耕作方式转变对冬小麦季农田温室气体排放和产量的影响*

赵力莹, 董文旭, 胡春胜**, 李佳珍, 陈 拓



耕作方式转变对冬小麦季农田温室气体排放和产量的影响*

赵力莹1,2, 董文旭1, 胡春胜1**, 李佳珍1,2, 陈 拓1,2

(1. 中国科学院遗传与发育生物学研究所农业资源研究中心/中国科学院农业水资源重点实验室/河北省节水农业重点实验室 石家庄 050022; 2. 中国科学院大学 北京 100049)

合理耕作方式对农业可持续生产和减缓全球气候变化有重要意义。为评价耕作方式转变对农田温室气体排放的影响, 本研究针对连续16年的长期旋耕小麦/玉米农田进行不同的轮耕处理, 采用原位静态箱-气相色谱法分析了小麦季农田土壤3种温室气体CH4、CO2、N2O排放规律。试验共设3个处理: 在前期旋耕基础上分别进行翻耕处理(XF)和深松处理(XS), 另外保持旋耕(X)作为对照。试验结果表明: CO2排放通量在耕作后1周有明显排放峰, XF处理显著低于X和XS处理; N2O排放通量在耕作和灌溉施肥后有明显排放峰, XS处理显著高于XF和X处理; 两种气体排放通量在越冬期出现最低值。CH4从耕作后到越冬期有持续明显的吸收过程, 其中XS处理的吸收通量显著高于XF和X处理。农田土壤在冬小麦生长季表现为CO2的源, 累积排放量为XS(5 241 kg·hm-2)>X(5 160 kg·hm-2)>XF(4 840 kg·hm-2), XS与X处理间差异不显著, 均显著高于XF; N2O的源, 累积排放量表现为XS(4.38 kg·hm-2)>XF(2.39 kg·hm-2)>X(2.26 kg·hm-2), XS与XF处理间差异不显著, 均显著高于X处理; CH4的汇, 累积吸收量为XS(6.14 kg·hm-2)>XF(5.64 kg·hm-2)>X(3.70 kg·hm-2)。将累积温室气体换算为CO2当量, 对增温效应的贡献表现为XF(5.32 t·hm-2)

冬小麦; 旋耕; 翻耕; 深松; 温室气体; 产量

由温室气体引发的全球气候变暖和臭氧层破坏已成为全世界面临的严重环境问题[1]。而我们赖以生存的农业向大气中贡献了大量的CH4、CO2和N2O[2]。农业产生的温室气体通量是复杂且异质的, 但是可以通过有效的农业管理系统实现减排[3]。长期单一的耕作方式会使农田土壤环境不利于作物生长发育[4], 如长期翻耕因作业深度浅及机械碾压等因素加剧耕层变浅, 导致养分库容降低[5]; 长期深松的土壤有机碳、氮储量表现为表层富集现象[4], 农作物病虫害加重[6]; 而长期旋耕使土壤耕层变浅[7], 亚表层容重增加[8], 土壤的紧实度增大[9], 使养分易聚集在土壤表层, 不利于作物根部对养分的吸收, 影响作物的产量, 且长期旋耕的土壤表现为碳的净损失[10], 不利于土壤质量提高和农田碳减排。农田土壤采用单一耕作模式, 导致土壤肥力和作物产量衰减期, 而实行不同的土壤轮耕模式有利于保持和提高土壤肥力, 确保持续高产[11]。

耕作方式对农田温室气体的产生与排放有重要影响。Badagliacca等[12]发现相比于常规翻耕, 免耕通过增加土壤容重、孔隙(WFPS, water-filled pore space)提高可获得有机碳量进而促进土壤N2O排放, 导致N2O排放量增加。Zhu等[13]在13年长期耕作试验发现相比于常规翻耕, 免耕减少土壤N2O排放的同时减少了CO2的排放。Lamptey等[14]发现与翻耕和旋耕相比, 免耕和深松增加了土壤孔隙度和土壤饱和导水率, 使土壤排放CO2量显著降低。

