Farming Systems In sub-Saharan Africa Research Articles

Weed emergence as affected by maize (Zea mays L.)-cover crop rotations in contrasting arable soils of Zimbabwe under conservation agriculture

Weed control in smallholder farming systems of sub-Saharan Africa is labour intensive or costly. Many researchers have therefore advocated for the use of cover crops in weed management as an affordable alternative for smallholders. Cover crops may be grown in rotations to suppress weeds and reduce the reliance on herbicides. The use of cover crops creates microenvironments that are either conducive or inhibitive to the emergence of certain weed species. A study, initiated in 2008 in contrasting soils at four different locations of Zimbabwe, investigated the effect of maize (Zea mays L.)-cover crop rotations on the emergence of weeds that showed dominance in those soils. Weed assessments were however, carried out from 2011 to 2014. The weed species Galinsoga parviflora Cav., Commelina benghalensis L., and Richardia scabra L. showed dominance in all four locations with weed densities as high as 500 plants m−2 being recorded for R. scabra L. in a sandy soil. Maize-cover crop rotations resulted in higher densities of Bidens pilosa compared with maize monocropping (control treatment) due to its high nitrogen (N) requirement to produce more seeds. On the other hand, the integration of cover crops such as pigeon pea [Cajanus cajan (L.) Millsp.] that had poor shading qualities, due to large gaps or spaces and slower initial growth, had limited effects on competitive weeds such as Cyperus esculentus L. which tend to dominate exhausted soils. The density of C. esculentus was 38% greater in maize–pigeon pea rotations compared with the control treatment. Variability between seasons and sites affected emergence of all weeds in the present study, which masked long-term trends. The results suggest that there is need to identify the germination and emergence requirements of specific weeds and select cover crops best suitable for their control. The study provides useful information for farmers and advisors on the best cover crops for control of certain problematic weeds in different soil types of Zimbabwe.

Diversity in crop residue management across an intensification gradient in southern Africa: System dynamics and crop productivity

Crop residues are important for livestock feed and nutrient cycling among many other functions on smallholder farming systems of sub-Saharan Africa. The objective of this study was to assess differences in resource endowment, crop productivity and crop residue management in selected sites in southern Africa. Three sites were selected along a gradient of intensification of crop production; Murehwa, Zimbabwe and Ruaca and Gorongosa, central Mozambique. Murehwa and Ruaca have mixed crop-livestock systems with more intensive crop production in Murehwa. Gorongosa is predominantly crop based with small livestock that do not impact on crop production. A combination of land size and cattle ownership was the major attribute that defined wealth status among farmers in mixed crop-livestock systems whereas land size and labor availability were important under crop-based extensification systems. Farm systems were more diverse where livestock was more important. The wealthiest farmers (resource group—RG1) in Murehwa produced an average of 2.2tha−1 maize crop residues, and productivity decreased with decrease in resource ownership with the poorest (RG4) achieving only 0.8tha−1. In Ruaca 1.3 and 0.5tha−1 was produced by RG1 and RG4 respectively, whereas in Gorongosa 0.4 and 0.2tha−1 was produced by RG1 and RG4. These crop residues are insufficient to achieve the minimum threshold of soil cover (30%) required for the practice of conservation agriculture. However, they can provide sufficient feed to sustain livestock of RG1 farmers in Murehwa for 63 days and 54 days for RG2 farmers. In Ruaca, they can feed cattle for 37 days for RG1 and 17 days for RG2 farmers. The product of livestock×population density determined the extent and manner in which crop residues are used. The population density limited the extent of the grazing area, increased grazing frequency and reduced the grazing quality leading to the need to supplement animal feed with crop residues. Farmers preferentially allocate crop residues to livestock where labor is available. The crop residues fed to animals allow farmers to increase manure quantity and quality which explains the major differences in crop productivity between the different resource groups. In the absence of cattle, crop residues are burned before the cropping season to facilitate land clearance. In conclusion, land size, cattle ownership and labor availability largely define the intensity of crop production and the fate of crop residues on smallholder farms in southern Africa.

