Effect of Humic Acid, Nitrogen Concentrations and Application Method on the Morphological, Yield and Biochemical Characteristics of Strawberry ‘Paros’

ABSTRACT The current study investigates the effects of humic acid concentration, its application methods as well as nitrogen ratios on the morphological, yield and biochemical characteristics of strawberry cv. Paros, during 2014–2015 in Ardabil Province, Iran. The study has been conducted within the framework of a double split plot randomized complete block design with three replications and density of 10 plants per replications. Different nitrogen levels (50, 100 and 150 kg ha−1) were examined in the main plots while application methods of humic acid (foliar and soil) and its different concentrations (0, 2, 4 and 6 kg ha−1) were considered in the subplots and sub-sub plots, respectively. The results of the analysis of variance (ANOVA) indicated that the interaction effects of different concentrations of nitrogen, humic acid and its application methods are significant on most of the measured variables at 5% probability level. Mean comparisons showed that the highest values for the leaf area, fruit yield, chlorophyll a, carotenoids and titratable acidity are associated with the combined treatments of nitrogen and humic acid with concentrations of 100 kg ha−1 and 4 kg ha−1, respectively. In three-way interactions, the highest shoot and root biomass and total chlorophyll content were obtained from the application of 100 kg ha−1nitrogen and 4 kg ha−1 foliar humic acid, while the highest nitrogen and protein contents of leaf and root were achieved upon applying 2 kg ha−1 foliar humic acid and 150 kg ha−1 nitrogen. Moreover, the highest amounts of ascorbic acid and total soluble solids were found at a concentration level of 100 kg ha−1 nitrogen along with applying 2 and 6 kg ha−1 foliar and soil humic acids, respectively. Finally, the best results of most of the studied traits were observed at 100 kg ha−1 nitrogen and 4 kg ha−1 foliar humic acid application.