Fertilizer burn is defined as leaf scorch resulting from over-fertilization, usually referring to excess nitrogen salts.
Fertilizer burn is the result of desiccation of plant tissues due to osmotic stress, creating a state of hypertonicity.
Fertilizers vary in their tendency to burn roughly in accordance with their salt index.
Fertilizer burn Wikipedia
Fertilizer burn can be remedied by soaking the soil with water to flush out excess salts. It can be prevented by applying only dilute or controlled-release fertilizer products.