Diversification and a multidisciplinary approach for raising agriculture production and attaining food security in smallholder farming systems of sub-Saharan Africa

Agriculture is the primary economic activity for between 50 and 90 percent of the population in Sub-Saharan African countries. Ninety five percent of the food that is produced in Sub-Saharan Africa is grown through rain-fed agriculture. This implies that the region will suffer most from climate change due to its dependence on rain-fed agriculture. Vulnerability to climate change will be especially significant among the resource poor smallholder farmers in African countries whose livelihoods depend on rain-fed agriculture in marginal areas. African agriculture is characterized by variations in farming systems with about 90% of the farming occurring in integrated systems. In these mixed farming systems, the food security challenge may require an integrated approach to match the existing systems. A rainbow evolution which emphasizes the need for diversified systems may be the best practice in raising agricultural productivity. A multidisciplinary approach based on the theory of embededdness whereby farmers, researchers, extension institutions, and political institutions work together can further raise agriculture production and improve food security. Social networks in communities of farmers provide channels for identifying problems and farmers? knowledge integrated with that of research and extension can provide sustainable solutions for food production in smallholder farming systems in Africa.?

Comparative analysis of tomato value chain competitiveness in selected areas of Malawi and Mozambique

AbstractThis paper discusses tomato value chain performance in Malawi and Mozambique using data collected from a market study commissioned by the International Centre for Tropical Agriculture as part of a regional research on conservation agriculture in maize-based farming systems in Sub-Saharan Africa. The results show that Malawi has a slightly higher competitive advantage in the production of tomato compared to Mozambique. Malawi’s relative competitiveness in tomato is mainly due to slightly higher productivity and the cost advantage in labor (low wages) and irrigation costs. The paper proposes policy implications aimed at raising the productivity and trade competitiveness of tomato, as this will ensure the overall productivity of the maize-based smallholder farming systems in the two countries.

Phosphorus in smallholder farming systems of sub-Saharan Africa: implications for agricultural intensification

Current efforts in combating food insecurity in sub-Saharan Africa (SSA) focus on agricultural intensification. Given the high soil nutrient depletions, replenishing soil fertility is a major component of such efforts. One of the key nutrients limiting crop production is phosphorus (P). Overcoming P deficiency in smallholder farming in SSA faces many challenges, mainly because the causes of P deficiencies vary, and viable options to replenish soil P have limitations. In some areas, P deficiency is associated with a low P reserve, while in others, it results from a high soil P-adsorption capacity. Numerous studies have focused on developing approaches and strategies with potential to replenish soil P or improve its availability to crops. This paper highlights approaches and strategies that have been studied, including the use of soluble P fertilizers, phosphate rocks and organic resources. The contribution of soluble P fertilizers is mainly limited by their high cost, while most phosphate rocks are not mined. Replenishing P through organic resources is constrained by their often low P content and inadequate availability in smallholder farms. Optimizing the P use efficiency appears as the most plausible target pending an increased accessibility of P sources to farmers. Practices towards this optimization include strategic crop sequences and P allocation to crops, use of P-efficient genotypes, and targeting the residual P. Research is needed towards gaps in understanding processes governing benefits associated with these practices. Since P replenishment is fertilizer dependent, greater attention is required in enhancing the accessibility of P fertilizers to smallholder farmers.

Adapting to climate change in the mixed crop and livestock farming systems in sub-Saharan Africa

Mixed crop and livestock farms are the backbone of African agriculture, yet there is little information on how these systems may be affected by changes in climate. Addressing this knowledge gap could help smallholders adapt to climate change. Mixed crop–livestock systems are the backbone of African agriculture, providing food security and livelihood options for hundreds of millions of people. Much is known about the impacts of climate change on the crop enterprises in the mixed systems, and some, although less, on the livestock enterprises. The interactions between crops and livestock can be managed to contribute to environmentally sustainable intensification, diversification and risk management. There is relatively little information on how these interactions may be affected by changes in climate and climate variability. This is a serious gap, because these interactions may offer some buffering capacity to help smallholders adapt to climate change.

