Effectiveness of sustainable land management measures in West Usambara highlands, Tanzania

Soil erosion is a serious problem that affects food security and social livelihoods in the highlands of East Africa. Sustainable land management (SLM) measures have been widely promoted to reduce erosion and increase crop yield, but the adoption of SLM measures has remained low. In order to understand the contribution of biophysical factors on adoption, this study was carried out to (i) determine the biophysical conditions of fields with SLM measures; (ii) assess the impact of different SLM measures on soil degradation; and (iii) determine the effects of SLM measures on crop productivity. The study was conducted in Lushoto District, north-eastern Tanzania. Sixty fields with five different SLM categories were studied. The five SLM categories ranged from no intervention at all (SLM 5 — control plots), to excellent land and crop management, including well-constructed bench terraces and application of farmyard manure (SLM 1). SLM 2 also has terraces, but the management is not as good as for SLM 1. SLM 3 has some poorly maintained terraces or grass trips, while SLM 4 has only poorly maintained grass strips. The bio-physical properties of the fields were determined, and measurements of meteorology, soil properties, soil erosion and crop yield were carried out during the period October 2009–June 2011. The results showed that the better SLM categories (SLM 1 and SLM 2) are preferentially implemented on less steep slopes, and they do stabilize the slope and reduce soil losses by water erosion significantly. The use of high amounts of farmyard manure (>6.0tonha−1y−1) on the terraces of SLM 1 and SLM 2 category fields resulted in a 3 to 4 times higher yield of maize compared to the control plots (SLM 5), while yield of beans increased 6 to 7 times compared to the control plots. Despite the use of farmyard manure on better managed fields, no significant improvements of soil fertility were found. This is probably because the amounts applied are too small to allow build-up of soil nutrients.