Contrasting water use patterns of two important agroforestry tree species in the Mt Elgon region of Uganda

Published online: 22 Jan 2019.Lack of information on water use of key agroforestry species is an obstacle to understanding their influence on crop productivity. Cordia africana and Albizia coriaria are the dominant tree species of smallholder farming systems in the Mt Elgon region of Uganda and have multiple uses in agroforestry systems. This study deployed six sap flow meters on stems of three selected trees each of C. africana and A. coriaria on-farm. The objective of the study was to assess the daily water use patterns of these agroforestry tree species at different times of the year. We measured the daily sap flow of these two species using the heat ratio method over a period of 18 months. There was a significant main effect of the interaction between tree species and season on daily water use. The two species show contrasting patterns of seasonal water use across leaf shedding stages characterised by episodes of reverse flow in A. coriaria at specific periods of the year. We propose that reverse flows in A. coriaria were triggered by leaf shading while the zero flows in C. africana, which occurred during rainfall events, could have resulted from a lag phase, an indication that the two species may have different water-use strategies. Although C. africana uses 12–15 l day−1 and A. coriaria uses 20–32 l day−1 based on the study trees, C. africana generally uses 12% more water than A. coriaria on a standardised daily basis. Albizia coriaria exhibited radial variation of sap velocities between the inner and outer thermocouples at different periods of measurement, a phenomenon worth investigating further. The leaf shedding patterns of the two trees provide an opportunity for maximising the temporal complementarities of agroforestry systems where these trees exist. This knowledge of C. africana and A. coriaria tree water use provides critical insight for developing successful long-term tree monitoring and management programs in agroforestry systems.J. Buyinza, C. W. Muthuri, A. Downey, J. Njoroge, M. D. Denton and I. K. Nuber

Trees For Food Security-2 Project, Overview and Achievements

The ‘Trees for Food Security phase 2 (T4FS-2) project stemmed from the successful completion of phase one’s four-year term project. Learnings obtained from the first phase showed that for enhanced food security and improved livelihoods, establishment of a greater diversity of trees on farms was essential. During the first phase, project stakeholders testified on the benefits obtained from the project. They also emphasized the need for project to reach more farmers in different sites or contexts. It is against this back drop that the second phase of the project was conceived with the aim of improving food security and smallholder livelihoods through the widespread adoption of appropriate locally adapted agroforestry practices in key agricultural landscapes in Ethiopia, Rwanda and Uganda

Assessing smallholder farmers’ motivation to adopt agroforestry using a multi-group structural equation modeling approach

This study applied the multi-group structural equation modeling technique to identify differences in farmer motivations to adopting agroforestry practices in the Mt. Elgon region of Uganda. Data were collected from interviews with 400 smallholder coffee farmers belonging to four categories which included: (1) those actively participating in an Australian-funded trees for food security (T4FS) project from phase 1 (2014); (2) farmers neighbouring those actively participating in the T4FS project; (3) farmers actively participating in the T4FS project from phase 2 (2017) and; (4) farmers living distant and unaware of the T4FS project. We used the theory of planned behaviour framework to assess the adoption behaviour of these farmer categories resulting from project interventions. About 40% of the variation in farmer motivation to integrate trees in their coffee plantations was explained by the significant variables of ‘attitude’ and ‘perceived behavioural control’ among farmers actively participating in the T4FS project from phase 1. However, the neighbors of participating farmers and farmers who had never interacted with the project were only motivated by ‘attitude’ and ‘social norms’ respectively. Farmer motivation resulting from social pressure was strongest among farmers who had never interacted with the project, and in the absence of project interventions, rely on existing social structures to drive change in their community. Farmers’ perceived behavioural control to overcome tree planting barriers and their attitude to the economic benefits of shaded coffee were significantly different among the four farmer categories (p < 0.05). The findings indicate that psychological factors are key drivers to the farmers’ internal decision-making process in agroforestry technology adoption and can be context-specific. The adoption behaviour of smallholder farmers is mainly shaped by existing community social norms and beliefs that tend to promote knowledge exchange, as opposed to the conventional knowledge transfer extension approaches. Norms are therefore an inherent part of social systems and can create distinct farming practices, habits and standards within a social group. Researchers and extension agents can act upon these identified positive attitudes, norms and perceived behavioural controls to guarantee adoption and sustainability of agricultural technologies

Psychological Factors Influencing Farmers’ Intention to Adopt Agroforestry: A Structural Equation Modeling Approach

The biophysical characteristics of the farm and farmers’ socioeconomic factors have been used to explain adoption of technologies in Africa. However, agricultural technology adoption requires that we also understand the psychological factors that can encourage or discourage farmer adoption of technologies. The aim of this article is to assess the psychological drivers of farmers’ intentions to adopt agroforestry technologies on their farms. We obtained data from 400 smallholder farmers in the Mt. Elgon region of Uganda. The Theory of Planned Behavior was used as the main framework. Quantitative data were analyzed using structural equation modeling to assess the impact of a set of psychological factors on farmers’ intention to integrate trees in coffee. The intention of farmers to integrate trees in coffee plantations was mainly driven by their evaluation of the benefits of shaded coffee (attitude) followed by beliefs about their own capability (perceived behavioral control). However, social pressure (subjective norm) was insignificant, implying that smallholder farmers tend to deny the influence of other people’s behavior on their actions. Therefore, farmers’ positive evaluation of shading coffee and the perceived capability to overcome tree planting barriers reinforced their intention to integrate trees in coffee. This renders attitude and perceived behavioral control as reliable predictors of farmer tree planting behavior, especially in the context of developing countries

