Drought and Salinity Tolerances of Castor Oil Plant.

Castor oil plant (Ricinus communis.) has been widely cultivated for oil with a wide variety of uses.and is expected as a biofuel crop rencently. Few quantitative data concerning its tolerance have been presented. We evaluated the tolerances of Castor oil plant to drought and salinity stresses in terms of parameter values in the widely used macroscopic root water uptake model. With such parameter values, root water uptake under stresses can be accurately predicted, which may contribute to efficient water management in arid and semiarid regions where irrigation is required to attain high yield. We conducted a column experiment using six columns with one plant each: three were under drought/salinity and others provided potential transpiration. Three soil moisture and salinity probes were inserted into each of the three columns under the stress to observe water content and electrical conductivity. The soil surface was covered to prevent evaporation. Weight of the columns was manually measured to obtain daily transpiration. After the stress period, root density distributions were obtained by dismantling the columns. Three parameter values were inversely determined by minimizing the sum of square differences between observed and calculated daily transpiration rates. Water uptake at each depth and time was calculated by substituting linearly interpolated matric and osmotic potentials into the stress response function. Optimized daily transpiration rates agreed well with the observations. Determined stress response functions indicate that Castor oil plant is less tolerant to drought compared to Jatropha, a major oil shrub. On the other hand, it is found to be more tolerant to salinity stress than jatropha.