程 功, 劉廷璽, 李東方, 段利民, 王冠麗

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生物炭和秸稈還田對(duì)干旱區(qū)玉米農(nóng)田土壤溫室氣體通量的影響*

程 功1,3, 劉廷璽1,2**, 李東方1,2, 段利民1,2, 王冠麗1,2

(1. 內(nèi)蒙古農(nóng)業(yè)大學(xué)水利與土木建筑工程學(xué)院 呼和浩特 010018; 2. 內(nèi)蒙古自治區(qū)水資源保護(hù)與利用重點(diǎn)實(shí)驗(yàn)室呼和浩特 010018; 3. 南京市水利規(guī)劃設(shè)計(jì)院股份有限公司 南京 210000)

為了研究生物炭及秸稈還田對(duì)干旱區(qū)玉米農(nóng)田溫室氣體通量的影響, 以內(nèi)蒙古科爾沁地區(qū)玉米農(nóng)田為試驗(yàn)對(duì)象, 采用靜態(tài)箱-氣相色譜法對(duì)分別施入生物炭0 t?hm-2(CK)、15 t?hm-2(C15)、30 t?hm-2(C30)、45 t?hm-2(C45)及秸稈還田(SNPK)的土壤進(jìn)行溫室氣體(CO2、CH4和N2O)通量的原位觀測(cè), 并估算生長(zhǎng)季CH4和N2O的綜合增溫潛勢(shì)(GWP)與排放強(qiáng)度(GHGI)。結(jié)果表明: 添加生物炭能夠顯著減少土壤CO2和N2O的排放量, 并促進(jìn)土壤對(duì)CH4的吸收作用。其中處理C15對(duì)CO2的減排效果最好, 與對(duì)照相比CO2排放量降低21.16%。隨著施入生物炭量的增加, 生物炭對(duì)N2O排放的抑制作用不斷增強(qiáng), 處理C45對(duì)減排效果最好, 與對(duì)照相比N2O排放量降低86.25%。處理C15對(duì)土壤吸收CH4的促進(jìn)效果最好, CH4吸收量增加56.62%; 處理C45對(duì)CH4的排放有促進(jìn)作用, 使生長(zhǎng)季土壤吸收CH4減少81.36%。SNPK對(duì)溫室氣體的減排作用接近處理C15。添加生物炭和秸稈還田對(duì)提高玉米產(chǎn)量和降低農(nóng)田GWP與GHGI均有顯著效果, 施用生物炭及秸稈還田均有效提高了科爾沁地區(qū)的玉米產(chǎn)量, 且玉米產(chǎn)量隨著施入生物炭含量的增大而提升。從GWP上來(lái)看, 施用15 t?hm-2生物炭對(duì)溫室氣體減排的整體效果最好。從GHGI上來(lái)看, 施用生物炭及秸稈還田均具有一定的經(jīng)濟(jì)效益和減排意義, 其中施用15 t?hm-2生物炭的綜合效益最高。因此綜合經(jīng)濟(jì)效益與環(huán)境因素, 建議科爾沁地區(qū)農(nóng)田在種植玉米時(shí)添加15 t?hm-2生物炭, 如不具備購(gòu)買(mǎi)生物炭條件, 可以考慮秸稈還田來(lái)實(shí)現(xiàn)玉米增產(chǎn)與溫室氣體減排。

生物炭; 玉米; 農(nóng)田; 溫室氣體; 秸稈還田; 干旱區(qū)

近年來(lái), 全球溫室氣體濃度劇增引起海平面上升、全球溫度升高等問(wèn)題已經(jīng)嚴(yán)重影響到地球生態(tài)環(huán)境, 并對(duì)人類(lèi)的生存和發(fā)展造成威脅[1]。農(nóng)業(yè)活動(dòng)是溫室氣體排放的重要來(lái)源, 全球農(nóng)業(yè)排放溫室氣體中, 有15%左右的CO2、47%的CH4和84%的N2O來(lái)源于土壤[2]。農(nóng)業(yè)活動(dòng)中施用化肥會(huì)對(duì)土壤溫室氣體的排放產(chǎn)生重要影響[3], 因此在農(nóng)田的種植與施肥中尋求降低溫室氣體排放的途徑是目前亟待解決的重要問(wèn)題。

