Increasing productivity with ISFM
Soil: natureâ€™s Pandoraâ€™s box
Bridging yield gap
Best practices in maize
ISFM for bananas
NRM in cassava and yam
Boosting productivity of cassava
Cocoa and REDD
CRPs and NRM
Commercial products for farmers
â€œThe soil nutrient losses in sub-Saharan Africa are an environmental, social, and political time bomb. Unless we wake up soon and reverse these disastrous trends, the future viability of African food systems will indeed be imperiled.”
– Dr Norman Borlaug, 14 March 2003, Muscle Shoals, Alabama, USA
IITA was the first major African link in the integrated network of international agricultural research centers. It was also one of the first centers that engaged inÂ farming systems research. In the 1980s and 1990s, the Institute had a very strong program on natural resource management (NRM), covering aspects of soil fertility management, cropping system diversification, and improved agronomy. This, along with the emphasis on the genetic improvement of the major food crops in the humid tropics, provided an integrated program of research on sustainable agricultural development.
Over the past fifteen years, the focus of research-for-development activities at IITA shifted away from NRM, party driven by changes in the investment portfolios of important donors. With the area of soils and natural resources back on top of the development agenda and recognizing that the potential of improved germplasm can only be realized in the presence of appropriate crop and nutrient management practices, IITA has recently decided to increase its investments on NRM research for development with a particular focus on soils.
The March 2012 issue of R4D Review commemorated IITAâ€™s 45 years. It focused on the successes, challenges, and prospects of the genetic improvement programs; these are key to the Instituteâ€™s success in improving food crop production in sub-Saharan Africa. Innovations in genetic improvement have shown how enhanced crop productivity, along with other ingredients, such as capacity building and policies, has helped to lift millions out of poverty.
This second issue for the year highlights our important work undertaken in partnership with national and international institutions in the area of sustainable NRM in sub-Saharan Africa. It also signals IITA’s renewed focus on this area of research. The articles cover the three main pillars of the NRM research-for-development agenda: (1) Integrated Soil Fertility Management, aiming at enhancing crop productivity following agroecological principles, with a livelihood focus, (2) Sustainable Land Management, aiming at rehabilitating soils for the provision of other essential ecosystem services, with a landscape focus, and (3) Climate Change, aiming at enhancing the resilience of farming systems to climate variability.
Bernard Vanlauwe, firstname.lastname@example.org
The need to grow more food without depleting important natural resources makes the intensification of African agriculture essential. The Green Revolution in South Asia and Latin America raised crop productivity through the deployment of improved varieties, water, and fertilizer. However, efforts to achieve similar results in sub-Saharan Africa (SSA) have largely failed. The sustainable intensification of agriculture in SSA has gained support in recent years, especially in densely populated areas where natural fallows are no longer an option.
There is growing recognition that farm productivity is a major entry point to achieving success in overcoming rural poverty. A recent landmark event was the launching of the Alliance for a Green Revolution in Africa (AGRA). AGRA has adopted integrated soil fertility management (ISFM) as a framework for raising crop productivity through a reliance on soil fertility management technologies, with an emphasis on the increased availability and use of mineral fertilizer (www.agra-alliance.org). Within the refreshed IITA Strategy 2012â€“2020, ISFM is one of the main pillars of the natural resource management (NRM) research area.
Whats is ISFM?
We defined ISFM as â€œA 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 principlesâ€ (Vanlauwe et al. 2011a). The definition focuses on maximizing the efficiency with which fertilizer and organic inputs are used since these are both scarce resources in the areas where agricultural intensification is needed. Agronomic efficiency (AE) is defined as the extra crop yield obtained per unit of nutrient applied and is expressed in kg crop produced per kg nutrient input.
Fertilizer and improved germplasm
In terms of response to management, two general classes of soils are distinguished: responsive soils, i.e., soils that show acceptable responses to fertilizer (Path A, Fig. 1), and poor, less-responsive soils that show little or no response to fertilizer due to constraints apart from the nutrients contained in the fertilizer (Path B, Fig. 1). Sometimes, where land is newly cleared or where fields are close to homesteads and receive large amounts of organic inputs each year, a third class exists where crops show little response to fertilizer since the soils are fertile.
The ISFM definition proposes that the application of fertilizer to improved germplasm on responsive soils will raise crop yield and improve AE relative to the current farmersâ€™ practice. This is characterized by traditional varieties receiving poorly managed nutrient inputs and/or too little of them (Path A, Fig. 1). Major requirements for achieving production gains on responsive fields within Path A (Fig. 1) include the following: the use of disease- resistant and improved germplasm, crop and water management practices, and the application of the â€œ4Râ€ Nutrient Stewardship Frameworkâ€”a science-based framework that focuses on applying the right fertilizer source at the right rate, at the right time during the growing season, and in the right place (Fig. 2). Poor, less-responsive soils should be avoided when deploying improved germplasm and fertilizer.
Combined application of fertilizer and organic 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 rates seldom release sufficient nutrients for optimum crop yield. Combining organic and mineral inputs has been advocated for smallholder farming in the tropics because neither input is usually available in sufficient quantities to maximize yields and because both are needed in the long term to sustain soil fertility and crop production. Substantial enhancements in fertilizer AE have been observed in an analysis related to N fertilizer applied to maize in Africa, but these were strongly influenced by the quality and application rate of the organic resources (Fig. 3).
An important question arises within the context of ISFM: Can organic resources be used to rehabilitate less-responsive soils and make these responsive to fertilizer (Path C in Fig. 1)? In southwestern Nigeria, the integration of residues from Siamese senna (Senna siamea), a leguminous tree, reduced topsoil acidification resulting from repeated applications of urea fertilizer (Vanlauwe et al. 2005).
Adaptation to local conditions
As previously stated, soil fertility status can vary considerably between fields within a single farm and between farms with substantial impacts on fertilizer-use efficiency (see photo on next page). In addition to adjustments to fertilizer and organic input management, measures with adaptation to local conditions are needed, such as the application of lime on acid soils, water harvesting techniques on soils susceptible to crusting under semi-arid conditions, or soil erosion control on hillsides, to address other constraints. Lastly, adaptation also includes considering the farming resources available to a specific farming household, often referred to as the farmerâ€™s resource endowment, the status of which is related to a specific set of farm typologies. ISFM options available to a specific household will depend on the resource endowment of that household.
Towards complete ISFM
Complete ISFM comprises the use of improved germplasm, fertilizer, appropriate organic resource management, and local adaptation. Several intermediate phases have been identified that assist farmers in moving towards complete ISFM, starting from the current average practice of applying 8 kg/ha of fertilizer nutrients to local varieties. Each step is expected to provide the management skills that result in improvements in yield and in AE, with technological complexity increasing towards the right (Fig. 1). Figure 1 is not intended to prioritize interventions but rather suggests a stepwise adoption of the elements of complete ISFM. It does, however, depict key components that lead to better soil fertility management. In areas, for instance, where farmyard manure is targeted towards specific fields within a farm, local adaptation is already taking place, even if no fertilizer is used. This is the situation in much of Central Africa.
