EFFECTS OF LAND-USE CHANGES ON SOIL CHEMICAL PARAMETERS IN KAKAMEGA-NANDI FOREST COMPLEX

Abstract

   Background. Carbon lost in form of carbon dioxide contributes to climate change corresponding to altered soil chemical properties and plant growth. Land-uses that minimize carbon loses are highly encouraged. Unfortunately, in the Kakamega-Nandi Forest Complex, the Kenyan government continues to promote shamba systems (now Plantation Establishment for Livelihood Improvement Scheme) where the forest adjacent communities are allocated bush land plots to provide land for small-scale agriculture, cash crop farming and planting of tree seedlings for a specified period of time inside the forest. Objective. This study analyzed six land-uses and their effect on the dynamics of soil chemical parameters using landsat images and recent soil geochemical surveys. Methodology. Land cover and vegetation changes were determined using a series of multispectral Landsat images. A total of seven sets of image datasets were downloaded from the Glovis web portal (http://glovis.usgs.gov/) for the years 1985 to 2015 with the cloud cover ranging from 1 to 10% taken in the dry season. The land-use/cover classification scheme adopted was based on expertise knowledge and literature of land-use/cover activities.  Results. The results show that (i) small-small agriculture has increased while bush-land has decreased between 1985 and 2015; (ii) smallholder farming of maize, pasture and sugarcane depleted soil organic carbon whereas perennial tree plantations (regenerated forests) increased soil carbon stocks; (iii) nitrogen decreased in all tested land-uses except in maize plantations; (iv) phosphorus remained unchanged in all land-uses, potassium significantly decreased in tea plantations while sugarcane and regenerated forests land-uses had decreased soil calcium stocks. Implications. The study provides evidence for the review of the shamba system. Conclusion. The study has shown that land-use changes through the application of the shamba system alter the dynamics of soil chemical parameters key among them are soil organic carbon, nitrogen and calcium. Cultivation of annual crops decreases soil carbon stocks which may lead to an influx of carbon dioxide in the atmosphere and increased vulnerability to climate change.