GREEN MANURE CROPS
By Roland Bunch & ECHO Staff
Published 1985
Introduction
Green manure crops are crops that are grown to be turned under to
increase soil fertility. Leguminous green manure crops, i.e. those which
can make nitrogen fertilizers from atmospheric nitrogen, can offer
small-scale Third World Farmers a tremendous number of advantages,
including:
| They provide large quantities of
nitrogen for the soil. |
| They add many tons of organic matter
to the soil, thereby improving topsoil depth, water-holding
capacity, nutrient content, friability, and texture of the soil. |
| Inasmuch as the green manure crop
grows in place, it presents no transportation problems, in
contrast to either compost or chemical fertilizers. |
| Green manure crops require
absolutely no capital outlay after the initial purchase of a
handful of seed. Because they require no chemical inputs,
dependency on outside sources of fertilizer, nutrients, and
pesticides is reduced. |
| Green manure crops can shade the
soil up to eleven months out of the year, a factor extremely
important in tropical climates for preservation of soil moisture
and organic matter. |
| The cover they provide for the soil
protects the soil from wind or water erosion. |
| Green manure crops provide generous
amounts of high protein fodder for animals, which can be
especially valuable if it is available during the last months of
the dry season (inasmuch as fodder at this time of year is the
limiting factor in traditional animal raising in much of the
Third World). |
| Some green manure crops provide
human food, including various kinds of edible beans, peas, and
pods. |
| Green manure crops can provide cash
income, by selling firewood, food or feed (and maybe seed). |
| They often provide an incentive for
people to abandon harmful traditional practices, such as burning
crop residues or letting animals loose in the dry season to
devour everything in sight. |
| Some green manures, when
intercropped with basic grains, can control most weeds, thereby
eliminating costly weeding operations. |
Something like 30% of all the increases in harvests achieved by small
farmers in the third World during the last three decades has been achieved
through the use of chemical fertilizers. Should petroleum prices shoot up
once again, as could easily happen sometime in the next decade, prices of
chemical fertilizers could easily become too expensive to be economically
feasible for use with traditional basic grains. Almost overnight, Third
world basic grain production could plummet, causing famines the extent of
which would make the present situation in Africa seem mild by comparison.
Widespread use of green manure crops could avert much of this impact.
Comparison with Compost
In as much as composting is a technology that is often recommended for
Third World development programs, it might be useful to compare composting
with the use of green manure crops.
|
Compost merely decomposes the organic matter one already has,
whereas a green manure crop can often add over 40 tons of
additional organic matter per hectare. Inasmuch as organic
matter is often in short supply on villagers' farms (or is
already being recycled), this is an important consideration.
|
|
At best, compost will return to one's field about 98% of the
nitrogen one started out with. A green manure crop, however,
will add considerable quantities of new nitrogen to the system.
|
|
A compost heap takes a tremendous amount of work, as anyone
who has personally made one can attest. Though compost will
often pay in a vegetable garden, it is not economical when used
on basic grain crops such as corn or millet. On the other hand,
although a green manure crop takes a bit of labor to plant
(Using a dibble stick) and a fair amount of labor to
incorporate, it takes nowhere near the labor a compost heap
does. And in some cases where the green manure crop is
intercropped among traditional crops (such as corn, sorghum, or
millet), it covers the ground so well that one or even two
weeding operations can be eliminated, thereby actually bringing
a net savings in labor.
|
|
A compost heap requires water. This often means it is made
near a water supply but at a fair distance from where it is to
be applied. Green manure crops are planted to take advantage of
available rain water, and are planted right where they will be
used.
|
|
Compost cannot be used as a food source, either for animals
or humans.
|
Cropping Systems
In spite of the advantages of green manures, their use has seldom
become common among farmers in the Third world. They cannot afford to give
up scarce cropland just to grow a soil amendment. If they do have the
land, they cannot afford the labor. Nor are they generally willing to
spend money to improve crops grown for subsistence, because they earn no
money to improve crops grown for subsistence, because they earn no money
from them with which to replace what they have spent.
