Composition of sulphur fractions and impact factors in calcareous soils

Sulphur fractions in twenty two top layer soils collected from Shaanxi, Hunan Provinces, etc. were determined. Results indicated that content of total S in soils was average 405.5111.8 mg/kg, among of which 85.4%10.0% was organic S. The contents of C-O-S, C-S and inert S in soils were 130.364.6mg/kg, 65.529.4mg/kg, 152.596.7mg/kg respectively, percentage of C-O-S, C-S and inert S in total S were 31.4%12.9%, 18.0%10.7% and 36.0%17.8%, and percentage of C-O-S, C-S and inert S in total organic S were 36.614.4%, 21.813.8% and 41.519.1%, respectively. The significant position correlation between contents of C-O-S (r=0.7334**), C-S (r=0.4426*) and organic C in soil were found. The contents of C-O-S in soils derived from calcareous parent material was significantly higher than that in soils from loess parent material. The slow soluble S was major inorganic S fractions in tested calcareous soils, average contents of which was 28.4mg/kg, and the percentage of which in total inorganic was 50.7%. The extremely significant position relationship between the contents of slow soluble S and total inorganic S (r=0.6040**), and CaCO3(r=0.6800**) in soils were found. However, the significant negative correlation between the contents of slow soluble S and total organic S, ( r= 0.5286*), C-O-S(r= 0.4417*) and organic C (r= 0.4786*) in soils were obtained. The content of slow soluble S, its distribution coefficient in total S and total inorganic S in soils derived from loess parent material were extremely significantly higher than that in soils from calcareous parent material. It is necessary to study the trend of transformation and produce for the slow soluble S in calcareous soils in order to evaluate fully supply capacity of sulphur in calcareous soils.