Biomass production of banana plants in the indigenous farming system of the East African Highland: A case study on the Kamachumu Plateau in northwest Tanzania

The Haya people in northwest Tanzania have thrived by practising a unique farming system in which banana (Musa acuminata and M. balbisiana) is a staple food. Recent population pressure and long-term shortage of manure, however, have caused disputes about the decline in banana production. In this study, to begin to solve the issue, the biomass of banana plants grown in Haya fields on the Kamachumu Plateau was estimated by using a non-destructive method. Twelve quadrats of 100 or 225 m2 were established. Pseudostem height and diameter of all banana plants in each quadrat were measured, and the pseudostem volume was calculated. The fresh weight (FW) and dry weight (DW) of each plant in the quadrats were calculated from the relationship between the pseudostem volume and FW and DW of various organs in 14 sampled plants. The total DW of banana plants in each unit field area varied greatly among quadrats (from 0.12 to 1.45 kg m−2), but it averaged 0.92±0.08 kg m−2 on a farm scale, which was reasonably homogeneous despite the differences in farm size of each household and fertility management. The annual production of banana bunches was estimated at 3.4 kg m−2 from the average bunch FW and the annual bunch-bearing proportion: it was much higher than in the surrounding areas. Nevertheless, owing to a small proportion of edible part in a banana bunch, the current system would provide a net dry matter yield (pulp) of 0.38 kg m−2 a year. This yield is comparable to a reasonably good yield (grains) of cereal crops in the tropics. However, the banana yield for each unit time should be at least halved because the plants need 1 year to produce the yield. The turnover rate of total dry matter was 0.7–0.9 a year, showing a dynamic exchange of photosynthates and nutrients in permanent banana fields. Further study is needed to strengthen the sustainability of the current farming system from wider perspectives, including the nutrient balance and socio-economic aspect.