Towards a Theoretical Grounding of Climate Resilience Assessments for Smallholder Farming Systems in Sub-Saharan Africa

Resilience assessments are increasingly used to inform management decisions and development interventions across sub-Saharan Africa (SSA). In light of current and future climate change and variability, there is growing interest in applying such tools and frameworks to assess and strengthen the climate resilience of smallholder farming systems. However, these assessments are often undertaken without explicit consideration of the resilience thinking in which they are grounded. This makes it difficult to understand how the conceptual aspects of resilience are translating into resilience assessment practice. This paper provides an important first step in tackling this gap, by identifying and using key characteristics of resilience thinking to evaluate existing resilience assessment tools and frameworks and drawing insights for assessing the climate resilience of smallholder farming systems. We find that power, politics, and agency, identified as important in the resilience literature, are not fully incorporated within current tools and frameworks. This leads to inadequate consideration of spatial and temporal trade-offs. We propose six recommendations for assessing the climate resilience of smallholder farming systems in SSA in order to enhance the linkages between resilience theory and practice. These are: (1) better integrate vulnerability and resilience; (2) recognize that resilience does not equal development or poverty reduction; (3) recognize the benefits and limitations of adopting flexible, participatory approaches; (4) integrate issues of power into assessment tools; (5) target specific systems; and (6) encourage knowledge sharing, empirical studies, and critical evaluation. Our findings contribute to improved understanding of applications of resilience thinking to enhance natural resource management.

Productivity limits and potentials of the principles of conservation agriculture.

One of the primary challenges of our time is to feed a growing and more demanding world population with reduced external inputs and minimal environmental impacts, all under more variable and extreme climate conditions in the future. Conservation agriculture represents a set of three crop management principles that has received strong international support to help address this challenge, with recent conservation agriculture efforts focusing on smallholder farming systems in sub-Saharan Africa and South Asia. However, conservation agriculture is highly debated, with respect to both its effects on crop yields and its applicability in different farming contexts. Here we conduct a global meta-analysis using 5,463 paired yield observations from 610 studies to compare no-till, the original and central concept of conservation agriculture, with conventional tillage practices across 48 crops and 63 countries. Overall, our results show that no-till reduces yields, yet this response is variable and under certain conditions no-till can produce equivalent or greater yields than conventional tillage. Importantly, when no-till is combined with the other two conservation agriculture principles of residue retention and crop rotation, its negative impacts are minimized. Moreover, no-till in combination with the other two principles significantly increases rainfed crop productivity in dry climates, suggesting that it may become an important climate-change adaptation strategy for ever-drier regions of the world. However, any expansion of conservation agriculture should be done with caution in these areas, as implementation of the other two principles is often challenging in resource-poor and vulnerable smallholder farming systems, thereby increasing the likelihood of yield losses rather than gains. Although farming systems are multifunctional, and environmental and socio-economic factors need to be considered, our analysis indicates that the potential contribution of no-till to the sustainable intensification of agriculture is more limited than often assumed.

Benefits of legume–maize rotations: Assessing the impact of diversity on the productivity of smallholders in Western Kenya

Agricultural intensification of farming systems in sub-Saharan Africa is a prerequisite to alleviate rural poverty and improve livelihoods. Legumes have shown great potential to enhance system productivity. On-farm experiments were conducted in different agro-ecological zones (AEZ) in Western Kenya to assess the agronomic and economic benefits of promising legumes. In each zone, trials were established in fields of high, medium and low fertility to assess the effect of soil fertility heterogeneity on legume productivity and subsequent maize yield. Common bean, soybean, groundnut, lima bean, lablab, velvet bean, crotalaria, and jackbean were grown in the short rains season, followed by maize in the long rains season. Alongside, continuous maize treatments fertilised at different rates were established. AEZs and soil fertility gradients within these zones greatly affected crop productivity, returns to land and labour of rotations, as well as the relative performance of rotations. Poorer soil fertility and AEZs with lower rainfall gave smaller legume and maize yields and consequently, smaller returns to land and labour. The cultivation of legumes increased maize yields in the subsequent long rains season compared with continuous maize receiving fertiliser at a similar rate, while the increase of maize after green manure legumes was stronger than that after grain legumes. Maize yield responded strongly to increasing amounts of N applied as legume residues with diminishing returns to legume-N application rates above 100kgNha−1. In the low potential zones, factors other than improved N availability likely also stimulated maize yield. Rotations with grain legumes generally provided better returns than those with green manures. Intercropping bean with maize in the long rains season provided an additional bean yield that did not come at the expense of maize yield and improved returns to land and labour, but more so in the high potential zones. The results demonstrate the strong impact of biophysical diversity on the productivity of the legumes and suggest the need for careful targeting of legume technologies to the different biophysical conditions.

