Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Should fertilizer recommendations be adapted to parkland agroforestry systems? Case studies from Ethiopia and Rwanda
Sida, Tesfaye Shiferaw ; Baudron, Frédéric ; Ndoli, Alain ; Tirfessa, Dereje ; Giller, Ken E. - \ 2019
Plant and Soil (2019). - ISSN 0032-079X - 16 p.
Agronomic use efficiency - Competition - Crop failure - Facilitation - Mineral fertilizer - Tree-crop interaction

Aims: This study aimed to disentangle tree-crop-fertilizer interactions in agroforestry systems, which has been suggested as an entry point for sustainable intensification of smallholder farming systems in sub-Saharan Africa (SSA). Although tree-crop systems generate multiple economic and ecological benefits, tree-crop competition commonly occurs. We hypothesized that mineral fertilizers affect facilitative and competitive interactions differently in tree-crop systems. Methods: Tree-crop-fertilizer interactions were explored for wheat growing under Faidherbia albida, and maize growing under Acacia tortilis and Grevillea robusta through omission trials of nitrogen (N) and phosphorus (P) in open fields and fields under tree canopy, using a split plot design. The experiments were conducted in Ethiopia and Rwanda, replicated four times, and over two seasons. Results: Our results demonstrated that the presence of F. albida significantly improved N and P use efficiencies, leading to significantly higher (P < 0.001) grain yields in wheat. This tree species contributed around 64 kg ha−1 yr.−1 of mineral N. The P use efficiency of wheat under F. albida was double that of open field wheat. By contrast, G. robusta and A. tortilis trees lowered nutrient use efficiencies in maize, leading to significantly less maize grain yields compared with open fields receiving the same fertilization. Probabilities of critically low crop yields and crop failure were significantly greater for maize growing under the canopy of these species. Conclusions: Our results showed that recommended fertilizer rates led to facilitative interaction only with F. albida, highlighting that fertilizer recommendations need to be adapted to agroforestry systems.

Is labour a major determinant of yield gaps in sub-Saharan Africa? A study of cereal-based production systems in Southern Ethiopia
Silva, João Vasco ; Baudron, Frédéric ; Reidsma, Pytrik ; Giller, Ken E. - \ 2019
Agricultural Systems 174 (2019). - ISSN 0308-521X - p. 39 - 51.
Extensification - Farm power - Frontier analysis - Intensification - Triticum aestivum L. - Zea mays L.

We investigated the role of labour in explaining the yield gap of cereals at both crop and farm levels on smallholder farms in Southern Ethiopia. A household survey containing detailed information of labour use at crop and farm level of ca. 100 farms in a maize-based system around Hawassa and ca. 100 farms in a wheat-based system around Asella was used for this purpose. Stochastic frontier analysis was combined with the principles of production ecology to decompose maize and wheat yield gaps. Actual maize and wheat yields were on average 1.6 and 2.6 t ha −1 , respectively, which correspond to 23 and 26% of the water-limited yield (Yw) of each crop. For both crops, nearly half of the yield gap was attributed to the technology yield gap, indicating sub-optimal crop management to achieve Yw even for the farmers with the highest yields. The efficiency yield gap was ca. 20% of Yw for both crops; it was negatively associated with sowing date and with the proportion of women's labour used for sowing in the case of maize but with the proportion of hired labour used for sowing and weed control in the case of wheat. The resource yield gap was less than 10% of Yw for both crops due to small differences in input use between highest- and lowest-yielding farms. The contribution of capital and farm power availability to crop yields, input use and labour use was analysed at the farm level. Labour calendars showed that crops cultivated in Hawassa were complementary, with peak labour occurring at different times of the year. By contrast, crops cultivated in Asella competed strongly for labour during sowing, hand-weeding and harvesting months, resulting in potential trade-offs at farm level. Oxen ownership was associated with capital availability, but not farm power in Hawassa and with both capital availability and farm power in Asella. Farmers with more oxen applied more nitrogen (N) to maize in Hawassa and cultivated more land in Asella, which is indicative of an intensification pathway in the former and an extensification pathway in the latter. Differences in land:labour ratio and in the types of crops cultivated explained the different strategies used in the two sites. In both sites, although gross margin per unit area increased linearly with increasing crop yield and farm N productivity, gross margin per labour unit increased up to an optimal level of crop yield and farm N productivity after which no further response was observed. This suggests that narrowing the yield gap may not be economically rational in terms of labour productivity. We conclude that labour (and farm power) is not a major determinant of maize yield gaps in Hawassa, but is a major determinant of wheat yield gaps in Asella.

