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 degrees 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 degrees C and 37% at 30 degrees 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 urea-hydrolysis 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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