Department of Plant Sciences

The study was carried out to evaluate the effects of long-term application of different organic fertilizers (farmyard manure, compost and sewage sludge) as compared to mineral fertilizers on total sulphur (S) content as well as on inorganic (water soluble and adsorbed SO4-S) and organic S binding forms ( sulphate ester and carbon bonded S). Total S concentrations ranged between 99 and 263 mg kg-1 soil and were highest in the treatments with the high compost (COM2) and sewage sludge application rate (SS2), respectively. The share of inorganic S of total S varies between 4.6 and 11.7 %. It consists mainly of water-soluble sulphate with a concentration ranging between 11.7 mg and 17.9 mg kg-1 soil. The organic S pool is dominated by ester sulphates. The enrichment of this fraction is highest in COM2 (156 mg S kg-1) and SS2 (116 mg S kg-1). Carbon-bonded S ranges between 18.7 mg S kg-1 soil (SS1) and 98.9 mg S kg-1 soil (SS2) with the highest amounts in COM2 and SS2. Overall, the different forms and amounts of S applied for about 45 years lead to varying absolute amounts of organic and inorganic S forms in soil. Nevertheless, the relative proportions of organic and inorganic S only vary in a rather small range. Obviously, soil and site characteristics are more important for this partitioning than quality and quantity of S fertilization.