Cassava Production Enterprise in the Tropics

Abstract

Cassava, a tropical root crop, provides the staple food for millions of people around the world. It is one of the tuber crops that could be cultivated on a small scale in an environment with erratic rainfall, and without necessarily needing heavy equipment and machineries. Cassava could be successfully cultivated by resource-poor farm family. Farmers’ productivity could be as much as 70 tonnes per hectares under favourable conditions. However, smallholder farmers do among other things improve productivity through proven cultural practices and a mix of organic and inorganic measures. Irrigation is very necessary for achieving bumper harvest in areas with shortage of rainfall and insufficient soil moisture content. The concept of sustainability in the practice of agriculture has been on the front burner world over in recent time. Therefore, the cultivation of cassava with the aim of increased productivity without jeopardising the factors of production meant for future time is encouraged. Practices that combine traditional knowledge with modern technologies that are adapted to the needs of small-scale farmers are on the increase around the world. Depending on the purpose, cassava could be harvested anytime from eight month. Cassava leaves could serve as vegetable and the stems use as fire wood.

1. Introduction

Cassava (Manihot esculenta), a shrub that could survive up to 3 years or more is planted mainly in tropic and the sub-tropic regions of the world. It is a food crop cultivated for the consumption of its roots (Figures 1 and 2) and other various end products. Cassava is a very important staple crop in Africa, Asia and Latin America. Due to its low cold tolerant nature, it does not do well in temperate regions of the world. It is a crop cultivated by majority of resource-poor farm families. Cassava is a crop that can withstand vagaries of weather condition; it can survive in a poor environment where other crops could hardly survive. It can survive in an acidic soil where other crops could hardly survive. There is a mutual relationship between cassava root and soil fungi which enable it to take phosphorus and other micronutrients from the surroundings. The whitish liquid (hydrogen cyanide) from cassava is deadly to both human and livestock. And as such it must be fermented and properly drained before fed to livestock or consume by man. Cassava maximizes available soil moisture content. Also, it is hardy and resistant to common pests and diseases of crops. With limited inputs, farmers can achieve a lot in term of output. The root is about 65–70% water but when processed, the dry matter could be as much as 3350 kg per tonne depending on the cultivar. It is a common staple food that could be afforded by the poor almost everywhere around the globe because it is relatively cheap. It is better harvested any moment from 6 month when it is to be consumed as food. The longer it stays in the soil the higher the starch concentration. It implies that those who cultivate it solely for starch would get more when it stays longer in the soil before harvesting.

Figure 1.

A typical cassava farm/plant/root.

Figure 2.

Cassava root and a leaf.

Cassava is very rich in carbohydrate, and the calorie is high. It is energy given food which seriously help to mitigate the incidence of famine among the rural poor in sub-Sahara Africa and other places where it is cultivated. Also, cassava is rich in vitamin C, thiamine, riboflavin and niacin [1]. It is normally peeled and cooked to remove the cyanide acid.

The cyanide gas is volatile and would escape in the course of processing, making it and its bye-products fit for consumption. Relatedly, cassava mash is processed (by drying, roasting or boiling) into coarse flour and other food products. Furthermore, cassava could be cultivated for the sole purpose of harvesting its leaf (Figure 3).

Figure 3.

Cassava leaves.

According to [2] the leaf contain about 27% protein when dried. Both the leaves and the roots can be fed to livestock, and the stem could serve as firewood. Also, starch, which is one of the by-products of cassava serves as raw materials in food manufacturing, pharmaceuticals, textiles, plywood, paper and adhesives, and for the production of ethanol.

2. Cultural practices

Cultural practices are the activities involved in the cultivation of cassava from the decision to plant it, site selection and right up to the harvesting and post harvesting operations. There have been campaigns worldwide against practices that are inimical to the human environment. Farmers are being enjoined to embrace eco-friendly agriculture. It has been observed overtime that the traditional ways of farming is not sustainable. Traditional methods such as plowing, harrowing, ridging and other operations which disturb soil structure and disrupts soil micro-organic activities are being replaced by environmental-friendly agriculture (zero or minimum tillage). Also, the use of bio-nutrients such as organic fertilizers, mulching and integrated pest management (IPM) are to be chosen instead of mineral fertilizers and chemical pesticides. Mineral fertilizers are volatile and as such release harmful gases into the air. Also, the leaching of the mineral fertilizers into water below the soil and runoff by erosion cause pollution to the water bodies. Also, the residue of the mineral fertilizer is toxic to the soil and the environment.

Moreover, in order to mitigate the vagary of challenges associated with agriculture, farmers engage in the mix of different crops on the same plot of land. This strategy helps to reinforce soil fertility, and lessen the perennial problem of market and or price instability peculiar to agriculture and its products. For instance, having a mixture of nutrient-demanding and nutrient-giving crops such as cassava and any leguminous crop helps to stabilize the soil nutrient. Also, crop specific pests and diseases will not have freedom of self-perpetuation. The intercrops among other things enriched soil organic matter and reduce if not eliminate soil erosion and leaching of nutrients beyond the reach of plants’ roots. Having more than a crop on a plot of land is a form of diversification which enhances food security.

