Benoit Galaup - Phosphorus Scarcity in SSA - 14062016

Literature Review

Phosphorus scarcity in Sub-Saharan Africa’s smallholder farms: causal elements and promising solutions to address the lack

of a critical resource.

Benoit Galaup

Registration number: 1578556

ID of study programme: H 066 500

Summer 2016

Version 14/06/2016

Agroecology, Cultural Ecology and Ethnoecology - The interdisciplinary discourse in natural resource

management (933.329)

Lecturer: Christoph Schunko

GALAUP//Phosphorus scarcity in SSA

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TABLE OF CONTENTS

1. Abstract ........................................................................................................................................... 3

2. Introduction .................................................................................................................................... 4

3. Methods .......................................................................................................................................... 5

4. Results and discussions .................................................................................................................... 7

4.1. The causes of phosphorus scarcity in Sub-Saharan African food systems ....................................... 7

4.1.1. The Global picture: Phosphorus supply and demand. ............................................................. 7

4.1.2. Phosphorus scarcity in SSA smallholder farms: a consequence of many factors. ..................... 9

4.2. Promising solutions for a future sustainable management of phosphorus in Sub-Saharan Africa . 12

4.2.1. Increasing phosphorus efficiency in agriculture .................................................................... 12

4.2.2. Increasing supply from renewable resources ........................................................................ 14

5. Conclusion ..................................................................................................................................... 15

6. References ..................................................................................................................................... 16

7. List of illustrations ......................................................................................................................... 17

8. Appendixes .................................................................................................................................... 18


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1. ABSTRACT

Phosphorus, a nutrient required by plants to ensure their growth and development, is an essential resource for yield establishment and food production. Today, modern agriculture depends on declining phosphate rock reserves to meet the growing demand for food and ensure food security in the world.

In addition, it is well known that the availability of food is unequal around the globe and especially in Sub-Saharan Africa where 40% of the population cannot secure adequate food on a day-to-day basis. This continent is the witness of an ironic situation: Africa holds the biggest world phosphate rock reserves while having widespread phosphorus deficiencies in its soils.

While other developing countries such as China and India have already known a green revolution that enabled them to significantly improve the performance of their agriculture, nutrient deficiencies in agricultural soils in Sub-Saharan Africa are the leading factor causing the fall of agricultural productivity. The low and declining yields prevent the population from leading a healthy and productive life, making them more susceptible to diseases such as HIV-AIDS, malaria, or even tuberculosis.

Based on the exploration of the most striking and recent literature in the field, this literature review firstly aims at explaining the causes phosphorus scarcity in Sub-Saharan African smallholder farms, with a focus on the accountability of the global management of the resource. The physical causes inherent to the African continent and the socio-economic causes explaining such a situation will also be detailed. In a second part, promising solutions to overcome this scarcity in a sustainable and local manner are suggested. Particularly those enabling an increased efficiency of P resources in agriculture and an increased supply from renewable resources will be discussed.

Key words: “phosphorus”, “phosphate rock”, “peak”, “Sub-Saharan Africa”, “smallholder farm”, “mineral fertilizers”, “ scarcity”, “recycling”, “sanitation”


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2. INTRODUCTION

Phosphorus is essential for life due to its implication in many biological functions at the cell scale. Phosphates are constituents of DNA, RNA, ATP, and the phospholipids, which form all cell membranes. Thus, phosphorus, being one of the main nutrients required for plant growth and development, has always been and still is an essential resource for yield establishment and food production (Cordell 2008).

Historically, agriculture relied on natural levels of phosphorus in the soils and the addition of locally available organic matter such as manure and human excreta. But in the 19th century, the use of local organic matter was substituted by phosphate mined rock and guano from distant sources. As a consequence, modern agriculture is heavily dependent on phosphate fertilizers from mined rock to replace the phosphorus taken away by harvested crops (Cordell et al. 2009).

Contrary to other areas that benefited from a green revolution, Africa shows widespread phosphorus deficiencies in its soils and 75% of Africa’s soil are phosphorus deficient (Cordell et al. 2009; Sanchez 2002). Consequently, it is widely acknowledged that negative nutrient imbalances in Sub Saharan Africa (SSA) is the leading factor explaining food insecurity and poverty in this region (Chianu & Mairura 2012). Indeed, agriculture is the economic sector that engages 70% of all Africans (Sanchez 2002). As a consequence, with 40% of Africans today that cannot secure adequate food on a day-to-day basis, this continent is often mentioned as being one of the most food insecure regions in the world.

This literature review aims at (1) summarizing the causes of phosphorus scarcity in small holder farms in Sub-Saharan Africa and at (2) suggesting potential solutions that would enable to tackle the phosphorus scarcity in a local and sustainable way. In order to answer those research questions, a literature research was done and a review of the recent and striking literature in the field had been conducted. Fourteen impactful scientific papers were selected and analysed.