但大多数学者多集中在对长期不同耕作方式下温室气体排放规律和总量的研究[15-18], 对在长期旋耕基础上改变耕作方式后温室气体排放特点及对增温效应的贡献研究鲜有报道。而华北平原是我国小麦()主产区, 小麦的产量占全国的41%[19], 对华北平原小麦季温室气体排放的研究有很好的代表性, 且该地区近年来的常规耕作方式为旋耕[20], 相对于免耕而言, 旋耕促进了农田土壤CO2、N2O的排放[21-24], 加强了对CH4的吸收[25-26], 但针对华北平原长期旋耕后调整耕作方式对温室气体排放的影响少有研究。一方面, 长期浅旋耕农田经深耕后会增加土壤扰动, 促进微生物活动而增加CO2等气体排放; 另一方面深耕使上下土层翻转, 把长期旋耕累积表层有机质翻转到下层, 可能会抑制CO2排放而有利于有机碳积累。鉴于此, 本研究设置长期旋耕、长期旋耕后深松和翻耕3种耕作处理, 研究不同耕作方式对温室气体排放规律、排放量、增温效应的贡献和小麦产量的影响, 探索生态效益和产量收益“双赢”的轮耕方式, 为调整本地区农田的耕作模式和分析温室气体排放规律提供理论依据。

1 材料与方法

1.1 试验区概况

试验地设在中国科学院栾城农业生态系统试验站(114°40′E, 37°50′N), 处于太行山山前平原的中部位置, 平均海拔为50.1 m。属于半湿润半干旱季风气候, 雨热同期, 年平均气温为12.3 ℃, 年平均降水440 mm, 小麦季气温和降雨情况如图1所示。年辐射总量543.3 kJ·cm-2, 年日照时数2 608 h, 种植制度为冬小麦-夏玉米()一年两熟。耕层土壤为粉壤土(含13.8%砂粒、66.3%粉粒、19.9%黏粒)。试验区土壤基本理化性质: 全氮1.06 g·kg-1, 碱解氮111.83 mg·kg-1, 速效磷6.00 mg·kg-1, 速效钾106.37 mg·kg-1。

图1 试验年份研究区冬小麦季日平均温度(a)和降雨量(b)

1.2 试验设计

该试验在长期旋耕试验地上进行(始于2001年)。在冬小麦-夏玉米的轮作制度下, 从2016年夏玉米后, 对耕作处理进行调整, 包括长期旋耕(X)、在长期旋耕上改为翻耕(XF)和长期旋耕改为深松(XS)3个处理, 各处理重复4次。具体措施如下: X, 夏玉米机械收获, 之后玉米秸秆粉碎还田, 旋耕机进行旋耕(耕深为10~12 cm), 冬小麦机械播种, 小麦机械收获, 小麦秸秆粉碎还田, 玉米机械播种, 最后玉米机械收获; XF, 夏玉米收获, 玉米秸秆粉碎还田, 铧式犁进行翻耕(耕深为15~18 cm), 冬小麦机械播种, 小麦机械收获, 小麦秸秆还田, 玉米机械播种, 最后玉米机械收获; XS, 夏玉米机械收获, 之后玉米秸秆粉碎还田, 震动深松铲深松(耕深为23~25 cm), 冬小麦机械播种, 小麦机械收获, 小麦秸秆还田, 玉米机械播种, 最后玉米机械收获。

供试冬小麦品种为‘科农2011’。冬小麦于2016年9月10日播种, 2017年6月初收获, 播种量为187.5 kg·hm-2, 行距为15 cm。在耕作前各处理均施底肥(2016年9月10日), 施肥量为375 kg·hm-2磷酸二铵(N=67.5 kg·hm-2, P2O5=172.5 kg·hm-2)和225 kg·hm-2(N=67.5 kg·hm-2)尿素, 在2017年4月23日表面撒施尿素225 kg·hm-2(N=67.5 kg·hm-2)进行追肥和灌溉。灌溉方式为喷灌。

1.3 测定项目和方法

1.3.1 气体采集与分析

气体采集用常用的静态箱法。采样箱由顶箱和底座两部分组成, 顶箱用透明的有机玻璃制成, 底座用聚乙烯塑料制成, 采样箱的宽、长、高为20 cm、60 cm、40 cm。采气频率为耕作后两周内2~3 d一次, 施肥、降水、灌溉后3 d内采一次, 其他时间每两周采一次; 采气时间为上午9:00—11:00。耕作后, 将底座插入到土壤中固定, 在小麦整个生长季不再移动, 去除底座里面的所有植物。采样时, 在底座的槽内填一定量的水, 然后将顶箱扣在底座的槽内, 同时将箱顶的风扇打开来混匀箱内空气。在扣箱0 min、15 min、30 min后, 用注射器从箱顶取样器口抽取50 mL气体打到真空状态下的气袋内, 并记录箱内空气的温度, 30 min后记录地表土壤温度。每次采完气后, 将顶箱移走, 保留底座不动。每个小区4个重复。