Successful uptake of ISFM practices
Several examples can be identified where ISFM has made a difference to smallholder farmers, including (1) dual-purpose grain legumeâ€“maize rotations with targeted fertilizer applications pioneered by IITA for the moist savannas (Sanginga et al. 2003) and (2) micro-dose fertilizer applications in legumeâ€“sorghum or legumeâ€“millet rotations with the retention of crop residues and combined with water harvesting techniques in the semi-arid agroecozone (Tabo et al. 2007).
As for the grain legumeâ€“maize rotations, the application of appropriate amounts mainly of P to the legume phase ensures good grain and biomass production. The latter in turn benefits a subsequent maize crop and thus reduces the need for external N fertilizer. Choosing an appropriate legume germplasm with a low harvest index will favor the accumulation of organic matter and N in the plant parts not harvested and choosing adapted maize germplasm will favor a matching demand for nutrients by the maize. Selection of fertilizer application rates based on local knowledge of the initial soil fertility status within these systems would qualify the soil management practices as complete ISFM.
In view of the many ongoing investments related to the dissemination of ISFM practices, it is expected that the examples of successful uptake will be amplified over large areas across various farming systems.
The principles underlying ISFM have also been observed to be applicable to cassava-based systems (see other articles in this publication). Notwithstanding the good prospects for impact generated through improved soil management, several technical issues remain to be resolved. These include (1) how farmers can diagnose the soil fertility status of their plots, including non-responsiveness, (2) how ISFM recommendations vary along such within-farm soil fertility gradients, (3) how non-responsive soils can be rehabilitated (or does this not make sense under certain circumstances?), (4) what minimal level of resource endowment is required to engage in ISFM, (5) how ISFM principles can be condensed to a set of easy-to-implement rules of thumb, adapted to a specific cropping environment, (6) whether efficient fertilizer use is a valid entry point towards sustainable intensification, (7) whether ISFM produces sufficient in-situ crop residues to ensure that soil carbon values remain about a minimal threshold, (8) what minimal conditions are needed (e.g., population density, policy) to allow large-scale uptake of ISFM, and (9) how ISFM relates to conservation agriculture.
Sanginga, N., K. Dashiell, J. Diels, B. Vanlauwe, O. Lyasse, R.J. Carsky, S. Tarawali, B. Asafo-Adjei, A. Menkir, S. Schulz, B.B. Singh, D. Chikoye, D. Keatinge, and R. Ortiz. 2003. Sustainable resource management coupled to resilient germplasm to provide new intensive cerealâ€“grain legumeâ€“livestock systems in the dry savanna. Agriculture, Ecosystems and Environment, 100: 305â€“314.
Tabo, R., A. Bationo, B. Gerard, J. Ndjeunga, D. Marchal, B. Amadou, G. Annou, D. Sogodogo, J.B.S. Taonda, O. Hassane, Maimouna K. Diallo, and S. Koala. 2007. Improving cereal productivity and farmersâ€™ income using a strategic application of fertilizers in West Africa. Pages 201â€“208 in: Advances in integrated soil fertility management in sub-Saharan Africa: Challenges and opportunities, edited by A. Bationo, B. Waswa, J. Kihara, and J. Kimetu, J. Kluwer Publishers, The Netherlands.
Vanlauwe, B, J. Diels, N. Sanginga, and R. Merckx. 2005. Long-term integrated soil fertility management in south-western Nigeria: crop performance and impact on the soil fertility status. Plant and Soil 273: 337â€“354.
Vanlauwe, B, A. Bationo,Â J. Chianu, K.E. Giller, R. Merckx U. Mokwunye, O. Ohiokpehai, P. Pypers, R. Tabo, K. Shepherd, E. Smaling, P.L. Woomer, and N. Sanginga. 2011a. Integrated soil fertility management: operational definition and consequences for implementation and dissemination. Outlook on Agriculture 39: 17â€“24.
Vanlauwe, B, J. Kihara, P. Chivenge, P. Pypers, R. Coe, and J. Six. 2011b. Agronomic use efficiency of N fertilizer in maize-based systems in sub-Saharan Africa within the context of Integrated Soil Fertility Management. Plant and Soil 339: 35â€“50.
Zingore, S. and A. Johnston. 2013. The 4R Nutrient Stewardship in the context of smallholder Agriculture in Africa, in: Agroecological Intensification of Farming Systems in the East and Central African Highlands, edited by B. Vanlauwe, G. Blomme, and P. Van Asten. Earthscan, UK, in press.
Laurence Jassogne, email@example.com, Piet van Asten, Peter Laderach, Alessandro Craparo, Ibrahim Wanyama, Anaclet Nibasumba, and Charles Bielders
Coffee is a major cash crop in the East African highland farming systems. It represents a high proportion of export values at the national level (for example >20% for Uganda). It is also crucial for the sustainability of the livelihoods of smallholder farmers.
During a survey in Uganda, smallholder farmers explained that the income generated by coffee had sent their children to school and helped to build permanent houses. Prices of coffee have also been increasing in the past decennia, motivating them to continue growing the crop.
Although coffee is a promising cash crop, smallholder farmers that grow coffee are still vulnerable. Soil fertility is declining, pest and disease pressure is increasing, populations are rising, and land is continuously fragmented. Above all, climate change is starting to take its toll and puts further pressure on the coffee-based farming systemsâ€”directly, because temperature and rainfall have an impact on the physiology of Arabica coffee, and indirectly because the incidence and severity of certain pests and diseases such as the coffee berry borer and coffee leaf rust will increase.
Current and future suitability of coffee growing areas
In collaboration with Dr Peter Laderach (CIAT), the direct effect of climate change on the suitability of coffee-growing areas in Uganda was mapped (Fig. 1).
If the current coffee crop systems do not change (i.e., same coffee varieties and management practices), these areas will move up the slope and the suitable surface area will decrease. In this light, climate-smart coffee- based systems need to be developed to sustain the existing coffee- based systems.
Adaptation strategies in coffee systems
IITA-led field surveys in the region, combined with a literature review, revealed that there is a multitude of coffee systems that exist. This diversity reflects the variability among farmers in terms of their resource availability, objectives, political history, and opportunities (Fig. 2).
Highest yields can be obtained in systems without shade or with low shade levels (Fig. 2). However, these same systems represent higher production risks and a higher use of external inputs. In polyculture systems and forest systems, on the other hand, highest yield quality can be obtained with the minimum use of external inputs. Furthermore, they allow, among others, a better adaptation to climate change, higher carbon stocks, and more ecological services. Quantifying these trade-offs and raising awareness among farmers and other stakeholders along the coffee value chain will help informed and sustainable decisions to be made about the coffee systems.
The more coffee is shaded, the more it is protected from rising temperatures and extreme weather events. Shade in coffee systems can reduce the average temperature in the lower coffee canopy by a few degrees. Although shade is an interesting technology to make coffee systems â€œclimate smartâ€ and hence, adapted to climate change, it is not the primary reason why farmers add shade to their coffee. Shade plants often produce fruit and/or timber. This diversifies the income of the farmer.
The same happens when farmers intercrop coffee with banana. Adding banana to the system increases food security, diversifies income, and adds shading to coffee. A country-wide survey in Uganda showed that coffee/banana intercropping was a common cropping system except in North and North-West Uganda. The incidence of coffee leaf rust was 50% when coffee was intercropped with banana.
