How do seeds determine if the conditions are suitable for germination

Light indicates soil disturbance or a position at the surface. Spectral quality of light informs the seed about the presence of competing plants. Alternating temperature can inform about time of year, but also depth in the soil and presence of competing plants. Nitrate levels in the soil can also inform the seed about the presence of competing plants. Increased sensitivity to nitrate enhances the germination response to light at any given temperature.