Overstory #111 - Land Husbandry
The following summarizes three and a half decades of extension in soil and water conservation and land husbandry strategies. The most important aspect of our 35-year process of learning about land husbandry around the world has been the follow-up studies and visits made one to fifteen years after the aide programs departed. We have repeatedly visited areas where programs previously worked to observe what aspects were sustained by the farmers on their own (Bunch and Lopez, Silsoe). These visits have been very instructive and sometimes sobering.
Land husbandry and soil conservation
The evolution in terminology in the area of land husbandry and soil conservation reflects how attitudes have changed about the problems of erosion, crop production, and farmer assistance programs. At first, we talked of soil conservation, pure and simple. When we realized that the water we saved was having more impact on yields than the soil we saved, terminology changed to, "soil and water conservation." In the early 1980's, it became clear that land husbandry had to achieve more than just stop the erosion. Productivity was not going to increase much, nor farmers become very motivated, if what little topsoil was left was not also improved. So the terminology became, "soil restoration" and "soil recuperation." Later, a movement in Africa began enlarging the concept once again by calling it "land husbandry," including everything a farmer does that conserves or improves the soil (Shaxson). We prefer the term "land husbandry," but do not use it very much because of one fatal flawit does not translate very well into many other languages.
The concepts behind the term "land husbandry" are very important. Soil conservation and recuperation should be seen as an integral part of agricultural development, not solely an end unto themselves. That is, we should not be making terraces or hedgerows without looking at the entire farming system, without working on other practices simultaneously, or without analyzing the over-all economic and social balance sheet. Also, soil improvement as an integral part of crop management is more important than any practices designed only to conserve or improve the soil. In other words, soil conservation and recuperation should be a result of good soil use throughout a farming system, not the result of one or more technologies implemented largely for this single purpose.
An ambitious goal
Land husbandry efforts have been shifting strongly over the last 30 years from structural technologies (e.g., terraces, bunds and ditches) toward vegetative or agronomic technologies (e.g., hedgerows, green manure/cover crops (gm/cc's) and dispersed shade). The economics of land husbandry have become increasingly important. Heavily subsidized structural conservation efforts are very expensive, and many such projects have had more negative than positive impact over the long term. Fewer and fewer outsiders are willing to finance structural soil conservation.
We can no longer claim that soil conservation is too expensive for small farmers. Increasingly, we are finding soil conservation and recuperation technologies that can pay for themselves within the first year of their application. These include many technologies involving organic matter (organic matter) use, green manure/cover crops (gm/cc's), improved fallows and dispersed trees.
A goal is in view that all agricultural techniques that impact positively on land husbandry should more than pay for themselves within the first year after adoption. This is an ambitious goal—one that requires that constantly searching for better technologies. In our experience this goal will accelerate the shift from structural to vegetative technologies.
It is worth noting here that farmers are as economically motivated with land husbandry as they are with any other investment. One five-year after study found that farmers developed more labor-intensive land husbandry practices where they had begun growing valuable vegetable crops aimed at good, nearby markets. On the other hand, farmers who only grow subsistence crops or live isolated from good markets generally invest very little in soil quality.
The following is a brief discussion of some of the drawbacks of structural technologies.
Contour rock walls We almost never use this technology any more. It is far too expensive in labor. If the presence of rocks is a major problem of the site (the damage they cause is often overestimated), they can be placed in narrow lines every two or three rows, on a contour, and farmers can then plant the rows between them.
A mainstay in Central America 25 years ago, we only promote ditches now where drainage is the limiting factor for productivity. In this case, they are given a 0.5 - 1.0% slope. Once again, a high labor requirement is the problem with contour ditches.
Although this conclusion is somewhat more controversial, we feel the actual construction of contour terraces more than one (or at most two) m in width is a waste of time and effort. Note that each time you double the width of the terraces, you also double the effort needed/ha (i.e., each terrace, covering twice as much area, requires four times as much work). The problem of topsoil getting buried beyond the root zone often is even more critical than cost.
In-row or strip tillage
Sometimes called "minimum tillage," in-row tillage consists of tilling only the row (perhaps a swath 35 cm wide), while leaving the soil between the rows (65 cm?) untilled. Organic matter is then applied, only in the tilled rows.
This technology is especially attractive because it forms microterraces (each one holding one row) over a period of three or four years, using less work than just plowing the whole field. It approximately doubles the concentration of organic matter in the crops' root zone, thereby almost doubling its impact, while the effect of the residual organic matter benefits future crops (planted in the same rows year after year) rather than future weeds.