生物炭(biochar)是指枯枝落葉、作物秸稈等農(nóng)林廢棄物和動(dòng)植物殘?bào)w等生物質(zhì)在完全無(wú)氧或部分缺氧的狀態(tài)下經(jīng)過(guò)高溫?zé)峤馓蓟a(chǎn)生的穩(wěn)定且富含碳的固態(tài)物[4-5]。在土壤中添加生物炭, 可以有效增加土壤肥力并改變土壤理化性質(zhì), 如增加土壤pH[6]、提升土壤保水持水能力[7]以及影響土壤中NH4+-N和NO3--N的含量[8-9]等。有研究表明, 在施用氮肥的條件下同時(shí)施用生物炭, 可以有效抑制土壤CO2和N2O的排放[10-11], 促進(jìn)土壤CH4吸收[12], 有效減少農(nóng)田溫室氣體排放。秸稈還田也是利用農(nóng)林廢棄物的一種重要方式[13], 有研究表明秸稈還田能夠抑制土壤CO2和N2O的排放并促進(jìn)土壤CH4吸收[14-15], 也有研究表明添加生物炭和秸稈還田會(huì)促進(jìn)農(nóng)田土壤排放溫室氣體[16-17]。生物炭因其來(lái)源、熱解溫度以及試驗(yàn)區(qū)的土壤質(zhì)地、施用量和作物的不同而對(duì)土壤溫室氣體通量有著不同的影響[18-21], 因此目前對(duì)施用生物炭和秸稈還田對(duì)土壤溫室氣體排放的影響尚未得出統(tǒng)一定論, 有待于進(jìn)一步驗(yàn)證。

玉米()是內(nèi)蒙古科爾沁地區(qū)農(nóng)田的主要作物之一, 該地區(qū)土地干旱, 玉米產(chǎn)量較低, 秋收后玉米秸稈一部分打碎留待過(guò)冬喂養(yǎng)牛羊, 一部分焚燒, 對(duì)環(huán)境造成嚴(yán)重破壞。如果能在施用生物炭和秸稈還田增加產(chǎn)量的同時(shí), 對(duì)農(nóng)田溫室氣體進(jìn)行減排, 不僅能夠解決當(dāng)?shù)孛磕赀z留玉米秸稈的焚燒問(wèn)題, 也能夠?yàn)橘Y源的可持續(xù)利用做出貢獻(xiàn)。本文以玉米秸稈生物炭和秸稈還田對(duì)當(dāng)?shù)剞r(nóng)田進(jìn)行改造試驗(yàn), 探究生物炭和秸稈還田對(duì)干旱區(qū)雨養(yǎng)農(nóng)田土壤溫室氣體(CO2、CH4、N2O)排放通量的影響, 估算溫室氣體在玉米生長(zhǎng)季的累計(jì)排放量并計(jì)算溫室氣體的綜合增溫潛勢(shì)及其排放強(qiáng)度, 對(duì)科爾沁地區(qū)進(jìn)行農(nóng)業(yè)活動(dòng)做出科學(xué)指導(dǎo), 并為農(nóng)田溫室氣體減排研究提供理論依據(jù)。

1 材料和方法

1.1 試驗(yàn)區(qū)概況

試驗(yàn)在位于內(nèi)蒙古自治區(qū)通遼市科爾沁左翼后旗阿古拉鎮(zhèn)的科爾沁沙地阿古拉生態(tài)水文實(shí)驗(yàn)站(122°39′18″E, 39°18′01″N)開(kāi)展, 地處科爾沁沙地東南邊緣, 海拔184~190 m。該區(qū)多年平均降水量387 mm, 主要集中在6—9月; 多年平均水面蒸發(fā)量(20 cm蒸發(fā)皿)1 408 mm, 主要集中在4—9月; 多年平均相對(duì)濕度55.7%; 多年平均氣溫6.9 ℃, 年極端最低氣溫-33.9 ℃, 年極端最高氣溫36.2 ℃, 晝夜溫差大; 年平均風(fēng)速3~4 m?s-1。農(nóng)田為草甸濕地開(kāi)墾多年而成, 主要作物為玉米, 整個(gè)生長(zhǎng)季無(wú)人為澆灌, 玉米生長(zhǎng)水分全部依賴于天然降水和地下水。研究區(qū)地理位置見(jiàn)圖1。