Most farmers have some shade trees in their coffee; many practice intercropping with common beans. The combination of short- and long-term benefits of such shade systems makes them ideal climate-smart candidates. Shade trees also sequester carbon, contributing to the mitigation of the effects of climate change. In the end, few farmers (<5%) have pure full-sun monocropped coffee.
Constraints in diversified systems
However, shade trees also compete with coffee for light, nutrients, and water. If this competition is not managed well, then the shaded coffee system risks collapse, especially in conditions of poor soil fertility. Due to increasing population pressure and land fragmentation, integrated soil fertility management (ISFM) will help to manage nutrient competition. In a shaded system, the turn-over of biomass contributes to nutrient recycling. Organic matter from shade trees or banana will act as in-situ mulch. However, soils in Uganda are poor and have some major nutrient deficiencies (Fig. 3).
Replenishing soil fertility by adding external inputs is necessary if farming systems need to be sustained. Adding small amounts of fertilizers adapted to site-specific deficiencies increases fertilizer use efficiency and forms part of the ISFM approach. Coffee can be a major driver for the adoption of fertilizers by smallholders since farmers are generally organized for access to output markets. The same organizational lines can then be used to provide access to input markets.
Understanding the farmersâ€™ objectives, perceptions, and constraints is critical in identifying the adoption pathways of production-increasing technologies. To continue this research, IITA will start a case study in Rakai (Uganda) at a site of the CGIAR Research Program on Climate Change, Agriculture, and Food Security (CCAFS). Here, climate-smart coffee scenarios will be developed in a participatory manner with smallholder farmers, based on data from previous projects, interviews with individual farmers and groups, and farm measurements. Greenhouse gas emissions will be quantified to measure the mitigation potential of the existing coffee systems. Furthermore, fertilizer trials throughout Uganda will be set up to test the site-specific recommendations. IITA also plans to further advance its collaborative research efforts on modeling trade-offs and synergies in coffee smallholder systems in East Africa.
Danny Coyne, firstname.lastname@example.org
Soil, a natural resource of overwhelming magnitude, is too often taken for granted, even if its importance is recognized at the highest levels. Franklin Delano Roosevelt, for example, lamented that â€œThe nation that destroys its soil, destroys itselfâ€ when reflecting on the USAâ€™s dustbowl era.
The “anchor” for the great majority of crops and plants, the soil is a physical support system for crop production and survival. However, it is also a paradoxical Pandoraâ€™s box of contrasts and opposing forces. As a refuge for pests and diseases capable of broad-scale crop devastation, it acts to harbor the death knell of the very life it supports. The soil-borne bacterium that causes bacterial wilt, Ralstonia solanacearum, for instance, can inflict 100% mortality to a field of tomatoes; cysts of some nematode species or spores of certain bacteria can lie dormant in the soil for decades, and then wreak havoc on susceptible crops when stimulated.
By contrast, the soil also acts as a treasure trove of beneficial microorganisms. Some are obligate parasites of crop pests and diseases, others facilitate plant access to nutrients, or enable plants to tolerate unfavorable conditions and toxic contaminants. The breadth of microbial biodiversity can also, in effect, be indicative of soil health. The rich tapestry of soil biodiversity involves a highly complex series of interactions, which facilitates biological equilibrium, including the suppression of pests and diseases. Determining how to measure this and relate it to soil health is currently a research topic at IITA. For instance, can a minimum number of non-parasitic nematode genera signify a healthy soil, as suggested by Ferris et al. (2001), and can we rapidly determine this using molecular barcoding? (e.g., Yu et al. 2012).
In Africa, our knowledge of the microbial diversity is particularly sparse and underexplored, and the biological rewards to be reaped vastly underrecognized. At IITA we intend to change this.
Intensifying agriculture in Africa
For Africa to reverse its current trend of declining crop productivity and raise it to a more globally reflective level (Hazel and Wood 2008) intensification of cropping systems is essential (see Vanlauwe this edition). The Asian Green Revolution was successful due to, among other things, the broad-scale use of pesticides to combat pests and diseases. However, their excessive use was a hard lesson learned, and numerous such pesticides are now no longer available.
More ecologically sensitive alternatives are now sought, increasingly so, with soil microbial biodiversity a clear target for exploration. Cropping intensification, however, needs to be carefully managed. The more intensified the system, the greater the selection pressure for pests and disease, and the more severe the problem. The appearance of nematode problems, regularly overlooked and famously misdiagnosed, is an initial indicator of the breakdown of a sustainable system.
At IITA, root-knot nematodes (Meloidogyne spp.) are a key focus of attention. With a short life cycle, rapid multiplication rates, broad host range, and scarcity of suitable management options, they pose a particular nuisance and are probably the most important biotic constraint across Africa (Coyne et al. 2009).
Intensification also results in reduced biodiversity, with many microorganisms unable to survive the heightened soil disturbance or a more uniform cropping pattern. At IITA, in collaboration with Basel University (Switzerland), we investigated the effect of cropping intensification on the diversity and occurrence of arbuscular mycorrhizal fungi (AMF) associated with yam (Dioscorea spp.) (Tchabi et al. 2008).
Yam is viewed as a nutrient-hungry crop, and thus often planted in more fertile soils following the removal (slash and burn) of forest or long-term fallow, an unsustainable and environmentally detrimental practice. It is also particularly afflicted by parasitic nematodes. AMF needs to attach to and grow on plant roots, forming a special relation which is mostly mutually beneficial, creating enhanced nutrient flow to plants. This relatively small and rather unique study showed that yam is associated with a wide array of AMF species and is highly mycorrhizal. The high diversity and incidence of AMF communities, however, decreased dramatically following the removal of forest and cropping intensification (Fig. 1).
Is there a link therefore between yam nutrient access and AMF? And can we exploit this AMF-yam relation to help preserve West African forests? Furthermore, yam tubers were less affected by yam nematodes in the presence of AMF! The limited knowledge of soil microbial diversity in Africa is acutely highlighted with this study, which alone led to four species being newly described and contributed to the revision of the Phylum Glomeromycetes (Oehl et al. 2011).
Balancing ecological equilibrium
At IITA we recognize the potential of healthy soils for crop productivity, in addition to the resource potential of beneficial soil microorganisms for use in pest and disease management. While specialists work on diagnostics, establishing economic importance and developing management solutions for soil-borne pests and disease, similar efforts are focused on the beneficial aspects of soil biodiversity and soil health.
We recently discovered, for example, that fungal antagonists isolated directly from Meloidogyne spp. eggs were far more effective against these pests than those isolated from the soil (see photo), as is the usual practice (Affokpon et al. 2011).
Our plan is to work towards the identification of biological elements, which enhance crop productivity, as well as specific organisms, such as AMF, nitrogen-fixing bacteria and Trichoderma spp., for development as potential products.
As with the pain and suffering that Pandoraâ€™s box in the Greek mythology inflicted upon the world, so can the destructive potential to crops that the soil environment harbors be moderated, providing hope by balancing the ecological equilibrium. IITA strives to harness this equilibrium by understanding the mechanisms of the dynamics of healthy soils and determining the key factors that will help curtail pest and disease development.
