Studies on the Genesis of Soils in Jong River Basin in the Northern Province of Sierra Leone

The soil resources of Sierra Leone remain an integral part of sustainable agricultural development but knowledge of the suitability of soils and their management requirements for a variety of land uses is still lacking to a greater extent. In this view, a detailed soil survey of three chiefdoms in Northern Sierra Leone was undertaken to evaluate the genesis of soils and interpret soil-landscape properties and their relationships using the toposequence and free style approach of soil survey. Three major soil types, viz, gravelly, gravel-free over gravel and gravel-free soils, formed either directly or indirectly from weathered and disintegrated parent materials of two geologic origins namely Rokel River Series (comprising of sandstone, shale and mudstone), and Granite and Acid Gneiss were identified. The gravelly soils are formed from sandstone and sandy shales of the Rokel River Series, which upon weathering released iron and hydrated oxides that hardened into plinthite upon drying. The gravel-free over gravel soils are formed from acid gneiss containing acid and intermediate igneous and metamorphic rocks, which upon weathering produced sandy clay textured soils whereas the gravel-free soils are derived from sedimentary rocks (shales and mudstones) of Rokel River Series, which upon weathering and action of organisms produced sandy clay loam and sandy clay textured soils. The gravel-free over gravel soils are mostly located in the summit and back slopes and show dark brown to dark yellowish-brown hue and moderate chroma, weak to moderate structure and absence of coarse fragments in the 0 - 40 cm layer, and a strong brown hue and high chroma, very weak fine angular blocky structure having abundance of coarse fragments from 40 cm and above. In these soils, the compactness of ironstone and sandstone gravels increases with depth. The gravel-free soils are found on three landscape positions, viz, back slopes, foot slopes and toe slopes. On the back and foot slopes, the soils are characterized by very dark brown to dark yellowish-brown hue and high chroma, sandy loam to sandy clay texture, coarse angular to moderate sub-angular blocky structure and absence of coarse fragments throughout the horizon. In these soils, the clay content and sand grain sizes were observed to increase with depth. On the toe slopes, the soils show black to greyish-brown hue and low chroma, silty loam to sandy loam, structureless and high water holding capacity.

Effect of Land Uses on Soil Erodibility in the Njala Area of Southern Sierra Leone

Soil loss through erosion continues to pose serious challenges to increasing the smallholder agricultural productivity in Sierra Leone. While emphasis on sustainable land use practices continue to gain attention among land users, however, the rate of adoption among smallholder farmers is still very low and hence, in most part of the country soil fertility has been declining at alarming rates. In the Njala area, studies have shown that soil loss ranges from moderate to high. Though soil erosion has been identified as a major soil fertility declining factor, however, the effect of land use practices on the inherent resistance of soil materials to erosion is lacking. This study was therefore conducted to assess the effect of land uses on soil erodibility. The results showed that the soils are coarse sandy loam with high sand content. The dispersion ratios and erosion indices of soils under cassava, plantain, maize and guava were above the minimum thresholds of 15.0 and 10.0 respectively, thus indicating that these soils are highly erodible compared to soils under fallow and sweet potato which have dispersion ratios and erosion indices below the minimum thresholds. Clay content was inversely proportional to and significantly correlated with dispersion ratio and erosion index while the correlations between silt + clay, dispersion ration and erosion index, and silt, silt + clay and dispersion ratio were negative and non-significant. Considering the coarse nature of soils, landscape features and high erodibility indices, these soils would need special soil and water conservation practices to counter further degradation. These may include following, agroforestry, silvi-pasture, controlled and rotational grazing. In addition, awareness of sense of self-responsibility and forest policies and regulations are needed.

Studies on Land Resource Inventory for Agricultural Land Use Planning in Northern Transition Zone of India through Remote Sensing and GIS Techniques

Land suitability analysis is a prerequisite to achieving optimum utilization of available land resources. Hence, a study on land resource inventory for agricultural land use planning was conducted in the Northern Transition Zone of India to determine land capability and develop a suitability map for wheat and sorghum-based on physical and climatic factors of production using remote sensing and GIS techniques. Detailed soil survey information was used for this exercise. Four series (Singhanhalli, Mugli, Bogur and Venkatapur series) were identified and mapped into seventeen mapping units. Land capability classification showed that a greater portion of the study area belonged to class III followed by class IV with limitations of erosion, wetness and varying soil properties. Four land capability classes viz., II, III, IV, and VI, and seven subclasses viz., IIsf, IIItsf, IVs, IVt, IVts, IVtsf and VIt were identified. Major limitations of these subclasses were slope, erosion, depth, texture, coarse fragments, pH, organic carbon and base saturation. Soil suitability assessment revealed that the soils are moderately suitable to permanently not suitable. About 234 ha (31.6%) is moderately suitable, 494 ha (65.0%) marginally suitable and 10.2 ha (1.3%) permanently not suitable for wheat;while 78.5 ha (10.3%) is moderately suitable, 633.4 ha (82.3%) marginally suitable and 32.6 ha (4.3%) permanently not suitable for sorghum respectively. The moderate, marginal and permanent non-suitability was due to moderate, severe and very severe limitations respectively. However, it is possible to achieve potential yield of the crops in the study area if these limitations are addressed.

Distribution of Micronutrients in Selected Pedons of Sugarcane Growing Vertisols in Northern Karnataka State of India

Micronutrients deficiency is a major limiting factor for increasing yield and productivity of major crops in India. Recent findings of multiple micronutrients interactions have evidenced the indispensable role played by micronutrients in plant nutrition. Though they are needed in smaller quantities, however, their availability in the Right amount, at the Right time, and for the Right crop has been a major limiting factor for improving the productivity and yield of Sugarcane in northern Karnataka state of India. This study was conducted to assess the level of Boron (B), Copper (Cu), Iron (Fe), Manganese (Mn) and Zinc (Zn) deficiencies in Sugarcane growing Vertisols of six micro-watersheds in northern Karnataka. The six selected micro-watersheds were intensively traversed and six representative pedons of standard dimensions were dug and horizon-wise soil samples collected and analyzed for various micronutrients using standard analytical procedures. Based on the optimum critical levels of micronutrients, B, Fe and Zn were deficient, ranging from 0.15 - 0.64, 1.23 - 5.92 and 0.11 - 0.64 mg⋅kg−1 respectively while Cu and Mn were in excess, ranging from 1.54 - 7.62 and 1.22 - 7.03 mg⋅kg−1 respectively. The distribution of B, Fe and Zn were inversely proportional to soil depth whereas that of Cu and Mn were irregular, which is an indication of the influence of pedoturbation in these soils. With the current rate of agricultural intensification, unbalanced fertilizer application, depletion of nutrients and no replenishment by smallholders, the results reveal that the current deficiency levels may increase further if appropriate and timely actions are not taken. We therefore recommend the use of site-specific nutrient management, balanced fertilizer application and good agronomic practices. These can enhance nutrient use efficiency in the study area.