A multi-piece solid golf ball is composed of a multilayer core having at least an inner core layer and an outer core layer, one or more cover layer which encloses the core, and numerous dimples formed on a surface of the cover layer. The seed flap is formed from a non-flexible material, such as an abrasion resistant steel, and pivotally mounted to the seed tube to permit the seed flap to trail behind the seed tube and control the placement of seeds andor fertilizer discharged from the seed tube. Note that the oxide region of the source electrode and the drain electrode is preferably formed by plasma treatment with a high frequency power of 300 MHz to 300 GHz and a mixed gas of oxygen and argon. This invention may be implemented by a small addition to control software. A method of forming such a door panel is also disclosed.