Date: Wednesday, November 19, at 15:30 (CET)
Venue: https://wur.yuja.com
The RAIZ Project through its implementing partners is pleased to invite you to the public defense of my PhD entitled:
Bouncing on the Pulse:
Sustainable Intensification and Resilience to Climatic Risk in Smallholder Fields of Sub-Humid Zimbabwe
This thesis was prepared within the UPR AIDA (Cirad) and PPS Group (Wageningen University & Research), under the supervision of François Affholder (promotor), Katrien Descheemaeker (promotor) and Gatien Falconnier (supervisor).
The defence will take place on Wednesday, November 19, at 15:30 (CET) in Omnia, WUR campus: Hoge Steeg 2, 6708PH Wageningen. The defence will be live-streamed at https://wur.yuja.com. The stream will go live 5 minutes before the start of the defence (click on the “bell” icon in the top right corner and then on my name).
Members of the Jury:
- Prof. Dr Jonne Rodenburg – Wageningen University & Research (Opponent)
- Dr Shamie Zingore – African Plant Nutrition Institute (Opponent)
- Prof. Dr Heidi Webber – Leibniz Centre for Agricultural Landscape Research (Opponent)
- Prof. Aurélie Metay – l’Institut Agro (Opponent)
Abstract:
Food insecurity, poverty and vulnerability to climatic risk are severely challenging smallholder farms in a context of a growing demand for food and climate change. Sustainable Intensification (SI) offers the prospect to substantially increase crop production and resilience to climate. However, interactions between SI options, climatic risk and farm resilience remain unclear.
This thesis adopts a systems approach to evaluate the potential of maize intensification with mineral fertilizer and diversification with legumes to increase smallholder farm resilience to climatic risk in sub-humid Zimbabwe. Based on a systematic review, an operational framework for a comprehensive assessment of smallholder farms resilience to climatic risk was developed and used to quantify this risk through multiple dimensions and metrics of performance. The STICS crop model was parameterised and calibrated with on-farm observations to simulate maize and legume yields in smallholder fields. Combined simulations and on-farm observations were then used to conduct a comparative yield gap analysis between maize and legumes. A virtual experiment was run over 27 growing seasons of historical climate to assess and compare the sensitivity of intensified maize and groundnut to rainfall variability. This virtual experiment was further developed to assess the agro-environmental performance of cropping systems combining maize intensification and diversification with groundnut to interannual rainfall variability. Once calibrated, STICS adequately reproduced variations of maize growth in response to water and N stress when the crop was free of biotic stress. In the case of legumes, the fit was less satisfactory because yield was systematically reduced by pests or diseases. In smallholder fields, maize yield was much more limited by nitrogen stress than water stress, while legume yields were driven mostly by pests and diseases. This yield gap exploration highlighted that appropriate management of biotic factors was critical to fully achieve legumes benefits, which are presented as a key component of sustainable intensification. In response to rainfall variability, simulated maize yield was primarily driven by nitrogen stress and occasionally by water stress, while simulated groundnut yield was driven by water stress. This analysis highlighted the importance to accurately assess nitrogen leaching in sub-humid climates to understand the sensitivity of intensified maize to rainfall variability. Over the 27 growing seasons, increasing levels of intensification and diversification increased grain and stover production and environmental performance of rainfed cropping systems. However, two key trade-offs were at play: one between high and stable production and another between stover production and soil fertility. Concentrating mineral fertilizer on a smaller surface to allocate land for a legume appeared as a promising option to enhance smallholders resilience to climatic risk, provided that biotic stressors were adequately managed. Finally, discussions with farmers revealed key social and economic constraints occurring at farm level that were not quantified in our resilience assessment. Further research should explore strategies to alleviate these constraints and foster smallholder farms trajectory towards food security and no poverty – in other words their ability to ‘bounce back better’