Rev Cs 356 Arable Crop Production 2024 2017 -2018 PDF

CS 356 ARABLE CROP PRODUCTION BROAD OBJECTIVE: To enable students, understand the principles and husbandry / agronomic practices in arable crop production. Learning Objectives After this course, students should be able to: ⚫ Choose crop varieties for the localities based on soil and climate. ⚫ Decide on site selection, land preparation methods and planting. ⚫ Adopt appropriate cultural / husbandry practices. ⚫ Identify and control pest and diseases. ⚫ Harvest, process, store and market arable crops. COURSE CONTENT: ⚫ Origin, botany, distribution and economic importance of selected crops ⚫ Principles and production management of selected crops 1. Cereals : maize, rice, sorghum, millet 2. Legume: cowpea, soybean, groundnut, bambara groundnut 3. Root and tubers: cassava, yam, cocoyam, sweet potatoes 4. Plantain and banana ⚫ Soil and climate requirements: soil pH, soil type/structure, organic matter etc, rainfall, temperature, humidity, wind ⚫ Husbandry / cultural practices: land preparation, planting, spacing, weed control, A A AMOAH 1 pests and disease control, irrigation, fertilization, maturity, harvesting, uses ⚫ Storage and processing REFERENCES ⚫ Principles of Arable Crop Production – F. Harper ⚫ Tropical Crops – Monocotyledon / Dicotyledons – J.W. Purseglove ⚫ Principles of Vegetable Crop Production – R. Fordham and A. G. Biggs ⚫ Vegetable in the Tropics – H.D. Tindall ⚫ Crop Production Principles and Practices – S.R. Chapman and L.P. Carter ⚫ Introduction to Crop Husbandry – J.A.R. Lockhart and A. J. L.Wiseman BACKGROUND TO CEREAL CULTIVATION Cereals belong to the Gramineae, a large monocotyledonous family of some 600 genera and around 10,000 species. The chief temperate cereals are wheat, barley, oats and rye, whilst those of the subtropical and tropical areas are chiefly rice, maize, sorghum and millet. Cereals are demanded consistently throughout the world, being a concentrated carbohydrate source with useful protein, fat, minerals, vitamins and fibre content. They have proved fairly stabled-priced commodities to trade. They are easily storable. They are transferable both in terms of ease of transportation and in terms of convertibility to various end products for different markets. A A AMOAH 2 Importance of cereal crops The importance of cereals in world Agriculture is great. Whilst quantitative terms such as area, yield and production indicate the extent of cereal importance, reasons for this must be sought in terms of uses, distribution and production characteristics. 1. USES Cereals are multipurpose, providing human diet, livestock feeds and a wide range of farm and industrial raw materials. Cereals consumed directly accounts for about 55% of human diet. Indirectly they contribute more owing to their inclusion in livestock diets producing meat, egg, milk and dairy products. Cereals may be fed as whole grains, ground, crushed, rolled, with ammonia or caustic soda treated. A range of industrial uses are made from cereals. Apart from the physical properties which make grains a source of adhesive they are also sources of specific chemicals, notably starch and dextrin. 2. DISTRIBUTION Cereals are adaptable, the different species and varieties tolerating a wide range of soil, climate and agronomic conditions. They are integral part of most arable systems of cropping. 3. PRODUCTION ⚫ They are relatively easy to produce in that a total failure of crop or market is very unlikely by contrast with many crops. The labour requirement is fairly low per ton A A AMOAH 3 produced. ⚫ Cereals have proved fairly straight forward to mechanize. ⚫ Relatively low capital investment per hectare is needed for a cereal production enterprise. ⚫ A cereal gives a relatively good ratio of energy output to energy input-per ha to produce it. It also gives a good yield in relation to seed planted (for instance, 40:1 for wheat in contrast with peas at around 15:1) CLIMATE AND CEREALS 1. Climate affects cereal cultivation in several ways both long and short term (weather variation) 2. Climate restricts species and indeed, cultivars of cereals which can be chosen. 3. Directly influences their establishment. 4. Determines their development and subsequent performance in both yield and quality aspects. 5. Affect the incidence and severity of problems- weeds, pest and diseases. The micro- climate within areas of a crop can provide a focal zone for disease development. 6. May directly damage crops e.g. drought, lodging by wind and rain. 7. Alters the responsiveness of crops to applied treatments both to promote and inhibit growth (such as fertilizers and PGR’s) A A AMOAH 4 STRATEGIES TO COMBAT WEATHER PROBLEMS 1. Choice of appropriate variety 2. Timely crop establishment and timely application of all treatments. 3. Adequate drainage and subsoil management to maximize the rooting potential. 4. Irrigation especially on sandy soils. FACTORS AFFECTING CEREAL YIELD AND QUALITY There are four main factors. These are; 1. Soil 2. Plant 3. Husbandry 4. Weather – climate, rainfall, temperature etc A A AMOAH 5 Planting Methods a. Broadcasting b. Dibbling c. Drilling d. Transplanting *Conduction of germination test for all seeds prior to planting For the test about 100 seeds are planted in a shallow trench and watered. The numbers that germinate are recorded. By standard procedure, if germination percentage is Above 85% - plant 2 seeds per hill 70 – 84 % - plant 3 seeds per hill 50 – 69 % - plant 3 to 4 seeds per hill Less than 50% - get new seed stock A A AMOAH 6 RICE – (Oryza sativa) Matured Rice Crop Rice has been cultivated in many parts of the world especially in South and South-East Asia as a staple crop. Important producing areas are China, India, Spain, Brazil, Italy and Southern U.S. It is now becoming important in West Africa especially Nigeria, Cameroon, Ghana as well as Sierra Leone. Rice plant is believed to have originated and evolved from South-East Asia where it spread to China, India, Africa and America. Thousands of cultivars are now available and more and more are being evolved by selection and breeding for better adaption to the many environments in which the crop can be grown. Nearly all varieties fall into 2 main classifications 1. Japonica (pearl types) – which are short grain 2. Indica-which are long or medium grain. There is the third group called Javanica- made of types which are restricted to areas of equatorial climate. There are three groups of rice cultivars distinguishable by their physiological requirements and growth habits thus: 1. Swamp varieties – which are grown in standing water during much of their life cycle although the water must be slow in its movement. 2. Upland varieties – which are grown under rain fed conditions and are adapted to very A A AMOAH 7 high altitudes. 3. Dual purpose varieties – which are usually grown under irrigation because they require lots of moisture. Description (rice) 1. Colour 2. Size or shape of grain. For size (length) i. Extra long – over 7mm ii. Long – 6 – 7 mm iii. Medium – 5-5.9mm iv. Short – less than 5mm For shape (length / breadth) i. Slender = over 3mm ii. Medium = 2.4 -3mm iii. Bold = 2-2.4 iv. Round = under 2mm Rice cultivars 1. NERICA 1 2. NERICA 4 3. SIKAMO 4. TOX3377-34-3-3-2 A A AMOAH 8 5. IRI 2979-26 (SARI) 6. IDSA 85 7. Agra Rice (CRI) 8. Amankwatia (CRI) 9. Jasmine 85 BOTANY The main botanical points of interest are as follows: 1. The plant belongs to the grass family – Gramineae, the genus is Oryza which contains a number of species, the most important being the Oryza sativa which is commercially cultivated species and the species Oryza glaberrima (red rice). 2. The plant is an annual, with erect culms. It varies in height from about 60cm-2m but generally being 1m to about 1.2m 3. They have a length of maturity varying from 90-240 days. The plant tillers freely from about 4-8 culms being common (new cultivars can tiller more). 4. The inflorescence is a loose terminal panicle each bearing a number of spikelets. Each spikelet consists of a shoot axis called the rachilla which bears a number of two ranked overlapping rachis. 5. The two lowermost bracts which have no flower in their axil are called the empty glumes. The florets are subtended above the empty glumes by two or more bracts. The lower is called the lemma and the upper is called the palea. At maturity the grain is enclosed by the lemma. Together, the lemma and palea form the hull / husk. Their colour may be straw yellow, red or black and have certain characteristic markings which serve as identification factors. A A AMOAH 9 The lemma sometimes bears a long process called an awn. This may be fully awned or partially awned or awnless. The presence of an awn and its length is an additional distinguishing characteristic. The rice grain is a fruit or caryopsis in which the pericarp and the testa are fused. The seed is endospermous-meaning the embryo is embedded in the stored food materials. The rice culm has hollow internodes and solid nodes with vascular bundles arranged in circles embedded in the stem. The epidermis typically contains long cells and two kinds of short cells. These short cells are silica and cork cells and are often seen occurring together. The silica cells are almost filled with silicon and shows varied shapes. The cork cells have suberised walls and often contain solid organic materials. The cortex has large air cavities. The presence of the silica and the cork cells in the epidermis and the air cavities in the cortex makes the rice plant to survive in flowing water. The rice caryopsis contains an aleurone layer which contains protein, vitamins and minerals. Polishing the rice grain after milling therefore removes this layer. Polished rice is therefore less nutritious than unpolished rice. The solution to this problem is the practice of par-boiling or partially boiling which results in the movement of the proteins, minerals and vitamins into the starchy endosperm so that after milling and polishing, a proportion of these nutrients can still be found in the starchy endosperm and the nutritive value of the grains is therefore maintained. A A AMOAH 10 GROWTH REQUIREMENTS CLIMATE The rice which is found between latitude 45ºN and 40ºS and from sea level to as high as 3000m is a versatile crop which does well under a wide range of climatic conditions provided that there is an adequate water through rainfall or irrigation. Thus upland rice grows very well under conditions of high rainfall which is evenly distributed throughout the growth period whilst swamp rice thrive on flat lowlands, river basins where flooding occurs during the growth period. Temperatures must range from 20-38ºC preferably between 30-35ºC during the day with a minimum of 20ºC at night. The temperature should be high enough to ensure good seedling development and vegetative growth. There must be abundant sunshine i.e. high solar radiation income especially during the period of reproduction or grain filling. Grain yields have been found to be positively correlated with solar radiation income. The crop is a short day plant, hence there is the need to select and grow cultivars which are insensitive to