Soil carbon in small-holder plantain farms, Uganda : a comparison between agroforestry and non-agroforestry

Sammanfattning: Smallholder farmers in Uganda suffer from declining productivity. With a rapidly increasing population, marginal land is taken into production and the current land management leads to loss in soil fertility and escalation in soil erosion. There are studies indicating that the use of agroforestry increases soil organic carbon (SOC) compared to systems without trees. Soils which are high in carbon have many advantages, for example better water holding capacity, which can reduce stress on crops during drought. The aim of this study was to determine the effect agroforestry has on SOC concentration in small-holder farming systems in Uganda. The intended system to study was farms practicing agroforestry methods or not in intercropped plantain (cooking banana) fields. The hypothesis was that the practice of agroforestry leads to a higher concentration of SOC. Field work was conducted in Kkingo region, Masaka, Uganda. Ten farms, of which five agroforestry and five non-agroforestry, were selected in cooperation with Vi Agroforestry. At each farm, soil samplings were taken close to a tree and in the middle of the field, respectively, to the mass equivalent depths of 0-20 and 20-40 cm. In total, 40 samples were analysed at Makerere University in Kampala for SOC concentration, water holding capacity, electrical conductivity, pH and texture. The results showed no significant difference in SOC between agroforestry and non-agroforestry. Other uncontrolled differences between farms and random variation probably masked potential effects of the categories agroforestry respective nonagroforestry. More comprehensive studies with a larger sample of carefully selected pairs of farms would be needed for being able to quantify the impact of agroforestry on SOC.