7. Sorghum
To include sorghum in a book on "lost" crops, on the face of it,
seems like a gross mistake.
After all, the plant is Africa's contribution to the world's top
crops.
The amount produced is not known for certain because sorghum's
production statistics (at least in some countries) are lumped together with
millet's. Annual world production of the two together exceeds 100 million tons,
of which 60 million is certainly sorghum. Based on the FAO figures for 1985, the
number of hectares under sorghum are: Africa, 18 million; Asia, 19 million;
North and Central America, 9 million; South America, 3 million. The main grain
production (in millions of tons) was in the United States (28.70), India
(10.30), China (an estimated 6.80), Mexico (6.60), Argentina (6.20), the Sudan
(4.25), and Nigeria (3.50). Indeed, it belongs to the elite handful of plants
that collectively provide more than 85 percent of all human energy. Globally, it
produces approximately 70 million metric tons of grain from about 50 million
hectares of land. Today, it is the dietary staple of more than 500 million
people in more than 30 countries. Only rice, wheat, maize, and potatoes surpass
it in feeding the human race.
For all that, however, sorghum now receives merely a fraction of
the attention it warrants and produces merely a fraction of what it could. Not
only is it inadequately supported for the world's fifth major crop, it is
under-supported considering its vast and untapped potential.
Viewed in this light it is indeed "lost."
But this situation may not continue much longer. A few
researchers already see that a new and enlightened era is just around the
corner. Accorded research support at a level comparable to that devoted
worldwide to wheat or rice or maize, sorghum could contribute a great deal more
to food supplies than it does at present. And it would contribute most to those
regions and peoples in greatest need. Indeed, if the twentieth century has been
the century of wheat, rice, and maize, the twenty-first could become the century
of sorghum.
First, sorghum is a physiological marvel. It can grow in both
temperate and tropical zones. It is among the most photosynthetically efficient
plants.
It has one of the highest dry matter accumulation rates. It is
one of the quickest maturing food plants (certain types can mature in as little
as 75 days and can provide three harvests a year).
It also has the highest production of food energy per unit of
human or mechanical energy expended.
Second, sorghum thrives on many marginal sites. Its remarkable
physiology makes it one of the toughest of all cereals. It withstands high
rainfall - even some waterlogging.
Recent research in Israel has shown that it also has some
tolerance to salt - an increasingly useful feature for any crop these days.
But most importantly, it can endure hot and dry conditions.
Indeed, it can produce on sites so burning and arid that no other major grain -
with the exception of pearl millet - can be consistently grown.
Its massive and deep-penetrating roots are mainly responsible
for this drought tolerance, but the plant has other drought-defying mechanisms
as well. For instance, it apparently conserves moisture by reducing its
transpiration when stressed (by rolling its leaves and possibly by closing the
stomata to reduce evaporation) and it can turn down its metabolic processes and
retreat into near dormancy until the return of the rains.
Third, sorghum is perhaps the world's most versatile crop. Some
types are boiled like rice, some cracked like oats for porridge, some "malted"
like barley for beer, some baked like wheat into flatbreads, and some popped
like popcorn for snacks. A few types have sugary grains and are boiled in the
green stage like sweet corn. The whole plant is often used as forage, hay, or
silage. The stems of some types are used for building, fencing, weaving,
broom-making, and firewood. The stems of other types yield sugar, syrup, and
even liquid fuels for powering vehicles or cooking meals. The living plants are
used for windbreaks, for cover crops, and for staking yams and other heavy
climbers. The seeds are fed to poultry, cattle, and swine. On top of all that,
sorghum promises to be a "living factory." Industrial alcohol, vegetable oil,
adhesives, waxes, dyes, sizing for paper and cloth, and starches for lubricating
oil-well drills are just some of the products that could be obtained.
Fourth, sorghum can be grown in innumerable ways. Most is
produced under rain-fed conditions, some is irrigated, a little is grown by
transplanting seedlings as is done with rice.
Like sugarcane, it can also be ratooned (cut down and allowed to
resprout from the roots) to provide crop after crop without replanting. It is
ideal for subsistence farmers on the one hand and can be completely mechanized
and produced on a vast commercial scale on the other.