Cassava requires soil with a loose texture to allow for initial root penetration and strengthening. It’s susceptible to weed competition and too much moisture in the soil. Because of these factors, it is typically planted on soil that has been loosened and weed-free. Conventional tillage makes it easy to fix stakes in degraded and unstructured soils and provides well-drained, aerated conditions for the root system [3]. Crop yields on the other hand, are determined by soil conditions rather than tillage. Cassava stakes can also be planted in non-tilled soil and give good yields, as long as the soil is healthy, well-structured, and free of compaction. Soils that are pliable and rich in organic matter are the best for its cultivation.

Farmers usually plant stem cuttings (planting materials) on manually created mounds or ridges where soils possess weak physical qualities. Conventional plowing, especially with tractor-mounted plows, harrows, and other heavy machines, bury the protective cover of the soil, kills soil microorganisms, promotes fast decomposition of organic matter, and damages soil structure by pulverizing soil aggregates. Season after season of plowing or hoeing the soil at the same depth results into a compacted soil layer commonly located below the topsoil, and that makes it difficult for water and roots to penetrate. For ongoing crop production in such soils, mechanical loosening will be required, but at the expense of increased soil degradation. Growing cassava without tillage in the same soil may result in poorer yields in the first few years. However, in the long run, by decreasing mineralization, erosion, and water loss, organic matter may build up while also ensuring soil aggregate stability and internal drainage. Zero tillage enhances root function to the greatest extent possible. Once soil health has been restored, untilled land can generate high yields at a cheaper cost to both the farmer and the farming system’s natural resource base [4].

3. Cover crops and mulching

Another fundamental strategy for enjoying the full benefits of conservation tillage is maintaining a continuous ground cover. Because cassava’s initial development is slow, the soil is exposed to direct rain at the first few months of its growth, and the wide spacing between planted stakes favors the appearance of weeds. Therefore, ground cover is very crucial in cassava cultivation. Farmers cover the soil surface with mulch, such as crop residues, or grow cover crops, to protect the soil surface, reduce runoff and erosion, and inhibit weed growth. With little or no effort, cassava stakes can be planted simply through the mulch cover. Even during lengthy droughts, mulch cover protects the soil, reducing daily temperature changes and water loss. It raises the organic matter content of the soil and creates a favorable environment for soil microorganisms and wildlife below ground. It favors higher yields by improving physical soil conditions: lower soil temperatures, higher levels of moisture, increased water infiltration capacity, and lower evaporation [5].

4. Mixed cropping

Cassava is widely cultivated as a single crop in Thailand and southern Brazil, but intercropping is done by small-scale farmers in many parts of the tropics. Small scale farmers do normally produce early crops such as common beans, mung beans, peanuts, corn, upland rice, and various types of grain legumes between the Cassava rows. This method has many advantages. It protects the soil from the direct effects of rain, reduces soil erosion due to runoff, and limits weed growth in the early stages of cassava development. Intercropping also produces crops that can be harvested at different times of the year, increasing total net income per unit area and reducing the risk of total crop failure. For example, in southwestern Nigeria, corn and cassava are often cultivated at the beginning of the twice-yearly rainy season. Corn is harvested during a short rain break, after which cassava continues alone. The two plants have different pest and disease and growth requirements, so if one fails, the other can survive.

5. Planting materials and species

Cassava does well on poor soils, and can withstand erratic rainfall. Its ability to produce good yields without fertilizer/agrochemicals and or other external resources makes it one of most widely grown staple. However, cassava’s potential will not be realized until some important production constraints are addressed by high yield and well adapted cultivars. Cassava are more affected by biological restrictions than drought and high temperatures [3]. As the importance of cassava as a food, animal feed and industrial feedstock grows worldwide, there is a growing demand for varieties with specific characteristics and adaptation to different ecosystems. In Africa, new varieties are being developed as cultivation expands to dry savanna, semi-arid and subtropical regions and the transition to market-oriented production accelerates. Providing high-yielding, adapted cassava varieties to small-scale farmers via a specific system is very crucial. The system consists of three parts: conservation and distribution of genetic resources, variety development, production of high-quality and healthy planting materials and delivery to farmers.

6. Breeding improved varieties

The early introduction of cassava to Africa and Asia presented a limited gene choice that limits the diversity available to farmers to select new varieties. For instance, a single clone was cultivated by majority of the farmers in Thailand until the 1990s [5]. As researchers across different institutes and several domestic breeding programs take advantage of the vast national breeding programs, they have excellent combinations of many useful traits. The availability of varieties has improved significantly in recent decades the genetic diversity available in gene banks. Breeding of high-yielding varieties with resistance or tolerance to biological and non-biological stress contributes to a significant increase in cassava yield and overall production.

