The study looked at how different amounts of nitrogen fertilizer affected rice yield when wheat straw and rice straw were returned to the field. They found that the nitrogen amount used during the wheat season didn't have much impact on rice yield. However, increasing nitrogen during the rice season led to more rice panicles per area, but also decreased seed setting rate and grain weight. Overall, higher nitrogen levels in the rice field increased rice yield, but there was no significant difference between the highest and second-highest nitrogen levels.