the changing photoperiod in order to prevent heading / flowering at the time when crops have not yet fully developed its photosynthetic system or vegetative growth. A A AMOAH 11 SOIL: Rice grows on most soil types ranging from sandy to loam to heavy clays and from shallow to deep soils provided that adequate moisture levels are maintained in the soil by rain or irrigation. The optimum pH range for rice is from 5.5-7.0 (acidic to neutral) even though the crop can be successfully grown on soils with values rising as high as 6- 9 or falling as low as 5-4. The crop shows a degree of tolerance to salinity. CULTURAL PRACTICES Choice of site- this depends on type of rice grown and the management practices envisaged. Upland or swamp rice requires different sites and whether the crop will be irrigated or not. 1. Land preparation- it must be very thorough with a maximum of two ploughing, preferably to a depth of 30cm. In situations where the land is being cleared for the first time, plant remains or organic matter may be incorporated into the soil. 2. Planting can be direct in the field by broadcasting or dibbling or drilling. The first two are manual and the last mechanical. Transplanting of seedlings can also be practiced. In this case, seedlings must be raised in nursery beds. With transplants, more clean seeds (35-45kg/ha) must be used and transplanting done at 21 days after seeding at a spacing of 20x20cm at 2 plants per hill. Do no transplant seedlings which are more than 35days due to early panicle exertion which severely reduces yield. Seed rate depends upon the method of planting, the spacing required and the tillering habit of cultivars. The rate varies from 84-112kg/ha for broadcasting, 56-67kg/ha for nurseries which A A AMOAH 12 also gives opportunity for selection at 28-35kg/ha for dibbling and drilling. Of course these figures are only guidelines and may be varied according to one’s circumstances. It is also presupposed that there is high percentage germination. The seeds are tested for fullness and adequate weight by soaking in brine/salt solution of specific gravity of 1.1-1.13. The light seeds or empty glumes float and are removed and discarded. The good ones are dried, treated against pests and diseases and can then be sown by broadcasting, dibbling, drilling in the nursery. 3. Weed control- many of the common arable weeds are controlled by flooding and standing water. Weeds are worst in broadcasting than when the plants are transplanted as the latter gives the better condition for control. Better weed control is achieved when the rice is drilled or transplanted in lines. Failure to control weeds can result in losses of 30% or more. Serious weeds are wild red rice and other grass weeds e.g Cyperus. Weed may be controlled by hand weeding or mechanically or chemically controlled. Hand hoeing or hand operated rotary hoes have been used in many parts of the world. Herbicides 2, 4-D, Lasso attrazine, roundup or gramoxone may be used as preplanting, pre-emergence or post-emergence treatment. 4. Diseases – Blast (Pyricularia oryzae) is most serious. It can attack the plant at all stages causing seedling blight, leaf blight in the active growing phase and neck rot when the heads are developing. The best control is to plant resistant cultivars or the use of copper fungicides. Mercurial dressing will also help. Other diseases are brown spot, leaf spot (caused by Cercospora oryzae) and stem rot (caused by Sclerotium rolfsii) A A AMOAH 13 5. Pest – Insects cause extensive damage to the rice crop in the field and to the grain during storage. The worst pests are stem borers, plant bugs, armyworms and grasshoppers. Others include rats or rodents and birds. 6. Fertilization – Apply 1.5 bags/ha of muriate of potash and 2.5bags/ha of triple supper phosphate as basal dressing. Apply urea in split doses, 2 bags/ha at transplanting and another 2 bags/ha top dress at panicle initiation stage or add 2.5 t/ha decomposed poultry manure or 5t/ha cow dung. 7. Harvesting – Early harvesting cultivars are usually harvested one month after full flowering and late ones at 6 weeks. Thus between 4-6 weeks after full flowering, harvesting should be done. The moisture content of the grain at harvest is usually between 18-25%. Harvesting is done by hand using knife or sickle or mechanized by combined harvesters. Threshing This is done to separate the grains with its enclosing husk from the stalk. It may be done manually by beating the sheath against a hard surface. Winnowing It is usually done by shaking and tossing the paddy backwards and forward with a basket tray with a narrow rim. After winnowing, the paddy is dried in the sun and is now ready for milling or transport to the mill. Using combine harvester, the paddy is harvested, A A AMOAH 14 threshed and bagged in one operation after which it is dried to safe moisture content of 11-14%. Storage / milling The paddy is stored in the husk as it is less susceptible to deterioration. It is essential that the paddy should be well dried before storage as this prevents heating and sweating, and reduces attack by storage pest and fungi. The optimum moisture content should be between 12.5-14% which also gives minimum loss and breakage at milling. The paddy may be parboiled before milling. Parboiling of paddy before milling gives less breakage of grains, more retention of nutrients (protein, vitamins and minerals) and better storage qualities. 100kg of paddy gives approximately 66kg of polished rice of which 50kg is whole grain and 16kg is broken grains. Yields vary and are between 4-5t/ha of milled rice in advanced countries and well managed fields. The average is between 2-2.5t/ha. For paddy, it is between 7-9t/ha. Yield analysis Factors which determine yield of rice are 1. Number of tillers per unit area. 2. Number of tillers head or panicle 3. Number of grains (spikelet) per head or panicle 4. Mean weight of individual grains or (1000 grain weight) A A AMOAH 15 These components are affected by other factors which can also be resolved into two a. Plant or varietal characteristics b. Environmental factors. Plant or varietal characteristics 1. The vigor with respect to seedling emergence and growth 2. The tillering capacity 3. Sensitivity to photoperiodism 4. Resistance to lodging 5. Resistance to pest and diseases 6. Resistance to grain shattering Environmental factors 1. Climatic factors ⚫ Light intensity and duration. ⚫ Rainfall and its distribution. ⚫ The prevailing temperature. ⚫ Wind – particularly the speed. 2. Soil ⚫ Texture and structure in relation to moisture retention, soil with plenty of organic matter. ⚫ Soil pH is also important. At low pH values, Al and Mn toxicity occurs. Phosphate is fixed at low pH. A A AMOAH 16 3. Cultural practices ⚫ Good tillage – to give good tilth for germination and establishment. ⚫ Use of pure and viable seeds. ⚫ Proper time of planting is required. ⚫ Good water management and or irrigation. ⚫ Maintenance of soil fertility by the application of crop remains or inorganic materials. ⚫ Weed control. ⚫ Disease and pest control. ⚫ Timely harvesting to reduce grain shattering i.e. harvesting at appropriate time. Varietal screening (field assessment) 1. Phenological studies- particularly days from emergence to: Days to heading and days to maturity 2. Plant height and lodging characteristics. 3. Those varieties that produce a lot of tillers. 4. Head tiller ratio. 5. Grain characteristics and cooking qualities. 6. Response to fertilization (this depends on the inherent characteristics of the soil) 7. Scoring of diseases infestation and pest attack 8. Average yield relative to the maximum possible yield or average yield in relation to other existing varieties. A A AMOAH 17 NB: All these assessments can also be used for maize. MAIZE (Zea mays) As a cereal, maize is a member of the family Gramineae. Evidence of its origin points to Central America. The plant varies in height from about 60cm – 4m. It is solid throughout with short internodes at the base which becomes longer and thicker and then starts tapering up to the terminal male inflorescence. The female inflorescence called the cob or ear consist of modified lateral branches arising from axillary lateral branch on the main stem and has compressed internodes whose leaf sheath overlap to cover the inflorescence as the husk. Each spikelet in the female inflorescence consist of two flowers a non functional lower flower and an upper flower containing knobbed-shaped ovary surrounded by short membranous lemma and palea. The ovary is surrounded by a long style known as the silk which emerges from the husk and is receptive along most of the length. The spikelet at the base matures first. The maize caryopsis is covered by a thin wall of layers of cells representing the fused pericarp and testa. Next to this layer is the nucellus and next to this is the endosperm. The outermost layer of which is the aleurone layer is high in protein and vitamins but the bulk of the endosperm is made up of the starch grain. There are two types of endosperm in the caryopsis. There is a hard flinty proteinaceous layer and a soft whitish starchy type. One type being predominant depending on the variety. The colour varies from white through yellow to purple. The embryo is rich in oil, protein and minerals and is more or less enclosed by scutellum and consists of the plumule which is protected by its sheath (coleoptiles) and gives rise to the shoot and the radicle A A AMOAH 18 which is protected by its sheath (coleorhizae) and gives rise to the root. The crown of the grain may be rounded or dented. The genus Zea contains one known species i.e. the Zea mays but so many varieties have been bred which fall into certain agricultural classifications depending on the structure and peculiarity. Classification 1. Indentata (dent maize) – It is the most widely grown type in the US and South America. The grains have dented crowns due to the rapid drying and shrinking of the soft starch it contains. The varieties under this species are usually late maturing but high yielding. The grains may be yellow or white although other colours may appear. 2. Indurata (flint maize) – This group has varieties predominantly grown in southern Europe, Asia, South and Central America. The grains are relatively small, hard, smooth and contain relatively little soft starch. They are generally early maturing, therefore vigorous and have high protein content but relatively low yielding. Because of the hardness of the grain they tend to be insect resistant during storage. 3. Amylacea (soft / flower maize) – They tend to be grown relatively on dry areas. The grains resemble the flint maize but are made up of virtually soft starch. This is the oldest type of maize known. It is easier to chew or grind and so it is principally used for food preparation. 