Last Links check and update: July 2018
This page approved by Roland Bunch June 14 2002 email
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Last Links check and update: July 2018
This page approved by Roland Bunch June 14 2002 email
Agricultural revolution: small farmer competes with mechanized production using selected legumes green manure (cover crop) maximizes organic matter fertility with little tillage reduces weed growth and feeds plants through mulch.Problem
Low fertility of soils, erosion, and rampant weed problems on small farms in developing countries give low yields leading to decreasing productivity, increased poverty, and migratory farming practices.
An agricultural revolution, allowing the small farmer to compete with mechanized production has occurred through the increased use of selected legumes as green manure. This green manure maximizes organic matter production thereby increasing the fertility of the soil over time, keeps the soil covered, needs little or no tillage, significantly reduces weed growth, maintains biological diversity, and feeds plants through the mulch.
Definitions of Main Concepts
Green Manure - (also cover crops) originated from practices of using primarily leguminous plants and plowing them under to fertilize soils. However, under different climatic and terrain conditions, the practice has changed in the tropics to refer to a series of plants, mostly leguminous, which are used by farmers for a whole range of purposes, one of which is the fertilization and improvement of the soil by applying the vegetation to the soil surface.
Detailed Solutions or Recommendations
Use of green manure principally in the form of
the velvet bean (mucuna pruriens).
Green manure, for a capital outlay of a handful of seed,
dramatically improves the yield and the fertility of the soil
year after year by adding organic matter and nitrogen
while reducing the need for fertilizers and herbicides,
weed control, burning, and tilling of the soil.
For discussion and listing of types of green manure producing plants, see typescovercrops
Bunch has stated that "Experience leads us to believe that, with the possible exception of very intensive farming systems such as irrigated vegetables and rice, green manure and cover crops systems can probably be introduced into many, if not most, of the world's small-scale farming systems." [Bunch2]
Problems within Solution
If green manure is used for food and fodder, its value to the soil is reduced. With no weeding and no tilling, non mechanized farms can compete with the mechanized in a world where trade barriers are falling.
In spite of the advantages named above, many farmers will not
plant green manures where they can plant either subsistence
or cash crops. Soil improvement and improvement in productivity
is not usually visible until the second cropping cycle or second
year. Green manures must either continue to grow or form a mulch
during the dry season, and grazing animals, agricultural burning,
termites, and a host of other problems may prevent their lasting
very long during this period. Extreme drought, extreme infertility,
extremes in pH, severe drainage problems will affect green manures
almost as much as traditional crops, thereby reducing their impact.
Limitations of Solution
It is generally believed that green manures and cover crops
would only be accepted by small farmers if they could be grown
on land that has no opportunity cost, could be intercropped
with other produce, grown under tree crops or on fallow land,
and be cultivated in periods of expected drought or extreme
cold. They would also be favoured if they involved no extra
labour and no out of pocket cash expense.
Preparations Needed: None
Some 45,000 farm-families in Honduras and Guatemala have
benefited from the adoption of sustainable agriculture,
increasing crop yields from 400-600 kg/ha to 2000-2500 kg/ha.
Farmers use green manures, cover crops, contour grass strips,
in-row tillage, rock bunds, and animal manures, which are
finely-tuned through experimentation to local conditions.
These programmes have regenerated local economies. Land prices
and labour rates are higher inside the project areas, and
families have moved back from capital cities. There are also
benefits to the forests. Farmers say they no longer need to
cut the forests, as they have the technologies to farm
permanently the same piece of land. Throughout Central America,
various NGOs have promoted the use of grain legumes, especially
velvet bean (Mucuna pruriens) to be used as green manure, an
inexpensive source of organic fertilizer to build up organic
matter. Taking advantage of well established farmer-to-farmer
networks, e.g. campesino a campesino movement in Nicaragua and
elsewhere, the spread of this simple technology has occurred
Personal Experiences Related to Solutions
Five key principles in agriculture for sustainability, based
on the natural processes of fertility found in humid tropical
For a discussion of these principles, see Crop Principles
Past Experience and Outcomes
Experience from many parts of the world confirms the value farmers' attribute to green manures and cover crops that have multiple uses. In most known traditional systems, legumes are appreciated not only because they maintain soil fertility, but because the seeds or pods can also be eaten. Examples include the Vigna spp. which is intercropped in Southern Honduras, El Salvador and South-east Mexico and the high-altitude scarlet runner bean (Phaseolus coccineus), which is widely used from upstate New York (Seneca bean) to Mexico (ayocote) and from Guatemala (piloy) to Honduras (chinapopo) and Northern Chile. The velvet bean (Mucuna spp) is easily the most popular of all the green manures/cover crops used today and was initially used and spread by farmers along the southern border of the Himalayas in Nagaland partly because it was such a valued source of food (Young 1989). In Central Honduras, where World Neighbours and COSECHA have taught farmers to intercrop velvet bean with maize, there has been a disappointing failure (35%+) to continue this technology except in those villages where it is consumed as a major component of coffee, hot chocolate, bread and tortillas. In fact, their value as green manures and cover crops as human food seems to be the strongest factor motivating their sustained adoption.