采完气后立即将气袋带回实验室, 采用CA-6气体样品进样仪进样, 用Agilent6820(G1180A)型气象色谱仪分析CO2、N2O、CH4, 采气后24 h内测完。CO2和CH4的检测器为FID(氢火焰离子检测器), 检测器温度为200 ℃, 柱箱温度为55 ℃, 载气(高纯N2)流速为30 mL·min-1, 助燃气(空气)流速为400 mL·min-1, 燃气(H2)流速30 mL·min-1。N2O检测器为ECD(电子捕获检测器), 检测器温度为330 ℃, 柱箱温度为55 ℃, 载气(高纯N2)流速为30 mL·min-1。

1.3.2 气体通量与总量计算

温室气体排放通量计算公式[27]:

式中:为气体的排放通量(mg·m-2·h-1),为目标气体标准状态下的密度(kg·m-3),为采样箱内高度(m),分别为采样箱内的实际温度(℃),为箱内目标气体浓度随时间变化的回归曲线斜率。

温室气体排放总量计算公式[28]:

式中:为农田土壤排放气体总量(kg·hm-2),为气体排放通量(mg·m-2·h-1),为第次, (t1t)为两次采样间隔天数,为采样次数。

1.3.3 土壤含水率和容重

越冬期未测定土壤含水率, 其他时间每个月用环刀按0~5 cm、5~10 cm、10~20 cm、20~30 cm分层取原状土, 105 ℃烘干测定土壤含水率。土壤容重在2017年玉米收获后用环刀法按0~5 cm、5~10 cm、10~20 cm、20~30 cm分层取原状土, 105 ℃烘干测定土壤容重。

1.3.4 小麦产量

冬小麦成熟期随机取20株小麦测量穗粒数和收获指数; 每小区选取有代表性的1 m双行植株, 6个重复, 测定小麦穗数和千粒重; 每小区选取200 cm×125 cm面积收割, 6个重复, 测定小麦产量; 并通过产量和收获指数计算地上生物量。

1.4 数据处理

采用单因素方差分析对试验数据进行处理, 处理间差异用Duncan法进行多重比较。所有数据分析均在Microsoft Excel 2016和SPSS 17.0环境下进行, OriginPro 9.0作图。

2 结果与分析

2.1 耕作方式转换对土壤温度、水分、容重和土壤有机质的影响

地表土壤温度在3种耕作处理下变化趋势一致(图2a)。土壤温度在耕作后和收获季较高, 在1月下旬出现最低值, 4月份灌溉后温度有所降低, 整体上X和XS土壤温度显著高于XF。

图2 不同耕作处理冬小麦田地表平均温度(a)和0~20 cm土层土壤重量含水率(b)的变化

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage.

土壤重量含水率变化如图2b所示, 0~20 cm的土壤含水率在耕作后呈不断下降趋势, 直到4月23日灌溉, 之后再次不断下降。耕作方式改变后提高了土壤水分含量, 11月和5月前后XS和XF处理的土壤含水量显著高于X处理, 其他时间点差异不显著。

从图3可以看出, 小麦收获后土壤容重随着土壤深度的增加而增大。0~5 cm土壤容重各处理间差异不显著, 5~10 cm、10~20 cm和20~30 cm土壤容重X>XF>XS。说明翻耕和深松后能降低土壤容重, 且深松后的效果更明显。

图3 冬小麦收获后不同耕作处理不同深度土壤容重

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。同一土层不同字母表示在0.05水平差异显著。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage. Different letters within a soil depth indicate significant differences at0.05.

土壤有机质含量变化如表1所示。长期旋耕基础上进行翻耕和深松处理后0~10 cm土层有机质含量降低, 10~20 cm土壤有机质含量提高。0~10 cm土壤有机质含量: X>XS>XF, 和XS相比XF显著降低了有机质含量; 10~20 cm土壤有机质含量: XF>XS>X, 处理之间差异不显著。旋耕后翻耕降低了20~30 cm土壤有机质, 但三者无显著差异。

表1 不同耕作处理下冬小麦田不同土层土壤有机质含量

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。数据为3次重复的平均值±标准误。同行不同字母表示在0.05水平差异显著。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage. Values are means ± S.E. (=3). Different letters within a row indicate significant differences at0.05.