1.2 土壤及生物炭理化性質(zhì)

采用玉米秸稈在360 ℃下不完全燃燒24 h制成的生物炭, 購(gòu)于遼寧金和福農(nóng)業(yè)開(kāi)發(fā)有限公司。供試土壤及生物炭基礎(chǔ)理化性質(zhì)如表1所示。

1.3 研究方法

1.3.1 試驗(yàn)設(shè)計(jì)

試驗(yàn)設(shè)置如圖1(右上)所示, 在農(nóng)田中選取20 m× 20 m的區(qū)域, 并將樣地分成9塊6 m×6 m(面積為36 m2)的試驗(yàn)田, 每塊試驗(yàn)田間設(shè)置1 m隔離帶。種植玉米品種為‘先玉1411’, 行距0.6 m, 株距0.4 m, 種植密度為65 000 株?hm-2。為研究施用不同含量生物炭和秸稈還田對(duì)玉米農(nóng)田溫室氣體通量的影響, 共設(shè)置5個(gè)處理, 每個(gè)處理均設(shè)置3個(gè)重復(fù), 分別為: 施用0 t?hm-2(CK)、15 t?hm-2(C15)、30 t?hm-2(C30)、45 t?hm-2(C45)生物炭, 和秸稈還田(SNPK)處理。SNPK處理為將玉米秸稈全部粉碎后與土壤混合?；什捎媚蛩亍⒘姿岫@和硫酸鉀, 按照N 200 kg?hm-2、P2O552.5 kg?hm-2和K2O 37.5 kg?hm-2在播種同時(shí)施用。玉米于2018年5月12—15日播種, 播種前使用旋耕機(jī)將生物炭與土壤均勻混合, 混合深度為30 cm。生育期內(nèi)依照年當(dāng)?shù)靥镩g種植管理, 無(wú)灌溉, 9月下旬收割, 稱(chēng)量并計(jì)算單位面積上的玉米產(chǎn)量。

1.3.2 樣品采集和測(cè)定

使用靜態(tài)箱-氣相色譜法, 于2018年5—10月內(nèi)每7 d左右選取晴好天氣的9:00—11:00時(shí)段, 在所設(shè)立的取樣點(diǎn)同時(shí)進(jìn)行溫室氣體通量(CO2、CH4、N2O)的原位觀測(cè)。靜態(tài)箱由厚2.0 mm的非透明PVC板制成, 包括頂箱和基座兩部分, 內(nèi)置小風(fēng)扇和溫度計(jì)。頂箱規(guī)格為50 cm×50 cm×50 cm, 基座邊緣設(shè)有水槽, 觀測(cè)時(shí)上下箱體用水槽中的水密封。在試驗(yàn)開(kāi)始1周前將靜態(tài)箱基座插入土壤中, 并在整個(gè)試驗(yàn)過(guò)程中不取出或挪動(dòng)基座?；袢肷疃仍? cm以上(實(shí)際計(jì)算通量時(shí)以地、箱高度為準(zhǔn))。采用30 min罩箱時(shí)間, 即每個(gè)采樣箱分別罩箱后的0 min、10 min、20 min和30 min抽取氣體樣品。采樣容器為100 mL帶三通閥的醫(yī)用注射器, 將注射器與箱體一側(cè)的三通閥相連, 抽取30~60 mL氣體樣品放入氣袋, 同時(shí)使用秒表記錄取樣時(shí)間和箱內(nèi)溫度計(jì)所觀測(cè)的箱內(nèi)氣溫。氣樣帶回實(shí)驗(yàn)室后, 3 d內(nèi)使用安捷倫7890B氣相色譜儀分析溫室氣體濃度。

