Relating sorghum yield to growing seasonal weather conditions for Chobe and Barolong agricultural district, Botswana
Tjitemisa, Jeomba Mavis
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Growing season rainfall is the most important factor in rain-fed arable agriculture in semi-arid climates. Knowledge of rainfall distribution is needed to make farmers aware of possible crop yield obtainable during and at the end of growing season and also help governments with information for the attainable of food security. The goal of this study was to examine the relationship between crop yield and growing season rainfall distribution in an attempt to contribute to food security early warning system. Specifically, the study determined the relationship between total seasonal rainfall, total number of rainy days, average maximum temperature and sorghum yield. The established relationship was then used to determine the most sensitive growth stage (s) for yield loss. The study explored the relationship between seasonal rainfall distribution and total seasonal rainfall with crop yield for Chobe agricultural district and Barolong agricultural sub-district In genera), seasonal rainfall showed a negative slope while sorghum yield had a positive gradient for Chobe agricultural district. For Barolong agricultural sub-district, a positive trend was observed in both seasonal rainfall and sorghum yield. Number of rainy days and sorghum yield indicated a positive slope for Chobe agricultural district while for Barolong agricultural sub-district, a negative slope in rainy days was observed while sorghum yield had a positive gradient. Exploratory results show that sorghum yield fluctuated with rainfall. Over the years, rainfall and sorghum yield fluctuated for both districts. Average maximum temperature at flowering stage had high correlation with sorghum yield (0.62) for Chobe agricultural district. For Barolong agricultural sub-district, the following showed high correlation with sorghum yield; total rainfall amount at maturity (0.85), total number of rainy days at pre-sowing stage (0.79) and total number of rainy days at maturity stage (0.72). There were no differences in sorghum yield for both districts because both confidence limits at 95% include the mean of sorghum yield for the respective study periods. Temperature at flowering stage was the only significant (P < 0.02) explanatory variable for yield for Chobe. For each degree Celsius increase in average maximum temperature at flowering stage, sorghum yield increased by 0.223 kg/ha for Chobe agricultural district. If there was no influence of average maximum temperature at flowering stage, yield would be less 5.483 kg/ha. For Barolong, rainy days at pre-sowing stage (P <0.02), rainy days at maturity stage (P < 0.002), and rainfall amount at maturity stage (P < 0.02) were significant. For each increase in number of rainy days at pre sowing stage, yield decreased by 0.829 kg/ha while at maturity stage, an increase in a number of rainy days, decreased sorghum yield by 3.376 kg/ha. An increase in rainfall at maturity stage increased sorghum yield by 0.912 kg/ha. The most sensitive stage (s) for sorghum grain yield loss due to high rainfall experienced in Chobe agricultural district was the flowering stage, with maximum temperature being the limiting factor while for Barolong agricultural sub-district were the pre-sowing (rainfall distribution more than enough) and maturity stages (total rainfall amount limiting and rainfall distribution more than enough).
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