Physiological aspects of productivity in coffee: some aspects of water relations and dry matter production of Coffea arabica L. in Kenya

Abstract

Several experiments designed to study the water relations of coffee cultivar SL28 and SL34 trees grown in a greenhouse or of trees planted at densities of 1111, 3333, 5980 or 6667/ha at Ruiru, Kenya (1600 m a.s.l.) are described. Results indicated that internal water balance was best indicated by leaf water potential measurements and that these should be used to monitor irrigation need. Coffee should be irrigated when leaf water potential falls to -20 bar between 13.00 and 14.00 h. Root resistance was identified as a major genetic factor limiting water uptake in coffee. Pruning to remove up to 25% of the total leaf surface area improved carbon assimilation and reduced transpiration losses. Application of N and K fertilizers increased the drought-resisting capacity of trees. High density planting maintained soil temperatures near the optimum for water uptake (25°C) and improved light utilization efficiency (by reducing leaf reflectance). It is concluded that coffee is a shade- and drought-tolerant crop, well adapted to high density planting.