Characterization of Soil-Water Retention with Coarse Fragments in the Densu Basin of Ghana

The presence of coarse fragments can have profound impact on soil moisture retention characteristics. The study was conducted to assess the effects of coarse fragments on the moisture retention characteristics of 16 soil series, developed over five different parent materials in the Densu basin. Soil profiles were excavated at five locations, to depths within 1.5 m in the field. Undisturbed soil core samples and disturbed samples were taken in triplicates from the major genetic horizons of each soil type within the effective root depth of 1 m. Coarse fragments content of soil more than 2 mm was measured on mass basis by sieving through a 2-mm mesh. Soil moisture retention was determined using the pressure plate apparatus at suctions of pF 1 (1.0 kPa), pF 2 (10.0 kPa), pF 2.5 (33.0 kPa) and pF 3 (100.0 kPa) for the undisturbed and pF 4.2 (1500 kPa) for the disturbed samples.The volumetric moisture content between field capacity (FC) pF 2.5 (33.0 kPa) and permanent wilting pointing (PWP) pF 4.2 (1500.0 kPa) was used to evaluate the available water content (AWC) by volume and then converted to root zone available water capacity (RZAWC) in millimetres (mm) assuming an effective root depth of 1 m within the basin. Results showed that soils formed over granite and its associations have high percentage of coarse fragments while soils developed over phyllites and its associations have high clay percentage. Soil organic matter was high in the topsoil of all profiles, ranging from 0.81 to 4.44% compared with the horizons below, and the bulk density of the topsoils were less than the limiting value of 1.6 Mg m-3. Site-specific moisture retention characteristics of the various soil series have been delineated. It was evident from the analyses that soils containing high clay content gave high RZAWC values compared with soils with high coarse fragments. Most of the topsoils of the profiles gave high RZAWC values compared with sub-layers with high amounts of coarse fragments. Critical water for plants establishment within the basin in the surface layer was quite favourable

Harmattan dust deposited in Ghana within 2000–2005

Between 2000–2005, a monitoring system for the collection of harmattan dust over Ghana was established. Three methods were used to sample the harmattan dust: i) bowls with water, ii) plastic mats and iii) plates made of plywood. This paper describes the establishment of the monitoring system, and the regional distribution of harmattan dust trapped in various agro-ecological zones by the bowls with water and the mats. The bowl values represent the total amount of dust falling over a unit area, and the mat values represents the amount of dust retained by vegetation. Theamount of harmattan dust captured is largest in the north where the mats retained about 20 g/cm3 compared to 5 g/cm3 in the south. The amount of dust retained differs significantly from year to year, and the particle-size of the dust becomes finer towards the south and with an increasing amount of organic matter. In the north, the median diameter was slightly above 15 mm and the organic carbon content was about 5% while in the south the median diameter was slightly above 5 mm and the organic carbon content was between 10 and 15%