7. Varieties and planting material

Stakes cut from healthy stems free of pests and diseases have a higher rate of sprouting and produce higher root yields. As a result, many farmers do not save cassava stems for planting and frequently source cuttings from neighbors or in local markets; under such conditions, assuring the quality of planting material is practically impossible. Effective systems for routine multiplication and distribution of disease-free planting material of improved varieties is essential for sustainable intensification. Although several protocols have been developed for the rapid multiplication of cassava, and could be scaled up for the dedicated production of material that meets quality standards [6], very few countries have a formal seed system for cassava multiplication.

For the production of cassava, it is essential to maintain genetic purity and use high quality planting materials that are free of diseases and pathogens. Because cassava propagates vegetatively (Figure 4), diseases and pests can continue for several generations.

Figure 4.

(a) Cassava stem (b) Planted cassava stem cuttings.

This is a negligible problem with plant seeds. In addition, cassava cuttings are perishable, bulky, and cumbersome to transport and require significant storage space. Subsistence farmers usually harvest in small portions over a year, so storing stakes until the next planting is logistically challenging. Stakes cut from healthy stems free of pests and diseases have high germination rates and high root yields. As a result, many farmers do not preserve cassava stalks for planting and often procure cuttings from their neighbors or local markets. In such situations, it is virtually impossible to guarantee the quality of the planting material. An effective system for the daily reproduction and distribution of disease-free planting materials of improved cultivars is essential for sustainable production. Several protocols have been developed for rapid breeding of cassava and can be extended for targeted production of materials that meet quality standards [6]. Few countries have a formal stem multiplication system for cassava breeding.

To increase the efficiency of cassava stem production, IITA and Nigeria’s National Root Crops Research Institute have developed a rapid multiplication technology, which involves cutting cassava stems into stakes with 2 or 3 nodes, rather than the usual 5–7. With efficient field management, cassava stems can be harvested twice a year, at 6 and 12 months after planting, yielding around 50 times more stems than were used for planting [7]. In the absence of a national cassava seed system, cassava development programmes in a number of African countries have used a 3-tier community-based system of rapid multiplication to supply farmers with improved, healthy planting material [8]. At the top level, material from breeders is multiplied under optimal agronomic conditions on research stations and government farms to produce disease-free foundation seed. The secondary level involves further multiplication on farms often run by farmer groups, community organizations and NGOs. Certified material is then distributed to tertiary multiplication sites, which are the main and most readily accessible source of stems [9].

High participation in grassroots growth was achieved through the Great Lakes Cassava Initiative, managed by the Catholic Relief Services Foundation and supported by the Bill & Melinda Gates Foundation. It established a network of 6500 small breeding plots with an average size of 0.3 ha, each serving about 350 local farmers and contributing to the breeding of a total of 33.6 million stems. This initiative also introduced a low-cost quality control protocol based on visual assessments to assess variety purity and pest and disease assessments. The use of poor-quality planting material will remain one of the major causes of low cassava yields, especially in Latin America and Africa for some time to come. In the absence of efficient systems of multiplication and distribution, farmers can help to improve the situation using some simple local practices:

1. Take stems from healthy plants that are 8–12 months old, free of pests and diseases, growing in fertile soil, and producing high root yields. The primary stems of late-branching types with long, straight primary stems are the best.

2. Store cut stems in the shade, erect, with the base of the stems resting on dirt that has been loosened with a hoe and is frequently watered. Stems that have only been preserved for 5 days before being cut into stakes will sprout faster.

3. Just before planting, cut stems into stakes 20 cm long with 5–7 nodes each. The stakes should have a diameter of at least 3 cm, and the pith should be less than half the diameter of the stem.

4. Soak the stakes in hot water for 5–10 minutes before planting to destroy any pests or disease-causing organisms that may be present. It’s also easy to get the proper water temperature by mixing equal parts hot and cold water [10]. The stakes’ mother plants should have been appropriately fertilized to achieve large yields. Cassava plants cultivated on low-nitrogen, low-phosphorus, and low-potassium soil produce stakes that are also poor in those nutrients. In addition, they are low in starch, reducing sugars, and total sugars. Plants produced from low-nutrient stakes have a reduced rate of sprouting, produce fewer stems, and have poorer root yields as a result [11]. Some plants develop faster and produce more roots than others, even in a uniformly treated field. Farmers can boost the quantity of their next cassava harvest by only using stems from plants with strong root yields as planting material.

