The carbohydrate crop of the American humid tropics is cassava.

II. Learning Objectives
 
 

	To understand the importance of cassava worldwide.
	To be able to describe how cassava is used.
	To know the climatic and edaphic requirements for cassava.

 
III. Overview

Cassava is an American crop, grown in Latin America as early as 800 B. C.  Cassava is a crop of the tropics and subtropics and is grown in both Africa and Asia (3/4 of production) as well as Latin America (1/4 of production).  Cassava has the highest caloric value of the tropical roots and tubers.

Cassava grows best in short day (10-12 hour daylight) and between 15 degrees N and 15 degrees S latitude.  Cassava grows in zones that receive 20-200 inches of water per year, preferring light, sandy loams of medium fertility.  A real strength of cassava is its tolerance of low pH and high aluminum in soils.

Cassava is part of the traditional slash and burn agricultural system.  The crop is grown for ten months to three years.  The longer it is grown, the greater the yield.  Tubers are often left unharvested (stored) underground as they deteriorate quickly when dug.

IV. Taxonomy

1. Family - Euphorbiaceae.

2. Genus and species - Manihot esculenta

3. Other common names - manioc, yuca, mandioca, tapioca plant

Origin and History

1. Origin: believed to be Brazil

2. History:

• Cassava spread throughout Latin America as early as 800 BC crop remains of cassava were found at the Columbia/Venezuela border
• In the post-Columbian era, Europeans transported cassava to other part of the world. In the 15th Century it was taken to Africa. In the 17th Century it was introduced to Asia by galleon trade from Mexico to the Philippines. Later the Portugese introduced it to Indonesia and the British introduced it to Malaysia and India. By the end of the 19th Century, it was widely grown throughout Asia.

1. Grown in the tropics and semitropics; 30 degrees N to 30 degrees S latitude; up to 2000 m elevation.

2. 3/4 of production shared equally between Asia and Africa; 1/4 from Latin America - (80% from Brazil).

3. Sub-Saharan Africa plants more than half the world's cassava area but produces less than half of the cassava because of low yields.

Economic Importance

1. Food source.

• Tubers
• 4th most important source of calories for humans in the tropics
• Has the highest caloric value of the tropical roots and tubers
• High in carbohydrate, calcium, and Vitamin C
• Low in protein
• Animal Feed.
• In China cassava is referred to as "the underground barn"
• Processed into chips and pellets for feed
• About 20% of cassava is processed into feed
• Cassava is a successful animal feed when combined up to 30% with other types of rations
• Starch.
• Cassava is a common raw material in starch production
• Thailand is the largest exporter of tapioca starch
• Alcohol production.
• Cassava is utilized as a famine reserve crop if all other crops fail

1. Perennial bushy shrub - 1-4 m high.

2. Large palmate leaves.

3. 5 to 10 tubers per plant.

4. Propagated by stem cuttings.

Environment

1. Light:

• Photo period controls tuber formation
• Short days - rapid flowering
• More than 10-12 hour daylight - tubering is delayed and yield is lower
• For this reason, cassava is most productive between 15 degrees N and 15 degrees S

• Best production in mean temperature range of 25 - 29 degrees C
• Below 10 degrees C (50 degrees F) growth stops
• Frost can kill

• Can be grown in rainfall regions of 500-5000 mm (20-200 inches) per year
• Best with 1000-5000 mm per year rainfall that is well distributed
• Cassava is well adapted to drought though
• It is a valuable crop where rainfall is uncertain. If moisture availability become low, the plant will cease growth and shed some older leaves reducing transpiration surface. When moisture is available again, the plant resumes growth and produces new leaves.

• Best: light sandy loam with medium fertility
• Soils bad for cassava: poorly drained (tuber rot); gravelly or stony (hinders root penetration); saline
• Tolerates low pH, high aluminum soils of the tropics
• Can have reasonably good yields on soils of low fertility
• Grows well in both acid and alkaline soils

Problems with Cassava

1. Toxicity

• Contains cyanogenic glucosides which hydrolyze to produce prussic acid, which is highly poisonous to humans and animals
• Level of glucosides varies with cultivar
• Bitter varieties: high levels distributed throughout tuber
• Sweet varieties: low levels confined mostly to the peel
• Level of glucosides varies with environmental conditions under which the plant is grown - high glucosides are present with high nitrogen, low potassium, and in wet regions
• Level of glucosides varies with the age of the tuber - the older, the higher the level
• Detoxified by various methods of preparation, but even carefully detoxified cassava products contain some prussic acid
• Chronic vs acute poisoning

• Protein present in small amounts and is also of low quality
• Cassava toxicity is more of a problem in people with low protein diets - cassava should not b a staple food

4. Mechanization Difficult Because of plant form, mechanization of planting and harvesting is difficult.

Cultivation

1. Land preparation.

• Traditional - slash and burn agriculture
• Most commonly planted on unplowed land soon after burning of bush
• Usually forest trees are felled and burned before land is planted to cassava: several forest trees act as hosts for white thread fungus which attacks cassava
• Planted on mounds - easier to harvest this way and reduces water logging (tuber rot).

• Soil is plowed and harrowed
• Planted flat, on ridges, or in furrows
• Spacing.
• Varies with cultivar and growing conditions
• Most common: rows 80-100 cm apart and plants 80-100 cm apart also within the row
• Fertilization.
• High requirement for K
• After burning, soil is naturally high in K, so plant soon afterwards
• Intercropping.
• Commonly intercropped with yam, maize, melon, okra
• Plant cassava when the intercrop is almost ready for harvest, so the first part of the field life of cassava is as an intercrop and the second part is as a pure stand
• Rotations.
• Occupies the field one and a half seasons - keep this in mind
• Cassava is usually the last crop in rotation before the land is returned to bush fallow in traditional agriculture because it will yield in depleted fertility and is suited to the dry spell that follows the growing season
• Don't plant cassava after a legume - high nitrogen levels produce high levels of glucosides

1. As tubers age, starch content ceases to increase and may decrease; tuber also becomes more lignified and fibrous.

2. Crop is grown 10 months to 3 years; the longer, the greater the yield.

3. Tubers often left unharvested ("stored underground") because of rapid deterioration.

4. Traditional farmers harvest with a machete, chopping the stem and loosening the ground with it.

5. Average yield on a worldwide basis is 10 ton/ha.

V. Summary
 
Cassava is the 4th most important source of calories for humans in the tropics.  Cassava is high in carbohydrates, calcium and Vitamin C, but low in protein.  Cassava can be processed into chips and pellets for animal feed and about 20% of cassava is used this way.

Cassava is propagated by stem cuttings and produces 5-10 tubers per plant.  It is a bushy shrub 1-4 m high.  Best production occurs with mean temperatures of 25-29 degrees C.  Fifty degrees (10 degrees C) stop growth and frost can kill cassava.

 Cassava contains cacogenic glucosides which hydrolyze to produce prussic acid which is  highly poisonous to humans and animals.   The level of glucosides varies with age of the tuber, the older the higher.  Cassava is detoxified by various methods, but even carefully detoxified cassava products contain some prussic acid.

VI. Self Assessment
 
 

	What is the origin of cassava?  How did cassava spread around the world?
	What are the most important nutritional components of cassava?  What about problems associated with cassava consumption?
	Where is cassava grown?  Why?
	How is cassava planted?  What is the growing season of cassava?  Where does cassava fit into a cropping system?
	How is cassava uniquely adapted to the region where it is grown?