CUPPA-Tea: A simulation model describing seasonal yield variation and potential production of tea. 1. Shoot development and extension

A simulation model describing the growth and yield of tea (Camellia sinensis L.) is described. The model simulates the behaviour of a population of shoots which develop and extend independently at different rates to simulate the variation observed in natural conditions. The development of each shoot is divided into three phases corresponding to the resting, quiescent and bud-burst phases in temperate trees, with the rate of development in each phase being influenced by temperature, photoperiod and saturation deficit. Photoperiod also influences the onset and release of bud dormancy, and therefore the numbers of actively growing shoots at any one time. As shoots are generally harvested at a specific developmental state or size, the number of shoots plucked at each harvest is the main determinant of yield variation. Sensitivity analysis using annual yields as the output indicated that the model was most sensitive to the values of the two critical photoperiod parameters controlling bud dormancy and shoot development. Good agreement was found between model predictions and observed yields for an experiment in well irrigated tea in the Southern Highlands of Tanzania, but further testing is necessary before it can be used with confidence in a wider range of environments.