Fertilizer helps summer maize plants grow better by improving their ability to photosynthesize. This means they can turn sunlight into energy more efficiently. The main factors that affect how well the plants can photosynthesize are how much light they get and how open their stomata (tiny openings on leaves) are. More light and open stomata mean better photosynthesis. So, adding fertilizer can make maize plants grow faster and stronger by helping them make more energy from sunlight.