Researchers conducted 3414 fertilizer experiments to determine the best amount and ratio of nitrogen, phosphorus, and potassium for different types of vegetables in Fujian. They found that the optimal fertilization levels varied for leafy vegetables, root vegetables, melons and fruits, and onions. The content of these nutrients in the soil matched well with the recommended fertilization levels. The study suggests that using a quadratic polynomial model can help predict the best fertilization practices for different vegetable species.