Influence of calcium chloride and ammonium thiosulfate on bermudagrass uptake of urea nitrogen

Abstract

Calcium chloride (CaCl₂) and ammonium thiosulfate (ATS) have demonstrated an ability to inhibit urea hydrolysis and NH₃ volatilization. The objective of this experiment was to determine the effect of rainfall and soil drying on the ability of CaCl₂ and ATS to increase bermudagrass nitrogen (N) uptake from surface‐applied urea. Urea fertilizer, labeled with ¹⁵N and amended with CaCl₂ or ATS, was surface‐applied to bermudagrass sod‐cores from Ships clay (C) and a Lufkin fine sandy loam (fsl) soils. Bermudagrass sod‐cores were subjected to either low or high rainfall regimes beginning seven days after fertilizer applications. After one month, bermudagrass was harvested and analyzed for total N and ¹⁵N content. Calcium chloride significantly increased bermudagrass N use efficiency (NUE) of surface applied urea by 33 to 47% on the Lufkin fsl, but had little effect on the Ships c. Apparently, CaCl₂ is most effective on coarse textured soil with low cation exchange capacity (CEC). Simulated rainfall had no effect on yield or NUE for the Lufkin fsl, but for the Ships c, bermudagrass yield and NUE generally increased with rainfall. The absence of differences among N treatments on the Ships c suggests that urea hydrolysis and N loss were limited due the combined effects of high soil CEC and rapid daily drying of the sod‐core surfaces. Ammonium thiosulfate did not affect bermudagrass yield or NUE for either soil or rainfall regime.