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Deposition of Nutrients from Harmattan Dust in Ghana, West Africa

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Deposition of Nutrients from Harmattan Dust in Ghana, West Africa Pedosphere 25(4): 613–621, 2015 ISSN 1002-0160/CN 32-1315/P c 2015 Soil Science Society of China Published by Elsevier B.V. and Science Press Deposition of Nutrients From Harmattan Dust in Ghana, West Africa Henrik BREUNING-MADSEN1,∗, Theodore Wola AWADZI2 and Gry LYNGSIE1 1Institute of Geosciences and Natural Resource Management, University of Copenhagen, Oster Voldgade 10, 1350 Copenhagen K (Denmark) 2Department of Geography and Resource Development, University of Ghana, PO Box LG 59, Legon, Accra (Ghana) (Received September 10, 2014; revised April 2, 2015) ABSTRACT In order to measure dust’s 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. Key Words: deposition rate, dust deposition, input of nutrient, long-range transported dust, nutrient concentration, traditional agricultural system Citation: Breuning-Madsen H, Awadzi T W, Lyngsie G. 2015. Deposition of nutrients from Harmattan dust in Ghana, West Africa. Pedosphere. 25(4): 613–621. INTRODUCTION parts of the year. In Ghana the Harmattan wind is ex- perienced in December to March, replacing the south- Ghana is located in West Africa and stretches for west monsoon wind. Throughout that period, storm about 1 000 km from the Gulf of Guinea towards the activities in the Bod´el´e Depression, located in the north. The traditional agricultural system throughout Chad Basin of Africa, raise large amounts of dusts into the country is shifting cultivation, a system characteri- the atmosphere, which are transported towards south- zed by a few years of cultivation followed by many years west by the predominant trade winds (Kalu, 1979; Mc- of fallow. It is a system of subsistence agriculture and Tainsh, 1980; Afeti and Resch, 2000; Washington et harvest crops are mainly for domestic use with little al., 2006; Warren et al., 2007). During a Harmattan surplus for sale. In this system, nutrient lost to the dust plume’s movement towards southwest, the coarse surroundings is limited and import of fertilizers and grain dust settles quickly and only the most fine grain manure is therefore not necessary. The loss of nutrients fraction stays in the atmosphere and can be transpor- due to leaching and soil erosion are replaced by atmos- ted thousands of kilometers as reported by Koren et pheric input from precipitation and dust deposition, al. 5 (2006) and Ben-Ami et al. (2010), who pointed and by weathering of primary subsoil silicates available out that the Bod´el´e Depression is the main source of (Szott et al., 1991). The atmospheric input of nutrient dust, and hereby nutrients, to the Amazon forests. is measured normally by the chemical compositions of The input of nutrients by dust can be determined rainwater, but wind-blow dust is an important agent by measuring the concentrations of nutrients in dust that can contribute with a significant portion of nu- deposited. The sampling strategy is important when trients to soil in some areas, i.e., countries along the determining the amount of deposited dust and the sam- Gulf of Guinea. In these areas, a dry dust-laden wind, plers should mirror the surface of the ground as good as the Harmattan wind, blows from the Sahara Desert in possible. In researches on Harmattan dust, dust sam- ∗Corresponding author. E-mail: [email protected]. 614 H. BREUNING-MADSEN et al. ples were collected mostly in different types of contai- ners or funnels, some dry, others filled with different liquids (McTainsh and Walker, 1982; Møberg et al., 1991; Tiessen et al., 1991; McTainsh et al., 1997; Ade- tunji et al., 2001; Breuning-Madsen and Awadzi, 2005; Goossens and Rajot, 2008). For determination of dust deposition in forests the drip canopy method was used (Stoorvogel et al., 1997). Several studies on Harmattan dust have been car- ried out in Ghana. Tiessen et al. (1991) investigated soils in northern Ghana and compared their chemi- cal properties with that of Harmattan dust captured on plastic sheets or funnels. Pelig-Ba et al. (2001) showed, indirectly, the influence of airborne dust on the amount of nutrients (Ca, Mg and K) and other ele- ments (Fe, Al, Mn, Zn, V, Cr, Cu and Pb) deposited around Tamale, Ghana. Breuning-Madsen and Awadz- i (2005) measured, at a regional scale, the amount of dust trapped in bowls with water, mats with plastic straw and wooden plates and showed the regional vari- ation in texture and organic matter content of dust. He et al. (2007) determined the clay mineralogy of Har- mattan dust in northern and southern Ghana. Lyngsie Fig. 1 Map showing the agro-ecological zones in Ghana and the et al. (2011) used water-filled bowls to capture dust for location of sampling sites. mineralogical investigation of dust in the Harmattan and southwest monsoon seasons at Tamale. Breuning- a long dry season. Madsen et al. (2012) used bowls and mats to collect In the coastal area of southeastern Ghana, the an- dust for determining the amount of dust deposited in nual precipitation is lower than 1 000 mm and a nar- Lake Volta. Few of studies investigated the annual and row coastal savannah zone with grasses and few trees is regional variation of nutrients due to Harmattan dust found. In the southwestern corner of Ghana, the vege- deposition. This variation may be significant for sub- tation is tropical rainforest (Fig. 1). This is surroun- sistence agriculture and natural systems, as mentioned ded by a moist semi-deciduous tropical forest with pro- above. Thus, the objectives of this work were to in- nounced litter fall in the dry season. Towards the north vestigate the annual amount of nutrients deposited via the moist semi-deciduous tropical forest turns into a Harmattan dust on surfaces with short vegetation like Guinea savannah with grasses, scrubs and a few trees. grasses in different agro-ecological zones of Ghana in In the dry north, the Guinea savannah zone turns into West Africa, and to evaluate if Harmattan dust de- a Sudan savannah zone. position had any significant influence on keeping soil In December–February the northeast Harmattan nutrients at an adequate level for plant production. wind dominates in northern Ghana, while the south- west monsoon wind dominates in southern Ghana. MATERIALS AND METHODS This means that most areas of Ghana are affected by Study areas the Intercontinental Convergence Zone (ITCZ). The location of the border between the two wind systems, Ghana is located in West Africa on the Gulf of Inter Tropical Discontinuity (ITD), is movable during Guinea and lies between 6◦–11◦ Nand1◦ E–3◦ W the Harmattan period (Engelstaedter et al., 2006; Sun- (Fig. 1). The mean monthly temperature is between nu et al., 2008). The ITD reaches its most southern lo- 25 and 30 ◦C. In the south of Ghana, two pronounced cation of Ghana, approximately 5◦ N, in the beginning rainy seasons exist, one in April to June and the other of January (Sunnu et al., 2008), but can move further in September to November. The minor dry season is toward south and the northeast Harmattan wind rea- in July to August, while the major dry season is in ches the Gulf of Guinea. Thus, the northeast Harmat- December to February. In the north of Ghana, there is tan wind dominates in northern Ghana (Bawku and only one rainy season from July to October, followed by Tamale) on a monthly basis in December–February, NUTRIENTS DEPOSITED FROM DUST 615 while it reaches the Central Ghana (Kintampo and occur during the Harmattan period, especially in the Kete Krachi) every year although it does not domi- south. The tube fed the water to a 36-L plastic contai- nate in all the three months (Awadzi and Breuning- ner. Second, at the other 4 sites located in Central and Madsen, 2007). The southwest monsoon dominates at southern Ghana another type of mat sampler was used the coast (Accra in southern Ghana) on a monthly ba- because erratic showers during the Harmattan period sis in December–February, but in more inland areas will fill the 36-L plastic containers, and thereby reduce at Kpong and Kade northerly wind blows occasional- the possibility of accurately calculating the amount of ly on a monthly basis (Awadzi and Breuning-Madsen, dust retained. A plate of plywood with a diameter of 2007). A study of Lyngsie et al. (2013) indicated that about 55 cm was placed in a bowl 2 cm from the top.
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