Effects of planting density and drought on the productivity of tea clones (Camellia sinensis L.): Yield responses

摘要

Tea is an important cash crop in Tanzania, contributing over US$45 million of annual exports and grown by over 30000 smallholder households, and a further 10000 people are employed by large estate producers. Over 70% of the national tea production comes from the Southern Highlands of Tanzania where expansion of tea estates under limited suitable land for tea is expected for the next two decades. Thus a client-demand driven field experiment was established in January 1993 to study and advice tea growers on the effects of plant density on the productivity and water use of young tea. The experiment comprised of two types of vegetative propagated tea plants (known as "clones") of contrasting growth behaviour (AHP S15/10: spreading type and BBK35: erect), six plant densities (labelled D_1. 8300 plants ha~(-1) to D_6: 83300 plants ha"1) and seven irrigation or drought levels (labelled I_0: un irrigated, to I_6: well irrigated condition) as the treatments. Clone AHP S15/10, with larger crop cover than clone BBK35, consistently out-yielded clone BBK35 at all densities and under both well watered and drought stressed conditions. The corresponding yields from clone BBK35 were 2620 and 5960 kg ha~(-1). Reciprocal of yield per plant- and asymptotic yield-density relationships were used to explain these responses to density. Yields from clone AHP S15/10 during the period of drought treatments decreased as the maximum soil water deficit increased at all densities, but there were no yield responses to drought from clone BBK35 at the low densities. The study recommends planting densities of 20000 and 40000 plants ha~(-1) for clones AHP S15/10, respectively for well irrigated conditions and a density of 20000 plants ha~(-1) for both clones under un-irrigated environments.