Novel Investigation on Ammonium Thiosulphate (ATS) as an Inhibitor of Soil Urease and Nitrification

Abstract

Among the numerous products so far promoted as effective urease and/or nitrification inhibitors, it is possible to detect a renewed interest in environmentally friendly tools, such as ammonium thiosulphate (ATS, (NH ₄ ) ₂ S ₂ O ₃ ) which is currently used as fertilizer for N and S nutrition. Among contradictory results accounted in the current literature, there is reported that ammonium thiosulphate (ATS) exerts inhibitory activity at large but unlikely agronomic rates of 2500 - 5000 mg · kg -1 soil. We carried out a novel experiment aimed to: a) verify the inhibitory action of ATS, even when applied in soil at low rates (25 and 100 mg · kg -1 soil as S-ATS), towards urease activity and nitrification in urea treated and not treated soils; b) investigate on the influence of ATS on the soil microbial biomass as it is generally assumed that soil microorganisms are the main agents of urea hydrolysis. For these purposes we selected an arable sandy soil and a grassland sandy-loam soil which are treated with urea or/and ATS. Results obtained from this novel investigation showed that a) ATS significantly decreased urease activity in both soil types and that the exerted inhibitory effect was moderate and short-term; b) ATS retarded the hydrolysis of urea and lowered nitrate production in the urea treated soils; c) the available fraction of iron and manganese in the used soils might be involved in the mechanism of inhibition; d) ATS did not affect the size of soil microbial biomass pool; e) the efficiency of ATS as urease and nitrification inhibitor was more evident in the sandy soil. Because of its properties, ATS may be applicable on many crops without being harmful on the soil microbial pool.