Landscape composition overrides field level management effects on maize stemborer control in Ethiopia
Kebede, Yodit ; Bianchi, Felix J.J.A. ; Baudron, Frédéric ; Tittonell, Pablo - \ 2019
Agriculture, Ecosystems and Environment 279 (2019). - ISSN 0167-8809 - p. 65 - 73.
African ecosystem - Busseola Fusca - Landscape ecology - Lepidoptera (Noctuidae)

Lepidopteran stemborers are a serious pest of maize in Africa. While farmers have adopted cultural control practices at the field scale, it is not clear how these practices affect stemborer infestation levels and how their efficacy is influenced by landscape context. The aim of this 3-year study was to assess the effect of field and landscape factors on maize stemborer infestation levels and maize productivity. Maize infestation levels, yield and biomass production were assessed in 33 farmer fields managed according to local practices. When considering field level factors only, plant density was positively related to stemborer infestation level. During high infestation events, length of tunnelling was positively associated with planting date and negatively with the botanical diversity of hedges. However, the proportion of maize crop in the surrounding landscape was strongly and positively associated with length of tunnelling at 100, 500, 1000 and 1500 m radius, and overrode field level management factors when considered together. Maize grain yield was positively associated with plant density and soil phosphorus content, and not negatively associated with the length of tunnelling. Our findings highlight the need to consider a landscape approach for stemborer pest management, but also indicate that maize is tolerant to low and medium infestation levels of stemborers.

How to increase the productivity and profitability of smallholder rainfed wheat in the Eastern African highlands? Northern Rwanda as a case study
Baudron, Frédéric ; Ndoli, Alain ; Habarurema, Innocent ; Silva, João Vasco - \ 2019
Field Crops Research 236 (2019). - ISSN 0378-4290 - p. 121 - 131.
East Africa - Intensification - Rainfed wheat - Resource-saving technologies - Yield gap - Yield-increasing technologies

As wheat demand is increasing in sub-Saharan Africa (SSA), domestic production is being encouraged. The potential to increase the productivity and profitability of wheat appears large in the region, but little is known about the concrete interventions needed to meet that potential. In this study, we selected a site in Northern Rwanda (representative of the cool humid climatic zone which accounts for most of the spring wheat production of SSA) and analysed the determinants of wheat productivity and profitability for 130 smallholder farms during two consecutive short rainy seasons, namely 2017A and 2018A (wheat is seldom grown during long rainy seasons: potato is the preferred crop then). Although wheat yields were found to be high when compared to typical yields in SSA (means of 3469 and 3052 kg ha −1 during the seasons 2017A and 2018A, respectively), large yield gaps were also found (1.977 t ha −1 on average, or 37.6% of the highest farmer's yield, defined as the average actual yields above the 90th percentile of this variable). Evidences presented in the paper suggest that wheat productivity could be increased through increased seeding rate (a 0.14% increase in wheat grain yield was found with a 1% increase in seeding rate), increased nitrogen (N) application combined with frequent weeding (a 0.02% increase in wheat grain yield was found with a 1% increase in N application and frequent weeding), and labour-saving technologies (e.g., herbicides and mechanization). If wheat profitability would also increase with frequent weeding and labour-saving technologies, it would decrease with increased input use in many cases. Indeed, seed, fertilizer and amendments represent most of the wheat production cost in the area. These results illustrate the importance of assessing the impact of narrowing the yield gap on profitability, not only productivity, as some yield-increasing technologies may not be desirable from an economic perspective. They also demonstrate that resource-saving technologies (input-saving e.g., precision agriculture, labour-saving e.g., mechanization) may be as much in demand by African smallholders as yield-increasing technologies, calling for a more balanced approach in current research and development initiatives on the continent.

Hide and seek: management and landscape factors affecting maize stemborers Busseola fusca (Fuller) infestation levels in Ethiopia
Kebede, Yodit - \ 2019
Wageningen University. Promotor(en): P.A. Tittonell, co-promotor(en): F.J.J.A. Bianchi; Frédéric Baudron. - Wageningen : Wageningen University - ISBN 9789463435864 - 176
Do open-pollinated maize varieties perform better than hybrids in agroforestry systems?
Ndoli, Alain ; Baudron, Frédéric ; Sida, Tesfaye Shiferaw ; Schut, Antonius G.T. ; Heerwaarden, J. van; Giller, Ken E. - \ 2019
Experimental Agriculture 55 (2019)4. - ISSN 0014-4797 - p. 649 - 661.
A large body of evidence demonstrates the agronomic superiority of maize hybrids over open-pollinated varieties (OPVs) in intensive monoculture. However, comparisons of the performance of hybrids and OPVs in agroforestry systems are scarce. In this study, the performance of four maize hybrids and four OPVs is compared in sole crop and under mature trees. Experiments were conducted on-farm during four seasons in Bugesera, Rwanda and two seasons in Meki, Ethiopia. Two tree species were selected in Bugesera (Grevillea robusta and Senna spectabilis) and one in Meki (Acacia tortilis), and three farms were selected for each tree species, each including two plots with almost identical trees in their centre and two plots without tree. In Bugusera, grain yield was higher for hybrids (2 Mg ha-1) than for OPVs (1.5 Mg ha-1), and the presence of trees reduced the harvest index more in OPVs than in hybrids. In this region, the estimated reduction in grain yield due to the presence of trees was 0.9 and 1.1 Mg ha-1 in hybrids and OPVs, respectively, while estimated reduction in biomass was 1.5 and 1.7 Mg ha-1, respectively. In Meki, the grain yield of OPVs (2.08 Mg ha-1) and hybrids (2.04 Mg ha-1) did not differ and the presence of trees reduced their grain yields in the same manner. Our results showed that hybrids yielded more than OPVs under G. robusta and S. spectabilis in Bugesera but performed equally well under A. tortilis in Meki. We conclude that agroforestry farmers could benefit from growing hybrids in the equatorial savannahs of Rwanda, but that the choice between hybrid and OPV in equatorial savannahs of Ethiopia can simply be based on other factors such as seed costs and availability.
Yield gaps and farm traps: what’s the scope for sustainable intensification at local level?
Silva, J.V. ; Reidsma, P. ; Laborte, Alice G. ; Baudron, Frédéric ; Giller, K.E. ; Ittersum, M.K. van - \ 2018
Unpacking the push-pull system : Assessing the contribution of companion crops along a gradient of landscape complexity
Kebede, Yodit ; Baudron, Frédéric ; Bianchi, Felix ; Tittonell, Pablo - \ 2018
Agriculture, Ecosystems and Environment 268 (2018). - ISSN 0167-8809 - p. 115 - 123.
Africa - Agroecology - Biocontrol - Busseola fusca (Fuller) - Ethiopia - Generalist predators - Habitat management - Landscape - Lepidoptera: Noctuidae