What characteristics should we look for, then, in a legume that will be
useful under these circumstances?
| It must be a non-woody annual with
vigorous growth. |
| It should grow well in the poorest
of soils in the area, without needing any kind of fertilizer. |
| One must be able to plant it in
local fields with no special soil preparation, and either with a
dibble stick or, preferably, by broadcasting the seed. |
| The plant must have few enough
natural enemies that it will grow vigorously without the use of
any pesticides or major labor requirements. |
| The legume should either be very
shade-resistant (for intercropping) or drought-resistant (for
growing into or through the dry season). |
| If possible, it should first cover
the ground well, then climb any stalks that remain in the field. |
| If possible, the green manure crop
should be edible by animals and/or humans. |
World Neighbors/Central America has found a number of ways to overcome
most of the problems associated with green manures to the extent that
farmers have accepted them faster than any other agricultural technology
with which we've worked through the years. One program sold 65 pounds of
seed last year to local farmers and 1500 pounds this year in the same area
with minimal promotion. In Central America our work has used the following
four ways to produce green manure without reducing the amount of land used
for other crops:
Green manure crops can often be planted among traditional row crops,
especially corn, sorghum, and millet, without decreasing the production of
the main crop at al the first year, and usually with major increases in
the major crop in succeeding years. The major instance in which this is
not possible is when people are already intercropping two or three other
crops with their major grain.
Green manure crops can often be intercropped with basic grains toward
the middle or end of the growing season, with the idea that their major
growth would occur during the dry season, thereby using land that would
not ordinarily be under cultivation.
Wherever multiple-year fallows and/or shifting agriculture is used,
green manures can be planted on land the first year it is to go fallow.
Thus the period of fallow can be cut to one year instead of three or more
years.
Use a green manure crop in conjunction with alley cropping.
What can be done in areas where animals are let loose during the dry
season while the green manure crop is still growing? One approach is to
first show people the results of the green manure plant on an enclosed
piece of land. Next get a good number of people to try it out, perhaps
timing the planting to get a good start before the animals are let loose.
Those who experiment first can often be motivated to spread the word to
others with the idea that the destruction for each person will be less if
more people plant it. Eventually, if enough people plant it, community
pressure will make everyone keep his animals locked up (except in cases
where the person with all the animals is a large landowner).
On very steep hillsides, something must be done to keep the organic
matter from washing away. Piling crop residues along roughly contour lines
can help, as can contour ditches. Another possibility is incorporating the
green manure immediately after cutting it, but this is hard work before
the rains come (if soil is a heavy one), and once the rains have come,
people generally do not have extra time.
On flatter land, the green manure should usually be cut and allowed to
dry for a couple of weeks before incorporating it (if during the dry
season). The labor saved in incorporating it will be worth more to the
farmer than the small amount of fertility lost. In one case farmers cut
holes in the Canavalia cover to plant corn when the rains came, cut down
the Canavalia entirely about two weeks later and replanted the Canavalia.
Then, two weeks later, they incorporated the dead Canavalia vegetation. In
this manner, they avoided both weeding operations in their cornfields!
Where weather is unreliable, a combination of similar plants, one of
which is more drought-resistant (e.g. jackbean and velvet bean) reduces
risk of total loss, yet assures a vigorous crop if rains are plentiful.
In West Africa, we are trying a system of planting a perennial every
sixth row (pigeon pea), and then gathering the corn or millet residues
under the pigeon pea plants at the end of the year, to be distributed six
months or so later when well-mixed with better C:N pigeon pea leaves. The
presence of the pigeon pea trees (already known as a cash crop) will also
prevent burning of residues.
On South and Southeast Asian hillside areas, Leucaena leucocephala is
planted as a contour barrier and constantly pruned, thereby providing
erosion protection, some green manure, and firewood (see the booklet
produced by World Neighbors called Leucaena-based Farming). This produces
less green manure than other systems, but can be sued where green manure
cannot be intercropped among traditional crops.