In the following pages, the methodology used to conduct the literature research and to select relevant scientific articles will firstly be described. After that, the factors causing the chronic phosphorus scarcity in Sub Saharan Africa’s food and farming systems will be summarized, including the role of the global phosphorus management and its impact on smallholder farmers in Sub-Sahara Africa. In a second part, promising sustainable and local solutions to tackle such a scarcity will be suggested. Those consist of increasing phosphorus efficiency in SSA’s agriculture and increasing supply from renewable resources.


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3. METHODS

This literature review focuses on summarizing research outcomes related to the causes of phosphorus scarcity in small holder farms in Sub-Saharan Africa and to the potential, sustainable and local solutions that would enable the overcoming of this scarcity. The goal in the following pages is to integrate and generalize findings related to this topic, and to present them as facts (neutral position). The audience addressed in this document are the supervisor of this course and the scholars within the field. A central approach has been favoured, meaning that only the most important and influential papers in the field of study have been selected.

To explore the causes and the potential solutions to address phosphorus scarcity in smallholder farms in Sub-Saharan Africa, a literature research was carried out and a review of some selected scientific articles in the field has been conducted. In order to state the most recent data in the field of study, articles that have been published before 2000 were excluded of the literature research. Only the most influential papers, with a number of citations higher than 15 have been selected. By defining this criteria of selection, the aim was to narrow down the number of scientific papers to the ones that have been the most relevant in this field of research, allowing then to present the most striking information in this literature review. Some of those papers contain relevant information extracted from other scientific papers. Due to that, and with the aim of getting the information at its original source, some of those papers were also used in this literature review. Other literature was excluded from the literature research because it was not accessible through BOKU university’s agreements.

A combination of key words such as “Phosphorus”, “phosphate”, “phosphate rock”, “mineral fertilizer”, “food security”, “Sub-Saharan Africa”, “Africa” (see details in Table 1) have been typed in the “Web of Science” and “Google scholar” to find relevant literature. Those key words have been combined with the aim of finding as few results as possible. When the number of citations referenced in the data base was higher than 15, a first screening of the tittle has been done to assess the relevance of the scientific papers for this study. Then, a reading of the abstract and of the introduction further allowed to evaluate the pertinence of the literature for this study.

Some terms regularly used through this literature review need to be defined in order to prevent the reader from being confused in the following pages. First of all, here is called Sub-Saharan Africa the area of the African continent which lies south of the Sahara Desert, below the African transition zone (see Figure 2). Geographically, the demarcation line is the southern edge of the Sahara Desert. This ecological demarcation is also clearly visible in Figure 1. A list of Sub-Saharan nations is also available in Appendix 1. The Figure 2 also provides a clear geographical delimitation of the five African sub-regions: North Africa, West Africa, Central Africa, East Africa and Southern Africa. Madagascar has not been taken in consideration in this study.

The key words used, the data bases, the date of the research, the papers selected for this literature review and the number of citation indicated in the data base used are summarized in the Table 1 below.


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Table 1: List of papers judged relevant this study, including the date of research, the data base, the key words used and the number of citations referenced in the data base used.

Date Data base Key words Paper selected Number of citation

23/04/2016 Google scholar “Phosphorus” AND “global food security”

(Cordell et al. 2009) 1805

23/04/2016 Google scholar “Phosphorus scarcity” AND “sustainability” AND “global governance”

(Cordell 2008) 16

14/05/2016 Google scholar “phosphorus” AND “Sub-Saharan Africa”

(VANLAUWE & GILLER 2006)

234

14/05/2016 Google scholar “phosphorus” AND “Sub-Saharan Africa”

(Sanchez 2002) 742

14/05/2016 Google scholar “Mineral fertilizers” AND “farm*” AND “Sub-Saharan Africa”

(Chianu & Mairura 2012)

17

14/05/2016 Web of Science

“phosphorus” AND “imbalance” AND “world”

(MacDonald et al. 2011)

128


“Phosphate rock reserve” AND “Africa” (Cooper et al. 2011)

45


“phosphate rock” AND “demand” AND “Africa”

(Van Vuuren et al. 2010)

121

25/05/2016 Google scholar Retrieved from (Cordell et al. 2009) (Smaling et al. 2006)

27

25/05/2016 Google scholar “peak” AND “production” AND “phosphorus”

(Cordell & White 2011)

114

25/05/2016 Google scholar “replenish*” AND “soil fertility” AND “Africa”

(Mafongoya et al. 2006)

116

25/05/2016 Google scholar “replenish*” AND “soil fertility” AND “Africa”

(Okalebo et al. 2006)

68

25/05/2016 Google scholar “phosphorus” AND “sanitation” AND “Africa”

(Cordell et al. 2011) 269

25/05/2016 Google scholar Retrieved from (Cordell et al. 2011) (Dagerskog 2010) 16

Figure 1: The African continent and its ecological delimitations http://www.newworldencyclopedia.org/entry/Sub-Saharan_Africa

Figure 2: The five sub-regions of the African continent http://www.lahistoriaconmapas.com/atlas/blank-map/blank-map-of-africa-regions.htm


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4. RESULTS AND DISCUSSIONS

4.1. The causes of phosphorus scarcity in Sub-Saharan African food systems 4.1.1. The Global picture: Phosphorus supply and demand.