Rainfall is the only source of water for almost 80% of the world’s cropland. Rainfed cassava production accounts for up to 60% of worldwide agricultural output, and millions of the world’s poorest farmers rely on it for their livelihoods and food security. Irrigated agriculture produces up to three times more from the same unit area of land due to higher cultivation intensities and average yields. Agriculture, both rainfed and irrigated, faces significant obstacles. Irrigation is under increasing pressure to produce more crops with fewer drops and to lessen its negative environmental implications, such as soil salinization and nitrate poisoning of drinking water, as competition for increasingly precious water resources intensifies. More precise water-saving methods, including drip and micro-irrigation, should be used. Rainfed agricultural production is in grave danger as a result of climate change. By 2050, most scenarios predict a 30% or more decrease in rainfall runoff across large areas of Sub-Saharan Africa, South Asia, and Latin America. Crop yields are expected to drop in many developing countries as water flows grow more erratic, and the frequency of droughts and floods rises [12]. Nonetheless, a comprehensive review of agricultural water management indicated that rainfed areas have the highest potential for productivity gains [13]. However, better and drought-tolerant cultivars should be cultivated. In addition, widespread adoption of conservation tillage, mulching, and other soil management measures, as well as land deterioration and irrigation reversal should be practiced. Cassava, unlike most other food crops, does not have a crucial period for blooming and seed formation during which adequate soil moisture is required. It also has various water-saving defense mechanisms, and its roots can reach enormous depths to access subterranean moisture stores [14]. Therefore, cassava can tolerate droughts for a long period of time [6].

8. Rainfed production

Cassava is nearly entirely a rainfed crop in most parts of the world. Rainfed cassava cultivation involves careful attention to planting dates, the use of planting methods and planting sites that make use of available soil moisture, and water-conserving soil management procedures. Cassava may be grown all year if rainfall is evenly distributed, but it cannot be planted during seasons of excessive rains or drought [15]. Farmers in locations where there is only one rainy season per year plant as soon as the rains begin, which is normally in April–May in the northern tropics and October–November in the southern tropics. As the topsoil begins to dry out with the coming of the dry season, new plants will grow deeper roots once established. Before the start of the 5-month rainy season in Andhra Pradesh, India, farmers plant cassava in well-watered nursery beds to induce sprouting and root development. The rooted stakes are relocated to the field as the rains begin. If the early rains fail to hold off and any of the transplanted stakes perish, they are replaced with newly sprouted stakes from the nursery beds. Farmers can make the most of the short wet season by using this method, which eliminates the need for irrigation. In lowland paddy fields, however, some farmers plant short-duration cassava in February, after the rice has been harvested and the soil is still wet.

In lowland paddy fields, however, some farmers plant short-duration cassava in February, after the rice has been harvested and the soil is still wet. During the dry months that follow, the crop benefits from the leftover soil moisture, and it is harvested after 8 months before the area is utilized again for rice. Because the plants receive adequate soil moisture throughout the most essential stage of their growth cycle, planting early in the rainy season will normally generate the largest yields. However, outputs depend on the cultivar of the crop planted. Also, the edaphic nature of the soil coupled with the maturity of the crop as well as the rainfall intensity reinforced to determine the harvest achieved by a farmer in a given year. Planting during the month of June for instance, resulted in yield of about 38 tonnes/hectare as against 26 tonnes/hectare at the beginning of dry season in October [15]. Later research at the same location in Thailand found that planting from August to November produced the highest average yield. A more recent experiment, this one conducted over 3 years, yielded a different outcome. Cassava root yields were highest when it was planted in December, early in the dry season, and harvested 11 months later, in November [16].

Under rainfed agriculture, planting practices must be adapted to the soil moisture levels. Plant stakes on the tops of ridges or mounds to keep the roots above the standing water when the soil is poorly drained and overly wet due to heavy rainfall. This will also help to prevent root rot. When cassava is planted on the flat land in Thailand during dry periods, the rates of stake sprouting and plant survival are much higher, owing to the somewhat increased soil moisture content in the top 30 cm of soil [17]. In heavy and wet soils, stakes should be planted at a shallow depth of 5–10 cm, but slightly deeper in light-textured and dry soils.

With minimal tillage, which enhances internal drainage, the risk of waterlogging is reduced. When tillage is employed, farmland is better worked during the time when the internal drainage of the soil is optimum. The advantage of this is that it gives room for the practice of zero tillage which further enhances the soil condition. Planting 2 months towards the end of rainy season is beneficial as it reduces weed menace.

9. Irrigated production

Cassava benefits from extra irrigation during rainless times when planted near the end of the rainy season or when the rainy season is relatively short. On level or almost flat land, flood or furrow irrigation can be used, but on sloping soil, overhead sprinklers or a spinning water cannon may be more practical. Irrigation at 100% of the crop’s water needs increased the root production attained without irrigation. It also marginally enhanced the starch content of roots while significantly lowering the hydrogen cyanide concentration [18].

Drip irrigation, which saves water while keeping soil moisture at a level that is very beneficial to crop growth, is more successful in terms of water use efficiency. Drip irrigation saves water by giving modest and frequent water applications (it also allows the farmer to water the cassava plants but not the weeds). Drip irrigation of cassava generated roughly the same yields as flood irrigation in trials in the severely arid zone. When drip irrigation was employed with the same amount of water as flood irrigation, yields increased significantly, reaching 67.3 tonnes somewhere in India [19]. Experiments conducted in south-western Nigeria yielded similar results. Rainfed cassava yielded root yields of fewer than 5 tonnes per hectare during the growing season. In plots with supplemental drip irrigation, yields increased dramatically as the amount of water provided increased. Irrigation resulted in yields of about 30 tonnes at 100% rainfall.

