Manganese is an important micronutrient, and its availability in soil is affected by a wide variety of factors. In properly aerated and drained soils, and during growth, it temporarily switches to a less available form, at the very moment when plants need it most. Changes in soil moisture can convert available forms into unavailable forms and vice versa. Rapid changes can either increase or decrease its availability, causing deficiency or even excesses to toxic levels. It is therefore important to consider environmental influences, in order to assess the deficiency risk and to interfere with foliar fertilization.