4.1.1.1. The supply: An African continent with great phosphate rock reserves.

Today, phosphorus fertilisers are mainly coming from phosphate rock mining and 90% of global demand of phosphorus is for food production, around 148 million tonnes of phosphate rock per year (Cordell et al. 2009). But, as emphasized by (Cordell 2008), phosphate rock is a declining resource and we have approximately 50-100 years left of current known reserves, with a forecast peak in production around 2030. However, this number should be considered with caution because the date at which this peak will occur is object to discussion in the literature. For example, (Van Vuuren et al. 2010) claim that it should not occur in the short and medium term. The prediction of such a peak may be variating because of many factors. First of all, it is acknowledged that there are uncertainties in remaining phosphate rock reserves’ estimations, and while the future global demand for phosphorus is likely to increase, its extent in the long run is not made clear in the literature because population growth, trends in changing diets, demand for biofuel production and future demand from P deficient countries cannot be precisely assessed (Cordell & White 2011; Van Vuuren et al. 2010; Cooper et al. 2011). While the occurrence of this peak is hardy predictable, it is however made clear that, even if the worldwide phosphorus scarcity is not eminent, the quantity produced, the quality and the accessibility of the remaining resources are likely to decrease in the future.

In addition to the finiteness of this resource, the current spatial distribution of phosphate rock reserves is heterogeneous and they are only concentrated in some countries in the world, as illustrated in Figure 3. For example, China , which holds 6% of the total phosphate rock reserves has imposed a 135% export tariff on phosphate, effectively preventing any exports in order to secure its own supply (Cordell et al. 2009). The US has approximately 25 years left of domestic reserves. Resources in Africa are mainly found in Morocco, which together with Western Sahara represent no less than 85% of the world’s reserves (Cordell & White 2011). Other significant reserves in Africa are located in Tunisia, South Africa, Egypt and Algeria (Van Vuuren et al. 2010; Smaling et al. 2006). However, Table 3 and Table 2 show that the major part of African phosphate rock production is not aimed at fertilizing African agricultural P deficient soils but is rather redirected towards the international fertilizer market. In short, the African continent is home to the world’s largest phosphate rock reserve, but most of the production is cheaply exported to other continents, where it is processed into fertilizers that are costly for SSA’s smallholder farmers (Chianu & Mairura 2012). Appendix 2 shows the major phosphorus flows in the production and trade of phosphorus commodities in Africa.


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4.1.1.2. A mitigated demand for fertilisers from SSA smallholder farmers

Following half a century of generous applications of phosphorus fertilizers, agricultural soils in Europe and North America are now very rich in phosphorus and, as a consequence, farmers in these regions only need to replace phosphorus taken away by harvested crops, explaining then the stabilizing or even decreasing demand of phosphorus (MacDonald et al. 2011; Cordell et al. 2009). It is also noticeable that exaggerated applications of phosphorus fertilizers in mostly developed countries led to environmental negative impacts such as eutrophication and the apparition of dead zones around the globe (Cordell & White 2011; Cordell 2008; MacDonald et al. 2011). However, in developing and emerging countries such as China and India, the demand for phosphorus fertilizers is forecast to increase by 50-100% along with the growth of the population and the change of alimentary customs toward a more meat and dairy products-based alimentation, which requires more phosphorus (Cordell et al. 2009).

In SSA, the demand for fertilizer is projected to slightly increase of 1,9% per year along with the expansion of urban consumer demand for meat, milk and eggs (Smaling et al. 2006). This huge gap between the actual need for phosphorus in SSA smallholder farms and the expressed demand is partly due the high fertilizer prices that most of the SSA’s smallholders cannot afford (Chianu & Mairura 2012). In other words, there is a great need for phosphorus in SSA agricultural soils, but most of the farmers have no access to it, partly due to the high and fluctuating prices of phosphate rock and phosphate fertilizers, higher storage and transport costs, which all together lead to a cost of P fertilizers for African farmers up to 6 times higher than the cost for European farmers (Cordell et al. 2009). For instance, in 2007-2008, the price of phosphate rocks and fertilizers showed an increase of 800% in a period of 14 months (See Figure 4) due to the inability

Table 2: Fertilizer export Volumes in Africa (2002, tons) from (Smaling et al. 2006)

Table 3: Fertilizer production in Africa (2002,tons) from (Smaling et al. 2006)

Figure 3: Remaining global phosphate rock reserves estimated in 2010 (Cordell & White 2011)


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of the global phosphate rock production to satisfy the growing global demand (Cooper et al. 2011). Along with other factors, those unstable prices discourage smallholder farmers in SSA from purchasing fertilizers, leading then to chronic low application rates in SSA soils (Smaling et al. 2006; VANLAUWE & GILLER 2006).

