عنوان مقاله [English]
Introduction: Green tea leaves are harvested in Iran from early May to November. In some months (mid-June to early September), the amount of rainfall is less than the water requirement of tea plants and the amount and quality of the product is greatly reduced due to water stress, which threatens the livelihood of farmers and the region's economy. Therefore, supplying the required water of the tea plant by using supplementary irrigation and correct principles of operation is the most important issue in increasing the quantity, quality and marketability of the tea product and its economic efficiency. The aim of study was to investigate the effect of different levels of drip irrigation treatment on yield, yield components and quality of green tea leaves during the dry period.
Materials and Methods: This research was conducted for the first time in 2017-2018 in tea plantation in Bazkiagoorab region, Lahijan (Guilan Province). The experiment was conducted as split plots in a randomized complete block design. Irrigation treatments considered included five levels of 0, 25, 50, 75 and 100 water requirement percentage. In the irrigation system of this research, on-line drippers (surface drip irrigation) of Netafim company with design flow rate of 4 l/hr were used. Sub-pipes (laterals) approximately 5 m long were placed in the middle of every two rows of tea plants throughout the experimental plot (except plots without irrigation). Seven drippers with a distance of 0.7 m (one dripper per plant) were installed on 16 mm laterals. Drip irrigation scheduling in water stress period was twice a week based on soil moisture monitoring during growth period by fertigation at plant root depth. In order to fertilize with irrigation water (fertigation), fertilizer solution was prepared and it entered the manifold pipes through injection in each plot. For non-irrigated treatment, nitrogen fertilizer was mixed with the soil in two equal installments of urea fertilizer in two application (first mid of May and first mid of July) and was added to the soil according to the custom of tea growing region. Yield during growth period and yield components and some quality characteristics of green tea leaves during water stress period were measured.
Results: Full irrigation of 2225 and 1610 m3/ha in two years of experiment caused the production of harvestable shoots in summer to be increased by 162 and 153 percent, respectively, as compared to rainfed condition. Increased water stress at deficit irrigation levels led to increase dry matter (semi hard) of tea shoots. Conversely, as the amount of irrigation water in drip irrigation system increased, the fresh weight of shoots increased. Biennial average of the highest yield of green tea leaves (9125 kg/ha) was obtained by providing 100% irrigation requirement and the lowest yield (3468 kg/ha) was obtained from no irrigation level. Improvement of tea quality characteristics such as total polyphenols, caffeine, total ash and nitrogen percentage of shoots was also observed by full irrigation in drip system.
Conclusion: Due to the significant increase in yield and quality improvement of green tea leaves due to the application of drip irrigation system in the period of water stress in tea growing region of Iran, it seems to recommend and promote the use of drip irrigation system in tea plantations, especially in sloping lands, to get rid of the problem of reducing production in water stress condition and improving the living condition of the beneficiaries of this product.