10. Crop nutrition

Agriculture must literally return to its roots to attain the increased production required to fulfill present and future demand by recognizing the value of healthy soil, drawing on natural sources of crop nutrition, and properly applying mineral fertilizer. The overuse of mineral fertilizer in agricultural production has resulted in severe environmental consequences, such as soil acidification, water contamination, and air pollution. Fertilizer use that is more focused and sparing would save farmers money while also ensuring that nutrients reach crops and do not harm the air, soil, or rivers. The environmental impact of mineral fertilizer is a matter of management. In other words, the way with which fertilizers are used, particularly nitrogen (N) and phosphorus (P), affects whether this component of soil fertility management is beneficial to crops or harmful to the environment. Experience shows that crop nutrients from a mix of mineral fertilizer and organic sources, such as animal manure and trees and bushes, enrich the soil with nutrients, resulting in better and more sustainable yields of crops. Other biological relationships, such as those between plant roots and soil mycorrhizae, can improve crop nutrition. The foundation of a sustainable crop nutrition system that yields more is a mix of ecological processes and judicious application of mineral fertilizer [12]. On soils where many other crops would fail, cassava may flourish and generate reasonable yields. It has a great tolerance for low-phosphorus and can often thrive without the use of phosphorus fertilizer. This is because cassava has created a favorable relationship with a fungus group known as “vesicular-arbuscular mycorrhizae” [13]. Mycorrhizae, which may be found in almost all natural soils, penetrate the cassava root and feed on the sugars it produces. In exchange, the fungi’s long filaments transfer phosphate and micronutrients to the plant from the surrounding soil. Cassava can absorb enough phosphorus for optimum growth because to this mutual relationship.

The plant tops contain the majority of the nutrients taken by cassava during its growth [6]. After the root harvest, returning stems and leaves to the soil as leaf litter or mulch nourishes the soil with new organic matter, and some of the nutrients are re-used by the following crop. When the plant tops are recycled, the root harvest eliminates less soil nutrients than most other crops [3]. A root yield of 15 tonnes per ha removes only about 30 kg of nitrogen, 20 kg of potassium (K), and just 3.5 kg of phosphorus [20]. Even after many years of continuous cassava production on the same land, there is little risk of phosphorus depletion. Cassava may be cultivated on very acidic and low-fertility soils due to its tolerance for low pH and the large levels of exchangeable aluminum that come with it. While maize and rice yields are typically negatively impacted when the soil pH is below 5 and aluminum saturation is above 50%, cassava yields are typically unaffected until the soil pH is below 4.2 and aluminum saturation is beyond 80%. As a result, cassava may not require a lot of lime on acidic soils where other crops would struggle to do well.

11. Mineral fertilizer

Cassava responds positively to mineral fertilizer application. Traditional methods of managing soil fertility, such as intercropping and mulching increase cassava requirement for fertilizer. The harvest removes considerable amounts of nitrogen and potassium when root yields are high and wastes are not returned to the soil. Cassava would require annual per hectare treatments of 50–100 kg nitrogen, 65–80 kg potassium, and 10–20 kg phosphorus to maintain both yields and soil fertility. The predominant nutrient constraint was lack of K in 12 trials, lack of N in five trials, and lack of P in just two trials, according to the results of 19 long-term fertility studies conducted over 4–36 years of continuous cassava planting on the same plots. When suitable amounts of mineral fertilizer (100 kg N + 22 kg P + 83 kg K) were supplied annually and plant foliage was returned to the soil before each new planting, high root yields of up to 40 tonnes per ha were maintained in Thailand. Due to nutrient depletion, notably of potassium, per hectare yields fell drastically when no fertilizer was provided and plant tops were removed from the field, from 30 tonnes in the first year to roughly 7 tonnes after 6 years. Similar effects have been observed in Colombia, India, Indonesia, Malaysia, Thailand, and Vietnam on a variety of soils [12].

Production of cassava on the same piece of land for several years would require adjustment in N-P-K balance to account for the removal of each nutrient during the root harvest. This can be accomplished by utilizing fertilizers with a 2:1:3 ratio of N, P2O5, and K2O, or any compound fertilizer high in K and N but low in P. Local fertilizer recommendations based on crop experiment outcomes and or simple fertilizer trials conducted in farmers’ fields should be considered first. Compound fertilizers should be used either when the stakes are planted or, preferably, at or shortly after planting. N and K should be sprayed in two parts, one at or soon after planting and the other 2–3 months later, when cassava reaches its maximum growth rate. The majority of mineral fertilizers dissolve quickly in soil water. They should be planted in 20–30 cm long, 4–5 cm deep bands dug at a distance of around 6–10 cm from the cassava stake or plant. The fertilizers should be covered with soil after application to prevent N volatilization and nutrient losses due to runoff and erosion. The plant’s roots will develop in the direction of the fertilizer solution to take up the nutrients.

