Climate Smart Agriculture in smallholder farming systems in the central rift valley of Ethiopia : potentials for improving productivity, climate change adaptation and mitigation

Climate Smart Agriculture (CSA) is an approach that aims at achieving sustainable food production and security through providing flexible but socially acceptable cultivation methods. For this, CSA seeks to sustainably increase yields, to build resilience to climate variability and change, and to reduce net greenhouse gas (GHG) emissions. Practices commonly subsumed under CSA are, among others, conservation agriculture (CA), agroforestry, inclusion of legumes, use of drought tolerant crop varieties and stress adapted livestock breeds, crop diversification and integrated soil fertility management. The success of implementing CSA practices is context specific and has to be adapted to fit local conditions. Hence, CSA has to be studied under specific regional settings. In my PhD thesis, I set up two conservation tillage plot experiments (Paper I) in the Ethiopian rift valley on soils with contrasting management histories, a high input field at the University farm of Hawassa and a low input field run by smallholders in Lokabaya. The experiments tested increasing levels of maize intensification under zero and conventional tillage, using split plot design, with tillage practices assigned to main plots and intensification levels to sub plots. Maize yields and selected soil properties were studied throughout two seasons. Seed priming with or without compost addition had no effect on maize yields at neither location, whereas mineral fertilizer addition increased yields, particularly when combined with mulching of maize residues at the drier Lokabaya site. However, mulching at a rate of 3 ton ha-1 did not significantly affect yields compared to mineral fertilizer addition alone, despite an increasing trend at Lokabaya. The effect of tillage practice was mixed, with zero tillage showing better (Lokabaya farm 1 in 2015 and Hawassa in 2016) or comparable (Lokabaya both farms 2016, farm 2 in 2015) yields with conventional tillage, with the exception of significantly lower yields at the humid Hawassa site with zero tillage during the dry 2015 season. In general, zero tillage did not lead to a consistent yield penalty at any of the sites (except at Hawassa in the dry 2015 season), suggesting that smallholder farmers in the area could achieve reasonable yields without having to till, thereby saving significant amounts of labor and money. Being a short-term experiment over just two growing seasons, there was no significant effect on soil properties like SOC, TN, bulk density