The Role of Potassium to Improve Growth, Water Use and Yield of Canola Under Varying Soil Water Conditions.

How does potassium influence transpiration and water use efficiency in canola under drought stress conditions? The role of potassium (K) in plants is manifold i.e. creating an osmotic gradient in roots and regulating stomata function. Our hypothesis is that drought tolerance in canola can be improved by manipulating potassium fertilization. We have investigated drought tolerance in canola under varying potassium treatments. Two months after planting, the samples were subjected to a drying cycle until they reached the wilting point and then they were rewetted. During the drying period we measured transpiration by weighing the samples at regular intervals and leaf turgidity by means of the pressure clamp technique by Zimmermann (2008). At the end of the drying cycle we measured root length distribution, shoot to root ratio, and K+ content in plants. The experiments have indicated that plants with sufficient supply of potassium developed a larger leaf area and a greater dry weight. Overall, plants with high K+ transpired more. However, the transpiration rate per leaf area was lower than for plants with no K+. The leaf pressure clamp was capable of monitoring variation of leaf turgidity due to diurnal variation of light intensity as well as the decrease and recovery of leaf turgidity during the drying phase and after rewetting, respectively. Interestingly, the leaf pressure clamps measured a stronger decrease of leaf turgidity in the samples with low K+ treatment. At the same water content, plants with high K+ treatment showed a relatively slower decrease in turgidity. These findings, together with the fact that the transpiration rate per leaf area of the high K+ treatments was smaller despite their higher dry mass, indicates the importance of K+ in regulating water use efficiency and drought tolerance in canola.