MSc theses with the Institute for Plant Production in the Tropics and Subtropics (380a) in the LegumeChoice and CONNESSA projects

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1 MSc theses with the Institute for Plant Production in the Tropics and Subtropics (380a) in the LegumeChoice and CONNESSA projects Context CONNESSA is an EU-funded project that started in 2014; the acronym stands for CONNEcting knowledge, scales and actors; An integrated framework for adaptive organic resource management, targeting soil aggradation and agroecosystems resilience in SSA. Sustainable intensification of smallholder agriculture is fundamental to food security, poverty reduction and conservation of natural resources in sub-saharan Africa (SSA). Soil degradation is a major driver of poor agricultural productivity. This implies low resource use efficiencies, including fertilizer, water and labour inputs, and entails low resilience of food systems to climate variability. Effective measures for rehabilitation (or aggradation) of degraded soils rely on organic amendments and agronomic practices that increase soil organic matter. However, variation in social and biophysical contexts across SSA underpins the need to target aggradation measures to the local context, including locally available soil amendments. In particular, there is an urgency to improve diagnosis of soil-related fertility constraints ( responsiveness of soils ). Optimization of the use of organic resources further needs to take into account trade-offs in resource availability and human well-being at different spatial and temporal scales.reallocation of organic resources may simply transfer nutrient depletion from one site to another, while changes in labour requirements may disproportionally affect certain social groups. Project Goals and Purpose This project builds on the premise that integrated solutions for sustainable land use, combined with local adaptation of soil fertility management are urgently needed to address the challenges associated with smallholder agriculture in SSA. We aim to develop a generic knowledge network that connects (it:connessa) scales and actors towards adaptive soil fertility management and agroecosystems resilience. The project objectives will be addressed in three interrelated Work Packages (WPs): aggradating degraded soils and enhancing resource use efficiencies (WP1), exploring diversity and optimizing trade-offs (WP2) and linking local capital and science for innovation (WP3). More information on project background and partners is online at Contribution University of Hohenheim Hohenheim leads WP2, integrating field measurements undertaken in WP1 into modelling approaches at plot and landscape level LegumeChoice LegumeChoice is a BMBF-funded project aiming at identifying legume-led crop rotations of interest to farmers and testing their biophysical benefits. The project is led by IITA in Kenya, with ILRI, Ethiopia, and

2 ICRAF and KALRO in Kenya participating. Hohenheim is involved with 3 PhD students who work on the C and N balance of the legume rotations and modelling of crop growth and environmental impacts at the plot and landscape scale. Field sites are in Kisii and Migori counties, Kenya, in Jeldu and Diga, Ethiopia, and in South Kivu, DR Congo. Sites and logistics CONNESSA sites are located in three countries, Kenya, Burkina Faso and Cote d Ivoire. The topic presented here will be based at one of the Western Kenyan CONNESSA sites or at the Kenyan LegumeChoice sites. All activities will be embedded in the respective project and support by our partner institutions sought. In LegumeChoice, a PhD student from Hohenheim will be on site during parts of the rainy season (Mar Sep) in 2016, who can contribute to supervision. Supervision Prof. Dr. Georg Cadisch, Eric Koomson and Dr. C. Marohn (marohn@uni-hohenheim.de).

3 MSc Topic: Optimising spacing and pruning regime of intercropped legume trees for crop production and stabilisation of soil organic matter stocks in Kenya Context Legume-led crop rotations and intercropping systems have the potential to sustainably increase crop yield and soil organic matter (SOM) levels in smallholder systems on degraded soils, which prevail in many parts of East Africa. Although technical options have been elaborated for decades, farmers (particularly smallholders) are often reluctant to adopt legume-based systems on their plots. The main reason for non-adoption is often reduction in yield levels of the main crop due to competition with the legume for water or light. Objectives This study aims at assessing different planting distances and pruning regimes in Calliandra Common bean Maize intercropping systems regarding maize yield and SOM stocks over various years. It is assumed that wider planting distances are of comparative advantage for crops in the short term, because competition with the legumes is reduced. In the longer term greater build-up of SOM stocks from legume prunings is expected to compensate to some extent for the competition effects. Regarding pruning, an optimum intensity shall be identified that minimises light competition and maximises litter and SOM production in the medium term. In this context, effects of heavy pruning on legume survival need to be considered. Approach A modelling approach will be taken to compare the different management scenarios. The WaNuLCAS (Water nutrients lights and carbon in agroforestry systems) model (v. Noordwijk and Lusiana 1999) operates at the plant stand and plot level at a daily time step. Inputs on soil organic matter pools, plant physiology, weather and soil are needed to run the model. Departing from a validated baseline of the model reflecting farmers practice, different pruning and spacing scenarios will be set up and compared regarding yield and SOM levels. Site, data needed and methods Weather data will be available and soil samples will have been collected by winter 2015, so that this study can focus on plant sampling: Allometric equations of legumes will be developed for the shrubs, based on the FBA approach (v. Noordwijk and Mulia 2002) implemented in WaNuLCAS or on own principles. Rooting patterns of both legume components and maize will be analysed using root sampling and image analysis software. Twigs and leaves will be sampled and analysed for lignin and polyphenol contents, which determine litter decomposition. Mulch quantities will be measured at pruning. Farmer interviews will be conducted in order to describe management practices, i.e. timing and extent of pruning etc.

