Improvement in Cassava Yield per Area by Fertilizer Application

*John Okoth Omondi and Uri Yermiyahu*

#### **Abstract**

Cassava is a source of carbohydrates to more than 200 million people in Sub-Saharan Africa, even though its production is 6–8 t ha−1, which is below the highest world production of 36.4 t ha−1 in India. To address this yield gap and increase cassava's availability, affordability, and adequacy, intensive but sustainable production is important. Additionally, being an emerging raw material in the animal feeds, pharmaceutical, beer industries etc., only increases its demand, however the current production levels cannot effectively sustain this. Therefore, this paper reviews: improvement in cassava yields per area under fertigation and banding of fertilizers, a common practice among many farmers; the advantage of fertilizer application on starch of the storage roots, which is the fundamental ingredient in most industries using cassava as a raw material; and the climate smart technologies for intensive sustainable cassava production. In the end, this review enhances knowledge about fertilizer application to cassava, both banding and fertigation, and expounds on effective intensive sustainable climate-smart production strategies.

**Keywords:** storage roots, irrigation, fertilizer, sustainability, climate smart, macro-nutrients

#### **1. Introduction**

Cassava is a root crop which provides starch to over 500 million people in the tropics and is the sixth most important crop in the world [1]. Its importance is gradually increasing in the beer and pharmaceutical industries due to demand for its starch [2]. Yet, its world production is only 262.6 million tonnes [3], in which the highest yield per hectare was achieved in India (36.4 t ha−1), while Sub-Saharan Africa (SSA) produced 6–8 t ha−1 [3]. Also, increase in population is not parallel to food production in sub-Saharan Africa leading to deficits that can only be filled by imports. This lack of synchrony between population growth and food output is attributed to an inability of crops to achieve their potential – the yield gap. Hillocks [4] cautiously reported that there was a 46% yield gap for cassava in Africa, while globally it was 36%. He linked such to a myriad of factors: from unpredictable rainfall distribution to poor adoption of technologies, scarcity of inputs, minimum usage of inorganic fertilizers and poor agronomic practices etc. Even though these factors contribute to the yield gap, poor soil quality or lack of fertilizer application [5] are key and hence require urgent solution [6]. In order to address this, Giller et al. [7] suggested that best-fit technologies that are compatible with farm practices are essential. Such technologies include integrated soil fertility management (ISFM) and conservation agriculture (CA).

#### **Figure 1.**

*Relationship between the agronomic efficiency (AE) and various components of ISFM. Source: [8].*

After developing integrated soil fertility management (ISFM) concept [8], Vanlauwe et al. [9] further proposed the inclusion of appropriate fertilizer application as a principle of conservation agriculture (CA), to which Sommer et al. [10] offered a rebuttal stating that it should just be a practice rather than a pillar of CA since in Sub-Saharan Africa (SSA) low fertilizer application is a common problem not only linked to CA. Despite their divergent views, they however agreed that fertilizer usage is fundamental in SSA agricultural systems to close the yield gaps. Interestingly, it has been observed that cassava root yield increase with fertilizer application even in Sub-Saharan Africa [11–13]. Recent studies on the effects of fertigation on growth and root yield of cassava, Omondi et al. [14] established fertigation concentrations at which maximum storage root yields were achieved in the field for three cassava varieties (Mweru, Nalumino and Kampolombo).

Looking at Vanlauwe et al.'s [10] **Figure 1** on ISFM, the jump in agronomic efficiency from the current practice to germplasm and fertilizer is greater than all the other ISFM practices. However, while reinforcing the importance of appropriate fertilizer application for intensive sustainable production of cassava to close the yield gap, this review does not negate the need for improved varieties, better agronomic practices/management, adaptation to local environment and usage organic fertilizers. Thus, this paper aims to evaluate and reinforce the clarion call that appropriate application of fertilizers through the 4R-Nutrient-Stewardship (right fertilizer source, right rate, right time, right placement) [15] through fertigation or banding, proper agronomic management and right management of the ISFM traits improve cassavas' yields.

#### **2. Cassava root yield under fertigation and banding**

**Table 1** shows that irrespective of the amount of fertilizer applied, there is an advantage of storage root yield against non-application. Of course, there

**115**

application.