Finally, sorghum is relatively undeveloped. It has a remarkable
array of untapped variability in grain type, plant type, adaptability, and
productive capacity.
Indeed, sorghum probably has more undeveloped and underutilized
genetic potential than any other major food crop.
With all these qualities and potentials, it is small wonder that
certain scientists regard sorghum as a crop with a great future. Undoubtedly, as
the world moves towards the time when its supplies of food will be insufficient
for its supplies of people, this plant will increasingly contribute to the
happiness of the human race. This will happen sooner rather than later.
Population is projected to almost double within most of our lifetimes. How to
feed billions of newcomers on diminishing amounts of prime cropland will likely
be the overwhelming global issue of the period just ahead. Obviously, vast
amounts of the less fertile and more difficult lands must be forced to produce
food. Moreover, if the much feared greenhouse effect warms up the world, sorghum
could become the crop of choice over large parts of the areas that are today
renowned as breadbaskets, rice lands, or corn belts.
In sum, it seems certain that no matter what happens sorghum
will assume greater importance, especially to backstop the increasingly
beleaguered food supplies of the tropics and subtropics. For a hot, dry, and
overcrowded planet, this crop will be an ever-more-vital resource.
This is in fact already starting. Despite only modest
international support, sorghum even now seems to be verging on a global
breakout. In the United States, its yield improvements have outstripped those of
all other major cereals.
In India, it is increasingly employed. And in Mexico, Central
America, and the Caribbean - a most unexpected part of the world for this
African plant - the most rapid growth of all is occurring.
Indeed, the rapidity with which Mexico has embraced sorghum is
little short of spectacular. Before 1953, the crop was so little used in Mexico
that, as far as international statistics were concerned, it didn't exist there.
However, by 1970 it was being planted on nearly I million hectares, and by 1980
on nearly 1.5 million hectares. The reason is a pragmatic one: sorghum is not
only cheaper to produce, it yields about twice as much grain as maize in Mexico
(2,924 kg per hectare versus 1,508 kg per hectare in one recent test). Also,
where rainfall is unreliable, sorghum is proving the more dependable of the two.
Mexico uses most of its sorghum grain for animal feed, but it is
increasingly relying on new, food-quality sorghums. These produce grains
suitable for making tortillas, the round flat bread that is Latin America's
staple food. In addition, sorghum is also being used to make breakfast cereals,
snacks, starch, sugars, and other products that currently come from maize. It is
even the basis for some (European type) beers in Mexico, a country renowned for
its brewing skills.
Although these developments demonstrate sorghum's capabilities
and almost certainly portend a coming boom in production throughout much of the
world, much remains to be done before this crop can truly fulfill its
international potential. At present, it has several drawbacks, including the
following:
· Lack of status. In global terms, sorghum is being held
back by the mistaken prejudice that it is a "coarse" grain, "animal feed," and
"food of the peasant classes."
· Low food value. In its overall nutrient
composition - about 12 percent protein, 3 percent fat, and 70 percent
carbohydrate - sorghum grain hardly differs from maize or wheat. However,
sorghum has two problems as far as food quality is concerned. One is tannins,
which occur in the seed coats of brown sorghum grains. When eaten, tannins
depress the body's ability to absorb and use nutritional ingredients such as
proteins. Unless the brown seeds are carefully processed, some tannins remain,
and this reduces their nutritional effectiveness. The other problem is protein
quality, which affects all sorghums, both brown and white. A large proportion of
the protein is prolamine, an alcohol-soluble protein that has low digestibility
in humans.
· Difficulty in processing. Sorghum is harder to process into
an edible form than wheat, rice, or maize.
Ultimately, none of these drawbacks is a serious barrier to
sorghum's grander future, but each is a drag that - like a sea anchor in the
tide of progress - is holding the crop from its destiny. Moreover, all of them
can be overcome, as the following chapters demonstrate.
