施肥对稻田温室气体排放及土壤养分的影响

郭腾飞, 梁国庆*, 周 卫, 刘东海, 王秀斌, 孙静文, 李双来, 胡 诚

(1中国农业科学院农业资源与农业区划研究所，北京 100081; 2 湖北省农业科学院植保土肥研究所，湖北武汉 430064)



施肥对稻田温室气体排放及土壤养分的影响

郭腾飞1, 梁国庆1*, 周 卫1, 刘东海2, 王秀斌1, 孙静文1, 李双来2, 胡 诚2

(1中国农业科学院农业资源与农业区划研究所，北京 100081; 2 湖北省农业科学院植保土肥研究所，湖北武汉 430064)

施肥; 稻田; 温室气体; GWP; GHGI; 产量; 土壤养分

已有研究表明，合理的施肥措施可以通过提高土壤碳库或减少CH4和N2O排放来降低温室气体的增温潜势，稻田可具有较大的温室效应减缓潜力[9]。Zou等[10]研究指出有机物料的投入会增加全球增温潜势，因此不建议施肥中投入有机肥，而Zhao等[11]研究表明将秸秆转化为生物碳可以减缓CH4排放，提高产量和土壤肥力。Das等[12]认为秸秆还田以及施入家禽粪肥对比单施化肥增加了温室气体增温潜势，然而在农业生产中同样不能忽视有机肥对产量和土壤肥力的积极影响[13]，本研究针对长江中下游典型的稻麦轮作区，在当地习惯施肥的基础上设置减氮和有机无机配施等不同优化施肥措施，研究其对稻季CO2、CH4、N2O的排放及其综合温室效应和土壤养分状况的影响，从而为农田可持续生产、温室气体减排提供依据。

1　材料和方法

1.1试验地概况

1.2试验设计

大田试验设置5个处理: 1)不施氮肥(CK); 2) 当地习惯施肥，氮(尿素)施用量为225 kg/hm2(FP); 3)尿素-N 165 kg/hm2(OPT); 4)有机肥N 33 kg/hm2+尿素-N 132 kg/hm2(OPT+M); 5)秸秆N 33 kg/hm2+尿素-N 132 kg/hm2(OPT+S)。每个处理3次重复，小区面积为40 m2，随机区组排列。小区田埂嵌入水泥砖并用覆膜覆盖，防止灌水后小区之间串水串肥。供试磷、钾肥分别为过磷酸钙和氯化钾，有机肥为江苏田娘农业科技有限公司产有机肥(C/N =21.72)，秸秆为上一季收获麦秆(C/N =86.59)。FP处理磷(P2O5)用量为 75 kg/hm2，其他处理均为 60 kg/hm2; 钾(K2O)用量均为 90 kg/hm2; FP处理氮肥基肥与分蘖肥比1 ∶1，其余处理均为基肥分蘖肥和穗肥比为4 ∶3 ∶3。磷肥、有机肥和秸秆全部基施，钾肥FP处理全部基施，其他处理基肥穗肥各半。田间管理措施同当地常规管理一致。

1.3采样方法及测定指标

CH4、N2O、CO2排放通量计算公式如下[16]:

F=ρ·h·dc/dt·273/(273+T)

(1)

其中，F为排放通量[以CH4和N2O计时为 mg/(m2·h), 以CO2计时，为g/(m2·h)]; ρ 为CH4、N2O、CO2在标准状态下的密度(kg/m3); h 是采样箱高度(m); dc/dt 为采样过程中采样箱内CH4、N2O、CO2的浓度变化率(ppmv/h); T 为采样时箱内的平均温度(℃); 273为气态方程常数。

1.4数据处理与分析

1)全球增温潜势(GWP)是将各种温室气体的季节排放总量(kg/hm2)的增温潜势换算为CO2当量，CH4和N2O在100 年尺度上为CO2的25倍和298倍[17]。计算公式为:

TCDE=CDE(CH4)+CDE(N2O)

(2)

2)温室气体排放强度(GHGI)是CH4和N2O总增温潜势同作物产量的比值，是综合评价各处理的温室效应的指标[18]。

GHGI=TCDE/Y

(3)