Nevertheless, three-year- and five-year-after studies have found that in-row tillage tends to be sustainable only when slopes are over 20% and either farmers have irrigation, they can plant fairly high-value market crops on the in-row tillage or they have traditionally plowed their fields either with animal traction or by hand, and will have to do less work than normal to adopt the in-row tillage. Generally, in-row tillage is also most popular with farmers who actively farm less than 1 ha of land in a given year.
Farmers in several countries (e.g., Haiti and highland Guatemala) have dedicated a lot of effort to gully control by using soil traps. These farmers generally own less than 0.5 ha of land.
We have had little personal experience with bunds, but the literature describing past experiences with this technology is heavily pessimistic, with sustainability reportedly close to zero. Furthermore, this technology has almost always depended on outsiders' tractors or heavy subsidization.
All of the above soil conservation structures require maintenance. If not maintained, they often make the situation worse. Studies have shown that their sustainability after program termination is almost nonexistent.
Prevention: the role of cover
Preventing erosion is far better than trying to stop soil that has begun moving down the hillside. One of the best ways to prevent soil erosion is to keep the soil covered, especially during the rainy season(s). I found it hard to believe when I first heard about the kinetic energy of raindrops and how the impact of a raindrop when it hits the soil is far more important in causing erosion than the flow of water over the surface. Experience has proven this point. For instance, in northern Honduras (humid tropics), an estimated 10,000 farmers use a system of growing maize year after year on the same soil that uses no structural soil conservation measures even though the average slope is 35%. One would expect heavy soil erosion. In fact, the soil in these fields, over the last 40 years, has become considerably more fertile (negative erosion?), with zero or minimal applications of chemical fertilizer. Why? First, the soil is constantly covered, year-round, by velvetbean (Mucuna spp.). Second, because of the tremendously high soil organic matter content has increased water infiltration. This example illustrates the two best ways to prevent erosion: vegetative cover and high soil organic matter.
More important than any other practice to control erosion are systems that are mulch-based, involving intercropping, dry-season cropping, and anything else one can do to maximize biomass production (i.e., in situ produced mulch material). It matters little whether trees, shrubs, vines or animals produce the biomass.
Vegetative or agronomic technologies
Contour hedgerows or contour vegetative barriers
Of the soil conservation practices widely used by soil conservation programs up through the 1960's, this is close to the only practice that continues to be used widely, with many positive, long-term results. Nevertheless, some important modifications in this practice have occurred.
Experience has proven that it is largely self-defeating to try to push farmers to plant hedgerows close together. Rather than planting them at 6 m intervals along the slope, as recommended in some programs, farmers much prefer planting them at 12 - 15 m intervals. When other effective practices are in place such as in-row tillage or good vegetative cover, every other hedgerow may be removed with no adverse effects.
The closer placements of hedgerows are recommended to stop every bit of erosion with this practice alone. We must remember that barrier practices such as these, should be used only as a last-gap measure, mostly for emergencies (i.e., "extreme events"). Our first and most important line of defense against erosion should always be soil cover and other agronomic practices.
A second major change made by farmers is in the selection of species used in the hedgerows. The hedgerows we in COSECHA promoted in the Guinope region in Honduras have been expanded, albeit slowly, since the program was active there in the 1980's. But more than half the farmers have pulled out the Napier grass (Pennisetum purpureum) and king grass (Pennisetum purpureophoides) we introduced. In their place, they have planted some 19 other species (Silsoe). Among these are lemon grass (for making tea), vetiver, various fruit trees, and a few woody gm/cc and fuelwood species (rather few because Guinope still has a lot of communal forest). Sugarcane is the most popular species, because of its many uses (for sale, cattle, consumption, etc.).
Some of the more innovative programs now call their hedgerows "multipurpose barriers." They first ask farmers what species they most want, and in what quantities. (Why does it always take us so long to conclude that what the farmer wants matters most?) The typical farmer plants a 100-m hedgerow of Napier grass for each grazing animal, then 20 m of lemon grass, 20-40 m of vetiver for medicinal purposes or thatch, and the rest in sugarcane. Tree species, for fruit, firewood or construction, are planted at intervals in among the other species, often resulting in a dispersed shade effect. Yes, the best farmers practice intercropping, even in their hedgerows.
I have seen farmers prefer a natural vegetative strip (NVS) over single-species or two-species hedgerows, but I have yet to meet a farmer choose to let naturally-occurring species grow in his or her fields when they realized they could instead grow a whole selection of useful species there.
The application of organic matter
Even if this were only a list of soil conservation practices rather than of land husbandry practices, this practice would belong here. Why? Because erosion only occurs when all of the rainwater is not absorbed through soil infiltration. Surface runoff rarely occurs in natural forests or even fields with sufficient soil organic matter. Erosion is therefore largely a symptom of insufficient soil organic matter.