4.1.2. Phosphorus scarcity in SSA smallholder farms: a consequence of many factors.

4.1.2.1. The lack of phosphorus in SSA soils: physical causes.

A poor and declining soil fertility in SSA is generally well recognized as being the main constraint to production in smallholder farming in the literature reviewed (VANLAUWE & GILLER 2006; Chianu & Mairura 2012). See Figure 5. Those deficiencies, both directly and indirectly, also impact the environment in Africa. The low fertilizer application rates negatively affect biodiversity, carbon sequestration capacity, and organic matter production, which lead to soil erosion (Smaling et al. 2006; Chianu & Mairura 2012). Problems of weeds, pests, diseases and parasitic plants are also causing low per capita food production in Africa (Sanchez 2002; Chianu & Mairura 2012). The widespread phosphorus deficiency in itself is also claimed to be a limiting factor for food production in this area. For instance, (Cordell et al. 2009) argue that 75% of agricultural soils in SSA are P-deficient.

Figure 4: Phosphate rock price 2006-2011, showing a spike in 2007/08 and a gradual increase in 2010 (Cordell & White 2011).

Figure 5: Deceasing of maize yields in Trans Nzoia district (1977–2002) due to declining soil fertility, Kenya, East Africa (One bag weighs 90 kg of sun-dried maize grain) (Okalebo et al. 2006).


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Those nutrient deficiencies in SSA can firstly be explained by physical characteristics inherent to the African continent. Since Africa is the world most ancient land mass, original soil phosphorus reserves have been depleted along with the development of an agriculture that favoured the use of new available fertile land, instead of the sustainable management of exploited agricultural areas (Smaling et al. 2006). Here, the author refers to an agricultural practice that was widespread in Africa and that is still used in some of its countries: the so called shifting cultivation (Okalebo et al. 2006).

Another important physical factor explaining the phosphorus deficiency in SSA soils is the pedological characteristic of most of the agricultural land of the continent. Indeed, agricultural soils in SSA are often very acidic, as a consequence, most of the critical nutrients required for agricultural production, including phosphorus, are not available for the roots of plants. Since the acidity in most of agricultural soils in SSA is ranging from 5 to 6, the bio-availability of phosphate nutrients in the soils are quite low (Sanchez 2002; Smaling et al. 2006; Chianu & Mairura 2012; Mafongoya et al. 2006). See Figure 6.

4.1.2.2. Human and social factors explaining phosphorus deficiencies in SSA.

In SSA, the main factor reported to explain the lack of phosphorus in the agricultural system is the low application rate of phosphate fertilizers by smallholder farmers (Smaling et al. 2006; Chianu & Mairura 2012). It is claimed that fertilizers are rather used by the commercial and the wealthiest farmers, or mainly on cash crops (VANLAUWE & GILLER 2006). (Cordell et al. 2009) reports that the African continent shows the world’s lowest fertiliser application rates with an average of 9-23kg/ha. Coherently, (Chianu & Mairura 2012) present data of fertilizer consumption in the five sub-regions of Africa that range from 0,9 kg/ha/year in Central Africa to 16,7 kg/ha/year in Southern Africa. In comparison, (Okalebo et al. 2006) report that an average of 80 kg/ha of fertilizers are yearly applied in the rest of the world.

Due to this lack of fertilisation, smallholder farmers often count on native soil phosphorus content to meet the requirement of crops. This strategy, often defined as “nutrient mining” in the literature, leads to an impoverishment on soil phosphorus reserves since the nutrients taken up by crops are removed from the field at the harvest, and never replaced by other organic or mineral phosphate inputs. In relation with those farming practices, soil erosion also plays a role in soil nutrient depletions (Smaling et al. 2006). The lack of soil fertility replenishment is then causing the fall of yields in SSA (Chianu & Mairura 2012; Cordell 2008; Okalebo et al. 2006).See Figure 5. For instance, (Sanchez 2002) mention a yearly average depletion of 2,5kg of phosphorus per hectare over the last 30 years in 37 African countries. (Chianu & Mairura 2012) provide average nutrient depletions in 2000 for selected countries in SSA that show similar results. For example, they calculated a yearly depletion of 2kg of phosphorus per hectare in Benin, Cameroon, Mali,

Figure 6: the relation between the pH.and the availability of nutrients for the roots of plants.


