The synchrotron based vacuum ultraviolet-pulsed field ionization-photoelectron (VUV-PFI-PE) spectrum of ammonia (NH3) has been measured in the energy range 10.12 - 12.12 eV using a room-temperature NH3 sample. In addition to extending the VUV-PFI-PE measurement to include the v(2)(+) = 0, 10, 11, 12, and 13 and the v(1)(+) + nv(2) + (n = 4 - 9) vibrational bands, the present study also reveals photoionization transition line strengths for higher rotational levels of NH3, which were not examined in previous PFI-PE studies. Here, v(1)(+) and v(2)(+) represent the N-H symmetric stretching and inversion vibrational modes of the ammonia cation (NH3+), respectively. The relative PFI-PE band intensities for NH3+(v(2)(+) = 0 - 13) are found to be in general agreement with the calculated Franck-Condon factors. However, rotational simulation indicates that rotational photoionization transitions of the P-branches, particularly those for the lower v(2)(+) PFI-PE bands, are strongly enhanced by forced rotational autoionization. For the synchrotron based VUV-PFI-PE spectrum of the origin band of NH3,+ rotational transition intensities of the P-branch are overwhelming compared to those of other rotational branches. Similar to that observed for the nv(2)(+) (n = 0 - 13) levels, the v(1)(+) + nv(2)(+) (n = 4 - 9) levels are found to have a positive anharmonicity constant; i.e., the vibrational spacing increases as n is increased. The VUV laser PFI-PE measurement of the origin band has also been made using a supersonically cooled NH3 sample. The analysis of this band has allowed the direct determination of the ionization energy of NH3 as 82158.2 +/- 1.0 cm(-1), which is in good accord with the previous PFI-PE and photoionization efficiency measurements. Using the known nd(v(2)(+) = 1, 1(0) <- 0(0)) Rydberg series of NH3 as an example, we have demonstrated a valuable method based on two-color infrared-VUV-photoion depletion measurements for determining the rotational character of autoionizing Rydberg states.