Tires Tire Pressure

[NewToy]

I recently purchased a Farmtrac 270DTC equipped with the industrial tires. The rear tires are rated for 48 psi max and the fronts 50 psi. When I picked it up from the dealed it had 38 psi all around and thats where I left it. What would be the safe minimum to keep in them? All I do is mow with a 60" rear mount finish mower.

Thanks,

John