land is higher than on the level lowland farm because
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.   If draft
animals are used, the labor requirement is higher; it takes
longer to cultivate the same amount of land with animals than
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.   There will
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.   However,
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 pasture--weed
control during the sod or pasture phase of rotation
becomes very important during the periods when field crops are
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 most
of the soil preparation itself.   The roots "plow" and "subsoil"
the ground and legumes capture nitrogen from the atmosphere and
help save on fertilizer expense.   The root action helps
distribute organic matter and nutrients to a great depth in the
soil, thus fostering the root growth of the cultivated crop that
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.   Contour bands
of sod between row crops will help catch eroding soil on steep
Many weeds that hinder cultivation in continually cropped fields
are smothered out during the sod portion of the rotation.  Broad
leaf weeds are hardest hit.  Either the weed seed is killed
before germination or it is consumed by livestock before it can
The only disadvantage to this system is in the time lost in the
spring during the month-long decomposition period.   Also, plowing-under
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 no-till
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.   Other herbicides
are used to kill subsequent sod and weed growth.
This third category of farming is confined largely to small areas
of intensively cultivated land where large amounts of organic
material are added regularly.   The main crops produced are
vegetables.  Often, 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 cultivation
and mulch gardening.  In deciding which techniques to use, the
gardener should consider the soil structure, the amount of time
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,
     *   prevents erosion,
     *   protects soil from traffic compaction,
     *   keeps soil from splashing on plants, and
     *   reduces the amount of equipment required, but,
     *   on the other hand, may possibly harbor insect pests and
Clear cultivation:
     *   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 cultivator,
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 the
same process.  In mulch gardening, thick layers of straw, leaves,
bark, plastic film, or newspaper are placed between the rows to
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 plants
that may break through the mulch.
Both clear cultivation and mulch gardening require the addition
of large amounts of manure, compost, and/or fertilizer to the
soil regularly; use as much manure as possible, up to 10 tons per
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 with
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 long
seasons of very heavy rains, it may be better to spread aged
manure over the garden just before planting.   Organic matter
decays completely very quickly in the tropics, and humus and
nutrients may be washed away by the rains before they can be of
use to the crop.
If tillage is to be employed, space the rows far enough apart to
accommodate the kind of equipment used.   Three to four-foot
spacing (1-1.2 meters) for an animal-drawn cultivator and three-foot
spacing (1 meter) for a power tiller are recommended.   Smaller-spaced
rows may be used with hand hoeing.
When mulch is used, the vegetables may be grown in beds approximately
four feet wide with traffic paths in between.   All walking
is done on the paths so as not to compact the soil in the beds.
Topsoil may also be dug from the paths and placed on the beds to
increase rooting depth.
Although gardens are extremely labor intensive, cultivating time
may be reduced by the use of machinery.   Manure spreading is the
hardest job.  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.   Row
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 systems.
However, the mulch helps retain soil moisture and so less frequent
irrigation is necessary.
The cost of a garden should be kept as low as possible.   When a
garden is combined with a rotational system that includes
livestock, a steady supply of manure is available.   This
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.   All machinery
should be lubricated properly and the surfaces of iron, steel,
and leather items oiled regularly.   Hoes should be kept sharp for
fine weeding.
The best way to ensure a large supply of animal manure is to
keep livestock in a barn, corral, or other enclosure at night.
Bedding straw retains urine and keeps manure drier.   This system
works exceptionally well with sheep or goats.
All farmers should make a land use survey of their farms.  Many
farms are composed of both good and poor land, in one field or in
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 next to
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 intervals.
Each of the three major types of agriculture can show up on a
farm.  Farmers will choose the type of agriculture and soil preparation
needed for each part of their farm.
Soil preparation technology has developed as people have built
bigger and bigger machinery.   However, the greatest mistake a
farmer can make is to buy machinery that is larger than the job
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 farmers to
think they need more equipment to work it.   Mixed livestock and
crop farming on sloping land needs no more than a small tractor
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 the
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 whose
land will not produce the grain yields obtained by prime bottom
land farms where farm technology is at its peak.
Rotational livestock grazing systems require less equipment than
cropping.  The more land grazed, the more manure is available for
the portion of land that is cropped.
Growing plants absorb nutrients from the soil.   These nutrients
must be replaced, or the soil will lose its ability to support
healthy plant life.  The major nutrients that have to be replaced
regularly are nitrogen, phosphorus, potassium, and calcium.  All
can be bought as commercial fertilizers, but they are also found
in all kinds of vegetable matter and animal waste products (see
Table 3).  Many of these resources can be obtained locally.
The best way to use plant wastes is to compost them.   Composting
breaks down fibrous vegetable matter and makes it easier to mix
with the soil.  Bacteria and fungi digest large vegetable parts,
turning the material into a nutrient-rich fertilizer.   Compost
piles are made by alternating layers of plant wastes, manure, and
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 hot,
wet weather it should be worked quickly into the ground for
sanitary reasons.  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 not
worked quickly into the soil.
     Table 3. Nutrients Found in Vegetable and Animal Wastes
Source                                      Nutrient Supplied
Stable manure                               Nitrogen, phosphorus,
                                           potassium, calcium
Human waste                                 Nitrogen, phosphorus,
                                           potassium, calcium
Waste vegetable parts                       Nitrogen, phosphorus,
                                           potassium, calcium
Leaves                                      Phosphorus, potassium,
Wood ashes                                  Potassium, calcium
Ground bones                                Calcium, phosphorus
Ground shells                               Calcium
Manure and fertilizer need to be spread evenly over a field.  If
allowed to remain in piles, it can burn plants, stunting their
growth.  It may also produce growth that is too rapid, causing
lack of buds, or lodging, in grain and vegetable plants that are
all vine.  Lime should also be spread evenly to be of greatest
In the future, the mechanical processes used in agriculture will
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, while
grain and livestock prices have remained stationary. Thus, there
is an ever-increasing need for farmers to manufacture their own
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 and
More research is needed to develop new varieties of legumes for
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 their
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 pasture.
Legumes such as alfalfa provide excellent pasture while
they enrich the soil.
Ensminger, M.E., and Olentine, C.G. Jr.   Feeds and Nutrition.
      Clovis, California:  Ensminger Publishing Co., 1978.
Hughes, H.D.  Forages.  Ames, Iowa:   Iowa State University Press,
Russell, F. Walter.  Soil Conditions and Plant Growth. London,
      England:   Logmans Green and Co., Ltd., 1961.
Archer, Sellers G.  Soil Conservation.  Norman, Oklahoma:  University
      of Oklahoma Press, 1969.