Every day on my commute to work I drive past a sod farm. Every spring I see them fertilize with liquid fertilizer, and water it.
Every summer I watch them peel off a layer of sod, leaving brown earth beneath it.
Yet I never see them replace the dirt!
While the sod farm is in a river valley, the river never floods further than a few feet beyond its bank, so I know the dirt is not getting replenished that way.
Can anyone fill me in on how sod farms keep from farming down to the clay/bedrock foundations?