Affokpon, A., D.L. Coyne, C.C. Htay, L. Lawouin, and J. Coosemans. 2011. Biocontrol potential of native Trichoderma isolates against root-knot nematodes in West African vegetable production systems. Soil Biology and Biochemistry 43: 600â€’608.
Coyne, D.L., D. Fourie, and M. Moens. 2009. Current and future management strategies in resource-poor regions. In: Root-knot Nematodes. CAB International, UK. pp. 444â€’475
Ferris, H., T. Bongers, and R.G.M. de Goede. 2001. A framework for soil food web diagnostics: extension of the nematode faunal analysis concept. Applied Soil Ecology 18: 13â€’29.
Hazell, P. and S. Wood. 2008. Drivers of Change in Global Agriculture. Philosophical Transactions of the Royal Society B-Biological Science 363: 495â€’515.
Oehl, F., G. Alves da Silva, I. SÃ¡nchez-Castro, B.T. Goto, L.C. Maia, H.E.V. Vieira, J-M. Barea, E. Sieverding, and J. Palenzuela. 2011. Revision of Glomeromycetes with entrophosporoid and glomoid spore formation with three new genera. Mycotaxon 117: 297â€“316.
Tchabi, A., D. Coyne, F. Hountondji, L. Lawouin,Â Wiemken, A. and F. Oehl. 2008. Arbuscular mycorrhizal fungal communities in sub-Saharan Savannahs of Benin, West Africa, as affected by agricultural land use intensity and ecological zone. Mycorrhiza 18: 181â€’195.
Yu, L., M. Nicolaisen, J. Larsen, and S. Ravnskov. 2012. Molecular characterization of root-associated fungal communities in relation to health status of Pisum sativum using barcoded pyrosequencing. Plant and Soil 357: 395â€’405.
Robert Abaidoo, email@example.com, Steve Boahen, Anne Turner, and Mahamadi Dianda
IITA and its partners have made significant progress in breeding grain legumes that are high yielding and drought tolerant, and have better disease and pest resistance as well as consumer-preferred traits, such as seed size, texture, and color. The use of these new improved varieties has contributed to increases in productivity on farmersâ€™ fields across sub-Saharan Africa.
While crop genetics is very important, the key to bridging the yield gap is to capitalize on the yield potential of a particular genotype and know how to manage it to maximize productivity in challenging environments. This is where the role of an agronomist becomes apparent: to design an integrated management system that reduces the effect of the biotic and abiotic stress factors limiting the productivity of a selected genotype in a given agroecology.Streaming and download Doctor Strange (2016)
Several collaborative projects, including N2Africa funded by the Bill & Melinda Gates Foundation through Wageningen University, are developing improved management options to enhance system productivity. The N2Africa project is being implemented in eight countries: DR Congo, Ghana, Kenya, Malawi, Mozambique, Nigeria, Rwanda, and Zimbabwe. It is a research-and-development partnership program that aims to develop, disseminate, and promote appropriate N2-fixation technologies for smallholder farmers, focusing on the major grain legumes. Although atmospheric air contains 78% N2, nitrogen (N) remains the most limiting nutrient for plant growth and also the most limited nutrient in degraded soils.
The good news is that legumes have the unique ability to fix atmospheric N through symbiotic association with root nodule bacteria. The opportunity exists through biological nitrogen fixation (BNF) to improve the yields of legumes in sub-Saharan Africa since current yields are only a small fraction of their potential. The integration of legumes in cropping systems can benefit associated cereal crops through N-sparing effects, N transfer, and non-N rotation effects. However, the process of BNF can be limited by several biotic and abiotic factors.
Evidence abounds that successful BNF depends on the interaction of environment (climate, rainfall day length, etc.), soil factors (acidity, aluminum toxicity, limiting nutrients), management (use of mineral fertilizers, planting dates and density, weed competition), legume species and variety, and rhizobium species and effectiveness. The current low crop productivity reported in legume-based systems can be attributed in part to the prevalence of these factors that limit BNF. In applying the study to legume-based systems, the N2Africa project expects that the identification of a combination of factors (see photos below), when appropriately managed, will optimize BNF and nutrient cycling in maize-based systems. This ability makes legumes a vital component of smallholder farming systems where the input of N fertilizer is almost negligible. Successful increases in legume productivity will lead to (1) increased availability of major sources of protein for direct consumption by rural households; (2) improved soil health through BNF and a reduced need for inorganic N fertilizers; (3) the breaking of pest and disease cycles of other crops when in rotation with legumes; and (4) improved income and health for the rural poor.
In collaboration with the national agricultural research and extension systems (NARES) in the eight countries, the project has isolated several indigenous rhizobia strains, notably in Kenya, Nigeria, Rwanda, and DR Congo, from local farmlands to identify and characterize superior strains for enhanced BNF. The goal is to develop inoculum production capacity using superior native rhizobial strains through collaboration with private sector partners. In addition, several commercial inoculant strains are being evaluated to identify improved varieties with enhanced BNF for integration into specific farming systems. Results of the project have shown that the inoculation of improved soybean varieties resulted in higher yields in several project sites.
However, grain yields may be constrained in P-deficient soils, hence the combined use of P fertilizers and inoculum consistently produced higher yields (Fig. 1). Note from the same figure that responses to inoculants and P fertilizer are highly variable with yield in amended plots ranging from 0 to over 3 t/ha under on-farm conditions. This further stresses the need for local adaptation (see Vanlauwe6) and the need to observe the main factors determining such variability.
Within the N2Africa project, having detailed monitoring and evaluation (M&E) tools within large-scale adaptation and dissemination field campaigns is an important component of the â€˜Research in Developmentâ€™ concept, at the core of its learning objectives. Where soil pH and levels of P are not too low, an application of 20 kg P/ha is adequate for the proper growth of soybean, cowpea, and groundnut but in soils deficient in P or with low pH,40 kg/ha is optimum.
The project is also identifying high-yielding legume varieties with varying maturity durations for specific environments to provide farmers with options that will enable them to match varieties to the length of the growing season. For example, when the rain is delayed in a particular year or for some reason farmers delay planting, they can select short-maturing varieties that can fit into the remaining growing period.
A major emphasis is being placed on determining the best time to plant various legumes in several agroecologies in combination with appropriate row spacing and plant population. Planting at the right time enhances yield in many ways: (1) the growing period coincides with good rainfall despite its variability in some years; (2) the crop is exposed to optimum temperature regimes; (3) growth coincides with the optimum solar radiation and daylength that regulate vegetative and reproductive growth phases in legumes due to their photosensitivity; and (4) plants escape the major pests and diseases that limit yield.
With project partners which include the national agricultural research and extension systems, nongovernmental organizations, community-based organizations, and farmersâ€™ associations, these technologies have been developed into recommended packages and are being demonstrated on-farm. The demonstration plots are established with the direct participation of farmers who are responsible for the day-to-day maintenance to encourage hands-on learning. Field days are also organized during the growing season for individuals and farmersâ€™ groups to create awareness about the technologies. The project encourages womenâ€™s participation as well. Other dissemination activities involve the distribution of inputs to project participants including improved seeds, inoculants, and P fertilizer and lime at agreed prices. The project has developed training programs to improve the skills of extension agents, farmers, and other stakeholders to ensure sustainability of the results after the project ends.
