  We present a Fourier analysis of the clustering of galaxies in the combined
Main galaxy and Luminous Red Galaxy (LRG) Sloan Digital Sky Survey (SDSS) Data
Release 5 (DR5) sample. The aim of our analysis is to consider how well we can
measure the cosmological matter density using the signature of the horizon at
matter-radiation equality embedded in the large-scale power spectrum. The new
data constrains the power spectrum on scales 100--600h^-1Mpc with significantly
higher precision than previous analyses of just the SDSS Main galaxies, due to
our larger sample and the inclusion of the LRGs. This improvement means that we
can now reveal a discrepancy between the shape of the measured power and linear
CDM models on scales 0.01<k<0.15hMpc^-1, with linear model fits favouring a
lower matter density (Omega_m=0.22+/-0.04) on scales 0.01<k<0.06hMpc^-1 and a
higher matter density (Omega_m=0.32+/-0.01) when smaller scales are included,
assuming a flat LCDM model with h=0.73 and n_s=0.96. This discrepancy could be
explained by scale-dependent bias and, by analysing subsamples of galaxies, we
find that the ratio of small-scale to large-scale power increases with galaxy
luminosity, so all of the SDSS galaxies cannot trace the same power spectrum
shape over 0.01<k<0.2hMpc^-1. However, the data are insufficient to clearly
show a luminosity-dependent change in the largest scale at which a significant
increase in clustering is observed, although they do not rule out such an
effect. Significant scale-dependent galaxy bias on large-scales, which changes
with the r-band luminosity of the galaxies, could potentially explain
differences in our Omega_m estimates and differences previously observed
between 2dFGRS and SDSS power spectra and the resulting parameter constraints.