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and in Senegal, 4kg in Ghana and Nigeria, 5kg in Tanzania, 7kg in Ethiopia, 10 kg in Malawi and 11 kg of phosphorus per hectare mined in Malawi in 2000. However, Zimbabwe showed a yearly positive nutrient balance (2kg/ha) and this balance was neutral in Botswana (0kg/ha).

The occurrence of those neutral and positive balances would also counteract the argument according to which phosphorus, and more generally, nutrient balances in SSA are always negative. (VANLAUWE & GILLER 2006) explain that smallholder farmers in SSA are not always mining agricultural soils and even some fields show very positive balances. Those positive balances are the result of management differences, partly because smallholders usually prioritize lands close to the homestead. Coherently, (MacDonald et al. 2011) found that small positive and negative phosphorus balances (0 ± 2 kg/ha/year) are the most common throughout Africa. Based on their calculations, they drew a map showing areas in Africa with P surpluses (P inputs are higher than crop P uptake) and P deficient areas (P inputs are smaller that crop P uptake), see Figure 7. Thus, P balances in SSA agricultural soils can range from slightly negative to small positive, and are not affecting the entire continent but are rather depending on the location and the agricultural practices in smallholder farming.

However, along with the high cost of phosphate fertilizers at the farm gate and inappropriate agricultural practices, it is worth to mention that other factors can explain the very low application rates in Africa that have been pointed out in the literature. Among them, the insufficient knowledge in the use of fertilizers among farmers, the lack of policy and institutional support, the weak fertilizer markets, the removal of farm input subsidies, the farmers’ lack of access to credit and farm inputs, the low quality and availability of fertilizers, the inappropriate fertilizer packaging sizes, the low profitability of fertilizer use, the inappropriate fertilizer recommendations, the adulteration practices in several African countries, the differences in crop response to fertilizers, the low food crop prices, the low farmer literacy and poverty, the gender inequity, the deteriorating soil science capacity, the weak agricultural extensions, and climate change have been reported (VANLAUWE & GILLER 2006; Chianu & Mairura 2012; Mafongoya et al. 2006; Cordell et al. 2009; Sanchez 2002; Smaling et al. 2006; Okalebo et al. 2006).

Figure 7: P surpluses (in colour) and P deficiencies (in grey) based on the magnitude of fertilizer or manure P applied relative to crop P use in different locations in Africa (MacDonald et al. 2011).


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4.2. Promising solutions for a future sustainable management of phosphorus in Sub-Saharan Africa

In this section will be enumerated some promising solutions that could enable the transition to a more sustainable and local management of phosphorus nutrients in smallholder farms in SSA. Those solutions can be organized around two concepts: the increase of phosphorus efficiencies in SSA agriculture and the increase supply from renewable sources.

4.2.1. Increasing phosphorus efficiency in agriculture

4.2.1.1. Applying local phosphate rocks in P deficient fields

The African continent, which holds more than 85% of world’s phosphate rock reserves, also contains local deposits of phosphate rock throughout its territory (Chianu & Mairura 2012). Those phosphate rocks can be used to replenish soil phosphorus fertility in SSA (Smaling et al. 2006; Chianu & Mairura 2012; Okalebo et al. 2006) and (Sanchez 2002) emphasizes that the low acidity of most SSA soils facilitates the dissolution of indigenous phosphate rocks which provide phosphorus to crops for several years. Although this seems to be a promising approach to replenish soil phosphorus content in P deficient areas of SSA, some limitations for its widespread adoption are also reported. Firstly, phosphate rocks are rarely accessible for smallholders. As an illustration, (Sanchez 2002) points out that the availability of phosphate rock is often limited by insufficient market development. Secondly, the low phosphorus content and the low reactivity of those rocks prevent them from being directly applied. For instance, (VANLAUWE & GILLER 2006) report that some phosphate rocks have both phosphorus content below 10% and a low solubility under non-acid soil conditions. They also stress that they often have high content of heavy metal, which can be toxic for plants, livestock and humans. Moreover, the bioavailability of some nutrients can be reduced under large application of phosphorus (Smaling et al. 2006). Although direct phosphate rock application in fields might be a promising way to replenish soil P content in SSA, their application to maintain agricultural productivity in the long run is threatened because reserves are finite and not renewable. But until they are depleted, (Chianu & Mairura 2012) call for the use of those local rocks thanks to the implementation of techniques increasing the solubility of less reactive rocks and the development of a better distribution and marketing of phosphate rock in areas with widespread P deficiencies. They also argue that Africa must develop its own fertilizer industry, which would enable the processing and the use of local phosphate rock within the continent.

