Abstract:
Indigenous soil and water conservation (SWC) technologies such as miraba (rectangular grass
strip bounds that do not necessarily follow contours) and micro ridges have been used widely in the
Usambara Mountains, Tanzania. However, their strengths and limitations to crop productivity have
not been investigated. This study aimed to determine soil fertility and crop yield variability under miraba, micro ridges and bench terraces as a way to explore and compare these SWC
technologies. A survey was carried out in Majulai watershed (with Acrisols as dominant soils) which
is highly affected by soil degradation due to water erosion. Composite soil samples were collected
from 0 - 30 cm depth in upper, middle and lower segments within bench terraces, micro ridges and
miraba at the upper, mid and lower slopes of the watershed. Contents of most soil nutrients (e.g.
+
2+
2+
available P, K , Ca and Mg ) and maize grain yields varied significantly (P=.05) between SWC
technologies, with the trend: bench terraces > micro ridges >miraba>control (fields with no SWC
measures). Similarly under all SWC technologies soil fertility and maize grain yields varied
significantly (P=.05) with slope position, showing the trend: lower slopes > mid slopes > upper
slopes. Moreover, soil fertility and maize grain yields varied significantly (P=.05) between segments
of the studied SWC technologies except for bench terraces. The trends for both soil fertility and
maize grain yields were as follows: lower segments > middle segments > upper segments under
micro ridges; lower segments > upper segments > middle segments under miraba. These
observations call for management strategies and technological adjustments that would reduce
pattern and magnitude of spatial variations of soil nutrients and crop yields under miraba and micro
ridges for improved crop production in the Usambara Mountains.
