The study looked at what happens to nitrogen fertilizer in a rotation of winter wheat and summer maize crops near Beijing. They found that using too much nitrogen didn't increase crop yield. More nitrogen was recovered and less was lost with lower application rates. After harvesting the crops, a lot of nitrogen was left in the soil, especially with high application rates. Some nitrogen was still there after multiple crop harvests. Most of the leftover nitrogen was in the form of nitrate, which can leach out of the soil.