*Improvement in Cassava Yield per Area by Fertilizer Application*

Lusaka (Zambia) 155–23-155 24.6\*

Lusaka (Zambia) 76–8-76 37.7\*

*These varieties were harvested at eight months after planting.*

*\*\*\*NPK application compared with the average farmer practice.*

*Fertilizer application advantage on storage root yield of cassava.*

**Site N-P-K (kg ha−1) % Fertilizer advantage on root yield** 

Kabangwe (Zambia) 100–22-83 31.0 [16] Mansa (Zambia) 100–22-83 32.9 [16] Akure (Nigeria) 60–60-60 37.0 [17] Kwang'amor (Kenya) 100–22-83 60.5\*\*\* [18] Mungatsi (Kenya) 100–22-83 68.3\*\*\* [18] Ugunja (Kenya) 100–22-83 68.3\*\*\* [18] Kisiro (Uganda) 100–22-83 64.2\*\*\* [18] Kerala (India) 100–300-100 56.2 [19] Lopburi (Thailand) 250–62.5-125 23.4 [20] Supanburi (Thailand) 250–62.5-125 19.6 [20] Chonburi (Thailand) 250–62.5-125 23.3 [20]

**against 0–0-0 NPK (kg ha−1)**

160–80-160 88.7\*\* [21]

(Mweru variety) [14]

(Kampolombo variety) [14]

**Source**

are variations in the levels of advantage due to different factors such as variety response, agro-ecological zones characteristics, agronomic and crop management practices etc. For example, under fertigation (application of fertilizers or other soil amendments intended to improve soil fertility through an irrigation system) in [14] study, all the cassava varieties receive similar treatments yet the fertilizer advantage is different – Kamplombo variety responding better to fertilizer

The highest fertilizer advantage is obtained under continuous cassava cultivation (**Table 1**), for example, [21]'s long term trials indicated decline in root yield under both non – and - fertilizer applications (**Table 1**). Although, under no fertilizer application, the decline was huge perhaps due high nutrient depletion without replenishment. This is an indication that continuous cassava cultivation requires continuous application of NPK including the other elements. Here [21], the fertilizer was banded, a placement of fertilizers in bands/rings/strips near the roots,

Also, in their long-term nine-years study of fertilization of cassava, [21] observed a decline in storage root yield regardless of fertilizer rate or individual nutrient rates, however, they concluded that highest cassava root yield were obtained at N-P-K of 160–80-160 kg ha−1 (**Table 1**). Such decline in cassava's

response to continuous nutrient application, especially K, on the same piece of land for five years was also observed by [22] in fourteen varieties. In both instances, [22] and [21] attributed the decline over the years to depletion of other elements such as Ca and Mg, which were not applied in their experiments. This indicates the importance of other nutrients to cassava even as many studies are focused on

often 5 cm to the side of the plant and 5 cm deep.

*DOI: http://dx.doi.org/10.5772/intechopen.97366*

**Banding**

Thai Nguyen (Vietnam)

**Fertigation**

*\*\*Data used are a mean of nine years.*

*\**

**Table 1.**


*Improvement in Cassava Yield per Area by Fertilizer Application DOI: http://dx.doi.org/10.5772/intechopen.97366*

*\*\*Data used are a mean of nine years.*

*\*\*\*NPK application compared with the average farmer practice.*

#### **Table 1.**

*Cassava - Biology, Production, and Use*

After developing integrated soil fertility management (ISFM) concept [8], Vanlauwe et al. [9] further proposed the inclusion of appropriate fertilizer application as a principle of conservation agriculture (CA), to which Sommer et al. [10] offered a rebuttal stating that it should just be a practice rather than a pillar of CA since in Sub-Saharan Africa (SSA) low fertilizer application is a common problem not only linked to CA. Despite their divergent views, they however agreed that fertilizer usage is fundamental in SSA agricultural systems to close the yield gaps. Interestingly, it has been observed that cassava root yield increase with fertilizer application even in Sub-Saharan Africa [11–13]. Recent studies on the effects of fertigation on growth and root yield of cassava, Omondi et al. [14] established fertigation concentrations at which maximum storage root yields were achieved in

*Relationship between the agronomic efficiency (AE) and various components of ISFM. Source: [8].*

the field for three cassava varieties (Mweru, Nalumino and Kampolombo). Looking at Vanlauwe et al.'s [10] **Figure 1** on ISFM, the jump in agronomic efficiency from the current practice to germplasm and fertilizer is greater than all the other ISFM practices. However, while reinforcing the importance of appropriate fertilizer application for intensive sustainable production of cassava to close the yield gap, this review does not negate the need for improved varieties, better agronomic practices/management, adaptation to local environment and usage organic fertilizers. Thus, this paper aims to evaluate and reinforce the clarion call that appropriate application of fertilizers through the 4R-Nutrient-Stewardship (right fertilizer source, right rate, right time, right placement) [15] through fertigation or banding, proper agronomic management and right management of the ISFM

**2. Cassava root yield under fertigation and banding**

**Table 1** shows that irrespective of the amount of fertilizer applied, there is an advantage of storage root yield against non-application. Of course, there

**114**

**Figure 1.**

traits improve cassavas' yields.

