Integrated Soil Fertility Management – a concept that could boost soil productivity
The need for sustainable intensification of agriculture in sub-Saharan Africa (SSA) has gained support, in part because of the growing recognition that farm productivity is a major entry point to break the vicious cycle underlying rural poverty. Fertiliser use is extremely low in much of the sub-Saharan Africa region (8 kg/ha on average), and this is one of the main factors explaining lagging agricultural productivity growth. Most of the soils in Africa are inherently infertile, and poor agricultural management practices during the past decades have led to a severe decline in their productive capacity. Given the low levels of fertiliser use and poor soils in SSA, fertiliser use must increase if the region is to reverse the current trends of low crop productivity and land degradation. There are renewed efforts to raise fertiliser use in SSA from the current 8 kg to 50 kg nutrients per ha by improving the marketing, policy and socio-economic environment to increase fertiliser availability at prices affordable to smallholder farmers. Since fertiliser is very expensive for most smallholder farmers in SSA, the Alliance for a Green Revolution in Africa (AGRA) has adapted Integrated Soil Fertility Management (ISFM) as a framework for boosting crop productivity through combining fertiliser use with other soil fertility management technologies, based on site conditions.
Taking smallholder farming conditions into account
Before proposing a definition for ISFM, it is important to sketch the context under which the smallholder farmer in SSA operates. At the regional scale, overall agro-ecological and soil conditions have led to diverse population and livestock densities across SSA and to a wide range of farming systems. Each of these systems has different crops, cropping patterns, soil management considerations, and access to inputs and commodity markets. At the national scale, smallholder agriculture is strongly influenced by governance, policy, infrastructure, and security levels. Within farming communities, a wide diversity of farmer wealth classes, inequality, and production activities may be distinguished. Analysis of farmer wealth classes in north-east Zimbabwe illustrates the variability that is typical of farmer communities in maize-based farming systems. Use of cattle manure and more fertiliser by the wealthier farmers results in higher farm-level productivity than on poorer farms. At the individual farm level, it is important to consider the variability between the soil fertility status of individual fields (see Figure), which arises due to farmers preferring to apply limited fertilisers and organic nutrient resources to small areas of the farms. Any definition of ISFM must consider these attributes.
What is Integrated Soil Fertility Management?
We define ISFM as ‘A set of soil fertility management practices that necessarily include the use of fertiliser, organic inputs, and improved germplasm combined with the knowledge on how to adapt these practices to local conditions, aiming at maximising agronomic use efficiency of the applied nutrients and improving crop productivity. All inputs need to be managed following sound agronomic principles.’ A conceptual presentation of the definition is shown in Figure 2. The definition includes a number of concepts that are described below.
- Focus on agronomic use efficiency. Fertiliser and organic inputs are both scarce resources in the areas where agricultural intensification is needed. This is why the definition focuses on maximising their use efficiency. Agronomic efficiency (AE) is defined as the extra produce generated (in kg) per unit of nutrients applied (in kg).
- Fertiliser and improved germplasm. In terms of response to management, two general classes of soils are distinguished: (i) soils that show acceptable responses to fertiliser (Step A – blue line, Figure 2) and (ii) soils that show minimal or no response to fertiliser due to other constraints besides the nutrients contained in the fertiliser (Step B – green line, Figure 2). We have classified above soils as ‘responsive soils’ and ‘poor, less-responsive soils’ respectively. In some cases, where land is newly opened, or where fields are close to homesteads and receive large amounts of organic inputs each year, a third category of soil exists where crops respond little to fertiliser as the soils are fertile. These soils need only maintenance fertilisation and are termed ‘fertile, less responsive soils’. The ISFM definition proposes that application of fertiliser to improved germplasm on responsive soils will boost crop yield and improve the agronomic efficiency relative to current farmer practice, characterised by traditional varieties receiving too little and insufficiently managed nutrient inputs (Step A – blue line, Figure 2). Major requirements for achieving production gains on ‘responsive fields’ within Step A include (i) the use of disease-resistant and improved germplasm, (ii) the use of the correct fertiliser sources, and rates, (iii) appropriate fertiliser use in terms of placement and timing, and (iv) crop and water management practices.
- Combined application of organic and mineral inputs. Organic inputs contain nutrients that are released at a rate determined in part by their chemical characteristics or organic resource quality. However, organic inputs applied at low rates commonly used by smallholder farmers in Africa seldom release sufficient nutrients for optimum crop yield. Combining organic and mineral inputs has been advocated as a sound management principle for smallholder farming in the tropics because neither of the two inputs is usually available in sufficient quantities and because both inputs are needed in the long run to sustain soil fertility and crop production.
- Adaptation to local conditions. As previously stated, soil fertility status within and between farms is highly variable and a challenge before the African Green Revolution is adjusting recommendations to include such variability in soil fertility status. Firstly, soil fertility status can vary considerably within short distances. Often, the soil organic matter (SOM) content is a good proxy for soil fertility status, provided that this parameter is not over-extrapolated across dissimilar soils. Soil organic matter contributes positively to specific soil properties or processes fostering crop growth, such as cation exchange capacity, soil moisture and aeration, or nutrient stocks. On land where these constraints limit crop growth, a higher SOM content may enhance the demand by the crop for N and consequently increase fertiliser N use efficiency.
