稻草生物炭对干湿交替稻田CH_(4)和N_(2)O排放的影响

Effects of rice straw biochar on CH_(4)and N_(2)O emissions in alternating wetting and drying rice fields

为探究稻草生物炭和灌溉方式对稻田CH_(4)和N_(2)O排放的影响,揭示生物炭在干湿交替稻田中的应用潜力,该研究采用大田裂区试验,设置常规淹灌(ICF)和干湿交替灌溉(IAWD)2种灌溉方式,不施生物炭(B0)和施20 t/hm^(2)生物炭(B_(2)0)2种施炭水平,连续3 a对稻田CH_(4)、N_(2)O排放和水稻产量进行了观测研究。结果表明:与ICF相比,IAWD在显著降低CH_(4)排放(63.03%~78.89%)的同时也促进了N_(2)O排放(100%~122.67%)。生物炭施加首年对CH_(4)排放无显著影响,但第2年和第3年分别显著减少CH4排放21.99%和38.21%;而对N_(2)O排放3 a均起到抑制作用,降幅达28.26%~33.10%。生物炭3 a平均增加土壤有机碳27.03%。施生物炭第1年水稻略有减产,但第2和第3年表现为正效应。主要是由于初期秸秆生物炭碱性较大,表现出了明显的石灰效应;但随着pH值逐步恢复正常后,生物炭固碳减排和缓释增效特性逐渐显现。尤其在2021年,B20较B0增产11.02%,显著降低37.50%的全球增温潜势(global warming potential,GWP)和42.86%的温室气体排放强度(greenhouse gas intensity,GHGI);同时,在B0条件下,IAWD较ICF增加137.21%的N_(2)O排放,但B20条件下降低IAWD处理32.52%的N_(2)O排放,有效抑制IAWD对N_(2)O排放增加的负面效应。整体来看,与ICFB0处理相比,IAWDB20处理显著降低CH4排放,降幅为83.78%,同时降低77.98%的GWP和78.95%的GHGI。该研究为揭示生物炭固碳减排的正效应及其在稻田生态系统中的应用潜力,同时全面探究其对稻田增产、CH_(4)和N_(2)O排放的年限影响,为缓解实际稻田生产过程中CH_(4)和N_(2)O的排放,实现稻田绿色、高效、可持续生产提供理论依据。

Biochar is widely used as one type of soil amendment to enhance soil properties and carbon sequestration in croplands.But it is still unclear on the influence of rice straw biochar application on CH_(4)and N_(2)O emissions from paddy fields,especially in Northeast China.The typical rice monoculture region is often used under the alternate regime of wetting and drying(IAWD)with the aging of biochar in soil.This study aims to further investigate the potential of biochar application in IAWD paddy fields.A split-plot field was designed with two irrigation regimes,two biochar additions,and three replications in 2019-2021.Among them,the irrigation regimes(I)included continuous flooding irrigation(ICF)and IAWD.The sub-plots within each main plot were subjected to two biochar(B)additions(biochar-free control and 20 t ha-1 biochar,represented by B0 and B20,respectively).Prior to the experiment,the surface soil was first sampled in the rice fields and then air-dried to measure the basic physicochemical parameters of the soil.Biochar was applied one day before transplanting in 2019.After that,there was no additional biochar in 2020 and 2021.The opaque static chamber was used to collect the CH_(4)and N_(2)O emissions over 3-4 days after topdressing,and 7-10 days between rice transplanting and harvesting.Gas samples were finally obtained to measure the CH4 and N_(2)O concentration using gas chromatograph(Agilent 7890B,Agilent Technologies,Inc.,USA).Results showed that the IAWD significantly reduced the CH_(4)emission by 63.03%-78.89%,global warming potential(GWP)by 62.02%-75.21%,greenhouse gas inventory(GHGI)by 62.31%-75.28%,compared with the ICF,although there was an increase in the N_(2)O emission of 100%-122.67%.The B20 treatment reduced the CH4 emission by 21.99%in 2020,and 38.21%in 2021,whereas,there was an increase in the soil organic carbon by 24.03%-28.88%,and N_(2)O emission by 28.26%-33.10%over three years.Moreover,biochar was used to inhibit the negative effect of IAWD on the increase of N_(2)O emissions.A correlation analysis showed that there was a significant negative correlation in the cumulative CH_(4)emissions with the soil redox potential(Eh)value,and soil organic carbon(SOC),whereas a significant positive correlation was found with the soil temperature.There was a significant negative correlation between the cumulative N2O emission and soil temperature,whereas,a significant positive correlation was between the soil Eh value.A positive effect of rice production was found in the second and third years,although there was a slight decrease in the first year of biochar application.The main reason was that the early straw biochar was more alkaline with a limited effect.A synergy effect was found in the biochar adsorption emission reduction and slow release with the pH value to the normal,indicating the increasing production.Especially,the B_(2)0 treatment significantly reduced GWP by 37.50%and GHGI by 42.86%in 2021,whereas there was an increase of 11.02%,compared with the B0.The IAWD B_(2)0 treatment reduced the CH4 cumulative emissions by 83.78%,GWP by 77.98%,and GHGI by 78.95%,compared with the ICF B0.It infers that the biochar combined with IAWD can be used to effectively reduce the GWP and GHGI.Anyway,biochar can be expected to reduce carbon sequestration and CH_(4)and N_(2)O emissions in paddy fields.The finding can also provide a strong theoretical reference to mitigate the CH_(4)and N_(2)O emissions after the biochar application in rice fields.