This plant's potential is so great that we have devoted the
following four chapters to its various types. The next chapter highlights
sorghum's promise for subsistence farmers - the millions in Africa and Asia (not
to mention Latin America) to whom the plant means life itself.
The subsequent chapter highlights commercial sorghums - the
types that are increasingly grown by farmers who produce a surplus. The chapter
that follows highlights specialty sorghums - unusually promising food types that
are now little known in a global sense but that have outstanding merits for the
future. Finally, there is a chapter on sorghum's promise as a source of energy
as well as on other special qualities that can benefit farms and farmers.
These divisions are of course arbitrary. They are simply a
convenient way to present the vast range of this plant's possibilities. There
are many areas that overlap and much common ground between the different types,
different purposes, and different users. In addition, major advances
specifically in Africa's sorghum production are likely to come from methods and
technologies that are beyond the scope of the following chapters: from
controlling birds, locusts, and parasitic weeds to new approaches to milling,
grain storage, and erosion control. These are discussed in appendixes A and B.
FIGURE: The extent to which Africa
stands to benefit from sorghum research can be seen from this map. The crop is
perhaps the continent's most widespread and important staple. Beyond the fact
that yields can be raised far above the present average, sorghum's adaptation to
a wide range of ecological conditions is an enormous asset.
Over the millennia' this ancient food was probably domesticated
several times. At least four major types arose in different places. These are
shown. One of the oldest, the durra(crook- necked) variety, was eaten in Egypt
more than 4,000 years ago. Ethiopia is its center of diversity, and durra
sorghum is still the staple food for most of the populace of the Horn of Africa.
The region from eastern Nigeria through Chad and western Sudan is a center of
diversity for the caudatum race. The region from western Nigeria to Senegal gave
rise to the guinea race. The area from Tanzania to South Africa is the center
for the kafir race. All of these separate sorghums have fed countless
generations.
Africa's Gift to Mexico
The rise of sorghum in Mexico has been so spectacular that it
has been called "the country's second Green Revolution." The crop has become the
third largest in terms of area (after maize and beans) as well as in terms of
value (after maize and cotton). Between 1958 and 1980, the number of hectares
sown expanded by almost 1,300 percent and the amount of sorghum production
increased 2,772 percent. More than 1.5 million hectares of sorghum were sown in
1980 - more than double the amount of land planted to wheat, Mexico's first
Green Revolution crop. Mexico has become the sixth largest
sorghum-producing country in the world; only the United States and China used
more of this originally African grain.
The fact that sorghum requires less water than maize or wheat is
a significant advantage in Mexico, which has large areas of arid land. This has
been true even in irrigated areas because the government has sometimes had to
limit irrigation water owing to depleted reservoirs. Also, sorghum is now grown
in some areas where irrigation has salinized the soil.
It requires between two and four irrigations per year, compared
to wheat's six or seven.
Although average yields per hectare are not as great as those of
wheat, they are substantially higher than those of maize.
At the beginning, most of Mexico's sorghum was grown for animal
feed. Already, this grain forms a substantial part of the diet of all the
chickens, pigs, cattle, sheep, and goats that are raised in the country.
Although the animal feed industry also uses maize, barley, wheat bran, soybeans,
and other products, sorghum supplies 74 percent of the raw material used in
animal feed in Mexico.
Now, however, more and more food-grain sorghum is being grown.
NUTRITION
Like other cereal grains, sorghum is composed of three main
parts: seed coat (pericarp), germ (embryo), and endosperm (storage tissue). The
relative proportions vary, but most sorghum kernels are made up of 6 percent
seed coat, 10 percent germ, and 84 percent endosperm.
In its chemical composition, the kernel (in its whole-grain
form) is about 70 percent carbohydrate, 12 percent protein, 3 percent fat, 2
percent fiber, and 1.5 percent ash. In other words, it hardly differs from
whole-grain maize or wheat. When the seed coat and germ are separated to leave a
stable flour (from the starchy endosperm), the chemical composition is about 83
percent carbohydrate, 12 percent protein, 0.6 percent fat, I percent fiber, and
0.4 percent ash.
The nutritional components are given in the tables and charts,
but some of the details are discussed below.