Some Plant Species Suitable for Green Manures
Although a good deal of research still needs to be done in finding
adequate plant species (far too much of the research has been done on
fertile experimental stations or with the use of chemical fertilizers,
thereby making it virtually useless to small farmers), there are a few
species that seem to fit most of the requirements for being a good green
manure. They are:
Canavalia ensiformis (jackbean) is an incredibly drought-resistant,
hardy legume that grows well in extremely poor, droughty soils (and
apparently less well in fairly fertile soils). There are two kinds of jack
bean, one that climbs and thoroughly covers the soil, and another that has
a bushy growth habit and does not climb at all. It begins flowering after
4-5 months, then produces seedpods continuously for at least the next
year. It will grow through some 5-6 months of dry season if above about
600 meters and can serve to shade the soil during this time to prevent
loss of organic matter. Under 500 meters it will often stop growing after
about 3 months without rain and may even drop its leaves if soils are thin
and temperatures exceptionally high. The stem will become somewhat woody,
but only if left for seed and under fairly warm conditions.
Jack beans grow vigorously at sea level, and can be used as a green
manure crop up to about 1600-1800 meters. It does not thrive in soils with
excess water. They do very well in cornfields, but are preferred over
velvet beans only when it is too dry for velvet beans to thrive. This
tends to be the case where corn has been replaced with sorghum or millet
due to insufficient rainfall.
The jackbean will be eaten by grazing animals, but is liked less than
other green manures. Hence jack beans are preferable where animal damage
is feared. Non-climbing varieties are proving to be very good for weed
control and nitrogen fixation under fruit trees. It has virtually no
natural pests or diseases. Its leaves are sprinkled on leaf-cutter
anthills to eliminate them. [Ed: I am told that ants carry leaves into the
mounds as food for the fungi upon which they live. Jack bean leaves
reportedly kill the fungi. Dr. Warwick Kerr in Brazil writes that planting
sesame near the mounds has a similar effect].
Jack bean should be planted in soil that has been cultivated within 3
years and weeded very recently (although at elevations below 500 meters or
in sandier soils, cultivation may not be needed). We use 4-5 seeds per
square meter in order to control weed growth. (In cornfields an important
advantage of this and the velvet bean is that use of these plants may
entirely eliminate at least the second weeding). Jack bean has even been
planted in fields already intercropped with both corn and beans in Haiti
(Bois de Laurence) without much adverse effect on even the beans. If
planted in a corn or sorghum field, it should be seeded within 15-30 days
of the primary crop, depending on climate, speed of growth of the other
crop, etc. It can be planted with a dibble-stick or broadcast, though if
broadcast it will take another 2 weeks or so to germinate unless soaked in
water overnight before planting.
People can eat immature pods like green beans when they are about 7-8
inches long. In Southeast Asia the mature beans are eaten, but we have not
been able to find out how. Cooking must be sufficient to eliminate certain
substances in the mature bean that inhibit the assimilation of calcium by
the body.
In summary, jack bean can be used in grain fields, under orchard trees
or to shorten fallow periods, but is not as vigorous as the velvet bean
and should be used only when conditions, perhaps mixtures of the two would
function best.
Mucuna deeringiana or Stizolobium pruriens (velvet bean) is the most
promising green manure that we have worked with in Central America. It
covers the soil completely and then climbs as high as its support allows
(up to well over 6 meters). It is highly palatable to animals and has
gained wide acceptance in our Honduras program areas as a coffee
substitute. Especially encouraging is that there are at least 4 large
areas where velvet bean use has spontaneously spread from village to
village without any outside intervention (in Mexico to shorten fallows and
in Honduras to intercrop with corn).
Velvet beans first cover the ground almost completely, then climb
vigorously. Where corn stalks are present, it will eventually form a mat
of leaves at about the top of the stalks, with little more than stems and
pods underneath. Stems remain thin and non-woody throughout the plant's
life. The plant dies after it has set seed. [Ed: Seeing velvet bean
growing to the tops of pine trees at ECHO prompts many to ask if it might
not take over like kudzu in the southeastern USA. This might happen were
it not that the plants die after seed set. It was a major US crop for
years, and I never heard of such problems.]
Sometimes velvet bean roots produce solid clusters of dark red nodules
that are 4 cm in diameter. We think that heavy nodulation occurs most
frequently in infertile or sandy soils. Like jack bean, the velvet bean
will volunteer heavily the second year if seed is allowed to mature and
fall on the ground. In fact, farmers in Chiapas get growth each year in
their cornfields without bothering to reseed it. They harvest 4 T/ha of
monocropped corn planted year after year on the same land under typical
jungle conditions, using chemical fertilizer plus velvet bean.