圖1 研究區(qū)地理位置與試驗(yàn)點(diǎn)布設(shè)示意圖

表1 供試土壤及生物炭基礎(chǔ)性質(zhì)

1.3.3 數(shù)據(jù)采集

氣溫和降雨量等氣象要素通過(guò)試驗(yàn)點(diǎn)附近布設(shè)的波文比-土壤環(huán)境監(jiān)測(cè)系統(tǒng)全天候24 h自動(dòng)采集, 氣溫由距地面2 m高處的傳感器(HMP45C, Vaisala, Helsinki, Finland)測(cè)量, 降雨量通過(guò)距地面0.7 m高處的自記雨量計(jì)(TE525MM, Texas Electeonices, Dallas, USA)測(cè)量; 土壤溫度、土壤水分通過(guò)分層位(10 cm、20 cm等)埋在土壤中的探頭(Hydra ProbeⅡ, Stevens, USA)測(cè)量。以上數(shù)據(jù)通過(guò)數(shù)據(jù)采集器(CR1000, Campbell, Logan, USA)每10 min在線采集一次, 計(jì)算平均值, 自動(dòng)存儲(chǔ)。由于氣象站不能輻射所有試驗(yàn)田, 因此每次觀測(cè)同時(shí)使用JM624手持溫度計(jì)記錄10 cm、20 cm處土壤溫度并使用鋁盒法測(cè)量不同取樣點(diǎn)的表層土壤含水率(10 cm及20 cm處), 并與氣象站數(shù)據(jù)相互驗(yàn)證。

1.3.4 氣體通量的計(jì)算

通量是指單位時(shí)間通過(guò)某單位面積輸送的物理量。氣體交換通量()計(jì)算公式為[22]:

式中:為箱內(nèi)氣體密度; Δ和Δ分別為一段時(shí)間內(nèi)箱內(nèi)氣體質(zhì)量和混合比濃度的變化;、、分別為采樣箱的底面積、體積和氣室高度; Δ/Δ為箱內(nèi)氣體濃度變化。當(dāng)為負(fù)值時(shí)表示吸收,為正值時(shí)表示排放。計(jì)算通量過(guò)程中, 通過(guò)公式中引入箱內(nèi)溫度和氣壓值, 對(duì)氣體濃度進(jìn)行矯正。

溫室氣體累計(jì)排放量(c)計(jì)算公式為[23]:

(2)

綜合增溫潛勢(shì)(GWP)是將各類(lèi)溫室氣體的增溫潛勢(shì)轉(zhuǎn)化為CO2的排放當(dāng)量, 100年時(shí)間尺度下的GWP計(jì)算公式為[23]:

溫室氣體排放強(qiáng)度(GHGI)是單位經(jīng)濟(jì)產(chǎn)出的CO2排放當(dāng)量, 其計(jì)算公式為[23]:

GHGI=GWP/(4)

式中:為單位面積產(chǎn)量。

1.4 數(shù)據(jù)分析

利用Office Excel 2013對(duì)原始數(shù)據(jù)進(jìn)行整理, 采用SPSS 19.0的one-way ANONA進(jìn)行差異性處理, 差異性水平選擇<0.05; Person相關(guān)系數(shù)分析溫室氣體通量與影響因素之間的相關(guān)性。圖中數(shù)據(jù)均為3個(gè)重復(fù)測(cè)定的平均值±標(biāo)準(zhǔn)誤差。

2 結(jié)果與分析

2.1 試驗(yàn)區(qū)玉米生長(zhǎng)季大氣、土壤水熱變化

2018年4—10月研究區(qū)累計(jì)降雨369.9 mm, 主要集中在7、8月份; 平均氣溫為7.1 ℃, 生長(zhǎng)季氣溫呈單峰型曲線, 在7、8月份達(dá)到較高值(圖2a)。生長(zhǎng)季玉米農(nóng)田土壤溫度與氣溫大致趨勢(shì)相同, 均呈單峰型, 并在7月中下旬達(dá)到最大值。土壤含水率由于冬季冰凍融化等原因, 在生長(zhǎng)季初期較高并呈下降趨勢(shì), 整個(gè)生長(zhǎng)季過(guò)程土壤含水率隨降雨波動(dòng), 并在生長(zhǎng)季末期大幅度下降, 20 cm土壤含水率明顯高于10 cm土壤含水率(圖2b)。

