Irrigating seedling tea in Southern Tanzania: effects on total yields, distribution of yield and water use

SUMMARY In a dry area of Southern Tanzania with a single rainy season irrigation during the six-month-long dry season (May-November) doubled the total annual yield of tea and at the same time evened its distribution over the year to some extent. Other factors including low temperatures limited growth rates during the period June-September despite irrigation, whilst a lull in production in November appeared to be unrelated to external factors. Roots were traced to depths of about 4·3 m and by the end of the dry season unirrigated bushes were drying the soil below 3m. In general total yields decreased with decreasing frequency of irrigation and quantity of water applied but because these plants were deep rooting they could withstand deficits up to 100 mm without a reduction in yield, equivalent to a loss of about 25% of the total available water in the profile. There was some evidence that the most economical use of water occurred when the soil was not rewetted to field capacity at each irrigation, although yields were then less. Irrigation also reduced the incidence of a stem canker, Phomopsis theae . The implications of these results to the tea industry of East Africa are discussed.