high quality / rich / good soil has a high number of nutrients / amount of nitrogen & fertile soil is high in quality ->  fertile soil has a high amount of nutrients / nitrogen  fertile soil has a high amount of nutrients / nitrogen & if something has something else then that something might be made of that something else ->  fertile soil is made of high amounts of nutrients / nitrogen  fertile soil is made of high amounts of nutrients / nitrogen & if something is made of something else then the formation of that something requires that something else ->  high amounts of nutrients / nitrogen are required for the formation of fertile soil  high amounts of nutrients / nitrogen are required for the formation of fertile soil & if something requires something else then that something else is important to that something ->  high amounts of nutrients / nitrogen are important for the formation of fertile soil  returning something is a kind of method for transporting something & if something is transported to a place then the amount of that something in that place increases ->  if something is returned to a place then the amount of that something in that place increases  if something is returned to a place then the amount of that something in that place increases & decomposition is when a decomposer recycles / returns nutrients / nitrogen from dead organisms to the soil by eating those dead organisms ->  decomposition of dead organisms increases the amount of nutrients / nitrogen in soil  high amounts of nutrients / nitrogen are important for the formation of fertile soil & decomposition of dead organisms increases the amount of nutrients / nitrogen in soil ->  decomposition of dead organisms is important for the formation of fertile soil  decomposition of dead organisms is important for the formation of fertile soil & a plant is a kind of organism -> plant decomposition is important for the formation of fertile soil