The push-pull system, a stimulo-deterrent cropping strategy consisting of intercropping cereals with herbaceous legumes and surrounded by fodder grasses, is presented as a promising crop diversification strategy for smallholder farmers in Africa as it may contribute to maize stemborer Busseola fusca (Fuller) suppression, while improving soil fertility and providing feed for livestock. The push-pull system has often been assessed at plot level and as a package (e.g., Maize + Desmodium + Napier grass). However, it is unclear how the system performs in different landscape settings or when companion crops are changed to better meet household needs. Here we evaluate the potential of the push-pull system to suppress maize stemborer infestations in three landscapes in the Rift Valley region of Ethiopia along a gradient of landscape complexity. Within each landscape, experimental plots were established on four representative smallholder farms. At each farm we used a split-plot factorial design with main plots surrounded or not by Napier grass, and subplots consisting of sole maize, maize-bean or maize-Desmodium. We assessed stemborer infestation level and maize grain and stover yields during two years, as well as natural enemies abundance and egg predation at two maize development stages in the second year. In the simple landscape, which was dominated by maize, all treatments had high stemborer infestation levels, irrespective of within-field crop diversity; the presence of Napier grass was associated with higher predator abundance, while egg predation rates were the highest in the maize-bean intercrop. In the intermediate complexity landscape, subplots with sole maize had higher stemborer infestation levels compared to maize-bean or maize-Desmodium. In the complex landscape, infestation levels were low in all treatments. However, none of these effects led to significant differences in maize grain and stover yields among treatments in any of the landscapes. The benefits of the push-pull system accrued from the companion crops (bean, Desmodium and Napier), rather than from stemborer suppression per se. Our findings highlight the importance of the surrounding landscape in mediating the performance of the push-pull system, provide new insights on the contribution of the different components of push-pull system and can guide the design of ecologically intensive agroecosystems.

Excessive pruning and limited regeneration: Are Faidherbia albida parklands heading for extinction in the Central Rift Valley of Ethiopia?
Sida, Tesfaye Shiferaw ; Baudron, Frédéric ; Deme, Dejene Adugna ; Tolera, Motuma ; Giller, Ken E. - \ 2018
Land Degradation and Development 29 (2018)6. - ISSN 1085-3278 - p. 1623 - 1633.
Scattered Faidherbia albida trees provide multiple ecological and production benefits across the Sahel. The intensive management and use of this important tree may impede its regeneration. Regeneration bottlenecks were explored and population dynamics modelled. On experimental plots in which seed of F. albida was sown, exposure to the first 2 months of dry season resulted in a quarter of seedling mortality. Exposure to season‐long free grazing and browsing caused significantly greater seedling mortality. Results from monitoring 100 permanent plots scattered over the landscape showed that adult population density was 4.2 ± 0.3 (mean ± SE) trees ha−1 and dominated by old age classes. Sixty percent of the total population were older than 30 years. The mean density for juveniles was 1.4 ± 0.2 (mean ± SE) individuals ha−1. The annual rates of decline were 1.2%, 51.3%, and 63.2% for adults, seedlings, and saplings, respectively. Our model predicted that the F. albida population will start to decline within 1–2 decades to eventually fall below 1 tree ha−1 within 60 years under current management. The model highlighted that the limited seed source, caused by excessive pruning, was the main constraint for recruitment. Appropriate land management policy to ensure adequate seed production would avert current trends in decline of F. albida population.
Conservation agriculture with trees amplifies negative effects of reduced tillage on maize performance in East Africa
Ndoli, Alain ; Baudron, Frédéric ; Sida, Tesfaye Shiferaw ; Schut, Antonius G.T. ; Heerwaarden, J. van; Giller, Ken E. - \ 2018
Field Crops Research 221 (2018). - ISSN 0378-4290 - p. 238 - 244.
Crop phenology - Equatorial savannah - Maize - Minimum-tillage

