Investigating the Relationship between Soil Acidity and Some Quality Characteristics of Tea Green Leaves in Tea Plantations of Gilan Province

Tea is a permanent and evergreen plant that grows adeptly in acidic soils. The tea plant naturally absorbs aluminum and accumulates it in various shoot parts. Although aluminum is essential for tea growth, it is harmful to human health. Evaluating aluminum status in both soils and tea green leaves is necessary to better understand their relationships in order to improve the quality as well as quantity of tea yields. For this purpose, 38 samples of the soils and the third green leaves of tea (as an index leaf) were collected randomly from tea plantations of Guilan Province. In soil samples, besides the general properties, the values of pHw, pHCaCl2, exchangeable aluminum, calcium and magnesium, total nitrogen and available concentrations of phosphorus and potassium were determined. Concentrations of the aforementioned nutrients along with iron and zinc were also evaluated in the tea leaves. Based on the results, the mean values of pHw and pHCaCl2, and the mean concentrations of soil exchangeable aluminum and leaf aluminum were 4.51, 4.04, 256 mg/kg, and 1362 mg/kg, respectively. The soil exchangeable aluminum had inverse power relationships with pHw and pHCaCl2 with the coefficients of determination of 66% and 84%, respectively. This indicated that the pHCaCl2 was more valid than pHw. Leaf Al concentration showed no significant correlation with soil pH, but had significant relationship with soil exchangeable aluminum (r=0.69**). Furthermore, the total polyphenol content of the green tea leaves had no significant correlation with leaf Al concentration, but had significant relationship with (Al/(Fe+Zn)) ratio in tea leaves (r=0.64***). According to the lower limit of optimum pH for tea plantations (pH=4.5), the maximum permissible concentration of soil exchangeable aluminum was estimated to be 153 mg/kg. In order to control soil exchangeable aluminum and adjusting soil pH, it is recommended to use lime or dolomite, based on the soil buffering capacity.