Sometimes, large amounts of organic matter are already locally available. If farmers are not using locally available coffee pulp, crop residues, sugarcane bagasse, or animal manure, they should be taught to use it. Composting may be useful for high-value species (e.g., commercial vegetables or fruits), but for most subsistence crops and grains, compost is too expensive. In most cases, we must find ways of applying this organic matter directly to the soil. For instance, coffee pulp just needs to be spread out in the sun to dry in order to become a high quality fertilizer.
The term gm/cc's (green manure/cover crops) refers to "any species of plant, often but not always leguminous, whether a tree, bush, vine or crawling plant, that is used by a farmer for one or several purposes, at least one of which is that of maintaining or improving soil fertility or controlling weeds." That is, a gm/cc can be a traditional subsistence crop (e.g., cowpea, mungbean or scarlet runner bean), a treefrom tephrosia to mother of cacao (Gliricidia sepium)—or even a non-legume, such as black oats, wild sunflower (Tithonia diversifolia) or cultivated sunflower (Helianthus annuus) (Monegat). What makes any of these a gm/cc or not, is whether the farmer plants that particular species in part because it will make the soil better or help control his or her weeds. As with "trap crops" or "nurse crops," the farmer's intention is a key part of the definition.
It is important to note that gm/cc does not refer here to growing a monocropped "green manure" and then burying it at the flowering stage. In most gm/cc systems, the gm/cc is grown intercropped with traditional crops, is cut down after the plant has been harvested, and is left on the soil surface as a mulch. Traditional "green manures" have been tried for centuries in developing countries, and virtually all have failed miserably.
We have found over 150 gm/cc systems in use by small farmers around the world, at least 60% of them developed by the farmers themselves. These systems involve over 70 gm/cc species. We are discovering additional systems out in the villages almost every week, and mathematical extrapolation from known systems indicates that over 500 such systems actually exist. These systems are frequently not noticed by agronomists—frequently I find such systems in countries where I have been told none existed (Bunch).
Books have now been written about gm/cc's (most are only in Spanish and Portuguese). We can't give the subject matter the space it deserves here, but I will mention a few salient points (Monegat, Calegari et al, Experiencias).
The gm/cc species are used for more than fifteen different purposes, but the most important, in approximate decreasing order of priority, are: human food, animal feed, weed control, sources of income, improved fallows or the elimination of fallowing, a necessary preparatory stage before using zero tillage, and the recuperation of wastelands.
The species most popular around the world are the scarlet runner bean (Phaseolus coccineus), pigeon pea (Cajanus cajan), velvetbean (Mucuna spp.), cowpeas (Vigna unguiculata) and other vignas, and the jackbean (Canavalia ensiformis). One should be creative in choosing species, first finding out what are farmers' highest priorities (stopping erosion or improving the soil is almost never the highest priority) and giving preference to locally known species, especially if they are locally consumed.
The advantages of these systems are numerous. They increase soil organic matter, fix nitrogen (often between 80 - 120 kg of N/ha/year), frequently cost less than the value of the benefits they provide (yes, we are talking, in many cases, about essentially free organic matter), control even the most noxious of weeds, provide soil cover, maintain soil moisture, and allow zero tillage. In an age of threatened globalization of commerce, perhaps one of the most important and least appreciated advantages of gm/cc's is that they may be the only way small farmers in countries such as Paraguay or Cambodia will ever compete with the mechanized agrobusinesses of the North. Mechanization's greatest advantages come in soil preparation and weed control. Since gm/cc's can control weeds and allow zero tillage, they can eliminate both operations. Eliminating weeds is even cheaper than mechanizing their removal (Bunch).
Strip cropping, crop rotations and intercropping
These are all important land husbandry technologies. I have little to say about them to add to what is already widely known.
Almost all crops grow better in the lowland tropics (under about 1,000 m) with a ten to fifteen percent shade. This allows for growing one tree about every ten to fifteen m each direction, in either cropped or grazed fields. Small farmers already use this technology in many areas around the world (Malcolm Cairns of ICRAF has found scores of such traditional systems in Southeast Asia, for instance). Those who know of these systems consider them to be probably the most promising agroforestry system known, both in terms of potential farmer acceptance and of the brute number of full-blown trees these systems could get planted around the world.
