Effect of continuous reduction of nitrogen application to a rice-wheat rotation system in the middle-lower Yangtze River region (2013–2015)

•No rice yield loss with 20–40% nitrogen fertilizer reduced in current season, but probable wheat yield loss.•No rice yield loss with 20–40% nitrogen fertilizer reduced in previous season, but probable wheat yield loss.•Nitrogen use efficiency was increased and soil nitrogen content was maintained with 20–40% reduced nitrogen fertilizer.