Quote Originally Posted by BuffaloJohn View Post
Keeps the moisture in the ground. The plants will be "poked" into the plastic and grow out of the dirt into the space above the plastic.
It also blocks any nuisance vegetation 'IE weeds', from sprouting while the crop plants are taking root. When planting crops from seeds the holes are poked at about 1" in diameter to plant the seeds through. The plastic also serves as a collector to absorb heat from the sun during the day allowing for earlier planting in cooler regions