12. Organic sources of nutrients

Mineral fertilizer can assist to reinforce yields. Nevertheless it cannot all alone sustain crop production for a long period of time on a depleted soil [21]. Farmers want to preserve and enhance soil best and fitness by the usage of different measures which include conservation tillage, alley cropping and manuring. Intercropping with grain legumes help fix atmospheric nitrogen to the soil. Although organic fixation cannot meet all of cassava’s nitrogen needs, it is however very important. Combining Leucaena with fertilizer bring about yields of greater than 20 tonnes. However, the benefit of alley cropping is limited in tropical soils which are largely barren or less productive. The mix of shrubs in rows of cassava in such area might bring about bumper harvest [6].

13. Pests and diseases

By cultivating insect-resistant cultivar, maintaining and encouraging biological control agents as well as regulating crop nutrient levels to minimize insect reproduction, agricultural losses to insects are kept to an acceptable minimum. Diseases are controlled through the use of disease-free planting material, pathogen-suppressing crop rotations, and the removal of affected host plants. To reduce weed growth, timely hand weeding and the use of surface mulching are required for effective weed management. Low-risk selective pesticides can be employed for targeted control as necessary, in the right amount and at the right time. Because all pesticides have the potential to be dangerous to people and the environment, they must be locally registered and approved, with explicit instructions on how to handle and use them safely. Cassava, like all important crops is susceptible to pests and diseases that can result in significant yield losses. In Africa, their impact is very severe. Asia had few severe pest and disease concerns until recently, but that may be changing as the crop is produced more intensively over bigger regions and planted all year for industrial processing. When pest or disease management measures are required, a non-chemical control plan should be examined before deciding to use pesticides. Pesticides are frequently inefficient and rarely cost-effective because cassava is a long-season crop that is exposed to pests and diseases for a longer period of time. As a result, insecticides should only be used in short-term, localized applications in areas where the pest is first noticed, and only when the pest is still in its early stages (vulnerable stage) of development.

A variety of non-chemical methods can assist farmers in reducing pest and disease losses while also safeguarding the agro-ecosystem [19]. First, planting material should come from mother plants that are free of disease symptoms and insect attacks, as well as types that have tolerance or resistance to the most common cassava diseases and pests. Stem cuttings can be soaked in hot water as an extra precaution to eliminate any pests or disease-causing organisms that may be present. Also, cuttings may need to be soaked in a fungicide and pesticide solution in extreme circumstances. Farmers who do so, however, must have obtained pesticide training and should select herbicides based on the recommendations of local plant protection professionals. Mulching, planting hedges, and intercropping are examples of ecosystem-based techniques that can provide refuge for natural enemies of insect pests. Early in the cropping cycle, increasing soil organic matter enhances pest-regulating populations. Applying proper quantity of manure and or fertilizer help to improve crop resilience. Insecticides should be applied with caution as they possess the chemicals that are deadly to the natural enemies of pests and diseases. Insecticides kill those biological control agents and other predators that feed on cassava pests. When this is the case, pest population rises prompting farmers to use more pesticides, repeating and exacerbating the pest harm cycle. Whiteflies, mealybugs, and variegated grasshoppers can all be controlled with biopesticides like neem seed oil extract. Sticky traps and spraying plants with soapy water can also help to minimize the amount of whiteflies and mealybugs.

Although the majority of cassava diseases are found in Latin America and the Caribbean, where the plant originated, several are now prevalent in Sub-Saharan Africa and Asia as well. Some have evolved individually in Africa and Asia, and others have evolved together. Some have evolved in Africa and Asia separately and have yet to reach the Americas. One of the most common and dangerous cassava disease is bacterial blight. It is spread mostly by infected planting material or infected agricultural tools. Rain splash, as well as the movement of people, machines, or animals from infected to healthy fields, can transfer it from one plant to another. The bacterium affects the leaves initially, which become brown in big patches and eventually die, then the petioles and woody stems’ vascular tissues. The impact of bacterial blight on yields varies according to region, variety, weather patterns, planting period, and planting material quality. Bacterial blight can jeopardize food security by lowering the yield of cassava leaves, a key source of vegetable protein in Central Africa. Despite its catastrophic potential, bacterial blight can be efficiently controlled by excellent agricultural techniques, viz.:

1. Use disease-free planting material or plants grown from meristem culture, rooted buds, or shoots

2. Soak stakes in hot water for about 50 minutes before planting. Stakes may be immersed in a cupper solution for 10 minutes in exceptional circumstances, and on the recommendation of a professionals.

3. Planting should be done towards the end of wet season

4. Infected tools should be sterilized

5. Plants should properly be fertilized, particularly in terms of potassium.

6. Burning infected plants and agricultural leftovers

7. Intercropping cassava with other crops to minimize diseases spread

8. Cassava should be rotated with other crops or left fallow in order to avoid disease transmission in the soil. The most common way for viral infections to spread is through the use of infected planting material.

