OBJECTIVES OF THE GIFS STRATEGY IN AFRICA
Background
Integrated soil fertility management can be defined as: “the application of soil fertility management practices adapted to local conditions and knowledge that maximise the efficient use of fertilisers and organic resources to improve crop productivity”, which necessarily includes the management of fertilisers and organic resources in an appropriate manner in combination with improved germplasm (Vanlauwe et al, 2010).
Integrated Soil Fertility Management (ISFM) is not characterised by a single practice, but the combination of these approaches, technologies available to maintain soil quality that allow us to increase crop productivity (Sanginga and Woomer, 2009). ISFM is a response to land management because soil degradation and nutrient depletion pose a serious problem for the lives and food security of people, especially in rural areas. (Sanginga and Woomer, 2009).
Among the ISFM technology packages, according to Smaling et al (1997), simple introduction of improved varieties and moderate use of fertilisers can increase crop yields but the agronomic efficiency of fertilisers remains relatively low. On the other hand, combining fertilisers with locally available organic matter enriches even crop residues, improves the agronomic efficiency of fertilisers and soil quality, and increases crop yields.
Other factors that can influence ISFM include farmers’ income, market development and the promotion of good agricultural policy that aims to promote the availability of inputs to farmers (Sanginga and Woomer, 2009).
Local conditions will influence the ISFM, as there is great variability in soil fertility even within a family farm. These variabilities range from regional to continental levels. This has consequences for fertiliser application and agronomic efficiency, i.e. response to fertiliser will depend on soil type. (Pypers, 2010; Sanginga and Woomer, 2009). In poor soils, there will be a low response to fertilisers and therefore agronomic efficiency will be low, hence the management is to combine chemical fertilisers with organic matter. The provision of organic matter in mechanisms to increase agronomic efficiency, particularly the increase in water and nutrient holding capacity and good timing of nutrient supply to crop demand, but also improves plant health through increased soil biodiversity and carbon sequestration (Sanginga and Woomer, 2009).
Fertilisers as an entry point for GIFS
The recommendation of the African Fertilizer Summit in 2006 suggested increasing fertilizer use from 8kg to 50kg by 2015. This recommendation reinforces the role of fertilisers as a key entry point for increasing soil productivity and improving food security for people in sub-Saharan Africa. The impact of the success of this target programme, however, will depend on the agronomic efficiency of these fertilizers. This efficiency varies across regions, countries, farmers and fields (Prudencio, 1993; Manlay et al, 2002 and Pypers, 2010). In soils that respond to fertilisers, the limitation due to nutrient deficiency can be solved in a sustainable way by applying fertilisers (Alley and Vanlauwe, 2009). In unresponsive soils, only fertilisers without the use of fertilisers is not sufficient to increase agronomic efficiency and yield (Zingore et al, 2007, Vanlauwe et al, 2006). Since the 1960s, several rounds of debate have been triggered on the role of fertilisers in tropical Africa.
The following table shows the different ideological currents that have led to the principle of integrated soil fertility management in tropical Africa.
Table 1: Changing ideas in tropical soil management and their effect on agricultural
management (Vanlauwe et al, 2006).
| Période | Idéologie/paradigme | Rôle des engrais | Rôle de la matière organique | expériences |
| 1960 et 1970 | 1er courant sur l’utilisation des intrants externes | L’utilisation des engrais seul améliorera le rendement et de façon durable | Joue un rôle minimal | Pas de succès à cause du manque des infrastructures, de politique et de système de culture adapté, etc. |
| 1980 | Courant sur l’utilisation des intrants organiques | Joue un rôle minimal | C’est la principale source des nutriments | La production de la matière organique exige des grandes surfaces et un travail laborieux, d’où l’adoption était limitée |
| 1990 | Courant de Sanchez | Il joue un rôle essentiel pour suppléer à la déficience en nutriment | C’est le point d’entré car servant comme fonction de base pour la libération des nutriments | Difficulté d’accéder à la MO limite l’adoption |
| 2000 | Gestion Intégré de la Fertilité des sols | L’engrais est le point d’entrer pour accroître le rendement et son apport exige la MO | L’accès doit tenir compte des dimensions sociales et économiques |
Based on this picture, ISFM was derived from Sanchez’s ideology of using organic matter to increase soil biological activity and optimise nutrient cycling by minimising external inputs and maximising their use efficiency. For Sanchez, the combination of fertilisers and organic matter was essential but the focus should be on organic matter as the point of entry (Alley and Vanlauwe, 2009; Sanginga and Woomer, 2009). But his ideology will come up against the problem of but its ideology will come up against the problem of the availability of organic matter by farmers who have to create farms for its production. Hence the latter current of ISFM which believes that fertilisers are the entry points for increasing yields and organic matter should be applied according to its availability (Alley and Vanlauwe, 2009).