4. Everata (pop corn) – The grains are principally grown in north and south America. They are small primitive. It is made up hard flinty endosperm with very little starch in the centre. On heating, the steam generated inside the grain causes it to explode / pop up and the endosperm becomes everted about the embryo to produce a white A A AMOAH 19 flinty mass. 5. Tunicata (pod corn) – This is the most primitive form of maize known. It is not commercially important but is genetically interesting. The grains are unusual in that each one is enclosed in its own husk. 6. Saccharata (sweet corn) – It is primarily grown in the US and Mexico. The grains contain a glossy sweetish endosperm because of the presence of a recessive gene which prevents the conversion of translocated sugar into starch. It has a commercial value in that it is usually canned and sold in supermarkets. Characteristics of Commercial Maize Varieties Variety Grain Plant Height 50% silk Days to Average color texture (cm) maturity ton/ha Dobidi White Dent 205 60 120 5.5 Okomasa ** White Dent 198 59 120 5.5 Golden crystal Yellow Dent/flint 200 55 110 4.6 Obaatanpa** White Dent 175 55 105 4.6 Abeleehi** White Dent 157 53 105 4.6 Aburotia White Dent 150 51 105 4.6 Dorke SR** White Dent 165 46 95 3.8 Safia-2 White Dent 165 47 95 3.8 Kawanzie Yellow Flint 160 46 95 3.8 *Agronomic data are averages from station varietal trials **Streak resistant Source: CRI A A AMOAH 20 Growth Requirements Climate Although maize can be found from latitude 55ºN to 40/45ºS, it is essentially tropical crop with some short term varieties bred for the cooler areas. Minimum temperature ranges between 10-25ºC but should be preferably between 20-25ºC with maximum temperature between 30-38ºC and that of optimum temperature between 30-35ºC. Maize can thrive under rainfall of 500mm provided that most of it comes within the growing season but performs best in areas with 750-1500mm of rain. Moisture stress during early growth delays flowering. The other moisture sensitive stages are the period from just before tasseling to silking and then the period of grain filling particularly during early grain growth. If soil moisture levels are not adequate, yields would significantly decrease. Maize requires very high levels of solar radiation income throughout its growth and therefore shading must be minimized if not completely prevented. Soil Maize will grow on most soils but will grow best on well drained deep loamy or silty loam with plenty of organic matter and well supplied available nutrients. The optimum pH ranges from 6.0-7.0 i.e. slightly acidic to neutral. Cultural Practices Land Preparation: This includes ploughing, harrowing and ridging. The crop responds to organic matter and crop residues so that in course of land preparation these must be included. Newly planted maize requires weed-free soil that is warm, moist, well supplied with air and fine enough A A AMOAH 21 to give good contact between the seed and the soil. Too much cultivation often destroys the crumb structure of the soil that surface crust may be formed which increases runoff and prevents water entering the soil. The amount of cultivation would depend upon the environment more particularly on the type of soil and the amount of available water or moisture. Planting Planting may be done by hand or mechanical planters. Various machines have been designed for this. The depth of planting depends on climate, soil moisture and texture and pest hazards. Deep planting may be necessary with dry and light soils while shallow planting may be necessary under conditions of moist heavy soils. Therefore, planting ranges from 2.5 through to 5-10cm. Sometimes depth of planting is related to the method and depth of fertilizer placement. Seed rate depends on the method of planting, variety, knowledge of soil moisture condition during the entire growth of the crop, the nutrient status of the soil as well as the purpose of planting. Example, for silage maize closer spacing is necessary and desirable and generally 30-40% more seeds is used than required in a given production. The usual spacing is between 40cm x (80-90cm) or (40x80cm / 40x90cm) with 2 seeds/hill and this may give 62500 plants/ha. How to Plant A germination test conducted 10 days before sowing may prevent problems arising from poor stand. Plant in line using a rope or sighting pole to mark the rows. You will need at least 3 poles. The more poles you use, the straighter your rows will be. The sighting poles should be A A AMOAH 22 straight and at least 2 metres long. Place one at each end of where the first row is to be and the others in between but, in line with the two end poles. Plant by walking in a straight line from pole to pole. As each pole is passed, move it over one row-width so that it is in position for the next row. Use a cutlass or a planting stick to plant 5-7cm deep, apply the full weight of your foot to loose soil above the seed. Deep planting and firming soil above the seed are important deterrent to partridge and rodent attack. In clay soils or soils that crust easily plant 2-3cm deep. Make sure that the seed is in good contact with the soil. Weeding The purpose of weeding is to remove weeds and stir up the soil surface where crust occurs. The operation should be done at shallow depth as possible enough to kill weeds and open up the soil but not to damage roots of crops. The frequency should be determined by the growth of weeds. Chemical weed control is being increasingly used and various herbicides are recommended. Gramoxone is applied at 4l/ha or 300ml/ 15litres of water into the knapsack for spray. The use of round up is more effective on perennial weeds and application rate is 4l/ha or 300ml/15litres of water. Pre-emergence herbicides e.g Lasso atrazine may be applied after planting at a rate of 2.5kg/ha or 4l/ha for primagram Irrigation Maize can be irrigated where the rainfall is not sufficient to sustain good yields or where the distribution is erratic to suppress growth at the most sensitive stages which are from the periods just before tasseling to the middle of grain filling. Also moisture stress during the early growth suppresses leaf area development and can delay flowering. To obtain A A AMOAH 23 high yield from irrigation, there should be an adequate supply of nutrients of which nitrogen is the most important. Irrigation may be provided by furrows or sprinklers. Disease and Pests Diseases: leaf blight, leaf spot, rust and maize smut (caused by Ustilago maydis). Galls are formed on the aerial portions of the plant which then produce masses of black spores. Head smut: here the inflorescence is changed into hard black spore masses. Seed treatment with organo mercurial helps to prevent seedling infection. Maize streak (virus): yellowish colour of the leaves. Control – get rid of the plant through cutting and burning. Because of breeding and selection, the above mentioned diseases are not common. Pests: stem borers, maize/ corn earworms and the pest of stored maize i.e. the grain weevil. Damage is also caused by rats, squirrels and other rodents. Other games and various birds may cause damage to maize especially on the field. Fertilizer Application Every attempt should be made to local sources of compost, organic waste and animal manure. When well decomposed these materials should be spread over the land prior to planting. To apply 50kg/ha of nitrogen apply either 7t/ha of cow dung or 4t/ha of poultry manure or 5t/ha of good quality compost to the crops. Generally the following rates may be considered for the forest zone application of starter dose. 1 bag/ acre (NPK) then 1 bag/acre of ammonium sulphate at 6weeks A A AMOAH 24 Transition – 2 bags /acre (NPK) – starter 1 bag/ acre (ammonium sulphate) at 6 weeks Where soils are inherently low in nitrogen, incorporation of non-leguminous crop residue can tie up nitrogen in the early part of the season, especially in the first year after clearing from fallow. In this case, additional amount of nitrogen may be required. A maize crop benefits considerably when rotated with a legume crop. Crops of groundnut, bambara, mucuna and cowpea, if well grown may add 20-50kg/ha of nitrogen which can be used by crops grown on the same piece of land the following season. If these organic sources of nitrogen are not available in sufficient quantities, chemical fertilizer should be used. In addition to whatever manure or compost is applied. The recommended rate depends on the soil type and the cropping history of the field. Studies have shown that soil-surface application of starter fertilizer do not lead to significant reduction in grain yield when compared to burying the starter fertilizer at the time of planting. Compound fertilizer (20-20-0 or 15-15-15) should be applied at planting for maximum benefit. However, if that is not possible it should be applied just after germination. Fertilizer should be distributed evenly among the plants, 5-8 cm away from the hills. The banding of starter fertilizer is recommended in soils low in phosphorus. Nitrogen is required by maize in large quantities, but because it easily leaches through the soil, it should not all be applied at planting time. Nitrogen must be side dressed later in the season. The most common forms of nitrogen fertilizers available in Ghana are urea and ammonium sulphate. Ammonium sulphate should be applied to the soil surface (except on slopping fields) 4-5 week after planting. Apply the fertilizer 5-8cm away from each A A AMOAH 25 hill, distributing it evenly among the plant in the field. Harvesting: Depending on the variety, harvesting can be undertaken from 7-8weeks after flowering when the vast majority of maize cultivar becomes physiologically matured. But harvesting can also be delayed depending upon the use of which the grain is to be put. During ripening, the following stages are passed by the grain. Milk stage: At this stage, the grains are fully developed but are still full of liquid, the plant being still green although the lower leaves start to yellow up. This is the stage which is harvested for immediate consumption by boiling or roasting or for processing and / canning. Soft-ripe stage: Also known as the dough stage. This is the stage at which the liquid inside the grain begins to solidify although the grains are relatively soft, the plant still looks greenish but more leaves begin to yellow. If harvested the cob should be dried and stored if not used immediately, otherwise, there is a danger of deterioration owing to relatively high moisture content that can prevail. Full-ripe stage: At this stage, the husk virtually dries out and the grains become hard. The whole plant looks dry. The upper part may still be greenish but all translocations within the plant ceases. The cobs may be harvested and dried for storage. A A AMOAH 26 Dead-ripe stage: The plant dries out at this stage. The husk become brittle and the roots decay. This is the optimum stage for harvesting the crop. Leaving the cob in the field for any length of time after this stage exposes the crop to pest damage particularly damage from birds and weevil. NB: This stage is not recommended especially, where combine harvester is used. Storage We can store in barns/ silo or cribs. In course of storage, grains are normally treated especially with actellic under local levels. Yields Vary tremendously in terms of variety, climate, soil and husbandry practices. Yield varies between 1-4t/ha. The average ranges from 3.5-4.5t/ha and up to 5t/ha is achievable but with well managed ones, 6-7t/ha can be obtained. Maize characters – Data collection 1. Plant establishment 2. Seedling vigor 3. Days to mid silk 4. Plant height (flag leaf) 5. Ear height 6. Root lodging A A AMOAH 27 7. Stem lodging 8. Open tip 9. Field weight 10. Number of plants harvested 11. Ear number 12. Rust, Streak,, Blight 13. Cob aspect (well filled, not diseased / rotten, grain size) 14. Ear diameter 15. Number of rows per cob 16. Number of kernels per row 17. Grain length 18. Grain width 19. Ear rot 20. Moisture content of grain 21. Number of cobs per plant 22. Thousand or hundred grain weight 23. Yield Other research observations 1. Pre germination count ten days before planting 2. Germination count on the net plot only 3. Leaf area two weeks after silking on 5 – 10 plants per plot on the guard rows 4. Ear leaf nutrient analysis also on the boarder rows, at flowering or not later than 2 weeks after flowering A A AMOAH 28 5. Plant height at harvest 6. 