2.2 施用生物炭后玉米農(nóng)田的CO2通量特征

5個(gè)處理的玉米田CO2通量在整個(gè)生長(zhǎng)季均呈現(xiàn)明顯的雙峰型(圖3)。試驗(yàn)初期溫度較低, CO2通量也處于較低的水平; 且之后土壤水分下降, CO2通量隨之下降; 5月12—15日玉米農(nóng)田進(jìn)行翻耕、種植后CO2通量出現(xiàn)明顯的上升趨勢(shì), 并在7月初和8月初分別出現(xiàn)排放峰值, 隨后呈現(xiàn)明顯的下降趨勢(shì)。在生長(zhǎng)季初期添加生物炭各處理的CO2通量明顯高于CK, 但在生長(zhǎng)中后期添加生物炭的各處理CO2通量低于CK, 說(shuō)明添加生物炭在生長(zhǎng)季初期對(duì)CO2的排放具有促進(jìn)作用, 而在生長(zhǎng)中后期則有抑制作用。處理CK、C15、C30、C45、SNPK生長(zhǎng)季CO2平均通量分別為: 405.15 mg?m-2·h-1、319.40 mg?m-2·h-1、347.03 mg?m-2·h-1、336.16 mg?m-2·h-1、323.39 mg?m-2·h-1, 與對(duì)照CK相比, 處理C15、C30、C45及SNPK分別降低21.16%、14.34%、17.02%和19.93%, 不同生物炭處理間差異顯著(<0.05)。從生長(zhǎng)季整體來(lái)看, 添加生物炭有效抑制了土壤CO2的排放, 其中處理C15和SNPK抑制效果較好。Person相關(guān)分析結(jié)果表明, 玉米生長(zhǎng)季CO2通量與土壤溫度和濕度均呈顯著(<0.01)正相關(guān)(表2)。

圖2 2018年玉米農(nóng)田生長(zhǎng)季氣溫、降雨量(a)和土壤溫、濕度(b)的變化

圖b中s為土壤含水率,s為土壤溫度。In figure b,smeans soil moisture,smeans soil temperature

圖3 不同生物炭處理土壤CO2通量季節(jié)動(dòng)態(tài)變化

CK為空白對(duì)照; C15、C30和C45為施用生物炭處理, 施用量分別為15 t?hm-2、30 t?hm-2和45 t?hm-2; SNPK為秸稈還田處理。CK is the control; C15, C30 and C45 are biochar application treatments with biochar rate of 15 t?hm-2, 30 t?hm-2and 45 t?hm-2, respectively; SNPK is treatment of corn straw incorporation.

表2 不同生物炭處理玉米生長(zhǎng)季土壤CO2、CH4和N2O通量與10 cm處土壤溫濕度相關(guān)性

*:<0.05; **:<0.01. CK為空白對(duì)照; C15、C30和C45為施用生物炭處理, 施用量分別為15 t?hm-2、30 t?hm-2和45 t?hm-2; SNPK為秸稈還田處理。CK is the control; C15, C30 and C45 are biochar application treatments with biochar rate of 15 t?hm-2, 30 t?hm-2and 45 t?hm-2, respectively; SNPK is treatment of corn straw incorporation.

