Make a Fetilizer Storage.
Collect Dung. Put it there = Fertilizer
How to get dung.
Reload your game 1st. Quickly go to the cows and see they are eating grass. Wait until they poop. thats the Dung. Cows will became FAT after some eating. when you see "!" it stops eating and time to Milk it. Now make a WOODEN BUKCEt >milk the cow.
P.S you dont need to reload just milk the cow :P