Understanding growth of East Africa highland banana: experiments and simulation

Key words: leaf area; radiation interception; QUEFTS model; fertilizer recovery fractions; nutrient mass fractions; crop growth; calibration; validation; radiation use efficiency; sensitivity analysis East Africa Highland banana yields on smallholder farms in the Great Lakes region are small (11−26 Mg ha−1 cycle−1 in Uganda, 21−43 Mg ha−1 cycle−1 in Burundi and 25−53 Mg ha−1 cycle−1 in Rwanda). The major causes of poor yields are declining soil fertility and soil moisture stress. In order to improve production, knowledge on highland banana physiology, growth patterns and response to fertilization is important, to establish the potential yield of the crop, to quantify the yield gaps between potential and actual yield, and to explore options for closing the yield gaps. Measurements of plant morphological characteristics, radiation interception and biomass (by destructive harvesting) were taken in experimental fields in central and southwest Uganda. Results showed that total leaf area can be estimated by using height and girth (used to estimate middle leaf area) and number of functional leaves. The light extinction coefficient, k determined from photosynthetically active radiation (PAR) measurements over the entire day was 0.7. Banana plants partitioned more dry matter (DM) to the leaves during first phase of vegetative growth, with the pseudostem becoming the dominant sink later with 58% of total DM at flowering, and the bunch at harvest with 53% of the total DM. Changes in dry matter partitioning influenced the allometric relationships between above-ground biomass (AGB in kg DM) and girth (cm), the relationship following a power function during the vegetative phase (AGB = 0.0001 (girth)2.35), and exponential functions at flowering (AGB = 0.325 e0.036 (girth)) and at harvest (AGB = 0.069 e0.068 (girth)). This thesis shows that allometric relationships can be derived and used to estimate biomass and bunch weights. In fertilizer trials, yield increases above the control