Optimizing the use of nitrogen fertilizer and irrigation water to improve the tea (Camellia sinensis (L.) O. Kuntze) yield and quality

Harvested Shoots of tea plant determine the quality of tea as a key factor and affect at least 70% of the quality of tea drink. Water and nitrogen fertilizer are the most important agricultural inputs in the production of tea leaves and shoots, which plays an important role in determining the quality and its marketability. Tea quality depends on nitrogen level , polyphenols and caffeine content of shoots. In this study for the first time in Feshalam tea research station in Guilan province, the effect of different levels of nitrogen fertilizer and irrigated water on yield and quality indicators of shoots were surveyed.
In order to evaluate and optimize the use of nitrogen fertilizer and irrigated water on yield and some quality index of tea leaves, split block experiment on randomized complete block design (line-source irrigation technique) was conducted for 3 years (2008-2010) in Feshalam tea research station in Guilan province. Treatments consist of six levels of nitrogen zero, 100, 200, 300, 400 and 500 kg N ha-1 and five levels of irrigation water. Irrigation schedul by monitoring moisture in root zone on basis of TDR and water balance equation was implemented twice weekly. In this experiment, weight of harvested green leaves in each plot was measured which 22.5% was converted to processed tea. Factors affecting the quality of tea, such as the total amount of nitrogen in the third leaf of active shoots and some quality characteristics such as caffeine percentage, soluble solids in water (aqueous extract) and polyphenols percentage in harvested shoots in three flash (spring , summer and autumn) were also measured.
The results showed that, increased use of nitrogen fertilizer in two splits (late May and mid-July) reduced the quality of tea and full irrigation during the dry months (July and August) increased the tea yield. Appling 300 to 350 kg N ha-1 under full irrigation (3424 m-3 of irrigation water) leading to a doubling performance as compared to no-irrigation conditions. Instead, with increasing the amount of nitrogen fertilizer reduced the amount of polyphenols and soluble solids in water and increased the amount of caffeine and nitrogen in the tea shoots. The impact of irrigation on improving the quality of tea shoots were observed only in summer.
In order to maintain a balance between yield and quality of tea production as well as economic and environmental considerations, for full irrigation, use of 200 to 250 kg N ha-1 and in rainfed condition , 100 to 200 kg N ha-1 is recommended.