Determination of carbon to nitrogen ratio in soils of a semi-desert dry climate

The carbon to nitrogen ratio (C/N) determination is one of the most important parameters of soil characterization. The validity of the methods used for determining organic carbon and total nitrogen in some Aridisols soils collected from Khartoum State, Sudan was studied. Organic carbon (O.C) was determined by wet combustion method which was considered as a reference or standard method against Walkley-Black and Tinsley methods that are widely used in the Sudan. In the latter two methods, the organic material was found to be poorly oxidized, and the use of their conventional conversion factors will thus lead to underestimation of O.C. Using the wet combustion method as standard, new conversion factors were suggested, which were about 30% and 20% higher than those used in Walkley-Black and Tinsley methods, respectively. The contribution of non-exchangeable nitrogen to total nitrogen was determined, and was found that it significantly affected the C/N especially in the subsoil.