The footprint on the soil works to compact the soil, reducing the air spaces in the soil, inhibiting water uptake by the soil and the flow of water through the soil. Stepping with great enough force could even kill some beneficial organisms such as earthworms. Also, the shoe which made the footprint might have bacteria or fungi on it, which would be transferred to the soil. Some could be beneficial, such as nitrogen-fixing bacteria, but others could be pathogens, harming soil organisms and plants.
Work Step by Step
Skim the chapter and look for properties of the soil which would be affected by pressure, which is what the soil would be subjected to by the boot. Also think about how organisms move together, which means that microorganisms would probably travel on the boot of the person who stepped there.