Project Abstract

Characterization and evaluation of four toposequences in a tropical rainforest in the Amazon region were conducted to understand the soil variability and its implications for ecosystem functions. The study area covered four different toposequences representing ridge, slope, footslope, and valley positions. Soil samples were collected at different depths (0-10 cm, 10-20 cm, and 20-30 cm) along each toposequence to assess soil properties. Results showed significant variations in soil properties among the different toposequences. The ridge positions were characterized by well-drained soils with lower moisture content compared to the valley positions, which had higher water saturation. Soil pH was slightly acidic across all toposequences, with the footslope soils showing the highest values. Organic matter content was highest in the valley soils, likely due to the accumulation of organic material transported downslope. Cation exchange capacity was highest in the footslope soils, indicating a higher nutrient retention capacity. Further analysis revealed differences in nutrient concentrations among the toposequences. The ridge soils had lower nutrient levels, particularly nitrogen and phosphorus, compared to the valley soils. This gradient in nutrient availability has implications for plant growth and species distribution within the forest ecosystem. The presence of distinct toposequences highlights the heterogeneity of soil properties and nutrient dynamics in the tropical rainforest environment. Evaluation of soil physical properties indicated variations in texture and structure along the toposequences. The ridge soils were sandy with lower clay content, while the valley soils had higher clay content and better aggregation. These differences in soil texture influence water infiltration and retention capacities, affecting the overall water balance within the ecosystem. Overall, the characterization of the toposequences provided insights into the spatial variability of soil properties and nutrient distribution in the tropical rainforest landscape. Understanding these variations is crucial for sustainable land management practices and conservation efforts in the Amazon region. Future research could focus on exploring the relationships between soil properties, vegetation composition, and ecosystem functions to enhance our understanding of the complex interactions within tropical forest ecosystems.

Project Overview

INTRODUCTION

            Characterization of soil provides a useful means for understanding soil distribution and variability. The modern soil survey is a fundamental basis for land use planning because it contains both qualitative and quantitative data which enable predictions of many kinds to be made. It aids in correlating and predicting the adaptability of   various crops, grasses, and trees, to soils and their behaviour and productivity under different management. Field studies that depict the variability and distribution of soil are panacea for total utilization of a given tract of land. Such understanding enables useful prediction to be made wherever such soils occur making it possible for soils of different parts of the world occurring under similar and different climatic condition to be compared (Buol et al 1980). Soil characterization goes beyond soil testing, it is an integration of both physical and chemical nature of soil. It analysis the inherent characteristics and properties of a given soil with the aim of characterizing them into similar soil units and capability land use units.

Soil suitability evaluation involves characterizing the soil in a given area for specific land use type. The information collected in soil survey helps in the development of land-use plans and to evaluate and predict the effects of the land use on the environment. The suitability of a given piece of land is its natural ability to support a specific land use type. Suitability may be a major kind of land use, such as rain fed agriculture, livestock production, forestry, etc.

As these qualities derived from the land characteristics, such as slope angle and length, and soil texture which are measurable or estimable, it is advantageous to use these latter values to study the suitability. For assessing the suitability of soils for crop production, soil requirements of crops must be known. Also, these requirements must be understood within the context of limitations imposed by land form and other features which do not form a part of the soil but may have a significant influence on use that can be made of the soil (FAO,1976).

Soil classification on the other hand helps to organize our knowledge and facilitate the transfer of experience and technology from one place to another and to compare soil properties. It provides a link between soil characterization and soil survey. According to Lark and Wheeler (2000), variation in soil properties has long been known and had been the subject of much research. It was in recognition of this that Sir Ronald-fisher, and then at Rothamsted, developed a formidable array of statistical methods.

Accordingly, horizons may differ in organic matter content, structure, texture, pH, base saturation, cation exchange capacity as well as many other soil physicals and chemical properties. According to Mullar and Mc Bratney (2001), variability in soil properties at the series level is often caused by small changes in topography that affect the transport and storage of water across and within the soil profile. Hunter et al (1982) and Yost et al (1982) reported that soil-forming factors affect different properties differently at different depths. Variability of soil pH, for e.g. increases with depth (Ogunkunle and Ataga, 1985). Ogunkunle (1993) working on Alfisols of southwestern Nigeria, observed that soil pH was the least variable (low variability) property, irrespective of depth. The variability of properties like organic matter, available phosphorus, total nitrogen and CEC, increases with depth. Properties, such as soil pH and porosity are among the least variable, while those pertaining to water or solute transport are among the most variable. Percentage sand ranges from low to moderate variability. Organic matter and % clay range from moderate to high variability. Available phosphorus and potassium were observed to be highly variable (Jury, 1986 et al, Beven et al, 1993, Wollenhaupt et al, 1997). In general the more variable these properties, the more variable the crop growth and yield. Thus, understanding soil variability is essential in applying location specific (precision-agriculture) management strategies. Therefore, the general objective of this study was to assess the degree of variability of some soil physical and chemical properties along four toposequence  for assessing their agricultural potentials.

The specific objectives were to: (i) characterize and classify the soils of  four toposequences. (ii) assess the effects of slope characteristics on physico-chemical properties.

(iii) evaluate the agricultural potentials of the four toposequences.