50% silk count from date of planting to when silk produced is 1 cm long 7. Days to physiological maturity, i.e. when a black layer forms at the base of the kernel 8. Root lodging, i.e. any plant bending at the base to more than 45 degrees 9. Stem lodging, i.e. mechanical damage to the stalk above the cob 10. Number of cobs harvested 11. Row length harvested 12. Number of plants within the row length harvested 13. Number of ears harvested 14. Weight of ears per plot 15. Number of cobs harvested 16. Number of rotten cobs 17. Weight of good ears harvested 18. Cob diameter for 10 cobs 19. Cob length in cm for the 10 cobs 20. Number of grains for the 10 cobs 21. Weight of grains for the 10 identified cobs 22. Moisture content at harvest 23. Weight of empty cobs (rachis) 24. The diameter of the rachis 25. Grain yield (kg/ha) A A AMOAH 29 SORGHUM (Sorghum vulgare or S. bicolor) Family: Gramineae Other names: great millet, guinea corn (West Africa); milo, sorgo (USA); kaoling (China); durra (Sudan); mtama (East Africa); jola, jwaarie, jowar, (India). Origin and Importance The greatest varieties of sorghums are found in North-East Africa. The crop was probably domesticated in Ethiopia. The original domesticated sorghums, used for food and for beer making, spread rapidly across east and West Africa and were taken to India at an early date and to China. The crop reached the Americas in the middle of the 19th century. Sorghum remains an important food crop in dry areas and on poor soils in many African countries, in India and in China; 50million/ha are grown in the world, producing over 58mt. Very little sorghum enters world trade except that exported by the United States for industrial use. Botany There is a very wide range of types of sorghum and new varieties are continually A A AMOAH 30 produced. Generally, local cultivars show a well-developed adaptation and resistance to pest and diseases within their own environment. Introduced hybrids rarely perform well, though attempts to overcome this group of problems are currently the subject of much intensive research. The sorghums may be grouped as follows; 1. Grain sorghums: they are grown mainly for grain, fodder, and sometimes silage. They may be divided into five main types according to the nature of their panicles and type of grain; Hybrids of different origin are becoming of increasing importance though the selection of composite types from mixed breeding populations has been relatively successful in a number of countries. The improvement of grain sorghums for the dry tropics is now coordinated by ICRISAT in Hyderabad, India in cooperation with its out station programs in Africa. 2. Sorgos: grown for fodder i.e. hay, silage and fresh consumption 3. Grass sorghum: Sudan grass is of some importance as fodder crop 4. Broomcorn: stiff, indurated inflorescence used for brooms. The plant is a grass (0.5-6.0m in height) that produces one or more stems (tillers). Some cultivars produce many tillers, the exact number varying, depending on the capacity to tiller, nutrition, spacing and seasonal weather. After germination the seedling is highly vulnerable to adverse conditions until it has transferred its reliance on a seminal root system to a fully developed permanent root system with strong lateral roots and extensive adventitious roots. Prop roots may also be produced at the stem base (as in maize). This deep and extensive root system probably accounts for the plants ability to withstand quite severe drought during the early development of the crop. The stem is quite solid and erect and variable in height, depending on cultivar. The A A AMOAH 31 number of leaves formed is also highly variable. The leaves can roll during a drought to reduce transpiration losses. The panicle emerges through the top leaf sheath at the apex of the plant. High temperatures during this stage of development have a critical effect on subsequent flowering and may make much of the flowering head sterile. High humidity also at this time may encourage the development of mildews. Flowering is usually spread over 6-9 days with the flowers opening in the morning for two hours. The plant is sensitive to day length and will generally adapt to the length of the local season. Most of the pollination is within the same plant and only 5-10% of the plants are cross pollinated. The grain reaches its maximum dry weight 25-55 days after flowering. The grain is usually partially covered by glumes which makes an important contribution to the final dry matter of individual grains. Grains of different cultivars vary in colour and degree of bitterness. Sorghum is always propagated by seeds. One kilogram of sorghum grain contains 25,000- 70,000 seeds. Some cultivars cannot be sown immediately after harvest because they are dormant for about a mouth. Most of the improvement of sorghum cultivars centers on selection and breeding for yield, early maturity, plant height, palatability, resistance to diseases and pest and resistance to witch weed (Striga spp). Ecology Sorghum has a wide range of adaptation but prefers hot, warm conditions, is killed by frost and will grow well from sea level to 2000m altitude and between 40ºN and S of the equator. It grows best in fertile soils but is one of the best cereals for poor conditions and uncertain rainfall. Sorghum is better able than maize to withstand drought periods A A AMOAH 32 because: 1. The root system is very deep and extensive and becomes well established before stem and leaf growth accelerates. 2. The root contains silica which maintains their form during a drought period 3. The leaf area is limited and can be reduced further by inward rolling during drought period. 4. Sorghum usually has much greater water use efficiency than maize. 5. The plant can suspend growth during periods of drought and resumes growth when conditions become favourable. It is generally accepted that maize cannot withstand severe drought for many prolonged periods. However, the stage of growth at which the drought occurs does have a strong bearing on the subsequent effect on yield. Well established young maize plants can be as resistant to severe drought as sorghum plants of the same age. Sorghum can grow well on heavy soils and can mature entirely on stored residual moisture in deep clays. It also grows well in lighter soils, though bulrush millet or other millets are generally referred for the very light, low nutrient soils. Sorghum shows a wide range of sensitivity to photoperiod and temperature changes but it is generally thought that the timing of the flowering of a sorghum cultivar is determined by the interaction between genotype, photoperiod and temperature. However, some work in northern Nigeria suggests that it may be the number of successively shorter days that induce flowering. A A AMOAH 33 Growth requirements The distribution of sorghum is between latitude 50ºN and 40ºS. In the tropical and sub- tropical areas within these limits, sorghum is generally grown for grain whilst in the temperate climate within the limits, it is usually grown for forage owing to the general attributes that the stem contains appreciable quantity of sugar. In the tropics and sub tropics sorghum can be cultivated at altitudes up to 3000m or higher. Its minimum germination temperature is 10ºC with 30-38ºC being the optimum day temperature. The mean water requirement during the growing period is within the range 500-750mm although sorghum can be found in wetter areas. Under dry land farming conditions sorghum can be planted at the beginning of the rains since not much water is required for germination. As long as the plant water potential is adequate, dry matter previously stored in the stem can be mobilized and translocated to the grain for grain filling or grain growth. This attribute is also exhibited by maize. In various places in the tropics and subtropics, sorghum can be grown after the rains on residual soil moisture. Soil moisture requirement Sorghum can be cultivated on many soil types but the importance of organic matter cannot be over emphasized. Sorghum can withstand both water logging and drought but are definitely killed by frost. Their growth is slow until their extensive root system is established. Sorghum produces about twice the number of secondary roots as maize. There are silica cells in the endosperm and therefore have some resistance to collapse. The evapotranspiration requirement of sorghum is about half that of maize and the plant itself requires 20% less water to produce the same amount of dry matter as maize. The plant A A AMOAH 34 competes well with weeds and can temporarily become dormant during drought and resumes growth when conditions improve. The crop can grow reasonably on most soil types. It shows some resistance to drought or has xerophytic characteristics which enhance its ability to withstand dry conditions. Cultivation and management Sorghum is frequently grown as a rain fed crop mixed with one or more crops but it may also be grown in rotation with other crops. It is rarely irrigated except in USA, parts of Sudan and India. The repeated growing of sorghum on the same land leads to the buildup of the parasitic weed striga spp which may eventually make it impossible to grow the crop. Land preparation is highly variable, but techniques are often adopted to ensure that germination and establishment are satisfactory. When the crop is grown on ridges or mounds an excess of seeds would be sown and thinned to a final stand after establishment. The crop can be grown as a full rainy season crop; planted at the beginning of the rains to take advantage of the greater initial nitrogen levels in the soil. In some areas (e.g. western Sudan and around Lake Chad) it is established before the end of the rains on sandy soils and then transplanted into heavy, deep clays after the rainy season floods have receded. Optimum plant population like that of maize is affected by cultivars, soil moisture availability and nutrient status of the soil. Seed rates are usually lower in dry areas (2- 3kg) but in moderately moist areas, there is some dispute as to whether a higher seed rate, producing a higher plant population, results in a lower evaporative demand than a lower plant population. Seed