Why do experienced gardeners fertilize the grooves located on the edges of the trunks of fruit trees, rather than distribute them evenly?

1) As the tree grows, the root system grows.
2) The roots absorb substances by the root hairs that follow the tip of the root, and therefore, in adult trees, they are located on the edges of the trunks.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.