Laberge G., Franke A.C., Ambus P., Høgh-Jensen H.
Department of Agricultural Sciences, Faculty of Life Sciences, University of Copenhagen, Højbakkegård Allé 9, 2630 Taastrup, Denmark; International Institute of Tropical Agriculture, Oyo Road, Ibadan, Nigeria; C/o Lambourn Ltd., Carolyn House, 26 Dingwall
Laberge, G., Department of Agricultural Sciences, Faculty of Life Sciences, University of Copenhagen, Højbakkegård Allé 9, 2630 Taastrup, Denmark; Franke, A.C., International Institute of Tropical Agriculture, Oyo Road, Ibadan, Nigeria, C/o Lambourn Ltd., Carolyn House, 26 Dingwall Road, Croydon CR9 3EE, United Kingdom, Plant Research International, Department of Agrosystems Research, Wageningen University and Research Centre, P. O. Box 16, Wageningen 6700 AA, Netherlands; Ambus, P., Plant Research International, Department of Agrosystems Research, Wageningen University and Research Centre, P. O. Box 16, Wageningen 6700 AA, Netherlands; Høgh-Jensen, H., Risoe National Laboratory, Technical University of Denmark, Frederiksborgvej 399, Roskilde 4000, Denmark
Nitrogen (N) rhizodeposition by grain legumes such as soybean is potentially a large but neglected source of N in cropping systems of Sub-Saharan Africa. Field studies were conducted to measure soybean N rhizodeposition in two environments of the Guinean savannah of Nigeria using 15N leaf labelling techniques. The first site was located in Ibadan in the humid derived savannah. The second site was in Zaria in the drier Northern Guinean savannah. Soybean N rhizodeposition in the top 0.30 m of soil varied from 7.5 kg ha -1 on a diseased crop in Ibadan to 33 kg ha-1 in Zaria. More than two-thirds of soybean belowground N was contained in the rhizodeposits at crop physiological maturity, while the rest was found in the recoverable roots. Belowground plant-derived N was found to constitute 16-23% of the total soybean N. Taking rhizodeposited pools into account led to N budgets close to zero when all residues were removed. If residues were left in the field or recycled as manure after being fed to steers, soybean cultivation led to positive N budgets of up to +95 kg N ha-1. The role and potential of grain legumes as N purveyors have been underestimated in the past by neglecting the N contained in their rhizodeposits. © 2008 Springer Science+Business Media B.V.