Leaching is the main pathway of nitrogen loss from a citrus orchard in Central China

Abstract

Due to the high application rates and low utilization efficiency of inorganic nitrogen (N) fertilizer, conventional citrus orchards tend to cause N losses and extensive pollution. In order to address these issues, it is essential to identify the leading cause of N loss by citrus orchard N mass balance. In the present study, a two-year field experiment was performed on 4 different treatments (CK: no N fertilizer; CF: conventional N fertilizer; NR: 70% of conventional N fertilizer; OM: NR with organic manure) to quantify the pathways of N loss in citrus orchards in Hubei Province, China. Our findings revealed that leaching (17.0%) was the dominant N loss pathway in the conventional citrus orchard of central China, followed by runoff (2.9%), NH3 volatilization (2.3%), and N2O emission (0.5%). Reduced N fertilizer rates (−30.0%) led to a significant reduction in gaseous N loss (−34.9%), runoff N loss (−20.3%), and N leaching (−13.0%) via the reduced content of soil NH4+ and soil NO3-. Interestingly, the presence of organic manure reduced 15.2% of runoff N loss, 3.8% of N leaching and 6.9% of total N loss via reduced soil NO3-, but increased 39.6% of gaseous N loss via increased soil DOC. On the other hand, the low N fertilizer rates suppressed N uptake of citrus by reducing the content of soil NO3-, while organic manure promoted N uptake of citrus via the increased content of soil DOC. Overall, using organic manure as a substitute provides a better solution to fertilization for the citrus orchards in central China compared to reducing N fertilizer rates.