*Fertilizer application advantage on storage root yield of cassava.*

are variations in the levels of advantage due to different factors such as variety response, agro-ecological zones characteristics, agronomic and crop management practices etc. For example, under fertigation (application of fertilizers or other soil amendments intended to improve soil fertility through an irrigation system) in [14] study, all the cassava varieties receive similar treatments yet the fertilizer advantage is different – Kamplombo variety responding better to fertilizer application.

The highest fertilizer advantage is obtained under continuous cassava cultivation (**Table 1**), for example, [21]'s long term trials indicated decline in root yield under both non – and - fertilizer applications (**Table 1**). Although, under no fertilizer application, the decline was huge perhaps due high nutrient depletion without replenishment. This is an indication that continuous cassava cultivation requires continuous application of NPK including the other elements. Here [21], the fertilizer was banded, a placement of fertilizers in bands/rings/strips near the roots, often 5 cm to the side of the plant and 5 cm deep.

Also, in their long-term nine-years study of fertilization of cassava, [21] observed a decline in storage root yield regardless of fertilizer rate or individual nutrient rates, however, they concluded that highest cassava root yield were obtained at N-P-K of 160–80-160 kg ha−1 (**Table 1**). Such decline in cassava's response to continuous nutrient application, especially K, on the same piece of land for five years was also observed by [22] in fourteen varieties. In both instances, [22] and [21] attributed the decline over the years to depletion of other elements such as Ca and Mg, which were not applied in their experiments. This indicates the importance of other nutrients to cassava even as many studies are focused on

NPK– adhering to Justus von Liebig Law of the Minimum - a limit in one nutrient limits the uptake of the others and hence decline in growth and yield [23].

#### **3. Fertilizer influence on starch qualities**

The importance of cassava storage roots as food and animal feed cannot be understated, especially among smallholder farmers. To enhance cassava's ability as an industrial cash crop, focus needs to shift to starch in its storage roots. However, there are many starch characteristics that are considered by various industries such as particle size, solubility, gelatinisation, purity etc. These require extensive study.

Cassava starch is being used in beer making, ethanol production [24, 25], pharmaceuticals, paper manufacturing, textile etc. [26]. In addition, it has been tested as a substitute for agar material in micropropagation in tissue culture studies with minimum success [27]. Therefore, as the usage of starch from cassava storage roots expands, factors that influence the starch suitability for various industries are of importance. Factors that influence crop growth and development like climate, soil fertility, abiotic and biotic incidences and the variety [28] are vital. Those that impact postharvest and processing are important too [29]. **Table 2** illustrates the effect of fertilizers and soil amendments on the characteristics of starch of cassava storage roots.

The response of cassava storage-root-starch varies under fertilizer application (**Table 2**). Some varieties increase storage root starch content while others decline, for example, four of the varieties tested by [32] had a decline in starch content within the storage roots. Despite these observations from [32], other studies have indicated an increase of 9–14% starch content in the storage roots on fertilizer application to cassava (**Table 2**). Remarkably, fertigating medium (Kampolombo) and long duration (Nalumino) cassava varieties improved starch content of storage


*- Variety not indicated from the source.*

*A negative in the % fertilizer advantage indicates that starch content under no fertilizer application was higher than under application.*

**117**

**5. Conclusion**

**Figure 2.**

*Improvement in Cassava Yield per Area by Fertilizer Application*

roots than banding in other varieties (**Table 2**). It is important to note that these varieties were not tested under banding, neither were the other varieties tested under fertigation. Therefore, a direct comparison of the two fertilizer application methods (fertigation and banding) is weak, even though the observations on

**4. Future of intensive sustainable climate-smart production of cassava**

Climate is changing, and human population is growing. Cassava is one of the crops that have been observed to be tolerant to the vagaries of climate, such as increase in atmospheric temperature, CO2 [33] and drought [34]. Furthermore, as stated in the introduction, its demand both as food and raw material for industries is increasing, to reduce the yield gap and meet the growing demand, its yield per area must improve. However, that intensive production must be sustainable and climate smart. To make it a climate-smart and a cash crop for smallholder farmers, intensive sustainable production approaches are required. Tweaking the [8]'s ISFM **Figure 1** with best of the 4R-Nutrient-Stewardship [15] of fertilizer application and other agronomic practices such as right planting time, population, pattern and proper management biotic and abiotic stresses would optimize intensive sustainable climate-smart production (**Figure 2**). Such modifications to the ISFM concept will encourage increased sustainable production not only of cassava, but other crops too

and consequently feed the bulging world's population effectively.

