Increasing productivity the ISFM way

Farm productivity has been cited as a major entry point to achieving success in overcoming rural poverty. Photo by IITA
Farm productivity has been cited as a major entry point to achieving success in overcoming rural poverty. Photo by IITA

Bernard Vanlauwe, b.vanlauwe@cgiar.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 2012–2020, ISFM is one of the main pillars of the natural resource management (NRM) research area.

Figure 1. Conceptual relationship between agronomic efficiency of fertilizers and organic resource and implementation of various ISFM components.
Figure 1. Conceptual relationship between agronomic efficiency of fertilizers and organic resource and implementation of various ISFM components.

Whats is ISFM?
We defined ISFM as “A set of soil fertility management practices that necessarily include the use of fertilizer, organic inputs, and improved germplasm combined with the knowledge on how to adapt these practices to local conditions, aiming at maximizing agronomic use efficiency of the applied nutrients and improving crop productivity. All inputs need to be managed following sound agronomic principles” (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 farmers’ 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 “4R” Nutrient Stewardship Framework—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.

Figure 2. The 4R Nutrient Stewardship model, International Plant Nutrition Institute.
Figure 2. The 4R Nutrient Stewardship model, International Plant Nutrition Institute.

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).

Figure 3. Agronomic efficiency of fertilizer N as affected by combination with different classes of organic inputs.
Figure 3. Agronomic efficiency of fertilizer N as affected by combination with different classes of organic inputs.

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 farmer’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.

A 3-week-old maize crop in two different plots within the same farm, Western Kenya
A 3-week-old maize crop in two different plots within the same farm, Western Kenya

Successful uptake of ISFM practices
Several examples can be identified where ISFM has made a difference to smallholder farmers, including (1) dual-purpose grain legume–maize rotations with targeted fertilizer applications pioneered by IITA for the moist savannas (Sanginga et al. 2003) and (2) micro-dose fertilizer applications in legume–sorghum or legume–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 legume–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.

Outlook
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.

References
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 cereal–grain legume–livestock systems in the dry savanna. Agriculture, Ecosystems and Environment, 100: 305–314.
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 farmers’ income using a strategic application of fertilizers in West Africa. Pages 201–208 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: 337–354.
Vanlauwe, B, A. Bationo,  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: 17–24.
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: 35–50.
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.

Effective commercial products for farmers

Martin Jemo, m.jemo@cgiar.org, Cargele Masso, Moses Thuita, and Bernard Vanlauwe

Farmer screening soybean varieties in Kabamba, DRC. Photo by IITA
Farmer screening soybean varieties in Kabamba, DRC. Photo by IITA

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.

Figure 1. Screening framework of commercial products in Ethiopia, Kenya, and Nigeria under COMPRO-I.
Figure 1. Screening framework of commercial products in Ethiopia, Kenya, and Nigeria under COMPRO-I.

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.

Product screening
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 most  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 benefit–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.

Table 1. Yield increase and benefit-cost ratio of selected products evaluated under various field conditions in Ethiopia, Kenya, and Nigeria.
Table 1. Yield increase and benefit-cost ratio of selected products evaluated under various field conditions in Ethiopia, Kenya, and Nigeria.

Analytical tools
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.

Figure 2. Electrophoresis gel showing fragments amplified with “INTRA” primers targeting ribosomal DNA of <em/>Glomus intraradices.
Figure 2. Electrophoresis gel showing fragments amplified with “INTRA” primers targeting ribosomal DNA of Glomus intraradices.

Future plans
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 farmers’ 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.

A farmer shows inputs used to get the healthy maize crop. Photo by FIPS
A farmer shows inputs used to get the healthy maize crop. Photo by FIPS

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.

NRM in cassava and yam production systems

Stefan Hauser, s.hauser@cgiar.org

Cassava has the potential to produce roots even under poor soil conditions. Photo by IITA
Cassava has the potential to produce roots even under poor soil conditions. Photo by IITA

Why are yields of cassava in Thailand and India three times higher than in Africa and production costs in Brazil only one-third of those here? Although Africa suffered from the Cassava Mosaic Disease pandemic and currently faces the threat of Cassava Brown Streak Disease, breeding tolerant and resistant germplasm has contributed to yield gains over the last three decades. Thailand, India, and Brazil have been successful in commercial cassava production with yields between 25 and 40 t/ha. The question arises: how can African farmers realize more of the >80 t/ha yield potential of cassava?