The other advantage of fertilisers is that they not only improve yield but also the crop residues (biomass) that is used as organic fertiliser by the previous crop (Bationo et al, 2004). According to Vanlauwe et al (2006), and Giller et al, (1998a), phosphorus inputs to legumes double crop biomass and increase the agronomic efficiency of fertilisers in cereals. Similarly, the strategic application of nitrogen improves the performance of many cropping systems and nitrogen fixation. According to Giller (2001) and Sanginga et al (2001b), the application of small amounts of nitrogen in legumes stimulates root growth leading to better nodulation and increasing the soil that can be returned to cereals in the rotation. Fractionation and strategic application of nitrogen especially during the critical period in maize improves crop yield and agronomic efficiency of fertilisers.
Importance of agronomic efficiency in the ISFM strategy
Background
Agronomic efficiency (AE) is a ratio that describes the increase in yield per unit of nutrient applied. The focus of ISFM is the beneficial increase in yield by applying fertilisers in two ways. Firstly, by providing organic matter in combination with mineral fertilisers, EI is increased and in many cases contributes to the addition of nutrients. AE is also improved by good nutrient retention and release which is linked to the ability of organic matter to improve the physicochemical and biological properties of the soil (Sanginga and Woomer, 2009).
The amount of nutrients taken up by the crop in relation to fertiliser inputs is often low. Only 10-15% of the phosphorus and 10-20% of the nitrogen applied in the form of fertiliser is taken up by the crop (Vanlauwe et al, 2001). Inefficient use of fertilisers thus discourages investment by poor farmers (African Fertiliser Summit, 2006). Several factors will influence this low nutrient uptake. Crops require nutrients in different amounts and proportions. Looking at Liebig’s law of minima, deficiency of one nutrient leads to a nutrient leads to reduced growth of the plant and thus reduces its ability to use other mineral elements well.
Many fertilisers are composed only of major elements, so the soil reserve is depleted of non-limiting elements in agricultural intensification and thus limits the efficient use of those fertilisers that do not contain them (Giller et al, 1998, Vanlauwe et al, 2002). However, by applying Liebscher’s law of optimum, which suggests that the deficiency of one nutrient influences the efficiency of uptake of other nutrients at non-limiting levels (See De Wit cited by Sanginga and Woomer, 2009). In this view, crop stresses are limited in their ability to efficiently use nutrient inputs. Water stress leads to poor development of the root system. Therefore, the nutrient composition of the fertiliser will be the second factor that will influence AE.
Several other factors will influence AE including soil compaction, pH, aluminium toxicity, diseases and pests and ineffective weed management. Finally, inefficient input management leads to nutrient loss and inefficient crop utilisation. Fertilisers must be applied at the right time when crops need them and under the right environmental conditions (Adesina, 1996).
Mechanisms affecting agronomic efficiency Crop yields and EI are affected by several factors including the efficient uptake and use of nutrients and the level of soil organic matter resulting from biomass production and nutrient recycling. Efficient uptake is defined as the capacity by which a nutrient is taken up by the crop, i.e. the amount of nutrient taken up per amount of nutrient applied. Efficient use (internal efficiency) is defined as the ability of the crop to convert the assimilated nutrient into yield, i.e. the yield obtained per amount of nutrient applied. The effectiveness of biomass production is the amount of biomass produced to give a yield. These three elements are the essential components of AE (Sanginga and Woomer, 2009).
Several factors will influence these three elements, including the timing and location of fertilisers, good water use, correction of soil acidity, control of pests and diseases, use of germplasm that is resilient to low nutrient concentrations, good management of crop residues and better integration of agriculture and livestock (Bouis et al, 1999; Sanginga and Woomer, 2009).