Advantages include a general increase in crop yields of about 50%. Even more important is the protection against either too little or too much rain (yields may drop 20% while neighboring farmers lose almost everything), thereby appealing to small farmers' aversion to risk. And then there is the trees' innate value—their production of high-value timber, fruit, firewood, etc. Compared, for instance, to alley cropping, this technology produces an increase in yields because the shade is distributed fairly evenly, rather than concentrated. Dispersed shade also produces a similar total tree biomass per unit area (though with fewer trees), and allows the trees to grow into full-grown trees, rather than being managed as short-stature shrubs. Dispersed tree systems have been successfully used with basic grains and pasture land, in intensive as well as extensive systems, and are found all the way from the semi-arid Sahel to Southeast Asia's rainiest rainforests.
Improved (or eliminated) fallows
The maize-mucuna system which has spread across the rainforests of Northern Honduras has allowed farmers working on poor, hillside fields under 2,000 mm of rain a year, to grow 2-ton/ha maize for forty-five years—every single year. I have also seen farmers who used a Leucaena species to grow maize 20 straight years in southern Ghana, farmers in Vietnam and Cameroon who reduced their 8-year fallows to only one year by broadcasting Tephrosia vogelii seed on their fields at the beginning of the fallow, and farmers all over the world who have cropped their tropical fields every year for one or two decades because of gm/cc's. Many farmers now laugh at the idea that fallows are necessary.
Improved fallows could probably single-handedly do more to solve Africa's food shortage, not to mention its problem of deteriorating soils, than any other single technology we know.
CIDICCO, et al. 1997. Experiencias Sobre Cultivos de Cobertura y Abonos Verdes, Tegucigalpa, Honduras.
Bunch, R. 2001. "A Proven Technology for Intensifying Shifting Agriculture, Green Manure/Cover Crop Experiences Around the World," In Shifting Cultivation, Towards Sustainability and Resource Conservation in Asia, International Institute for Rural Reconstruction (IIRR), Cavite, Philippines.
Bunch, R. and G. López. 1995. Soil Recuperation in Central America, Sustaining Innovation After Intervention, Gatekeeper Series No. 55, International Institute for Environment and Development (IIED), London.
Calegari, A., et al. 1993. Adubacao Verde no Sul do Brasil, (Second edition) Assessoria E Servicios a Projetos em Agricultura Alternativa (AS-PTA), Rio de Janeiro.
Monegat, C. 1991. Plantas de Cobertura do Solo, Características e Manejo em Pequenas Propriedades, Claudino Monegat, Chapeco, Santa Catarina, Brazil.
Shaxson, F. 1999. New Concepts and Approaches to Land Management in the Tropics with Emphasis on Steeplands (Soil Resources, Management and Conservation Service of the Food and Agriculture Organization (FAO), Rome, Italy.
Silsoe. No date. Research Institute, "Adopción de Tecnologías de Conservación de Suelos y Agua en el Distrito de Guinope, El Paraíso, Honduras."
This is an invited article submitted by Roland Bunch to The Overstory.
Bunch, R. 2002. Land Husbandry. The Overstory #111, Permanent Agriculture Resources, Holualoa,Hawaii. Web: overstory.org
About the author
Roland Bunch pioneered farmer-to-farmer extension and participatory technology development in the late 1960's, and wrote about these and other facets of farmer-empowering agricultural extension in his book Two Ears of Corn: A Guide to People-Centered Agricultural Improvement. The book has now been published in ten languages. Since then he has worked in some 35 nations as a consultant to the Ford Foundation, OXFAM, ILEIA, HELVETAS, GTZ, several national governments and many other development organizations, while coordinating the work of COSECHA, a Honduran nongovernmental organization. Roland was nominated in 1999 for the World Food Prize.
The Association of Consultants for a Sustainable, Ecological a People-Centered Agriculture (know by is Spanish acronym COSECHA), is a not-for-profit, non-secretarian, non-governmental development organization based in Honduras, Central America. COSECHA'S primary purpose is to spread the knowledge and effective use of the "people-centered development" process, as described in Two ears of corn, A guide to People-Centered Agricultural Improvement by Roland Bunch, Agricultura Ecologicamente apropiada by Bernard Neugebauer, et al, and Desarrollo Agropecuario, De la Dependencia al Protagonismo del Agricultor by the Food and Agriculture Organization of the United Nations.
COSECHA's mailing address is: Apartado 3586, Tegucigalpa, Honduras Tel and Fax: (504) 766-2354
Related editions to The Overstory
- The Overstory #81--Soil Foodweb
- The Overstory #80--Forests and Water
- The Overstory #70--Rhizosphere
- The Overstory #66--Carbon Sequestration: Storing Carbon in Soils and Vegetation
- The Overstory #61--Effects of Trees on Soils
- The Overstory #29--Tropical Green Manures/Cover Crops
- The Overstory #22--Pioneering Difficult Sites
- The Overstory #20--Five Fertility Principles
- The Overstory #17--Microcatchment