- A move towards ‘complete ISFM’. Several intermediary phases are identified that assist the practitioner’s move towards complete ISFM from the current 8 kg ha-1 fertiliser nutrient application with local varieties. Each step is expected to provide the management skills that result in yield and improvements in agronomic efficiency (Figure 2). Complete ISFM comprises the use of improved germplasm, fertiliser, appropriate organic resource management and local adaptation. Figure 2 is not necessarily intended to prioritise interventions but rather suggests a need for sequencing towards complete ISFM. It does however depict key components that lead to better soil fertility management. For less-responsive soils, investment in soil fertility rehabilitation will be required before fertiliser AE will be enhanced.
Integration of ISFM principles in farming systems
Principles embedded within the definition of ISFM need to be applied within existing farming systems. Two examples clearly illustrate the integration of ISFM principles in existing cropping systems: (i) dual purpose grain legume – maize rotations with P fertiliser targeted at the legume phase and N fertiliser at rates below those recommended that are targeted at the cereal phase in the moist savanna agro-ecozone (Sanginga et al., 2003) (Figure 3) and (ii) micro-dose fertiliser applications in legume-sorghum or legume-millet rotations with retention of crop residues and combined with water harvesting techniques in the semi-arid agro-ecozone (Bationo et al., 1998). As for the grain legume-maize rotations, application of appropriate amounts of mainly P to the legume phase ensures good grain and biomass production, with the latter in turn benefiting a subsequent maize crop and thus reducing the need for external N fertiliser (Sanginga et al., 2003). As for the micro-dose technology, spot application of appropriate amounts of fertiliser to widely spaced crops such as sorghum or millet substantially enhances its use efficiency, with further enhancements obtained when combined with physical soil management practices aiming at water harvesting.
Dissemination of ISFM
The gradual increase in complexity of knowledge as one moves towards complete Integrated Soil Fertility Management (Figure 2) has implications on the strategies to adapt for widespread dissemination of ISFM. Furthermore, a set of enabling conditions can favour the uptake of ISFM. The operations of every farm are strongly influenced by the larger rural community, policies, supporting institutions and markets. Not only are farms closely linked to the off-farm economy through commodity and labour markets, but the rural and urban economies are also strongly interdependent. Farming households are also linked to rural communities and social and information networks, and these factors provide feedback that influences farmer decision-making. Because ISFM is a set of principles and practices to intensify land use in a sustainable way, uptake of ISFM is facilitated in areas with greater pressure on land resources.
The first step towards ISFM acknowledges the need for fertiliser and improved varieties. An essential condition for its early adoption is access to farm inputs, produce markets and financial resources. To a large extent, adoption is market-driven as commodity sales provide incentives and cash to invest in soil fertility management technologies, offering opportunities for community-based savings and credit schemes. Policies towards sustainable land use intensification and the necessary institutions and mechanisms to implement and evaluate these are also a factor that facilitates the uptake of ISFM. Policies favouring the importation of fertiliser, its blending and packaging, or smart subsidies are needed to stimulate the supply of fertiliser as well. Specific policies addressing the rehabilitation of degraded, non-responsive soils may also be required since investments to achieve this may be too large to be supported by farm families alone.
While dissemination and adoption of complete ISFM is the ultimate goal, substantial improvements in production can be made by promoting the greater use of farm inputs and germplasm within market-oriented farm enterprises. Such dissemination strategies should include ways to facilitate access to the required inputs, simple information fliers, spread through extension networks and knowledge on how to avoid less-responsive soils. A good example where the ‘seeds and fertiliser’ strategy has made substantial impact is the Malawi fertiliser subsidy programme. Malawi became a net food exporter through the widespread deployment of seeds and fertiliser, although the aggregated agronomic efficiency was only 14 kg grain per kg nutrient applied (Chinsinga, 2008). Such AE is low, and ISFM could increase this to at least double its value with all consequent economic benefits to farmers. As efforts to promote the ‘seed and fertiliser’ strategy are under way, activities such as farmer field schools or development of site-specific decision guides that enable the tackling of more complex issues can be initiated to guide farming communities towards complete ISFM, including aspects of appropriate organic matter management or local adaptation of technologies. The latter will obviously require more intense interactions between farmers and extension services and will take a longer time to achieve its goals.
Resources and further reading:
- Bationo, A., Lompo, F. and Koala, S. 1998. Research on nutrient flows and balances in west Africa: state-of-the-art. Agriculture, Ecosystems and Environment 71: 19 – 35.
- Chinsinga, B. 2008. Reclaiming Policy Space: Lessons from Malawi’s 2005/2006 Fertilizer Subsidy Programme Future Agricultures, Institute of Development Studies, Brighton, UK
- Sanginga, N., Dashiell, K., Diels, J., Vanlauwe, B., Lyasse, O., Carsky, R. J., Tarawali, S., Asafo-Adjei, B., Menkir, A., Schulz, S., Singh, B. B., Chikoye, D., Keatinge, D. and Rodomiro, O. 2003. Sustainable resource management coupled to resilient germplasm to provide new intensive cereal–grain legume–livestock systems in the dry savanna. Agriculture, Ecosystems and Environment 100: 305–314.
- Vanlauwe, B., Tittonell, P. and Mukalama, J. 2006. Within-farm soil fertility gradients affect response of maize to fertilizer application in western Kenya. Nutrient Cycling in Agroecosystems 76: 171–182.
International Institute of
Tropical Agriculture (IITA)