2.2 耕作方式转变对CH4、CO2、N2O通量的影响

2.2.1 冬小麦季CO2通量

CO2通量在3种耕作处理下变化趋势一致。在10月初进行X、XF、XS耕作处理后, 农田排放CO2排放通量有快速的响应(图4), 在短时间内排放通量均出现最高值, 分别为353 mg·m-2·h-1、321 mg·m-2·h-1、294 mg·m-2·h-1; 冬季通量降到了最低, 然后随着温度的回升, 通量逐渐变大, 到收获期出现较高的排放峰值, 分别为186 mg·m-2·h-1、206 mg·m-2·h-1、178 mg·m-2·h-1。从实施耕作到10月底期间, 除个别采样时期外, CO2通量在X和XS处理下显著高于XF处理, 之后这种趋势逐渐消失; 11月到3月份, 排放通量较小, 各处理间变化不规律, 其中XS处理波动较大; 3月中旬到5月中旬, XS下CO2排放通量略高于XF和X处理, 多数测定时期差异不显著。

图4 不同耕作处理下冬小麦田CO2排放通量的变化

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage.

2.2.2 冬小麦季N2O通量

如图5所示, N2O排放通量在耕作后和施肥灌溉后出现明显排放峰值, 其他时间段通量差异较小。耕作后第3天, 在X和XF耕作处理下, N2O通量达到最大值, 分别为0.29 mg·m-2·h-1和0.28 mg·m-2·h-1, 而XS处理下N2O通量最大值出现在耕作后第9天(0.70 mg·m-2·h-1); 10月初到10月底N2O排放通量在XS下显著高于X和XF处理。4月23日施肥和灌溉后N2O有显著的排放高峰, 且XF>XS>X。

2.2.3 冬小麦季CH4通量

耕作后冬小麦季CH4通量变化如图6所示。在3种耕作处理下, CH4通量起伏变化较大。从耕作的短期效应看, 耕作1周内土壤对CH4的吸收通量表现为XS>XF>X, 耕作后第5天CH4吸收通量明显增大, XF下最大为-0.32 mg·m-2·h-1, 其次XS为-0.23 mg·m-2·h-1, X最小为-0.15 mg·m-2·h-1, 之后吸收通量均减小。整体上, 在耕作后和2016年12月—2017年3月初通量波动大, 其他时间波动较小。

图5 不同耕作处理下冬小麦田N2O排放通量的变化

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage.

图6 不同耕作处理下冬小麦田CH4排放通量的变化

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage.

2.3 耕作方式转变对冬小麦季温室气体累积排放量的影响

表2为3种耕作处理下冬小麦季温室气体总排放量、CO2当量以及增温效应的贡献。结果表明, 冬小麦季华北平原为CO2和N2O的排放源、CH4的吸收汇。CO2排放量在X和XS处理下差异不显著, 但均显著高于XF处理。N2O排放量在XS处理下显著高于X和XF处理, 且后两者间没有显著差异。XS耕作处理下农田CH4的吸收量最大, 其次为XF处理, 2个处理间差异显著。

冬小麦季农田CO2当量XS处理下最大, 其次是X, XF处理下最小, 且三者差异达显著水平。CO2对增温效应的贡献最大, 占84.15%~91.22%; N2O的贡献为10.61%~18.62%; CH4的贡献率最低, 为负贡献。

2.4 耕作方式转变对冬小麦产量及其构成因素的影响

不同耕作处理产量测定结果见表3。耕作方式改变对冬小麦产量影响显著, X最高, 显著高于XS, XF和两处理差异均不显著; 穗数在不同耕作间差异不显著; 穗粒数为X>XS>XF, 处理间差异显著; 千粒重表现为XF≈X>XS, 且XF和X显著高于XS, 而X和XF间差异不显著; 地上部生物量X>XF>XS, XF和XS、X差异不显著, 但XS显著低于X; 3种耕作处理下小麦收获指数无显著差异。结合表2中CO2当量和表3中冬小麦产量计算出不同耕作下冬小麦单位产量CO2当量, XS为1.01, XF为0.82, X为0.79。

表2 不同耕作处理下冬小麦田温室气体累积排放量和对增温效应的贡献

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。数据为4次重复的平均值±标准误。同列不同字母表示在0.05水平下差异显著。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage. Values are means ± S.E. (=4). Different letters within a column indicate significant differences at0.05.