About the only soils in which velvet bean has not done well for us are
those that are waterlogged or have a pH of 4.5 or less. Like the jack
bean, it needs to be planted in a field that is either sandy or has been
cultivated within the last 3 years. Velvet bean will take a bit cooler
climate than jackbean, but still does best at sea level and does poorly
over 2,000 meters. In cool climates it will grow 3-4 months into the dry
season, but is not as drought-resistant as jack bean.
The velvet bean is presently our species of choice, in most cases, for
growing in cornfields, rehabilitating depleted land, and weed control. It
has been used in Guatemala and parts of Honduras to eliminate serious
weeds such as nutgrass (Cyperus rotundus), Bermuda grass (Cynodon dactilon)
and imperata grass (Imperate cylindrica). I am not aware of what is
required to do this, though I would guess that the grass must be cut back
and the velvet bean then allowed to grow a full 6 months in order to choke
out the weeds.
It is an extremely good, fairly palatable high-protein fodder for most
animals, especially cattle, and is eaten by virtually all animals except,
sometimes, chickens. Thus, like the lablab bean, it can be an important
source of high protein fodder well into the dry season, when many domestic
animals are losing weight for lack of food.
We were taken off guard by the degree of acceptance of the dry beans as
a coffee substitute. Having introduced it as a coffee stretcher (to be
used 50-50 with coffee), we found that people were soon drinking it
straight. Use is so widespread after just one year that a group of women
is roasting and grinding the bean and selling some 40 pounds a week under
the name "nutricoffee".
Like the jack bean, velvet bean is native to Central America. However,
there are two kinds. The more common one has an extremely irritating itchy
powder on the mature pod. Villagers who know this plant will not want to
plant the non-itchy-powder varieties until they've been shown that the
pods are harmless. We would under no circumstances recommend that anyone
use the irritating kind with small farmers.
Slugs damage velvet bean in warm climates (though much less than
regular dry beans). Rabbits, leaf-cutter ants (its only serious insect
pest here) and iguanas are other pests. In some locations rats used the
velvet bean stems to climb up and eat the corn. Planting the beans later
or cutting its tendrils when it gets too large has helped with this
problem. It must be watched and cut back if planted near trees.
Everything that was said above about planting jackbean also applies to
velvet bean. However, fine-tuning is needed to determine when to plant
velvet bean in local cornfields. This is affected by speed of growth of
the native corn, climate, soil fertility and existence of problems with
rats. One should plant as soon after the corn as possible to get maximum
velvet bean growth and weed control, but not so soon that the velvet bean
outgrows the corn or causes rat problems. Especially in fertile or heavily
fertilized soils, the velvet bean grows very rapidly and may even need to
be pruned once to retard its progress.
Corn crops growing where velvet bean or jackbean have been incorporated
can often do extremely well without any initial fertilization with
chemicals, but will often show signs of nitrogen deficiency by tassling
time. Farmers in our programs in Honduras almost always add a side
dressing or urea to these crops. In general we recommend this practice
where fertilizer is available and affordable. Over the long run, one would
think phosphorous would also be needed, but in the short-run neither
visible symptoms nor level of yields would indicate much problem with this
element. Quite likely the increased organic matter is increasing the
availability of soil phosphorous enough that deficiencies just are not a
problem.
In corn fields, the velvet bean produces an average of about 6-7 pounds
of above-ground organic matter (wet weight) per square meter (30 T/Ha),
but has produced twice that. The effect on subsequent plantings is roughly
equal per pound to that of cow manure or half that of chicken manure,
although this varies from field to field. When incorporated into the soil,
the velvet bean often approximately doubles subsequent corn yields and
when used as mulch increases yields by about 35%. Even dry bean yields
following velvet beans have shown yield increases of over 100%.
[Ed: Even though leaving the residue as a mulch has many benefits
(erosion control, weed control, moisture retention), the greater effect on
corn yields after incorporation might lead you to incorporate residues
rather than leave them as a mulch. All nutrients probably become available
in one season when incorporated, whereas they are more slowly released
when left as mulch, accounting for the greater effect. However, almost
surely some or much of the remaining nutrients will benefit the second and
subsequent corn crops. Rolland and I asked during a regenerative
agriculture conference at Rodale International for a perspective on this
question. The consensus was that over several years the total amount of
nutrients available for plants is about the same whether residues are left
as mulch or incorporated. We would welcome your input on this question. I
tend to vote for a no-till approach except in famine situations where
immediate yield is imperative.]