In Sub-Saharan Africa, cassava mosaic disease (CMD) is endemic. Misshapen leaves, chlorosis, mottling, and mosaic are all common signs. Stunting and general decline occur in plants, and the more severe the symptoms are, the lower the root output. Corky necrosis in roots caused by cassava brown streak disease (CBSD) renders them unsafe for ingestion. Farmers may not realize their crops are infected until they harvest the roots because the signs of CBSD are not visible on the cassava leaves or stems. Because there are no visible indications above ground, disease-infected planting material is more likely to be used. Strict adherence to quarantine measures during international cassava germplasm exchange, as well as cultural methods, particularly the use of resistant or tolerant cultivars and virus-free planting material are two critical suggestions for controlling both CMD and CBSD. CMD and CBSD-free planting material has been developed and distributed with great success. In January 2012, the United Republic of Tanzania released four high-yielding cassava varieties that are resistant to CMD and tolerant to CBSD. Researchers at different institutes across the globe have been working to develop series of CMD-resistant lines [22]. Root rots are abundant in Africa, Asia, and Latin America, and they occur primarily in poorly drained soils during periods of heavy rain. They are caused by a variety of fungal and bacterial infections and result in leaf loss, stem and shoot death, and root degeneration as the crop matures or during post-harvest storage. Post-harvest farm implements and plant leftovers are frequently contaminated with disease-causing fungus and serve as sources of spores that infect new plants. Other cultural methods that control root rots include:

1. Immerse stakes in hot water for roughly 50 minutes if no disease-free planting material is available;

2. Plant on light-textured, fairly deep soils with good internal drainage.

3. Reduce tillage and use surface mulches to improve drainage.

4. Cassava should be rotated with cereals or grasses, and unhealthy plants should be uprooted and burned.

Immersion of the stakes in a suspension of Trichoderma viride is very efficient biological control for root rot [21]. Two groups of preserved cassava roots were injected with four pathogenic fungus in Nigerian tests. A culture filtrate of T. viride was also given to one of the groups. The incidence of rot in the group without T. viride ranged from 20 to 44% after 3 weeks; in the group inoculated with the biocontrol agent, there was a drastic reduction in the range and number of the target fungi after 3 weeks, with the incidence of rot ranging from 0 to 3%. T. viride inoculation eliminated the need for frequent synthetic fungicide application [23].

14. Weed management

Compared to several other crops, the initial growth of cassava is slow. As a result of this and the wide spacing between planted stakes, weed emergence and competition with the crop for available soil nutrients and sunlight is rife. In the first 4 months after planting, cassava can easily be overwhelmed by competition from weeds, and other leguminous plants. In East Africa, weeds are often a more serious production constraint than insect pests or diseases and may reduce yields by about 50% [24]. In Nigeria, farmers expend more resources controlling weed than other aspect of crop production. Once the cassava canopy has closed, it’ll shade out most weeds and keep the sector almost completely weed-free (Figure 5). Six to eight months after planting, when cassava starts to shed many leaves (especially during the dry season), weeds may reappear, but this generally does not seriously affect yields. Excessive late weed growth may make harvesting harder, but also can protect the soil from erosion if post-harvest rains are heavy.

Figure 5.

Cassava canopy checks weeds.

While cultural controls might not perfectly control weed, they are effective in reducing weed competition, and thus the necessity for mechanical or chemical weeding [25]. Cultural control begins with selection of high-quality planting material from varieties with vigorous early growth and tolerance or resistance to diseases and pests. High planting density and therefore the correct type and rate of fertilizer can stimulate early crop growth and rapid canopy closure. Planting within the season under drip irrigation also can encourage the expansion of cassava but not that of weeds. The soil should be covered with a thick layer of mulching material such as rice straw or maize residues to stop weed. Also, intercropping cassava with fast-growing plants, like melons, squash, pumpkins, common beans, groundnuts, soybeans, mungbeans and cowpeas proved to be effective in controlling weeds. Since those are short-duration crops, they will be harvested after about 3 to 4 months, when the cassava canopy closes and weeds are shaded out. While intercrops may reduce cassava root yields, they markedly reduce weed growth, and offer an eco-friendly and fewer expensive alternative to spraying with herbicides. A study in Nigeria of legume cover crops during a mixed cassava/maize system reported significant improvements in cassava root yields when velvet beans were grown to suppress weeds [26]. Common among the smallholder cassava farmers is mechanical control measures–by hoeing, starting after emergence. Research in Colombia found that with hand-weeding at 15, 30, 60 and 120 days after planting, cassava root yields were 18 tonnes per ha compared with only 8 tonnes/ha were obtained when weeds were controlled with herbicides. When weeds were not controlled in the least, yields fell to only 1.4 tonnes.