Conservation agriculture (CA) is widely promoted in sub-Saharan Africa both in open fields and in agroforestry where the practice is known as ‘conservation agriculture with trees’ (CAWT). Although advantages and disadvantages of CA are well studied under sole cropping, less is known about its impact in agroforestry systems. The performance of open pollinated maize varieties under CA, CAWT, sole maize under conventional tillage (CT) and conventional tillage with trees (CTWT) was compared on-farm in equatorial savannah areas over four consecutive seasons in Rwanda and two seasons in Ethiopia. The tree species considered in the study were mature Grevillea robusta (A. Cunn.) and Senna spectabilis (DC.) in Rwanda and mature Acacia tortilis (Forssk.) in Ethiopia. Both CA and the presence of trees consistently reduced maize emergence, leaf area (LA), plant height, and maize yields. Crop emergence was significantly reduced under CAWT compared with CTWT. Maize emergence rates in CAWT and CTWT were respectively 46.9% and 70.1%, compared with 74.7% and 79.8% in sole maize under CA and CT. Grain yield in CAWT and CTWT were respectively 0.37 t dry matter (DM) ha−1 and 1.18 t DM ha−1 as compared with 1.65 t DM ha−1 and 1.95 t DM ha−1 in CA and CT. We conclude that CAWT strongly reduces crop yield in the equatorial savannah of East Africa. CA is incompatible with agroforestry under the conditions of our study. There is an urgent need for rigorous research to revisit if, when and where CAWT can generate benefits for smallholder farmers.

Implications of changes in land cover and landscape structure for the biocontrol potential of stemborers in Ethiopia
Kebede, Yodit ; Bianchi, Felix ; Baudron, Frédéric ; Abraham, Kristin ; Valença, Anne de; Tittonell, Pablo - \ 2018
Biological Control 122 (2018). - ISSN 1049-9644 - p. 1 - 10.
Agroecosystem - Busseola fusca (Fuller) - Land use - Landscape ecology - Maize - Natural enemies
The land cover and structure of agricultural landscapes may influence the abundance and diversity of natural enemies of crop pests. However, these landscapes are continuously evolving due to changing land uses and agricultural practices. Here we assess changes in land use and landscape structure in a landscape in the Rift Valley region of Ethiopia, and explore the impact these changes are likely to have on the capacity of the landscape to support communities of natural enemies of maize stemborers Busseola fusca (Fuller). Land use and landscape structure were assessed in three periods over the last 30 years using focus group discussions with farmers and land use analysis through remote sensing. Natural enemies were sampled in maize fields adjacent to simple hedgerows, complex hedgerows, enset fields and khat fields at 1, 10 and 30 m using pitfalls and yellow pan traps in 2014 and 2015. The landscape analysis indicated that landscapes in the study area changed from maize dominated to more diverse small-scale and fragmented agroecosystems with a higher proportion of perennial crops. Maize fields adjacent to enset and complex hedgerows hosted significantly more predators (15.1 ± 9.8 and 22.3 ± 5.1 per trap at 1 m from the border, respectively) than maize fields adjacent to khat and simple hedgerows (7.2 ± 1.1 and 7.3 ± 1.7 per trap at 1 m from the border), and the effects of border type decreased with distance from the border. The abundance of parasitoids and parasitic flies were not influenced by border type. Our findings suggest that the changes in land use and landscape structure may have influenced the capacity of the landscape to support populations of natural enemies of stemborers in different ways. On the one hand smaller field sizes have resulted in more field borders that may support relatively high predator densities; on the other hand, the area of khat increased and the area of enset decreased, which may have a negative effect on predator densities. The overall outcome will depend on the interplay of these opposing effects.
Affordances of agricultural systems analysis tools : A review and framework to enhance tool design and implementation
Ditzler, Lenora ; Klerkx, Laurens ; Chan-Dentoni, Jacqueline ; Posthumus, Helena ; Krupnik, Timothy J. ; Ridaura, Santiago López ; Andersson, Jens A. ; Baudron, Frédéric ; Groot, Jeroen C.J. - \ 2018
Agricultural Systems 164 (2018). - ISSN 0308-521X - p. 20 - 30.
Bio-economic farm models - Farming systems analysis - Fuzzy cognitive mapping - Literature review - Role play and serious games - Stakeholder participation
The increasingly complex challenges facing agricultural systems require problem-solving processes and systems analysis (SA) tools that engage multiple actors across disciplines. In this article, we employ the theory of affordances to unravel what tools may furnish users, and how those affordances contribute to a tool's usefulness in co-design and co-innovation processes. Affordance is defined as a function provided by an object through an interaction with a user. We first present a conceptual framework to assess the affordances of SA tools. This framework is then applied in a literature review of three SA tools used in agricultural systems research (fuzzy cognitive mapping, bio-economic whole-farm models, and role play and serious games). Through this exercise, we extend the SA tool design and implementation dialogue by illuminating (i) links between lower-level affordances, tool design, and heuristic functioning, and (ii) the central role of use setting and facilitation in mobilizing higher-level, productive affordances. Based on our findings, we make five propositions for how SA tool design and implementation in participatory problem-solving settings can be improved.
Crop vs. tree : Can agronomic management reduce trade-offs in tree-crop interactions?
Sida, Tesfaye Shiferaw ; Baudron, Frédéric ; Hadgu, Kiros ; Derero, Abayneh ; Giller, Ken E. - \ 2018
Agriculture, Ecosystems and Environment 260 (2018). - ISSN 0167-8809 - p. 36 - 46.
Agroforestry - Income diversification - Multifunctional landscape - Sustainable intensification - Trade-off analysis - Yield penalty
Scattered trees dominate smallholder agricultural landscapes in Ethiopia, as in large parts of sub-Saharan Africa (SSA). While the inclusion of scattered trees could provide a viable pathway for sustainable intensification of these farming systems, they also lead to trade-offs. We carried out a study to: 1) explore the rationale of farmers to maintain on-farm trees beyond crop yield; 2) quantify the impact of agronomic practices on the outcome of tree-crop interactions; and 3) analyse partial economic trade-offs for selected on-farm tree species at farm scale. We recorded agronomic practices within the fields of 135 randomly selected farms from seedbed preparation to harvesting. A multivariate analysis showed that farmers maintained on-farm trees because of their direct timber, fencing, fuelwood, and charcoal production values. Trees generally had a significant negative effect on maize yield. Mean grain yields of 1683, 1994 and 1752 kg ha−1 under the canopies of Cordia, Croton and Acacia, respectively, were significantly lower than in their paired open field with mean yields of 4063, 3415 and 2418 kg ha−1. Besides, more income from trees was accompanied by less income from maize, highlighting trade-offs. However, agronomic practices such as early planting, variety used, improved weed management, fine seedbed preparation and higher rates of nitrogen fertilizer significantly reduced yield penalties associated with trees. We found an inverse relationship between land size and on-farm tree density, implying that the importance of trees increases for land-constrained farms. Given the expected decline in per capita land size, scattered trees will likely remain an integral part of these systems. Thus, utilizing ‘good agronomic practices’ will be vital to minimize tree-crop trade-offs in the future.
Sustainable intensification of smallholder farming systems in Ethiopia : what roles can scattered trees play?
Sida, Tesfaye Shiferaw - \ 2018
Wageningen University. Promotor(en): K.E. Giller, co-promotor(en): F. Baudron. - Wageningen : Wageningen University - ISBN 9789463437189 - 191

