Disposal of industrial lump sulphur by-product in soil. Influence on soil chemical and biochemical properties and on yield and quality of sugar beet (Beta vulgaris L)

A field experiment was carried out to evaluate modifications on the chemical and biochemical parameters of an agricultural alkaline soil (pH=8.31) under sugar beet (Beta vulgaris L.) by applying different amounts of sulphur by-product coming from oil desulphurization process. Soil chemical properties such as sulphate formation, pH, soil electrical conductivity (EC), total and extractable organic carbon (TOC and TEC), and biochemical parameters such as microbial biomass carbon content (MBC) and total hydrolytic capacity (FDA-hydrolysis), arylsulphatase (ArS-ase) and o-diphenoloxidase (o-DPO), were monitored. Commercial parameters of yield and quality production of sugar beet (yield of roots, % of polarization, extractable saccharose content and purity of thick juice) were also determined. All soil chemical and biochemical properties and commercial parameters of sugar beet were monitored in plots treated with 1 (S1), 5 (S5) and 10 (S10) t ha -1 of sulphur by-product and compared with untreated plots (SO). In S1, 60 days after amendment the highest values of sulphate formed (310 mg kg -1 ) and the EC (1596 μS cm -1 ), were observed. In S5, the sulphate formed was 2583 mg kg' and soil EC was 4138 μS cm -1 after 210 days, while in S10 the amount of sulphur added probably exceeded soil oxidation capacity since it continued more slowly till the end of the experiment. After 210 days, soil pH reached the lowest value in all the treated plots and it was 7.75, 7.52 and 7.26 in S1, S5 and S10, respectively. No significant modifications were made on soil biochemical parameters tested by the different amounts of sulphur added. A decrease in the production yield of sugar beet (27.2%) was found only when the highest amount of sulphur was applied. In contrast, no worsening of main commercial parameters was observed.