The researchers studied soybean production in Northeast China to understand how to balance fertilizer use with plant nutrient needs. They found that soybean grain yield varied widely, with most nitrogen and phosphorus stored in the grain, and potassium in the straw. A model showed that increasing yield required more nitrogen, phosphorus, and potassium, but at a certain point, the ratio of these nutrients leveled off. This information can help farmers use the right amount of fertilizer to maximize yield without harming the environment.