If decomposers [Earth Worms, Bacteria, Fungi] were not around the producers such as plants would not get the needed nutrients such as [carbon and nitrogen] and that would affect the herbivore population drastically (the population will decline), this will also affect the predators of the herbivores like the carnivores and omnivores. When animals or plants may reach their maximum life decomposers clean up the environment and use the once living matter for themselves and others. There are "nitrogen-fixing" bacteria in the roots and in the soil, which turns the nitrogen into ammonium (through the process of ammonification) and then through the process of nitrification (thanks to the nitrifying bacteria ) it gets converted to nitrites and then into nitrates which would then get taken up by the plant or goes up into the atmosphere.