Each of these three elements can be improved by the use of a variety of technologies.
Each of these three elements can be improved by specific practices and technologies. For example, efficient uptake can be increased by localised and timed applications of fertilisers (strategic nitrogen application, or ‘top dressing’). Internal efficiency can be improved by the use of resilient germplasm, i.e. germplasm with low nutrient requirements, and finally effective biomass production can be improved by the use and incorporation of promising, high biomass-yielding legumes into the cropping system. (Bouis et al, 1999, Sanginga and Woomer, 2009; Giller, 2001; Pypers, 2010).
COMPONENTS OF IFSM
The ISFM strategy is based on 4 main components including
- The use of improved germplasm
- Use of mineral fertilisers
- Organic matter management
- Adaptations to local conditions
In addition to these four main components, farmer knowledge is essential for technology adoption. (Pypers, 2010; Vanlauwe et al, 2010). But we will talk about the second and third component.
Mineral fertilizer management in ISFM in Africa
The application of fertilisers to the soil by small-scale farmers is essential for agricultural production in Africa. A diverse range of soils are found in Africa, from young alluvial and volcanic soils to ancient ferrasols (FAO cited by Sanginga and Woomer, 2009).
Some soils are extremely degraded or poor and have low fertiliser retention potential making application difficult (Sanginga and Woomer, 2009). Nitrogen, potassium, magnesium and calcium are easily leached out under conditions of excess rainfall. Many soils also have a high capacity to immobilise
Many soils also have a high capacity to immobilise phosphorus, which makes phosphorus less available to the plant even when fertilisers are applied. In addition, a diverse range of African regions have highly acidic soils combined with aluminium toxicity (Wambeke, 1998; Pypers et al, 2005; Sanginga and Woomer,
2009).
The use of fertilisers is essential to overcome nutrient constraints and is a central element in the practice of integrated soil fertility management to improve agricultural production (Sanginga and Woomer, 2009).
Of the potential arable land in sub-Saharan Africa, only 165 million hectares are cultivated. Approximately 1.38 million tonnes of fertiliser were applied per year to arable land in sub-Saharan Africa in 2002, an average of 8.3kg per hectare. This represents only 2% of global consumption (Morris et al, 2007).
But more than 55% of countries consume less than 5kg per hectare and only 5 countries consume around 25kg per hectare.
Availability, quality and use of mineral fertilisers in Sub-Saharan Africa
Plant nutrient requirements depend on the environment and change with time and the need to intensify agricultural production. Poor storage of fertilisers results in loss of quality and discourages agricultural investment in fertilisers. In addition, there is a lack of fertiliser manufacturing industries, which results in insufficient information on the quantities to be applied (Sanginga and Woomer, 2009).
A major problem with the effective use of fertilisers and ISFM practices in Africa has been the inability to have appropriate recommendations among smallholder farmers. The latest recommendations on fertiliser use have focused on economic crops such as maize, tea and cotton and have not taken into account the resources available to farmers (Sanginga and Woomer, 2009). There is therefore a need to formulate recommendations on the use of ISFM practices that take into account their problems. Firstly, a proper diagnosis of soil and plant constraints must be made to propose appropriate fertiliser types and mixtures (Bationo et al, 2006).
To achieve this objective, it is necessary that research institutions and scientists seek solutions to soil problems taking into account the limited resources of farmers.
In many cases, cereal production in sub-Saharan Africa does not exceed 0.5 tonnes per hectare, while the potential yield of 6 to 8 tonnes per hectare is achieved in station trials and by some large producers. This yield gap can be attributed to several biological constraints including varieties, weeds, diseases and pests, water and nutrient deficiencies and socio-economic constraints including costs and access to input credits, etc. (Bationo et al, 2006).
Organic matter management in ISFM in Africa
General
Organic resources are abundant in Africa because they are derived from both crops and nature, but there is an underutilization of these resources in the context of integrated soil fertility management. Indeed, the availability of organic resources as food and fibre and the requirement for collection and processing is laborious. Plant residues and animal manure decompose rapidly in hot and humid climates, causing nutrient release (Muyers et al, 1994). Therefore, the application of organic matter must be carefully considered.
According to Vanlauwe et al, 2006, in many cases most of the available organic resources have a low nutrient concentration. This limits the use of organic matter as a main source of nutrients.
