Theodore W. Awadzi

Mineralogy of dust deposited during the Harmattan season in Ghana

Abstract In Ghana, a dust-laden Harmattan wind blows from the Sahara in the period November to March. Some of the dust is trapped in the vegetation, in lakes and other inland waters, and a little on the bare land, whereas the rest of the dust is blown further away to the Ivory Coast or out into the Atlantic Ocean. In this project, we studied samples of dust and topsoils in various agroecological zones, from the north to the south of Ghana, focussing mainly on the mineralogy of these materials. Some data about grain sizes and morphology of the samples are also presented. Feldspars, together with quartz, are the common minerals found in Harmattan dust, but the relative contents of K-feldspars and plagioclase vary markedly in the different zones. This variation is consistent with changes in the relative content of the feldspars in the topsoil, indicating a substantial local contribution to the Harmattan dust. This conclusion is supported by the clay mineralogy of the samples. However, the pH of the dust is significantly higher than that of the local soils, indicating that a substantial amount of the dust comes from the Sahara.

The Role of Termites in Soil Formation in the Tropical Semi-Deciduous Forest Zone, Ghana

Abstract Soil Macrofauna especially insects have been recognized as being an important factor in regulating soil processes and thereby the soil profde development. The influence of earthworms is well documented and it is the dominant member of the soil macrofauna influencing the soil formation processes in the temperate zone. In the tropics, termites and ants play the major role in the nutrient recycling and the movement and transportation of soil material. This paper describes the influence of termites on the soil formation in the tropical wet semi-deciduous forest in Ghana at the north coast of the Gulf of Guinea. The termites form distinct soil horizons especially at the summits of the landscapes where gravel free soil horizons are formed upon gravel rich horizons, and in some cases soil heaps are formed after the decomposition of huge trees.

Deposition of Nutrients From Harmattan Dust in Ghana, West Africa

In order to measure dusts nutrient input on farmland in different agro-ecological zones, Harmattan dust was sampled by mats with plastic straw in Ghana between 2002-2006. The inputs of total nutrients by Harmattan dust in Ghana per Harmattan period were about 1-2 kg Ca ha-1, 0.5-2 kg K ha-1, 0.5-1.5 kg Mg ha-1 and less than 0.5 kg P ha-1. Compared with the annual input of nutrients by precipitation, the dust accounted for 10% or less of Ca, Mg and K but approximately 20%-40% of P. The input of nutrients by dust was only valid for areas with vegetation, because in areas with none or sparse vegetation, loss of soil due to wind erosion and hereby loss of nutrients might be significant. In farmland areas with bare and vegetated fields there seemed to be an internal redistribution of the nutrients and not a net gain of nutrients from outside the area (long-range transported dust). The input of P by dust might be of some importance in the traditional shifting cultivation systems, while the inputs of other three nutrients of Ca, Mg and K were so low that they must be considered insignificant. In the intensive agriculture systems with huge inputs of manures and fertilizers the nutrient input by dust is insignificant and could be neglected. (Less)

A scientific evaluation of the agricultural experiments at Frederiksgave, the Royal Danish plantation on the Gold Coast, Ghana

Abstract In the 1830s agricultural experiments were carried out at the Danish state plantation Frederiksgave at the Danish Gold Coast Establishments, in order to establish an economical sustainable plantation system which could produce export crops to among others the European market. Experiments were made with coffee, tobacco, sugar cane and some other crops and spices, but they failed. Based on climatic data from Frederiksgave for the year 1835 and from nearby climatic stations in the 20th century combined with soil data from the dominant soil types analysed in 1999, the natural reasons for the lack of success are discussed.

Comparison of magnetic particles in airborne dust on Mars and in the Harmattan dust from south of Sahara

Abstract The magnetic properties experiments on the Mars Pathfinder mission indicate that Martian airborne dust is slightly magnetic (average saturation magnetisation: σs = 4 Am2 kg−1). For purposes of comparison, similar experiments on the magnetic properties of terrestrial airborne dust on the Earth have been performed at the University of Ghana. The main result of these experiments is that the airborne Harmattan dust in Ghana is substantially less magnetic than the dust suspended in the Martian atmosphere. Geografisk Tidsskrift, Danish Journal of Geography 100: 1–6.