4.2.1.2. Correcting soil acidity with local agro-minerals

As aforementioned, the high acidity of most soils in SSA often reduce the availability of nutrients to the crops. Hence, another approach aiming at overcoming the low fertility consists of correcting the acidity of those soils by applying agro-minerals (Smaling et al. 2006). For instance, limestone, dolomite and gypsum are found in local deposits throughout Africa and can effectively correct pH. However, those are often exploited for industrial purposes, excluding fertilizer production (Chianu & Mairura 2012).


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4.2.1.3. Increasing mineral fertilizers application rates, efficiency and profitability

It is widely acknowledged that application rates of mineral fertilizers must increase to overcome soil fertility challenges in SSA (VANLAUWE & GILLER 2006; Sanchez 2002; Smaling et al. 2006). However, many factors prevent smallholder farmers from using those fertilizers. Among them, the high and increasing fertilizer prices, the weak access of farmer to credits, the farmer’s insufficient knowledge of fertilizer use, the weak fertilizer markets, the low profitability of fertilizer use, the inappropriate packaging sizes, the inadequate policies and institutional support, and the gender inequity have already been mentioned.

To overcome this situation, (Chianu & Mairura 2012) suggest the return to subsidies for subsistence farmers, the duty-free importation of fertilizers and agro-minerals, and the implementation of other tax incentives that would incite farmers to make use of fertilizers more often. They also call for the creation of public–private partnership for addressing the problems posed by weak markets and institutional constraints to widespread fertilizer adoption.

Policies, also, are critical for addressing soil fertility challenges in SSA (VANLAUWE & GILLER 2006). They could continuously monitor the use of fertilizers by embedding all related aspects, including their impact on agricultural productivity and on the environment (Smaling et al. 2006). (Sanchez 2002) argues that they could help to reduce the gap between the world market’s price of mineral fertilizers and their prices for smallholders in SSA. Further, such policies can foster the implementation of economic incentives and reverse the reduction in soil science capacity (Chianu & Mairura 2012). The most important is the will of African governments to act (Sanchez 2002).

Moreover, farmers’ training, and knowledge sharing are reported as being requirements to incite farmers’ fertilizer use and to implement a productive and sustainable agriculture in SSA. For instance, farmers’ participatory approaches, such as experiential learning and farmer field schools, help to test and widespread knowledge in farmer communities (Chianu & Mairura 2012; VANLAUWE & GILLER 2006; Sanchez 2002). Sharing this knowledge should be done in the frame of the integrated soil fertility management, which is “a set of agricultural practices adapted to local conditions to maximize the efficiency of nutrient and water use and improve agricultural productivity” (IFDC 2015) and enables smallholder farmers to increase the profitability of the use of fertilizers (Chianu & Mairura 2012). Some agricultural practices claimed to be successful for soil fertility replenishment in SSA consist of the combination of organic and mineral fertilisers (VANLAUWE & GILLER 2006), agroforestry (Smaling et al. 2006; Mafongoya et al. 2006; Sanchez 2002), the combination of grain legumes and cereals through rotation or intercropping (Chianu & Mairura 2012; Mafongoya et al. 2006; Okalebo et al. 2006), or the addition of soil inoculants such as mycorrhizal fungi (Cordell et al. 2009). Moreover, precision agriculture techniques, such as the small and located application of fertilizers, referred as micro-dosing, are efficient and profitable for smallholders in SSA (Cordell et al. 2009; Chianu & Mairura 2012).


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4.2.2. Increasing supply from renewable resources

Another promising way to overcome the phosphorus scarcity in the farming system in SSA consists of reusing locally available resources such as human or animal excreta, manure, food waste, wastewater from cities and other (such as algae, ash, bone meal)(Cordell et al. 2009). In the literature reviewed, the great potential of human excreta to replenish soil phosphorus content is well recognized (Cordell et al. 2009; Cordell et al. 2011; Van Vuuren et al. 2010). (Dagerskog 2010) estimated human fertilizer production for the ten countries of West Africa. An average person in these countries annually excretes 2,8 kg of nitrogen, 0,45 kg of phosphorus and 1,3 kg of potassium through urine and faeces. See Figure 8. And particularly urine has an interesting potential because it is relatively easy and cheap to collect and represents a substantial and neglected source of plant nutrients. Furthermore, if not mixed with faeces, urine is sterile and easily storable (Cordell et al. 2011; Dagerskog 2010).

In general, the majority of nitrogen and potassium are excreted with the urine while phosphorus is more evenly distributed between urine and faeces (Dagerskog 2010). Although urine only contains between 0.02% and 0.07% of phosphorus against an average of 0,52% of phosphorus in the faeces, they are excreted in larger quantities (Cordell et al. 2011). See Figure 8. Because of their high content in phosphorus and organic material, faeces are also considered as a suitable base fertilizer when correctly treated (Dagerskog 2010).

