The need to take account of spatial variability of soil properties when modeling soil forming and environmental processes is now clear and known. Understanding the distribution of soil properties in the field and its variability are important in refining agricultural management practices, (Mc Bratney and Pringle, 1999) while minimizing environmental damage.
Spatial relates to space and position, size and shape of things in it; that is changes taking place within this period. Spatial variability occurs when a quantity that is measured at different spatial locations exhibits values that differ across the locations. The spatial variability of soil properties is poorly understood, despite its importance in designing appropriate experimental sampling strategies. As preparation for a farm-scale agro-ecosystem services monitoring project, the Cross River Basin Development Authority Farm programme, needs to assess the spatial variability of the soil chemical and physical properties. This will aid in designing a suitable soil management system to be used in selecting appropriate agronomic practices for the farm.
Soil management systems play an important role in sustainable agriculture and environmental quality. Soil management practices have greater effect on the direction and degree of changes in soil properties. Conversions of an area from native ecosystem to cultivated land may be the reason of soil degradation and decreases of quality as a result of disturbing the properties of the soil. Soil management systems such as soil tillage, fertilizers and irrigation often create unsuitable changes in soil quality. Jaiyeoba, (2003) and Dunjo et al., (2003) studied the changes in the soil quality and its effects on the ecosystem. The most important effect of soil tillage is the decrease of cation exchange capacity (CEC) which is attributable highly to the reduction of soil organic matter (SOM) (Paz-Gonzalez et al., 2000).
Soil tillage systems may lead to increase of soil pH, base saturation, and extractable phosphorus. Soil organic carbon (SOC) and total nitrogen decreased in cultivated soils compared to pasture (Chan and Hulugalle, 1999). Soil physical and chemical properties are strongly influenced by soil management systems and changes in land use. The greater percentage of mechanically dispersible clay, lower pH and electrical conductivity were found in cultivated soils in an Assessment of Spatial Variability of Soil Properties in Areas under agronomic practices compared to pasture. The mean gravel content is much higher for cultivated areas (Paz-Gonzalez et al., 2000).
Soil properties vary spatially from a field to a larger regional scale affected by both intrinsic (soil forming factors) and extrinsic factors (soil management practices, fertilization, and crop rotation) (Cambardella and Karlen, 1999). The Variation is a gradual change in soil properties as a function of landforms, geomorphic elements, soil forming factors and soil management (Buol et al., 1997). The variation of soil properties should be monitored and quantified to understand the effects of land use and management systems on soils. geostatistical methods have been used successfully for predicting spatial variability of soil properties (Zebarth et al., 2002; Lark, 2002; Dercon et al., 2003).
The Cross River Basin Farm in Itu, Akwa Ibom State covers an area of 3,514 hectares and comprises of both the upland and flood plain (wetland) soils. It is a major food producing centre in Akwa Ibom State involved in large-scale, rain fed and wetland/irrigated agricultural practices. Food produced include vegetables such as; fluted pumpkin (Telfaria occidentalis), cucumba, pepper (Capsicum spp), okro, garden egg, tomato. Tuber crops such as water yam (Dioscorea alata), cassava (Manihot esculenta) cocoyam, and groundnut. Other crops include fruits and tree crops; such as plantain, mango, etc.
In view of the importance of the farm in food production, and in order to contribute to the national programme on food security, the research project was carried out with the aim of assessing the variability of some soil properties in the Cross River Basin Development Authority (CRBDA) farm, Itu, Akwa Ibom State. In order to achieve the above aim, the following objectives were set up:
To determine some physical and chemical properties of the properties of the soils derived from the alluvial and sandstone parent materials
To assess the variability of the soil characteristics in the farm.SPATIAL VARIABILITY OF SOIL PROPERTIES AS INFLUENCED BY PARENT MATERIALS