Clay minerals constitute an important component of the soil system and knowledge of their role in soil fertility is imperative for sustainable soil management and productivity. The aim of this work is to overview the influence of clay minerals on some major soil fertility attributes. The rationale for carrying out this work is that most soil fertility studies rarely incorporate soil mineralogy. Clay minerals, through their physical and chemical properties, affect soil fertility by controlling nutrient supplies and availability, through the sequestration and stabilization of soil organic matter, by controlling soil physical properties through microaggregate formation, by influencing soil acidity and controlling soil microbial population and activity. The main processes involved in these relationships are dissolution-precipitation and adsorption-desorption processes, alongside mechanisms involving the formation of short-range-ordered phases. Although the determination of soil mineralogical properties is very costly and time-consuming, information about a soil's mineralogy is imperative for a holistic understanding and proper management of soil fertility. Therefore, the development of rapid, low-cost, reliable and efficient techniques of soil mineralogical analysis, directly applicable to soil fertility investigations, constitutes a major challenge. Also, future research should investigate the relationships between clay minerals and soil nitrogen vis-à-vis sequestration and stabilization. Lastly, clay minerals should be considered in studies dealing with soil quality assessment, especially in the choice of soil quality indicators.
This research work was aimed to assess the quality of agricultural soils of Awing-North West Cameroon by elucidating some physicochemical properties and heavy metals in the soils. Agricultural yields in Awing have witnessed a decline in recent years and farmers have repeatedly used fertilizers to improve on their agricultural yields. It is thus important to test the soil in order to ensure not only high productivity but its quality as well and suggest methods to increase agricultural yields, while preventing soil and water pollution. Twenty soil samples were randomly collected from four sites, Achialum, Meupi, Nepele and Ala'amiti, in Awing and analysed for physicochemical and heavy metal properties using standard methods. Results showed that all the soils had low bulk densities (0.76-0.89 g cm -3 ), low pH values (4.1-6.0), low electrical conductivities (0.02 -0.11 mS cm -1 ), low available phosphorus (1.55-14.26 mg kg -1 ) and the soil textural class was dominated by loam. The mean available concentrations of heavy metals ranged from 0.24-2. 73, 0.64-5.13, 13.79-34.51, 29.45-92.27, 0.00-0.80, 0.24-4.54, 0.68-1.39, 0.30-0.47 mg kg -1 for Zn, Cu, Mn, Fe, Pb, Ni, Cr and Cd respectively. Results of heavy metal analysis showed that the soils were contaminated to different levels (above FAO/WHO limits) by the different heavy metals. Natural origins, fertilizer application and domestic waste were identified as the major sources of heavy metals in the soils. Future research should focus on the development of methods to quantify lime-enhanced mobilization of nutrient ions and lime-induced immobilization of heavy metals in these soils.
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