The ecological sanitation, which is “one form of sustainable decentralised sanitation and refers to the containment, sanitization and recycling of human excreta to arable land” (Cordell et al. 2011) has a great potential for soil fertility replenishment in SSA. For instance, (Dagerskog 2010) reports two successful examples of ecological sanitation in Niger and Burkina Faso that allowed the improvement of local nutrient management, food security and health in smallholder farms. They showed that urine and faeces from a family of ten person contain nutrients equivalent to approximately 100 kg of chemical fertilizer, locally worth 80 US$. In those two sanitation projects, farmers were trained on how to produce liquid and solid fertilizers from urine and faeces, thanks to the correct use of urinals and composting or dry latrines.

But those solutions can present some limits. Faeces need to be sanitized before being used as solid fertilizer and urine can contain significant concentrations of sodium (3,1g/L), which may be toxic for plants. It is also reported that the application of those solutions require both a change of mindset as human excreta are often seen as dirty and the support from researchers and local stakeholders to spread the knowledge among farmer communities.

Figure 8: The average annual fertilizer production per person in West Africa (Dagerskog 2010).


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5. CONCLUSION

Phosphorus scarcity in smallholder farms greatly contributes to food insecurity in Sub-Saharan Africa. Widespread soil nutrient deficiencies lead to low and declining yields and food production in this region. As a result, 40% of the population cannot secure a supply of food on a day to day basis, making them more susceptible to diseases and preventing them from leading healthy and productive lives.

This literature review firstly aimed at explaining the causes of phosphorus scarcity in smallholder farms in Sub-Saharan Africa and, secondly, suggesting potential solutions that could address the scarcity in a sustainable and local manner. A literature research was conducted, and influential, relevant and recent scientific articles have been selected and analysed to fulfil the aims described above.

Our modern agriculture is highly dependent on phosphate fertilizers processed from phosphate rocks to maintain its productivity and feed the growing population. Soon or later, those reserves will be depleted and supply of phosphate fertilizers coming from those rocks will have to be replaced by phosphorus from other sources. Until the depletion of those reserves, the African continent remains the home of more than 85% of world’s phosphate reserves.

But in spite of those great sources of phosphate nutrients, there is chronic soil phosphorus deficiencies in SSA that can be explained by low application rates of fertilizers by smallholder farmers. In that sense, the continent is victim of the international liberalist market because the phosphate fertilizers processed from phosphate rocks mined in Africa are unaffordable and inaccessible for SSA smallholders. Due to this phenomena, application rates of fertilizers are forecast to remain insufficient compared to the actual needs in the future. Although the high and fluctuating prices of phosphate fertilizers can explain the low use of fertilizers by smallholders, other political, economic, agronomic and social factors play a role in this equation.

Soil P fertility in SSA needs to be replenished in order to counteract the growing soil nutrient deficiencies causing the fall of yields and agricultural productivity. Promising solutions have already been reported and implemented in SSA. Those can be divided in two categories. Firstly, an increased phosphorus efficiency in SSA’s agriculture can be implemented by applying indigenous phosphate rocks. Furthermore, the soil acidity should be corrected with the help of locally available agro-minerals and political, economic and social measures should be implemented in order to attain an improved use, efficiency and profitability of fertilizers for smallholders in SSA. Secondly, techniques allowing an improved use of phosphorus from renewable resources at a local scale should be widespread in SSA’s smallholder communities. Here, we discuss successful examples from Niger and Burkina Faso to emphasize the potential of ecological sanitation to replenish soil fertility in SSA’s subsistence farming.


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6. REFERENCES

Chianu, J. & Mairura, F., 2012. Mineral fertilizers in the farming systems of sub-Saharan Africa. A review. Agronomy for sustainable development.

Cooper, J. et al., 2011. The future distribution and production of global phosphate rock reserves. Resources, Conservation and Recycling, 57, pp.78–86.

Cordell, D., 2008. The story of Phosphorus: Missing global governance of a critical resource, Preliminary findings from 2 years of doctoral research. … . Paper prepared for SENSE Earth System Governance …, pp.1–25.

Cordell, D. et al., 2011. Towards global phosphorus security: A systems framework for phosphorus recovery and reuse options. Chemosphere, 84(6), pp.747–758.

Cordell, D., Drangert, J.O. & White, S., 2009. The story of phosphorus: Global food security and food for thought. Global Environmental Change, 19(2), pp.292–305.

Cordell, D. & White, S., 2011. Peak Phosphorus: Clarifying the Key Issues of a Vigorous Debate about Long-Term Phosphorus Security. Sustainability, 3(12), pp.2027–2049.

Dagerskog, L., 2010. Opening minds and closing loops: Productive sanitation initiatives in Burkina Faso and Niger.

IFDC, 2015. Integrated Soil Fertility Management | IFDC on WordPress.com. Available at: https://ifdc.org/integrated-soil-fertility-management/ [Accessed June 5, 2016].

