Researchers studied what happens to nitrogen fertilizer used in rice fields in the Taihu Lake region. They found that only about a third of the fertilizer was taken up by the rice plants, with a small amount remaining in the soil for the next wheat crop. After two cycles of rice and wheat, only a small portion of the nitrogen fertilizer was left in the soil. Most of the fertilizer was lost through processes like ammonia emission and nitrification-denitrification. Interestingly, adding more nitrogen and phosphorus did not increase crop yield or nitrogen use efficiency.