氮肥与生物炭施用对稻麦轮作系统甲烷和氧化亚氮排放的影响

【目的】以我国稻麦轮作系统为对象,研究氮肥和小麦秸秆生物炭联合施用对CH4和N2O排放规律的影响;结合小麦和水稻总产量进而评估对该生态系统综合温室效应(GWP)和温室气体强度(GHGI)的影响,为生物炭在减缓全球气候变化及农业生产中的推广应用提供科学依据。【方法】生物炭通过小麦秸秆在300 500℃条件下炭化获得。田间试验于2012年11月至2013年10月进行,为稻麦轮作体系。采用静态暗箱—气相色谱法观测CH4和N2O排放通量;试验共设置不施氮肥不施生物炭(N0B0)、不施氮肥施20 t/hm2生物炭(N0B1)、施氮肥不施生物炭(N1B0)、氮肥与20 t/hm2生物炭配施(N1B1)、氮肥与40 t/hm2生物炭配施(N1B2)等5个处理,各处理3次重复。【结果】单施氮肥(N1B0)与不施氮肥(N0B0)处理相比,增加了稻麦轮作产量82.8%,增加了CH4排放0.6倍,增加了N2O排放5.5倍。单施生物炭(N0B1)与不施生物炭(N0B0)处理相比,显著增产25.4%,却不能减少CH4和N2O的排放。在施氮的同时,配施20 t/hm2生物炭与单施氮肥处理相比,显著增加稻麦轮作产量21.6%,小麦和水稻总产量也比配施40 t/hm2生物炭处理高;配施40 t/hm2生物炭与单施氮肥处理相比,显著降低稻麦轮作系统CH4排放11.3%和N2O排放20.9%,CH4和N2O排放量也比配施20 t/hm2生物炭的排放量低。随着生物炭配施量的增加,CH4和N2O减排效果更明显。单施生物炭并不能有效地减少GWP,但却可以显著增加作物产量,从而减小GHGI。对N0B0、N0B1、N1B0、N1B1四个处理进行双因素方差分析发现,氮肥和生物炭在CH4和N2O排放、作物产量、GWP和GHGI方面都不存在明显的交互作用。各处理在100 a时间尺度上总GWP由大到小的顺序为N1B0N1B1N1B2N0B0N0B1,GHGI值由大到小的顺序则为N1B0N1B1N0B0N1B2N0B1。单施生物炭与配施生物炭都能降低稻麦轮作系统的GWP和GHGI,配施40 t/hm2生物炭处理降低效果更好。【结论】稻田麦季施用不同水平生物炭都能在保产或增产的同时,降低稻麦轮作系统CH4和N2O的排放及GWP和GHGI。在当前稻麦轮作系统中,与20 t/hm2的生物炭施用量相比,40 t/hm2的生物炭施用量显著降低GWP,但增产效果不明显,因此二者GHGI相当,需要根据温室效应与作物产量权衡选择生物炭实际施用量。

Combined effects of nitrogen fertilization and biochar incorporation on methane and nitrous oxide emissions from paddy fields in rice-wheat annual rotation system

【Objectives】The potentials of biochar application in mitigating global warming in agriculture systems need assessed through field experiments. The effects of combined N fertilization and biochar incorporation on the global warming potential(GWP)caused by CH4 and N2O emissions, the greenhouse gas intensities(GHGI), and grain yield are need to be investigated to provide a scientific base for the biochar application in a rice-wheat annual rotation system. 【Methods】Biochar used in the study was prepared by carbonization of wheat straw at 350-500℃. A field experiment was carried out during the wheat and rice seasons between November 2012 and October 2013. Five treatments were adopted in triplicate: no N fertilization without biochar amendment(N0B0), no N fertilization with 20 t/hm2 biochar amendment(N0B1), 250 kg/hm2 N fertilization without biochar amendment(N1B0), 250 kg/hm2 N fertilization with 20 t/hm2 biochar amendment(N1B1), 250 kg/hm2 N fertilization with 40 t/hm2 biochar amendment(N1B2). The CH4 and N2O gas emission fluxes were monitored with a static chamber and gas chromatography method.【Results】In N1B0 treatment, the yield of rice and wheat was increased by 82.8%, the CH4 and N2O emissions were 1.6 and 6.5 times of those in N0B0 treatment. In N0B1 treatment, the wheat and rice production was significantly increased by 25.4%, no pronounced difference in CH4 and N2O emissions was found with in the N0B0 treatment. In contrast with the N1B0 treatment, CH4 emission decreased by 3.7% and 11.3%(P＜0.05), N2O emission decreased by 6.1% and 20.9%(P＜0.05), the yield of rice and wheat increased by 21.6%(P＜0.05)and 10.0% in the N1B1 and N1B2 treatments, respectively. The N1B2 treatment significantly reduced the CH4 and N2O emissions than in N1B1 treatment. The mitigation effect on CH4 and N2O emissions became more noticeable with higher biochar amendment. Based on a 100 years horizon, the order of ranks in the annual total GWPs of CH4 and N2O total emissions over the entire rotation cycle was N1B0 N1B1 N1B2 N0B0 N0B1, the GWPs per unit crop grain yield were in order of N1B0 N1B1 N0B0 N1B2 N0B1. Significant difference in the GWPs existed between the treatments with and without N fertilizer, not in the GHGIs. There was no significant difference between the N0B0 and N0B1 treatments in the GWPs, but significant in the GHGIs. The noticeably higher GWP and GHGI were found in the N1B0 than in other treatments, which indicated that the single N fertilization could increase the GWP and GHGI. Both nitrogen and biochar combination treatments could reduce the GWP and GHGI. The single biochar amendment did not effectively reduce the GWP, but significantly increased crop yield and reduced GHGI. A two-way analysis of variance for treatments of N0B0, N0B1, N1B0 and N1B1 indicated that no obvious interaction between N fertilizer and biochar on CH4 and N2O emissions, crop yield, GWP and GHGI. All the single biochar application and the combined application with N fertilizer could reduce the GWPs and GHGIs, and biochar incorporation of 40 t/hm2 produced better results than that of 20 t/hm2. 【Conclusion】 The single N fertilization, and the biochar and N incorporation in wheat season increase the wheat and rice production, decrease CH4 and N2O emissions, thus simultaneously lowered GWP and GHGI in a rice-wheat rotation system. Biochar amendment of 40 t/hm2 could mitigate more GHG emissions than that of 20 t/hm2, while improved insignificant grain yields. Thus the two biochar amendments produce comparable GHGI. It is therefore an unanswered issue for decision when balanced between GHG mitigation and grain yield.