Effect of Soil Micronutrient Status on the Fermentation Characteristics and Organoleptic Quality of Nigerian Tea

The status of micronutrients (Cu²⁺, Zn²⁺, Fe²⁺ and Mn²⁺) in soils and foliage of three commercial tea clones 68, 143, and 35 collected from the Ardo-Gore tea estates of the Mambilla Plateau in Gongola State of Nigeria was evaluated. Leaf samples were also batch-processed and examined for fermentation characteristics including average fermentation time and organoleptic cup quality, and analytical quality indices, namely total phenol and tannin. Results showed that while Cu and Mn contents are adequate, Fe and Zn are marginal. A high negative correlation was obtained for soil Fe and leaf Cu (r = 0.98) and Zn (r = 1.00) probably due to substitution ability of these essential nutrients which could have limiting consequences on the fermentation process. Leaf Cu showed a significantly positive relationship with total phenol and tannin contents of the samples (r = 0.77 and 0.73, respectively) while the relationship between leaf Zn and total phenol (r = 0.64) was statistically insignificant. Sensory evaluation of the samples from the three clones showed that close 35 had the least fermenting ability and poorest cup quality. This trend was in agreement with the levels of leaf Cu, Zn, total phenol and tannin of the samples, indicating high variability in clonal requirements of micronutrients for physiological and processing functions.