表3 不同耕作处理对冬小麦产量及其构成因素的影响

X: 旋耕; XF: 旋耕后翻耕; XS: 旋耕后深松。数据为6次重复的平均值±标准误, 同列不同字母表示0.05水平下差异显著。X: rotary tillage; XF: rotary tillage converting to deep plowing tillage; XS: rotary tillage converting to subsoiling tillage. Values are means ± S.E. (=6). Different letters within a colum indicate significant differences at0.05.

3 讨论

3.1 不同耕作对温室气体排放的影响

不同的耕作处理对土壤中的生物、水分和热量等造成了不同程度的影响[31-32], 这些因素影响着农田温室气体排放量。冬小麦季土壤对CO2的排放量表现为XS≈X>XF, 对N2O的排放量表现为XS>XF≈X, 对CH4的吸收量表现为XS>XF>X。

CO2通量变化趋势呈三峰态, 变化趋势与Liu等[33]的研究结果相似。耕作后短期内CO2出现排放高峰, 因为耕作对土壤的扰动破坏了原有的结构, 使得土壤有机质有一个较高的转化率[34]。长期旋耕会使土壤养分表聚, 相对于XS和XF, X表层土壤会为微生物提供更多的养分, 促进CO2排放。到第2和第3个峰时, 植物根呼吸占主体, 同时温度较高, 促进微生物活动, 使CO2通量较高。本研究中X处理CO2排放总量高于XF处理, 这与前人的研究结果[21]不一致。主要因为长期旋耕使农田土壤有机质表聚, 经过翻耕和深松处理后将土壤表层有机质混合到较深层土壤中, 而0~10 cm土层的土壤呼吸强度高于10~20 cm土层[35]。其次因为X和XS处理地表温度均高于XF处理, 而CO2排放通量与土壤温度呈正相关关系[36], 使XF和XS处理下土壤有机质矿化速率降低, 抑制了CO2的产生。XF处理0~10 cm有机质含量下降, 而深层含量呈升高的趋势。因此, 本研究证明长期旋耕农田进行单次翻耕处理, 并未造成土壤CO2排放升高, 这为农田轮耕管理提供有力的数据支撑。

N2O通量在耕作和施肥灌溉后出现明显的峰值, 在冬季出现最低值。Krauss等[37]试验结果也发现在耕作后短时间内, 会出现高N2O排放通量。因为耕作后农田表层土壤孔隙度增大, 秸秆和底肥为微生物提供了碳和氮源, 有利于N2O的产生和释放。在耕作后接近1个月时间XS处理N2O排放通量显著高于XF和X处理, 因为XS处理土壤大孔隙增多, 利于土壤水分下渗和存储, 加之该时期降雨量大,激发了深层土壤中N的释放。且XS增加土壤的上下通透性, 利于N2O向土壤表层扩散。而XF将粉碎的秸秆和肥料翻到了土壤深层, 底层土壤温度较低且深层土壤微生物含量较少, 不利于N2O的形成[38]。与前人研究一致[38-42], N2O排放通量在施氮肥和灌溉后出现峰值。因为氮肥为土壤硝化和反硝化微生物提供了充足的氮源[43], 使微生物更加活跃, 促进N2O产生; 灌溉后, 土壤孔隙不断地充满水, 使土壤中氧气不断减少, 进而促进了反硝化作用, 也加速了N2O的产生[44]。冬小麦季农田土壤N2O累积排放量表现为XS>XF≈X。与本研究结果相同, 张贺等[23]和Forte等[45]也得出N2O排放量在翻耕和旋耕处理下差异不显著的结论, Tian等[46]发现土壤经深松后比旋耕后排放更多N2O。已有研究确定影响农田土壤N2O排放的关键因素是水分、温度和硝态氮含量[47]。本研究经耕作处理后, XS和XF土壤中水分含量高于X, 而N2O产生和排放与水分呈正相关关系[48]; 且有研究发现深松处理下植物根际土壤的硝态氮含量比翻耕和旋耕高[49], 促进了反硝化作用, 使N2O排放量较高。