式中，TCDE为CH4和N2O综合增温潜势(CO2kg/hm2); Y为该处理单位面积平均产量(t/hm2)。

所有试验数据运用Excel 2010进行统计，Origin9.0作图，SAS 9.0进行方差分析。

2　结果与分析

2.1稻田CH4、N2O、CO2排放特征

对甲烷排放特征分析得出，各处理CH4排放通量变化趋势均呈先升高后降低的单峰曲线，除FP处理在移栽后第12 d达到最大峰值外，其余处理均在移栽后的第8 d达到最大峰值(图1)。其中CH4平均排放通量大小顺序为OPT+S>OPT+M> FP> OPT>CK，平均排放通量依次为6.65、5.75、5.69、4.94和4.58 mg/(m2·h)(表1)。就整个生育期的排放特征而言，不同处理CH4排放均主要集中在水稻生长前期，在中期复水后第38 d有小的排放峰值，生长后期几乎没有CH4排放，这与众多关于稻麦轮作农田CH4排放规律的研究结果一致[19-21]。

水稻季CO2排放呈现多峰趋势，主要排放分布在水稻生长返青期和孕穗期，主要由于水稻移栽前的耕作，使得土壤通气性良好，有利于CO2的产生和排放[24]，而且孕穗期水热条件良好促进了稻田呼吸作用。不同施肥处理下水稻生长季CO2平均排放顺序为OPT+S > OPT+M>FP >OPT >CK，这与CH4排放大小顺序一致。对比FP处理，有机肥及秸秆还田均增强CO2的排放，其中秸秆还田增加最为明显，表明投入有机物料增加稻田土壤有机质积累促进土壤呼吸[25]。

图1　不同施肥处理对稻田CH4、N2O和CO2排放的影响Fig.1　Effects of different fertilizer treatments on CH4, N2O and CO2 emissions from the paddy field

2.2稻田温室气体排放季节总量

稻田是甲烷的主要排放源。由表1可知，不同处理的CH4季节总排放量顺序为OPT+S>OPT+M> FP>OPT> CK。与CK相比，四种不同施肥处理的CH4季节总排放量均显著提高，无论化肥还是有机肥均增加了稻田CH4的排放，其中秸秆还田OPT+S显著高于其余处理。伴随秸秆还田，土壤中有机碳增多，产生CH4前体增加，有效促进CH4排放[26]。OPT处理CH4的排放小于FP处理，说明稻田CH4排放随氮肥用量增加而增加。

稻田N2O的排放量很少，整个生育期总排放顺序为: FP>OPT+M>OPT> OPT+S >CK。N2O的排放量随施氮量的增加而增加。不同于增加CH4排放，秸秆还田减少了稻田N2O的排放并且减排效果显著，这同Vanlauwe等[27]研究结果一致。然而有机肥替代比单施化肥增加了稻田N2O排放，这可能与投入土壤有机物料的C/N比及其腐熟程度有关[26]。

另外，不同处理稻田CO2排放大小顺序为OPT+S>OPT+M> FP>OPT> CK，同CH4趋势一致。相比化肥，有机肥以及秸秆还田提高了CO2排放量。

表1　不同施肥处理CH4, N2O和CO2平均排放量与排放总量

注(Note): CK—无氮肥对照 No N fertilizer; FP—习惯施肥Farmer’s customary fertilization; OPT—推荐氮量 Optimum N rate; OPT+M—推荐氮肥+猪粪 OPT plus manure; OPT+S—推荐氮肥+秸秆OPT plus wheat straw return. 同列数值后不同字母表示差异达到5%显著水平Values followed by different letters are significantly different among fertilizer treatments at 5% level.

2.3稻田温室气体的综合温室效应

由表2可以看出，在100 a尺度下不同处理的增温潜势大小同其CH4季节总排放量顺序相同，由于稻田排放N2O的量非常少，因此稻季CH4对温室气体综合增温潜势影响明显，稻田减缓温室气体增温潜势的主要目标就是减少CH4排放。对比当地习惯施肥，OPT、OPT+M和OPT+S三种优化施肥措施中，单施化肥OPT处理同时减少CH4和N2O的排放，增温潜势显著降低了9.1%，OPT+M处理同时增加CH4排放减少N2O的排放，增温潜势基本相同，而秸秆还田由于显著增加了CH4排放，同时显著减少N2O的排放，其增温潜势增长幅度较小仅为0.72%。