This review has elucidated the advantage of fertilizers to cassava storage root yield and starch content. However, this advantage is only valuable to most smallholder farmers if markets are available to absorb their produce. To improve cassava's status as a cash crop through starch production: extensive evaluations of

*The components leading to intensive sustainable climate-smart production of cassava. Mgt – Management.* 

*A modified ISFM concept from [8] to achieve intensive sustainable climate-smart production.*

*DOI: http://dx.doi.org/10.5772/intechopen.97366*

response of each variety are insightful.

#### **Table 2.**

*The advantage of applying fertilizers on the starch content of storage roots of cassava.*

*Improvement in Cassava Yield per Area by Fertilizer Application DOI: http://dx.doi.org/10.5772/intechopen.97366*

*Cassava - Biology, Production, and Use*

storage roots.

**Banding**

**Fertigation**

*under application.*

*- Variety not indicated from the source.*

**3. Fertilizer influence on starch qualities**

NPK– adhering to Justus von Liebig Law of the Minimum - a limit in one nutrient

The importance of cassava storage roots as food and animal feed cannot be understated, especially among smallholder farmers. To enhance cassava's ability as an industrial cash crop, focus needs to shift to starch in its storage roots. However, there are many starch characteristics that are considered by various industries such as particle size, solubility, gelatinisation, purity etc. These require extensive study. Cassava starch is being used in beer making, ethanol production [24, 25], pharmaceuticals, paper manufacturing, textile etc. [26]. In addition, it has been tested as a substitute for agar material in micropropagation in tissue culture studies with minimum success [27]. Therefore, as the usage of starch from cassava storage roots expands, factors that influence the starch suitability for various industries are of importance. Factors that influence crop growth and development like climate, soil fertility, abiotic and biotic incidences and the variety [28] are vital. Those that impact postharvest and processing are important too [29]. **Table 2** illustrates the effect of fertilizers and soil amendments on the characteristics of starch of cassava

The response of cassava storage-root-starch varies under fertilizer application (**Table 2**). Some varieties increase storage root starch content while others decline, for example, four of the varieties tested by [32] had a decline in starch content within the storage roots. Despite these observations from [32], other studies have indicated an increase of 9–14% starch content in the storage roots on fertilizer application to cassava (**Table 2**). Remarkably, fertigating medium (Kampolombo) and long duration (Nalumino) cassava varieties improved starch content of storage

**against 0–0-0 NPK (kg ha−1)**

**Source**

**Variety N-P-K (kg ha−1) %Fertilizer advantage on starch content** 

TMS 30572 22.5–22.5-22.5 10.7 [30] TMS 419 22.5–22.5-22.5 10.2 [30] — 60–60-150 5.6 [31] M98/0040 24–24-24 9.6 [32] 98/0002 24–24-24 −1.3 [32] 99/6012 24–24-24 −1.7 [32] 92b/0061 24–24-24 −6.8 [32] 82/00058 24–24-24 −7.5 [32]

Mweru 155–23-155 9.7 [14] Kampolombo 76–8-76 14.0 [14] Nalumino 54–5-54 12.5 [14]

*A negative in the % fertilizer advantage indicates that starch content under no fertilizer application was higher than* 

*The advantage of applying fertilizers on the starch content of storage roots of cassava.*

limits the uptake of the others and hence decline in growth and yield [23].

**116**

**Table 2.**

roots than banding in other varieties (**Table 2**). It is important to note that these varieties were not tested under banding, neither were the other varieties tested under fertigation. Therefore, a direct comparison of the two fertilizer application methods (fertigation and banding) is weak, even though the observations on response of each variety are insightful.

#### **4. Future of intensive sustainable climate-smart production of cassava**

Climate is changing, and human population is growing. Cassava is one of the crops that have been observed to be tolerant to the vagaries of climate, such as increase in atmospheric temperature, CO2 [33] and drought [34]. Furthermore, as stated in the introduction, its demand both as food and raw material for industries is increasing, to reduce the yield gap and meet the growing demand, its yield per area must improve. However, that intensive production must be sustainable and climate smart. To make it a climate-smart and a cash crop for smallholder farmers, intensive sustainable production approaches are required. Tweaking the [8]'s ISFM **Figure 1** with best of the 4R-Nutrient-Stewardship [15] of fertilizer application and other agronomic practices such as right planting time, population, pattern and proper management biotic and abiotic stresses would optimize intensive sustainable climate-smart production (**Figure 2**). Such modifications to the ISFM concept will encourage increased sustainable production not only of cassava, but other crops too and consequently feed the bulging world's population effectively.

