A study looked at different types of rice plants to see how they use nitrogen to grow. They found that as the rice plants produced more grain, they also took in more nitrogen from the soil. The plants were able to use the nitrogen efficiently to increase their yield. This means that the more nitrogen the plants absorbed, the more grain they produced. The researchers classified the rice plants into six groups based on their yield levels and found that the plants with higher yields had better nitrogen uptake and use efficiency.