对不同处理产量进行分析得出，OPT、OPT+M和OPT+S三种优化施肥措施相对于FP处理都增加了水稻产量，增产率分别为3.6%、14.3%和8.5%，均在减少化肥施用的情况下获得增产，其中OPT+M处理增产最明显。

表2　不同处理综合增温潜势和温室气体排放强度

注(Note): E-CH4—100年尺度下排放的甲烷相当的CO2当量 CO2equivalent of CH4emitted on a scale over 100 years; E-N2O—100年时间尺度下排放的N2O相当的CO2当量CO2equivalent of N2O emitted on the scale over 100 years. 同列数值后不同字母表示差异达到5%的显著水平 Values followed by different letters are significantly different among fertilizer treatments at 5% level.

温室气体排放碳强度(GHGI)是一项可综合温室效应与产量而评价温室效应的指标[28]。不施氮肥不仅降低作物产量，而且不断消耗土壤肥力(表2、表3)，因此在本研究中不考虑其温室气体排放强度。由表1可知，温室气体排放碳强度顺序为FP(0.56)>OPT+S(0.52)> OPT(0.50)>OPT+M(0.49)，其中OPT和OPT+M显著低于当地习惯施肥处理，OPT+M温室气体排放强度最低，是综合温室效应评价下最佳处理。

2.4不同处理对土壤养分状况影响

表3　不同施肥处理下土壤养分状况

注(Note): 表中数据为平均值±标准误Data are means ± SE,n=3; 同列数值后不同字母表示差异达到5%显著水平 Values followed by different letters are significantly different among fertilizer treatments at 5% level.

3　讨论与结论

目前针对不同施氮量及不同施肥措施对温室气体排放影响已有较多报道，结论尚不一致[34-36]。本研究结果显示，调控氮磷施肥OPT处理较当地习惯施肥减少了CH4和CO2排放，同时显著降低N2O排放，邬刚等[34]报道了调控施肥配比与当地传统施肥相比可显著降低N2O排放量，此外刘运通等[37]也得出了优化施肥可以显著降低N2O排放的结论。本试验中有机肥无机肥配施(OPT+M)和秸秆还田(OPT+S)都促进了CH4和CO2的排放，有研究指出施用有机肥可以改善土壤有机质来促进植物根系的生长和活力以及土壤微生物活性，从而促进CO2的排放[25]，并且有机肥和秸秆中含有比较容易被分解的易矿化碳，这样就为CH4排放提供大量前体[38]。

有机肥施用对稻田N2O排放的影响结果尚不一致，有研究[39-40]表明施用有机肥能够减少稻田N2O的排放，原因可能是化学肥料适合硝化和反硝化反应作用，使氮素随着水稻生育期分解较为彻底，从而导致N2O排放较高; 同时也有施用有机肥可以增加N2O排放的报道[41-42]，邹建文等[19]研究得出N2O排放不但受到土壤的供氮水平和外源碳氮供应的影响、土壤微生物对有机碳的分解作用及对氮的竞争、作物对氮利用等因素制约，而且跟有机肥料的类型和腐熟程度有关。土壤C/N是影响N2O排放的重要因素，在稻田生态系统中投入有机物料的C/N，数量和种类是影响氮素矿化与固定的主要环境因子[43]。在我们的研究中投入C/N为86.59的小麦秸秆进入稻田，异养微生物对氮的利用起主导作用并且和硝化细菌竞争氮源，从而促进了植物可利用氮的固定，因此减少了反应生成N2O的底物[12，44]。而施用有机肥(C/N=21.72)，有机物料的分解产生了大量易矿化碳，促进反硝化细菌的生长，最终产生更高的N2O的排放[45]。

温室气体排放强度是温室效应综合评价指标，其将温室效应与作物经济产出相结合，用于评价稻田综合温室效应。本研究中，OPT+M处理增温潜势最小，即单位产量的产出所排放温室气体产生的增温潜势最小，为本试验的评价体系下的最优处理。本试验中，秸秆还田对比习惯施肥和OPT处理均增加了稻田产量，但由于显著增加了CH4排放量使其GHGI大于其它处理，因此秸秆还田处理增温潜势不能作为最佳发展可持续农业的选择，目前相关的报道只是按照严格施肥类型来加以对比，如果考虑到将其它处理的秸秆因饲料、焚烧或丢弃于田间，最终以温室气体计算的话，结果还有待深入研究。本试验中秸秆还田对改善土壤养分的趋势明显(表3)，秸秆还田可以稳定甚至提高土壤的有机碳贮量，增加农田总固碳量[49]; Pan等[50]认为，稻作农业的土壤固碳潜力十分突出。因此，综合农学效应，环境效应及经济效应，对秸秆还田还需进一步研究。

