CALCIUM-CHLORIDE AND AMMONIUM THIOSULFATE AS AMMONIA VOLATILIZATION INHIBITORS FOR UREA FERTILIZERS

Surface-applied urea fertilizers are susceptible to hydrolysis and los s of nitrogen (N) through ammonium (NH3) volatilization when condition s favorable for these processes exist. Calcium chloride (CaCl2) and am monium thiosulfate (ATS) may inhibit urease activity and reduce NH3 vo latilization when mixed with urea fertilizers. The objective of this s tudy was to evaluate the effectiveness of CaCl2 and ATS as urea-N loss inhibitors for contrasting soil types and varying environmental condi tions. The proposed inhibitors were evaluated in the laboratory using a closed, dynamic air flow system to directly measure NH3 volatilizati on. The initial effects of CaCl2 on ammonia volatilization were more a ccentuated on an acid Lufkin fine sandy loam than a calcareous Ships c lay, but during volatilization periods of greater than or equal to 192 h, cumulative N loss was reduced more on the Ships soil than the Lufk in soil. Calcium chloride delayed the commencement of NH3 volatilizati on following fertilizer application and reduced the maximum N loss rat e. Ammonium thiosulfate was more effective on the Lufkin soil than the Ships soil. For the Lufkin soil, ATS reduced cumulative urea-N loss b y 11% after a volatilization period of 192 h. A 20% (v/v) addition of ATS to urea ammonium nitrate (UAN) was most effective on the coarse te xtured Lufkin soil whereas a 5% addition was more effective on the fin e textured, Ships soil. Rapid soil drying following fertilizer applica tion substantially reduced NH3 volatilization from both soils and also increased the effectiveness of CaCl2 but not ATS. Calcium chloride an d ATS may function as limited NH3 volatilization inhibitors, but their effectiveness is dependent on soil properties and environmental condi tions.