Experiences of World Neighbors in Central America

ILEIA Newsletter •5 nº 2 • July 1989

Experiences of World Neighbors in Central America

Green manure crops could be critical to mankind. Probably something around 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, 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.

Farmers' acceptance of green manures

After some four years of farmer-run research and dialogue with farmers, World Neighbors/Central America has found a number of ways to overcome most of the problems farmers have with accepting green manures. The following is a list of four ways a farmer can produce green manure without reducing at all the land he uses for his other crops:

1. Green manure crops can often be planted in among traditional row crops, especially in the cases of corn, sorghum, and millet, without decreasing the production of the main crop at all the first year, and usually with significant increases in succeeding years. The major instance in which this is not possible is when farmers traditionally intercrop two or three other crops with their major grain.

2. Green manure crops can often be relay-intercropped with basic grains towards the middle or end of the growing season, timed so that their major growth will occur during the dry season, thereby utilizing cropland during months when normally nothing is planted on it.

3. Wherever multiple-year fallows and/or shifting agriculture are used, green manures can be planted on the land the first year it is to be fallowed or abandoned. In this way the fallow period can be cut to one year, and abandoned land put back into use. Near Vera Cruz, Mexico, villagers now use velvetbean to cut what used to be about a ten-year fallow down to one year.

4. In certain areas where fruit or coffee trees are common, green manures can be grown successfully around or under the trees, both increasing the growth and health of the trees and providing green manure, forage, or high-protein human food in addition. Velvetbean is our specie of choice Although a good deal of research still needs to be done in finding adequate plants, there are a few species that seem to be very effective: Stizolobium spp, or Mucuna pruriens (velvetbean) is presently our species of choice, in most cases, for growing in cornfields, rehabilitating depleted land, and eliminating certain serious weeds e.g. nutgrass (Cyperus rotundus), Bermuda grass (Cynodon dactilon), and Imperata cilindrica.

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, 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. When incorporated, the velvetbean often approximately doubles subsequent corn yields; when used as a mulch, it increases yields by about 35%. Even dry beans following velvetbeans have shown yield increases of over 100%. The dry velvetbean can also be made into a coffee substitute, the acceptance of which here in Honduras has caught us totally off guard. Having introduced it as a coffee stretcher (to be used half and half with coffee), we found out a month or so later that people in many communities we re 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 lbs. a week under the name "nutricoffee" (the bean contains 22% protein and no caffeine). This is one of those rare cases when families can save money (on coffee) and increase their protein intake at the same time.

Recently villagers’ nutrition groups have discovered that by roasting the velvetbean somewhat less than they do to make coffee, they have been able to produce a really passable hot chocolate, and by grinding the flour finely, they have been able to use a recipe for soybean cake to make "velvetbean cake".

Limitations of Velvetbean

About the only soils we have tried in which the velvetbean does poorly are waterlogged soils or those with very low pH-values (4.5 and under). It also, like the jackbean, needs to be planted in a field recently weeded, and where the soil is either sandy or has been cultivated within the last three years. Velvetbean will take a bit cooler climate than jackbean, but still does best at sea level and poorly over 2,000 m. In cool climates it will grow three or four months into the dry season, but is not as drought-resistant as the jackbean.

Other problems encountered with the velvetbean include damage by slugs in warm climates, damage by rabbits, and occasional problems with leaf-cutter ants and iguanas. In some locales, when it was grown in cornfields, rats used the velvetbean sterns to climb up and eat the corn. Planting the velvetbean later or cutting its tendrils when they get too large has helped to solve this problem. Velvetbean has to be watched and cut back if planted near trees. Except for leaf-cutter ants, the velvetbean has no serious insect pests here.

Corn crops growing where velvetbean 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 have therefore almost always added a side dressing of urea to these crops. In general we would recommend this practice where fertilizer is available and affordable. In the long-run, one would think phosphorus would also be needed, but in the short-run neither visible symptoms nor level of yields would indicate much problems with this element. Quite likely, the increased organic matter is increasing the availability of soil phosphorus enough that deficiencies just are not a problem yet.

Jackbean for poor, droughty soils

Canavalia ensiformis (jackbean, horse bean, sword bean, haba blanca, etc.) is an incredibly drought-resistant, hardy legume that grow well in extremely poor, droughty soils. There are two kinds of jackbean, one that climbs and covers the soil quite well, and another that has a bushy growth habit and does not climb at all. The varieties of jackbean that do not climb are proving to be very good for weed control and nitrogen fixation under fruit trees. It has virtually no natural pests Dr diseases; its leaves are even sprinkled on leaf-cutter ant hills to eliminate them. Canavalia grows vigorously at sea level, but will grow sufficiently well for use as a green manure crop up to about 1,600 to 1,800 m. It does very well in droughty, depleted soils, and apparently does less well in fairly fertile soils.

The jackbean does not produce at all well in soils with excess water. It also requires one weeding at planting time, and does much better in a soil that has been hoed sometime within the previous three years, although under any of these adverse conditions, it will do better than the 10 velvetbean. If planted in a corn or sorghum field, it should be seeded within 15 days to one month after the corn, sorghum, or beans, depending on climate, speed of growth of other crops, etc. In human consumption, the immature pod can be eaten like green beans when they are about seven to eight inches long. In South-east Asia they are also eaten as beans.

Lablab bean for fertile soils

Dolichos lablab or Lablab purpureus (Lablab bean) is a legume very similar in appearance to the velvetbean, 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 velvetbean or jackbean has already increased fertility sufficiently. The lablab bean is almost as drought-resistant as the jackbean, is very shade-tolerant, and is among the most palatable of legumes for animals (definitely preferred by animals to either the velvetbean or jackbean). The lablab bean grows well from sea level up to about 1,500 m and does well in medium to fertile, well-drained or even droughty soils. It is also edible, and in some places, such as Haiti and West Africa, it is widely appreciated as a regular food.

Much more experimentation is needed

We certainly would welcome any experience you have on this subject. Much more experimentation is needed. We are just really getting started at this, but the incredibly positive response we've had from hundreds of villagers in our program areas has made us decide to share what we know so far even though our knowledge is still so incomplete.

If you have been experimenting with green manures, please send me whatever information you have put together. I would think that right now, the most important subjects we need to learn more about are:

a)  What legumes will work above 1,800 m?
b)  What additional plants will work at any elevation?
c)  In what ways must these recommendations be modified for areas outside of the Caribbean basin area from which these have come?
d)  What green manures will work best under wet tropical conditions?