Soil fertility management in yam cropping systems in Côte d’Ivoire: exploring perceptions, solutions and knowledge transfer

Abstract

Soil fertility management is a challenge in yam cropping systems in West Africa. Traditional yam cropping systems are characterised by low yields, forest loss and accelerated soil degradation due to soil organic matter (SOM) decline. SOM is a key element to sustain food production, especially in low-input systems, for example by storing water and nutrients to promote crop growth. Strategies to improve crop productivity and halt the decline of SOM need to be implemented to sustain yam production in this region. Such interventions will require improved agricultural practices and the engagement of farmers and other actors. Different aspects of soil fertility management were studied in this thesis. These included: i) assessing biochar as a soil amendment with the potential to improve crop productivity and soil properties; ii) exploring farmers’ perceptions about soils and soil fertility management; and iii) evaluating the use of a serious game as a tool to disseminate knowledge about innovations and soil fertility management to relevant groups. In Chapter 1, field experiments were installed on two sites in Côte d’Ivoire, representing different levels of soil fertility. The effect of biochar was assessed on yam tuber and cowpea grain yields, biological nitrogen fixation (BNF) by cowpea, and soil properties. Results did not show a significant effect of biochar on neither crop productivity nor BNF. Although carbon (C) stocks increased in the low-fertility soil, our findings suggest mineralisation of SOM across all treatments and sites. Biochar did not significantly affect soil properties. In Chapter 2, a total of 30 yam farmers were interviewed in the two experimental sites, to explore their mental models about soils. The results show that farmers have a large degree of shared knowledge about soils, but also revealed contrasting views, for example regarding burning of the field. Preparing a “clean field” was crucial to most yam farmers. Farmers who still possessed enough land to practice fallow, did not perceive soil fertility to be of concern. The concept of SOM was not mentioned by any farmer and is probably a missing key element of their mental models of soils. This knowledge gap should be addressed in further initiatives to improve soil fertility management. Chapter 3 evaluated the use of the serious game J’igname as a tool for dissemination of knowledge about innovations and soil fertility management practices. A total of 25 game sessions were conducted in Côte d’Ivoire and Burkina Faso, involving yam farmers, extension agents and researchers. Results show that the local context had a stronger influence on players’ decisions than their background. Local cultivation practices were reflected in the players’ behaviour during the game, which were associated with crop choices and fertilisation regimes. We conclude that the game J’igname accurately serves as a model of a yam cropping system and can be used as an educational tool and to better understand people’s preferences and objectives. In conclusion, addressing the challenge of improving soil fertility management in yam cropping systems will require an integrated approach, involving the biophysical, agronomic and human dimensions of soil fertility. Further research is needed to assess if, and in what settings, an innovation would be beneficial to farmers. Evaluations need to be based on both the agronomic performance of the innovation and the motivations and objectives of the farmers.