It is expected that these agronomic interventions should lead to increased diversification of N2-fixing legume species in smallholder farming systems in sub-Saharan Africa, expansion in the cultivation of grain, greater productivity in legume-based farming systems, and enhanced family incomes and nutrition. In collaboration with microbiologists, plant breeders, and the private sector, the selection and dissemination of efficient rhizobial inoculant strains and improved varieties of grain legumes with enhanced BNF capacities adapted to various environmental stresses will improve the prospects of increasing legume components in cropping systems as well as enhancing the production of expanded ecosystem services.
James Gockowski, firstname.lastname@example.org, Valentina Robiglio, Sander Muilerman, Nana Fredua Agyeman, and Richard Asare
In the humid lowlands of Africa, the expansion of extensive low-input agriculture is the most important driver of tropical deforestation and forest degradation with a negative impact on biodiversity and climate change (Norris et al. 2010; Phalan et al. 2011).
A recent global analysis of the climate change impact of agriculture estimated that between 8.64 and 15.1 million square km of land were spared from the plow as a result of yield gains achieved since 1961 (Burney et al. 2010). These land savings generated avoided greenhouse gas (GHG) emissions representing between 18% and 34% of the total 478 GtC emitted by humans between 1850 and 2005. A similar land use change analysis conducted for West Africa estimated that over 21,000 km2 of deforestation/forest degradation that occurred between 1988 and 2007 could have been avoided if the improved seeds/fertilizer already developed in the 1960s had been adopted (Gockowski and Sonwa 2011).
A methodology for quantifying and qualifying the impact of agricultural intensification on deforestation and poverty has been developed. This is based upon (a) the remote sensing analysis of land use change, (b) structured interviews with a random sample of rural households, and (c) an anthropological case study, all conducted in a defined benchmark area. The 1201 square km benchmark in the Bia district, Ghana, is the most important cocoa-growing area in the country whose increasingly diminished forests are home to the endangered Roloway monkey and are a global conservation priority. Cocoa producers in this benchmark have experienced rapid yield gains as a result of a sequential series of intensification policies that began in 2003.
Measuring deforestation and land use intensification
The retrospective household survey chronicled the land-use and migration history of each household in establishing a mean rate of deforestation from 1960 to 2003. More recent estimates were determined from the interpretation of satellite imagery from 2003 Landsat, 2006 Spot, and 2011 ALOS. Based on these analyses, the mean average rate of deforestation has fallen from 1,006 ha/year prior to the initiation of intensification policies to 212 ha/year.
Most of the deforestation still occurring has entailed encroachments in the Bia Game Reserve and the Krokosua Hills Forest Reserve and, to a lesser degree, Bia National Park whose environs are more stringently protected (Fig. 1). Outside these reserves there is scarcely any forest remaining.
The intensification policies initiated in the early 2000s focused on the acquisition and distribution of subsidized fertilizers and pesticides to farmers. The impact of these policies on yields and incomes was evaluated by comparing predicted outputs at 2000 and 2011 levels of input use with a micro-econometric model of household cocoa production constructed with data from the household survey (Table 1). Yields in the benchmark nearly tripled mainly because of the increased use of fertilizers and household income doubled (Gockowski et al. 2011).
Supporting smallholder fertilizer use instead of forests through REDD
The objective of Reducing Emissions from Deforestation and Forest Degradation (REDD) is to reduce GHG. The method is designed to use market valuation and financial incentives to reward deforestation agents, such as the cocoa farmers of Ghana, for a reduction in emissions.
To produce the output achieved in the benchmark area of our study using the extensive cocoa technology of 10 years ago would require an additional 150,000 ha of rainforest. The amount and value of carbon not entering our atmosphere because of avoided deforestation are an external value that is not captured in the market price received by the farmers intensifying production. Consequently there will be a socially suboptimal level of investment in intensification. REDD is envisaged as a mechanism for addressing this market failure.
Fertilizer use in Africa is the lowest of any region in the world. Not only does this perpetuate poverty it also contributes to emissions of GHG and loss of biodiversity. We have developed a methodology for determining the amount of deforestation avoided through increased use of fertilizer. Thus, it is a relatively simple matter to value the emissions that are also avoided. More difficult is the question of how to distribute these resources so as to correct this perceived market failure. Directly paying farmers for environmental services has proven to be a costly endeavor and has rarely been successful with smallholders.
As an alternative we propose a government-to-government transfer of earmarked funds for supporting agricultural intensification through investments in improved public infrastructure, extension services, agricultural research, and, yes, fertilizer subsidies. There is a risk that more productive technologies lead to greater deforestation, at least at the local level. To address this, a portion of the REDD funds should be used to enforce protected forest boundaries from encroachment. When properly implemented, agricultural intensification can relieve poverty, conserve biodiversity, and reduce emissions of GHG.
Burney, J.A., S.J. Davis, and D.B. Lobell. 2010. Greenhouse gas mitigation by agricultural intensification. Proceedings of the National Academy of Sciences 107(26): 12052â€“12057.
Gockowski, J. and D. Sonwa. 2011. Cocoa Intensification Scenarios and their Predicted Impact on CO2 Emissions, Biodiversity Conservation, and Rural Livelihoods in the Guinea Rain Forest of West Africa. Environmental Management 48(2): 307â€“321.
Gockowski, J., V. Robiglio, S. Muilerman, and N.F. Agyeman. 2011. Agricultural Intensification as a Strategy for Climate Mitigation in Ghana: An evaluative study of the COCOBOD High Tech Program, rural incomes, and forest resources in the Bia (Juaboso) District of Ghana. Final report to CGIAR Challenge Program on Climate Change, Agriculture and Food Security (CCAFS)â€”Poverty Alleviation through Climate Change Mitigation.
Norris K., A. Asase, B. Collen, J. Gockowski, J. Mason, B. Phalan, and A. Wade. 2010. Biodiversity in a forest-agricultural mosaicâ€”the changing face of West African rainforests. Biological Conservation 143: 2341â€“2350.
Phalan, B, M. Onial, A. Balmford, and R. Green. 2011. Reconciling Food Production and Biodiversity Conservation: Land Sharing and Land Sparing Compared. Science 333: 1289.
Bernard Vanlauwe, email@example.com, Alpha Kamara, Stefan Hauser, and Piet Van Asten
Over the past few years, the CGIAR system has been engaged in a substantial, research-led restructuring of its research agenda through the creation of the CGIAR Research Programs (CRP), supported by a Consortium Office, a Fund for international agricultural research, an Independent Science and Partnership Council, and an Independent Evaluation Arrangement. A total of seven CRPs are now active with several having a crop-specific focus, others a farming system focus, and others addressing themes related to natural resource management (NRM) or the creation of an enabling environment for the uptake of improved options. IITA is leading the Humidtropics CRP and contributing significantly to the CRPs on Water, Land, and Ecosystems (WLE) and the Climate Change, Agriculture, and Food Security (CCAFS), all of these having significant NRM components. This article highlights these components in the context of the overall CGIAR research framework and the specific contributions of IITA towards the success of these CRPs.
