5 research outputs found
Iddingsitisation of olivine and kaolinitisation of biotite in two contrasting tephra-derived soils along the Cameroon Volcanic Line (CVL)
No full textPedotransfer functions for cation exchange capacity estimation in highly weathered soils of the tropical highlands of NW Cameroon
No full textCation exchange capacity (CEC) is a very important soil property widely used in the assessment of soil quality. Unfortunately, its determination in the laboratory can be very tedious, especially when samples are many, necessitating high costs and time. To curb these challenges, pedotransfer functions (PTFs) can be used as indirect and reliable tools for CEC estimation using easy-to-measure soil properties such as pH, soil organic carbon (OC), and texture. Soil survey data from 98 soil profiles in the North West region of Cameroon, belonging to eleven Reference Soil Groups (RSGs) classified as Acrisols, Andosols, Cambisols, Ferralsols, Fluvisols, Histosols, Regosols, Nitisols, Alisols, Luvisols, and Chernozems were used to develop pedotransfer functions for estimating CEC in these soils. Pedotransfer functions were developed using linear and non-linear regressions, while their reliability was evaluated using the error ratio (ER), the geometric mean error ratio (GMER), and root mean square error (RMSE). Predicted and measured CECs were equally compared using non-parametric tests to assess the deviations observed. To enhance the quality of the PTFs, stratifications of the data were done at various levels; (i) pooled data for all soil samples, (ii) within each RSG and (iii) within pedogenic soil horizons. Results indicate that PTFs obtained within the various reference soil groups were better than those obtained from pooled data due to the reduced variability of soil properties. Best results were obtained when soils were stratified according to pedogenic soil horizons. The best PTFs were observed in the most highly weathered soils, the Ferralsols, probably associated with their existence in the near steady state with greater stability and equilibrium among various soil properties. In most of the cases, OC proved to be the dominant soil property contributing to CEC. Results of this study will enable estimation of CEC from available soil survey data in the study area and similar environments, as well as the need to consider stratifications in terms of soil types and pedogenic soil horizons as reported in the literature to improve the reliability of PTFs
Origin and evolution of soil materials of the Paleo-Chadian linear-dune landscape in the Far North Region of Cameroon
No full textThe dynamics of single spike-evoked adenosine release in the cerebellum
No full textThe purine adenosine is a potent neuromodulator in the brain, with roles in a number
of diverse physiological and pathological processes. Modulators such as adenosine are difficult
to study as once released they have a diffuse action (which can affect many neurones) and,
unlike classical neurotransmitters, have no inotropic receptors. Thus rapid postsynaptic currents
(PSCs) mediated by adenosine (equivalent to mPSCs) are not available for study. As a result
the mechanisms and properties of adenosine release still remain relatively unclear. We have
studied adenosine release evoked by stimulating the parallel fibres in the cerebellum. Using
adenosine biosensors combined with deconvolution analysis and mathematical modelling, we
have characterised the release dynamics and diffusion of adenosine in unprecedented detail.
By partially blocking K+ channels, we were able to release adenosine in response to a single
stimulus rather than a train of stimuli. This allowed reliable sub-second release of reproducible
quantities of adenosine with stereotypic concentration waveforms that agreed well with predictions
of a mathematical model of purine diffusion. We found no evidence for ATP release
and thus suggest that adenosine is directly released in response to parallel fibre firing and does
not arise from extracellular ATP metabolism. Adenosine release events showed novel short-term
dynamics, including facilitated release with paired stimuli at millisecond stimulation intervals
but depletion-recovery dynamics with paired stimuli delivered over minute time scales. These
results demonstrate rich dynamics for adenosine release that are placed, for the first time, on a
quantitative footing and show strong similarity with vesicular exocytosis
Cambios en el arreglo estructural y la mocroconstitucion de un vertisol (Typic Hapluderts)bajo tres sistemas de labranza
No full textDisturbed and indisturbed Vertisol samples were collected from the top soil in the agricultural area in the San Andres Tuxtla, Ver. district Mexico, in fields with Vertisol tilled with minimum tillage (MT) and traditional tillage (TT), as in a field with the same soil without tillge (WT) covered with secondary vegetation. These samples were taken in transects along the length of the fields at 20 m intervals. The variations of the physical properties and the Vertisol microconstitution under the different tillage systems were compared, through analysis, as well as the relationship between the structural arrangement, the morphology of the porous space, the pedological features, and the level of tillage. The organic matter content in the Vertisol with TT (5%) was higher compared with levels fund in soil with MT and WT. The Vertisol showed a different structural arrangement with each of the different tillage system. In the MT system, there was a tendency toward soil compaction in the furrows between the beds.The mean size of aggregates varied between 1.24 mm in WT and 1.56 in the furrows between the beds in MT, thus showing the soil compaction. The mean size of the pares varied between 0.23 and 0.13 mm in the same two systems. The lineal porosity dropped from 0.21 in WT to 0.13 in the MT furrows. Mean pare size was 20% greater in TT than in MT. Soil System structure entropy values reached a high of 0.66 in WT, dropped to 0.6] in the TT, and reached their lowest point of 0.50 in the furrows between the beds of MT, thus confirming their maximum compaction. These values are derived from site soil structure information and form the measure of the structure variability. The predominant pedological features in the Vertisol, under all three systems, were the amorphous and singular cryptocrystalline ferrogineous nodules with clear and regular limits. The yellow-orange nodules composed of Lepidocrocite 6 - FeO(OH)) were abundant in the MT soil. Red Hematite (X- Fe2 03) nodules were predominant ¡n Vertisol TT.The abundance, size, and nature of the nodules indicated high immigratio and precipitation of iron solutions. These were highestin Vertisol TT. A The circular form of the nodules allows for the conclution that these are of biogenic nature ( bacterial activity ) and the larger size in the TT Vertisol indicates that the aerobiosis conditions were greater under this system. Smaller size and greater nodule hydration in MT soil confirms a greater anaerobiosis. These nodules indicate periodic surface hydromophism on the Vertisol in this study
