Influence of nitrogen fertilizer rates and harvesting intervals on the clonal tea green leaf fatty acids levels in the Lake Victoria Basin of Kenya

Abstract

Tea agronomic recommendations in Lake Victoria basin are uniform, despite different regions producing teas of different qualities and yields. It is not known if these differences arise from variations in cultivars, agronomic inputs, management or the environment. A trial was conducted in Kenya to determine if noted differences persist in the same cultivar under same agronomic inputs, and management. Green leaf chemical quality precursors influence black tea quality. Unsaturated fatty acids in green tea leaves break down producing volatile flavour compounds, key tea aroma compounds. The C6 aldehydes, alcohols and acids, heptanal, heptanol, nonanol, nonanal, E-2-nonenal, Z-2,Z-4-nonadienal and E-2,E-4-nonedienal in black tea are products of unsaturated fatty acids breakdown during processing. They impart green grassy aroma to tea thereby reducing its quality. Nitrogenous fertilizer and harvesting are the most expensive agronomic inputs in tea production. Effects of these inputs on fatty acid levels in clone BBK 35 grown in five sites in Kenya are reported herein. The shoots contained lauric, myristic, palmitic, palmitoleic, stearic, oleic, linoleic and linolenic acids. Linolenic acid dominated the acids followed by linoleic acid and there were significant (P≤0.05) variations in the amounts of acids. The order of the other acids changed with location of production. The acids increased with rise in the rates of nitrogenous fertiliser and long plucking intervals. The rates and extent of increase in the fatty acid levels due to increasing nitrogenous fertiliser rates varied with locations leading to significant (P≤0.05) interaction effects. Significant (P≤0.05) interaction effects were also observed between location of production and plucking intervals, and nitrogenous fertiliser rates and plucking intervals. To produce low levels of fatty acids thereby increasing black tea quality, low levels of nitrogen and short plucking intervals are necessary. Despite using same rate of nitrogen or plucking intervals, the fatty acid levels, hence aroma quality will change with location of production. Different regions therefore require specific nitrogen fertiliser rates and plucking intervals to produce optimal amounts of fatty acids for production of high quality black tea. Development of region specific agronomic inputs is recommended to produce high quality black teas.