COMPARATIVE ANALYSIS OF THE PHYSICAL CHARACTERISTICS OF WATER STABLE AGGREGATES IN SOME FOREST AND CULTIVATED

CHAPTER ONE
1.0     INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Aggregate stability expresses the resistance of aggregates to breakdown when subjected to potentially disruptive processes (Hillel, 1998). The structural stability of soil aggregates upon wetting has been the subject of a lot of research around the world (Boucher, 2006). Eynard (2004) indicated that measurement of stability of soil aggregates in water is generally used to estimate structural changes due to cultivation, as water is the main agent of aggregate breakdown in cultivated soils of the humid tropics.
The quality of any soil depends on its degree of aggregation. Soils that are well aggregated, which remain stable when wetted, are important for erosion resistance, water retention and availability and root growth. Mbagwu (2003) reported that factors that influence aggregate stability are important in evaluating the ease with which soils erode, the potentials of soils to crust or seal, soil permeability and quasi-steady state infiltration rates, seedling emergence and in predicting the capacity of soils to sustain long term crop production. Some researchers observed that soils with low Mean Weight Diameter (MWD) have the potential to erode faster than those with high MWD because detachability is lower with the later (Igwe and Ejiofor 2005).
The stability of soil aggregate is affected by soil properties that change relatively little, that is, the inherent composition (texture, type of clay, calcium, sodium, aluminum and iron content) and properties that change in response to vegetation and management (Carter, 2002). According to Seta and Karanthanasis (1996), dispersibility of clay and silt sized particle fractions when immersed in water has been found to affect a number of soil physical properties, such as shrink-swell, water retention characteristics, hydraulic conductivity and hard-setting characteristics of the soils. Also Igwe and Nwokocha (2005) reported that soils with high water dispersible clay (WDC) have high potential to disperse. They added that when such soil disperses on saturation with water, it leads to soil aggregate breakdown, forming seals and crusting and reduces permeability of