The researchers studied how different amounts of nitrogen fertilizer affect the yield of spring maize. They used a specific type of maize and tested six levels of nitrogen application. They found that increasing nitrogen levels up to 300 kg/ha can significantly boost maize yield. However, when nitrogen levels go above 300 kg/ha, the yield increase slows down or even decreases slightly. The leaf area index (LAI) also increased with higher nitrogen levels, reaching a peak during the silking stage. Overall, adding the right amount of nitrogen, around 300 kg/ha, can greatly improve maize yield in dry-land conditions.