Effect of Soil Water Environment and Simulated Savanna Climate on Growth and Mineral Nutrition in Jatropha curcas L.

This study aimed to determine the optimal soil water conditions for J. curcas L. cultivation under the bi-annual rain seasons of the African Savannah climate. Changes in J. curcas L. seedling biomass and mineral nutrient uptake and movement patterns were examined under soil water matric potentials of -2.5, -2.9, -3.4 and -4.0kPa, and two rain seasons separated by a dry spell. The bi-annual savannah rain conditions were simulated using automated buried-type tensiometer system. During the first rain season (irrigation), -3.4kPa soil water matric potential showed the highest water-use efficiency (2.44 g dry weight L-) and biomass yield (57.14g). Seedlings were variously affected by the subsequent dry spell, including total defoliation and stunting. On re-irrigation, seedling recovery (biomass and water use efficiency) was less as compared to the first rain season. Among the nutrients monitored, N, P and K were the most predominantly uptaken, with N showing the closest correlation with seedling growth. Soil matric water potential of 3.4 kPa is the optimum soil water environment for J. curcas cultivation in the savannah conditions; additionally, irrigation during the dry season is essential for a stable harvest.