Natural resource management (NRM), agronomy, and crop husbandry have hardly ever been credited with “breakthrough” solutions to hunger and poverty. However, when more than 50-75% of the cassava yield potential is not being realized, major improvements are clearly possible through NRM, agronomy, and appropriate crop husbandry.

Agronomy and crop husbandry
For West Africa there is still a dearth of agronomic information on cassava. Currently a density of 10,000 plants/ha is the standard, while further increases are being recommended without concrete data on the yield responses to increased density by different growth types. Cassava varieties vary widely in their branching height and level of ramification, leading to different levels of ground cover by single plants and of the start and intensity of intra-specific competition. Cassava yield distribution within the same variety is highly biased (Fig. 1), raising questions on the optimum plant density and issues such as genetic uniformity and crop responses to edaphic (soil) factors.

Figure 1. Relative contribution to yield of individual plants of cassava variety Zizila in DRC.
Figure 1. Relative contribution to yield of individual plants of cassava variety Zizila in DRC.

One future effort will be to determine optimum plant densities for monocrops by major cassava growth types.

Intercropping cassava with maize or grain legumes is still widely practiced and needs to be improved. The short-term intercrops are cleared from the field, leaving space unused that can be invaded by weeds, thus there needs to be a follow-up either with weed control or a second crop to occupy the open space. Various crops will be tested for their capacity to perform between developed cassava plants and their contribution to total system productivity.

Weed control remains a problem as there are no postemergence herbicides that cassava would tolerate. Combinations of preemergence herbicides with appropriate planting techniques have the potential to reduce weed competition and labor. For instance, a preemergence herbicide can be applied before planting cassava. The herbicide kills germinating seeds as they break through the herbicide-sealed soil surface. The cassava stakes need to be planted in a vertical position and the orientation needs to be correct so that no emerging cassava leaves touch the soil surface. Such technologies combined with the follow-up use of postemergence herbicides with shields can drastically reduce labor and increase productivity as weeding can be done at the most efficient time.

Fertilizer
Fertilizer use is low in Africa yet it appears certain that fertilizer or other forms of soil nutrient replenishment can contribute to yield increases, higher farm incomes, possibly to lower consumer prices, and thus to better livelihoods. Using average nutrient uptake into all cassava plant parts (dry matter basis) of 6.2 kg N/t, 1 kg P/t, and 5.3 kg K/t, a total supply of 165–25–145 kg N-P-K/ha is required to attain 50% of the current potential yield (45 t/ha fresh roots). Such amounts are unlikely to be supplied by the soil and thus nutrient supply is a crucial factor in achieving higher cassava yields.

There are no recent fertilizer response curves for cassava and yam in West Africa, hence, farmers do not know the composition and amounts of fertilizer to apply. The nutrient(s) most limiting to cassava production have not been quantitatively determined. The replenishment of any most limiting nutrient would lead to substantial yield increases. Depending on the limiting nutrient, productivity and profitability increases may be possible at a very low cost and risk. IITA uses a stepwise approach, first determining the most limiting nutrient(s) followed by elaborating the optimum quantity required and the construction of recommendations for optimal nutrient composition and quantities. IITA is currently working with the International Fertilizer Development Center on testing special fertilizer blends for cassava, addressing the augmentation of neglected nutrients such as sulfur, magnesium, zinc, and boron.

Use of other nutrient sources
Compost, manure, mulch, and rock phosphate have all been proposed as means to improve soil nutrient status and crop production. However, none of these sources has had a major impact as farmers need land to produce biomass or else infrastructure is required to mine, process, and distribute rock phosphate. Although the biological sources are important, constraints in biomass production need to be overcome first.

Figure 2. Crop yield response to planted herbaceous fallow in West and Central Africa.
Figure 2. Crop yield response to planted herbaceous fallow in West and Central Africa.

Mineral fertilizers alone cannot sustain crop production on degraded land. Soil organic matter and  soil micro-, meso-, and macro-fauna are important in maintaining soil quality and health. Traditionally, fallow phases between crops were replenishing the soils’ production capacity. With increased population densities, fallow phases have been shortened or no longer exist. Thus, soils do not recover but continue to lose their production potential. Farmers do not seem to invest in soil fertility but look for ways of coping with ever less fertile soils, thereby degrading them to a stage where cropping becomes unprofitable.

