As was explained in the first of these four papers on green manure/cover crops, it is the lack of rainwater infiltration into the soil that is by far the most important cause of what Antonio Guterrez, the Secretary General of the United Nations, has famously called the “Hurricane of Hunger.” Green manure/cover crops (gm/ccs) are by far the cheapest and easiest way to solve this devastating problem—a disaster that otherwise could well result in the deaths of up to 60 million Africans within the coming decade, making it the worst famine in human history.
By gradually adding more and more of the right gm/ccs and other forest species to these fields of maize and gliricidia, we can gradually “imitate the forest,” thereby achieving all the benefits that forests achieved during thousands of years. Note that even the maize several rows from the edge of this field is tall and dark green, in spite of (no, because of) the dense growth of plants around it that have softened the soil and fertilized it.

The Advantages of Gliricidia Trees

Gliricidia trees (Gliricidia sepium), commonly known as “mother of cacao,” are the most useful trees we presently know of for helping farmers to overcome the “droughts.” They have the following very desirable characteristics

1. Gliricidia tree leaves do a better job of fertilizing the soil and increasing crop production than any other known leguminous trees except for Leucaena (Leucaena spp) and severalspecies of Piliostigma. We know this because we experimented with the leaves of dozens of tree species in Honduras during the 1980s, placing them around maize plants to see which tree leaves caused the maize to produce the best. Compared to Leucaena and Piliostigma trees, we prefer gliricidia because Piliostigma trees require about ten years to achieve their full size instead of the four years required by gliricidia trees, and Leucaena trees can become invasive, while gliricidia trees, as far as we know, never do. Furthermore, gliricidia trees have a long list of additional advantages.
2. Like most other trees, gliricidia trees have the advantage that they protect grain crops from excessive heat. Maize in the lowland tropics already loses something like 20% of its productivity because of excessive heat. It actually stops growing for an hour or two in the early afternoon every day. And this problem will get progressively worse as global warming becomes more serious. However, with trees producing dispersed shade in one’s field, one can merely prune fewer branches off the trees as the environment heats up further, thereby largely solving the problem.
3. Gliricidia trees planted all across farmers’ fields can also, like many other trees, act as windbreaks. This means they reduce both the transpiration from leaves and the evaporation rate from the soil, preventing needless drying out of the soil, especially during the dry season. This factor is obviously very important in areas where lack of soil moisture is the limiting factor to crop growth.
4. Almost any tree grown in a cropped field must be pruned, but gliricidia trees have the advantage that they can be pruned with a machete while one is standing on the ground. Also, if necessary to prevent overshading, every single branch of the gliricidia can be cut off at shoulder height without the tree ever dying (unless it is attacked by termites, a problem that can usually be prevented by leaving two or three limbs on the tree so more of the trunk remains living). Furthermore, the prunings make good firewood, so women can make a lot fewer trips all the way to the forest—trips which often involve walking from three to five kilometers to the forest, climbing trees to cut the firewood, and then carrying it all back home on their heads.
5. The petals of the flowers of the gliricidia tree are edible, and widely eaten in southern Honduras, where they are native. They tend to appear soon after the rain stops, and are usually eaten together with scrambled eggs or stewed together with tomatoes.
6. In seriously droughty areas (with normal rainfall below about 700 mm/year), such as the northern Sahel, gliricidia’s unusual habit of starting to grow plentiful leaves three months before the rainy season starts is highly appreciated by smallholder farmers. After a rainy season that is droughty, farmers’ cattle often start dying for lack of forage about three months into the dry season. However, farmers with gliricidia trees can then start feeding their cattle gliricidia leaves. These leaves are so nutritious and plentiful that the cattle will continue to fatten up even during the last three months of the dry season.
7. The bark of the gliricidia tree contains a high-quality rat poison, which can be used to prevent rats from eating people’s stored grain. It can be released from the bark merely by boiling a couple of pieces of the bark on a cooking fire for 20 minutes, after which the water can be used for poisoning the rats. However, like any rat poison, it must be handled with great care, to prevent children or domestic animals from being killed. For instance, the trees should not be planted right near one’s house, where babies or little children might gnaw on the bark and get poisoned. Also, in areas where people customarily brush their teeth with twigs. they should be warned never to use gliricidia twigs for this purpose. Doing so will give them a very bad headache. When this poison is used to kill rats, it must be placed under a large stone or log, where the rats can reach it, but children and domestic animals cannot.
8. A number of scientists have claimed that gm/ccs cannot work in droughty areas because cattle and goats will favor the gm/ccs, with their high protein content, over other natural pastures, leaving no gm/ccs to fertilize the soil. But gliricidia leaves are not tasty, so cattle only eat them when they are fairly hungry. Thus, when cattle are eating these leaves during the dry season, they will automatically stop eating the gliricidia leaves just as soon as the next rainy season starts and fresh green grass starts sprouting everywhere. For this reason, there will still be plenty of gliricidia leaves to use as gm/ccs. Of course, very inexpensive fences made of monkey thorn trees that will last for 80 to 100 years can also solve this problem of cattle and goats eating the gm/ccs.
9. Even though gliricidia trees are exotics in Africa (being native to Central America), they have no known serious disease or insect problems in Africa, except that of termites, which, as mentioned above, are fairly easy to control. However, if one is worried about their being exotics, one can plant a Piliostigma tree right next to each gliricidia tree, pruning it into a small bush each year or two. In this case, if the gliricidia is attacked by some disease or insect pest, the Piliostigma, a native of Africa, will have grown a good root system and therefore can, within three or four years, become a good-sized tree, with several of the positive characteristics of the gliricidia.
10. As do all trees that live for at least several decades, gliricidia has semi-permanent roots in the ground that allow a large number of beneficial soil microorganisms to thrive.
11. If planted with a good number of other plants in a maize field (being careful not to include plants that will compete with the maize or shade it too much), the gliricidia trees and other gm/ccs will have all the many advantages of a tropical forest. The fields will never have problems with droughts; they will have no need of human labor (including for soil preparation, the making of planting stations or ridges); they will produce tremendous amounts of biomass; they will prevent insect pests and plant diseases from killing the plants; and they will sequester huge amounts of carbon in the soil. (See the papers in this series on lablab beans, pigeon peas, or jack beans for a more ample explanation of these advantages of gm/ccs.)

