Tofully understand why it is necessary to feed a lawn, and whenyou should, it is helpful to know a little about grasses asplants. All plants use their leaves in the food assimilationprocess which then keeps them healthy most of the time andare able to go through life without too much help or hindrancefrom human beings.
The lawn in the image, never gets fed - and rarely watered! It is subjected to the public walking over it week in week out!
If you strip the leaves off a perennial plant, they will normally re grow but a little bit smaller and weaker. If you keep taking the leaves off, the plant will eventually weaken and die. No matter how good the soil below is, if the plant cannot turn soil chemicals into the food that it requires, it will starve.
Leaves are responsible for assimilation of soil chemicals into life-giving nutrients to feed the whole plant. The stem, roots, flower buds and new leaves; all are dependent upon those life-supporting leaves.