MacDonald, G.K. et al., 2011. Agronomic phosphorus imbalances across the world’s croplands. Proceedings of the National Academy of Sciences of the United States of America, 108(7), pp.3086–91.

Mafongoya, P.L. et al., 2006. Appropriate technologies to replenish soil fertility in southern Africa. Nutrient Cycling in Agroecosystems, 76(2-3), pp.137–151.

Okalebo, J.R. et al., 2006. Available technologies to replenish soil fertility in East Africa. Nutrient Cycling in Agroecosystems, 76(2-3), pp.153–170.

Sanchez, P. a, 2002. Soil fertility and hunger in Africa. Science (New York, N.Y.), 295(5562), pp.2019–2020.

Smaling, E., Moctar, T. & de Ridder, N., 2006. Fertilizer Use and the Environment in Africa : Friends or Foes ? Background Paper Prepared for the African Fertilizer Summit.

VANLAUWE, B. & GILLER, K., 2006. Popular myths around soil fertility management in sub-Saharan Africa. Agriculture, Ecosystems & Environment, 116(1-2), pp.34–46.

Van Vuuren, D.P., Bouwman, A.F. & Beusen, A.H.W., 2010. Phosphorus demand for the 1970–2100 period: A scenario analysis of resource depletion. Global Environmental Change, 20(3), pp.428–439.


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7. LIST OF ILLUSTRATIONS

List of figures:

Figure 1: The African continent and its ecological delimitations http://www.newworldencyclopedia.org/entry/Sub-Saharan_Africa ________________________________________________________________________________ 6 Figure 2: The five sub-regions of the African continent http://www.lahistoriaconmapas.com/atlas/blank-map/blank-map-of-africa-regions.htm _____________________________________________________________ 6 Figure 3: Remaining global phosphate rock reserves estimated in 2010 (Cordell & White 2011) ________________ 8 Figure 4: Phosphate rock price 2006-2011, showing a spike in 2007/08 and a gradual increase in 2010 (Cordell & White 2011). __________________________________________________________________________________ 9 Figure 5: Deceasing of maize yields in Trans Nzoia district (1977–2002) due to declining soil fertility, Kenya, East Africa (One bag weighs 90 kg of sun-dried maize grain) (Okalebo et al. 2006). ______________________________ 9 Figure 6: the relation between the pH.and the availability of nutrients for the roots of plants. ________________ 10 Figure 7: P surpluses (in colour) and P deficiencies (in grey) based on the magnitude of fertilizer or manure P applied relative to crop P use in different locations in Africa (MacDonald et al. 2011). _____________________________ 11 Figure 8: The average annual fertilizer production per person in West Africa (Dagerskog 2010). ______________ 14

List of tables:

Table 1: List of papers judged relevant this study, including the date of research, the data base, the key words used and the number of citations referenced in the data base used. .................................................................................... 6 Table 3: Fertilizer export Volumes in Africa (2002, tons) from (Smaling et al. 2006) .................................................... 8 Table 2: Fertilizer production in Africa (2002,tons) from (Smaling et al. 2006) ............................................................. 8 List of appendices:

Appendix 1: Nations of sub-Saharan Africa ................................................................................................................. 18 Appendix 2: Major phosphorus flows in the production and trade of phosphorus commodities in Africa, including phosphate rock, phosphorus fertilizers and food commodities. For details, see (Cordell et al. 2009). ........................ 19


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8. APPENDIXES Appendix 1: Nations of sub-Saharan Africa

There are 42 countries located on the sub-Saharan African mainland, in addition to six island nations (Madagascar, Seychelles, Comoros, Cape Verde and São Tomé and Príncipe). According to this classification scheme, the countries of sub-Saharan Africa are:

Central Africa

Democratic Republic of Congo Republic of Congo Central African Republic Rwanda Burundi

East Africa

Sudan Kenya Tanzania Uganda Djibouti Eritrea Ethiopia Somalia (including Somaliland)

Southern Africa

Angola Botswana Lesotho Malawi Mozambique Namibia South Africa Swaziland Zambia Zimbabwe

West Africa

Benin Burkina Faso Cameroon Chad Côte d'Ivoire Equatorial Guinea Gabon The Gambia Ghana Guinea Guinea-Bissau Liberia Mali Mauritania Niger Nigeria Senegal Sierra Leone Togo

African island nations

Cape Verde (West Africa) Comoros (Southern Africa) Madagascar (Southern Africa) Mauritius (Southern Africa) São Tomé and Príncipe (West Africa) Seychelles (East Africa)

Territories, possessions, départements

Mayotte (France) Réunion (France)


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Appendix 2: Major phosphorus flows in the production and trade of phosphorus commodities in Africa, including phosphate rock, phosphorus fertilizers and food commodities. For details, see (Cordell et al. 2009).

Benoit Galaup - Phosphorus Scarcity in SSA - 14062016

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