Farmers in areas with enough moisture for two crops of corn or sorghum
have recently started doing the following. The green manure (velvet bean
or jack bean) is intercropped with the first grain crop. After harvesting
the grain they cut the residue and green manure down, leaving this on the
surface as mulch. The second crop is planted 20 days later with a dibble
stick right through holes cut in the mass of dead velvet bean. There is
usually a net saving of labor because planting and cutting of the green
manure requires less work than the two weeding operations that are thus
saved with the second crop. This is the sort of technology one dreams of,
but rarely finds: net savings of labor, zero cash cost and decreased risk
(the mulch gives some protection from erosion and drought), increased
productivity, increased soil fertility and increased protein intake for
animals or people.
In Togo velvet bean grew well and was incorporated into the soil 5
months before planting corn. There was virtually no response to the green
manure. Our hypothesis is that the green manure was burned or leached out.
We are now testing whether under such conditions a green mulch (jack bean
for instance) throughout the dry season will be able to reduce surface
temperatures sufficiently to maintain organic matter. We have serious
doubts about the claims that organic matter in tropical soils are
impossible to maintain.
Recently villager nutrition groups have discovered that by toasting the
velvet bean somewhat less than they do to make coffee, they have been able
to produce a really passable hot chocolate. By grinding the flour finely,
they have even been able to use a recipe for soybean cake to make
"velvet bean cake".
Dolichos lablab or Lablab purpureus (lablab bean) is a legume very
similar in appearance to the velvet bean, but even faster growing where
soils are fairly fertile. It has not been as valuable to us because of its
need for somewhat more fertile soils and occasional insect problems, but
may well be important to us later on when the other green manures have
raised fertility sufficiently. The lablab bean is almost as
drought-resistant as the jack bean, is very shade-tolerant, and is among
the most palatable of legumes for animals (definitely preferred over
velvet bean or jack bean). Lablab beans grow well from sea level up to
about 1500 meters. They require well-drained soils. In pure stands, lablab
beans should be planted about 10/square meter. We have not found a good
system yet for planting in cornfields because of its rapid growth, but it
should be possible with heavy pruning (which it withstands well). The
lablab bean requires either a recently cultivated or a sandy soil.
Lablab beans start flowering after 3 months and continue most of the
first year, producing seed as well as remaining green. If soils are deep
enough and other conditions permit, it will grow right through the dry
season. I have seen plants that survived 3 years in droughty areas of the
central plateau of Haiti. [Ed: in the sandy soils at ECHO lablab beans get
nematodes so badly that it is difficult to keep them alive an entire
year]. It nodulates profusely, producing mostly white nodules. Whereas the
velvet bean growth is reduced if it has nothing to climb, plants in thick
stands of lablab beans will begin to climb up each other. Another
difference from the velvet or jack bean is that the lablab bean can be cut
off nearly at ground level and will grow again, although with somewhat
less vigor.
Though we have had problems with insect attacks, its growth is so
vigorous that it still usually grows as fast as the velvet bean. Because
animals prefer it to almost anything else, lablab beans cannot be grown
where animals run free. Where it grows well, the lablab bean has produced
a phenomenal 11 kg per square meter (110 T/Ha) of above ground organic
matter (wet weight).
Lablab beans are traditionally planted toward the end of the
agricultural cycle in come villages in Honduras to provide dry-season
pasture for animals. It is also edible, and in some places, such as Haiti
and West Africa, is widely appreciated as a regular food. Young pods or
immature beans can be eaten green (beans taste similar to a sweet pea - a
white seeded variety is best for this). Dry lablab beans can be
substituted for dry beans in most recipes.
Clitoria ternatea is even more drought-resistant then the Canavalia,
although being small-leafed, it does not cover the soil well. We really do
not have much experience with this plant yet. It grows well at sea level.
