INFLUENCE OF CALCIUM-CHLORIDE AND AMMONIUM THIOSULFATE ON BERMUDAGRASS UPTAKE OF UREA NITROGEN

Calcium chloride (CaCl2) and ammonium thiosulfate (ATS) have demonstra ted an ability to inhibit urea hydrolysis and NH3 volatilization. The objective of this experiment was to determine the effect of rainfall a nd soil drying on the ability of CaCl2 and ATS to increase bermudagras s nitrogen (N) uptake from surface-applied urea. Urea fertilizer, labe led with N-15 and amended with CaCl2 or ATS, was surface-applied to be rmudagrass sod-cores from Ships clay (C) and a Lufkin fine sandy loam (fsl) soils. Bermudagrass sod-cores were subjected to either low or hi gh rainfall regimes beginning seven days after fertilizer applications . After one month, bermudagrass was harvested and analyzed for total N and N-15 content. Calcium chloride significantly increased bermudagra ss 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 capac ity (CEC). Simulated rainfall had no effect on yield or NUE for the Lu fkin fsl, but for the Ships c, bermudagrass yield and NUE generally in creased with rainfall. The absence of differences among N treatments o n the Ships c suggests that urea hydrolysis and N loss were limited du e the combined effects of high soil CEC and rapid daily drying of the sod-core surfaces. Ammonium thiosulfate did not affect bermudagrass yi eld or NUE for either soil or rainfall regime.