在耕作的同时施用了底肥, 增加了土壤中NH4+的含量, 部分CH4氧化菌参加氨氧化[50], 影响了甲烷氧化菌的氧化作用, 使耕作后短期内CH4的吸收通量很低。随着时间推移, NH4+含量逐渐减少, 更多的甲烷氧化菌参与到氧化CH4的过程中, 到耕作后第5天耕作与甲烷氧化菌共同作用使CH4吸收通量增大。冬小麦整个生育季农田土壤对CH4吸收量表现为XS>XF>X。Wolff等[51]也发现对土壤扰动最小的耕作方式土壤CH4吸收量最小。其原因是XS、XF处理比X处理更好地改善了土壤的通气状况, 使甲烷氧化菌群更容易获得适宜的生存条件和好氧环境[25], 提高了土壤对CH4的氧化能力, 使CH4吸收通量更高[26]。董玉红等[52]已表明通气状况良好的土壤是CH4的最大吸收汇。冬小麦季CH4通量的变化起伏大, 因为不同的耕作影响土壤的物理性状、肥力状况、生物学特性、水分和温度[53], 这些因素对CH4的产生和传输产生影响, 但是具体的影响机制尚不清楚, 需要更深一步的研究。

无论是哪种耕作方式下CO2-eq均为正值, 即土壤排放的3种温室气体对增温的综合效应均为正效应。其中CO2对增温效应贡献最大, N2O对增温效应的贡献较小, 而CH4对增温效应最小为负贡献; XF处理下CO2-eq是最低的, 即增温贡献最小, 相对于X和XS处理, 利于缓解农田温室气体的增温贡献率。相对于X处理, XS处理尽管明显提高CH4的吸收量, 但由于N2O排放量更大, 总体上显著增加了综合温室效应。因此, 在本区域内实施深松改善土壤结构的耕作管理时, 应综合考虑水分效应, 减少综合温室气体排放。

3.2 不同耕作下的冬小麦产量

在长期旋耕的基础上进行翻耕和深松, 虽然改善了土壤的通透性, 但没有提高小麦的产量, 而使产量降低。这与前人的研究结果有所不同, 于淑婷等[4]发现冬小麦产量在翻耕/旋耕轮耕模式显著高于连年旋耕模式。研究发现[27,54], 农田深松有利于作物产量的提高。郑侃等[55]通过Meta分析我国北方地区深松对作物产量的影响, 也得出小麦产量在旋耕深松耕作模式下比连年旋耕下的要高。本研究中, 虽然深松改善了土壤的物理性状, 但对小麦的产量没有提高, 可能是因为XS后粉碎的秸秆仍保留在表层土壤中, 有机质没有进入到深层土壤中(表1), 对深层土壤环境改善效果不显著, 使作物产量受到了影响, 这与Pierce等[56]的研究结果相似。也有研究[57]认为深松技术虽有较好的保土保水作用, 但是耕层松紧不一, 土块较大, 不利于作物的生长发育。经过翻耕后小麦穗数降低, 可能是因为在出苗期降雨量较大且XF后土壤温度低影响了出苗率; 而XF和X处理千粒重显著高于XS处理, 可能是因为灌浆期XS处理表层土壤水分蒸发快, 影响了粒重; 改变耕作方式后, 穗粒数均降低, 具体影响机理尚不清楚。轮耕对作物产量影响需要针对不同气候年型进一步深入研究。

4 结论

冬小麦季农田在长期旋耕基础上经深松和翻耕后, CO2、N2O、CH4排放有显著变化, 但农田土壤均表现为CO2和N2O的源、CH4的汇, 温室气体换算为CO2当量排序为: XS>X>XF。综合来看经过翻耕后, 农田温室气体排放显著降低。

从当前短期影响看, 冬小麦产量经过XF和XS后较X有所降低, XF和X单位产量下CO2当量均小于XS。综合考虑温室气体排放和冬小麦产量, 短期看旋耕深松模式不利于华北农田小麦生产和控制温室气体排放, 旋耕翻耕可能是较适宜的轮耕模式, 但需要加强对不同轮耕模式长期效应研究, 为确定合理的耕作模式提供依据。

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Effect of tillage method change on soil greenhouse gas emission and yield during winter-wheat growing season*

ZHAO Liying1,2, DONG Wenxu1, HU Chunsheng1**, LI Jiazhen1,2, CHEN Tuo1,2

(1. Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences / Key Laboratory of Agricultural Water Resources, Chinese Academy of Sciences / Hebei Key Laboratory of Water-Saving Agriculture, Shijiazhuang 050022, China; 2. University of Chinese Academy of Sciences, Beijing 100049, China)