Pueraria phaseoloides (tropical kudzu or puero) grows vigorously and
can even smother the vigorous native imperata grass if the grass is
manually bent over. This is not the same kudzu that took over so much land
in Alabama and elsewhere. They then cut circles perhaps 2 meters wide and
plant fruit trees, coffee, etc. in the middle. It had not rained for 60
days when he visited and the ground in the circles was hard and dry. But
one arm length under the ground cover the soil was moist and could be
molded with the hand! [Ed: This account was provided Pete Ekstrand after
his visit to the Paul Carlson Medical Program in Zaire.]
Crotalaria ochroleuca (sunn hemp) is reported to be receiving
widespread acceptance as a versatile green manure in East Africa according
to Fr. Gerold Rupper in Tanzania. The jackbean, velvet bean and lablab
bean are all vines. Sunn hemp is a vigorous upright legume growing 2
meters tall. When planted in narrow rows, mature plants tend to fall over.
When planted in the field plants tend to hold each other up. While sunn
hemp has a different growth habit than most of the green manures we have
featured, the uses are much the same, including weed control, livestock
feed, and erosion control.
Sunn hemp is especially suited for weed control in fruit groves
because, unlike vining ground covers, continual vigilance to keep it from
covering the trees is not necessary. It is being used with banana,
plantain, citrus, and coconut. It can be cut at any time and left in the
field as mulch. If it is cut one foot (30 cm) from the ground it will grow
a second time. Fr. Rupper stresses that not less than 10 kilo of seed per
acre must be planted.
Fr. Rupper wrote, "In Hanendi, sunn hemp was planted in an orchard
affected badly by insects. When it had grown a bit, the insects left the
trees and started to live on the sunn hemp. When the sunn hemp was cut for
mulching, the insects returned to the orange trees." "Just this
week we were informed that insects which attacked the freshly planted
maize moved to inter-cropped sunn hemp, ate the roots and are
perishing."
Crotalaria is known to contain toxins, but this variety is free of
toxin, except perhaps the seed. It is cut about 3 months after planting.
It is best cut in the morning, but keeps until evening. Later in the
season cattle can be allowed to graze in the sunn hemp field. One farmer
noted that after first spending an hour in a grass field, his cows even
ate the dry stems. Fr. Rupper mentions that cattle must not be allowed to
spend more than about one hour in the area. [He does not say why.] He also
says that the seeds should not be stored in a closed room where people are
working.
Sunn hemp seeds are used to keep weevils from stored rice and maize.
Sunn hemp seeds are spread over the ground and bags put on top of the
seeds. This procedure is continued, layering sunn hemp seed and bags of
stored grain. After about 9 months, the process must be repeated.
When we asked our EDN readers for suggestions on how to keep monkeys
out of the garden, Fr. Rupper wrote: "Early in the campaign for
planting sunn hemp (also called zanziberica), we got a report from a youth
group that monkeys had been afraid to traverse a belt of sunn hemp around
their field of maize. I could not ask the monkeys why they did so. But one
can imagine that first of all it is a strange sight to see sunn hemp
growing together and forming a barrier. Secondly, the husks give a
clattering sound, which may disturb the monkeys. [Editor: The genus for
rattlesnake is Crotalus coming from the Greek root crotal meaning a rattle
or castanets]. Thirdly, if they are caught stealing maize, it is almost
impossible to flee through the sunn hemp field as the branches form a
rather strong network like wire. In the case of maize [corn] there is some
synchronization between the crop and sunn hemp. The husks of both crops
form about the same time (depending on the variety of maize). People like
to let the corn dry in the fields, at which time the barrier effect of
sunn hemp becomes important. Meanwhile we have developed a new method of
planting sunn hemp; two rows of maize alternate with one row of sunn hemp.
Here the maize is well protected against monkeys."
As with velvet bean, farmers are especially appreciative of its
usefulness in controlling weeds and improving the texture of the soil. He
tells farmers, "If you have no chemical fertilizer when the season
starts, plant sunn hemp between your food crops. If fertilizer arrives you
may still be able to use it. If not, use sunn hemp and you will at least
get a modest crop." According to Fr. Rupper sunn hemp will completely
kill striga. A simple alley cropping system has been developed for
controlling this important weed. When a field is ploughed and sowed to
corn or sorghum, sunn hemp is sown along with the grain at a rate of 10
kilos (mixed with 20 kilos of sand) per acre. At weeding time, sunn hemp
is left standing in every third row, knowing that it will kill the crop.
