1. UNIVERSITY OF HOHENHEIM
PHD STUDIES
UNIVERSITY OF HOHENHEIM

2. Background and Problem statement
Soil fertility decline is a major constraint to the productivity of major crops in Eastern and
Central Africa.
Soil fertility variability within farm, field and watershed is common in Eastern and Central
Africa due to variability in resource endowment and management (typology).
Multipurpose legumes provides food, feed, income, fuel , improve soil fertility and natural
resources status.
Enhancing soil fertility through optimized decomposition processes, which is influence by
the efficiency of microbes is vital for natural resource improvement in the mid to long
term. 2 2

3. Background Thematic areas of the research proposed by the PhD studies:
Nitrogen cycling,
Carbon cycling,
Biophysical modelling of legumes based-cropping systems. 3

4. General objective of PhD research
The objective of the three core research proposal is to provide knowledge on legume-based cropping systems for enhancing soil fertility, crop productivity and environmental sustainability in Eastern and Central Africa. 4

5. Integrating seasonal and perennial legumes for soil fertility improvement in small-holder farming systems in East and Central Africa

6. Background
Many soils in Africa are severely depleted of nitrogen making it difficult for small-holder farmers to produce the required yields to sufficiently feed the growing human population (Giller, 2013).
Organic input have a number of direct effects on nutrient availability (Palm et al., 1997).
Residues deriving from different legume types have contrasting biochemical quality determining their decomposition and hence actual N release to soil (Rasche and Cadish, 2013). 6

7. Hypothesis
Perennial legumes have generally a more complex quality (i.e., higher polyphenol–to-N ratio), and hence lagged decomposition than seasonal with lower.
Seasonal legumes have a supposedly a more efficient decomposition in the short-term, while a time-shifted decomposition can be expected from perennial legumes.
Integration of perennial legumes has a more beneficial effect on the long-term soil N status (i.e., residual effects) between different farm typologies as affected by input use. 7

8. Objective Study Objectives
To assess contribution of legume residues to improve soil fertility and crop productivity through N cycling in different agro-ecology and farm typologies in smallholder farming systems of East and Central Africa.
Study Objectives
To determine the effect of biochemical quality of organic inputs on soil N dynamics in field.
To assess particularly microbial N dynamics in response to biochemical quality of different legume types under farms typologies in target agro-ecosystems.
To investigate microbial processes in N cycle under different soil fertility status, contrasting agro-ecological conditions, and to evaluate the important influence of environmental conditions. 8

9. Work plan 9 Major activities 2015-2016 2016-2017 2017-2018
Modules class performance, Revision proposal and setting up at Hohenheim
Soil fertility status knowledge (soil and plant analysis) at Hohenheim
Development of lab procedure and set-put of incubation experiment ( chemical and biochemical as well molecular analysis)
Performance of field experiment (application of legume residues to soil) plant growth parameters, soil chemical and microbial N dynamics)
Data integration
Dissemination of scientific outputs and Thesis defense 9

10. Outputs
Better understanding of soil microbial decomposition and mineralization processes in N cycles as regulated by organic input quality.
Three scientific articles
Doctoral thesis to become a PhD in Agricultural Sciences.
Recommendation for best site-suited integration of legume types in the target small-holder farming systems in contrasting agro-ecologies of East and Central Africa considering the beneficial effects on soil fertility in the short and long-term. 10

11. SOIL CARBON DYNAMICS IN LEGUME BASED LAND USE SYSTEMS IN EASTERN AND CENTRAL AFRICA11 11

12. Background
Enhancing soil fertility through optimized decomposition processes, which is influenced by the efficiency of microbes is vital in tropical small-holder farming systems.
Therefore, it is very important to know microbial carbon use efficiency (CUE) for organic resources decomposition.
CUE is the fraction of microbial assimilation that is allocated to biosynthetic processes (e.g., growth), with the remainder typically respired (Steinweg et al., 2008; Manzoni et al., 2012).
The CUE also depends on microbial abundance, enzymatic activities of microbes and agro-ecological conditions. 12

13. Research Hypothesis
High biochemical quality legume-derived residues have a lower microbial CUE in tropical soils.
Increased temperature and precipitation with improved management due to typological difference reduces microbial CUE. (Increased temperature and precipitation enhance decomposition and hence CUE)
High bacteria-to-fungi ratio lowers CUE which can be linked with the biochemical quality of residues and can used as indicator to evaluate the decomposition capacity of microbes in the soil. 13

14. General objectives Study Objectives
To investigate the relationship between the biochemical quality of legume residues with CUE of microbial decomposers under different soil types and climates in Eastern and Central Africa.
Study Objectives
To evaluate the effect of biochemical quality of legume residues on microbial CUE.
To investigate the influence of soil type, temperature and soil management due to typological difference on microbial CUE.
To identify the contribution of the ratio bacteria-to-fungi on CUE as an indicator for soil fertility evaluation. 14 14

15. Work Plan
Assessing the general fertility status of the soil with respect to farm typology.
Reconnaissance survey and collection of first hand information about the implementation sites has been conducted. 15