Such situations have been encountered in southern Bénin. Soil fertility and quality management techniques, such as cover crops, manure application, or any other form of organic matter and nutrient recycling have not been adopted at larger scales. In retrospect, there have been constraints to the adoption that were not considered in the process of technological development. Today, with more options available and a stronger and earlier involvement of farmers in research for development, such approaches are worth reconsidering. One such technology, using leguminous cover crops, had little if any success in cassava (Fig. 2).

Controlling the cover crop was a major problem. Consequently IITA works today on efficient and effective control methods. Pueraria phaseoloides was introduced to smallholders in southern Cameroon but it was not readily accepted as farmers immediately identified it as an aggressive weed, able to destroy crops. However, two years into the use of Pueraria, fallow farmers noticed that the weeds most difficult to control had disappeared and that it was easier to clear Pueraria than the natural fallow. Some farmers burned the Pueraria only to find the land ready to crop without major labor input. Yields of cassava, maize, and groundnut were generally higher after Pueraria, whereby the labor-saving burning produced the highest yields (Fig. 3).

Figure 3. Cassava fresh root yield in burned and mulched maize-cassava and burned maize-cassava-groundnut intercrop.
Figure 3. Cassava fresh root yield in burned and mulched maize-cassava and burned maize-cassava-groundnut intercrop.

Considering farmers’ needs
Pueraria was introduced for soil fertility replenishment but was adopted for its labor-saving effects. Soil fertility was not perceived as a problem and thus positive effects on the soil could be compromised (by burning) without compromising yields. Effects such as weed suppression and the reduction of soil-borne pests and diseases may contribute to the yield increases after Pueraria.

Livestock integration and the search for synergies
Few farmers adopted the use of green manures for soil fertility improvement because they have no direct benefits from it. Herbaceous legumes have rarely been used to feed livestock, although there is (anecdotal) evidence that livestock feed on them and that they are beneficial to growth and reproduction. In the IITA-led CRP on Humidtropics, livestock integration will be a major aspect. It will add value to green manure species when these are used to feed livestock that will also benefit from the canopies of root and tuber crops (cassava leaves) remaining at root harvest. Thus, there will be an increase in returns of animal manure to fields, and to crop yields through the combined use of green and animal manures for improved food security and farm incomes.

Outlook
Efficient combinations of agronomic practices, nutrient supply, and soil management practices will be developed to increase the productivity of cassava and yam while improving the status of the natural resource base. Synergistic effects between these measures and the integration of livestock or fish farming will increase resource use efficiency and income generation as well as the quality of the farm food supplies. Due consideration of social and gender aspects in farm household operations will identify the entry point best suited for IITA’s interventions. Farmers’ feedback and innovations will be integrated into approaches on sustainable intensification to increase food production and improve rural livelihoods while enhancing the capacity of the agroecosystems to deliver essential services.

References
Hauser, S. and C. Nolte. 2002. Biomass production and N fixation of five Mucuna pruriens varieties and their effect on maize yields in the forest zone of Cameroon. Journal of Plant Nutrition and Soil Science 165: 101–109.
Hauser, S., C. Nolte, and R.J. Carsky. 2006. What role can planted fallows play in humid and sub-humid West Africa? Nutrient Cycling in Agroecosystems 76: 297–318.

Boosting the productivity of cassava-based systems in DR Congo

Bernard Vanlauwe, b.vanlauwe@cgiar.org, Patrick Mutuo, Nzola Mahungu, and Pieter Pypers

The intensification of African agriculture is an essential response to the increasing demands for more food without endangering important natural resources, including the forests in the Congo basin.

Because of its potential to produce some roots, cassava is often considered a crop that “likes” poor soils but, as all other crops, it responds to and requires a sufficient amount of nutrients to produce attainable yields. The transformation of cassava from a food security to a cash crop in many countries in Africa further stresses the need for nutrient replenishment strategies in cassava-based systems since the transport of cassava roots to processing plants can accelerate the amount of nutrients exported from the farm.

In recent years, integrated soil fertility management (ISFM) (see article by Vanlauwe et al. this publication) has been accepted by many organizations as the underlying technical framework for the sustainable intensification of smallholder systems in Africa. This article highlights the progress of work on the application of ISFM principles in the context of cassava-based systems in DR Congo.