Overview of holistic application of biogas for small scale farmers in Sub-Saharan Africa

Holistic farming systems provide designs for the whole farm that make long term sustainable use of nutrients, water, labour, finances and energy. In using organic residues to produce energy, and safely recycling the digested residues back into the farming system, a biogas digester could be a central component of many holistic systems. This paper discusses the influence of environmental, socioeconomic and cultural constraints on the use of biogas digesters in holistic farming systems in Sub-Saharan Africa. In higher altitude areas where maintenance of optimal temperature can constrain anaerobic digestion, floating drum or fixed dome digesters are a better option than flexible balloon digesters because they are less susceptible to temperature changes. If water is a key constraint, rainwater harvesting could be used to reduce the additional labour needed to collect water. If energy is the most limiting resource in the farming system, the optimum use of organic residues might be as a fuel for anaerobic digestion, whereas, if water is limiting, energy production by burning or pyrolysis might be a better option. The bioslurry from anaerobic digestion can be used in fish ponds to produce plankton to feed fish, and can be applied to fertile fields and fields of intermediate fertility, while biochar from pyrolysis is better used to improve the soil in infertile fields. If labour is limiting, it is particularly important that the system design minimises any additional labour needed to process the organic residues on a daily basis, considering trade-offs between labour and other resources.

Sense and nonsense in conservation agriculture: Principles, pragmatism and productivity in Australian mixed farming systems

Adoption of conservation agriculture (CA) principles in Australia increased rapidly during the 1990s and it now boasts the highest adoption rates worldwide. These principles of (1) diverse rotations (2) reduced (or no-) till systems and (3) the maintenance of surface cover make good sense in extensive, mechanised, rain-fed cropping systems on erosion-prone, structurally-unstable soils. Indeed reduced fuel and labour costs, soil conservation and moisture retention are the most commonly stated reasons for adoption of CA principles by farmers in Australia. Yet even in Australia, while broadly applicable, the adaptation and application of CA principles within specific farming systems remains pragmatic due to the diverse biophysical and socio-economic factors encountered. Most “no-till” adopters continue some strategic tillage (∼30% cropped area) for a range of sound agronomic reasons, intensive cereal systems dominate, and partial removal of crop residues as hay or by grazing livestock is commonplace within the largely mixed-farming systems. Although this challenges the notion of “ideal” CA principles (zero-till with no soil disturbance, full stubble retention and >3 species in rotations) this high degree of flexibility in CA principles as practiced in southern Australian mixed farming systems makes sense to optimize both economic and environmental outcomes. In addition, some proposed ecosystem service benefits of CA such as soil carbon sequestration and energy efficiency have been recently questioned. Though the socio-economic factors of small-holder farming systems in Africa and south Asia are more diverse and clearly different to Australian farms, some of the biophysical challenges and economic realities are shared (infertile soils, variable and extreme climates, relatively low input levels, integrated crop–livestock systems, small profit margins, highly variable income). It is therefore useful to consider from a biophysical standpoint why a pragmatic approach to CA principles has been necessary, even in a relatively high-adopting country like Australia, and why we should expect similarly ‘imperfect’ adoption of CA (if at all) in the diverse smallholder systems of Sub-Saharan Africa and South Asia. We review aspects of CA adoption in Australia in an effort to draw out important lessons as CA principles are adapted elsewhere, including the smallholder farming systems of Sub-Saharan Africa and South Asia.

Unexpected high decomposition of legume residues in dry season soils from tropical coffee plantations and crop lands

Crop residues are essential fertilizer source of low-input farming systems in Sub-Saharan Africa. However, crop residues provide nutrients only if they decompose in the soil. Decomposition is assumed to be very low during the dry season due to the scarcity of water, but there are few quantitative knowledge on decomposition under such conditions. Therefore, we studied the decomposition of legume residues, haricot bean (Phaseolus vulgaris L.), and pigeon pea (Cajanus cajan L. (Millps) using litterbag experiments in two coffee and two crop land agroecosystems of southern Ethiopia. The residues were surface applied and subsoil buried under irrigated and non-irrigated conditions and were then retrieved after 30–180 days. We measured mass loss, decay rate constant (k), and C and N concentrations. Results demonstrate an unexpected high decomposition in seasonal dry soils, even when the litterbags were placed on the soil surface. Interestingly, 89 % of the initial N of pigeon pea and 85 % of haricot bean were released after 150 days, on the average. Thus microbial decomposition is unexpectedly high during the dry season. This finding has implications for the effect of plant residues on the supply of mineral N to crops growing during subsequent wet season.

