The application of fertilizer can have a positive impact on the growth and thickness of grass. Fertilizers provide essential nutrients such as nitrogen, phosphorus, and potassium, which are necessary for the healthy development of plants. These nutrients help to promote strong root growth and increase the density of foliage, which can result in thicker, lusher grass. However, it's important to note that excessive use of fertilizer can have negative effects on grass, such as burning or yellowing of the foliage, and can also harm the surrounding environment. Therefore, it's essential to follow the recommended guidelines for fertilization and to use the appropriate type of fertilizer for the specific type of grass being grown.