THE USE OF LEAF APPEARANCE RATES ESTIMATED FROM MEASUREMENTS OF AIR-TEMPERATURE TO DETERMINE HARVEST INTERVALS FOR TEA

The effects of temperature (13-20 degrees C) and potential soil water deficit (0-350 mm on the leaf appearance rates of six contrasting clon es of tea (Camellia sinenis) were studied over twenty-five months to p rovide guidance to tea growers in southern Tanzania on the choice of h arvest intervals. Within the fully irrigated treatments (potential soi l water deficit < 65 mm) the mean time period between a shoot unfurlin g its second and third true leaf (a phyllochron) ranged from 5.8-7.9 d during the warm-wet season to 11-19 d during the cool-dry season. Bet ween 61 and 79% of the weekly variation in the mean leaf appearance ra te (l/phyllochron) for each clone could be explained by an asymptotic relation with the mean air temperature. Building on research in India which has suggested that appropriate harvest intervals for tea can be derived from measurements of leaf appearance rates, a simple procedure is described for determining harvest intervals from the daily mean ai r temperature. Corrections to account for the effects of drought and c lonal differences in responses to temperature are also explained.