Mineral fertilizers in the farming systems of sub-Saharan Africa. A review

In sub-Saharan Africa (SSA), traditional farming methods have led to severe nutrient depletion, low crop yields, and poverty, leaving many farm families disappointed. The situation is aggravated by low use of fertilizers by farmers, lack of policy and institutional support, weak fertilizer markets, farmers’ lack of access to credit and inputs, inappropriate fertilizer packaging sizes, deteriorating soil science capacity, and weak agricultural extension. This leads to a huge gap between the actual and potential crop yields and widespread poverty. Opportunities, options, and innovations are available to turn around this situation and reduce poverty in Africa. We reviewed the status of agricultural soils of sub-Saharan Africa, the factors contributing to their current status, and the existing and emerging opportunities for addressing the soil fertility challenges. The major points are (1) the soils in SSA have continued to be characterized by huge and widespread negative nutrient imbalances and low productivity, and (2) the factors contributing to declining soil fertility in Africa are not abating. The way forward includes: balanced fertilization; input–output market development; improved crop management, and the use of nutrient budgets to inform policy and ensure that farmers and other land managers enjoy the profitable use of farm inputs including mineral fertilizers and agro-minerals.

The effect of system innovations on water productivity in subsistence rainfed agricultural systems in semi-arid Tanzania

Abstract Rainfed subsistence farming systems in sub-Saharan Africa generally obtain low crop yields as a result of highly erratic rainfall seasons. This paper presents results of research conducted to test the effects of improvements in farming techniques for subsistence rainfed systems. The research was carried out in the Makanya catchment of northern Tanzania where rainfall of less than 600 mm a −1 and spread over two agricultural seasons per year is clearly insufficient to support staple food crops under the present farming systems in the area. The research sought to prove that, with improved efficiency in tillage techniques, grain yields can improve even under the existing challenging hydro-climatic conditions. The research tested farming system innovations (SIs) at four sites located within a spatial distance of 10 km where a combination of runoff diversion (RD), on-site rain water harvesting (WH) and conservation tillage (CT) were compared against the traditional farming methods of hand-hoeing under strict rainfed conditions (Control). For RD, runoff generated from natural storms was directed into infiltration pits dug along the contour with the excavated soil deposited upward of the trenches ( fanya juus ). The impact of these techniques on maize yields under different SIs was investigated. The results showed that the innovations resulted in increased maize grain yields of up to 4.8 t ha −1 compared against current averages of less than 1 t ha −1 . The average productivity of the available water over four seasons was calculated to range between 0.35 and 0.51 kg m −3 . For the SIs that were tested, the distribution of yields within a cultivated strip showed variations with better yields obtained on the down slope side of the cultivated strip where ponding effects resulted in higher water availability for infiltration and storage. However, due to the large seasonal climate variability, statistical analysis did not show significant differences in the yields ( p The study showed that there is scope to improve grain yields with the little available rainfall through the adoption of techniques which promote water availability and retention within the field. The re-partitioning of water within the field creates mitigation measures against the impact of dry spells and allows alternative cropping in addition to the traditional maize cultivated in the rainfall seasons.

A research agenda to explore the role of conservation agriculture in African smallholder farming systems

Controversy surrounds the promotion of conservation agriculture (CA) in smallholder farming systems in sub-Saharan Africa. The introduction of CA is a profound change in farm management. Benefits in reduced erosion and stabilized crop production may be obtained, but technical performance at field level is but one of the determinants of adoption. For various reasons, all of the CA principles are not always fully implemented by farmers and results not as favourable as expected. As with other approaches to increasing agricultural productivity, the production constraints, farmers’ objectives, and the expected benefits and costs of implementing CA are important aspects that influence adoption. At farm and village levels, trade-offs in the allocation of resources become important in determining how CA may fit into a given farming system. At a regional level, factors such as the market conditions, interactions among stakeholders and other institutional and political dimensions become important. At each level, opportunities or difficulties emerge that enhance or impede development, adaptation and adoption of CA. The ex-ante identification of situations for where CA (and which form of CA) is appropriate demands research from a multi-stakeholder, multi-level, and interdisciplinary perspective. Recommendations are made where research is required to address key knowledge gaps.

