If you hang out with enough English nerds, you'll probably hear the word "edenic" thrown around every now and then. This basically means that something is "like the Garden of Eden" (in its perfection, beauty, etc.). With this definition established, we can now safely say that the countryside setting in Ralegh's poem is the opposite of edenic, a total contrast to the pastoral countryside portrayed in Marlowe's poem.
In Marlowe's countryside, much like in the Garden of Eden, flowers are always blooming, the land is always fertile, and nature provides everything that people need to survive. In Ralegh's poem, the opposite is true. Marlowe's rivers are shallow, Ralegh's are raging. Marlowe's flowers are blooming, Ralegh's are withered and rotten. Marlowe's countryside is one where natural resources are given freely and happily, whereas Ralegh's fields are in debt, and being punished by winter for their springtime fertility.
Put another way, if Marlowe's setting is Disneyland, then Ralegh's setting is a day-long insurance seminar (no offense to you budding insurance agents out there). Still, for someone who writes in glowing detail about the beauties and resources of the New World, this cynical portrayal of nature is a little bit surprising. It is, however, a very effective strategy if Ralegh's main target is not nature itself, but the too-good-to-be-true representation of romance portrayed in Marlowe's poem. Much of the allure of "The Passionate Shepherd" depends on the beauty of nature being seductive to the shepherd's love. Everything is green and groovy over there. If Ralegh can establish that the shepherd's countryside is nothing but a load of phooey, the shepherd's argument comes undone at the seams and the nymph is left with the easiest choice ever. The question that then emerges is why is Ralegh's view of love so jaded and who was the ex-girlfriend that burned him so badly?