After seven or eight months sunn hemp seeds are harvested and the dry
stems are placed in the furrows and buried. If this is practiced each year
you have a sustainable system free of striga. Other uses for sunn hemp
include applying the dry stems and any husks to trees or gardens as mulch,
or as bedding for livestock.
The seeds, about the size of millet, are mixed with two parts of coarse
sand and broadcast by hand. They do not need to be covered, although it
might be well to draw a branch across the newly planted field. They sprout
after a few days and develop a strong root. Growth is rather slow until
they reach about one foot, then they quickly grow to 2 meters or more.
Sunn hemp is fairly drought resistant, recovering well when rains return.
Plants bare seed after 3-4 months and die after 6 months. However, if they
are cut back to about one foot (30 cm) above the ground, they again
develop new leaves. If planted densely in a well-prepared field, no
further work is needed (except to keep out animals). Sometimes sunn hemp
is interplanted with maize. Some species of Crotalaria are also useful in
suppressing nematodes, but we do not know if this is one of them.
ECHO also carries another species of sunn hemp, Crotalaria juncea.
Variety 'Tropic Sun', released by the University of Hawaii, is included in
rotation with vegetables, ornamentals and others to add nitrogen, organic
matter, suppress weeds, control erosion and reduce root-knot nematodes. In
60 days it can produce 145 pounds of nitrogen and 3 tons of dry matter per
acre. Seed should be broadcast at the rate of 40-60 pounds per acre and
covered 1/2 inch deep. High populations make the stems more succulent and
hence better for incorporation into the soil. If allowed to grow too tall,
stems become fibrous and difficult to deal with. Seeds can be inoculated
with cowpea inoculant to maximize nitrogen fixation [presumably not needed
where cowpeas are commonly grown]. It also lacks the poisonous alkaloids
that make some species of Crotalaria poisonous to livestock.
Where can I get seed?
ECHO will send a small packet of any seed mentioned in this article. If
you want to purchase larger quantities of seed we will try to find a
source. [Yates Seed Company is an excellent source of seed for a large
number of tropical pastures (Yates Seed Co., P.O. Box 117, Rockhampton,
4700 Australia).]
We also have the "90" day " velvet bean that was grown
in the southeastern part of the USA 50 years ago. At the time of the last
corn cultivation, farmers would plant 90-day velvet bean. Both corn and
beans were left in the field. Cattle were allowed to feed in the fields a
couple of hours each day in the fall and winter, reportedly getting very
fat. This variety is not sensitive to day length so produces 3 months
after planting. The tropical type of velvet bean only produces when days
are short (flowering starts in November at ECHO). The 90-day type has some
of the itch-producing hairs Rolland refers to, but not nearly as many as I
have seen on the wild "pica-pica" in Honduras.
The following is an English translation of a pamphlet used to introduce
farmers in rural Columbia to the use of green manures. While it contains
no new technical information, we feel that it complements our Technical
Note on the subject.
The Poor Man's Plow (Plough)
by Lewis Baker
The plow is used to prepare the land for planting. The plow does
several things, but most importantly it removes from the surface of the
soil the vegetation that would interfere with planting, such as weeds and
residues of previous crops. The plow requires a lot of energy to turn over
the upper layer of soil, and so a powerful tractor is used to pull the
plow. But tractors cannot be used on steep slopes; and even if they could,
they are very costly to buy and operate. Therefore, farmers with scarce
economic resources have to use other means to prepare their land for
planting. In some areas farmers use oxen to pull their plows, or they use
heavy hoes powered by human energy to prepare the soil; however, most poor
farmers use fire to prepare the land for planting.
Fire is the poor man's plow because it, like the tractor or ox-drawn
plow, removes from the surface of the soil the vegetation that would
interfere with planting. The tractor-drawn plow does this by turning over
the upper layer of soil and covering and mixing with the soil, the weeds,
and residues of previous crops. But the use of fire converts them all to
ashes and smoke.
Although fire clears the surface of the land to facilitate planting, it
also does a lot of harm because it destroys the organic materials. (The
organic materials of rotted leaves, branches, and stems add nutrients to
the soil and help it to hold the moisture that the growing plants need.)