Establishing Gliricidia Trees To Produce Dispersed Shade

Gliricidia trees do the best job of providing all the above advantages if they are spaced across a field of maize or some other grain, in what we call a “dispersed shade” pattern. This means they are far enough apart, and pruned often enough, so that the crops have a partial shade (usually between 25 and 50%, meaning that quarter to one half of the land under the trees is in the shade, and the rest is receiving direct sunlight). To accomplish this feat, the best distance between the trees will be something close to 5 mt. square (that is, 5 meters along parallel lines through the field, with five meters between each line.)

Getting the gliricidia trees started in a new area is probably the biggest single problem in using them. There are a good number of gliricidia trees already growing in many parts of central and southern Mali, in Nairobi and southeastern Kenya, in northern Tanzania, in central and eastern Zambia, in northern Zimbabwe, in southern Malawi, in eastern Madagascar, and probably in other parts of Africa I have not personally visited. Where they do already exist, and farmers have used them as we do—as dispersed shade in crop fields—they are usually highly popular and spreading to new villages fairly quickly. In these cases, gliricidia may well be the first thing one should do in a new area, or perhaps do it together with jack beans, pigeon peas or lablab beans. However, if gliricidia cuttings or seeds have to be brought from fairly far away, it is usually best to wait to introduce the gliricidia until after farmers have already had visible success with one of the other species of gm/cc. That is, because the introduction of gliricidia cuttings is fairly complicated, they are normally best introduced when farmers have already become enthusiastic about gm/ccs.