rates of up to 16kg/ha are use in some area with irrigation. A A AMOAH 35 Sorghum grows well as an intercrop with a number of legumes, particularly pigeon pea (Cajanus cajan). The combined output from the mixed crop is greater than if the two crops are grown separately and the difference is most marked under stress or low fertility conditions. Artificial fertilizers are usually only applied under assured rainfall conditions or irrigation as responses is poor in the drier areas. The time from emergence to maturity may vary from 90-200 days and some cultivars may be harvested, the plant cut down and a ‘ratoon’ crop allowed to develop from the base of the plant to produce a second grain harvest. If stem borer is present however, the potential of this crop is much reduced. Yields of grain from sorghum can vary between 300 and 3000kg/ha with irrigation. An increase in the yield / unit area can often only be achieved as a result of greatly increased input and such a strategy usually involves the grower in greater risk. Apart from the problem of range of weeds that compete for moisture and nutrients during the very early growth of the crop, sorghum is one of the groups of plants that is attacked by the parasitic weed Striga spp. these weeds are semi parasites that attach themselves to the roots of flowering plants, mostly grasses. Striga asiatic (L) is common in south, central and east Africa and in India and has red flowers. Striga hermontheca occurs in east, north and West Africa and has purple flowers. These are the most common in Africa but Striga densiflorais also important in India. The Striga can produce many thousands of seeds which can remain viable in the soil for many years. Much of the damage is caused before it emerges and when it is entirely parasitic on the sorghum roots. The weed can result in up to an 80% reduction in yield of the host crop. It can be controlled or its activity reduced by rotation or by growing ‘trap’ crops, and by increasing the use of nitrogen fertilizer. Some cultivars show some resistance to Striga spp attack. A A AMOAH 36 Harvesting and storage Sorghum has same storage as maize. Best moisture content for storage is 8-12%. Species contain high Hydrogen Cyanide (HCN) and therefore not good for animal feed. Uses It is the fourth most important tropical cereal after wheat, rice and maize. It is the staple in many of the drier tropical areas of Africa, India and China as it is resistant to drought and can consistently out yield maize under rain fed conditions in areas with variable annual rainfall. In many parts of Africa sorghum has been replaced by maize as the latter is preferred as food as well as having other advantages. Maize is a high risk crop in the drier areas where as sorghum can usually produce some grain even under low rainfall. However millet is better adapted than sorghum to extremely dry conditions. 90% of the sorghum food grain in the dry tropics is utilized in five main ways: 1. Unleavened bread (chapatti) 2. Leavened bread (injera, khisra, tortilla) 3. Gruel/porridge (to, tuwo, couscous, bogove, ugali, kali) 4. Boiled whole grain or pieces after removal of the pericarp 5. Beer Sorghum flour can also be added to wheat or maize flour in different proportion. The sweet sorghums, called sorgos, have juicy, sweet stems with up to 10% sugar which are chewed fresh and used for the manufacture of syrup. The grain can also be useful stock feed though its use for this purpose is rare in the poorer countries. The inflorescence of A A AMOAH 37 some cultivars are used for broom-making and the residues from most grain sorghums are used as stock feed, house building material, for basket and as fuel. PEARL MILLET (Pennisetum americanum) Family: Gramineae Other names: spiked millet, cat-tail, bulrush millet (English); bajra (India). The cereal species refers to as millet is a wide range of small grains cultivated in the tropical, subtropical and warm temperate regions of the world for human consumption. After wheat, rice, maize, sorghum; millet is the most important. In the tropics and subtropics areas they contribute an important group of cereals. They belong to the family gramineae, subfamily Panicoideae and the tribe Paniceae except the species known as the Eleusine coracana – African or finger millet which belong to the tribe Chlorideae and is a member of the subfamily Poideae. The most important Panicoideae millet in West Africa is Pennisetum americanum which probably originates in Central tropical Africa and is given the common name as pearl millet. Origin and Importance The greatest number of wild and cultivated forms of pearl millet occurs in West Africa. A A AMOAH 38 The crop was taken to East Africa and India where it was a useful alternative, in many areas to other millets. It now has importance as a grain crop outside India and Africa. In the United States, it is grown for forage. Botany Pearl millet has a number of cultivated races which are grouped in a single species. The plant is an erect annual grass 0.5-5.0m tall. The stem is solid and the plant has variable capacity to produce tillers most of which produce an inflorescence. The inflorescence is a false spike borne at the apex of the plant and varies in length and rigidity. In non- photosensitive types, the spike emerges approximately 10 weeks after sowing and the grains ripen 6 weeks later. Photosensitive, short day cultivars may not flower for 100+ days, depending on sowing date. The crop is always propagated by seed. Current efforts to improve the crop, centre on the development of composite, hybrid and synthetic varieties; the improvement of nutritional value; the adaptation of varieties to different growing seasons; yield; seeding vigour; pest and disease resistance and the potential for nitrogen fixation by bacteria association with the root system. Ecology The crop is usually grown as a rainfed crop in the dry tropics and is the most important cereal in the Sahel zone south of the Sahara in Africa. Further south in the Sudan zone it has an importance comparable to sorghum. A number of cultivars mature more rapidly than sorghum so they can be grown with less rainfall. It is drought avoiding rather than drought resistant as it cannot withstand drought as sorghum can. It is often dry planted before the rains arrive in other to take advantage of the flush of nitrogen in the soil that A A AMOAH 39 occurs with the first rains. It is well adapted to light, sandy, low nutrient soils and will generally produce some yield every year in areas where sorghum might periodically fail. Growth requirement In general, the climate and soil are less exacting than those of sorghum. Thus they thrive on less rainfall and poorer soils. Their culture or cultivation is similar to that of sorghum except that many of the species or varieties are small seeded that it is often necessary to rise in sheltered nurseries to be transplanted later. They have short periods of maturity. The Pennisetum millet requires some amount of rain during the growing periods. The Panicum millet thrives in very hot and dry areas owing partly to the fact that they have the shortest period of maturity. Cultivation is same as that of sorghum. Ripening is similar to the other grains and when harvested, the grains are threshed, decorticated after which they can be used for making flour/ beer. The grains store better than sorghum and are less subjected to attack by pests which are less numerous than in the case of other grains. Cultivation and management The crop may be grown in pure stand but is often grown together with other cereals or pulse. Early maturing varieties may be planted in mixed crops to provide some grain before the main cereal crop is harvested. Little land preparation is carried out unless the crop is grown on ridges. Seed rates vary from 3-9kg/ha. If planted by hand, a number of seeds (6-30) may be planted in shallow holes 1.5-2m apart, chopped out by a hoe and the seeds covered using the foot. The crop A A AMOAH 40 is usually weeded and thinned out and the second crop may be inter-planted. Fertilizers are rarely applied in most areas in Africa though nitrogen and phosphate fertilizers are recommended in parts of Nigeria. Organic manures are applied in some areas of India. The crop is harvested when the ears are ripe and this may occur over a period due to uneven ripening. Yields are highly variable and range from 250-3000kg/ha. With irrigation yields can even be higher. Weeds, Pest and Diseases Pearl millet is much less susceptible to witch weed (Striga spp) than sorghum and therefore will be preferred where Striga has become common. However, it is highly susceptible to bird damage and in many of the wetter part of the semi-arid regions it has been replaced by short season maize. The plant is attacked by a number of leaf eating caterpillars and by the stem borer. The major disease problems are downy mildew, (Sclerospora graminicola) which can be controlled by the use of resistant cultivars or good field hygiene; smut, which affects the grains; ergot and rust, which affects the leaves of the plant but rarely causes severe damage. Harvesting and processing The crop is usually harvested by cutting off the head when they are fully ripe. This may be over a few weeks if there is uneven ripening due to the production of many late tillers. Threshing is carried out using a stick or by treading with animals. The grain generally stores well provided the moisture percentage is low. Uses : Pearl millet is the staple food in many of the drier parts of tropical Africa and India. A A AMOAH 41 It is generally eaten as porridge or as cake or unleavened bread made from baked or boiled seed ground into flour. In several African countries it is used to produce beer and the grain may also be fed to livestock. The residue of the plant can also be fed to livestock but it is more commonly used for house building, fencing and for fuel. LEGUMES GROUNDNUTS (Arachis hypogaea) Origin and Distribution The crop has South America as the place of origin. It has become widely distributed throughout the continent. It is found in tropical and subtropical areas. The cultivars can be grouped into two – the Virginia and the Valencia. Virginia Valencia 1. Alternate branch forms Sequential branch forms 2. True runner or the spreading branch Erect branch forms forms 3. Weakly perennials or long season Annual, short season 4. Darker in colour Lighter in colour 5. Seeds exhibit dormancy No dormancy 6. Seeds typically 2 per pod 2 – 6 seeded 7. Testa of matured seeds invariably Exhibit wide range of kernel size and testa deep brown colour but when brown they are light brown or bronze 8. Moderately resistant to Cercospora Highly susceptible to Cercospora leaf leaf spot spot. Varieties: Chinese, Adepa, Azivivi, Jenkaar, Nkosuor, Manipinta etc. A A AMOAH 42 Growth Requirements Groundnut is grown in latitude 40ºN and 40ºS of the equator. It is a warm season crop and is killed by frost. Most of the crops are produced in areas with 1000mm of rain or more. There should be at least 500mm in the growing season of 3-4months. Dry weather is required for ripening and harvesting. The most suitable soils are well drained, loose, friable, sandy-loam, well supplied with calcium and moderate amount of organic matter. It can be grown on heavier soils but this makes harvesting more difficult as the soil adheres or sticks to the nuts and stains the nuts. Soils with crust are unsuitable because of difficult of ‘peg’ or carpophores penetration. Well aerated soil, with good drainage is essential as the crop cannot tolerate water logging. Botany It is an erect/ trailing sparsely hairy annual herb of 15-60cm high. Arachis hypogeae has no tuberous roots but has a well developed tap root with many lateral roots. The arrangement of the branches is of two distinct types. 