#### **Figure 2.**

*The components leading to intensive sustainable climate-smart production of cassava. Mgt – Management. A modified ISFM concept from [8] to achieve intensive sustainable climate-smart production.*

#### **5. Conclusion**

This review has elucidated the advantage of fertilizers to cassava storage root yield and starch content. However, this advantage is only valuable to most smallholder farmers if markets are available to absorb their produce. To improve cassava's status as a cash crop through starch production: extensive evaluations of fertilizers effect on the characteristics of starch of storage roots of best performing improved varieties is required. There should be a concerted effort to match the high root yields obtained from fertilized cassava fields with the starch requirements of industries. This should be the next major frontier of research if cassavaproducing-smallholder farmers' financial earnings is to increase exponentially.

#### **Acknowledgements**

The authors thank the Centre for Fertilization and Plant Nutrition (CFPN) and the International Potash Institute (IPI) for funding the publication, and the International Institute of Tropical Agriculture (IITA) for offering a conducive environment for development and writing of this review.

#### **Author details**

John Okoth Omondi1 \* and Uri Yermiyahu<sup>2</sup>


\*Address all correspondence to: okoth05@gmail.com; jo.omondi@cgiar.org

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**119**

*Improvement in Cassava Yield per Area by Fertilizer Application*

et al. Integrated soil fertility

2010;39(1):17-24.

management: Operational definition and consequences for implementation and dissemination. Outlook Agric.

[9] Vanlauwe B, Wendt J, Giller KE, Corbeels M, Gerard B, Nolte C. A fourth

principle is required to define Conservation Agriculture in sub-Saharan Africa: The appropriate use of fertilizer to enhance crop productivity. F Crop Res [Internet]. 2014;155:10-3. Available from: http://dx.doi. org/10.1016/j.fcr.2013.10.002

[10] Sommer R, Thierfelder C, Tittonell P, Hove L, Mureithi J,

principle is required to define

from: http://dx.doi.org/10.1016/j.

https://doi.org/10.1016/j. heliyon.2018.e00759

[12] Fermont AM, Tittonell PA,

Baguma Y, Ntawuruhunga P, Giller KE. Towards understanding factors that govern fertilizer response in cassava: lessons from East Africa. Nutr Cycl Agroecosystems [Internet]. 2009 Apr 29 [cited 2014 Apr 18];86(1):133-51. Available from: http://link.springer. com/10.1007/s10705-009-9278-3

[13] Fermont AM, Obiero HM, A VAPJ, Baguma Y, Okwuosa E. Improved cassava varieties increase the risk of soil nutrient mining: an ex-ante analysis for

fcr.2014.05.012

Mkomwa S. Fertilizer use should not be a fourth principle to define conservation agriculture. Response to the opinion paper of Vanlauwe et al. (2014) 'A fourth

conservation agriculture in sub-Saharan Africa: The appropriate use of fe. F Crop Res [Internet]. 2014;169:145-8. Available

[11] Biratu GK, Elias E, Ntawuruhunga P, Sileshi GW. Cassava response to the integrated use of manure and NPK fertilizer in Zambia. Heliyon [Internet]. 2018;4(8):e00759. Available from:

*DOI: http://dx.doi.org/10.5772/intechopen.97366*

[1] Lebot V. Cassava: origin and history. In: Atherton J, Rees A, editors. Tropical root and tuber crops: cassava, sweet potato, yams and aroids. 1st ed. CABI;

[2] Balagopalan C. Cassava in Food, Feed and Industry, in Cassava: biology, production and utilization. In: Hillocks RJ, Thresh JM, Bellotti AC, editors. Cassava: Biology, Production and Utilization. eds. CAB; 2002.

[3] FAO. FAOSTAT. FAOSTAT. 2017. p.

[4] Hillocks RJ. Addressing the yield gap in Sub-Saharan Africa. Outlook Agric.

[5] Crawford E, Kelly V, Jayne T., Howard J. Input use and market development in Sub-Saharan Africa: an overview. Food Policy [Internet]. 2003 Aug [cited 2014 Dec 15];28(4):277-92. Available from: http://linkinghub.

[6] Tittonell P, Giller KE. When yield gaps are poverty traps: The paradigm of ecological intensification in African smallholder agriculture. F Crop Res [Internet]. 2013;143:76-90. Available from: http://dx.doi.org/10.1016/j.

[7] Giller KE, Tittonell P, Rufino MC, van Wijk MT, Zingore S, Mapfumo P, et

[8] Vanlauwe B, Bationo A, Chianu J, Giller KE, Merckx R, Mokwunye U,

al. Communicating complexity: Integrated assessment of trade-offs concerning soil fertility management within African farming systems to support innovation and development. Agric Syst [Internet]. 2011;104(2):191- 203. Available from: http://dx.doi. org/10.1016/j.agsy.2010.07.002

elsevier.com/retrieve/pii/ S0306919203000599

fcr.2012.10.007

http://www.fao.org/faostat/

**References**

2008. p. 3-12.

p. 301-18.

en/#data/QC.