In most farming communities, the demand for animal manure is always higher than the supply from the farm. Farms that do have manure have serious problems collecting and transporting it (Lekasi et al, 2003). This difficulty does not predispose to the use of organic matter as an input but rather requires that it be used in a cost-effective and efficient manner. ISFM technology packages will aim to increase crop production through improved nutrient AE. This approach necessarily involves the use of available organic resources and appropriate agronomic practices adapted to local conditions.
Quality of organic matter
Although the use of organic matter as an input is not new to tropical agriculture, early work on organic matter decomposition and management was contributed by Swift (Sanginga and Woomer, 2009).
This work established conceptual frameworks for understanding the decomposition of various organic materials that involve soil microorganisms in order to provide a medium with favourable physical, chemical characteristics for plant development. These interactions regulate the mineralisation and release of nutrients during the decomposition and transformation of soil organic matter (Woomer et al, 1994).
Studies on the nutrients contained in several organic resources available to farmers have been carried out by TSBF-CIAT and other research organisations and a database has been compiled that includes information on the quality of organic resources, macronutrients present, lignin, polyphenols, contained in leaves, stems, roots, detritus of about 300 species of plants used in tropical agroecosystems.
Importance of organic matter combined with chemical fertiliser.
Despite their low and variable nutrient content, organic matter plays an important role in managing soil fertility and improving soil structure. Organic matter holds a lot of nutrients, which is important in sandy soils that hold very little (Schoel, 1998; FAO and IFA, 2003).
Due to these properties, organic fertilisers are the basis for obtaining the best effects from the use of mineral fertilisers (IPNM). The combination of organic and mineral fertilisers creates the best production conditions because organic matter improves soil properties while mineral fertilisers provide plants with the nutrients they need and increase agronomic efficiency (FAO and IFA, 2003; Sanginga and Woomer, 2009).
Other reasons for this combination include the deficiency of essential crop nutrients in common mineral fertilisers while organic resources contain them (Sanginga and Woomer, 2009). To overcome this problem, Kenyans have developed a fertilizer, MAVUNO, which is a combination of NPK and micronutrients such as Ca, Mg, S etc. This fertilizer is more effective than NPK and is more efficient than organic fertilizer. This fertilizer is more effective than NPK because NPK in degraded soils does not respond sufficiently due to micronutrient deficiency (Pypers, 2010 and Pypers et al, 2010).
Organic matter alone is often not sufficient because it is not available in large quantities to ensure the level of production expected by the farmer (FAO and IFA, 2003; Vanlauwe and Sanginga, 2005; Cadisch and Giller, 1997). Available phosphorus increases with applying organic matter. Organic matter will also interact with soil acidity and aluminium toxicity (Pypers et al, 2005). The application of fertilisers increases biomass and crop residues when applied in an efficient way. Vanlauwe et al (2006) showed that in the absence of phosphate fertilisers, improved varieties in western Kenya accumulated higher biomass than local varieties and the application of phosphorus doubled the yield in soybean. Hence the combination of organic matter increases nutrient use efficiency but the effectiveness of this strategy is the proper management of fertiliser by applying it at the right place and time.
Forms of organic matter used in tropical agriculture
1°) Crop residues
Crop residues are unharvested parts of the crop and often available to smallholders as a source of organic matter. Crop residues often have relatively low nutrient content and high lignin content (Sanginga and Woomer, 2009).
In the cereal-based cropping system, the mass of crop residues is mainly culms and stems, while in legumes it consists of leaves. The amount of crop residues available at harvest is inversely proportional to the harvest index. The harvest index is the main objective of improvement as it gives some importance to crop residues. A high proportion of crop residue does not necessarily give an advantage to a farmer who does not have organic matter on his farm. A difficulty in managing crop residues when using mulch is that it can carry insect germs (Sanginga and Woomer, 2009). To hope to produce a large quantity of residues, promising leguminous varieties that provide large quantities of biomass can be used (Pypers, 2010).