1. The alternate branch form which occur in the true runners or the spreading bunch types (upright) of the Virginia cultivars and 2. Sequential branched forms which occur in the true erect bunch forms of the Spanish Valencia cultivars. A A AMOAH 43 Leaves are spirally arranged. Flowers are born on compressed spikes in the axil of foliage leaves and never at the same nodes as vegetative branches. Flowers are most abundant at the lower nodes. Immediately after fertilization, fruits first appear at the end of pointed- like structure known as the peg (carpophores). The peg is positively geotropic (has the tendency to grow downwards) elongate and penetrate the soil. The young peg is conical in shape and until maximum penetration of soil is reached, the tip retains this shape. The time taken for peg to reach the soil depends on the initial distance from the soil. If this is more than 15cm it usually fails to reach the ground and the tip dies. The mature fruit is structurally dehiscent but functionally indehiscent legume, oblong and may contain 1-6 seeds. Mature seeds are elongated and cylindrical. Colour, shape and size of testa of seed may vary with cultivars. But colour ranges from white, pink, red, purple and shades of brown. The seeds have thin testa and contain no endosperm. Pegs / Carpophores A A AMOAH 44 Method of cultivation All commercial production is from seeds but can be propagated vegetatively from cuttings. Before planting, seed bed should be thoroughly prepared. They may be planted on the flat or on ridges. Narrow ridges should be avoided as bunch types will find it difficult in terms of peg penetration. Seed dressing before planting is necessary. Planting distances may vary according to soil condition but recommended plant population range is around 10.8plants/m2 (30cm x 30cm). Planting distances may vary according to soil moisture and fertilization and may go below or above these recommended rates. Little cultivation is necessary between planting and harvesting except when weeds are found to threaten the crop in which case they must be removed and when it may be necessary to earth up. Fertilization Although groundnuts are usually grown on sandy soils of poor fertility, the response to fertilizer is often low. The crop is unpredictable in its response to fertilizers. Nitrogen gives a response to nodulation in some areas. Sulphur and calcium increase the amount of nodulation. Groundnut can utilize phosphorus at a lower level and there is a little response to phosphorus in many areas. However, high economic returns and long residual effects have been obtained from single supper phosphate. Application of 50kg/ha P2O5 is recommended. Groundnuts make a heavy drain on soil potash, yet response to potash application is uncommon particularly in Africa because of the natural burning. It also makes heavy drain on calcium. It has been found that fertilizers that improve yields are Ca, K and Mg. The last 2 having no effect alone except with Ca, then the combination of A A AMOAH 45 the 3 give higher yield. Ca improves the shelling percentage by reducing the number of pods or the number of empty shells. Nitrogen also increases the kernel yield. Diseases and Pests Diseases: The major diseases are caused by 1. Cercospora spp: These cause serious leaf spot – dark spot surrounded by yellow rings. 2. Sclerotium rolfsii: This produces wilt causing death of branches or entire plant with reddish fruiting bodies on the stem at ground level. 3. Aspergillus flavus: Produces aflatoxins that attack stored seeds and has also been found on living plants. 4. The rosette virus: The vector is aphids. It is the most serious disease. The whole plant is stunted. Younger leaves are chloritic and mottled with excessive leaves becoming smaller, curled, distracted and yellowish. Insect / Pest: Caterpillers, beetles, thrips and aphids and rodents e.g. squirrels Harvesting / maturity Towards the end of the growing season, regular inspection including sampling of plant should be carried out to determine when the nuts are ripped and ready for harvesting. The general look of the plant with an estimated 50% old age (senescence) is a good indication. The most definite indication is when the seeds are felt moving when the pods are shaken after periodic sampling. Harvesting can be done by the use of hand or the machine. The time to maturity is 3.5 months for the erect bunch type the 4 months for the spreading A A AMOAH 46 type. The crop is often harvested by pulling and turned over in the sun to dry before stripping off the nuts. It is necessary to harvest at optimum time to combine the maximum yield with minimum losses from shelling and in the case of erect bunch type from sprouting. Losses are heavy when the soil gets hard. Yields Yields are variable and usually range between 480-1680kg/ha and roughly 500- 1680kg/ha. But up to 2242kg/ha are being obtained. Shelling percentage is about 80%. It is advisable that nuts should be stored in the shell if possible as quality and viability deteriorate rapidly after shelling. Processing Nuts can be processed into oil and other constituent products. In industrial processing the kernel or the shell nuts are cleaned and reduced in a series of cracking rolls to grit size particles. These are then heated and rolled into uniform flakes. The heating causes coagulation of protein and the rapture of oil containing cells. From then on, oil may be extracted by hydraulic pressing; continuous screw pressing or solvent extraction. In Ghana (under local conditions) after heating and grinding, the mass is moulded and the oil pressed by hand or sometimes by other queer method. After oil extraction the cake which remains can be used for various purposes particularly animal feed. A A AMOAH 47 Uses 1. The non drying oil is used as a substitute for olive oil as salad and cooking oil. 2. It is used in the manufacture of margarine 3. The inferior quality oil is used for soap making and as a lubricant 4. The high quality oil is used in the pharmaceutical industry 5. After the extraction of oil, the cake is used as high protein livestock feed 6. The best quality cake may be ground into powder for human consumption 7. The nuts are eaten raw or after roasting and here, the Virginia types are preferred for they contain little oil than the Spanish type which is better for oil extraction. BAMBARA GROUNDNUT (Vigna subterranean; syn. Voandzeia subterranean) Hilum Bambara groundnut crop Seeds of Bambara groundnut Bambara groundnut is a small herb that grows to about 0.30-0.35m in height, and like the groundnut has compound of three leaflets. Both prostrate and erect forms occur. The much-branched stems root at the nodes to form a bunched herbaceous annual with a thick taproot which forms a profusion of lateral roots towards its tip. After pollination and A A AMOAH 48 fertilization, a smooth glandular swelling at the top of the peduncle or flower stalk grows down into the soil dragging the ovary behind it so that the pod develops around the stem just beneath the surface of the soil. The ripe pod or fruit contains one or rarely two large; round seeds which are usually white but may be reddish brown, black or mottled. The white hilum or “eye” is usually surrounded by a black ring. The seeds are consumed either immature or in mature state, but dry seeds are hard and difficult to cook and may be ground before use. Bambara groundnut is a typical short-day plant which thrives under hot climatic conditions. It is very drought-resistant. For good yields, it requires moderate rainfall of 750-1,000mm during the rainy season and a dry period for harvesting. It matures in 90- 150 days, forming its fruits underground. It has a preference/tolerance for dry, poor soils and high temperatures, and it has a very low insect pest and disease susceptibility. In Ghana it is grown almost exclusively in the Guinea and Sudan Savanna zones. It forms an important part of the rotational system of cereals/legumes. The crop is also adapted to a wide range of soils, especially light loams and sandy loams but may be successfully grown on heavier soils than groundnuts. Light soils make harvesting easier; soil rich in nitrogen may produce excessive vegetative growth which is undesirable for seed production. Varieties grown are mostly traditional types and in Ghana they include the following: ⚫ Zhei: A composite variety which matures in 105 days; it is grown mainly in the northern Ghana. ⚫ Chichel Balgu: Intermediate type grown in northern Ghana. It matures in 105-110 days. A A AMOAH 49 ⚫ Piel Kargu: Also grown in northern Ghana. ⚫ Ada: Intermediate type grown in southern Ghana; it matures in 97 days ⚫ Jabajaba : Bunch type grown in southern Ghana, and matures in 90 days Other local varieties include Ex-Akatsi, Shuna, Kpalig, Simkpala, Nubig, and Nun varieties from Burkina Faso such as the Ex-Binduri series capable of yielding up to 2,400kg/ha are often grown in northern Ghana. In the deprived savanna zone two crops are possible, the first crop sown in May-June and the second crop in October. In the north, the main planting period is between August- September. Land preparation and cultural practices are similar to those of groundnut (Arachis). Whole pods are sometimes planted but it is better to sow seeds alone about 5cm deep. The normal planting distance is 30-60cm between ridges or rows and 30 cm or less within the rows. A well –prepared friable seed bed is required. Bambara groundnut is usually cultivated by resource-poor farmers in the semi-arid zone of sub-Saharan Africa, and although indigenous to the sub-region it has received little research attention. The crop is able to meet its nitrogen requirements but is known to respond favourably to application of about 4bags/ha of single super phosphate applied before planting, although the economics of fertilizing the crop, in view of its subsistence level, needs to be worked out. It is often more beneficial to plant bambara groundnut after a cereal crop such as sorghum, maize or millet which has received adequate level of phosphorus the previous season. The plants are hand-weeded when 10cm high and mounded or earth up at flowering time to encourage development of the pods A A AMOAH 50 underground. The crop is harvested when the foliage turns yellow and withers. The pods may be left in the soil to dry but in wet soils this may cause the seeds to germinate in the pods. Normally the plants are uprooted with a hoe or pulled by hand and spread thinly on cleared ground and sun-dried for 1-4 weeks. Threshing is usually