The present inventors have recognized that a pressure gradient or differentialin aproduct distribution line for conveying granular particulate material, such asseed orfertilizer, in an air flow to an agricultural field consistently decreases asair speed(velocity) in the product distribution line decreases until a critical airspeed is reached.Below the critical air speed, the particulate material may become susceptibleto fallingout of the air flow to potentially cause a blockage in the system.Accordingly, pressuresensors arranged in the product distribution line can be used to generate anair flow at anoptimum operating velocity above the critical air speed yet below a maximumair speedassociated with inefficient operation. In one aspect, the air flow can beadjusted tomaintain an optimum operating velocity despite changes in the type ofparticulatematerial and/or rate at which the particulate material is metered.