The humid tropics is home to 2.9 billion of the world’s poorest people. It is the part of the world with the biggest gap between its ecological and economic potential and human welfare. The Humidtropics CRP aims to realize more of that potential to improve the livelihoods of the majority of the population and protect their environment and natural resources from the usual rapid degradation when used for agriculture or forest (timber) exploitation. Humidtropics seeks intensification pathways and critical points of intervention to design superior crop, livestock, fallow, and perennial (tree) production systems along with improved soil, water, and vegetation management practices, and the identification of investment strategies for sustainable natural resource base management.
Interventions will increase overall farm and system productivity and income while improving the natural resource base, particularly soil quality. Humidtropics will strategically select critical entry points that foster more diverse system components to generate more equitable agricultural growth in which rural communities move beyond commodities, reduce their risks, sustainably manage their natural resources, and effectively reduce rural poverty.
Humidtropics is led by IITA in partnership with the International Center for Tropical Agriculture (CIAT), International Livestock Research Institute (ILRI), World Agroforestry Centre (ICRAF), International Potato Center (CIP), Bioversity International, International Water Management Institute (IWMI), International Centre of Insect Physiology and Ecology (icipe), Forum for Agricultural Research in Africa (FARA), The World Vegetable Center (AVRDC), and Wageningen University. It will operate in various action areas in Africa, Latin America, and Asia with the Western Humid Lowland and the East and Central African Highland Action Areas led by IITA. Humidtropics is a systems research program that covers all lowland humid and subhumid ecologies (between dry land and aquatic), draws on research in commodity CRPs, and integrates technologies and forecasting ability from the CRPs on Policies and Markets, Nutrition and Health, Water and Land, and Climate Change (see diagram).
Water, Land, and Ecosystems (WLE)
The global population in 2050 will be about 9 billion, with most of the increase between now and then taking place in developing countries. To feed the world in 2050 and beyond, we need to intensify agricultural production. Many observers believe that intensification will cause unacceptable harm to the environment, perhaps undercutting the ecosystems that support agriculture. WLE challenges this perspective and examines how we can intensify agriculture while protecting the environment and lifting millions of farm families out of poverty.
To achieve the vision of sustainable intensification, we must redouble our efforts to increase agricultural productivity, while protecting the environment, and we must conduct new and integrative research on agricultural and ecosystem interactions. Consequently the objective of WLE is to learn how to intensify farming activities, expand agricultural areas and restore degraded lands, while using natural resources wisely and minimizing harmful impacts on supporting ecosystems.
Within the broad topic of WLE, we have identified five strategic research portfolios (SRPs): Irrigated Systems, Rainfed Systems, Resource Reuse and Recovery, River Basins, and Information Systems. The Rainfed Systems SRP, to which IITA is contributing, targets 80% of the worldâ€™s farmland that is largely rainfed. Although many farmers in rainfed areas capture and store water for use as supplemental irrigation, millions more entirely depend on rainfall. In many areas, increasing populations have placed substantial pressure on rainfed cropland and on the land and water resources used by livestock. As a result, the land and water resources in many areas are degraded and unproductive. WLE researchers will determine ways to restore degraded resources using multifunctional landscape management approaches, and will develop integrated soil and water management techniques.
In pastoral systems, extensive land degradation and the loss of access to water and land resources threaten the livelihoods of millions of pastoralists, leading to conflicts in some areas. WLE researchers will determine the changes in land and water management and the complementary policies needed to support pastoral livelihoods. The Rainfed System SRP currently works around five problem sets: (1) Recapitalizing African soils and reducing land degradation; (2) Revitalizing productivity on responsive soils; (3) Increasing agricultural production while enhancing biodiversity; (4) Enhancing availability and access to water and land for pastoralists; and (5) Reducing risk by providing farmers with supplemental irrigation.
Climate Change, Agriculture, and Food Security (CCAFS)
Climate change is an immediate and unprecedented threat to the livelihoods and food security of hundreds of millions of people who depend on small-scale agriculture. To overcome these threats, the CGIAR and Earth System Science Partnership have united through CCAFS, a strategic ten-year partnership. Farmers, policymakers, donors, and other stakeholders are strongly involved to integrate end-user knowledge and needs. Synergies and tradeoffs between climate change, agriculture, and food security are studied to promote more adaptable and resilient agriculture and food systems. CCAFS is structured around four thematic research areas: (Theme 1) Adaptation to Progressive Climate Change, (Theme 2) Adaptation through Managing Climate Risk, (Theme 3) Pro-poor Climate Change Mitigation, and (Theme 4) Integration for Decision Making. Place-based research is focused on five regions: East Africa, West Africa, South Asia, Latin America, and Southeast Asia.
IITA is one of the 15 CGIAR centers involved and it particularly contributes to research on:
â€¢Â Â Â Theme 1 on crop G Ã— E interactions. The major focus is on the IITA crops cassava, maize, soybean, yam, cowpea, and banana, but with other crops in the system being investigated as well, including horticultural crops and tree crops such as coffee and cocoa.
â€¢Â Â Â Theme 2 on plant health Ã— climate change: IITA has a strong plant health team that is currently exploring the relationship between climate variables and major pest and disease threats, with the same crop focus as listed under G Ã— E.
â€¢Â Â Â Theme 3 on analyzing trade-offs and synergies in climate change adaptation and mitigation in perennial-based crop systems in the humid tropics: The research focuses particularly on coffee and cocoa-based systems (see page 44 in this issue).
â€¢Â Â Â Theme 4 on communicating the results of the trade-off and carbon-footprinting analysis to the stakeholders, in particular policymakers, certification bodies, and the private sector.
The future of NRM
Most CRPs have moved into an implementation phase and all facilitating structures have been put in place, which is probably the most exciting change in the way of doing business within the CGIAR since its inception. From the foregoing summary, the crucial role of IITA as a whole and the NRM research areas more specifically is clear, especially for the African continent. Although IITA may have lost some of its NRM capacity over the past decade, as shown in some of the articles in this publication, much NRM innovation, strategic thinking, and practical solution development is still happening at IITA and will only be strengthened over the coming decade with the renewed investment of IITA in NRM.
Martin Jemo, firstname.lastname@example.org, Cargele Masso, Moses Thuita, and Bernard Vanlauwe
Background and issues
More and more commercial products, such as biofertilizers, biopesticides, and chemical agro-inputs, are being sold to smallholder farmers in sub-Saharan Africa (SSA). However, their quality and efficacy, especially for the microbiological products, are not properly evaluated before they are commercialized, because regulations are lacking or inadequate. There is a crucial need to implement appropriate regulatory mechanisms.
When microbiological products are used as directed, they are generally more environmentally friendly than synthetic fertilizers. Also, they mainly improve soil fertility by either biological nitrogen fixation (BNF) (rhizobium inoculants) or by increasing the availability or uptake of plant nutrients already in the soil (e.g., phosphorus- solubilizing Pseudomonas putida). Unlike microbiological products, synthetic fertilizers N and P chemical fertilizers) are sometimes associated with nutrient loss to the environment causing greenhouse gas emissions or eutrophication. Hence, one of benefits of using microbiological products in integrated soil fertility management (ISFM) is to preserve the natural resource from degradation, while sustaining adequate crop production.
The goal of the Commercial Products (COMPRO-II) project is therefore to improve crop yields, improve food security, and minimize the negative impacts of bad or inadequate agricultural practices on the environment.