Linking agricultural development to school feeding in sub-Saharan Africa: Theoretical perspectives

This paper takes as a starting point the proposition that social protection interventions involving food can be used to promote transformational change in family farming systems in sub-Saharan Africa. The purpose is to highlight the complexity of pathways to agricultural transformation associated with the seemingly simple idea of home-grown school feeding (HGSF), an idea that is increasingly held up as “win–win”. By reviewing the HGSF literature and the main theories underpinning it – structured demand, localism, family farmer development – we expose areas of inconsistency across the literature and programmes as well as possible tensions that may arise in attempting to pursue both market and social objectives in the same initiative. The arguments presented herein aim to provide a basis for moving towards clarity on (1) a theory of change for HGSF programmes; (2) the conditions under which HGSF programmes are more able to yield positive agricultural development outcomes and; (3) an agenda for moving forward on research and impact evaluation. This research agenda also speaks more broadly to important under-researched areas within the general social protection and agricultural development discourse.

Biological nitrogen fixation and socioeconomic factors for legume production in sub-Saharan Africa: a review

Low crop productivity is a general problem facing most farming systems in sub-Saharan Africa (SSA). These low yields are pronounced in grain legumes and are often associated with declining soil fertility and reduced N2-fixation due to biological and environmental factors. Unfortunately, the majority of African small farmers are now unable to afford the high mineral fertilizer prices. More than 75% of the fertilizers used in Africa are imported, putting pressure on foreign exchange. Low cost and sustainable technical solutions compatible with the socioeconomic conditions of small farmers are needed to solve soil fertility problems. Biological nitrogen fixation (BNF), a key source of N for farmers using little or no fertilizer, constitutes one of the potential solutions and plays a key role in sustainable grain legumes (e.g., soybean) production. Given the high cost of fertilizer in Africa and the limited market infrastructure for farm inputs, current research and extension efforts have been directed to integrated nutrient management, in which legumes play a crucial role. Inoculation with compatible and appropriate rhizobia may be necessary where a low population of native rhizobial strains predominates and is one of the solutions which grain legume farmers can use to optimize yields. It is critical for sustained yield in farmlands deficient in native rhizobia and where N supply limits production. Research on use of Rhizobium inoculants for production of grain legumes showed it is a cheaper and usually more effective agronomic practice for ensuring adequate N nutrition of legumes, compared with the application of N fertilizer. Here, we review past and ongoing interventions in Rhizobium inoculation (with special reference to soybean) in the farming systems of SSA with a view to understanding the best way to effectively advise on future investments to enhance production and adoption of BNF and inoculant technologies in SSA. The major findings are: (1) complete absence of or very weak institutions, policy and budgetary support for biotechnology research and lack of its integration into wider agricultural and overall development objectives in SSA, (2) limited knowledge of inoculation responses of both promiscuous and specifically nodulating soybean varieties as well as the other factors that inhibit BNF, hence a weak basis for decision-making on biotechnology issues in SSA, (3) limited capacity and lack of sustainable investment, (4) poorly developed marketing channels and infrastructure, and limited involvement of the private sector in the distribution of inoculants, and (5) limited farmer awareness about and access to (much more than price) inoculants. The lessons learned include the need: (1) to increase investment in Rhizobium inoculation technology development, and strengthen policy and institutional support, (2) for public private partnership in the development, deployment and dissemination of BNF technologies, (3) to develop effective BNF dissemination strategies (including participatory approach) to reach farmers, (4) for greater emphasis on capacity building along the BNF value chain, and (5) for partnership between universities in SSA and those in the North on BNF research.