done by hand by cracking the pod with a pestle and mortar, and the husks are winnowed off. Yields are lower than those of groundnuts, 300-800kg/ha being the average in most areas in the North. Bambara groundnut is an important pulse in the drier areas of Africa. It is high in protein but unlike ordinary groundnuts contain very little oil. COWPEA (Vigna unguiculata) Origin and Distribution As the wild Vigna unguiculata is wide spread in tropical Africa, it seems reasonable to assume that the crop was domesticated in that region and that it spread from there through Egypt to Asia and then the Mediterranean. Botany It is erect/prostrate or climbing, glabrous annual herb. Tap roots are stout with numerous spreading laterals in surface soil. Nodules are large, globular about the size of small peas often collected in groups. Stems are erect or sub-erect usually procumbent, twining anti-clockwise and may be tinge purple. Leaves are trifoliate with stout and grooved petiole. It has axillary inflorescence with few flowers crowded near the tip in alternate pairs on thickened nodes. Peduncles A A AMOAH 51 are stout and grooved. Pods are variable and may be linear, smooth or rounded, 8-20 seeded. Seeds are variable in size, shape and colour, 2-12mm long, globular and kidney shaped. It may be smooth or wrinkled, white, red, brown or black, mottled, blotched or eyed. Growth requirements Cowpea beans can be grown under a wide range of conditions. They are sensitive to cold and they are killed by frost. They will tolerate heat and relatively dry conditions and can be grown with less rainfall and under more adverse conditions. They can be grown successfully on a variety of soils provided they are well drained. They are sometimes grown on poor acid soils as a soil improver. Cultivation They are grown from seeds. In tropical Africa they are grown in mixed cultures or they are grown with other crops or in pure stands. In Ghana various varieties and their growth habits, seed colour, days to maturity and average yield have been evaluated and may be given as follows. Characteristics of commercial varieties Variety Growth Seed colour Days to Maturity Average habit maturity group yield (t/ha) Ayiyi Erect White 65-70 Early 2.0 Soronko 1/2 erect Brown 70-80 Medium 1.4 Asontem 1/2 erect Light red 60-65 Extra early 1.7 Bengpla Erect White 62-67 Early 1.8 Other varieties – Adom, Asetenapa, Tona A A AMOAH 52 Planting This is usually by seed and germination tests are conducted prior to planting. Cowpea should be planted such that maturity and harvest coincide with the dry periods. Normally, depending on the agro-ecology, planting may be done with inter-rows spacing of 50-80cm and intra-rows spacing is 20cm. Seeds are planted and thinned later. Seed rate is 22-34kg/ha. If it is grown for forage, they are planted closer in 15-20cm apart with seed rate of about 100kg/ha. They are sown 3-5cm deep, depending on the soil type and seed size. The 3cm depth is recommended for clay soils which crust easily while 5cm is recommended for light soils to ensure that the seed is in contact with adequate soil moisture. Optimum population is needed for high yield. This also decreases weed problems because the crop canopy rapidly shades emerging weeds between the rows. Fertilizer Application On continuously cropped site where no phosphorus-bearing fertilizers have been applied for several years, response to the application of 50-60kg/ha P2O5 is likely. The fertilizer should be applied preferably at planting time but not later than 2 weeks after emergence. Phosphorus is essential for increased grain yields. Weed control Weed control is very important especially during the first 4 weeks after planting. By the 6th week, the crop canopy should have closed and weed competition consequently reduced. One hand weeding 2-3 weeks after planting is normally sufficient to control A A AMOAH 53 weeds in cowpea. A second hand weeding may be necessary depending on the weed pressure. Diseases and pests Cowpea is attacked by several fungi, bacterial and viral diseases. The use of disease free and treated seeds and crop rotation will minimize the incidence of most diseases especially where seeds and crop residues are sources of initial infection. The recommended cowpea varieties are moderately resistant or tolerant to most of the major diseases. Most diseases may be prevented from spreading by pulling out and burning infested plants. E.g. cowpea wilt caused by Fusarium oxysporium, charcoal rot by Sclerotium and cowpea mosaic virus transmitted by the vector bean leaf beetle. Pest Insect pests constitute the single most important constraint to cowpea production in Ghana. A severe attack by flower buds thrips for example can cause a total crop failure. Efficient control of insect pest can increase grain yield 5 times or more. In addition to following recommended cultural practices and practicing crop rotation, it is important to spray the crop with appropriate insecticide for protection against insect pests. Insect pest control An important pre-flowering insect pest is the flower bud thrip. The insect and other flowering insects are effectively controlled by spraying synthetic – pyrethroids e.g. Karate (Lambda cyhalothrin) and Decis (Deltamethrin) at 1 l/ha. To control, post flowering insects, apply either Thiodan 2 l/ha or perfekthion 2 l/ha or Roxion (Dimethoate) 4 l/ha. Thiodan is preferred as it is effective against wider range of A A AMOAH 54 post-flowering pests. Application times and rate for the recommended insecticides are summarized in a table. If cowpea leaves are to be eaten, it is recommended that leaves should be picked before the insecticide application. Alternatively, a small area should be selected and not sprayed. Major Cowpea Insect Pest found in Ghana Insect Damage Pre-flowering Aphids Feed on young leaves and shoot Leaf hoppers Feed on leaves, cause cupping leaves and stunting of plants Foliage beetles Damage leaves, vector of the cowpea yellow mosaic virus Variegated grasshopper* Feeds on leaves and young pods Flowering (from flower bud stage to fall of the petals) Flower thrips Damage flower buds and flowers Legume pod borers Destroy flower buds Post-flowering Legume pod borers Damage pods, stems, peduncles and petioles Cowpea seed moths Damage seeds inside green pods Pod sucking bugs/ aphids Suck sap from green pods causing them to shrivel Cowpea storage beetles (Bruchids) Damage grain in storage, causing loss in weight and viability *These grasshoppers may attack during any stage of growth of the plant A A AMOAH 55 Recommended Insecticides Rates for Cowpea Insecticides Active Ingredient /ha Amount of Insecticide/ha Pre-flowering -g- -ml- Decis 1.2 EC 12.5 1000 Karate 2.5 EC 15 600 Post- flowering Roxion 40 EC 400 1000 Perfekthion 20 EC 400 2000 Thiodan 35 EC 750 2000 Dimethoate 40 EC 400 1000 The use of insecticides on the improved varieties of cowpea is strongly recommended. Farmers who do not spray their field risk total crop failure. High yield can be achieved through the use of improved varieties with the recommended insecticides. Harvesting and storage Pods should be promptly harvested after they mature to prevent bruchid infestation, seed shattering and mould. More than one harvest may be necessary. After harvesting, dry the pods in the sun for about one week before threshing. (Seed should be further dried to about 9-11% moisture content). Grains should be treated with Actellic 25EC or Actellic 2% dust before storage. Cowpea treated with Actellic can be stored up to six months without any significant weevil damage. Mix the dust with shelled cowpea and store the cowpea in bags. Five teaspoons A A AMOAH 56 of Actellic dust should be thoroughly mixed with one bag (100kg) of shelled cowpea. The half kg satchet of Actellic 2 % dust currently being sold will treat 10 bags of cowpea. Dilute 5ml Actellic 25 EC with 190ml water in a hand pump sprayer (the type used to spray mosquitoes). This is sufficient to spray one bag (100kg) of grain. Five milliliters Actellic 190ml water is the same as one teaspoonful. Groundnut oil can be used to preserve small quantities of cowpea from damage by storage insects. Add 5-10ml of the oil to 1kg of grain (i.e. 1-2 teaspoonful of oil per two margarine tins of grain). One and half beer bottles of cooking oil are needed to treat one maxi-bag of cowpea. Uses The dry seeds are important pulse crop (grain legume) in the tropics and subtropics particularly in Africa. The dry seeds may be ground into meal which is used in a number of ways. The fresh seeds and immature pods are eaten and may be canned or frozen. The young shoot and leaves are eaten as spinach. It is useful as a fodder plant or hay or silage or pasture. It is used as green manure or cover crop. A A AMOAH 57 SOYBEAN (Glycine max) Growth Requirements Climate: It is a subtropical plant but cultivation now extends from the tropics to 52ºN. General climatic requirement is about the same as maize. They are grown mainly in areas where the summer is hot and rather damp. They will not withstand excessive heat and severe winter but are less susceptible to frost than cowpea. The crop can be grown on a wide range of soils but thrives best on a sandy or clay-loam and alluvial soils of good fertility. It is short-day plant and all cultivars flower more quickly when given 14-16 hours of darkness and some cultivars will not flower at all if given a period of darkness less than 10hours. Most cultivars have a narrow range in which they will mature and produce satisfactory yield. Period of maturity varies from 75- 200days. Structure Most cultivars are erect, bushy and pubescent annuals, 20-180 cm tall with grey hairs on stem or leaves, and pods. Both determinate (terminal buds develop into terminal inflorescence) and indeterminate (those whose stems do not terminate in an inflorescence) growth habits exist. The flowers are borne on the short clustered axillary racemes of 3-15 flowers and up to 30 flowers are recorded in terminal raceme of determinate types. 