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Impact of exotic tree plantations on carbon and nutrient dynamics in abandoned farmland soils of southwestern Ethiopia

Lemma, Bekele (2006). Impact of exotic tree plantations on carbon and nutrient dynamics in abandoned farmland soils of southwestern Ethiopia. Diss. (sammanfattning/summary) Uppsala : Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae, 1652-6880 ; 2006:108
ISBN 91-576-7257-1
[Doctoral thesis]

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The impact of exotic tree plantations in Ethiopia on soil organic carbon (SOC), soil nutrients and decomposition processes was analysed and factors contributing to differences in SOC sequestration identified using the CO2Fix model. Forest clearing followed by continuous cultivation for 75 years reduced total SOC by 43% (75.4 Mg ha-1), and forest-derived SOC by 73% (128.4 Mg ha-1) within 0-50 cm depth. Total N decreased by 38% (6.8 Mg ha-1) and base cations and available P were significantly decreased within 0-20 cm depth, while δ15N increased within 0-10 cm depth. Farmland afforestation led to net SOC accretion of 69.6 Mg ha-1 (63.3 Mg ha-1 tree-derived) under Cupressus lusitanica and 29.3 Mg ha-1 (24.2 Mg ha-1 tree-derived) under Pinus patula stands after 20 years. Afforestation with Eucalyptus grandis on an area with pasture plus cropping restored SOC stocks to pre-deforestation levels. Total N increased by 5.7 Mg ha-1 under C. lusitanica and 2.0 Mg ha-1 under P. patula (0-50 cm soil depth). After afforestation, δ15N decreased more in surface layers with C. lusitanica than with P. patula. Afforestation had little impact on available P and exchangeable Mg++. Exchangeable K+ increased significantly (0-30 cm depth) under C. lusitanica and P. patula, while Ca++ increased significantly (0-5 cm depth) only under C. lusitanica. The δ15N pattern in E. grandis soil reflected residual effects of C4 organic matter from pasture. Leaf litter decomposed in the order C. lusitanica> native forest> E. grandis~ P. patula, whereas fine roots decomposed in order P. patula> native forest> C. lusitanica~ E. grandis. SOC sequestration under the exotic trees might be explained by the higher leaf litter decomposition transferring fresh C to mineral soil and lower fine root decomposition, which occurs directly in mineral soil. The CO2Fix model confirmed that total litter input and proportion of fine woody litter explained differences in SOC. Increasing degree of litter decomposition decreased extractives concentration, holocellulose concentration and O-alkyl C spectral regions, and increased spectral regions of alkyl, methoxyl, aromatic and phenolic C and proximate lignin concentration. Fast-growing trees can thus influence SOC and nutrient status within 20 years through their litter input and litter mineralisation rate.

Authors/Creators:Lemma, Bekele
Title:Impact of exotic tree plantations on carbon and nutrient dynamics in abandoned farmland soils of southwestern Ethiopia
Series Name/Journal:Acta Universitatis Agriculturae Sueciae
Year of publishing :2006
Number of Pages:42
ALLI. Lemma, B., Berggren, D., Nilsson, I. & Olsson, M. 2006. Soil carbon sequestration under different exotic tree species in the southwestern highlands of Ethiopia. Geoderma (in press). II. Lemma, B. & Olsson, M. 2006. Soil δ15N and nutrients under exotic tree plantations in the southwestern Ethiopian highlands. Forest Ecology and Management (in press). III. Lemma, B., Nilsson, I., Berggren, D., Olsson, M. & Kinker, H. 2006. Decomposition and substrate quality of leaf litter and fine roots from three exotic trees and native forest in the southwestern highlands of Ethiopia. Soil Biology and Biochemistry (submitted). IV. Lemma, B., Berggren, D., Olsson, M. & Nilsson, I. 2006. Factors controlling soil organic carbon sequestration under exotic tree plantations: A case study using the CO2Fix model in the southwestern Ethiopia. Forest Ecology and Management (submitted).
Place of Publication:Uppsala
ISBN for printed version:91-576-7257-1
Publication Type:Doctoral thesis
Full Text Status:Public
Agrovoc terms:cupressus lusitanica, pinus patula, eucalyptus grandis, forest trees, forest plantations, afforestation, soil organic matter, carbon, nitrogen, leaves, plant litter, roots, soil fertility, carbon cycle, nmr spectroscopy, ethiopia
Keywords:Afforestation, natural 13C abundance, natural 15N abundance, soil organic carbon, soil nutrients, exotic trees, leaf litter, fine roots, microcosm decomposition, CPMAS 13C NMR, CO2Fix model
Permanent URL:
ID Code:1274
Department:(NL, NJ) > Dept. of Forest Soils (until 081001)
Deposited By: Bekele Lemma
Deposited On:28 Nov 2006 00:00
Metadata Last Modified:02 Dec 2014 10:10

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