The Effect of Potassium (K) and Boron (B) Foliar Application on MorphoPhysiological Responses and Root Yields of Sugar Beet (Beta vulgaris L.) under Drought Stress Conditions

Drought stress is the most important factor of yield reduction in sugar beet. Therefore, adopting effective strategies for diminish of the drought adverse effects in sugar beet is necessary. This field experiment was conducted in order to study the effects of foliar application of potassium (K) and boron (B) on morpho-physiological responses, quality and root yields of sugar beet (Beta vulgaris L.) under drought stress conditions, using a split plot experiment based on randomized complete block design with three replications, in Shahrekord University, in 2019. The main plots were allocated to irrigation treatments including: irrigation after 70, 100 and 130 mm (I1, I2 and I3, respectively) cumulative evaporation from class A evaporation pan and the sub plots were allocated to fertilizer treatments in the form of foliar spraying including: control (no fertilizer application), K, B and B + K. Results showed that the effect of irrigation, foliar spraying and interaction of irrigation × foliar spraying treatments was significant regarding to leaf area index (LAI), leaf proline content, relative water content (RWC), extractable sugar, sodium and potassium content of sugar beet. The highest value of LAI and RWC was related to interaction of I1 irrigation and B + K spraying treatments. The highest value of leaf proline content was obtained by interaction of I3 irrigation and K spraying treatments. The highest percentage of extractable sugar was observed in interaction of I2 irrigation and B treatments. In other words, I2 irrigation treatment slightly increased the percentage of extractable sugar, which did not have significant difference with I1 irrigation treatment. The lowest amount of root sodium and potassium content was obtained under interaction of I1 irrigation and B + K treatments. The effect of irrigation and foliar application treatments on total plant dry weight, chlorophyll index, extraction coefficient of sugar (ECS), sugar and root yield was significant, as the highest amount of mentioned traits were recorded in B + K and I1 irrigation treatments. Interaction of irrigation×foliar spraying did not have a significant effect on these traits. Alkalinity coefficient was only affected by foliar spraying treatments and the highest amount of alkalinity coefficient was observed in K fertilizer treatment. Generally foliar application of B and K significantly improved the morpho-physiological, quantitative and qualitative properties of sugar beet and reduced the adverse effectss of drought stress, probably due to the important role of these elements in the osmotic adjustment and other plant physiological and biochemical processes. Therefore, in sugar beet cultivation especially under drought stress conditions, spraying of B and K is recommended.Drought stress is the most important factor of yield reduction in sugar beet. Therefore, adopting effective strategies for diminish of the drought adverse effects in sugar beet is necessary. This field experiment was conducted in order to study the effects of foliar application of potassium (K) and boron (B) on morpho-physiological responses, quality and root yields of sugar beet (Beta vulgaris L.) under drought stress conditions, using a split plot experiment based on randomized complete block design with three replications, in Shahrekord University, in 2019. The main plots were allocated to irrigation treatments including: irrigation after 70, 100 and 130 mm (I1, I2 and I3, respectively) cumulative evaporation from class A evaporation pan and the sub plots were allocated to fertilizer treatments in the form of foliar spraying including: control (no fertilizer application), K, B and B + K. Results showed that the effect of irrigation, foliar spraying and interaction of irrigation × foliar spraying treatments was significant regarding to leaf area index (LAI), leaf proline content, relative water content (RWC), extractable sugar, sodium and potassium content of sugar beet. The highest value of LAI and RWC was related to interaction of I1 irrigation and B + K spraying treatments. The highest value of leaf proline content was obtained by interaction of I3 irrigation and K spraying treatments. The highest percentage of extractable sugar was observed in interaction of I2 irrigation and B treatments. In other words, I2 irrigation treatment slightly increased the percentage of extractable sugar, which did not have significant difference with I1 irrigation treatment. The lowest amount of root sodium and potassium content was obtained under interaction of I1 irrigation and B + K treatments. The effect of irrigation and foliar application treatments on total plant dry weight, chlorophyll index, extraction coefficient of sugar (ECS), sugar and root yield was significant, as the highest amount of mentioned traits were recorded in B + K and I1 irrigation treatments. Interaction of irrigation×foliar spraying did not have a significant effect on these traits. Alkalinity coefficient was only affected by foliar spraying treatments and the highest amount of alkalinity coefficient was observed in K fertilizer treatment. Generally foliar application of B and K significantly improved the morpho-physiological, quantitative and qualitative properties of sugar beet and reduced the adverse effectss of drought stress, probably due to the important role of these elements in the osmotic adjustment and other plant physiological and biochemical processes. Therefore, in sugar beet cultivation especially under drought stress conditions, spraying of B and K is recommended.