Background: Land use changes from natural ecosystems into managed ecosystems may have deleterious effects on soil structure and quality. This study characterise the soils under, and assesses the effects of different land use systems on selected soil physicochemical properties in the North West region of Cameroon. Six land use systems including: natural forest, natural savanna, grazing land, afforested land, farmland and Eucalyptus plantation were identified. Ninety soil samples were collected from each at the 0-15 cm depth. Fifteen soil physicochemical properties were measured. Results:The conversion of natural forest or savanna to farmland reduces the silt contents, moisture content, organic matter, organic carbon, total nitrogen, available phosphorus, pH, cation exchange capacity and exchangeable bases, but increases bulk density, electrical conductivity, exchangeable acidity and sand content significantly (P < 0.05). The results revealed that deforestation and subsequent cultivation of soil had negative effects on the measured soil properties. Conclusions:Land use change has ruined soil quality in the North West region. To reverse soil degradation and promote restoration, emphases should be placed on promoting the use of sustainable land management practices within the savanna, grazing, agricultural and forest management systems.

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.

Fallows improve soil fertility and allow sustainable agriculture. Soil fertility was assessed under different types of fallow through pH, nutrient concentrations and particulate organic matter (POM) quantity and quality. The two year-fallows were under Chromolaena odorata, Calliandra calothyrsus and Pueraria phaseoloides on a Typic Kandiudult. Soils were sampled from 0-10 cm and 10-20 cm depth. The weight of POM was 2 mg g −1 of soil under Calliandra, 3.9 mg g −1 under Chromolaena and 3.7 mg g −1 under Pueraria in the 0-10 cm layer. The tPOM-C (proportion of C in the total POM) and tPOM-N (proportion of N in total POM) were 26.1% and 14.5%

Soils are the universal reservoirs through which living organisms get the resources for their livelihoods either directly like plants and indirectly like other organisms and animals. The ability of soils to serve as a universal reservoir depends on its fertility. Agroforestry practices have been seen to improve and conserve soil fertility. This research work carried out from the 10th of May 2015 to the 10th of November 2015 was aimed at assessing the role of agroforestry practices in the improvement of soil fertility in the study area. Information was collected using questionnaires, field surveys and the analysis of soil samples in the laboratory. The results obtained were subjected to regression and correlation analysis using the Statistical Package for Social Sciences (SPSS). These results showed that the main agroforestry practices in this area include live fences and scattered trees on farmlands. It was also observed that farmers use indicators such as yields, softening of soil, wilting of the crops, rotten tubers, erosion and rains to determine soil fertility. There was no significant difference between various soil parameters (pH, acidity, CEC, ECEC, C/N, and exchangeable Al) in the two major agroforestry practices identified. There was equally no significant difference between the various soil elements and yields in the two major systems identified. The only element that showed a significant difference (P<5%) in the two systems and also for yields was phosphorous. Since only phosphorous significantly influenced yields in this area, a model was established to show that crop yields are dependent on phosphorous as indicated by the equation Yields = 1.77+ 0.03 P. Scattered trees on farm lands were recommended to farmers, the practice of improved fallow using a local fertilizing species identified as well as the use of Guatemala grass (Tripsacum laxum) and Vetiver grass (Vetiveria zizanoides) should be introduced on slopes to control erosion.

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