2014;43(2):85-90.

*Improvement in Cassava Yield per Area by Fertilizer Application DOI: http://dx.doi.org/10.5772/intechopen.97366*

#### **References**

*Cassava - Biology, Production, and Use*

**Acknowledgements**

fertilizers effect on the characteristics of starch of storage roots of best performing improved varieties is required. There should be a concerted effort to match the high root yields obtained from fertilized cassava fields with the starch requirements of industries. This should be the next major frontier of research if cassavaproducing-smallholder farmers' financial earnings is to increase exponentially.

The authors thank the Centre for Fertilization and Plant Nutrition (CFPN) and the International Potash Institute (IPI) for funding the publication, and the International Institute of Tropical Agriculture (IITA) for offering a conducive

environment for development and writing of this review.

**118**

**Author details**

John Okoth Omondi1

\* and Uri Yermiyahu<sup>2</sup>

2 Agricultural Research Organization, The Volcani Centre, Israel

\*Address all correspondence to: okoth05@gmail.com; jo.omondi@cgiar.org

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

1 International Institute of Tropical Agriculture, Malawi

provided the original work is properly cited.

[1] Lebot V. Cassava: origin and history. In: Atherton J, Rees A, editors. Tropical root and tuber crops: cassava, sweet potato, yams and aroids. 1st ed. CABI; 2008. p. 3-12.

[2] Balagopalan C. Cassava in Food, Feed and Industry, in Cassava: biology, production and utilization. In: Hillocks RJ, Thresh JM, Bellotti AC, editors. Cassava: Biology, Production and Utilization. eds. CAB; 2002. p. 301-18.

[3] FAO. FAOSTAT. FAOSTAT. 2017. p. http://www.fao.org/faostat/ en/#data/QC.

[4] Hillocks RJ. Addressing the yield gap in Sub-Saharan Africa. Outlook Agric. 2014;43(2):85-90.

[5] Crawford E, Kelly V, Jayne T., Howard J. Input use and market development in Sub-Saharan Africa: an overview. Food Policy [Internet]. 2003 Aug [cited 2014 Dec 15];28(4):277-92. Available from: http://linkinghub. elsevier.com/retrieve/pii/ S0306919203000599

[6] Tittonell P, Giller KE. When yield gaps are poverty traps: The paradigm of ecological intensification in African smallholder agriculture. F Crop Res [Internet]. 2013;143:76-90. Available from: http://dx.doi.org/10.1016/j. fcr.2012.10.007

[7] Giller KE, Tittonell P, Rufino MC, van Wijk MT, Zingore S, Mapfumo P, et al. Communicating complexity: Integrated assessment of trade-offs concerning soil fertility management within African farming systems to support innovation and development. Agric Syst [Internet]. 2011;104(2):191- 203. Available from: http://dx.doi. org/10.1016/j.agsy.2010.07.002

[8] Vanlauwe B, Bationo A, Chianu J, Giller KE, Merckx R, Mokwunye U,

et al. Integrated soil fertility management: Operational definition and consequences for implementation and dissemination. Outlook Agric. 2010;39(1):17-24.

[9] Vanlauwe B, Wendt J, Giller KE, Corbeels M, Gerard B, Nolte C. A fourth principle is required to define Conservation Agriculture in sub-Saharan Africa: The appropriate use of fertilizer to enhance crop productivity. F Crop Res [Internet]. 2014;155:10-3. Available from: http://dx.doi. org/10.1016/j.fcr.2013.10.002

[10] Sommer R, Thierfelder C, Tittonell P, Hove L, Mureithi J, Mkomwa S. Fertilizer use should not be a fourth principle to define conservation agriculture. Response to the opinion paper of Vanlauwe et al. (2014) 'A fourth principle is required to define conservation agriculture in sub-Saharan Africa: The appropriate use of fe. F Crop Res [Internet]. 2014;169:145-8. Available from: http://dx.doi.org/10.1016/j. fcr.2014.05.012

[11] Biratu GK, Elias E, Ntawuruhunga P, Sileshi GW. Cassava response to the integrated use of manure and NPK fertilizer in Zambia. Heliyon [Internet]. 2018;4(8):e00759. Available from: https://doi.org/10.1016/j. heliyon.2018.e00759

[12] Fermont AM, Tittonell PA, Baguma Y, Ntawuruhunga P, Giller KE. Towards understanding factors that govern fertilizer response in cassava: lessons from East Africa. Nutr Cycl Agroecosystems [Internet]. 2009 Apr 29 [cited 2014 Apr 18];86(1):133-51. Available from: http://link.springer. com/10.1007/s10705-009-9278-3

[13] Fermont AM, Obiero HM, A VAPJ, Baguma Y, Okwuosa E. Improved cassava varieties increase the risk of soil nutrient mining: an ex-ante analysis for

western Kenya and Uganda. In: Bationo A, editor. Advances in integrated soil fertility management in Sub-Saharan Africa: Challenges and opportunities. eds. Springer; 2007. p. 511-9.

