**2. Importance of application of physical methods on plant growth**

Chemical additives used for increasing plant productivity cause the contamination of raw materials required for food production [20]. Physical methods are applied for enhancing crop yield and plant growth and development. These methods include the plant treatment with electromagnetic waves, particularly optical emission, ultrasound and ionizing radiation, and magnetic field [20]. Using physical methods for stimulating plant growth has recently increased [21, 22, 29–32]. Additionally, further studies demonstrated that the development of the living organisms is recognized by the effect on physical factors, such as magnetic field, electromagnetic spectrum, and gamma rays [20, 27]. Those factors define the environment for plant growth. Upon physical treatment, the energy in cells is involved in facilitating molecular transformations; therefore, the cells are provided with the required substances [20]. This work discusses the physical methods and properties for stimulation of plant development and seed invigoration. Current research trends, future research directions, and challenges are also discussed.
