System - that part of the universe that is being studied using thermodynamics. It could be an individual chemical reaction or something as big as an attempt to model the recycling of P in the soils of the Great Plains. Exists in theory only. O, H and G are at a minimum, and S is at a maximum. Equilibrium occurs only in a closed system.
Steady state can occur in an open system.
See Fig. 1.7 on p. 16 and Fig. 1.8 on p. 17 of Buol et al. These figures show that the soil as an open system. Because soils are open systems, they never reach thermodynamic equilibrium. Rather, if given enough time for formation and weathering, soils approach a condition of steady state.