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Accueil du site → Doctorat → Allemagne → 2013 → Spatio-temporal Dynamics of Bush-fire Nutrient Losses and Atmospheric Depositional Gains across the Northern Savanna Region of Ghana

Rheinischen Friedrich-Wilhelms-Universität Bonn (2013)

Spatio-temporal Dynamics of Bush-fire Nutrient Losses and Atmospheric Depositional Gains across the Northern Savanna Region of Ghana

Kugbe Joseph Xorse

Titre : Spatio-temporal Dynamics of Bush-fire Nutrient Losses and Atmospheric Depositional Gains across the Northern Savanna Region of Ghana.

Auteur : Kugbe Joseph Xorse

Université de soutenance : Rheinischen Friedrich-Wilhelms-Universität Bonn

Grade : Doctoral thesis 2013

Résumé
This study estimates the nutrient balance between annual fire-induced nutrient transfers and bulk (wet plus dry) atmospheric nutrient deposition. In the subsistence-based and fertilizer-limited agriculture of northern Ghana the population depends on productivity of the native soils for crop production. Fifty three percent of this region is burned annually. This study quantifies the nutrient losses resulting from the annual fires as well as the nutrient acquisition through atmospheric deposition which may compensate for the losses. A quantification of the soil-atmosphere nutrient cycling would help policy-makers in setting incentives and disincentives to regulate the burning culture of the region. Gross seasonal and annual elemental-losses/gaseous-emissions were quantified in the field for each combusted vegetation type. Annual spatial/temporal wet and dry deposition samples were collected across 15 sites. Data were analysed by a variety of analytical techniques including descriptive statistics, time series analyses, pairwise t-testing, ANOVA, linear correlations, linear regression, remote sensing and GIS. The field measurements of elemental-losses/gaseous-emissions and nutrient-depositions combined with the temporal-geospatial dynamics of these processes were analysed by various statistical means and extrapolated to the entire region using 10-year (2001-2010) GIS/remote sensing data. The results show that combusted fuel load varies across different vegetation types by season of burn and by plant tissue, with highest combustion taking place in the herbaceous/grass tissues. Lower combustion of twigs suggests a safe storage of carbon (C) in the woody parts of plants. In the early-burn season (November) high tissue-nitrogen (N) concentration renders burns vulnerable to high N losses/emissions per unit burnt biomass. However, high tissue moisture impedes the early burns, resulting in patches of burned and unburned vegetation that reduce the occurrence of late burns and the total losses of plant-nutrients. The patches of unburned vegetation also enhances tree seedling establishment to ages when these are relatively resistant to fires. The magnitude of gaseous emissions and nutrient losses follows the monthly order December>November>January>February. Calcium (Ca) and Magnesium (Mg) are lost in particulate forms, phosphorus (P) and potassium (K) in both, particulate and non-particulate forms, whereas C and N are mostly lost in gaseous forms. Dry and wet nutrient deposition varied with latitude and month. The interaction of latitude and longitude on nutrient deposition suggests that fire-induced nutrient transfers are directed by atmospheric currents (northeast to southwest) at the time of burn. An estimated negative N balance is not a cause for concern, as most N losses could be replaced through biological N2-fixation. Positive balances for K, Ca, Mg and sodium (Na) indicate an external source for these nutrients besides the redistribution of nutrients originating from fires, possibly Saharan dust. A net negative balance for P (-18 to -1 Gg), however, should be of major concern across the region given the inherently low P-content of the soils and the inability to derive P from other sources. The negative P balance poses a serious challenge to future food production across the area. Phosphorus losses can however be reduced when burning is undertaken in the early dry-season.

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Page publiée le 24 janvier 2016, mise à jour le 12 novembre 2021