Soil and Environmental Effects on Urease Inhibition by Ammonium Thiosulfate
1992
Sullivan, D. M. | Havlin, J. L.
Soil urease inhibition by ammonium thiosulfate [ATS, (NH₄)₂S₂O₃ 12-0-0-26S] in fluid fertilizer mixtures with urea-ammonium nitrate (UAN, 32-0-0) has been demonstrated for a limited number of soils. The objectives of this study were to (i) identify soil properties affecting ATS efficacy, (ii) measure ATS effects on gaseous NH₃ losses, (iii) evaluate the effects of soil moisture and temperature on ATS efficacy, and (iv) measure the S species present after application of UAN + ATS. Urea hydrolysis inhibition by ATS ranged from 18 to 48% in eight Kansas soils varying in pH, clay, organic C, and carbonate content in an incubation at 20 °C and −0.1 MPa soil matric potential. Ammonia loss was significantly reduced in seven of the eight soils tested (48% in four noncalcareous soils and 22% in three calcareous soils). Urea-hydrolysis inhibition averaged 29% at 20°C and 37% at 30°C; inhibition averaged 28% at −0.03 MPa and 38% at −0.1 MPa. Tetrathionate (S₄O²⁻₆) was the dominant S anion produced by S₂O₃²⁻ oxidation, ranging from 17 to 88% of the applied S. The amount of S₄O²⁻₆ present was not significantly correlated with the degree of ureahydrolysis inhibition. Ammonium thiosulfate inhibited urea hydrolysis in all soils; its efficacy was greatest for soils low in clay and organic C at high temperatures and low soil moisture contents.
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