Scattered trees dominate smallholder agricultural landscapes in Ethiopia, as in large parts of sub-Saharan Africa (SSA). While the integration of scattered trees with crops could provide a viable pathway for sustainable intensification of these farming systems, they also lead to trade- offs. Trade-off minimization and benefit maximization from these trees in the system require the processes that underlie tree-crop interactions to be unravelled. This study explored tree- based pathways for the sustainable intensification (SI) smallholder crop production systems in contrasting agroecologies of Ethiopia. Combination of methodologies from agronomy, socio- economics and conservation sciences were utilized to understand the potential roles of scattered trees in smallholder farming systems. Results indicated that farmers maintained on-farm trees because of their direct timber, fencing, fuelwood, and charcoal production values, regardless of their effect on crop productivity. A trade-off analysis revealed that economic gains from trees were not large enough to compensate for tree-induced crop yield penalties in tree-crop mixed farming systems. Under farmers’ practices, most scattered trees generally had a significant negative effect on maize yield. For example, mean maize grain yields were 59%, 42% and 26% less under the canopies of Cordia africana, Croton macrostachyus and Acacia tortilis, respectively, compared with corresponding open field yields. The yield reductions dropped to as low as 5% under ‘good agronomic practices’, such as early planting, variety selection, improved weed management, fine seedbed preparation and higher rates of nitrogen fertilizer. Similar yield reduction was observed in maize under the canopy of Grevillea robusta. Application of nitrogen and phosphorus fertilizers to under canopy maize in Grevillea robusta and Acacia tortilis improved crop yields, compared with non-fertilized maize under the canopies of these tree species. However, recommended rates of nitrogen and phosphorus fertilizers produced significantly less maize yields compared with the open fields. Faidherbia albida is an exceptional scattered tree species that improved soil water, nitrogen and phosphorus use efficiencies, leading to significantly higher yields in wheat gunder tree crown. Available N was 35-55% larger close to the crowns of Faidherbia compared with open fields, apparently contributing as much as 64 kg ha-1 yr-1 mineral N. In addition, this tree significantly reduced photosynthetically active radiation (PAR), reaching the canopy to optimum levels for wheat growth and development. Under the crowns, midday temperature was about 6oC less compared with nearby open fields. Regardless of the triple-win effects (crop production, adaptation and mitigation) of this tree species, over-utilization caused tree population decline. Under the current management, Faidherbia population would decline to a critical density of less than one tree ha-1 within six decades. The current study underlined that conservation of scattered trees can never be achieved through promotions based on neither the trade-offs nor crop productivity benefits involved. Scattered trees can be maintained even when trade-offs with crop production are overriding. Contrarily, these trees may be endangered even if they provide all-round benefits. Thus, a ‘whole sale’ approach that advocates scattered trees on their theoretical environmental and crop production values could jeopardize both conservation and crop production goals. A ‘process-based’ rather than ‘technology-based’ recommendation is required to harness the promising potential that scattered trees offer as a starting point for sustainable intensification of smallholder farming systems.