Weeds are often controlled with herbicides. Although many herbicides are highly toxic and, being water soluble and protracted within the environment, are often washed away to contaminate ground and surface water. Farmers got to exercise care within the choice of the herbicide to be used and follow the recommendation of local plant protection specialists. Pre-emergence herbicides do not kill existing weeds. Instead, they prevent weed seeds within the soil from emerging or, at least, reduce their rate of growth. Pre-emergence herbicides are either incorporated into the soil before planting or applied on the soil surface with a knapsack sprayer immediately after planting. Pre-emergence herbicides that are selective for cassava are often applied over the vertically planted stakes without affecting cassava sprouting or yield. The application of pre-emergence herbicides can maintain a cassava field almost weed-free for 6–8 weeks after planting. Farmers may apply a mix of two herbicides; one that controls the grassy weeds and the other on the broad-leaf weeds. A lower dosage is suggested on light-textured soils, while a higher dosage could be needed in heavy soils, like clay-loamy. Special care must be taken when cassava is grown in association with other crops, because the pre-emergence herbicides normally used for cassava may harm the intercrop. At about 2 months after planting, weeds may have to be controlled again to scale back competition with cassava. This is often usually done by hoeing or using an animal or tractor-mounted cultivator, counting on the peak of the growing cassava plants and therefore the extent of cover closure. When most of the weeds are grassy species, it’s also possible to use a selective post-emergence herbicide, which kills grasses but does not affect the cassava plant. Post-emergence herbicides are often used about 4–5 months after planting, when some bottom leaves start to drop off. It is best done on a windless days and with a nozzle shield to stop spray from reaching the cassava stems or leaves.

15. Harvest

Cassava is due for harvesting any time from 6 month. The crop does not have a specific time or season for its harvest; it can be harvested all-year-round. The fact that it can stay long and be preserved in the soil gives it the utmost advantage of being harvested piecemeal over a long period. The root is cooked and consumed as a local delicacy. Also, it could be processed to give a varieties of products (Figures 6–8) as a result of value addition. Cassava leaves can be fed upon as vegetable, and it is used as such in many homes where they are planted in West African countries. Moreover, cassava leaves and root serve as a good source of nutrients for livestock. The leaves are rich in vitamins.

Figure 6.

Cassava coarse (grains) flour.

Figure 7.

Cassava (smooth) flour.

Figure 8.

Cassava end (food) products.

Cassava has a number of advantages, one of which is, it does not have a set harvesting season. They can be collected whenever needed during times of food scarcity, frequently one plant or even one root at a time. Harvesting for human consumption takes roughly 8–10 months; for industrial purposes, a longer growth time yields a higher root and starch output. Roots can be eaten directly by farm families, given to livestock, or sold for processing into a wide range of value-added products, from coarse flour (‘Garri’)to high-tech modified starch gels. The root of the plant is not the only portion that can be useful. The green section of the upper stem, which includes the leaves and petioles, is fed to cattle and buffaloes in several countries, while the leaf blades are fed to pigs and chickens. Fresh leaves are used to raise silkworms in China, Thailand, and Vietnam. Woody stems are crushed up and used as a substrate for growing mushrooms. Stumps are burned as fuelwood [12].

Cassava roots are typically collected by cutting the stems approximately 20 cm above ground and then dragging the entire root system out of the ground using the stump. If the soil is too hard or the roots are too deep, it may be necessary to remove the soil around the roots with a hoe, spade, or pick while avoiding injury to the roots. A harvesting blade mounted to a tractor is occasionally employed in heavy soils that can become quite hard in the dry season. The sword slashes through the soil material. The tractor’s forward momentum pulls the root clusters to the surface as the blade slices through the dirt right below the roots. The roots are then removed from the stump and transported in baskets or bags.

Large cassava fields are frequently harvested by middlemen who employ teams of labourers and deliver the roots to marketplaces or processing plants via trucks. Plant tops are harvested after the root harvest. Plant tops are generally left to dry on the ground after root harvesting and then integrated into the soil to help preserve its fertility. However, by trimming the green tops every 3 months during the plant’s growth cycle, farmers can considerably increase the total amount of cassava foliage available for feeding to animals. Within 2–3 months after each trimming, the remaining stems will sprout and produce a new crop of leaves. Cassava stakes should be planted at a closer spacing of about 60 × 60 cm for maximum foliage output. Young leaves harvested at regular intervals during the cassava growth cycle have a higher protein and lower fiber content than those gathered at the end of the cassava growth cycle, when plants are generally harvested between 11 and 12 months. Younger leaves are more pleasant and give better nutrition.

The ultimate root production decreased as the frequency of leaf cutting increased, from roughly 40 tonnes per ha when leaves were collected only once at the time of root harvest to less than 25 tonnes when leaves were removed 5 times [27]. This approach may or may not be cost-effective, depending on labour costs and the relative pricing of fresh roots and dry leaves. Harvesting the plant tops four or five times over a one-year growth cycle takes a substantial amount of nutrients, particularly nitrogen, from the field, and would be unsustainable unless large amounts of mineral fertilizer were applied to maintain soil fertility.