ABSTRACT

This study aimed to investigate the effects of using controlled release fertilizers with reduced application rates on nitrous oxide (N₂O) gas emissions. For this, we monitored the N₂O emissions released from soybean fields converted from rice paddies in Japan for three years, i.e., from 2017 to 2020, under six nitrogen fertilizer treatments: conventional (AC: ammonium chloride, 20 kg N ha⁻¹), controlled release coated urea (CRCU: ammonium chloride, 5 kg N ha⁻¹, coated urea, 15 kg N ha⁻¹, total 20 kg N ha⁻¹), controlled release coated nitrate (CRCN: coated calcium nitrate, 20 kg N ha⁻¹), CRCU at a reduced rate (CRCU-R: 10 kg N ha⁻¹), CRCN at a reduced rate (CRCN-R: 10 kg N ha⁻¹), and no nitrogen fertilizer (NF: 0 kg N ha⁻¹). The soil of the field was classified as Gleyic Fluvisol.

The annual N₂O emissions of the CRCN treatment were significantly lower than those of the AC in the first and second years (p < 0.05) and were not significantly different in the third year, with reductions of 17–32%, while the same yield was maintained. The annual N₂O emissions of the CRCU treatment tended to be lower than those of the AC for the three years, with reductions of 14–19%, although not statistically significant. This suggests that coated nitrate fertilizers were more effective in reducing N₂O emissions, since nitrate produces this gas via denitrification only. In addition, the N₂O emissions of the CRCU-R and CRCN-R treatments were 22–37% and 24–41% lower than that of the AC treatment, respectively. Although not statistically significant, these reductions were slightly greater than those obtained for the N₂O emissions of CRCU and CRCN, suggesting the effect of further mitigation of N₂O emissions through the reduction of application rate. Furthermore, the N₂O emissions per yield tended to decrease due to the use of controlled release fertilizers for the three years, and further decrease due to the reduction of application rate. In conclusion, the use of controlled release fertilizers with reduced application rates can be regarded as an improved climate-smart soil management in soybean fields converted from rice paddies.

摘要

本研究旨在调查使用降低施用量的控释肥料对一氧化二氮 (N ₂ O) 气体排放的影响。为此，我们监测了日本从稻田转化的大豆田中释放的 N ₂ O 排放量，即从 2017 年到 2020 年，在六种氮肥处理下：常规（AC：氯化铵，20 kg N ha ^-1 ), 控释包衣尿素 (CRCU: 氯化铵, 5 kg N ha ^-1 , 包衣尿素, 15 kg N ha ^-1 , 总计 20 kg N ha ^-1 ), 控释包衣硝酸盐 (CRCN: 包衣硝酸钙, 20 kg N ha ^-1），CRCU 降低（CRCU-R：10 kg N ha ^-1)、降低的 CRCN (CRCN-R: 10 kg N ha ^-1 ) 和无氮肥 (NF: 0 kg N ha ^-1 )。该田地的土壤被归类为 Gleyic Fluidol。

CRCN处理的年N ₂ O排放量在第一年和第二年显着低于AC（p < 0.05），并且在第三年没有显着差异，减少了17-32％，而相同产量保持不变。三年来，CRCU 处理的年 N ₂ O 排放量往往低于 AC，减少了 14-19%，尽管没有统计学意义。这表明涂层硝酸盐肥料在减少 N ₂ O 排放方面更有效，因为硝酸盐仅通过反硝化作用产生这种气体。此外，N ₂CRCU-R 和 CRCN-R 处理的 O 排放量分别比 AC 处理低 22-37% 和 24-41%。尽管在统计上不显着，但这些减少量略大于CRCU 和CRCN的N ₂ O 排放量，表明通过降低施用率进一步减少N ₂ O 排放量的效果。此外，由于连续三年使用控释肥料，单位产量N ₂ O排放量呈下降趋势，并由于施用量减少而进一步下降。总之，在由稻田改造的大豆田中，使用降低施用量的控释肥料可被视为一种改进的气候智能型土壤管理。