Farmer-led approaches to increasing tree diversity in fields and farmed landscapes in Ethiopia

Increasing tree cover and managing trees better on farms in Ethiopia supports livelihoods and the environment but most tree-planting schemes promote only a few species. This research aimed to understand farmers’ tree planting priorities in Oromia, Ethiopia and address challenges involved in meeting them. Tree species and planting niches were elicited through focus group discussions. Participatory trials compared 17 tree species across seven on-farm planting niches and seedling survival and growth patterns were evaluated. Farmers suggested a high diversity of tree species suitable for each niche with fruit species mainly selected for homesteads. The diversity of desired tree species is much higher than that typically available in nurseries or promoted by tree planting projects. Meeting planting demands was difficult because the existing seedling supply does not support diversity. Evaluation of tree survival showed striking differences among species, farms, agroecologies and planting niches. There was high variation in seedling survival amongst the tree species planted on 1893 farm/planting niche locations, indicating impact of local level risk factors attributable to management, biotic and abiotic causes. Growth differences of the six shared species common to both agroecologies across different niches, showed that the effects of species and niche were significant on growth. A farmer-led approach to increasing tree cover that couples understanding of species and planting niche preferences with appropriate seedling supply and management is proposed as a means to increase the diversity of trees in farmed landscapes

Trees For Food Security-2 Project, Ethiopia Highlights

The ‘Developing integrated options and accelerating scaling up of agroforestry for improved food security and resilient livelihoods in Eastern Africa' project also known as Trees for Food Security phase 21 (T4FS-2) is an Australian Centre for International Agricultural Research (ACIAR) funded project aimed at improving food security and smallholder livelihoods through the widespread adoption of appropriate locally adapted agroforestry practices in key agricultural landscapes

Trees For Food Security-2 Project, Uganda Highlights

The ‘Developing integrated options and accelerating scaling up of agroforestry for improved food security and resilient livelihoods in Eastern Africa’ project also known as Trees for Food Security phase 2 (T4FS-2) is an Australian Centre for International Agricultural Research (ACIAR) funded project aimed at improving food security and smallholder livelihoods through the widespread implementation of appropriate locally adapted agroforestry practices in key agricultural landscapes of Rwanda, Uganda and Ethiopia

Modelling the effects of leafing phenology on growth and water use by selected agroforestry tree species in semi-arid Kenya

The WaNuLCAS (Water, Nutrient and Light Capture in Agroforestry Systems) model was used to investigate the impact of tree leafing phenology on the growth and water use of selected agroforestry tree species in semi-arid Central Kenya. Three agroforestry species, grevillea (Grevillea robusta), alnus (Alnus acuminate) and paulownia (Paulownia fortunei), respectively providing evergreen, semi-deciduous and deciduous leafing phenologies, were intercropped with maize. It was hypothesized that the deciduous habit of alnus and paulownia would reduce demand for water relative to the evergreen grevillea under conditions of limited supplies. WaNuLCAS simulations showed that altering leafing phenology from evergreen through semi-deciduous to deciduous decreased water uptake and interception losses by the trees, but increased crop water uptake, drainage and soil evaporation rates for systems containing all three tree species. Drainage and soil evaporation were respectively 14 and 17% greater in the deciduous paulownia system than in the evergreen grevillea. Simulated water uptake and biomass accumulation by grevillea were more than double the corresponding values for paulownia, while crop water uptake in the grevillea and paulownia systems was reduced by 6% and 0.2% respectively relative to sole maize. The simulations imply that water use by paulownia is lower than for grevillea and suggest that leafing phenology is a key attribute affecting water use by trees. The significance of these observations for watershed management and stream flow are discussed

Evaluating factors influencing heterogeneity in agroforestry adoption and practices within smallholder farms in Rift Valley, Kenya

Understanding the structure, densities and utilization of tree populations in agricultural landscapes is useful in determining the species influencing agroecosystem function. Our study evaluated agroforestry adoption and practices within smallholder farms in a former large-scale maize growing area of Trans Nzoia County, Rift Valley Province, Kenya. This was followed by investigation of factors influencing heterogeneity in the adoption and practices. The factors include: household resource endowment, land tenure and time under current management. Five settlement schemes which were formerly large estates dominated by maize mono-cropping were selected for the current study. Tree inventories of the farms were obtained through transect walks across each settlement. A total of 123 farms were assessed representing households of different resource endowment levels, tenure and number of years under current management. Different analyses were carried out including farm size and tree number, tree density, tree diversity and utilization of the dominant tree species. In total, we identified 44 tree/shrub species, 24 of which were indigenous and the rest exotic. However, the exotic tree species dominated strongly in abundance with Eucalyptus spp. being the most frequent taxon and constituting 34.6% of all trees. Species richness was found to be low compared to other agricultural landscapes in the region. Resource constrained households were found to prefer fruit tree species and maintained high tree diversity on their farms. Households with secure tenure had higher tree diversity than those without who had higherspecies richness and opted for fast growing fodder and fertilizer/firewood trees. Younger farms had fewer trees but higher species richness than older farms. The study, therefore, explains heterogeneity in agroforestry adoption in terms of variation in household resource endowment, land tenure and time under current management levels