Effect of Humic Acid and Mycorrhiza Application on Morphological Traits and Yield of Cotton under Drought Stress

In order to evaluate the effect of irrigation, humic acid and mycorrhiza application on morphological traits, yield and water use efficiency (WUE) of cotton, an experiment was carried out as a factorial split-plot based on a randomized complete block design with three replications in the research farm of Islamic Azad University of Birjand, Iran in 2016. Three irrigation levels (40, 70 and 100 percent of plant water requirement) were as the main plot and the combination of two mycorrhiza levels (non- application and application) and two humic acid levels (0 and 10 L. ha-1) were considered as sub-plot. The results showed that with reducing the supply of cotton water requirement from 100 to 40 percent significantly reduced plant height, stem diameter, branch number of main stem, seedcotton yield and biological yield by 29.6, 31.8, 48.3, 68.7 and 60.5, respectively. However, the water use efficiency for seedcotton production in the treatment of 70 percent water requirement supply was significantly higher (19.2 and 44.5%, respectively) than treatments of 100 and 40 percent water requirement supply. Also, application of mychorhiza significantly increased the plant height, stem diameter, branch number of main stem, seedcotton yield and biological yield, water use efficiency for seedcotton and biomass production by 10.9, 12.5, 30, 48, 26.8, 48.8 and 24.8%, respectively. In addition, application of 10 L. ha-1 humic acid significantly increased the plant height, stem diameter, branch number of main stem, seedcotton yield and water use efficiency for seedcotton production by 9.9, 9.4, 14.2, 23.5 and 20.7%, respectively. In general, the results showed that the use of mycorrhiza and humic acid decreases the negative effects of water deficit stress, especially in moderate stress conditions. Considering the water use efficiency and cotton yield, it is possible to consider the treatment of moderate water stress and mycorrhiza application for the cultivation of this plant in Birjand.