Integrated Soil Fertility Management

Integrated soil fertility management: operational definition and consequences for implementation and dissemination B. VanlauweA, J. ChianuA, K.E. GillerB, R. MerckxC, U. MokwunyeD, P. PypersA, K. ShepherdE, E. SmalingF, P.L. WoomerG and N. SangingaA A Tropical Soil Biology and Fertility Institute of the International Centre for Tropical Agriculture, PO 30677, Nairobi, Kenya. Department of Plant Sciences, Wageningen University, P.O. Box 430, 6700 AK Wageningen, The Netherlands. C Faculty of Bioscience Engineering, Kasteelpark Arenberg 20, 3001 Leuven, Belgium. D Director, Mokwunye Enterprises, International Consultants, 4th Ayiku Lane, Baatsonaa, Accra, Ghana. E World Agroforestry Centre (ICRAF), PO 30677, Nairobi, Kenya. F International Institute for Geo-information Science and Earth Observation (ITC), P.O. Box 6, 7500 AA Enschede, NL G FORMAT, PO Box 79, The Village Market, Nairobi, Kenya. B Abstract Traditional farming systems in sub-Saharan Africa depend primarily on mining soil nutrients. The African Green Revolution aims at intensifying agriculture through dissemination of Integrated Soil Fertility Management (ISFM). In this paper we develop a robust and operational definition of ISFM, based on detailed knowledge of African farming systems and their inherent variability and of optimal use of nutrients. We define ISFM as ‘A set of soil fertility management practices that necessarily include the use of fertilizer, organic inputs, and improved germplasm combined with the knowledge on how to adapt these practices to local conditions, aiming at maximizing agronomic use efficiency of the applied nutrients and improving crop productivity. All inputs need to be managed following sound agronomic principles.’ The integration of ISFM practices into farming systems is illustrated with the dual purpose grain legume-maize rotations in the savannas and fertilizer micro-dosing in the Sahel. Finally, the dissemination of ISFM practices is discussed. Key Words Agronomic use efficiency, fertilizer, micro-dose, organic inputs, soil organic matter, soybean-maize rotation. Introduction The need for sustainable intensification of agriculture in SSA has gained support, because in part of the growing recognition that farm productivity is a major entry point to break the vicious cycle underlying rural poverty. Since fertilizer is an expensive commodity, the Alliance for a Green Revolution in Africa (AGRA) has adapted Integrated Soil Fertility Management (ISFM) as a framework for boosting crop productivity through reliance upon soil fertility management technologies, with emphasis on increased availability and use of mineral fertilizer. Various definitions for ISFM have been proposed but most definitions are incomplete in the sense that they fall short of defining principles that are unique to ISFM. The objectives of this paper are: (i) to develop a robust definition of ISFM that can be used as a practical means for objectively evaluating its implementation; (ii) to apply the definition to relevant technologies with great potential for dissemination to smallholder farmers; and (iii) to highlight factors that will facilitate the adoption of ISFM practices. 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 level, 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. At the individual farm level, it is important to consider the variability between the soil fertility status of individual fields, which may be as large as differences between different agro-ecological zones. The above section sketches a summary of the farming conditions in SSA and the variability that exists at different scales. Any definition of ISFM must consider these attributes. © 2010 19th World Congress of Soil Science, Soil Solutions for a Changing World 1 – 6 August 2010, Brisbane, Australia. Published on DVD. 194 Agronomic efficiency Operational definition of ISFM We define ISFM as ‘A set of soil fertility management practices that necessarily include the use of fertilizer, organic inputs, and improved germplasm combined with the knowledge on how to adapt these practices to local conditions, aiming at maximizing 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 1. The definition includes a number of concepts that are described below. e eas r c In in ge led w o kn A C B Current practice Germplasm & fertilizer Responsive soils Poor, less-responsive soils Germplasm & fertilizer’ + Organic resource mgt Move towards ‘complete ISFM’ Germplasm & fertilizer + Organic resource mgt + Local adaptation ‘Complete ISFM’ Figure 1. Conceptual relationship between the agronomic efficiency (AE) of fertilizers and organic resource and the implementation of various components of ISFM, culminating in complete ISFM towards the right side of the graph. Soils that are responsive to NPK-based fertilizer and those that are poor and less-responsive are distinguished. The ‘current practice’ step assumes the use of the current average fertilizer application rate in SSA of 8 kg fertilizer nutrients/ha. The meaning of the various steps is explained in detail in the text. At constant fertilizer application rates, yield is linearly related to AE. Focus on agronomic use efficiency The definition focuses on maximizing the use efficiency of fertilizer and organic inputs since these are both scarce resources in the areas where agricultural intensification is needed. Agronomic efficiency (AE) is defined as incremental return to applied inputs or: AE (kg/kg) = (YF - YC) / (Fappl) [1] where YF and YC refer to yields (kg/ha) in the treatment where nutrients have been applied and in the control plot, respectively, and Fappl is the amount of fertilizer and/or organic nutrients applied (kg/ha). Fertilizer and improved germplasm In terms of response to management, two general classes of soils are distinguished: (i) soils that show acceptable responses to fertilizer (Path A, Figure 1) and (ii) soils that show minimal or no response to fertilizer due to other constraints besides the nutrients contained in the fertilizer (Path B, Figure 1). 