Managing dry spell risks to improve rainfed maize productivity in the semi-arid central rift valley of Ethiopia
The existing evidences support that some eighty percent of the world’s agricultural land is rainfed, contributing to the tune of sixty percent to food production worldwide. This empirical research was conducted on-station during June to September main growing season over two years (2000 and 2001) to substantiate that, managing dry spell risks through development of compatible technologies can improve rainfed maize productivity in the semi-arid zones of Ethiopia. Firstly, two soil water conserving tillage practices i.e a metal handled-Erf and Mofer attached MB plough and Tie Ridger (TR) both of which are simple tillage tools were used. Secondly, varying plant population level was linked to the inseason dry spell length for 5, 7, 10, 15, 20 and more, as well as to the crop water requirement and plot soil water content at land preparation stage. The result revealed that the shorter dry spells have higher probability of occurrence, compared to the longer dry spells in general. On the other hand, the probability of dry spells is higher during the early parts of the growing season, with a declining trend until the peak of the rainy season and slopping up towards the end of the rainy season. The result on water requirement information under Melkassa climate shows that a total of 315 mm of soil water is required for maize throughout June/July to September growing period. MB plowing realized significantly highest grain yield at 5% alpha level (1849 Kg.ha-1) at the recommended plant population (53,333 plants ha-1), whereas, TR resulting in nearly similar yield for the same population. Although the study area is known for water scarcity and hence lower plant population is preferred, it was possible to achieve high yield at this population level. This could be because, the crop water requirement was met at physiological maturity stage in both seasons and at flowering in one (2000) of the two seasons. The water requirement for vegetation was met in both seasons; however, it was followed by lower WRSI at least in one of the seasons, which could have caused a reduction in yield at this plant population level. Further, 70% of the variability in maize grain yield was explained by the root zone available soil water at planting. For instance, grain yield was 1480 kg ha-1 at 119 mm of available soil water at planting; while the same was 1845 kg ha-1 at 136.5 mm of soil water. Overall, the paper provided empirical evidence that management of dry spell risks is possible, but it demands for the innovative management practices that outsmart the business as usual (BAU) approach i.e. the miraculous drought tolerant or drought escape crop cultivar development strategy.
Keywords: Dry spell, Plant population, Risk, Soil water, Tillage, WRSI