Symbiotic nitrogen fixation in eight Acacia senegal provenances in dryland clays of the Blue Nile Sudan estimated by the 15N natural abundance method |
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Authors: | El Amin Yousif Raddad Ahmed Ali Salih Mohamed Ahmed El Fadl Vesa Kaarakka Olavi Luukkanen |
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Institution: | (1) Viikki Tropical Resources Institute (VITRI), University of Helsinki, P.O. Box 27, FIN 00014 Helsinki, Finland;(2) Forestry Research Centre, P.O. Box 7089, Khartoum North, Sudan |
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Abstract: | The symbiotic biological N2fixation by Acacia senegal was estimated using the 15N natural abundance (δ
15N) procedure on eight provenances collected from different environments and soil types grown in a clay soil in the Blue Nile
region, Sudan. Balanites aegyptiaca (a non-legume) was used as a non-N2-fixing reference plant to allow 15N-based estimates of the proportion of the Acacia N derived from atmospheric N2 (Ndfa) to be calculated. Results show variation in leaf δ
15N between A. senegal and the reference plant and among years. The relative δ
15N values (‰) were higher in B. aegyptiaca than in the N2-fixing acacia provenances. Provenances originally collected from clay soils fixed little N in the first year, but the amount
fixed increased as the trees aged. All provenances showed a decrease in δ
15N with age. The Ndfa varied between 24% (Mazmoom provenance) and 61% (Rahad provenance) 4 years after planting. There was no significant difference
in δ
15N between provenance groups based on soil type or rainfall at original growing site. The amount of Ndfa increased significantly with age in all provenances. The above-ground contribution of fixed N to foliage growth in a 4-year-old
A. senegal was highest in the Rahad sand–soil provenance (46.7 kg N ha−1) and lowest in the Mazmoom clay-soil provenance (28.7 kg N ha−1). Our study represents the first use of the δ
15N method for estimating the N input by A. senegal to the clay plain soils of the gum belt in the Sudan. |
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Keywords: | Acacia senegal agroforestry Balanites aegyptiaca gum belt Ndfa N2-fixing species reforestation |
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