In DR Congo application of 2 bags of NPK fertilizer per hectare results in root yield increases from 30% to 160%.
In DR Congo application of 2 bags of NPK fertilizer per hectare results in root yield increases from 30% to 160%.

Current situation
In the highlands of Sud-Kivu province, cassava and common beans are among the main food crops traditionally cultivated in mixed cropping systems. Cassava monocropping is done only in marginal fields where other crops fail to yield. Farmers generally allocate about 0.2–0.3 ha (30–45% of their farm area) to cassava–legume intercropping and obtain average yields of 400–800 kg/ha of legume grains and 10–15 t/ha of cassava fresh roots. Pressure on land is very heavy due to high population densities and justifies agricultural intensification and investment in soil productivity.

In Bas-Congo province, on the other hand, farmers practice slash-and-burn agriculture. Cassava is grown for 1 or 2 years, followed by fallow periods of 2 to 4 years. In the past two decennia, the population has grown by more than 50% leading to more demands for food, especially from nearby Kinshasa. Improved and sustainable, fire-free production systems are urgently needed. In DR Congo, most farmers have no access to improved varieties and have very limited options to improve soil fertility.

Fertilizer and germplasm
First, the use of improved, pest-and disease-resistant varieties in combination with appropriate rates of NPK fertilizer was observed to result in a 30–160% increase in cassava root yields in eastern DR Congo. A visible increase was observed in yields of the stems, important for the production of planting material (see photo). In western DR Congo, cassava yields doubled from 12 to 25 t/ha with the application of moderate rates of NPK and reached over 40 t/ha with higher rates. Several initiatives are taking place to ensure that large quantities of planting materials reach smallholder farmers with specific attention being given to those varieties resistant to cassava mosaic disease and the brown streak virus.

Figure 1. Cassava storage root yields as affected by application of compound fertilizer (17 nitrogen: 17 phosphorus: 17 potassium) at rates of 0 (F0), 40 (F1), 120 (F2), and 200 (F3) kg K/ha, and green manure (TI = <em/>Tithonia sp.; CH = <i>Chromolaena </i>sp.) at 2.5 t dry matter/ha alone or together with compound fertilizer at 40 kg K/ha in two trial locations in Bas-Congo, DRC. SED: standard error of difference at P<0.05. Source: Adapted from Pypers et al. 2012
Figure 1. Cassava storage root yields as affected by application of compound fertilizer (17 nitrogen: 17 phosphorus: 17 potassium) at rates of 0 (F0), 40 (F1), 120 (F2), and 200 (F3) kg K/ha, and green manure (TI = Tithonia sp.; CH = Chromolaena sp.) at 2.5 t dry matter/ha alone or together with compound fertilizer at 40 kg K/ha in two trial locations in Bas-Congo, DRC. SED: standard error of difference at P<0.05. Source: Adapted from Pypers et al. 2012

Combined application of fertilizer and organic inputs
Fertilizer response and the effect of combining inorganic and organic nutrient resources were also evaluated on cassava systems. The most common fertilizer, NPK 17:17:17, was applied in western DR Congo with or without green manure made from Tithonia sp. or Chromolaena sp., and the effects on storage root yield were evaluated in two locations with a differing soil fertility status (Fig. 1). Both plants are commonly found in fallow vegetation in western DR Congo. Control yields were similar at the two sites (12 t/ha), but the response to fertilizer differed between the sites: storage root yields reached 40 t/ha at Kiduma but only 20 t/ha at Mbuela with the addition of 200 kg K/ha. A much larger response to Tithonia sp. green manure was also observed at Kiduma, which was likely to have been related to the higher quality and nutrient contents of the green manure grown at that site.

Combining organic and inorganic nutrient resources did not result in positive interactions. No significant differences were observed between the yields after the sole application of either fertilizer or green manure to the control and those obtained with the combined application of both nutrient sources (Pypers et al. 2012). In maize-based systems, positive interactions between organic and inorganic fertilizers often arise from better synchrony in N release and N uptake by the crop. In cassava systems, where K is more often the most limiting nutrient, such a mechanism is likely to be less relevant.

In the highlands of eastern DRC alternative spacing of cassava  (2 × 0.5 m instead of 1 × 1 m) allows integration of four lines of legumes during one season and two lines of legumes during the second season without affecting cassava densities and yields.
In the highlands of eastern DRC alternative spacing of cassava (2 × 0.5 m instead of 1 × 1 m) allows integration of four lines of legumes during one season and two lines of legumes during the second season without affecting cassava densities and yields.

