  The baryonic mass composition of ultrahigh energy ($\gtrsim 10^{18}$ eV)
cosmic rays (UHECRs) at injection accompanied by their interactions on
universal photon backgrounds during propagation directly governs the UHECR flux
on the Earth. Secondary neutrinos and photons produced in these interactions
serve as crucial astrophysical messengers of UHECR sources. A modeling of the
latest data obtained by the Pierre Auger Observatory (PAO) suggests a mixed
element composition of UHECRs with the sub-ankle spectrum being explained by a
different class of sources than the super-ankle region ($> 10^{18.7}$ eV). In
this work, we obtain two kinds of fit to the UHECR spectrum -- one with a
single population of sources comprising of $^1$H and $^2$He, over an energy
range commencing at $\approx 10^{18}$ eV -- another for a mixed composition of
representative nuclei $^1$H, $^4$He, $^{14}$N and $^{28}$Si at injection, for
which a fit is obtained from above $\approx 10^{18.7}$ eV. In both cases, we
consider the source emissivity evolution to be a simple power-law in redshift.
We test the credibility of H+He composition by varying the source properties
over a wide range of values and compare the results to that obtained for
H+He+N+Si composition, using the Monte Carlo simulation tool CRPropa 3. The
secondary electrons and photons are propagated using the cosmic ray transport
code DINT. We place limits on the source spectral index, source evolution index
and cutoff rigidity of the source population in each case by fitting the UHECR
spectrum. Cosmogenic neutrino fluxes can further constrain the abundance
fraction and maximum source redshift in case of light nuclei injection model.
