Research

Nutrient Balances as Indicators of Sustainability in acacia senegal Land use Systems in the Semi-arid Zone of North Kordofan, Sudan

*B. A. El Tahir¹, M. A. Daldoum² and J. Ardö³

¹ El Obeid Agricultural Research Station, P.O. Box 429, El Obeid, Sudan

² Faculty of Forestry, University of Khartoum, P.O. Box, 32, Shambat, Khartoum North, Sudan

³ Department of Physical Geography and Ecosystem Science, Lund University, Sweden

*Correspondence Author Email: eltahirba48@yahoo.com

Accepted 14 June 2013

Abstract

The objectives of this study were: (1) to assess nutrient flows and balances at land management systems and cropping seasons levels, and (2) to determine rate of nutrient depletion. The study was conducted in dry lands of Northern Kordofan, Sudan, at El Demokeya Forest Reserve (lat.13° 16¢ N; long. 30° 29¢ E, and alt. 560 m), over three cropping seasons (2002, 2003 and 2004). Flows and balances of organic carbon (OC), nitrogen (N), phosphorous (P) and potassium (K) in pure and intercropped sorghum, roselle and grasses with Acacia senegal at low- and high-tree density (LD 266 and HD 433 trees ha^-1, respectively) were investigated. Sources of nutrient inflows were organic matter (OM) from trees, gum Arabic, crop roots, atmospheric deposition, and N₂ fixation. Outflows were harvested products, crop residues, leaching, gaseous losses and wind erosion. Nutrient balances were positive in grass systems, but negative in pure sorghum and roselle. Large variations exist between inter cropped sorghum and roselle systems. Nutrient balances were positive during the poor cropping season (2002), while negative during the good season (2003). Nutrient depletion was severe for all studied nutrients in pure sorghum and roselle, but P depletion was remarkably more severe in roselle systems. For all systems, P availability is the major determinant of sustainability. The study demonstrated that OM was essential for positive nutrient balances. Hence, intercropping is considered as an appropriate option to enhance soil fertility. Ways for adjusting the negative balances in the context of sustainability were suggested.

Keywords: Organic carbon; Nutrient depletion; Sustainability; cropping seasons; Gum Arabic