Vol. 5(1), pp. 13-19, January, 2014 DOI: 10.5897/JSSEM13.0408 ISSN 2141-2391 ©2014 Academic Journals http://www.academicjournals.org/JSSEM Journal of Soil Science and Environmental Management Full Length Research Paper Soil sulfur availability due to mineralization: Soil amended with biogas residues Mewael Kiros Assefa 1 *, S. von Tucher 2 and Urs Schmidhalter 2 1 Department of Plant Sciences, Aksum University, Shire- campus P. O. Box 314, Shire-endaslassie, Ethiopia. 2 Plant Nutrition, Technische Universität München, Emil-Ramann-Straße 2, 85350 Freising-Weihenstephan, Germany. Accepted 20 December, 2013 Sulfur, an essential element for plant growth, has received lesser attention than it deserves. Current inputs of sulfur to agricultural soils from atmospheric deposition have reduced to less than the amount sulfur required by most crops. In such soils the release of sulfur from organic matter is vital for the supply of sulfur. A pot experiment without plant (incubation study) in a green house was conducted at the experimental station Dürnast TU Weihenstephan to investigate the potential of biogas residues as sources of available sulfur. The pot experiment comprised 20 different fertilization variants; 16 biogas residues and 3 mineral sulfur fertilizer variants, that is, S- 30, S-60, and S- 90 mg/pot, and a control (S- 0), replicated trice. Pots were arranged in completely randomized design. Soil SO 4 2- -S and NO 3 - -N contents upon were measured trice during the study period. Soil SO 4 2- -S and NO 3 - -N content were significantly influenced by fertilizer treatments at all times. Generally, liquid biogas residues tend to show higher soil SO 4 2- -S and NO 3 - -N content. Soil SO 4 2- -S content varied from 26.1 to 100.20 mg pot -1 (625-S, S-90); 30.4 to 100.4 mg pot -1 (621-S, 626-L) and 31.4 to 98.2 mg pot -1 (S-0, 626-L), in first, second and third sampling times, respectively. Soil NO 3 - -N content also varied from 114.5 to 526.5 mg pot -1 (629- S, 616-L); 99.0 to 1054 mg pot -1 (620-S, 616-L); 114.8 to 1045.4 mg pot -1 (620-S, 616-L), in first, second and third sampling times, respectively. Biogas residues containing more than 0.1% S t in fresh matter and C org : S ratio lower than 30 could replace short term sulfate limitation. Key words: Biogas residues, sulfur mineralization, sulfur availability, C org :S ratio. INTRODUCTION Sulfur, an essential element for plant growth, has received lesser attention than it deserves. In recent years, deficiency of sulfur in crops has increased worldwide and has been recognized as a constraint in crop production (Eriksen et al., 2004; Girma et al., 2005; Mascagni et al., 2008). The main reasons are: (1) the environmental control of sulfur dioxide emissions in industrial areas, (2) the increasing use of high-analysis, sulfur free fertilizers, (3) the decreasing use of sulfur- containing pesticides and fungicides, (4) the adoption of high-yielding crop cultivars which demand a high fertility level and results in greater exploitation of soil reserve nutrients and removal of much larger quantities of nutrients in the harvested crop, and (5) the increased cropping intensity (intensive cultivation) (Scherer, 2001). microfauna, have been widely documented (Heimann Current inputs of sulfur from atmospheric deposition are less than 10 kg ha -1 in most Western European countries (Hu et al., 2005), which is less than the amounts of sulfur required by most crops (McGrath et al., 2002 as cited in *Corresponding author. E-mail: mewaelk@yahoo.com