KARI-University of Nairobi-NAK NO.M74 2008

Abstract

The interactions between soils, landscape characteristics, land use and management, when integrated with farmers' perceptions ofBGBD, forms an integral part of the decision support tool for the identification of the appropriate strategies for sustainable management of land resource base including BGBD. Soils in Embu benchmark sites are developed from volcanic footridges, uplands, plateaus and bottomlands. The geology is volcanic rocks consisting of basic and intermediate rocks mainly phonolites. Based on physiography, geology and soil characteristics, five soil mapping units were identified. The interactions between land use, soils and physiography are very important in evaluating the degree of aggregation and degradation of soil particles in terms of soil structure attributes that influence soil quality, soil health and ecosystem services. Therefore, conceptualization of the links between human interventions and environment is facilitated by understanding the interactions between land use, management and environment. In this respect, it was observed that steep slopes under tea had very good surface cover, while those under coffee had bench terraces, thereby controlling erosion in these land units. However, where land conversion took place from tea to annual cropping, severe land degradation was observed mainly in form of rill erosion. In intensively cultivated area under maize and beans, the type of degradation taking place was soil structure deterioration, resulting into unfavourable pore size distribution. This causes increased leaching of nutrient bases resulting in low pH, high acidity and aluminum toxicity, thereby creating unfavourable environment for belowground biodiversity. The fertility status of the area was found to be extremely low. Since the use of soil organisms to restore soil fertility and productivity in these critically degraded areas is one of the core issues addressed by the BGBD project, the results of biophysical site characterization provide the basis of characterizing the functional significance of different groups of soil biota in sustaining ecosystem processes, functions and services. These results include characterization of the dimensions, properties and dynamic nature of the microenvironments in which the soil organisms interact. An appreciation of these results by the scientists, extension workers and farmers is prerequisite for understanding the effects of management on soil quality and soil health as well as the role of soil organisms in enhancing these important attributes and soil productivity.