Farming with trees: a balancing act in the shade
Ndoli, Alain - \ 2018
Wageningen University. Promotor(en): K.E. Giller, co-promotor(en): F. Baudron; A.G.T. Schut. - Wageningen : Wageningen University - ISBN 9789463437196 - 131

The smallholder agriculture sector in East Africa is the dominant economic and social activity for millions of farm households who are often resource-poor, food-insecure and most vulnerable to climate change. In this region, population pressure has led to shorter fallow periods or continuous cropping even on hillslopes causing erosion and leading to reduced soil organic matter content and nutrient mining without replenishment. Consequently, poor agricultural productivity has led to food shortages and these problems are likely to intensify in the region, as the human population is growing faster than in other parts of the world. Agroforestry, a low-input technology, was shown to contribute to the enhancement of food production while ensuring sustainability in sub-Saharan Africa. Agroforestry may improve food security by increasing soil fertility and providing additional income from tree products. Thus, agroforestry is now receiving increasing attention as a sustainable land-management option and some countries in East Africa (e.g. Rwanda) have pledged to restore up to 100% of their agricultural land mainly through agroforestry by the year 2020. Nevertheless, crop yields reduction in agroforestry are frequent due to competition for resources among trees and crops. In recent studies, tree canopy and root pruning were tested to improve light availability and resource use efficiency but studies that tackle crop management and tillage options to optimize crop productivity in the agroforestry systems are scarce.

This thesis aims to assess the importance of agroforestry across Rwanda and its implication on crop productivity and food security of farm households, explore and recommend the maize varieties and tillage options that could minimize tree-crop competition in the equatorial savannah of Rwanda and Ethiopia. The approach combined household survey on the contribution of trees on household income and food security in six agroecologies of Rwanda, experiments on the microclimate and fertility effects of trees on crops in sub-humid region of Rwanda, maize variety testing in agroforestry systems and trials on conservation agriculture with trees in the equatorial savannah of two East African countries: Rwanda (Bugesera site) and Ethiopia (Meki site). The survey in Rwanda found that food security increases with increasing farm size and farmers with more trees tended to be wealthier (e.g. with larger land and more often higher crop and livestock income) and therefore tended to be more food secure in half of the agroecologies. The proportion of household income that came from tree products was the least among sources of income suggesting that most tree products are not sold but kept by farmers for their own use. Yet tree income was important for about 12% of the farmers, contributing more than 20% of their overall income. Households having low food security relied more on income from tree products than those with higher food security status. Therefore, income from tree products can be seen as a ‘safety net’ for the poorest households.

Experiments in the sub-humid environment of Rwanda assessed the effects of mature Alnus acuminata (Kunth) and Markhamia lutea (Seem.) on maize at different distances from tree trunk for four consecutive seasons. Nutrients availability was higher under A. acuminata compared with M. lutea, because of higher litter fall but maize nutrient uptake increased only under A. acuminata 3 m from tree trunk during a wetter season. None of tree species affected water availability for maize in the topsoil. Total solar radiation, photosynthetically active radiation (PAR), and day air temperature were reduced by both tree species. Whereas crops consistently underperformed in M. lutea system, the competitive effect of A. acuminata for light was to some extent compensated by extra N input in the wetter seasons (2015 A and 2015 B) at 3 m but not at 1 m from the tree trunk. In an APSIM modelled scenario under low N fertilization, larger N input from trees could compensate for yield loss caused by reduction in radiation and temperature in about 60% of the seasons. This study suggested that adequate pruning and high leaf litter recycling can reduce the negative effect of shade in low intensity farming systems. The low competition of A. acuminata with crops was also perceived by Rwandan farmers, who ranked this tree species as the least competing among all the other upper story trees grown on-farm in the highlands.

Experiments compared the performance of four maize hybrids and four OPVs was compared in sole crop and under mature Grevillea robusta and Senna spectabilis – in Bugesera, Rwanda or Acacia tortilis – in Meki, Ethiopia. In Bugusera, grain yields of hybrids (2 t ha-1) was significantly better than OPVs (1.5 t ha-1). Further, the presence of trees significantly reduced maize grain yield and total biomass in both hybrids and OPVs in the same manner. However, trees reduced harvest index significantly more in OPVs than in hybrids, suggesting that competition had a greater impact on grain yield of OPVs than on biomass production. In the experiments in Meki, the grain yield of OPVs (2.08 t ha-1) and hybrids (2.04 t ha-1) did not significantly differ and the presence of trees reduced their grain yields in the same manner. We concluded that agroforestry farmers could benefit from growing hybrids in the equatorial savannahs of Rwanda, but not in the equatorial savannahs of Ethiopia. It appears that the relevance of using either hybrids or OPVs in agroforestry systems depends on local conditions and the comparative advantages in seed costs. Experiments in the same regions of Rwanda and Ethiopia were carried out to assess the effect of conservation agriculture with trees (CAWT) on crop productivity as compared to conventional tillage with trees (CTWT) in the equatorial savannah. Crop emergence was significantly reduced under CAWT compared with CTWT. Maize emergence rates in CAWT and CTWT were respectively 46.9% and 70.1%, compared with 74.7% and 79.8% in sole maize under conservation agriculture (CA) and conventional tillage (CT). Grain yield in CAWT and CTWT were respectively 0.37 t dry matter (DM) ha-1 and 1.18 t DM ha-1 as compared with 1.65 t DM ha-1 and 1.95 t DM ha-1 in CA and CT. It was concluded that CAWT likely exacerbates tree-crop competition for water and nutrients and reduce crop yields and was therefore not considered as a viable alternative to CTWT or to CT in the studied systems.

