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

Abstract

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 SO₄^2–) 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.