**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

*Cassava Production Enterprise in the Tropics DOI: http://dx.doi.org/10.5772/intechopen.104677*

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.:


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:


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].
