Title: Soil and Water Conservation Through Terracing in Makueni County, Kenya
Category: Land Management
Country: Kenya
Audience: Farmers, Extension officers
Introduction
Soil and water conservation consists of activities carried out to prevent loss of soil and water in order to maintain land productivity. In areas prone to soil erosion, lack of soil and water conservation measures leads to degradation of land through deterioration of soil, water and vegetation.
Soil erosion and water loss are major environmental challenges in dry lands of Kenya. The major drivers of soil erosion and surface run-off in drylands include; erratic and high intensity rainfall, long dry periods which often lead to poor ground cover both on crop and grazing land, vulnerability of soil to water erosion and surface sealing. Makueni County is one such region that suffers from soil erosion.
Makueni County is located in Eastern Kenya and lies between latitude 10 35’ and 30 00’ South, and longitude 370 10’ and 380 30’ East. The County is generally dry exhibiting semi-arid conditions. The average annual rainfall, evaporation and temperatures are 600 mm, 2000 mm and 230C respectively. Rainfall in the County is bimodal with long rains occurring from March to May and short rains from November to December. The short rains are more reliable than the long rains with about 60% of the annual rainfall being received during the short rains. However, Makueni County is characterized by frequent droughts and extended dry periods that greatly reduce soil moisture. Soils within the County can be described as; medium fertile, sandy to sandy loam, and deep in some areas. The gradient of land is generally gentle, but some areas are hilly and/or steep in nature. Due to its climatic and biophysical conditions, Makueni County is prone to soil erosion mainly through surface run-off. To address soil erosion and water losses, conservation structures such as terracing are necessary on farms within the County. One farmer, who has successfully terraced his farm in dryland Makueni County is Mr. Johnson Mulinge.
Objective
The objectives of terracing are:
Approach
Mr. Mulinge acquired soil and water conservation knowledge from various stakeholders including; Kenya Forestry Research Institute (KEFRI), University of Nairobi and Mukau Farmers Association, organizations which were involved in development, promotion and implementation of the terracing practice, as it requires a multidisciplinary approach.
To prevent surface run-off and soil erosion on sloping farm land, channels and ridges are constructed across the slope. Contour lines are marked by use of a leveling board and spirit level to determine the gradient and flow of run-off. Contour line is marked by use of pegs and a string. A terrace is then made by digging a trench along the contour, while throwing the soil upslope to form an earthen embankment (bund) creating a fanya juu terrace. A small shelf or berm of about 15 -30 cm is left between the trench and the bund to prevent soil from the bund from sliding back into the trench. The excavated trench should be about 60 cm wide and 60 cm deep, while the bund should be about 50 cm high and about 150 cm across the base. The bund acts as a barrier to soil erosion while surface run-off accumulates in the trench and slowly infiltrates into the soil. If there is no trench below the bund, the run-off will pass downslope and cause further damage to the land through soil erosion. The terrace should be make before the onset of the rains.
To reduce risk of breakage and slippage of the bund, the ground on which the bund is constructed should be cultivated beforehand so that the soil of the bund is integrated with that below. During construction of the bund, the loose soil should be compacted thoroughly to reduce risk of breakage. Terraces should be constructed in sequence starting from the top of the land. Spacing between the terraces is between 9 m – 20 m. The steeper the slope the closer the terraces.
Planting grasses and trees along the banks stabilizes the bunds and also increases land productivity and plant biodiversity. Bunds can also be stabilized by use of a stone wall.
Bunds should be checked for breakage after rains and any damage repaired immediately. Periodic de-silting of the trench is necessary. Silt from the trench should be thrown upslope onto the bund.
Impact
Construction of terraces on-farm has reduced erosion by preventing; splash erosion, gully formation, and breakdown of soil structure, hence increased infiltration and conservation of water on site.
Terracing has resulted in: improved productivity of crops such as green grams, sorghum and cowpeas; pasture and fodder. The practice has led to improved food security due to improved land productivity. Aesthetic value of the land has also been enhanced.
Innovation
The farmer changed the design of the terraces from straight shaped ones to curvy shaped terraces. The modified terrace greatly reduces surface runoff and soil erosion, as well as increases water infiltration.
Constraints
Some of the constraints experienced include;
Lessons
Lessons learnt include the following:
Conclusion
Terracing is a useful technology for addressing soil and water conservation in dryland areas that have steep and gradual slopes, as well as under various land-use systems. The practice contributes to enhanced land productivity.