The Effect of Vermicompost, Humic Acid, and Manure on Yield, Biochemical Characteristics, and Enzymatic Activities in Sugar Beet (Beta vulgaris L.) under Water Deficit Conditions

To investigate the effect of organic fertilizers on the quantitative and qualitative characteristics of sugar beet under different moisture conditions, a study was conducted as a split plot experiment based on a randomized complete block design with three replications in Mahabad city in 2021. Irrigation treatments, including irrigation after 60 (normal), 90 (mild stress), and 120 (severe stress) mm evaporation from the class A evaporation pan, and organic fertilizer treatments (control, vermicompost, manure, and humic acid) were placed in main plots and sub-plots, respectively. Severe water stress conditions reduced the content of chlorophyll a (22.82 %) and relative water content (RWC) (24.35 %) and increased the content of proline (47.43%), beta glycine (17.89%), catalase (21.30 %), malondialdehyde (47.95 %) and water use efficiency (WUE) (23.83%) compared to normal irrigation conditions. Also, the application of vermicompost increased the amount of chlorophyll a, RWC, proline, glycine beta, catalase content, and WUE by 29.11, 20.15, 34.83, 14.98, 13.70, and 21.56 percent, respectively, and decreased the content of malondialdehyde about 18.53% in comparison to control. In this study, the highest stomatal conductivity (51.01 mol.m-2s-1), chlorophyll b content (16.3 mg.g-1FW), carotenoid (4.27 mg.g-1 FW), roots yield (78.33 t.ha-1) and the lowest content of hydrogen peroxide (0.96 μmol.g-1FW) allocated to the vermicompost treatment under normal irrigation conditions. Root yield showed a positive and significant correlation with stomatal conductance, chlorophyll b, carotenoid, RWC, and WUE, but a negative and significant correlation with catalase enzyme activity, hydrogen peroxide content, malondialdehyde, and sugar content.