Soil loss research in Kambi ya Simba village


The village of Kambi ya Simba is located in Karatu District, Arusha Region, sandwiched between the Northern Highlands Forest Reserve (to the north) and the Rift Valley escarpment (to the south). The village occupies an area of approximately 40 sq-km and a north-south distance of approximately 11 km. Along this north-south axis, there is a 500 m change in elevation, which has a strong effect on climate. The village is divided into three geographically distinct regions - Northern, Central and Southern - as shown below.

Kambi ya Simba is inhabited by the Cushitic-speaking Iraqw. The Iraqw are the largest ethnic group in Karatu district and their language is related to the Afro-Asiatic languages spoken in northeast Africa (e.g., in Somalia and Ethiopia) rather than the Bantu languages spoken in most of Sub-Saharan Africa (e.g., Swahili). They are less commonly known as the Mbulu (which is somewhat pejorative) and the name ‘Iraqw’ has several alternate spellings, such as Iraqu and Erokh. Traditionally, Iraqw are agro-pastoralists, meaning that they keep farms and herd livestock (i.e., cows, sheep and goats), though nowadays, many rely solely on subsistence agriculture.

The main crops grown in the village are wheat, maize, and beans (red beans, soybeans, etc.). The decision whether to grow wheat or maize is largely economic: wheat is a cash crop, whereas maize is grown mostly for subsistence. Climatic factors also play a role: a dryer, hotter climate in the Central and Southern regions prevents wheat cultivation in most areas. Fruits and vegetables are also cultivated in and around settlements, but only in small (< 1 acre) plots. In addition, barley, millet, and sunflowers are grown by some farmers, but these are less common than fields of wheat and maize. 

Nearly all crops are rain-fed, however, a bimodal rainfall pattern provides potential for two successive growing seasons. The main growing season is from March to June-August with the other possible from late November to February. Using both growing seasons has become increasingly common, though it occurs at the direct expense of a fallow period.

Since the mid-1970's, the population in the village has quadrupled - from around 1500 to a present estimate of around 6000 - while crop yields have declined precipitously. In the case of wheat, yields have plunged from 5.0 – 6.0 t/ha in the early-1970's to 0.8 – 2.0 t/ha as of 2003-4.

These changes have been accommodated and induced, in part, by extensive deforestation and a burgeoning livestock population. Land shortage, a more recent phenomenon, effects considerable grazing pressure and has compelled increasing numbers of farmers to settle marginal lands. 

Methods of soil conservation remain basic and, ostensibly, have been only moderately effective in reducing soil loss. These include use of vegetated contour ridges (i.e., bunds), application of manure, and tethering of livestock to prevent overgrazing; more effective means of intervention (e.g., terracing, strip-cropping with frequent rotation, zero-tillage systems) are not utilized.

Using an approach combining satellite and soils data with social research, we have prioritized areas in the village of greatest erosion risk (see publications for method details and results) and are currently in the process of implementing a broad range of programs to address the problem.

The above figure depicts estimated soil loss rates in the village of Kambi ya Simba as of October 2002. The base image was generated from ASTER satellite data, where the color 'red' corresponds to infrared reflectance (e.g., the forest area just above the village's northern border), 'green' corresponds to that which is actually red on the ground, and 'blue' corresponds to that which is actually green on the ground. Within the village perimeter, however, colors correspond to estimated rates of soil loss (as shown in the key). Data is missing from the gray areas (i.e., due to cloud cover), and the village's soil types are outlined in black. For more information, please visit our publications section.

 

MESO - The Multi-Environmental Society
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(C) Copyright 2004

 


Most natural vegetation has been cleared for fields


In some areas, gully erosion is quite severe


Old grazing paths can form large gullies on valleysides


Wheat is the major cash crop in the village


After harvests, crop residues are often grazed, leaving soils dry and crusty


Soil sampling in the field


Drying out soil samples collected for research


Taking a break on the job


Targeting priority areas


Educating farmers about different methods