The study looked at how different types and amounts of fertilizer affect soil quality and crop yields in Tonghai county. They found that using less nitrogen fertilizer can actually improve crop yield and quality. Applying only inorganic nitrogen can make the soil more acidic and decrease its nutrients, while using only organic fertilizer can improve soil quality but may not provide enough nutrients for crops. However, using both nitrogen and organic fertilizer together can improve crop quality, increase yield, and enhance soil quality effectively.