Nitrogen dynamics in a winter-wheat field in Ehime, southwestern Japan

Abstract

ABSTRACT Nitrogen (N) is the most important and limiting factor in crop production. Thus, a clear understanding of its cycle is important to improve its efficiency and reducing environmental pollution. A 2-year experiment was conducted to investigate the N flows on a winter-wheat field during 2017 to 2019 in Ehime Prefecture, Japan. We also evaluated N budgets based on N input and N output among different N flows in a N dynamic model. Full fertilizer (coated urea at 120 N kg ha−1) application was used. Two additional treatments: no and low fertilizer N were set up in a randomized block design with four replications to estimate N sources of plant uptake and emitted N2O. Direct and indirect N2O emission were measured and estimated using a closed chamber technique and emission factor, respectively. N leaching and soil mineralized N were estimated using microlysimeters. Bulk N deposition was measured using the rain trap. Total plant N uptake (208 kg N ha−1) and aboveground yield (190 kg N ha−1) were major N outflows from the field. N in plants originated from fertilizer and soil N were 58.1% and 41.9%, respectively. Leached N (30.1 kg N ha−1) from the surface 30-cm depth of soil was also a major outflow. Mineralized soil N was estimated as 104 kg N ha−1 in the surface soil and contributed to 91% of leached N. Higher mean nitrogen use efficiency (101%) of fertilizer N was possibly because of utilization of coated fertilizer and climatic conditions in the field. Indirect and direct N2O emissions were quite low. A negative N budget (−86.8 kg N ha−1) suggested that supplementation of N by organic matter, such as compost and biochar, which can suppress N leaching, would be required to maintain soil N status and environmentally friendly farming.