MODELLING BANANA GROWTH AND SOIL ORGANIC MATTER DYNAMICS WITH THE CENTURY MODEL

A major concern to food security in Uganda is banana yield reduction, a condition locally known as 'matoke decline'. Computer simulation is one means of understanding the complex interactions between plants, organic matter dynamics and soil but require that much be quantified within systems before models may be applied. We have initialised the CENTURY model to simulate a banana re-establishment experiment in Mukono District, Uganda. The initialisation required assumptions concerning assimilate allocation patterns between shoots, roots and bunches. The complex pattern of grass fallow, burning, maize, chemical fertilisation and banana receiving different managements could be simulated using schedule routines of the model, but some adjustments were necessary to allow for perennial growth. Two separate harvest files were constructed to account for harvest of bunches and the removal of basal offshoots. At the first harvest (18 months after planting) the simulation of treatments receiving no inputs and that having 10 t napier grass ({I}Pennisetum purpureum{/I}) differed by 5.0 and 1.0 t ha{SUP}-1{/SUP} in total aboveground biomass (dw) and fresh bunch yield. After six years of harvest, average annual yields were 5.1, 6.1 and 7.6 t ha{SUP}-1{/SUP} in the control, livestock manure (10 t ha{SUP}-1{/SUP} y{SUP}-1{/SUP}) and napier grass treatments, respectively. Simulated soil organic carbon content increased from 2.2% to 3.8% in the treatment receiving napier grass and harvest residues but increased only slightly in the complete control (2.5%). Model outputs suggest that a near 'steady-state' in banana biomass is achieved due to periodic senescence of mature pseudostems, bunch harvest and offshoots. Model outputs suggest that external organic inputs of 10 t ha{SUP}-1{/SUP} y{SUP}-1{/SUP} influence banana productivity to a greater extent than the retention of banana residues