The project is built on public-private partnerships to develop effective laws and regulations for biofertilizers and other agro-inputs in SSA. It is expected that the large-scale impact of this project will be a significant reduction of inefficacious agro-inputs in the marketplace, resulting in improved crop yields.
Products evaluated under the COMPRO project are grouped into three categories: I: rhizobium inoculants, II: other microbial inoculants, and III: non-microbiological products. However, COMPRO-II mainly focuses on categories I and II.
The product evaluation has three key steps: laboratory/greenhouse testing, field testing, and the application of appropriate ISFM (Fig. 1). An additional step consists of the scaling up of the mostÂ promising products retained after the three key steps.
Overview of COMPRO-I results
Over 100 commercial products from the three categories were evaluated under field conditions in Kenya, Nigeria, and Ethiopia from 2009 to 2011 in the first phase of the project (COMPRO-I). A significant economic benefit to farmers was found for only a few products (Table 1). On average, the benefitâ€“cost ratio (BCR) for rhizobium inoculants in soybean was found to be US$4.1/dollar and maize seeds coated with plant nutrients resulted in a BCR of $4.6/ dollar. A BCR of 2.5 is considered satisfactory for the adoption of the technology. The photo below also shows a significant growth improvement for faba bean following treatment with a rhizobium inoculant.
A better understanding of the fate and dynamics of the strains in microbiological products after their application to the soil requires adequate analytical tools. In COMPRO-I molecular tools to detect the Mitochondrial Large Subunit (mtLSU) DNA of the isolate Glomus intraradices in commercial products (e.g., Rhizatech) was developed (Fig. 2). The yield increase following the application of Rhizatech was associated with faster root colonization by arbuscular mycorrhizal fungi (AMF) as determined by the mtLSU DNA tool.
COMPRO-II is further investigating the information provided by a certain region of AMF DNA (mtLSU) and the use of Real Time PCR approach to discriminate different species and isolates of AMF. For example, such tools will be used to determine factors that control BNF in cowpea, a crucial food crop, to develop appropriate inoculants for the benefit of smallholder farmers in Africa.
Based on the economic analysis, a relatively low percentage of the commercial products evaluated under COMPRO-I showed a significant benefit to smallholder farmers. Hence, there is a need to implement adequate regulations to prevent the proliferation of inefficacious products in the marketplace and also to disseminate the most promising products by increasing farmersâ€™ awareness about them. Such a goal can be reached only when adequate resources are available. COMPRO-II intends to address those issues based on the lessons learned from COMPRO-I. Scaling-up of efficacious microbiological products will not only contribute to improved crop yields, increased food security, and reduced rural poverty, but will also, when used in adequate ISFM, contribute to preventing agricultural land degradation caused by a lack of agricultural inputs or the heavy application of chemical fertilizers.
Inadequate crop production systems generally result in degraded agroecosystems and reduced crop yields, and therefore have negative impacts on NRM. Biofertilizers are considered environmentally friendly and, when properly used, contribute to improved soil fertility (e.g., BNF and phosphorus availability), and preserve natural resources. However, in SSA, many smallholder farmers are not familiar with those products, while regulations are virtually non-existent in many countries. The COMPRO project intends to address those gaps by: (1) screening commercial products including biofertilizers through a stringent scientific scrutiny, (2) communicating information on, and disseminating products proven best or promising, and promoting ISFM, (3) developing adequate regulations to ensure the safety, efficacy, and quality of commercial products, and (4) building the capacity of countries in SSA to implement and enforce such regulations.
Alpha Y. Kamara, email@example.com
In the past two decades, maize has spread rapidly into the moist savannas of West Africa, replacing traditional cereal crops such as sorghum and millet, particularly in areas with good access to fertilizer inputs and markets.
In the West African moist savannas, higher radiation levels, lower night temperatures, and a reduced incidence of diseases and insect pests have helped to increase maize yield potentials compared with traditional areas for maize cultivation (Kassam et al. 1975). Because of the availability of short-season early maturing varieties, cultivation has gradually spread to the Sudan savanna where the growing period is 90â€“100 days. Despite the expansion in these production areas, maize yields in farmersâ€™ fields average from 1 to 2 t/ha in contrast to the higher yields of about 5 to 7 t/ha reported on breeding stations in the region (Fakorede et al. 2003).
Maize production in the savannas is faced with several production constraints which limit productivity. Poor soil fertility, drought, and Striga hermonthica parasitism combined can reduce on-farm yield by over 70% even with the use of high-yielding varieties. Land-use intensification in the northern Guinea savanna has resulted in serious land degradation and nutrient depletion (Oikeh et al. 2003). Nitrogen (N) is the nutrient most deficient in the soils and it most often limits maize yield (Carsky and Iwuafor 1995). Unfortunately, due to high cost and poor infrastructure, the availability of N fertilizers is limited.
The problem of poor soil fertility in the Guinea savanna is compounded by recurrent drought at various stages of crop growth. For maize, drought at the flowering and grain-filling stages can cause serious yield losses (Grant et al. 1989). This indicates that farmersâ€™ fields are rarely characterized by only one biotic stress. It would, therefore, be desirable to increase the tolerance of crops to several stresses that occur in the target environment (BaÃ±ziger et al. 1999).
Surveys in the northern Guinea and Sudan savannas of Nigeria showed that Striga has remained a serious problem, attacking millet, sorghum, maize, and upland rice (Showemimo et al. 2002). In northern Nigeria, over 85% of fields planted to maize and sorghum were found to be infested (Dugje et al. 2006). Grain yield losses ranged from 10 to 100% for these crops (Oikeh et al. 1996). In addition to the damage from parasitic weeds, significant losses occur in maize if other weeds (grassy and broadleaf) are left to compete freely with the crop.
To maintain a good crop and increase grain yield/unit area, agronomic best practices should be undertaken to address these constraints. Appropriate soil fertility management, drought adaptation, and proper weed management can help to close the yield gap for maize in the West African savannas.
Soil fertility management
Maize is a heavy feeder particularly in terms of mineral N. Because soils in the West African savannas are low in plant nutrients, the crop cannot be grown without the application of some form of mineral and/or organic inputs. Farmers often see a dramatic increase in the response of maize to mineral N. If the fertilizer is applied wrongly, however, use efficiency will be reduced and the benefit will be minimal. For optimum economic yield, we recommend 50 kg/ha each of N, P, and K in the form of NPK 15:15:15 at planting if moisture is sufficient or at one week after planting (WAP), and 50 kg N/ha in the form of urea at 3â€“4 WAP. Increased use of organic and mineral fertilizers, together with diversification in cropping to include legumes grown in rotation is an important tool in restoring or sustaining soil fertility of the intensifying cropping systems of the dry savannas (Sanginga et al. 2003).
These so-called â€œbalanced nutrient management systemsâ€ can be further enhanced through the use of improved cultivars that are drought tolerant and can use available nutrients efficiently, such as maize cultivars developed at IITA. This approach that has come to be known as integrated soil fertility management (ISFM) is not characterized by unique field practices, but is a fresh approach to combining available technologies in ways that preserve soil quality while promoting its productivity (Sanginga et al. 2003).
