Minimizing nitrate output from soil organic nitrogen mineralization in citrus orchard catchments through green manure mulching

Abstract

In the catchments predominantly occupied by citrus orchards in central China, the discharge of nitrate (NO₃⁻) poses a significant threat to the downstream aquatic ecosystems, elevating the risk of eutrophication. It is imperative to comprehend the origins, factors influencing, and methods of regulating NO₃⁻ release in these catchments to effectively manage and mitigate NO₃⁻ pollution. This research utilized a continuous catchment-scale monitoring experiment in areas with varying percentages of citrus orchards (CW: citrus orchards catchment; RR: cropland catchment with few citrus orchards), along with a field experiment involving different treatments (CK: no fertilizer; CF: conventional fertilizer; OM: CF with organic manure; GM: CF with green manure) to investigate the sources and influencing factors of NO₃⁻ output as well as to evaluate control measures. The results indicated a noteworthy increase in NO₃⁻ output with an increase in the percentage of citrus orchards, with NO₃⁻ loss predominantly stemming from runoff and leaching as a result of soil organic nitrogen (SON) mineralization in citrus orchards. The implementation of green manure mulching emerged as an effective measure to reduce NO₃⁻ output caused by SON mineralization, leading to a substantial 33.2 % reduction in NO₃⁻ loss compared to conventional fertilizer and a 10.5 % reduction compared to organic manure. These findings offer valuable insights for the regulation of NO₃⁻ output and the enhancement of agricultural sustainability in agricultural catchments.