50-80% of flowers drop without forming pods i.e. there is high floral abortion. Pods are borne in clusters of short stalks in groups of 3-15. They may be hairy, pale yellow, grey, black, slightly curved and A A AMOAH 58 usually somewhat compressed and may be 3-7cm x 1cm, dehiscent, 1-5 seeded but most cultivars have 2-3 seeds. The seeds are more or less spherical in most cultivars but others have flattened seeds. Testa may be yellow, green, brown or black or blotch and mottled or in combination of these colours. Husbandry The crop can be mechanized with ease. It is usually grown in rotation with maize, rice or sorghum and millet in various parts of the world. It can also be intercropped with maize and cassava. It requires a well –prepared firmed seed bed. Spacing depends on cultivar and the purpose for which the crop is required. It is usually grown at 60-90cm x 10- 12.5cm at a seed rate of 40-67kg/ha at depth of 2.5-5.0cm. Soybean responds to phosphate and potash fertilizer and to calcium on lime deficient soils. The usual recommendation is 30-60kg/ha P2O5, 15-30kg/ha K2O and on poor soil about 15-30kg/ha nitrogen. For compound fertilizer, we need 100-200kg/ha NPK about 2-4bags/ha. Disease and Pest The common disease is bacteria blight (pseudomonas). Others are cercospora leaf spot. The root knot nematode (Meloidogyne sp.) is also becoming important. The soybean mosaic virus and the yellow bean mosaic virus are equally important. Soybean are comparatively free from insect pest but the most serious is soybean pod borer. In many locations, insect damage to soybean may be negligible and there may not be the need to apply insecticide. At some locations however, leaf eating caterpillars, pod sucking bud constitute a major problem. Rats, rabbits, mice and other rodents can cause serious A A AMOAH 59 damage to seedlings especially in the forest area by eating the leaves, top of plants and also the green pods. Harvesting When grown for seeds, harvesting should be done before the pods shatter, thus timely harvesting is very important. It must be done at physiological maturity. Plants are cut at ground level or pulled. They are then dried for some time before threshed. Combined harvester could be used. Storage The beans should be stored at a moisture content of 12% or less. The crop is relatively free from serious epidemic, but disease incidence is now becoming increasingly important. Yields Yields vary tremendously and are between 600-2700kg/ha. Yields vary with cultivar, soil, husbandry practices etc. Uses 1. One of the world’s most important sources of oil and protein. 2. Important food crop 3. It is processed to give soymilk which is a valuable protein supplement in infant feeding 4. Can be made into cheese and soya sauce A A AMOAH 60 5. The seeds give edible oil which is used as food, used in the manufacture of margarine 6. On the industrial field, the oil is used for manufacture of paint, soap, insecticide disinfectants, linoleum etc. 7. The residue of soymilk is a very rich protein source for livestock 8. The lecithin, a by-product of the oil industry is used as a stabilizing and swelling agents in food, pharmaceuticals, cosmetics, leather, paint, plastic, soap and detergent industries. It is also used in the manufacture of adhesives, textiles, fire fighting, foam and water proofing products 9. It is made into flour and used in the bakery and the other food products 10. Soybean plants are important pasture/ fodder crops; they are made into hay and silage preparation. They also used as green manure or cover crops A number of cultivars are recognized which vary in ⚫ Time to maturity ⚫ Height ⚫ Plant type (canopy development) ⚫ Size ⚫ Colour ⚫ Protein content of seed ⚫ Uses Common varieties include Bengbie and Anidaso A A AMOAH 61 TUBER CROPS YAM (Dioscorea spp) The tuber crops particularly yam and cassava are very important and dependable sources of food in the tropics. The principal ones yam, cassava, cocoyam and sweet potato are commonly grown in the wetter areas of the tropics for their starchy tubers mainly used for human consumption and to some extent livestock feeding. Yam is a member of the family Dioscoraceae and belongs to the largest of the ten genera which make up the family. The genus Dioscorea is made up of large number of herbaceous plants with underground tubers twining or climbing stem/ vines. Some yams flower but the vast majority of the cultivated species do not flower and hence propagated vegetatively by cuttings or whole tubers or small tubers. The leaves are spirally arranged or alternate. During development tubers are initiated which grow by secondary thickening and are used as storage organs for storage of photosynthate principally in the form of starch. It is these underground tubers that are harvested and used as food or in industrial processing. The most important West African yam species are 1. Dioscorea alata (water yam): It has squarish spineless stems or vines with four distinct wings. The leaves are large, ovate and opposite. The tubers are rather large and of a light watery consistency. The species does better on drier and poorer soils than other species and matures 8-10 months. The tubers are of inferior quality, do not store very well and are not very palatable. 2. Dioscorea rotundata (white guinea yam): This species is the commonest in the yam trade, of the best quality in terms of the characteristics of the tubers. The species takes about 8 months to mature. It is especially suitable for the drier parts of the A A AMOAH 62 humid tropics e.g. the derived savannah/transitional zone of Ghana. The leaves are relatively long, narrow and are roughly triangular in shape, pale green in colour and there are spines on the stems and some on roots. The tubers can be lobed, fairly straight and of various sizes depending on time of harvest. 3. Dioscorea cayenensis (yellow guinea yam): In Akan, it is called ‘nkani’. The tubers are yellowish fleshed somewhat watery in consistency, do not store well. Tubers take about 12 months to mature. The leaves are broader, darker and smoother than those of Dioscorea rotundata but in general the plants are hardier. 4. Dioscorea dumetorum (bitter yam): This is the 3-leaf yam. Distinguished by its compound leaf of 3 leaflets and bitter tubers as well as the clockwise direction of twining by its vines. 5. Dioscorea bulbifera (bulbil bearing yam): This yam is not grown on any large scale. It is particularly characterized by edible swelling on the leaves. Swelling which is termed bulbil stores starch and these are picked or plucked, cooked and eaten. Growth requirements Essentially yams are tropical crops requiring high temperature of 25-35ºC and high rainfall although they do exhibit certain degree of drought tolerance. Minimum rainfall is about 1000mm with 1250-1500mm as optimum. Soils Yam requires light soils in which the tubers can develop without much resistance. The presence of organic matter to increase porosity of soil is very desirable. A A AMOAH 63 Cultural methods Land preparation involves land clearing, controlled burning, windrowing. In the very initial stages, ploughing, harrowing and ridging should be done but if these have been done earlier on the arable land, they may not be necessary. In the process, attempts are made to leave smaller trees where they occur to be utilized later as stakes. Mound making and Planting In making mound, a hole of about 60cm across and anything from 50-60cm deep is made. It is then filled with top soil or soil mixed with organic residue. Soils from adjacent areas are then scraped on top of this to build a mound which is usually about 60cm or more in height. The mounds are usually spaced between 0.5m-2m apart. In Ghana the period from November to early March is usually devoted to mound making and planting. Whole or part of tubers can be used as planting material or setts. A technique has been developed which makes use of very small tubers as planting material and this is called the minisett technique. The whole tuber is cut into small pieces of 25-60g setts. They are treated against pest and diseases and then planted in pots or tray with combination of media (sand, saw dust, rice straw). They are monitored until they develop smaller tubers, which are removed and planted on top of the mounds. The mound is then capped with soils or plant residues to act as mulching particularly during the hot dry season. On sprouting of the sett the cap may be removed and when the vines are long enough they are then trailed onto sticks (stakes). Staking is essential if good yield are to be obtained and these permit higher leaf area per vine. Height of stake is A A AMOAH 64 usually about 2-4m. There should be greater leaf exposure for sunlight interception. Fertilization 12-50 t/ha of farmyard manure or organic matter may be put on ridges or banks before planting. Better results are shown by the application of 112-135kg/ha of NPK. Other remaining cultural practices are weeding, repair of mounds/ridges and replacement of damaged or fallen sticks. Pruning As tuber formation proceeds, smaller tubers can be pruned leaving relatively fewer numbers into which photosynthate can be translocated for storage. Harvesting Maturation period varies with variety. In some cases, small size tubers referred to as early year can be harvested and sold in about 6 months. In others, tubers are allowed to develop fully before harvesting from 8-12months. In some species the period of maturity is extended beyond this. After harvesting, tuber storage follows. The two main considerations to ensure during storage are: ⚫ Protection from the sun and moisture ⚫ In addition, the tubers must be kept away from soil. Free aeration is necessary during storage Storage Storage may be done in barns, lath houses and in the soil. Here care should be taken to line the trench with straw to prevent soil-tuber contact. Another way of storage is A A AMOAH 65 staggering harvest. Yields They vary widely depending on the environment, species or cultivar sown, standard of cultivation or management practices. It varies between 7.5-18t/ha or more. A A AMOAH 66 CASSAVA (Manihot species) It is the most important and commonest root crop grown in the tropics. It is heavy yielding and relatively cheap to cultivate. It originated from tropical South America from where it spread to other places reaching West Africa from Brazil. It is cultivated on a large scale for industrial purposes mainly in the manufacture of starch and “tapioca” and in small scale holding in West Africa for food. A value has been added to the crop for the production of chips. It is referred to by various names including tapioca, Brazilian arrow root, manioc, yuca and mandioca. Botany It is a member of the family Euphorbiaceae, genus Manihot and species esculenta. The species essentially is a shrub, ranging in height when matured from 2-4m. The stems are often branched and are greenish when young, later ageing and becoming variously coloured from silvery grey to brownish depending on the variety. The leaves are large alternate and palmately lobed. The lobes vary in number from about 3-9 and carried on a long petiole varying in colouration. The petioles are subtended by strong stipules. Lactiferous vessels (latex) are present in all parts of the plant. The root system is essentially fibrous adventitious which spread both vertically and horizontally. In terms of management, the horizontal ones are better than the vertical ones which tend to break. Tubers develop when some of the roots become enlarged by secondary thickening leading to formation of matured tubers, each made up of an outer skin or periderm differing in colour from other varieties. Starch is the principal material formed and contributes about 30% of the matured tuber. A A AMOAH 67 The tubers usually become lignified if they remain unharvested for too long. The cassava plant including the tubers also contains a substance called linamarine which is cynogenetic glucoside (in other words it produces cyanide). The skin contains the highest amount as far as the tuber is concerned, followed by the cortex and the main storage area has the least amount. On the basis of the linamarine content cassava varieties can be classified into sweet and bitter. The bitter varieties contain more of linamarine

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