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 class of soil exists where crops respond little to fertilizer as the soils are fertile. These soils need only maintenance fertilization and are termed ‘fertile, less responsive soils’. The ISFM definition proposes that application of fertilizer to improved germplasm on responsive soils will boost crop yield and improve the AE relative to current farmer practice, characterized by traditional varieties receiving too little and insufficiently managed nutrient inputs (Path A, Figure 2). Major requirements for achieving production gains on ‘responsive fields’ within Path A (Figure 1) include (i) the use of disease-resistant and improved germplasm, (ii) the use of the correct fertilizer formulation and rates, and (iii) appropriate fertilizer, crop and water management practices. © 2010 19th World Congress of Soil Science, Soil Solutions for a Changing World 1 – 6 August 2010, Brisbane, Australia. Published on DVD. 195 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 realistic levels 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-term to sustain soil fertility and crop production. Two other issues arise within the context of ISFM: (i) does fertilizer application generate the required crop residues that are needed to optimize the AE of fertilizer for a specific situation and (ii) can organic resources be used to rehabilitate ‘less-responsive soils’ and make these responsive to fertilizer (Path C in Figure 2)? The first issue is supported by data obtained in Niger by Bationo et al (1998). Where fertilizer was applied to millet, sufficient residue was produced to meet both farm household demands for feed and food as well as the management needs of the soil in terms of organic inputs and surface protection of the soil from wind erosion. Evidence also supports the second rehabilitation issue. In Zimbabwe, applying farmyard manure for 3 years to sandy soils at relatively high rates enabled a clear response to fertilizer where such response was not visible before rehabilitation (Zingore et al. 2007). Applying above principles to maximize AE will require adaptation to the prevailing soil fertility status (SFGs) and other site-specific modifiers of crop growth. Adaptation to local conditions As previously stated, farming systems are highly variable at different scales and a challenge before the African Green Revolution is adjusting for site-specific soil conditions. Firstly, soil fertility status can vary considerably within short distances. A good proxy for soil fertility status is often the soil organic matter (SOM) content, 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 the fertilizer N use efficiency. On the other hand, SOM also releases available N that may be better synchronized with the demand for N by the plant than fertilizer N. Consequently a larger SOM pool may result in lower N fertilizer AEs. Evidence from Western Kenya shows that for fertile soils, AE for plant nutrients is less than that for less intensively managed outfields (Vanlauwe et al. 2006). 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 fertilizer nutrient application with local varieties. Each step is expected to provide the management skills that result in yield and improvements in AE (Figure 1). Complete ISFM comprises the use of improved germplasm, fertilizer, appropriate organic resource management and local adaptation. Figure 1 is not necessarily intended to prioritize 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 fertilizer 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 illustrated the integration of ISFM principles in existing cropping systems: (i) dual purpose grain legume – maize rotations with P fertilizer targeted at the legume phase and N fertilizer at rates below recommended rates targeted at the cereal phase in the moist savanna agro-ecozone (Sanginga et al. 2003) and (ii) micro-dose fertilizer 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. 1997; Tabo et al. 2007). As for the grain legume-maize rotations, application of appropriate amounts of mainly P to the legume phase ensures good grain and biomass production, the latter in turn benefiting a subsequent maize crop and thus reducing the need for external N fertilizer (Sanginga et al. 2003). As for the micro-dose technology, spot application of appropriate amounts of fertilizer to widely spaced crops as sorghum or millet substantially enhances its use efficiency with further enhancements obtained when combined with physical soil management practices aiming at water harvesting. Recycling crop residues can reduce wind and water erosion (Bationo et al. 1998) and thus further benefit growth and nutrient demand of a following cereal. Certain conditions enable the dissemination and retention of ISFM practices. © 2010 19th World Congress of Soil Science, Soil Solutions for a Changing World 1 – 6 August 2010, Brisbane, Australia. Published on DVD. 196 Dissemination of ISFM The gradual increase in complexity of knowledge as one move towards complete ISFM (Figure 1) has implications on the strategies to adapt for widespread dissemination of ISFM. Furthermore, a set of enabling conditions can favor the uptake of ISFM. The operations of every farm are strongly influenced by the larger rural community, policies, and supporting institutions, and markets. Not only are farms closely linked to the off-farm economy through commodity and labor 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 fertilizer 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, providing 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 that facilitates the uptake of ISFM. Policies favoring the importation of fertilizer, its blending and packaging, or smart subsidies are needed to stimulate the supply of fertilizer as well. Specific policies addressing the rehabilitation of degraded, nonresponsive 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 fertilizer’ strategy has made substantial impact is the Malawi fertilizer subsidy program. Malawi became a net food exporter through the widespread deployment of seeds and fertilizer, although the aggregated AE 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 fertilizer’ strategy are under way, activities such as farmer field schools or development of site-specific decision guides that enable tackling more complex issues can be initiated to guide farming communities towards complete ISFM, including aspects of appropriate organic matter management of 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. References Bationo A, Lompo F, Koala S (1998) ‘Research on nutrient flows and balances in west Africa: state-. 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 RJ, Tarawali S, Asafo-Adjei B, Menkir A, Schulz S, Singh BB, Chikoye D, Keatinge D, 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. Tabo R, Bationo A, Gerard B, Ndjeunga J Marchal D, Amadou B, Annou G, Sogodogo D, Taonda JBS, Hassane O, Maimouna K Diallo, Koala S (2007) Improving cereal productivity and farmers’ income using a strategic application of fertilizers in West Africa. In ‘advances in integrated soil fertility management in Sub-Saharan Africa: Challenges and opportunities’. (Eds A Bationo, B Waswa, J Kihara, J Kimetu), pp 201-208. (Kluwer Publishers: The Netherlands). Vanlauwe B, Tittonell P, 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. Zingore S, Murwira HK, Delve RJ, Giller KE (2007) Soil type, management history and current resource allocation: Three dimensions regulating variability in crop productivity on African smallholder farms Field Crops Research 101, 296–305. © 2010 19th World Congress of Soil Science, Soil Solutions for a Changing World 1 – 6 August 2010, Brisbane, Australia. Published on DVD. 197