Soil Science

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    ANALYSIS OF CLIMATE VARIABILITY AND CHANGE AND ITS IMPACTS ON WATER PRODUCTIVITY AND NUTRIENT USE EFFICIENCY OF MAIZE (Zea mays) IN THE GREAT ETHIOPIAN RIFT VALLEY BASINS
    (Hawassa University College of Agriculture, 2021) FITIH ADEME MAMO
    Climate variability and change are a global phenomenon affecting many nations. Smallholder farmers in Ethiopia have been facing severe climate related hazards, in particular highly variable rainfall and severe droughts that negatively affect their livelihoods. Anticipated climate change is expected to aggravate some of the existing challenges and impose new risks beyond the range of current experiences. This study aimed at understanding current climate variability and future climate change, and its associated impacts in particular for maize production. The climate analysis was conducted in the Great Rift Valley Basins (GRVB), which represents diverse agroecology and farming systems. The climate variability and change impact study were conducted in the Central part of the Rift Valley (CRV), which represent a major cereal-based farming system of the semi-arid environments of Ethiopia. Empirical statistical analyses using field experimental data in combination with crop-climate simulation modelling were used to achieve the objectives of the study. A high spatial resolution regional climate models and a well-known crop growth simulation model were used for the modelling analysis, which is an innovative feature of the methodology used in this thesis. The analysis revealed that rainfall exhibited high interseasonal variability (coefficient of variation 13-37%) during the period 1981-2010 in the GRVB. The mean annual temperature significantly increased by +0.43 ºC [0.27 ºC to 0.58 ºC] per decade in the same period. Projections for future climate suggested that annual rainfall will change by -25 to +6% and the annual temperature is expected to increase in the range of 2.5-5.1oC by the end of this century. A corresponding change in length of growing period (LGP) from -5.66 to -25.5% for central semiarid and +3.9 to -16.4% for central sub-humid highlands was simulated in the near century. Maize grain yield was strongly (P<0.01) and positively correlated with seasonal rainfall (r=0.67-0.69) in the CRV while day temperature affected grain yield negatively (r= -0.44) at Ziway (P<0.05) during the simulation period. Simulated water-limited yields showed high inter-annual variability (coefficient of variation, ~24%) and about 47% of this variability was explained by the xvii variation in growing season rainfall. The observed farmers’ yield was 28, 48 and 57% lower than the researcher-managed, water--limited and potential yield of the crop, respectively, indicating wide maize yield gap in the region. Analysis of climate change scenarios showed that maize yield will decrease on average by 16.5 and 23% by mid and end of this century, respectively due to climate change. Similarly, water productivity is expected to decline on average by 2.2 and 12% in the CRV by mid and end centuries with respect to the baseline. Nutrient uptake and corresponding nutrient use efficiency (NUE) might also be negatively affected by climate change. Phosphorus uptake probably will decrease in the CRV on average by 14.5 to 18% by mid-century. Nitrogen and P use efficiency indicators showed decreases in the range between 8.5 to 10.5% and between 9.3 to 10.5%, respectively by midcentury relative to the baseline average. The simulation under no water and nutrient limitation condition ensured improvements of both water and nutrient use efficiency in the changed climate which could ensure modest production in the future. The high estimated impact of climate variability and changes on crop yield and associated resources use in the CRV imply greater risks on rainfed crop production in the region. Hence, the study recommends further assessment of potential adaptation options and economic impact of climate related risks in the region to provide full-fledged evidence for better policy decisions.