The researchers conducted a field experiment in central Hubei to find the best amount of nitrogen fertilizer for rapeseed-rice rotation. They discovered that in medium-fertility paddy soil, applying the right amount of nitrogen increased crop yield by 3.9% to 41.5% for rapeseed, 7.3% to 42.5% for rice, and 8.3% to 41.3% for the whole year. The maximum nitrogen application amounts were 78.1 kg/hm2 for rice, 62.3 kg/hm2 for rapeseed, and 72.4 kg/hm2 for the whole period. The best nitrogen application amounts were 75.8 kg/hm2 for rice, 58.0 kg/hm2 for rapeseed, and 70.9 kg/hm2 for the whole period. The soil's available nitrogen levels were closely related to the yield increase for rapeseed and rice. The increase in available nitrogen before and after applying nitrogen fertilizer was directly related to the amount of nitrogen applied.