NUTRITIONAL PROMISE
In composition sorghum is similar to maize. Starch is the major
component followed by protein, fat, and fiber. Compared with maize, however,
sorghum generally contains 1 percent less fat and more waxes. Its complex
carbohydrates have properties similar to those from maize.
The protein content is quite variable. The American literature
reports several instances of levels ranging from 8.3 to 15.3 (these were
measured on the milo sorghum that is grown throughout the Midwest). Most samples
fall in the 9 percent protein category and are almost always 1 or 2 percent
higher than in maize.
However, for human nutrition sorghum protein is "incomplete." It
is deficient in critical amino acids, most importantly lysine. Today's standard
sorghums provide about 45 percent of the recommended lysine requirement.
Although a primary food for millions of Africans, Asians, and
Latin Americans, sorghum is low in protein digestibility. It must be properly
processed to improve its digestibility. It is perhaps for this reason that much
of Africa's sorghum is subjected to fermentation before it is eaten.
Carbohydrate is the grain's major component, with starch making
up from 32 to 79 percent of its weight. The remaining carbohydrates are largely
sugars, which can be quite high in certain rare varieties of sorghum grains.
The starches in most sorghums occur in both polygonal and
spherical granules, ranging in diameter from about 5µ to 25µ (average
15µ). Chemically, the starch is normally made up of 70-80 percent branched
amylopectin (a non-gelling type) and 20-30 percent amylose (a gelforming type).
However, some sorghum starches contain as much as 100 percent amylopectin;
others, as much as 62 percent amylose.
In its properties, sorghum starch resembles maize starch, and
the two can be used interchangeably in many industrial and feed applications.
When boiled with water, the starch forms an opaque paste of medium viscosity. On
cooling, this paste sets to a rigid, nonreversible gel. The gelatinization
temperature ranges from 68° to 75°.
Sorghum's protein content is more variable than that in maize
and can range from 7 to 15 percent.
In most common cultivars, as mentioned above, the kernel
contains about 12 percent, which is 1-2 percentage points higher than maize.
The protein's amino-acid composition is much like that of maize
protein. Lysine is the first limiting amino acid, followed by threonine.
The protein contains no gluten. A large proportion of it is
prolamine, a cross-linked form that humans cannot easily digest. In fact,
prolamine makes up about 59 percent of the total protein in normal sorghum. This
is higher than in other major cereals, and it lowers the food value
considerably.
In the long term, sorghums that have less prolamine may come
available for routine use. A few of these more nutritious types have already
been found: two in Ethiopia and one in the Sudan, for instance. Until such
quality-protein sorghums are perfected, however, sorghum grain needs to be
processed if its full protein value is to be realized.
Generally, sorghum contains about I percent less fat than maize.
Free lipids make up 2-4 percent of the grain and bound lipids 0.1-0.5 percent.
The oil's properties are similar to those of maize oil. In other words, the
fatty acids are highly unsaturated. Oleic and linoleic acids account for 76
percent of the total.
Compared to maize, sorghum contains higher levels of the B
vitamins pantothenic acid, niacin' folate, and biotin; similar levels of
riboflavin and pyridoxine; and lower levels of vitamin A (carotene). Most B
vitamins are located in the germ.
Pellagra - a disease caused by too little niacin in the diet -
is endemic among certain sorghum eaters (as it is among some maize eaters).
The grain's ash content ranges from about I to 2 percent. As in
most cereals, potassium and phosphorus are the major minerals. The calcium and
zinc levels tend to be low. Sorghum has been reported to be a good source of
more than 20 micronutrients.
Recently, the status of sorghum's future as a global food was
thrown into disarray by nutritional experiments conducted on malnourished
children in Peru. The conclusion was reached that sorghum was "unfit for human
consumption."
Part of the problem was due to the fact that the samples used in
Peru came from milled flour (comprising only the grain's endosperm) and they
were merely boiled into porridge and fed directly. In Africa, by contrast, the
whole grain is ground up (so that the protein- and vitamin- rich germ is also
included) and often some form of fermentation is also employed.