Farmers usually prefer to use cuttings because in this way, they can have almost full-grown trees within about four years, and they save the labor involved in making and caring for seedbeds. But to establish cuttings in a new area, the cuttings must be transported and planted in the new location within one or, if necessary, two days after being cut. They need to be planted about one month before the rains start, and the holes where they are planted each have to be at least 50 cm deep. The cuttings must not be watered during the first two or three weeks after being planted, because the recently planted cuttings are susceptible to rotting. They must also be protected from animals and children, because if they are moved or bumped against within a month of being planted, their small roots will be broken, and they will die. Farmers will be reluctant to do all this work and preparation if they are not highly convinced that these trees will be very useful to them. So starting this work where farmers have not seen the success of gm/ccs themselves, in their own fields or in nearby farmers’ fields, is a real challenge.
The cuttings must be 1.5 mt long, and at least 6 cm in diameter at their narrowest point, with all the side branches eliminated. If the cuttings are smaller in diameter than this, most or all of the cuttings will die. Being this size, the cutting should be buried 50 cm deep in the soil, with the upper end of the cutting standing one meter out of the ground. This means that the cutting will be forming a 1-mt-long trunk for the new tree right from the day it is planted. The cutting must be planted with the end of the cutting that was nearest to the trunk of the original tree buried in the ground.

As always, we should have the farmers experiment on a patch of land that is no larger than 20 mt by 20 mt. In that case, they would have 5 trees going in each direction (including the trees on each border of the plot) for a total of 25 trees.

Frankly, we are still experimenting with slightly different spacings. Some farmers with experience want to plant them every 4 mt. so there will be more leaves to fertilize the soil and more shade the first few years. This may be even better, but we want to see if this does not cause problems of too much shade when the trees are mature. A few farmers with experience are even planting them every 3 mt, with the idea that when the trees become mature, they will eliminate some of the trees. But we want to see how difficult it is to eliminate full-grown trees before we recommend this practice more widely.

Managing Gliricidia Trees as Dispersed Shade

As with other gm/ccs, very little management is required to use gliricidia trees as gm/ccs once they are established. The only major job is that of pruning them once a year. This job is best done right before the coming rainy season begins to increase labor demands on the farmers—usually about three weeks to a month before the rains start. The pruned material can be stripped of its leaves and taken immediately to the house for use as firewood. In some areas the women prefer to save even more labor by just leaving the pruned branches on the ground until the ants or termites have stripped off all the leaves and then taking the bare branches to the house.

Farmers can prune all the branches off the trees in order to leave maximum sunlight for their crops, or prune all but four or five branches either to prevent termite damage to the tree trunks, to have some shade for their crops right from the start of the season, or to allow some of the branches to continue growing thicker so they can be used a year or two later as cuttings. This decision should be made by individual farmers themselves after they have had some experience with each way of managing their trees, since different farmers in each village may have different levels of termite infestation, different levels of weed infestation, different levels of demand for cuttings and different food crops that do best with different ambient temperatures.

By the second or third year of growth, the gliricidia trees will usually have enough leaves on the unpruned branches a month after the maize is planted to strip off just these leaves for a “side dressing” of additional nitrogen for their crops.

After this, there is usually almost no labor required by the gliricidia trees until the next pruning a year later, although a slight pruning might be needed six months later in an area of bimodal rains.

Gliricidia trees should always either be planted where other gm/ccs are already in use, or should be followed two or three years later with the planting of other gm/cc species in the same fields. Working together, the gliricidia trees and other species of gm/ccs could well triple maize production and end the droughts in just four or five years, instead of the usual five or six years.

If anyone reading this paper wishes to see any of the other three papers (one on the role of gm/ccs in overcoming the droughts, a second one on jack beans, and a third one on lablab beans and pigeon peas), feel free to write me at rbunchw@proton.me.