Branch growth dynamics, photosynthesis, yield and bean size distribution in response to fruit load manipulation in coffee trees

Key message: The study unraveled the dynamics of mechanisms causing biennality in coffee, its consequences for competition for carbon and nitrogen and suggests means of adequately managing the problem.Abstract: Imbalance in fruit load and branch growth plays a role in the occurrence of biennial bean production patterns in coffee (Coffea arabica L.). Effects of fruit load manipulations were studied in two field experiments in the Jimma region, Ethiopia, over two consecutive years. Treatments consisted of reducing fruit loads in the pinhead stage to 25, 50, 75 % and controls keeping 100 % of the fruits per tree (treatments coded T25 through T100). Treatments were applied in the first year only. Branch growth and the formation of new leaves, drop of old leaves, light saturated rate of leaf photosynthesis (Amax), nitrogen content of leaves on selected branches, as well yield and bean characteristics were evaluated throughout the experimental period. The study revealed that branch growth, and leaf N content per unit leaf area, Na, were inversely associated with fruit load, whereas loss of basal leaves on branches increased with fruit load and over time. Amax was strongly and linearly associated with Na and declined with increase in fruit load. In the year of treatment green bean yield increased with fruit load, but in the second year the reverse was true. On aggregate over 2 years, treatment T25 and T50 out yielded treatments T75 and T100. Fruit thinning shifted the bean size distribution to larger sizes. In conclusion, fruit thinning modulated the balance between branch growth and fruit development. Thus enhanced branch growth, improved bean size and stabilized yield over years.