Overall, this study found that mixing trees and crops produced a worthwhile, if somewhat reduced, crop yield, and that on-farm trees can provide substantial income for the poorest households of Rwanda.

Climate-smart agroforestry: Faidherbia albida trees buffer wheat against climatic extremes in the Central Rift Valley of Ethiopia
Sida, Tesfaye Shiferaw ; Baudron, Frédéric ; Kim, Haekoo ; Giller, Ken E. - \ 2018
Agricultural and Forest Meteorology 248 (2018). - ISSN 0168-1923 - p. 339 - 347.
Climate change - Competition - Crop physiology - Facilitation - Heat stress - Local adaptation
Faidherbia albida parklands cover a large area of the Sudano-Sahelian zone of Africa, a region that suffers from soil fertility decline, food insecurity and climate change. The parklands deliver multiple benefits, including fuelwood, soil nutrient replenishment, moisture conservation, and improved crop yield underneath the canopy. Its microclimate modification may provide an affordable climate adaptation strategy which needs to be explored. We carried out an on-farm experiment for three consecutive seasons in the Ethiopian Central Rift Valley with treatments of Faidherbia trees with bare soil underneath, wheat grown beneath Faidherbia and wheat grown in open fields. We tested the sensitivity of wheat yield to tree-mediated variables of photosynthetically active radiation (PAR), air temperature and soil nitrogen, using APSIM-wheat model. Results showed that soil moisture in the sub-soil was the least for wheat with tree, intermediate for sole tree and the highest for open field. Presence of trees resulted in 35–55% larger available N close to tree crowns compared with sole wheat. Trees significantly reduced PAR reaching the canopy of wheat growing underneath to optimum levels. Midday air temperature was about 6 °C less under the trees than in the open fields. LAI, number of grains spike−1, plant height, total aboveground biomass and wheat grain yield were all significantly higher (P < 0.001) for wheat associated with F. albida compared with sole wheat. Model-based sensitivity analysis showed that under moderate to high rates of N, wheat yield responded positively to a decrease in temperature caused by F. albida shade. Thus, F. albida trees increase soil mineral N, wheat water use efficiency and reduce heat stress, increasing yield significantly. With heat and moisture stress likely to be more prevalent in the face of climate change, F. albida, with its impact on microclimate modification, maybe a starting point to design more resilient and climate-smart farming systems.
Disentangling the positive and negative effects of trees on maize performance in smallholdings of Northern Rwanda
Ndoli, Alain ; Baudron, Frédéric ; Schut, Tom ; Mukuralinda, Athanase ; Giller, Ken E. - \ 2017
Field Crops Research 213 (2017). - ISSN 0378-4290 - p. 1 - 11.
Agroforestry - Crop morphology - Crop phenology - Microclimate - Soil fertility
In the sub-humid parts of East Africa, high population density and pressure on land have led farmers to integrate multipurpose trees on farm. Although mixing trees and crops generates numerous benefits (e.g., fuelwood, timber), it often reduces crop yields. Whereas the effects of mature trees on crops are well studied in semi-arid parklands, there are only few studies for the sub-humid environment. The effects of mature Alnus acuminata (Kunth) and Markhamia lutea (Seem.) on crops were studied on-farm for four seasons in the sub-humid environment of northern Rwanda. Five sampling points for A. acuminata and M. lutea were: (i) 1 m from tree trunk without maize, (ii) 3 m from tree trunk without maize, (iii) 1 m from tree trunk with maize, (iv) 3 m from tree trunk with maize and (v) sole maize away from any tree. Nutrient availability and uptake, soil water, air temperature, solar radiation, crop growth and yields were measured. The APSIM-maize module was used to assess the sensitivity of maize yields to changes in these variables. Nutrients availability was higher under A. acuminata compared with M. lutea, because of higher litter fall but maize nutrient uptake increased only under A. acuminata 3 m from tree trunk during a wetter season. None of tree species affected water availability for maize in the topsoil. Photosynthetically active radiation (PAR), total solar radiation and day air temperature were reduced by both tree species. Maize crop at 1 m and 3 m from the tree trunk was shorter in height but had the same number and size of leaves when compared to sole maize plots. Crop yield was generally reduced more at 1 m than at 3 m from the tree trunk. A positive interaction between A. acuminata and maize was only apparent at 3 m from the tree in one of the four seasons following higher litter fall, suggesting that the negative effect of shade was offset by extra N input during that season. In a modelled scenario under low N fertilization, larger N input from trees could compensate for yield loss caused by reduction in radiation and temperature in about 60% of the seasons. Our findings suggest that adequate pruning and high leaf litter recycling can reduce the negative effect of shade in low intensity farming systems.
Ecological Intensification: Local Innovation to Address Global Challenges
Tittonell, P.A. ; Klerkx, L.W.A. ; Baudron, F. ; Félix, G.F. ; Ruggia, A.P. ; Apeldoorn, D.F. van; Dogliotti, S. ; Mapfumo, Paul ; Rossing, W.A.H. - \ 2016
In: Sustainable Agriculture Reviews Springer (Sustainable Agriculture Reviews ) - ISBN 9783319267760 - p. 1 - 34.
The debate on future global food security is centered on increasing yields. This focus on availability of food is overshadowing access and utilization of food, and the stability of these over time. In addition, pleas for increasing yields across the board overlook the diversity of current positions and contexts in which local agriculture functions. And finally, the actual model of production is based on mainstream agricultural models in industrialized societies, in which ecological diversity and benefits from nature have been ignored or replaced by external inputs. The dependence upon external inputs should exacerbate the negative impacts on the environment and on social equity. Strategies to address future global food security thus require local innovation to increase agricultural production in a sustainable, affordable way in the poorest regions of the world, and to reduce the environmental impact of agriculture and its dependence on non-renewable resources. Ecological intensification, the smart use of biodiversity-mediated ecosystem functions to support agricultural production, is portrayed as the most promising avenue to achieve these goals.

