Nitrogen rhizodeposition from soybean (Glycine max) and its impact on nutrient budgets in two contrasting environments of the Guinean savannah zone of Nigeria
Nutrient Cycling in Agroecosystems
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
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.
belowground biomass; cropping practice; nitrogen cycle; nutrient budget; root system; savanna; soybean; Africa; Ibadan; Kaduna [Nigeria]; Nigeria; Oyo; Sub-Saharan Africa; West Africa; Zaria; Glycine max