Impact of climate change on agricultural productivity under rainfed conditions in Cameroon—A method to improve attainable crop yields by planting date adaptations

Rainfed farming systems in sub-Saharan Africa are suffering from low productivity. Prolonged dry spells and droughts often lead to significant crop losses, a situation that is expected to be exacerbated by climate change. In this study, the impact of climate change on attainable yields of maize and groundnut, as major alimentary crops in sub-Saharan Africa, is evaluated at five stations in Cameroon under rainfed conditions. It is focussed on the contribution of future climate change in terms of the direct fertilisation effect of the expected CO 2 alteration and the indirect effects of the expected temperature and precipitation change. As improved agricultural management practices in rainfed systems are crucial to increase agricultural productivity, the impact of the planting date is analysed in detail. For this purpose, a fuzzy logic-based algorithm is developed to estimate the agriculturally relevant onset of the rainy season (ORS) and, thus, the optimal planting date. This algorithm is then connected to the physically based crop model CropSyst, hereinafter referred to as optimal planting date following crop modelling system. A Monte Carlo approach is used to optimise the ORS algorithm in terms of maximising the mean annual crop yields (1979–2003). The optimal planting date following crop modelling system is applied to past and future periods, mainly for two reasons: (i) to derive optimal fuzzy rules and increase mean attainable crop yields; and (ii) to reliably estimate the impact of climate change to crop productivity with (‘optimal planting date scenario’) and without planting date adaptations (‘traditional planting date scenario’). It is shown that the fuzzy rules derived for assessing the optimal planting dates may allow for significantly increased crop yields compared to the existing planting rules in Cameroon under current climatic conditions, especially for the drier northern regions. A change in the climatic conditions due to global warming will reduce the growing cycle and, thus, the crop yields. However, the positive effect of CO 2 fertilisation is likely to outweigh the negative effects of precipitation and temperature change for the 2020s and partly for the 2080s. When additionally considering planting date adaptations, groundnut yield is expected to increase for the 2020s and the 2080s, with maximum yield surpluses of about 30% for the 2020s compared to the extended baseline period. For maize, crop yield is likely to increase (decrease) for the 2020s (2080s) by approximately 15%. For the driest stations analysed, the negative impacts of temperature and precipitation change could be mitigated significantly by planting date adaptations.

Drivers of land use change and household determinants of sustainability in smallholder farming systems of Eastern Uganda

Smallholder farming systems in sub-Saharan Africa have undergone changes in land use, productivity and sustainability. Understanding of the drivers that have led to changes in land use in these systems and factors that influence the systems’ sustainability is useful to guide appropriate targeting of intervention strategies for improvement. We studied low input Teso farming systems in eastern Uganda from 1960 to 2001 in a place-based analysis combined with a comparative analysis of similar low input systems in southern Mali. This study showed that policy-institutional factors next to population growth have driven land use changes in the Teso systems, and that nutrient balances of farm households are useful indicators to identify their sustainability. During the period of analysis, the fraction of land under cultivation increased from 46 to 78%, and communal grazing lands nearly completely disappeared. Cropping diversified over time; cassava overtook cotton and millet in importance, and rice emerged as an alternative cash crop. Impacts of political instability, such as the collapse of cotton marketing and land management institutions, of communal labour arrangements and aggravation of cattle rustling were linked to the changes. Crop productivity in the farming systems is poor and nutrient balances differed between farm types. Balances of N, P and K were all positive for larger farms (LF) that had more cattle and derived a larger proportion of their income from off-farm activities, whereas on the medium farms (MF), small farms with cattle (SF1) and without cattle (SF2) balances were mostly negative. Sustainability of the farming system is driven by livestock, crop production, labour and access to off-farm income. Building private public partnerships around market-oriented crops can be an entry point for encouraging investment in use of external nutrient inputs to boost productivity in such African farming systems. However, intervention strategies should recognise the diversity and heterogeneity between farms to ensure efficient use of these external inputs.

Integrated Soil Fertility Management

Traditional farming systems in Sub-Saharan Africa depend primarily on mining soil nutrients. The African green revolution aims to intensify agriculture through the dissemination of integrated soil fertility management (ISFM). This paper develops a robust and operational definition of ISFM based on detailed knowledge of African farming systems and their inherent variability and of the optimal use of nutrients. The authors 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, aimed at maximizing agronomic use efficiency of the applied nutrients and improving crop productivity. All inputs need to be managed in accordance with 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.