Assessment of Climate Change Impact on Sorghum Production in Machakos County

Abstract

The APSIM (Agricultural Production Systems sIMulator) model was used to assess the impact of climate change on sorghum production in the semi arid low lands of Machakos County under three future scenarios of climate change (2010-2039, 2040-2069 and 2070-2099) using two Representative Concentration Pathways (RCPs): RCP 4.5 and RCP 8.5. The APSIM model was calibrated and evaluated using field experimental data obtained from a two-year experiment (2014 to 2015) of sorghum parameters carried out at Kenya Agricultural and Livestock Research Organization (KALRO) in Katumani. Model evaluation shows that APSIM sorghum model was capable in quantifying the response of sorghum to nitrogen (N). The values of root mean square error obtained were low for all the sorghum parameters studied. Higher values of modified index of agreement showed more precise simulation of total biomass and grain yield. The observed and simulated sorghum parameters for both cultivars during the long and short growing seasons depicted good correlation with r2values ranging between 45 % and 99%. Across all the GCMs projected mean changes on phenological dates (days to 50% flowering and physiological maturity) showed a consistent decline for both sorghum varieties during the long and short growing seasons with the application of different rates of fertilizer. These trends were more manifested in the RCP8.5 than RCP4.5 and in the end century (2071-2100) of the simulation. With the RCP8.5 flowering dates reduced by 24 and 28 days and the crop cycle duration shrinked by 35 and 38 days in the end century (2071-2100) for gadam and seredo, respectively. There was slight increase or decrease in biomass for both varieties under climate change with no fertilizer application. However, with application of 50kgha-1N, there was a slight increase of biomass. It has been noted that under changing climate sorghum grain yields will constantly increase for both cultivars over the three future time periods with almost 85.3% increase as we approach the end of the century (2070-2099). The extent of yield change was higher for seredo than for gadam.