Fire also destroys many of the beneficial microbes of the soil, which are
very necessary for its fertility. And, then, fire leaves the land bare and
defenseless when the heavy rains come. On hilly land the rains wash away
the bare earth, and carry much of the good soil to the creeks and rivers
where it is lost forever. Thus it is that the poor farmer, by using fire,
is destroying the health and wealth of the land that God has been
preparing for thousands of years.
But God is very great and very wise. God has given to humankind--to the
poor farmer--some plants that fertilize the soil, and these same plants
also protect the soil from eroding when the heavy rains come. These plants
cover the soil and choke out the weeds, but once they are cut they dry up
and rot very quickly. In other words, God has given to the poor farmer
another plow that improves the soil and does not harm it as fire does.
There are several kinds of these plants, all of them legumes, which can be
used as the poor man's plow, and God has arranged things in such a way
that beneficial microbes which fertilize the soil can live and multiply in
the roots of the leguminous plants.
One of these plants is called Velvet Bean (Mucuna deeringiana), but you
may know it by some other name. It is a spreading and climbing vine with
many leaves similar to those of ordinary beans, but larger. The pods
appear at the beginning of the dry season and they form in bunches. They
look something like bean pods, but they are much thicker, and they are
covered with fuzz when they are immature. This fuzz does not irritate the
skin, as does the fuzz on the pods of some similar plants. The mature pods
turn black, and the seeds are round. They may be black, white, gray or
mottled.
The velvet bean is very easy to grow and once established it will cover
the ground, and in a very few months it will smother out all the weeds.
After the weeds are gone it is relatively easy to chop up the lush growth
of the velvet bean. Since it rots very quickly it presents little
difficulty to the farmer who plants by hand. Without burning, one can then
plant corn, rice, or any other crop in the soil which is protected by the
mulch formed from the velvet bean. The plants of velvet bean which sprout
up after a different crop is planted can be pulled out quite easily, so
they do not present a serious problem.
Another plant not quite so well known is called Tropical Kudzu (Puerariaphaseoloides)
(not the same species as found in southern USA). It is also a vigorously
growing vine that covers the ground, fertilizes it, protects it against
erosion, and chokes out the weeds. The leaves are very similar to those of
the velvet bean, but the pods and the seeds are quite different. The pod
is long and very thin--almost as thin as the lead of a pencil. Each pod
has about 30 small round seeds, brown in color, and very hard. When the
pods are mature they turn black, and with the heat of the sun they spring
open to scatter the seeds.
Another leguminous plant native to some forested areas is known
variously as Ox's Eye or Deer's Eye (We at ECHO are unfamiliar with this
species). It has similar properties to the velvet bean and kudzu, in that
it fertilizes and protects the soil and smothers out the weeds. The vine
is heavier than either of the other two plants mentioned, and the leaves
are larger but with the same general shape. The seeds are less numerous,
but they are very large. Each pod usually has from two to four of these
black seeds shaped something like large checkers. They remind people of
the eye of an ox, cow, or deer--hence, the popular name.
It may be necessary to experiment with different ways and times of
planting to learn how to obtain the greatest benefits from any of these
plants. For example, in one area a person could try planting velvet bean
with corn when the corn is knee-high, using three seeds per hill, with the
hills two meters apart. In other areas, different times, different
densities, and different distances could be tried with a view to comparing
the results. The goal would be to have the legume well established when
the corn is harvested, without the corn having suffered. After the corn is
harvested, the velvet bean should be given enough time to cover the ground
and smother out the weeds. Also, enough velvet bean seed should be
harvested for replanting before cutting it down to plant another crop of
corn.
God has made these leguminous plants--velvet bean, kudzu, cow's eyes,
and others--to help maintain and increase the fertility of the soil. But
farmers must cooperate with God by gathering the seed and planting it at
the appropriate time in the appropriate place. With God's guidance we can
learn to use these marvelous plants that He has given us, and farmers rich
and poor can have a better life--a life that glorifies Him who has placed
us as stewards over the earth and all that is in it.
ECHO, 17430 Durrance Rd., North Ft. Myers FL 33917, USA
|