Perhaps the second most common use of green manures and cover crops is in weed control. In South-east Asia, a perennial species of the velvet bean is use to improve fallow and to control weeds. More modern practices include using jack bean (Canavalia ensiformis, tropical kudzu (Pueraria phaseoloides) and perennial peanuts (Arachis pintoi) under a variety of plantation crops, including coffee, citrus, and African oil palm. The velvet bean is also used to control imperata grass (Imperata spp.) and this practice is spreading rapidly throughout Benin, Togo, and Columbia. Velvet bean and jack bean are used to control paja blanca (Saccharum spp.) in Panama and to combat nutgrass in several other countries.
A third practice, which is now more widespread but which is still under appreciated, is the use of green manures and cover crops to stabilise swidden agriculture. Since decreased fertility and weed infestation are the two most important reasons why farmers abandon their fields today, and since green manures and cover crops can, to some extent, often solve both these problems, they have proved to be an effective way of stabilising shifting cultivation in many countries. One dramatic example can be drawn from the work of the Centro Maya in Guatemala's northern Peten region. In this humid forest area, farmers could only grow maize for one or two years and then the ground had to be left to regenerate. Now hundreds of farmers are growing velvet bean intercropped with maize on the same fields year after year. Those who initially adopted this system have been growing maize on the same land for eleven consecutive years and productivity has improved over time. Another interesting example is that of Central Ghana, where village farmers are inventing their own ways of stabilising their agriculture, including one system in which 30,000 leucaena trees (Leucaena spp.) are intercropped with maize and burned very lightly each year. This practice has allowed maize to be planted on the same land for 20 years in succession.
A fourth potential benefit that will
probably acquire more significance as experience increases,
is the use of green manures as animal feed. Most green manures
and cover crop species, with the major exception of Melilotus
albus cannot be grazed well, but many can be used for cutting
and carrying even after months of drought, the most notable
examples of this type being Lathyrus nigrivalvis and lablab
bean (Dolichos lablab). Seeds also provide fodder, one good
example being the seeds of the velvet bean which in Campeche,
Mexico are cooked for a half-hour, mixed with an equivalent amount
of maize and then ground into pig feed. The University of
Yucatan calculated that this velvet bean feed costs less than
commercial feeds per unit of weight gained. Green manure and
cover crops can be used in other ways as well. Two years after
Alter-Vida stopped working in El Naranjito, Paraguay, farmers
abandoned using velvet beans as a green manure, but continued
to use them when they wanted to prepare their land for tobacco.
In Southern Brazil, hundreds of thousands of farmers regularly
use some 25 different species of green manure and cover crops
for soil improvement partly because this allows them to increase
the amount of organic matter in their soil to the point where
tilling is no longer necessary. The financial as well as
ecological advantages of zero-till systems are tremendously
Authorities and Contacts
Roland Bunch, Director of COSECHA email: email@example.com
Professor Jules Pretty, Director of the Centre for Environment and Society at Essex University
Other Organizations, Groups dealing with problem
COSECHA (the Association of Consultants for a Sustainable, Ecological and People-Centred Agriculture) Apartado 3586, Tegucigalpa, Honduras
Management of Organic Inputs in Soils of the Tropics (MOIST) covers green manures and cover crop research and exchange. Site includes CIEPCA Newsletter (Eng & Fr), TropSCORE, the consortium for Tropical Soil Cover and Organic Resource Exchange, Learning modules for agroforestry and organic resources, Symposium on Fallow Management in the Tropics, CIAT-Uganda Extension Guides, and Mucuna News. The Management of Organic Inputs in Soils of the Tropics (MOIST)
University of California, Sustainable Agriculture Research and Education Program: UC SAREP Cover Crop Database includes over 5,000 items concerning the management and effects of more than 32 species of plants usable as cover crops and more than 400 different cover crop images. Reports on research related to cover cropping UCDavis UC SAREP Cover Crops Database Part of the Sustainable Agriculture Research and Education Program
Other Relevant Sites, Contacts
Centre for Research and Information on Low External Input and Sustainable Agriculture Independent organization with the mandate to contribute to poverty alleviation through the promotion of agro-ecological approaches. http://www.ileia.org/
People & the Planet
Showing the way
Listing of PLANTS: Green Manures And Cover Crops Source
[Bunch20 1985] Bunch, Roland The Overstory #20 Five Fertility Principles Discovering Principles of Agriculture for the Humid Tropics from original at http://www.echonet.org/edn58t.htm
[Bunch29 1995] Bunch, Roland, The Overstory #29- -Tropical Green Manures/Cover Crops
The Overstory is published by Permanent Agriculture Resources, P.O. Box 428, Holualoa, HI 96725 USA; Tel: 808-324-4427; Fax: 808-324-4129 email: firstname.lastname@example.org; site: http://www.agroforester.com/
ECHO International Agriculture Conference 2016 (2017-01-19) Green manure/cover crops Presented by Dr. Tim Motis
Green manure/cover crops and crop rotation in Conservation Agriculture on small farms
The promising spread of sustainable agriculture in Asia Jules Pretty, Rachel Hine 2009
FAO's Digital Resoource Centre Search for 'sustanaible agriculture' or for specific topics desired in Spanish French English.
Pettifer, Julian (BBC Correspondent), The Magic Bean, BBC Video The Magic Bean, BBC Video