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Effect of fertilizer management on greenhouse gas emission and nutrient status in paddy soil

GUO Teng-fei1, LIANG Guo-qing1*, ZHOU Wei1, LIU Dong-hai2, WANG Xiu-bin1, SUN Jing-wen1, LI Shuang-lai2, HU Cheng2

(1InstituteofAgriculturalResourceandRegionalPlanning,CAAS,Beijing100081,China;2InstituteofPlantProtectionandSoilFertilization,HubeiAcademyofAgriculturalSciences,Wuhan430064,China)

【Objectives】 The impact of greenhouse gas caused by the agricultural activities on global warming has been recognized broadly. The aim of this study was to evaluate the effects of different fertilizer treatment on greenhouse gas emissions, crop yield and soil fertility of paddy soil. 【Methods】 The fertilization treatments were designed under the rice-wheat rotation system in Yangtze River as follows: no nitrogen fertilizer (CK), farmer’s customary fertilization (FP), optimum N fertilization (OPT), OPT plus manure (OPT+M), and OPT plus wheat straw return (OPT+S). Static opaque chamber method was used to measure the CH4, N2O and CO2flux during the rice-growing season and the global warming potential (GWP). The crop yield, carbon emission intensity and soil chemical property of rice production (GHGI) were comprehensively evaluated and a fertilizer management system was proposed.【Results】 1) The cumulative emission of CH4in different treatments was in order of OPT+S>OPT+M>FP>OPT>CK (99.02-143.69 kg/hm2), that of NO2was FP>OPT+M>OPT>OPT+S >CK (0.95-3.57 kg/hm2), and that of CO2showed the same trend as CH4’s, ranging from 7231.64 to 13715.24 kg/hm2. 2) Calculated as the CO2-equivalents on the scale over 100 years, the GWP from the CH4and N2O emissions in different treatments were in order of OPT+S>OPT+M> FP> OPT> CK. The contribution of N2O to the total GWP were only 10.31%，26.39%，21.51%，22.91%, and 11.58%, and that of CH4were 89.69%，73.61%，78.49%，77.09% and 88.42% in CK, FP, OPT, OPT+M and OPT+S respectively. The overall assessment of the GWP was dominated by CH4emissions and much lower by N2O. The rice yield in treatment of OPT, OPT+M and OPT+S was 3.6%, 14.3% and 8.5% more than in FP. The most significant yield increase was obtained in treatment of the combined application of organic manure with chemical fertilizer. 3) The GHGI was in order of FP(0.56)>OPT+S(0.52)> OPT(0.50)>OPT+M(0.49). The GHGI in treatment OPT and OPT+M were significantly lower than in FP, and the lowest value was in OPT+M. 4) The highest soil organic carbon, total nitrogen, available phosphorus and potassium content were all appeared in the OPT+S treatment. 【Conclusion】 Fertilization influence the emissions of CH4, N2O and CO2. The application of manure and chemical nitrogen fertilizer increase the emissions of all the three greenhouse gases, the straw return increases the emissions of CO2and CH4, but reduces that of N2O. Mitigation of CH4emissions should be considered in the paddy soil with priority. As the chemical fertilizer plus manure (OPT+M) produces the lowest GHGI, the pattern is recommended as relatively better fertilizer management in this region. Although the straw return will increase the emission of CO2from soil, it is still a prosperous management as it could reduce the total CO2emission from possible burning of straw. Further research on proper amount of straw return should be conducted.

fertilization; paddy soil; greenhouse gas; GWP; yield; GHGI; soil nutrient

2014-12-10接受日期: 2015-01-20网络出版日期: 2015-02-13

国家自然科学基金项目(31471943); 国家重点基础研究发展计划项目(2013CB127401)资助。

郭腾飞(1991—)，男，河南宝丰人，硕士研究生，主要从事农业可持续利用方面的研究。E-mail: tracygtf@163.com

E-mail: liangguoqing@caas.cn

S506.2; X16

A

1008-505X(2016)02-0337-09