| Soils, Crops and Fertilizer Use |
|Chapter 8: Using organic fertilizers and soil conditioners|
Also known as shifting cultivation, this traditional cropping system was once widely practiced throughout the humid tropics. Because of increasing population pressure on the land, it's now confined mainly to the dense forest areas of the Amazon Basin and S.E. Asia. Here's a brief description:
• Land is incompletely cleared by hand-cutting and burning trees and vegetation. Although burning destroys some nutrients like N and S, most of the others remain in the ash as fertilizer. The organic matter in the burned vegetation is lost, but HS we'll see, this isn't serious.
• Crops are grown on the land for 2-3 years, usually in a mixture of short-cycle staples like grains, pulses, and vegetables along with longer-term ones like yams and cassava. The plants utilize the naturally-accumulated nutrients built up from the fallow period (see below). Yields are fair the first year, but then rapidly decline, forcing the land to be temporarily abandoned after several years of cropping.
• The land then reverts to a natural vegetation fallow for 5-10 years which rejuvenates the soil in several ways. Deep-rooted tree species recycle leachable nutrients like N and S which are returned to the soil surface in the leaf fall. Some of the fallow vegetation may be leguminous and actually add N to the soil. The fallow period also increases the amount of soil humus and helps prevent a buildup of insects and diseases.
Slash-and-burn farming requires no outside inputs and is in complete harmony with the environment, as long as an adequate fallow period can be maintained. Unfortunately, in many areas, population pressures have resulted in shorter fallows and increased burning which kills off trees and brush, leading to deforestation, erosion, and soil depletion.
This is another traditional system that is self-sustaining in fertility. Like slash-and-burn, it's best adapted to the the humid tropics where rainfall is adequate for year-around crop production. Unlike slash-and-burn, it's a permanent system with no fallow period and is practiced on smaller plots (typically 300-500 sq. meters), since it involves no staple grain production (although root crops like yams and cassava are usually grown). The major features of mixed gardening are:
• It is an integrated mixture of up to 30 or more annual and perennial crops plus several types of livestock like pigs and poultry; it may even include a fish pond. It provides the family with vegetables, fruits, spices, cooking oil, eggs, meat, fiber, medicines, weaving and building materials (i.e. bamboo, coconut palms), and firewood, etc.
• The crops are selected and interplanted to complement each other and achieve maximum land use efficiency. A mixed garden resembles a tropical forest with a multi-storied canopy. At ground level, there will be low-growing or trailing plants like sweet potatoes, taro, squash, herbs, and vegetables. At the next level may be coffee, cassava, banana, and papaya. Taller trees like avocado, citrus, and breadfruit will form the next canopy, followed by another of higher coconuts. Some of
the trees and even the home's walls and thatched roof may be used to support climbing vines like yams and yardlong beans. This multi-storied arrangement provides maximum plant density and utilization of space.
• The system is self-sustaining in fertility because of nutrient recycling from manure and compost production, kitchen wastes, leaf fall, and N fixation from legumes. It's also virtually immune to soil erosion because of the ground cover.
Until recently, the value of mixed gardening was often ignored by development "experts" or even derided as being outdated or unproductive (from a cash-cropping viewpoint). Fortunately, its value has now been "rediscovered". It's important to note that it,in some cases, it may be possible and advisable to combine elements of Western gardening and mixed gardening. The Peace Corps/ICE office has several useful pamphlets on mixed gardening (see the bibliography in Appendix H).
This is a land use system that combines trees with crop plants and/or livestock to increase overall production and income and to improve ecological stability. Some agroforestry systems are centuries old, but, like mixed gardening, this is a fairly new field of research. In fact, mixed gardening is a type of agroforestry. Although agroforestry doesn't always rely solely on organic fertilizers or self-sustaining fertility, most systems will decrease the dependence on chemical fertilizers. Agroforestry systems may have several benefits:
• Stabilization of hilly land.
• Maintenance and improvement of soil fertility: The deep taproots of trees can recyle nutrients lost be leaching. In addition, leguminous trees such as leucaena (Leucaena leucocephala and Sesbania can fix considerable nitrogen.
• Improvement of the micro-climate through the effects of partial shading and the mulching effect of the leaf litter, which reduces the drying and hardening of the soil.
Here are two examples of agroforestry systems:
• Alley-cropping: In this system, leguminous trees like leucaena and madre-de-caceo (Gliricidia) are planted in
rows 3-4 meters apart with food or forage (animal feed) crops grown in-between. The trees enrich the soil by fixing nitrogen from the air, and their leaves and pods provide a high-protein animal feed. The leaves, which are high in N, can be cut and carried to the non-legume crop for use as fertilizer or mulch; they can also be used for composting.
• Livestock/forage systems: Many leguminous trees like Leucaena, Gliricidia, Calliandra, and Sesbania have nutritious leaves palatable to livestock. (Leucaena leaves are toxic to non-ruminants.)
The Regenerative Agriculture Movement
Also known as "biological" or "sustainable" agriculture, the origins of this movement go back a century or more. It has received new impetus (mainly in the U.S. and Europe) during the past 10 years, due to ever-increasing ag chemical prices and growing concern over pesticide usage, accelerated erosion, and other problems like nitrate pollution. The latter is partly attributable to the overuse of N fertilizers. The main principles and practices of regenerative agriculture are:
• It aims to sustain and support the environment instead of exploiting it.
• The use of insecticides, herbicides, and other biocides is minimized or eliminated. Control of weeds, insects and diseases is accomplished through natural, biological, or mechanical controls such as crop rotations, cultivation, resistant varieties, predator insects, and biological insecticides.
• Chemical fertilizers are minimized or eliminated. Soil fertility is maintained or improved by:
•• Crop rotations involving legume cover crops and green manures to add nitrogen.
•• The use of animal manure and "natural" fertilizers such as rock phosphate.
•• Stimulating a beneficial level of soil mioroorganisms that improve the availability of nutrients like nitrogen and phosphorus.
• Soil erosion is controlled by the use of crop rotations and cover crops that provide erosion protection with their ground cover.
• Livestock is usually included in regenerative farming systems to utilize forage rotation crops and provide manure. Hormones and the prophylatic use of antibiotics is eliminated.
Although much more needs to be learned about regenerative ag before it can be widely and profitably adopted, some U.S. and European farmers have been making a successful transition toward this system, even on larger farms. Regenerative ag is not merely conventional farming without chemicals; nor is it simply a matter of reverting to the traditional practices of earlier years. Given the modern-day economic realities of farming and the advances in pertinent research areas such as soil microbiology and covercropping, new practices and techniques need to be developed and tested. Over the years, the USDA, U.S. ag universities, and agribusiness haven't shown much interest in regenerative ag. However, since the mid-1970's, there has been an increasing amount of long-awaited, valid organic farming research done by universities or by private organizations like the Rodale Research Institute in Emmaus, Pennsylvania.
As with most ag research, that concerning regenerative ag is very location-specific and has limited transferability from one area to another. This means that considerable adaptive research will be needed.
(For a summary of the current status of "organic" farming, see the American Soc. of Agronomy Special Pub. 46 listed in the bibliography in Appendix H.)