Here we first review examples of ecological intensification from around the world. Functional diversity at plant, field and regional scales is shown to hold promise for reducing pesticide need in potato production in the Netherlands, increasing beef production on the pampas and campos in south-east South-America without additional inputs, and staple crop production in various regions in Africa. Strategies range from drawing on high-tech breeding programs to mobilizing and enriching local knowledge and customs of maintaining perennials in annual production systems. Such strategies have in common that larger spatial scales of management, such as landscapes, provide important entry points in addition to the field level.

We then argue that the necessary innovation system to support transitions towards ecological intensification and to anchor positive changes should be built from a hybridization of approaches that favour simultaneously bottom-up processes, e.g. developing niches in which experiments with ecological intensification develop, and top-down processes: changing socio-technical regimes which represent conventional production systems through targeted policies. We show that there are prospects for drawing on local experiences and innovation platforms that foster co-learning and support co-evolution of ecological intensification options in specific contexts, when connected with broader change in the realm of policy systems and value chains. This would require dedicated system innovation programmes that connect local and global levels to sustainably anchor change towards ecological intensification.
Trajectories of farming systems and land use changes in Southern Ethiopia
Kebede, Y. ; Baudron, F. ; Bianchi, F.J.J.A. ; Abraham, Kristin ; Woyessa, K.L. ; Tittonell, P.A. ; Kooistra, L. - \ 2015
Multi-scale trade-off analysis of cereal residue use for livestock feeding vs. soil mulching in the Mid-Zambezi Valley, Zimbabwe
Baudron, F. ; Delmotte, S. ; Corbeels, M. ; Herrera, J.M. ; Tittonell, P.A. - \ 2015
Agricultural Systems 134 (2015). - ISSN 0308-521X - p. 97 - 106.
conservation agriculture - systems - nitrogen - africa - model - knowledge - village - quality - carbon - apsim
Cereal residues represent a major resource for livestock feeding during the dry season in southern Africa. When kept on the soil surface instead of feeding them to livestock, crop residues can contribute to increasing soil fertility and maintaining crop productivity in the short- and the long-term. We explored these trade-offs for smallholder cotton–sorghum farming systems in the semi-arid Zambezi Valley, northern Zimbabwe. The analysis was done using simulation models at three scales, the plot, the farm and the territory, to simulate the effects of different sorghum residue allocations to livestock feeding vs. soil mulching, in combination with different application rates of mineral nitrogen fertilizer on crop productivity. The plot-scale simulations suggest that without N fertilization soil mulching has a positive effect on cotton yields only if small quantities of sorghum residues are used as mulch (average cotton yields of 2.24 ± 0.41 kg ha-1 with a mulch of 100 kg ha-1 vs. 1.91 ± 0.29 kg ha-1 without mulch). Greater quantities of mulch have a negative effect on cotton yield without N fertilization due to N immobilization in the soil microbial biomass. With applications of 100 kg N ha-1, quantities of mulch up to 3 t ha-1 have no negative effect on cotton yield. Results at farm-scale highlight the fundamental role of livestock as a source of traction, and the need to feed a greater proportion of sorghum residues to livestock as herd and farm sizes increase. Farmers with no livestock attained maximum crop production when 100% of their sorghum residue remained in the field, as they do not have access to cattle manure. The optimum fraction of crop residue to be retained in the fields for maximum farm crop production varied for farmers with 2 or less heads of cattle (80% retention), with 2–3 heads (60–80%), with 4 or more heads (40–60%). At the scale of the entire territory, total cotton and sorghum production increased with the density of cattle, at the expense of soil mulching with crop residues. The results of our simulations suggest that (i) the optimum level of residue retention depends on the scale at which trade-offs are analyzed; (ii) the retention of all of the crop residue as mulch appears unrealistic and undesirable in farming systems that rely on livestock for traction; and (iii) crop residue mulching could be made more attractive to farmers by paying due attention to balancing C to N ratios in the soil and by promoting small-scale mechanization to replace animal traction.
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