Sulfur fractions in particle-size separates as influenced by long-term application of mineral and organic fertilizers

A field experiment established in 1962 was chosen to investigate the effect of long-term application of farmyard manure (FYM), compost (COM) and sewage sludge (SS), respectively, in two increments as compared to mineral fertilizer on inorganic and organic S fractions in particle-size separates (< 0.002 mm, 0.002-0.02 mm, 0.02-2 mm). Independent of the particle-size the application of the high amounts of COM and SS resulted in the highest total S contents. It is evident that the particle-size fractions < 0.002 mm contained the majority of total soil sulfur (S). The content of plant available S (water-soluble and adsorbed SO42-) decreased with increasing particle-size, while the influence of the kind and amount of organic fertilizers was negligible. As compared to C-bonded S sulfate esters were the dominant organic S fraction in size separates. The content of both organic S fractions was highest in the particle-size fraction < 0.002 mm and lowest in the particle-size fraction 0.02-2 mm. The influence of the application of organic fertilizers was less pronounced. Only high application rates of COM and SS, respectively, resulted in the highest contents of both organic S fractions in the particle-size fractions 0.002-0.02 mm and 0.02-2 mm.