4 Expected results The comparison of different existing and hypothetical management strategies will allow to assess effects on crop production and environmental impacts of the different systems. Identifying potentials for improved crop production may help convincing farmers to implement intercropping systems which contribute to soil conservation. Time frame The field part will take place in the rainy season in Kenya, starting in March or April Part of the model parameterisation can be done beforehand, based on existing data. Soil samples will also be available in winter 2015 and soil analyses for model parameterisation can be part of the thesis. Requirements (candidate) The candidate should have a good understanding of soil and plant processes and be able to relate these processes to varying environmental conditions. Ability of abstract thinking and mathematical / statistical evaluations are needed. For the field campaigns, the candidate should be used to plant and soil sampling in rural areas of tropical countries. He / She should be able to react flexibly to unforeseen events and to work largely independently. References Van Noordwijk M, Mulia R Functional branch analysis as tool for fractal scaling above- and belowground trees for their additive and non-additive properties. Ecological Modelling 149:41 51.

5 MSc Topic: Comparing impacts of different organic matter types and quantities on soil fertility indicators in Kenya using a modelling approach Context Organic matter inputs plant litter, harvest residues, animal manure and others have the potential to sustainably increase crop yield and soil organic matter (SOM) levels in smallholder systems on degraded soils, which prevail in many parts of East Africa. Inputs differ in their chemical composition and thus in decomposition rates, which in turn determine the organic matter structure and release of plant available nutrients. While organic matter influences water holding capacity, aggregate stability and other soil physical factors, it also forms a source of soil nutrients. In agriculture, timing of nutrient release should be in line with crop demand, while erodibility should be low and aggregate stability and porosity should be high. Identifying best options for soil rehabilitation needs to consider weather, soil, plants and topography for a specific site over a longer time as build-up of organic matter is slow. Field experiments are resource intensive, while models, properly calibrated, can simulate various sources and amounts of organic inputs within short time and at low cost. Objectives This study aims at comparing different organic soil amendments with respect to their effects on soil organic matter, bulk density, nutrient supply for plants and crop yields over years. Approach A modelling approach will be taken to compare the different management scenarios. The WaNuLCAS (Water nutrients lights and carbon in agroforestry systems) model (v. Noordwijk and Lusiana 1999) operates at the plant stand and plot level at a daily time step. Inputs on soil organic matter pools, plant physiology, weather and soil are needed to run the model. Site, data needed and methods The study site is Machanga in Central Kenya. Long term experiments on soil fertility under different organic amendments have been conducted there for ten years and data on soil organic matter, litter inputs as well as weather data are available. A socio-economic survey has also been conducted by our partners. Additional data on soil and litter inputs can be collected on site, but the study can also be conducted as a pure desktop study. Expected results The calibrated model will resemble SOM dynamics observed under at least two treatments (control and one amended treatment) during the long-term experiment. With these baselines as starting point, further scenarios will be developed to simulate further types of organic matter inputs (based on data of plant NPK, lignin and polyphenols) and application rates over longer time spans (up to 20 years). Longterm effects of the inputs on soil fertility and crop productivity will be analysed on the basis of the scenario simulations.

6 Time frame Starting between February and May 2016, the modelling will take about 4 months. If a field phase is intended, the thesis may take longer than 6 months overall. Requirements Solid knowledge of soil processes (decomposition of litter and mineralisation of organic matter) is crucial for this study. Ability of abstract thinking and mathematical / statistical evaluations are also needed. For the field campaigns, the candidate should be used to plant and soil sampling and learn methods related to litter quantification and decomposition (e.g. litter traps, litter bags, Eisenbeis rods). He / She should be able to work in rural areas of tropical countries, react flexibly to unforeseen events and to work largely independently. Refernces and further reading Chivenge, P, Vanlauwe, B, Gentile, R, Six, J Organic resource quality influences short-term aggregate dynamics and soil organic carbon and nitrogen accumulation. Soil Biology & Biochemistry 43: Chivenge, P, Vanlauwe, B, Gentile, R, Six, J Comparison of organic versus mineral resource effects on short-term aggregate carbon and nitrogen dynamics in a sandy soil versus a fine textured soil. Agriculture, Ecosystems and Environment 140: Gentile, R, Vanlauwe, B, Kavoo, A, Chivenge, P, Six, J Residue quality and N fertilizer do not influence aggregate stabilization of C and N in two tropical soils with contrasting texture. Nutr Cycl Agroecosyst 88: Muema, EK, Cadisch, G, Röhl, C, Vanlauwe, B, Rasche, F Response of ammonia-oxidizing bacteria and archaea to biochemical quality of organic inputs combined with mineral nitrogen fertilizer in an arable soil. Applied Soil Ecology 95: Van Noordwijk M, Mulia R Functional branch analysis as tool for fractal scaling above- and belowground trees for their additive and non-additive properties. Ecological Modelling 149:41 51.