Some Biochemical Characteristic Changes of Grapevine ‘Bidane-Ghermez’ Influenced by Drought Stress using Organic and Inorganic Fertilizers

 the lack of water resources in arid and semi-arid regions is one of the most important limiting factors of the growth of plants, especially fruit trees. Grapevines are one of the most important horticultural products in the world as well as in Iran. The water content of plant tissues, their growth, and the availability of different nutrients in the soil are significantly reduced under water stress conditions. Therefore, the successful production of the plant under water stress conditions depends on the management of plant nutrition. By application of organic and chemical fertilizers, the physical, chemical, and biological properties of soil can be improved. Besides, it can reduce the adverse effects of drought stress conditions.    

 To evaluate the effect of compost, biochar, and potassium sulfate application on dry matter, relative water content (RWC), chlorophyll a, b, total, and carotenoid contents, as well as the concentration of macro-and micronutrients of leaves of grapevines ‘Bidane-Ghermez’ under two drought stress conditions, this experiment, was conducted in the research greenhouse during 2017-2018. The experiment was carried out as a factorial experiment based on a randomized complete block design (RCBD) with two factors and four replications. The first factor, without drought stress conditions (80% field capacity (FC)), and drought stress conditions (40% FC), and fertilizer treatments included potassium sulfate (1.25 g.kg-1), compost (5 % w/w), and biochar (10% w/w).
  

 The results of the analysis of variance (ANOVA) showed that the interaction effect of drought stress ×fertilizers application was not significant for dry matter, and RWC (P>0.05). Also, the results of ANOVA indicated that the simple effect of drought stress conditions was not significant for dry matter but the simple effect of fertilizer application was significant for leaf dry matter (P<0.01). Without drought stress conditions, there were no significant differences in leaf dry matter between different fertilizer treatments. However, under drought stress conditions, the highest dry matter of grapevine leaves was observed in biochar, compost, and potassium sulfate, respectively. Also, there were no significant differences in leaf dry matter of grapevine between biochar treatment under drought stress conditions and all fertilizer treatments without drought stress conditions. The simple effect of drought stress conditions was significant for leaf dry matter (P<0.05). The results of ANOVA revealed that the interaction effect of drought stress ×fertilizer application was not significant for chlorophyll a, b, total, and carotenoid contents of grapevine leaves. However, the simple effects of drought stress conditions and fertilizer application were significant for chlorophyll a, b, total, and carotenoid contents of grapevine leaves (P<0.01). Relative water, chlorophyll a and carotenoid contents of grapevine leaves were not significantly different among fertilizers treatments. The increase of chlorophyll a/b ratio compared with control was changed in order biochar>potassium sulfate>compost. Moreover, the interaction effect of drought stress ×fertilizer application was significant for nitrogen (N), magnesium (Mg), ferrous (Fe), zinc (Zn), and copper (Cu) concentrations of grapevine leaves (P<0.01). The ANOVA indicated that the simple effects of drought stress conditions and fertilizer application had a significant effect (P<0.01) on macro- and micro-elements concentrations of grapevine leaves. By application of biochar, the concentration of P, K, Mg, and Cu of grapevine leaves significantly were higher than compost and potassium sulfate applications. This consequently resulted in higher chlorophyll a/b ratio and dry matter of grapevine leaves in biochar treatment for control under drought stress conditions.

 Based on the results of this research, it can be concluded that the application of fertilizers reduced drought stress effects on biochemical characteristics and dry matter of grapevine leaves. According to the results, at first the application of biochar is recommended, then potassium sulfate and compost. Our previous results indicated that by application of compost, the available sodium (Na) of soil was increased 8.53 and 60.52 % for potassium sulfate and compost treatments compared to control, respectively. While, by application of biochar, the available Na of soil reduced 3.73 % in comparison with control. This finding is so important regarding the Na effects on soil structure, the toxicity of Na for plants as well as the interaction between Na and K. Considering K is a critical element to regulate the water content of plant tissue and reduces the hazards of water stress conditions, the higher concentration of Na prevents K uptake from the soil solution by plant.