Spatial Variability Of Soil Properties As Influenced By Parent Materials

Spatial Variability Of Soil Properties As Influenced By Parent Materials

Abstract

Spatial variability of soil properties as influenced by parent materials in areas under different land use. Land conversion from native ecosystem to agricultural use may alter soil physical, chemical and biological properties depending on duration and the type of tillage. The objectives of this study were to determine some physical properties of the soil between the soil alluvial and sandstone parent materials, to determine some chemical properties of the soil between the soil alluvial and sandstone parent material and to assess the variability of the soil characteristics. The study area is located at Cross River Basin Development Authority Farms, Itu, Akwa Ibom State – Nigeria. Soil pH, electrical conductivity (EC), Cation Exchange Capacity (CEC), Soil Organic Matter (SOM), total N, plant available P and soil texture were analyzed soil samples collected from Cross River Basin Development Authority Farms, Itu, Akwa Ibom State – Nigeria. In addition, spatial variability of the soil properties under each land use was defined using statistical analysis. Soil pH had the minimum variability compared to other soil properties. Soil tillage caused significant changes in soil properties. Soil organic matter, total N, available P, CEC, and EC, clay content and silt content decreased significantly (P<0.01) while K+, Na+, pH and sand content increased with cultivation. The variables of the cultivated soils generally had a lower nugget than the variables of the native grassland. The degree of spatial dependence for CEC, clay, silt, sand and ph was low. The variation of the soil variables was fairly homogenized in the cultivated fields compared to the native grassland.

Chapter One

1.1 Introduction

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:

1. To determine some physical and chemical properties of the properties of the soils derived from the alluvial and sandstone parent materials
2. To assess the variability of the soil characteristics in the farm.

Chapter Five

Summary, Conclusion and Recommendation

5.1 Summary

The study of spatial variability of soil properties as influenced by parent materials in the Cross River Basin Farms in Itu Local Government Area, Akwa Ibom State. The study recorded variability in the soil physical and chemical characteristics of the soils studied. The result of the study site has shown that soils in Cross River Basin Farm were slightly acidic, low in organic carbon with a high coefficient of variation in many parameters.

5.2 Conclusion

Data collected in this study were computed into tables. The mean, Standard deviation, coefficient of variation (CV %) and Auto correlation were calculated for each property. Normality of data was examined by kurtosis and skewness (p < 0.05) data were transformed.

Coarse sand recorded (4950.00g/kg) mean variability, clay recorded mean variability of (257.64 g/kg) also total porosity (TP) recorded mean variability of (5.30cm3/cm).

However, the study recorded significant variation across the chemical properties of topsoil (0-20cm) alluvial parent materials. Some of the chemical properties considered in the study includes organic matter, total nitrogen, electric conductivity, pH(H20),pH (KCL), and others. On the other hand there was marked variation across the soil chemical properties of the sandstone (20-45cm)

5.3 Recommendations

In view of the variation observed, I therefore recommend that:

1. Promotion of community awareness to farmers to considered the study area as a good site for cultivation of arable crops.
2. Government to consider the variability of the soil properties in the study area in order to adopt a better management approach to maintained soil fertility and boost productivity.
3. Further study on the spatial variability of soil properties in the study area should be encouraged as the soil is dynamic in nature.

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