In eastern DR Congo, the use of improved germplasm did not result in yield increases without the simultaneous implementation of other ISFM components. Modifying the crop arrangement by planting cassava at 2 m between rows and 0.5 m within the row, intercropped with four legume lines, increased bean yields during the first season and permitted a second bean intercrop. This can also increase the total legume production by up to 1 t/ha and resulted in additional revenues of almost $1000/ha (see photo). The crop arrangement or a second legume intercrop did not affect cassava root yields. Fertilizer application increased both legume and cassava yields, and net revenue by $400–700/ha with a marginal rate of return of 1.6–2.7. Replacing the common bean intercrop by groundnut increased net revenue by $200–400/ha, partly because of the higher market value of the grains, but mostly due to a positive effect on yield of cassava storage roots. Soybean affected cassava yields negatively because of its high biomass production and long maturity period; modifications are needed to integrate a soybean intercrop into the system.

Local adaptation
Due to the high variability in soil fertility status, the varying landscape features, and the variation in access to inputs, local adaptation is required to ensure that the investments made by cassava-producing households  result in the highest returns, in line with the resources (e.g., cash, land, labor) that these households have (see photo). Such adaptation efforts are best led by extension and development partners that have the required skills and capacity to implement such efforts at scale. In eastern DR Congo, erosion is the most urgent issue to be tackled to enhance the sustainability of cassava-based systems. Results from Southeast Asia with the use of live hedges should be explored for these environments.

Cassava land preparation varies widely in DRC partly affected by slope and water status of the land.
Cassava land preparation varies widely in DRC partly affected by slope and water status of the land.

Outlook
These findings demonstrate the large potential of ISFM to increase productivity in cassava–legume systems in DR Congo. This is crucial in view of the fact that cassava is changing from being almost only a food security crop to one for which there is high demand in local and urban markets. The intensification of production is thus a prerequisite for sustaining cassava-producing households and ISFM can assist in achieving such benefits. However, these benefits were not observed in all study sites. In poor soils, productivity increases were variable or absent, and soil amendments are required. Better targeting and local adaptation of the technologies are possible with a better understanding of the conditions under which positive effects occur.

References
Pypers, P., J.M. Sanginga, K. Bishikwabo, M. Walangululu, and B. Vanlauwe. 2011. Increased productivity through integrated soil fertility management in cassava–legume intercropping systems in the highlands of Sud-Kivu, DR Congo. Field Crops Research 120: 76–85.
Pypers, P., W. Bimponda, J.P. Lodi-Lama, B. Lele, R. Mulumba, C. Kachaka, P. Boeckx, R. Merckx, and B. Vanlauwe. 2012. Combining mineral fertilizer and green manure for increased, profitable cassava production. Agronomy Journal, in press.

Made to measure: smart natural resources management approaches

Coffee-banana intercropping. Photo by P. van Asten, IITA.
Coffee-banana intercropping. Photo by P. van Asten, IITA.

Coffee and banana yields in the East African highlands are often only 10 to 30% of those achieved in commercial farms in Latin America and Asia. This is the result of a mixture of biotic stresses on the crops such as pests, diseases, and weeds, and abiotic constraints such as poor soil quality and drought.

Poor crop management practices that do not sufficiently address these constraints prevent farmers from reaping maximum benefits from their efforts.

However, the importance of these yield-limiting factors differs from region to region. The natural resources management (NRM) approach therefore starts with identifying the gap between the actual, attainable, and potential yields for each location.

Diagnostic surveys and analytical tools such as the boundary line analysis are used to rank and quantify the causes of low yields. This then guides the development of tailor-made measures and actions for farmers.

Smart use of mineral fertilizer and organic matter
Poor soils are one major cause of low yields in the East African highlands. Much of Africa’s soils are old and poor, situated on very old continental plates. Only a few places have soils that still have substantial nutrient stocks, such as those derived from young volcanic material and metamorphic rocks.

Years and years of soil erosion and poor farming methods that mine minerals have worsened the situation.

IITA is working with farmers to combine organic manure and mineral fertilizer to replenish soil nutrients to meet the needs of banana and coffee.

