Effect of continuous N fertilizer reduction on N losses and wheat yield in the Taihu Lake region, China

Rainfed agriculture is important to meet the increasing demands of food production . However, there is a lack of knowledges for the rainfed wheat systems in abundant rainfall areas, where the erratic rainfall may constrain the wheat yield and increases N losses from wheat fields with excessive fertilizer inputs. In the present study, a 6 consecutive years field experiments were conducted to investigate the wheat yield and N losses responses to different N fertilizer rates in the Taihu Lake region. Despite the fluctuations in the wheat yield, a 10–30% reduction of the district average N input sustained the current-level of wheat yield for the 6 consecutive years. The N rate of 168 kg ha −1 might be the threshold N application rate, because if it was exceeded, it was no longer the predominant factor determining the wheat yield, but significantly increased the N losses fluxes. The seasonal total N losses fluxes were 69.2 kg N ha −1 , which accounted for 28.8% of district averaged N input. Runoff was the predominant pathway of N loss from the wheat field, followed by ammonia volatilization and leaching. Nitrate was the predominant form in the runoff and leakage water. Seasonal cumulative nitrate losses via runoff and ammonia volatilization averaged 25.2 and 20.1 kg ha −1 per wheat season, respectively, corresponding to 10.5% and 8.38% of the regional N application rates. However, the seasonal nitrate loss via leakage was the lowest, less than 8.98 kg ha −1 . Reducing the fertilizer N rates significantly decreased the N losses via runoff and ammonia volatilization, but not by leaching. Our findings indicated that reducing N fertilizer was impressive for the sustainable development of agriculture in Eastern China and 168 kg N ha −1 was recommended for the rainfed wheat. • Reducing N inputs (168–216 kg ha −1 ) sustained current-level of wheat yields for 6 years in rice-wheat rotation. • N loss (kg ha −1 ) was affected by, in order, N runoff (30.7) > ammonia volatilization (20.1) > nitrate leaching (11.0). • Precipitations, solar radiations and sunshine durations were the critical factors determining wheat yields.