At the heart of the issue of sorghum's nutritive effectiveness
is the above-mentioned fact that almost 60 percent of the protein is in the
highly cross-linked form called prolamine. Human digestive enzymes are unable to
break up this indigestible protein. Even bodies desperately in need of more
muscle, enzymes, blood, and brain continue passing prolamine that might
otherwise provide the necessary amino acids.
However, sorghum has a second problem as far as food quality is
concerned. Tannins, which occur in the seed coats of dark-colored sorghum
grains' block the human body's ability to absorb and use proteins and other
nutritional ingredients. Unless the grain is a low tannin (yellow or white) type
or unless brown seed coats are carefully removed, some tannins remain' and this
reduces sorghum's nutritional effectiveness.
Yet a third problem is that when sorghum grain is germinated, a
cyanogenic glucoside is formed. In the shoots, enzymes act on this to produce
cyanide. This is a potential hazard only with germinated sorghum, and not with
the grain itself.
Synonyms Sorghum vulgare Pers., S. drummondii, S. guineense, S.
roxburghii, S. nervosum, S. dochna, S. caffrorum, S. nigricans, S. caudatum, S.
durra, S. cernuum, S. subglabrescens.
Sorghum comes in many types. All, however, are canelike grasses
between 50 cm and 6 m tall. Most are annuals; a few are perennials. Their stems
are usually erect and may be dry or juicy. The juice may be either insipid or
sweet-. Most have a single stem, but some varieties tiller profusely, sometimes
putting up more than a dozen stems. These extra stems may be produced early or
late in the season. Plants that tiller after the harvest has occurred can be cut
back, allowed to resprout, and grown without replanting (like sugarcane).
Soil permitting, the plant produces a deep tap root (see
picture, opposite). However, a large number of multibranched lateral roots
occupy the upper soil levels, particularly the top meter. They can spread
laterally up to 1.5 m.
The leaves look much like those of maize. A single plant may
have as few as 7 or as many as 24 leaves, according to cultivar. At first they
are erect, but later curve downward. During drought they roll their edges
together. Rows of "motor cells" in the leaves cause the rolling action and
provide this unusual method of reducing desiccation.
The flower head is usually a compact panicle. Each carries two
types of flowers: one type has no stalk (sessile) and has both male and female
parts (perfect); the other is stalked (pedicellate) and is usually male
(staminate).
Pollination is by wind, but self-pollination is the rule. The
degree of cross-pollination depends on both the amount of wind and the panicle
type, open heads being more liable to cross- pollination than compact ones.
Grains are smaller than those of maize but have a similar
starchy endosperm. Most are partially covered by husks (glumes). The seed coat
varies in color from pale yellow through purple-brown. Darkcolored types
generally taste bitter because of the tannins in the seed coat. The endosperm is
usually white and floury as in normal maize, but in some types the outer portion
is hard and corneous, as in popcorn.
The crop is always grown from seed. Some seeds show dormancy and
will not germinate for a month or so after harvesting. It is a littleknown fact
that the plant can also be propagated by stem cuttings: nodes along the stem
have tissues (primordia) that can produce both roots and sprouts and thereby
grow a new plant.
This African crop is now known almost worldwide. Dhows, which
have been crossing the Indian Ocean for some 3,000 years, probably first carried
it away from Africa and took it to India more than 2,000 years ago. It was
almost certainly put on board as seamen's provisions. The sorghums of India are
related to those of the African coast between Somalia and Mozambique.
Sorghum probably traveled overland from India and reached China
along the silk route about 2,000 years ago. It might also have gone by sea
directly from Africa: Chinese seamen reached Africa's east coast more than about
1,000 years ago (probably in the eighth century
AD)1 and they may well have carried some seeds home.
Cross-pollination with a wild Chinese sorghum seems the most likely reason why
the sorghum now found in China (the kaoliang group) has its own distinctive
character.
Broomcorn was first grown in Italy in the 1600s and later spread
elsewhere in southern
Europe. This form of sorghum has produced most of the Western
world's brooms and brushes ever since. Today, Mexico is a major producer.