[14] Omondi JO, Lazarovitch N, Rachmilevitch S, Boahen S, Ntawuruhunga P, Sokolowski E, et al. Nutrient use efficiency and harvest index of cassava decline as fertigation solution concentration increases. J Plant Nutr Soil Sci. 2018;181(5):644-54.

[15] Johnston AM, Bruulsema TW. 4R Nutrient Stewardship for Improved Nutrient Use Efficiency. Procedia Eng [Internet]. 2014;83:365-70. Available from: http://dx.doi.org/10.1016/j. proeng.2014.09.029

[16] Biratu GK, Elias E, Ntawuruhunga P, Nhamo N. Effect of chicken manure application on cassava biomass and root yields in two agro-ecologies of Zambia. Agric. 2018;8(4).

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[18] Fermont AM, van Asten PJA, Tittonell P, van Wijk MT, Giller KE. Closing the cassava yield gap: An analysis from smallholder farms in East Africa. F Crop Res [Internet]. 2009 Apr [cited 2014 Apr 9];112(1):24-36. Available from: http://linkinghub. elsevier.com/retrieve/pii/ S0378429009000343

[19] Susan John K, Venugopal VK, Saraswathi P. Yield maximization in cassava through a systematic approach in fertilizer use. Commun Soil Sci Plant Anal [Internet]. 2007;38(5-6):779-94.

Available from: http://dx.doi. org/10.1080/00103620701220783

[20] Kaweewong J, Tawornpruek S, Yampracha S, Yost R, Kongton S, Kongkeaw T. Cassava nitrogen requirements in Thailand and crop simulation model predictions. Soil Sci [Internet]. 2013 May [cited 2014 May 7];178(5):248-55. Available from: http:// content.wkhealth.com/linkback/openurl ?sid=WKPTLP:landingpage &an=00010694-201305000-00005

[21] Nguyen H, Schoenau JJ, Nguyen D, Van Rees K, Boehm M. Effects of long-term nitrogen, phosphorus, and potassium fertilization on cassava yield and plant nutrient composition in North Vietnam. J Plant Nutr [Internet]. 2002 Mar 25 [cited 2014 May 6];25(3):425-42. Available from: http://www.tandfonline. com/doi/abs/10.1081/PLN-120003374

[22] El-Sharkawy MA, Cadavid LF. Genetic variation within cassava germplasm in response to potassium. Exp Agric. 2000;36(3):323-34.

[23] Ebelhar S, Chesworth W, Paris Q. Law of the Minimum. In: Chesworth W, editor. Encyclopedia of Soil Science Encyclopedia of Earth Sciences Series. eds. Dordrecht: Springer; 2008.

[24] Nguyen TLT, Gheewala SH, Garivait S. Full chain energy analysis of fuel ethanol from cassava in Thailand. Environ Sci Technol. 2007;41(11):4135-42.

[25] Adeleye TM, Kareem SO, Bankole MO, Atanda O, Adeogun AI. Ethanol production from cassava starch by protoplast fusants of Wickerhamomyces anomalus and Galactomyces candidum . Egypt J Basic Appl Sci [Internet]. 2020;7(1):67-81. Available from: https://doi.org/10.1080/ 2314808X.2020.1746884

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micropropagation for sustainable seed systems in developing countries. Acta

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[29] Adejumo O, Okoruwa V, Abass A, Salman K. Post-harvest technology change in cassava processing : A choice paradigm. Sci African [Internet]. 2020;7:e00276. Available from: https:// doi.org/10.1016/j.sciaf.2020.e00276

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[31] Cuvaca IB, Eash NS, Zivanovic S, Lambert DM, Walker F, Rustrick B. Cassava (*Manihot esculenta* Crantz) tuber quality as measured by starch and cyanide (HCN) affected by nitrogen, phosphorus, and potassium fertilizer rates. J Agric Sci [Internet]. 2015;7(6). Available from: http://www.ccsenet.org/

journal/index.php/jas/article/

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[15] Johnston AM, Bruulsema TW. 4R Nutrient Stewardship for Improved Nutrient Use Efficiency. Procedia Eng [Internet]. 2014;83:365-70. Available from: http://dx.doi.org/10.1016/j.

