When considering nutrient burn, it is important to consider how water moves with osmotic pressure once inside the plant. Osmotic pressure is “water flowing through a permeable membrane in the direction of higher salt concentrations. Water will continue to flow in the direction of the highest salt concentration until the salts have been diluted to the point that the concentrations on both sides of the membrane are equal” – David Whiting, “The Science of Gardening” p.55. When a plant experiences nutrient burn it is because the salt concentration in the soil is higher than the salt concentration of the plant roots. Therefore, the roots push out water in an attempt to find an equilibrium between the salt concentration in the soil’s water and the salt concentration in the roots themselves.
The easiest nutrient to over-do is Nitrogen and it quickly shows. Leaf tips become elongated, begin to turn bright yellow and eventually burn away.