Life needs nutrients to grow and thrive. Babies drink their mother's milk, healthy adults eat a balanced diet, and lions consume the meat of spry gazelles. Your lawn's no different – grass is a form of life that needs the same nutrients as anything else.
Okay, maybe not the exact same nutrients – you won't see turfgrass rearing up to eat small savannah animals anytime soon. Lawns draw their sustenance from the soil they're planted in, in the form of nitrogen, phosphorus, potassium and a host of other nutrients.
Over time, however, hungry lawns and plants suck the available nutrients out of the ground, leaving behind empty soil. Lawns rooted in empty soil become malnourished and grow limp and brown.