Agronomic practices for drought adaptation
Agronomic practices that enable farmers to adapt to the effect of mid- and end-of-season drought will increase maize productivity in the West African savannas. Several strategies have been developed for the conservation of soil and water to maintain productivity including rainwater harvesting, live barriers, supplementary irrigation, minimum tillage, mulching, bunded basins, and tree planting (Drechsel et al. 2004).
A central approach to increasing crop production in the dry savannas is the planting of well-adapted cultivars at the optimum date. The short growing season and frequent droughts require early and extra-early maturing crop cultivars with drought tolerance. Late- and medium-maturing cultivars, should also be drought tolerant and planted by mid-June after the rains have established. Breeders at IITA and partner institutions have developed cultivars that are early maturing, tolerant of drought, high temperatures, and low contents of soil nutrients and resistant to pests and diseases. These early maturing cultivars can be planted between mid-June and 25 July in the Guinea savannas and between the first week of July and mid-July in the Sudan savanna.
Different approaches are recommended in managing parasitic weeds on the one hand and grassy and broadleaf weeds on the other. An integrated approach is recommended for the control of parasitic weeds. Because Striga attacks the plant underground and causes damage before emergence on the host, the use of postemergence herbicides and hand pulling cannot be recommended. Damage in maize can be reduced by growing varieties that are tolerant of or resistant to Striga or by planting trap crops such as varieties of groundnut (Arachis hypogaea), soybean (Glycine max), cowpea (Vigna unguiculata), and sesame (Sesamum indicum) that stimulate the Striga seeds to germinate without providing a viable host (Carsky et al. 2000).
Some studies have shown that applying N fertilizer reduces Striga emergence and numbers, and boosts cereal grain yield (Showemimo et al. 2002; Kamara et al. 2009). Applying N fertilizer may not be feasible as a stand-alone solution to managing Striga in maize because of the high cost but the combined use of N fertilizer and Striga-tolerant/resistant varieties has shown promise in the West African savannas (Showemimo et al. 2002; Kamara et al. 2009). However, control is most effective if a range of practices is combined into a program of integrated Striga control (ISC) that can provide sustainable control over a wide range of biophysical and socioeconomic environments. Ellis-Jones et al. (2004) showed that growing Striga-resistant maize after a soybean trap crop more than doubled economic returns compared with continuous cropping with local (nonresistant) maize. Kamara et al. (2008) showed that these practices reduced Striga infestation and damage on farmersâ€™ fields and increased productivity by more than 200%.
Although manual weeding is an age-old practice in West Africa, it is no longer sustainable because of high labor costs and the aging farming population. Judicious use of herbicides is recommended to control weeds effectively and increase maize productivity. We normally recommend the use of postemergence herbicides to kill weeds before land preparation and planting. Two common types are Glyphosate and Paraquat. Glyphosate (Round-up, Glycel, Force-up) is usually strictly applied before planting, whereas Paraquat (Gramazone) can be mixed with Pendimenthalin (Stomp, Pendilin) and applied immediately after planting. Paraquat kills any live weeds in the field; Pendimenthalin kills preemerging weeds.
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Banziger, M., G.O. Edmeades, and H.R. Lafitte. 1999. Selection for drought tolerance increases maize yields across a range of nitrogen levels. Crop Science 39(4): 1035â€“1040.
Carsky, R.J., D.K. Berner, B.D. Oyewole, K. Dashiell, and S. Schulz. 2000. Reduction of Striga hermonthica parasitism on maize using soybean rotation. International Journal of Pest Management 46: 115â€“120.
Carsky, R.J, and E.N.O. Iwuafor. 1995.Â Contribution of soil fertility research and maintenance to improved maize production and productivity in sub-Saharan Africa. In: Proceedings of Regional Maize Workshop, 29 Mayâ€“2 June 1995, IITA, Cotonou, Benin Republic
Drechsel, P., A. Olaleye, A. Adeoti, L. Thiombiano, B. Barry and K. Vohland. 2004. Adoption driver and constraints of resource conservation technologies in sub-Saharan Africa. Available at http://westafrica.iwmi.org/Data/Sites/17/Documents/PDFs/AdoptionConstraints-Overview.pdf.
Dugje, I.Y., A.Y. Kamara, and L.O. Omoigui. 2006. Infestation of crop fields by Striga species in the savanna zones of northeast Nigeria. Agriculture, Ecosystems andÂ Environment 116: 251â€“254.
Ellis-Jones, J., S. Schulz, B. Douthwaite, M.A. Hussaini, B.D. Oyewole, A.S. Olanrewaju, and R. White. 2004. An assessment of integrated Striga hermonthica control and early adoption by farmers in northern Nigeria. Experimental Agriculture 40: 353â€“368.
Kamara, A.Y., A. Menkir, S.O. Ajala, and I. Kureh I. 2005. Performance of diverse maize genotypes under nitrogen deficiency stress in the northern Guinea savanna of Nigeria. Experimental Agriculture 41(2): 199â€“212.
Kamara, A.Y., F. Ekeleme, A. Menkir, D. Chikoye, and L.O. Omoigui. 2009. Influence of nitrogen fertilization on the performance of early and late-maturing maize cultivars under natural infestation with Striga hermonthica. Archives of Agronomy and Soil Science 55(2):125â€“145.
Kamara, A.Y.,Â J. Ellis-Jones, P. Amaza, F. Ekeleme, A. Menkir, L. Omoigui, I.Y. Dugje, and N. Kamai. 2008. A participatory approach to increasing productivity of maize through Striga hermonthica control in northeast Nigeria. Experimental Agriculture 44 (3):349â€“364.
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Menkir, A., B. Badu-Apraku, S. Ajala, A.Y. Kamara, and A. Ndiaye. 2009. Performance evaluation of early-maturing maize landraces and improved varieties under contrasting moisture supply. Plant Genetic Resources: Characterization and Utilization 7(3): 205â€“215.
Oikeh, S.O. 1996. Dynamics of soil nitrogen in cereal-based cropping systems in the Nigerian Savanna. Ph.D. dissertation, Ahmadu Bello University, Zaria. Nigeria.
Oikeh, S.O., R.J. Carsky, J.G. Kling, V.O. Chude, and W.J. Horst. 2003. Differential N uptake by maize cultivars and soil nitrate dynamics under N fertilization in West Africa. Agriculture, Ecosystems andÂ Environment 100: 181â€“191.
Oikeh, S.O., V.O. Chude, G.J. Kling, and W.J. Horst. 2007. Comparative productivity of nitrogen-use efficient and nitrogen-inefficient maize cultivars and traditional grain sorghum in the moist savanna of West Africa. African Journal of Agricultural Research 2(3): 112â€“118.
Sanginga, N., K. Dashiell, J. Diels, B. Vanlauwe, O. Lyasse, R.J. Carsky, S. Tarawali, B. Asafo-Adjei, A. Menkir, S. Schulz, B.B. Singh, D. Chikoye, D. Keatinge, and Rodomiro Ortiz. 2003. Sustainable resource management coupled with resilient germplasm to provide new intensive cerealâ€“grain legumeâ€“livestock systems in the dry savanna. Agriculture, Ecosystems and Environment 100: 305â€“314.
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