2°) Green manures
These are green, non-leguminous plants (or parts of plants) that are buried in the soil and constitute sources of nutrients for the crops that are grown (Schoël,1998; Hudgen, 2000). This practice is based on two mechanisms. The legumes that provide the nutrients are actively symbiotic and accumulate large amounts of nitrogen fixed by the process of biological nitrogen fixation. When used, they add nutrients to the soil and improve soil properties for previous crops (Sanginga and Woomer, 2009). The beneficial characteristics of green manures arethe beneficial characteristics of green manures are weed suppression, reduced pest and disease pressure, maintenance of soil organic matter and improved soil porosity (Eilitta et al, 2004; Schoël, 1998).
3°) manure
Manure is composed of animal excrement, usually mixed with leaves or straw. The quantity and quality of the dung depends on the animal feed (Schoël,
1998). Manure provides organic matter to the soil and allows for nutrient recycling.
Many farming systems use manure as a source of organic matter. The use of manure as a source of fertilizer was introduced by settlers throughout Africa. For example, in Zimbabwe farmers used 40t per hectare of manure in maize in 1920, an amount that was reduced when mineral fertiliser became available. In Kenya, the recommendations on fertiliser use set 5t per hectare of manure (Sanginga and Woomer, 2009).
CENTRAL ROLE OF LEGUMES IN GIFS
Central role
In the wake of high fertiliser prices, legumes are a strong entry point into the African approach to integrated soil fertility management. Until recently, the increased use of chemical fertilisers was seen as the best solution for restoring the fertility of degraded soils to improve food security, as highlighted by the African Heads of State Summit in 2006. In the recent past, fertiliser prices have skyrocketed by up to 130% as a result of rising oil prices (Sanginga and Woomer, 2009).
Simply stated, fertilisation practices that were profitable in 2004 are less so in 2008 due to the increase in fertiliser prices. Considering that all the recommendations could be justified in 2004, only the MBILI technology package had performed well in 2008 due to the convenience of the fertiliser price. The MBILI technology package relies on biological nitrogen fixation by legumes and provides advantages to maize as the latter combined with legumes is at the higher stage (WOOMER et al, 1997).
Manure and crop residues provided by legumes benefit soils through their biological nitrogen fixation and thus reduce the cost of expensive fertilisers (Sanginga and Woomer, 2009 and Pypers, 2010). A smallholder farmer who incorporates legumes into his field has an easy time improving his family’s welfare and achieving a standard of living (Lavelle, 1996). Legumes have a wide tolerance to variability they have a wide range of climatic characteristics and adaptability to different soil types but are often susceptible to diseases and pests. Symbiotic nitrogen fixation allows legumes to satisfy their nitrogen requirement from the atmosphere rather than from the soil, and in case of deficiency, effective nodulation can correct it from the rhizobium within (Ojiem, 2006).
Smallholder cereal farmers have two main options for increasing the yield of their legumes by growing them either in association or in rotation with cereals. Maize in association is a common practice in Africa. However, this combination of crops does not yield better in most cases because of the poor performance of the legume varieties used (Giller, 2001). One of the solutions offered by integrated soil fertility management is to diversify legume varieties by creating and using legume varieties that produce quantitatively and qualitatively better than those used by farmers and that will consequently allow them to ensure food and economic security of their households. Another legume-based technology for restoring soil fertility is that based on total and permanent cover by legumes (Cowford et al, 2003, Bingen et al, 2003 and Ojiem, 2006). N-free fertilisers and mineral elements such as phosphate rock and stones can greatly benefit legumes in low fertility soils. These inputs are available everywhere but are not widely sold by farmer traders. Some of them sell improved legume seeds, but many do not use them, so they need to be stimulated (Giller, 2001).
Low adoption
Rapid adoption of legume-based technology in integrated soil fertility management requires good input use and investment by farmers as well as their ability to use surplus crops from improved farming (Cowford et al, 2003; Bingen et al, 2003). The marketing of
The marketing of legumes is not well organised, particularly for seeds with industrial applications such as oil extraction. The adoption of new technologies based on improved varieties does not only depend on marketing but also on the knowledge and culture of the farmer. Many farmers are unaware of the beneficial interactions between legumes and cereals and even nodulation is not well understood (Woomer et al, 1997). Many farmers lack the information and experience needed to adapt legumes to their specific conditions. Finally, households are not familiar with the benefits of legumes and how to use them better (Graham and Welch 1999).
For these reasons, farmer knowledge has a key role to play in integrated soil fertility management and the adoption of legumes in traditionally poor households.
Source: africmemoire.com