Do you notice sometimes, when you buy fertilizer, a big bag says NPK?
你们注意到了吗，当你去买化肥的时候会看到一个袋子上写着NPK？
英语百科
Labeling of fertilizer
（重定向自NPK）
The labeling of fertilizers varies by country in terms of analysis methodology, nutrient labeling, and minimum nutrient requirements. The most common labeling convention shows the amounts of nitrogen, phosphorus, and potassium in the fertilizer.