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tandfonline.com/doi/abs/10.1080/0365

[18] Fermont AM, van Asten PJA, Tittonell P, van Wijk MT, Giller KE. Closing the cassava yield gap: An analysis from smallholder farms in East Africa. F Crop Res [Internet]. 2009 Apr

[cited 2014 Apr 9];112(1):24-36. Available from: http://linkinghub.

[19] Susan John K, Venugopal VK, Saraswathi P. Yield maximization in cassava through a systematic approach in fertilizer use. Commun Soil Sci Plant Anal [Internet]. 2007;38(5-6):779-94.

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[22] El-Sharkawy MA, Cadavid LF. Genetic variation within cassava germplasm in response to potassium. Exp Agric. 2000;36(3):323-34.

[23] Ebelhar S, Chesworth W, Paris Q. Law of the Minimum. In: Chesworth W, editor. Encyclopedia of Soil Science Encyclopedia of Earth Sciences Series. eds. Dordrecht: Springer; 2008.

[24] Nguyen TLT, Gheewala SH,

[25] Adeleye TM, Kareem SO,

by protoplast fusants of

2314808X.2020.1746884

Bankole MO, Atanda O, Adeogun AI. Ethanol production from cassava starch

Wickerhamomyces anomalus and Galactomyces candidum . Egypt J Basic Appl Sci [Internet]. 2020;7(1):67-81. Available from: https://doi.org/10.1080/

[26] Breuninger WF, Piyachomkwan K, Sriroth K. Tapioca/Cassava Starch:

Environ Sci Technol. 2007;41(11):4135-42.

Garivait S. Full chain energy analysis of fuel ethanol from cassava in Thailand.

[21] Nguyen H, Schoenau JJ, Nguyen D, Van Rees K, Boehm M. Effects of long-term nitrogen, phosphorus, and potassium fertilization on cassava yield and plant nutrient composition in North Vietnam. J Plant Nutr [Internet]. 2002 Mar 25 [cited 2014 May 6];25(3):425-42. Available from: http://www.tandfonline. com/doi/abs/10.1081/PLN-120003374

[20] Kaweewong J, Tawornpruek S, Yampracha S, Yost R, Kongton S, Kongkeaw T. Cassava nitrogen requirements in Thailand and crop simulation model predictions. Soil Sci [Internet]. 2013 May [cited 2014 May 7];178(5):248-55. Available from: http:// content.wkhealth.com/linkback/openurl

**120**

[27] Acedo VZ, Hinay NG, Binongo MM, Antona JQ. High-value application of cassava starch in root crop micropropagation for sustainable seed systems in developing countries. Acta Hortic. 2017;1179:293-8.

[28] Defloor I, Dehing I, Delcour JA. Physico-chemical properties of Cassava Starch. Starch/Starke. 1998;50(2-3):58-64.

[29] Adejumo O, Okoruwa V, Abass A, Salman K. Post-harvest technology change in cassava processing : A choice paradigm. Sci African [Internet]. 2020;7:e00276. Available from: https:// doi.org/10.1016/j.sciaf.2020.e00276

[30] Rasaq SA, Shittu TA, Fadimu GJ, Abass AB, Omoniyi O. Effect of cassava variety, fertiliser type and dosage on the physicochemical, functional and pasting properties of high-quality cassava flour (HQCF). Qual Assur Saf Crop Foods. 2020;12(1):18-27.

[31] Cuvaca IB, Eash NS, Zivanovic S, Lambert DM, Walker F, Rustrick B. Cassava (*Manihot esculenta* Crantz) tuber quality as measured by starch and cyanide (HCN) affected by nitrogen, phosphorus, and potassium fertilizer rates. J Agric Sci [Internet]. 2015;7(6). Available from: http://www.ccsenet.org/ journal/index.php/jas/article/ view/46254

[32] Shittu TA, Dixon A, Awonorin SO, Sanni LO, Maziya-Dixon B. Bread from composite cassava-wheat flour. II: Effect of cassava genotype and nitrogen fertilizer on bread quality. Food Res Int. 2008;41(6):569-78.

[33] Cruz JL, Alves AAC, Lecain DR, Ellis DD, Morgan JA. Elevated CO2

concentrations alleviate the inhibitory effect of drought on physiology and growth of cassava plants. Sci Hortic (Amsterdam) [Internet]. 2016;210:122- 9. Available from: http://dx.doi. org/10.1016/j.scienta.2016.07.012

[34] Orek C, Gruissem W, Ferguson M, Vanderschuren H. Morphophysiological and molecular evaluation of drought tolerance in cassava (*Manihot esculenta* Crantz). F Crop Res [Internet]. 2020;255:107861. Available from: https://doi.org/10.1016/j. fcr.2020.107861

Section 4

Cassava Post-Harvest

Processing

**123**

Section 4