Piet van Asten, IITA systems agronomist based in Uganda, says the approach stresses the judicious use of mineral fertilizer that is moderate in quantity, applied at the right time and in the right way, and combined with locally available organic matter.

“The combination of fertilizers and organic matter provides much-needed additional nutrients that are efficiently used up by the crops. The organic matter helps to retain mineral fertilizers applied in the topsoil and reduces losses from leaching,” he says. “It also improves the soil physical properties which help to retain soil humidity and control the temperature. Plants thrive in such humid and temperate environments as the roots are better able to take up nutrients.”

Poster on banana fertilizer recommendations for Uganda. Courtesy of P. van Asten, IITA.
Poster on banana fertilizer recommendations for Uganda. Courtesy of P. van Asten, IITA.

Sources of local organic matter are mulch, urine, manure, and compost.

Research has shown that adding mineral fertilizers and mulch to both coffee and banana nearly doubles their yields. However, the fertilizer type and dose have to supply the nutrients that are lacking.

Through mapping soil and plant nutrient status, IITA identified the missing nutrients in each region. Subsequently, it developed region-specific recommendations for using fertilizer and organic mulch in parts of Uganda.

Training materials were also developed to teach farmers how to identify nutrient deficiencies in their own farms by observing plant leaves. This should ultimately help them to localize their fertilizer needs down to the farm level.

Halting and preventing soil erosion by placing contour bunds stabilized by forage/mulch grasses and leguminous plants are also important to conserve and improve soil quality.

Smart intercropping systems
IITA has been working on promoting the intercropping of banana/plantain and coffee as research has clearly shown that intercropping works better than monocropping either crop.

Coffee, a shade-loving plant, performs well when grown under banana/plantain. Research findings showed that creating space for the banana/plantain does not reduce the yield of coffee but instead, the farmer gets bonus income from the banana.

Such intercropping systems, says van Asten, spread the socioeconomic risks of farmers as they become less vulnerable to the price fluctuations of a single crop.

“The two intercrops provide farmers with permanent piecemeal harvests from banana and annual or biannual cash booms from coffee,” he said.

Intercropping has other benefits. It leads to sharing of inputs, such as fertilizers purchased through the cash crop system, such as coffee farmers’ cooperatives. It also improves fertilizer-use efficiency, as fertilizer applied to the cash crop also benefits the food crop.

Coffee plants perform better when grown under the shade of banana plants. Photo by P. van Asten, IITA.
Coffee plants perform better when grown under the shade of banana plants. Photo by P. van Asten, IITA.

Intercropping improves the biophysical efficiency of the systems by providing better and more permanent canopy and soil cover that reduce erosion. It improves soil organic carbon stocks (carbon sequestration) through the biomass produced.

Another benefit, says van Asten, is that intercropping can sometimes increase the quality of some crops. For instance, under suboptimal growing conditions, shade-grown coffee is often of better quality and thus could fetch more money on the market.

Linking to input and output markets
In a study of the factors that limit farmers’ usage of mineral fertilizers for their banana plants, Uganda farmers cited lack of access as one constraint. Moreover, they said it was not available in smaller packaging and more affordable sizes. IITA is working to encourage farmer cooperatives that are organized around postharvest handling, sorting, and bulking to organize the supply of inputs such as fertilizer for their members.

According to van Asten, cooperatives have better access to input/output markets and improved powers of negotiation. They have improved access to market information, bulking and storage facilities, savings and credit schemes through collaboration, and agreements with input/output dealers. They can also facilitate the exploration of niche markets through the certification of products in terms of quality, production, and techniques.

Smart extension services
To meet the information needs of farmers, IITA and partners are exploring options to make location-specific information accessible. This includes the use of extension publications, videos, and mobile phone services.

Farmer detrashing banana intercropped with coffee. Photo by P. van Asten, IITA.
Farmer detrashing banana intercropped with coffee. Photo by P. van Asten, IITA.

Together with the Grameen Foundation, IITA is exploring how information can be tailored to the location of the farmer through a (decision-tree) series of questions. The more information a farmer can provide, the more precise the recommendations will be.

The NRM work on coffee and banana shows that there are practical, readily available measures that farmers can use to increase yield and contribute towards the fight against poverty and hunger. However, they have to be region- and crop-specific for maximum impact.

“For all these measures to be successful, they must start with using clean and resistant planting materials. Investing in fertilizers for use on diseased plants is a futile exercise,” concludes van Asten.