USE OF CALLIANDRA-NAPIER GRASS CONTOUR HEDGES TO CONTROL EROSION IN CENTRAL KENYA

Authors: ANGIMA, S - PURDUE UNIVERSITY; Stott, Diane; O'NEILL, M - ICRAF, NAIROBI, KENYA; ONG, C - ICRAF, NAIROBI, KENYA; WEESIES, G - USDA-NRCS

Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2001
Publication Date: 6/1/2002
Citation: N/A

Interpretive Summary: The central Kenyan Highlands are utilized by small scale farmers who use mixed farming systems as a step toward sustainability. The average farm size is about four acres, and can have up to two dozen types of crops as well as some animal production. These farms are frequently on steep slopes of 20 to 40%. While there were once terraces on many of these slopes, most are failing due to neglect. The farmers view the terrace as land taken out of production, when there is need to plant as much as possible on their small acreage. A project was started to look at an alternative to earthen barriers, the use of contour hedgerow systems consisting of various combinations of tree and grass species that will cause a natural terrace to form along the plant row. In an early phase of the project, two plant species were identified as being of particular interest, napier grass for its effectiveness in forming a natural terrace, and a species of the leguminous shrub, Calliandra. Calliandra is favored by farmers, as it provides a high-protein fiber for their animals. We found that a combination of Calliandra and napier grass formed a natural terrace that significantly reduced sediment loss from the mid-slope area, retained N and P that was in the above slope runoff, and produce about 12 thousand lbs acre-1 of fodder. Calliandra alone was less effective. Napier grass alone was more effective, but did not produce a good fodder, and therefore was not preferred by the farmers. The small-scale farmers were more likely to use the mixed contour hedges because of the perceived benefit of good fodder. This soil conseration technology could be used by farmers in the highlands of Central Kenya who practice mixed farming systems as a step towards sustainable farming.

Technical Abstract: Contour hedgerow systems consisting of various combinations of tree and grass species can be used on sloping lands to minimize erosion, restore fertility, and improve crop productivity. There is a need to evaluate the effectiveness of each hedgerow system for its suitability to any locality for effective erosion control. The objective of this study was to determine the amount of soil conserved by contour calliandra-napier hedgerows, and hence develop a support practice p-subfactor for use in conservation planning in Central Kenya. Biomass yields as well as N and P retention by the hedgerows was determined as a benefit beyond soil conservation. Runoff and soil loss from contour hedges and control plots on two slopes of 20 and 40% were compared. Data for five cropping seasons from 1997 to 1999 indicated that the contour hedges on 20% slope conserved more soil averaging 168 Mg ha*-1 than on the 40% slope that averaged 146 Mg ha*-1 compared to the control plots. This is equivalent to a p-subfactor of 0.7 for both slopes for use in soil erosion prediction using RUSLE. The advantages of using hedges as soil conservation strips were observed in N & P retention as well as biomass production. The N and P losses between the hedges and control were statistically significant on the 20% slope but non-significant for the 40% slope (P=0.05). Combined biomass yield from calliandra and napier was 12 Mg ha*-1 yr*-1 for the 20% slope and 9 Mg ha*-1 yr*-1 for the 40% slope indicating a direct benefit beyond soil conservation. The results show that this soil conservation technology could be used by small-scale farmers in the highlands of Central Kenya who practice mixed farming systems as a step towards sustainable farming.