For perhaps 20 centuries, sorghum has been a staple of South
Asia. Today, for example, it occupies at least 20 million hectares in India,
more area than any other food crop except rice. In monetary terms "jowar," as it
is locally called, is perhaps India's third most valuable food plant, exceeded
only by rice and wheat.
Outsiders have often dubbed this African grain "the great millet
of India." And no wonder.
Jowar is an important food over much of the country, and
especially in the dry areas of the central and southern states. Millions of
Indians eat it. Some use it like rice, but most jowar is milled into flour. More
or less white in color, this flour is used especially for making traditional
unleavened breads (chapatis). Usually the whole-grain flour is employed, but
some jowar is also polished to remove the germ and create a flour with a long
shelf life. This can be blended with wheat flour (up to 25 percent) for
preparing even Western-style raised breads.
Jowar grain is also malted (germinated), and in this form it
finds its way into various processed products, including beer and baby foods.
The grains of certain varieties pop like popcorn when heated. Indians eat the
light and tasty product directly or as a flavoring in baked goods.
And sorghum feeds more than just India's people: its stalks are
a major source of fodder.
According to some reports, nothing can match its combination of
high yield and nutritional quality. Varieties with juicy, sweet stalks have been
developed. Cattle find those particularly delicious.
Perhaps 80 percent of India's cultivated sorghums are those
(known as "durras") that are the dominant type in Ethiopia, North Africa, and
along the Sahara's southern fringes. Many improved strains have been developed.
They are grown mainly in the plains and rely on the summer rains, although some
are grown under irrigation.
Jowar is notably important on the black-cotton soils, which are
notoriously difficult to farm. It is one of the few crops that withstands the
wildly fluctuating water tables that produce bottomless mud in the wet season
and something resembling cracked concrete in the dry.
An ability to extract moisture from deep in the heavy vertisol
clay is among the crop's greatest qualities for India.
This crop comes in such an array of widely different types that
various botanists have previously recognized 31 species, 157 varieties, and 571
cultivated forms. However, these all cross readily and without barriers of
sterility or differences in genetic balance, so it seems preferable to group
them into a single species, Sorghum bicolor. Some botanical authorities also
include certain wild sorghums, designating them as varieties within the species.
The ease with which cultivated sorghums cross with wild species
(such as S. arundinaceum) may be a headache for the taxonomist, but it provides
great scope for the plant breeder. Indeed, to synthesize new cultivars, a vast
range of genetic characters can be brought together in bewildering numbers of
combinations. As a result, many cultivars are recognized in Africa, India, the
United States, and elsewhere, and new ones are being continually produced (see
later chapters).
Sorghum is adapted to a wider range of ecological conditions
than perhaps any other food crop. It is essentially a plant of hot, dry regions
but takes cool weather in stride and may also be grown where rainfall is high
and even where temporary waterlogging can occur.
Daylength Although many cultivars are insensitive to
photoperiod, sorghum is basically a short-day species. Most traditional
varieties differentiate from vegetative to reproductive growth when daylengths
shorten to 12 hours. This switch to flowering often happens just when the rains
diminish, and the crop matures in the dry season that follows, a feature that
greatly helps the farmer. Some of these traditional forms are extremely
susceptible to photoperiod and reach impossible heights if not planted as
daylengths shorten. On the other hand, the dwarf sorghums of the temperate zone
are unaffected by daylength and can be planted year-round where climates permit.
Rainfall Although part of the crop is grown in rainy regions,
sorghum is remarkably drought- resistant and is vitally important where the
climate is just too dry for maize.
Low Temperature The plant is killed by frost. Optimum growth
occurs at about 30°C.
High Temperature It is essentially a plant of the tropics or
subtropics, roughly between 40° of the equator. However, in the United
States it is being pushed ever farther into the cooler latitudes.
Soil Type Sorghum tolerates an amazing array of soils. It can
grow well on heavy clays, especially the deep-cracking and black cotton soils of
the tropics. It is equally productive on light and sandy soils. It can withstand
a range of soil acidities (from pH 5.0-8.5) and tolerates salinity better than
maize.
