Traditional and adapted composting practices applied in smallholder banana-coffee-based farming systems: Case studies from Kagera and Morogoro regions, Tanzania

In Tanzania, about 90% of the banana-coffee-based farming systems lie in the hands of smallholder farmer families. In these systems, smallholder farmers traditionally add farm waste to crop fields, making soils rich in organic matter (humus) and plant-available nutrients. Correspondingly, soils remained fertile dur-ing cultivation for over a century. Since the 1960s, the increasing demand for food and biofuels of a growing population has resulted in an overuse of these farming systems, which has occurred in tandem with deforestation, omitted fallows, declined farm size, and soil erosion. Hence, humus and nutrient contents in soils have decreased and soils gradually degraded. Inadequate use of farm waste has led to a further reduction in soil fertility, as less organic material is added to the soils for nutrient supply than is removed during harvesting. Acknowledging that the traditional use of farm waste successfully built up soil fertility over a century and has been reduced in only a few decades, we argue that traditional composting practices can play a key role in rebuilding soil fertility, if such practices are adapted to face the modern challenges. In this chapter, we discuss two cases in Tanzania: one on the traditional use of compost in the Kagera region (Great African Rift Valley) and another about adapted practices to produce compost manure in the Morogoro region (Uluguru Mountains). Both cases refer to rainfed, smallholder banana-coffee-based farming systems. To conclude, optimised composting practices enable the replenishment of soil nutrients, increase the capacity of soils to store plant-available nutrients and water and thus, enhance soil fertility and food production in degraded banana-coffee-based farming systems. We further conclude that future research is needed on a) nutrient cycling in farms implementing different composting practices and on b) socio-economic analyses of farm households that do not successfully restore soil fertility through composting.