Method to determine elemental sulphur in soils applied to measure sulphur oxidation
1996
Zhao, F.J. | Loke, S.Y. | Crosland, A.R. | McGrath, S.P.
A method was established for the determination of elemental S (S degrees) in soils. The S added to four arable soils was extracted with chloroform, digested with fuming HNO3-KNO3 and determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The method gave recoveries of between 96.6 and 100.4% in air-dried soils and in the same soils at 50% of the water holding capacity (WHC), with CVs varying between 0.4 and 5.6%. Complete recoveries were also obtained at soil moisture contents of 2 and 4 times of WHC, although precision was poorer. In contrast, the digestion method using HClO4<HNO3 was not suitable, because it resulted in only about 80% recovery of S degrees. An incubation study showed that the net amount of sulphate-S produced was substantially less than the decrease of S degrees in four soils. After 38 days of incubation at 25 degrees C, the percentages of total oxidised S appearing as sulphate-S were greater in the two sandy soils (64-78%) than in the two clayey soils (34-40%). The difference between the oxidation of S degrees and the production of sulphate-S was probably due to microbial immobilisation. It is suggested that both measurements are needed to study the oxidation of S degrees in soils and the availability of oxidised S to crops.
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