Under long-term rotary tillage, soil bulk density, carbon decomposition and nutrient in sub-surface soil in the shallow plow layer significantly increase, but wheat growth and soil carbon sequestration become limited. However, subsoiling and deep plowing can break the bottom of the plow layer and reduce soil bulk density, which are conducive for good growth of plant root and absorption of nutrients to ensure high crop yield. The objectives of this study were to analyze changes in greenhouse gases emission and wheat yield after 16 years (2001-2016) of rotary tillage (X) treatment and conversion into other tillage treatments, including rotary tillage-deep plowing (XF) and rotary tillage-subsoiling (XS) treatments in 2016, and to determine the best rational tillage strategy. Carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4)emission fluxes in the three tillage treatments were sampled and measured using static chamber-gas chromatography. Soil temperature at the 0 cm depth, soil gravimetric moisture content, soil bulk density at different depths and other related factors were monitored during wheat growth period and winter wheat yield analyzed after harvest. The experimental results showed prominent high fluxes of CO2and N2O one week after the three tillage treatments and during harvest, with minimum emission fluxes of CO2and N2O during winter period. Compared with XF treatment, X and XS treatments significantly increased CO2emission fluxes from the start of the three tillage treatments to the end of October. Compared with X and XF treatments, N2O fluxes under XS treatment were significant high after tillage treatment, fertilization and irrigation. CH4fluxes fluctuated from November 2016 to February 2017, and became more stable from March 2017. From January 2017 to the harvest season, soil uptake of CH4under XS treatment was higher than those under XF and X treatments. The fields under the three tillage treatments during winter wheat growth were the sources of CO2and N2O. The cumulative fluxes of the three tillage treatments served as CH4sink. In winter wheat fields, cumulative CO2emission was in order of XS > X > XF, with total CO2emissions of 5 241 kg·hm-2, 5 160 kg·hm-2and 4 840 kg·hm-2, respectively. Cumulative N2O emission was in order of XS > XF > X, with total N2O emissions of 4.38 kg·hm-2, 2.39 kg·hm-2and 2.26 kg·hm-2, respectively. Cumulative CH4sink was in order of XS > XF > X, with total CH4absorptions of 6.14 kg·hm-2, 5.64 kg·hm-2and 3.70 kg·hm-2, respectively. The contribution of cumulative greenhouse gases to CO2-equivalents was expressed as XS > X > XF, which were 6.23 t·hm-2, 5.66 t·hm-2and 5.32 t·hm-2, respectively. Using deep plowing and subsoiling, soil organic matter decreased in the 0–10 cm soil depth, but increased in the 10–20 cm soil depth. Soil organic carbon was the main source of CO2. Reduction in soil organic matter led to reduction in CO2. Winter wheat grain yield under X treatment was higher than that under XS and XF treatments. Considering the changes in soil physical properties, greenhouse gas emission and wheat yield, XF treatment was the most suitable tillage practice. However, more and longer research work was needed to determine an ideal tillage treatment to ensure future ecological benefits and grain yield.

Winter wheat; Rotary tillage; Deep plowing tillage; Subsoiling tillage; Greenhouse gases; Yield

, E-mail: cshu@sjziam.ac.cn

Mar. 7, 2018;

May 30, 2018

S157.4+2; S512.1+1

A

1671-3990(2018)11-1613-11

10.13930/j.cnki.cjea.180219

* 公益性行业(农业)科研专项(201503117-5)和国家重点研发计划项目(2017YFD0800601)资助

胡春胜, 主要研究方向为农田生态系统碳、氮、水循环及土壤生态过程。E-mail: cshu@sjziam.ac.cn

赵力莹, 主要研究方向为农田生态系统碳循环。E-mail: zlydlkx@163.com

2018-03-07

2018-05-30

* This study was supported by the Special Fund for Agro-scientific Research in the Public Interest of China (201503117-5) and the National Key Research and Development Program of China (2017YFD0800601).

赵力莹, 董文旭, 胡春胜, 李佳珍, 陈拓. 耕作方式转变对冬小麦季农田温室气体排放和产量的影响[J]. 中国生态农业学报, 2018, 26(11): 1613-1623

ZHAO L Y, DONG W X, HU C S, LI J Z, CHEN T. Effect of tillage method change on soil greenhouse gas emission and yield during winter-wheat growing season[J]. Chinese Journal of Eco-Agriculture, 2018, 26(11): 1613-1623