16. Incubation Study Field Study
Two most contrasting legume residues will be used
Two different soil types
This incubation will be done under two different temperature regimes
From the incubation important data for SC dynamics will be taken and data CUE will be estimated
Decomposition and mineralization studies will be conducted under field condition using litter bag studies in different typology farms.
This study will be conducted on different soil types and temperature regimes with contrasting biochemical quality of legume residues.
Validate the incubation experiment field experiment will be conducted. 16 16

17. Summary of work plan 17 Activities 2015 2016 2017 2018
Proposal writing
Course work and proposal improving
Initial survey of the study areas
Collection of soil and legume residues
Laboratory analysis of soil and Legume residues
Biochemical characterization of legumes
Incubation studies (UoH)
Field experiment execution (Ethiopia)
Laboratory analysis of soils (UoH)
Data analysis and interpretation
Finalize the study
Paper editing
PhD thesis submission 17

18. Expectations
The influence of typological difference for soil organic matter management will be known
Knowledge on the biochemical quality of legume residues and the influence of soil type and environment on decomposition process to build up of soil organic carbon will be improved
Better understanding on the contribution of microbial abundance, enzymatic activities of microbes and agro-ecological conditions on CUE . 18 18

19. Assessing Potential Benefits and Trade-offs of Legume-led Crop Rotations on Natural Resources at the Plot and Landscape Scale Using an Integrated Modeling Approach.

20. Background
The dominance of cereals/root crops in most systems is unsustainable: nutrient depletion through continual removal of biomass.
Rainfall, altitude & soil fertility gradients between farms and fields within farms are common (Ojiem et al.,2007; Vanlauwe et al., 2006).
Assessment of environmental impacts of promising legume-led crop rotations as consequence of land-use and mgt, e.g. on C stocks, surface run-off, soil erosion, OM turnover, requires integrated long-term monitoring.

21. Hypotheses
H1: Legumes have the potential to stabilize yields of the main crop (e.g. maize) under adverse conditions and increase yields on predominantly N limited soils.
H2: Thorough selection of the legume component, optimized timing of interventions and residue management strongly influence the success of a legume intervention.
H3: Soil erosion is severe at most of the study sites. We expect that permanent soil cover in the headwater areas of a micro-catchment through legumes will have a significant effect on sediment loads in the entire landscape.

22. Objectives
To identify best legume-led options for site-specific niches from the view of farmers and other stakeholders (e.g. extensionists, researchers).
To assess impact of legume-led options on soil fertility and environment from ongoing experiments.
To test a range of mid- to long-term scenario adaptations using established crop-soil-hydrology models (WaNuLCAS, LUCIA) for impacts on food security and environment.

23. Study plan Year 1 Year 2 Year 3 Year 4 Activities/Quarter 1 2 3 4
Field work, Kenya (Apr-Sep 2015)
Identification of cropping systems, soil sampling, plant sampling, (N,P, K partitioning, biomass, yield), mgt data, climate data.
Lab analysis + Course work (Oct 2015-March 2016)
Field work, Kenya & Ethiopia (Apr-Oct 2015)
Soil sampling (modelling), plant sampling (N,P, K partitioning, biomass, yield), Catchment data [soil, landuse, topography, runoff(IWMI)]
Lab analysis (Nov 2016-Jan 2017)
Modelling activities (Feb 2017-Sept 2017)
Compilation of input data, Calibration, Validation [yield, biomass, SOC (Machanga/Embu), Runoff (IWMI)], Simulation, Scenario development
Thesis development (Sep 2017-Jul 2018)
Writing of manuscripts and Thesis, submission
Thesis defence (Sep 2018)

24. Expectations
Qualified options for sustainable intensification and soil rehabilitation through legume-based crop rotations and intercropping systems:
Identification of best-fit legume interventions within the context of the model sites through thorough selection of the legume component.
Trade-off analysis of different legume systems and related management on practical relevant options such as: fodder use vrs ground cover & soil improvement; tree legume mulch or stake vrs firewood; space for hedgerows vs. space for annual crop.
A pool of tested scenarios will be available for partners that can be easily modified for specific data subsets such as crop rotations, management options or site characteristics to enable scenario testing under further specific conditions.
Three peer reviewed journal articles will be produced as pre-condition for thesis submission.

25. Cross country soil fertility assessment
Results
Cross country soil fertility assessment
Organic resource management on wealthy and poor farmers’ field is similar in the three countries .
Low available P in Kenya and Ethiopia may be due to the fixation problem.
The effort of wealthy farmers was not better than the poor

26. Cross country soil fertility assessment
Results
Cross country soil fertility assessment
No difference in TN & exch K in Kenya & DRC.
The difference in TN and exch. K in Ethiopia indicates that the
management of wealthy farmers is better than poor farmers.

27. Conclusion LegumeCHOICE output delivery:
Studies on the effects of farm typology on soil fertility and how this may regulate the decomposition of biochemically contrasting legume residues.
Data from C & N cycling will be transferred to the modelling platform to test the contribution of different legumes and management to soil fertility and natural resource status.
Provide and promote sustainable best fitted options of legume-based cropping systems in Eastern and Central Africa.

28. THANK YOU!
DANKE!
ASANTE!