TN #20 Selecting the Best Plants for the Tropical Subsistence Farm

How to Find the Best Plants for the Small Farm

Number and Classes of Useful Plants

In one attempt to list all of the food plants of the world, Tanaka recorded 10,000 species in a thick volume (Tanaka,T. 1976, Tanaka’s Cyclopedia of Edible Plants of the World). Others claim that the world may contain 20,000 or even 40,000 edible plants, though these claims are not substantiated. Perhaps with the correct processing, every plant is potentially edible.

In addition to the edible plants, a very large number of plants are useful to humankind in a wide variety of other ways. Plants may serve as feed for livestock. They may also provide humankind with needed items including shelter, clothes, fibers, pipes, fishing poles, toothpicks, etc. There are also ecologically beneficial plants that protect and improve the soil and that can influence conditions such as light and wind.

Though nearly all plants are useful in some way, they are not equally valuable. For example, wheat, rice and corn may be considered the most valuable plants in the world based on the vast acreage planted to these crops, their vital role in feeding humankind, and their enormous economic value. Using various criteria, one might consider 10, 25, or even 200 species as the world’s most valuable plants. Yet, under some situations, by some people, or for some special reason, other plants produced and used on a very small scale might be precious and indispensable. The question, “Which are the most valuable plants for the small farm?”, then, becomes breathtaking.

The Problem of Adaptation

Adaptation as defined here is the range of environmental conditions under which a plant can survive, grow and produce. If a plant is widely adapted, it can be grown under many conditions. This is especially important when one tries to compare plants for their values. A widely-adapted plant is more valuable than one adapted to a narrow range of conditions, even if the use of the narrowly-adapted plant is of great importance. When comparing values of plants, we frequently consider their adaptation to growing conditions on small farms.

The small farms throughout the world often represent marginal areas not always well suited to agriculture. The best farming areas are frequently in the hands of a few who own or control vast acreages. There is a macrodiversity among small farms, from flat, easy-access terrain to those places where farming is very difficult such as hillsides, swamps, brushlands, extreme altitudes, rocklands and small valleys. In addition, there is a microdiversity that easily occurs within “pockets” of space with their own microclimates. This phenomenon is caused by great variability in factors such as slope, amount of soil and its nature, and the amount of rainfall, humidity, or light received. Plants respond differently to such conditions.

Now, these differences among small farms increase the problem of choosing the right plants. The problem can be seen in Central America where small farms usually produce the crop(s) necessary for their own household first, then staple foods for marketing as an income source. Often called the basic grains, these staple crops include corn, sorghum, pearl millet, rice, and beans. To this group must be added cassava and potatoes, both of great importance in many regions. The crops that are grown, and the varieties of such crops, are extremely critical, for these crops must be produced under prevailing rainfall conditions. Crops or varieties respond differently to abnormal amounts (too little or too much) and patterns (rainy season constant or intermittent; too long or too short). The problems of producing these life-sustaining crops are so great that farmers may not concern themselves with home vegetable gardens that could balance the diet for their children. On these small farms the right crops or the right varieties may differ radically from one place to another, and it is difficult to accurately predict what crop might do well in a particular location.

Criteria of Value as Defined Here

Because of the diversity of plants that are useful on the small farm, when thinking of their values it is useful to first classify plants by their uses. For example, in comparing plants for their values it is not reasonable to compare cereal grains to windbreaks. Therefore, all of the discussion that follows is based on the comparison of useful plants within categories as defined by the uses themselves. A very helpful list of plant uses is found as part of the Table of Contents section on the first page of this document. That list serves as an orientation to this publication.

Nevertheless, the classes of uses themselves are of different values. Judgments have been made of these values, and the categories of useful plants are listed somewhat in the order of importance in the Table of Contents. For example, food crops are listed first, and among the food crops, those great staple foods including the most important of all, cereal grains. The weakness of this classification of uses is seen in the expression, “Humankind does not live on bread alone”. Thus, in some places and under some circumstances the order of values would vary.

Within each use category, suggested criteria for deciding the value of and selecting a crop are:

• The wideness of adaptation of the crop.
• The quality of the crop for the use in question.
• The useful yield for the use in question.
• Problems in production.
• Storage or durability.

Using the Tables of Useful Plants

For the avid student who wishes to learn about tropical plants and their many uses, there is never enough information. Of the hundreds of species covered by this publication, some are well known and information on them may be available in other literature. Others are inadequately known. By compiling lists of useful species and presenting them in tables, much useful information is lost, and the author apologizes. However, probably no publication can ever be adequate, for agriculture by its nature must always include local trial and learning from experience.

Information for the various categories of plants is presented in forms of generalities as text, and more specific information is given in the tables. The information in tables always includes one common name and the scientific or species name, and may include other information such as growth habitat, edible parts and uses, principal nutrients, and adaptation in terms of temperature, day length, flooding, drought, or climate region. Sometimes negative factors are mentioned. In addition, the various species are usually rated for their relative values for multiple purposes including food, animal feed, fiber, construction materials, fuel, soil amendment (soil improvement), erosion control, and climatic modification. These uses are more fully discussed in the corresponding portion of the manuscript dedicated to such crops.

Descriptions of Useful Plants Plants for Food: Staple Crops

Cereal and Non-Leguminous Grains

Three kinds of edible seed from annual plants can be distinguished: the cereal grains from grasses, the pulses from legumes, and a miscellaneous group which, for convenience here, is called non-leguminous grains. All are annuals that are propagated from seeds.

Cereal grains are the staff of life for most of the people of the world, and wheat is number one. Rice follows, but while extremely important is low in protein. Corn has long been an important life support crop; however, as is the case with other cereal grains, it normally lacks sufficient lysine to fulfill all human dietary protein requirements. However, several high lysine corn varieties have been developed, making this crop the most important member of its class and a potentially useful lifesaver everywhere. The high protein grain triticale also has great promise. Choice of variety suited for the locale is always important for the cereals. Time of planting and harvest may also be critical.

The non-leguminous grains are an assortment of minor crops having special value in isolated regions. They should be considered as potentially valuable but experimental and only rarely could they replace a cereal grain.

On selecting a grain crop, familiarize yourself with the grain crops already grown in the region, including the varieties and their problems. Search first for improved varieties. Try to substitute high lysine (high quality protein) varieties of corn for current varieties. Then, add a little additional fertilizer to the soil and you will be repaid with generous yields. All of the grain crops in the following tables are annuals propagated from seed.

Root and tuber crops throughout the world include: (1) annual, enlarged roots and tubers of little food value and (2) perennial roots and tubers high in starch. These structures are used by the plant for regrowth after an unfavorable season. Roots and tubers are widely used throughout the tropics as staple crops, and indeed are major sources of carbohydrates. Because they are limited in protein, excessive reliance upon them for food may be detrimental to health. It is difficult to pick the best because each has its advantages and disadvantages; however, cassava is the worst because of its low, poor-quality protein. Some people favor the sweet potato because it can be produced in four months, leaving the ground free for other crops. Root and tuber crops are usually widely adapted and easy to grow, but there is frequently a problem of obtaining good varieties.