Simulating yield gap of winter wheat in response to nitrogen management in North China Plain based on DSSAT model

Abstract: Yield gap analysis is important to reveal factors that limit crop production and identify management practices that can potentially increase crop yield. Although nitrogen (N) fertilizer played an important role in wheat yield increase in the past 30 years in China, excessive nitrogen application became a common practice in some farms, which increased input by farmers, reduced farm profitability, and caused significant environmental issues in recent years. Due to the complexity of the system, crop growth models such as the DSSAT model (Decision Support System for Agro-technology Transfer) have been widely used by many researchers across the world to analyze crop yield gap and determine the impact of N fertilizer on yield gap. In this study, the DSSAT model was coupled with data from experiments and a farm survey was employed to assess the impact of N fertilizer management on the yield gap of winter wheat in the North China Plain, to determine the average yields and yield gaps under distinct N fertilizer management scenarios over the years, and to identify the distribution of yield gaps and the agronomic efficiency of applied N fertilizer (AEN) among different fields. The field experiments were conducted in Wuqiao, China from 2008 to 2011. Yield and management data were collected from the experiments to calibrate and validate the DSSAT model and the analysis of AEN in the experiment. The simulated yields of the DSSAT model were closely correlated to the actual yield in the field experiments with different application levels of N fertilizer, indicating that the model was adequate for analyzing the yield gap of winter wheat in the region. Results from a farm survey, conducted in Wuqiao in 2010, indicated that there were remarkable differences among winter wheat yields in different fields, ranging from 5250 to 8630 kg/hm2 with a relatively lower coefficient of variation. The N fertilizer rates ranged from 30 to 495 kg/hm2 with significant variations among different fields, indicating a wide range of N fertilizer application rates among farmers in the region and room for improvement in management practices. Based upon the simulation results, the optimum N application rate was 222 kg/hm2 with the corresponding maximum attainable yield (AYmax) of 7618 kg/hm2. There were considerable differences between AYmax and crop yields from the survey, ranging from -1007 to 2 368 kg/hm2. The gap narrowed gradually as the N fertilizer rate increased and plateaued at a 222 kg/hm2 N fertilizer rate. The N application rates in farmers' fields were commonly higher than the optimum rate with low AEN. Almost 75% of the fields in the survey were in the range of relatively high N rates, indicating excessive N fertilizer applications in the wheat crop in the region. The results indicated that winter wheat yield could be significantly improved with better management practices. Possible optimization strategies to achieve both high yields and high N use efficiency in winter wheat in North China Plain should focus on adjusting N fertilizer application rates to an optimal range, improving N fertilizer application timing, and adjusting the practices according to local soil conditions and climates. Greater efforts in education and on-farm demonstration are needed to help farmers in improving N fertilizer management practices.