2.3 施用生物炭后玉米農(nóng)田的CH4通量特征

試驗(yàn)期間玉米農(nóng)田CH4通量如圖4所示, 其正值代表土壤排放CH4, 負(fù)值代表土壤吸收CH4。播種前農(nóng)田土壤CH4吸收值逐漸增大。5月12—15日玉米農(nóng)田翻耕、種植后土壤CH4通量發(fā)生較大變化, 其中處理C45由CH4的吸收轉(zhuǎn)為排放, 其余處理CH4吸收值均大于CK。6—8月玉米生長(zhǎng)盛季, CH4吸收較強(qiáng)且波動(dòng)較大, 生長(zhǎng)季后期處理C45重新轉(zhuǎn)變?yōu)镃H4的吸收, 其他處理也逐漸接近CK。處理CK、C15、C30、C45、SNPK生長(zhǎng)季CH4平均通量分別為:-44.03 μg?m-2?h-1、-68.96 μg?m-2?h-1、-58.14 μg?m-2?h-1、-8.20 μg?m-2?h-1、-61.79 μg?m-2?h-1。與CK相比, 處理C15、C30及SNPK的CH4吸收值分別增加56.62%、32.05%和40.35%, 處理C45的CH4吸收值與CK相比降低81.36%, 不同生物炭處理間差異顯著(<0.05)。其中處理C15、C30和SNPK顯著促進(jìn)了CH4的吸收, 而處理C45顯著增加了CH4的排放。土壤中添加適量生物炭有助于促進(jìn)土壤對(duì)CH4的吸收, 其中處理C15和SNPK對(duì)CH4的減排效果較好。Person相關(guān)分析結(jié)果(表2)表明, 各處理的CH4通量與土壤溫度均顯著相關(guān)(<0.01); 處理C30及C45的CH4通量與土壤含水率均無(wú)顯著相關(guān), 而處理C15、SNPK的CH4通量與土壤含水率呈顯著(<0.05)負(fù)相關(guān)。

圖4 不同生物炭處理土壤CH4通量季節(jié)動(dòng)態(tài)變化

CK為空白對(duì)照; C15、C30和C45為施用生物炭處理, 施用量分別為15 t?hm-2、30 t?hm-2和45 t?hm-2; SNPK為秸稈還田處理。CK is the control; C15, C30 and C45 are biochar application treatments with biochar rate of 15 t?hm-2, 30 t?hm-2and 45 t?hm-2, respectively; SNPK is treatment of corn straw incorporation.

2.4 施用生物炭后玉米農(nóng)田的N2O通量特征

圖5所示為試驗(yàn)期間玉米農(nóng)田N2O通量變化, 其正值代表土壤進(jìn)行N2O排放, 負(fù)值代表土壤吸收N2O。生長(zhǎng)季初期N2O通量逐漸增大。5月12—15日農(nóng)田種植玉米后土壤N2O通量產(chǎn)生巨大差異, 其中處理C45的N2O通量出現(xiàn)明顯的負(fù)值, 各處理N2O通量均低于CK。生長(zhǎng)季末期處理C45的土壤N2O通量重新由吸收轉(zhuǎn)為排放。處理CK、C15、C30、C45、SNPK生長(zhǎng)季CH4平均通量分別為: 9.23 μg?m-2?h-1、6.98 μg?m-2?h-1、3.99 μg?m-2?h-1、1.27 μg?m-2?h-1、6.62 μg?m-2?h-1, 與CK相比, 處理C15、C30、C45及SNPK的N2O通量分別降低24.42%、56.83%、86.25%和28.28%, 不同生物炭處理間差異顯著(<0.05)。添加生物炭明顯抑制了土壤N2O的排放, 其對(duì)土壤N2O排放的抑制效果隨生物炭施用量而逐漸提升, 各添加生物炭處理對(duì)土壤N2O排放的抑制均在前期較強(qiáng), 而后期較弱, 這可能是因?yàn)榍捌谟衩咨L(zhǎng)過(guò)程中根系、土壤微生物等活動(dòng)旺盛, 對(duì)土壤中的生物炭響應(yīng)更強(qiáng)烈所致。Person相關(guān)分析結(jié)果(表2)表明, 除處理C45, 其他處理的N2O通量與土壤溫度均顯著(<0.05)或極顯著(<0.01)相關(guān); C30及C45的N2O通量與土壤含水率均無(wú)顯著相關(guān), 而處理C15、SNPK的N2O通量與土壤含水率呈顯著(<0.05)或極顯著(<0.01)負(fù)相關(guān)。

圖5 不同生物炭處理土壤N2O通量季節(jié)動(dòng)態(tài)變化

CK為空白對(duì)照; C15、C30和C45為施用生物炭處理, 施用量分別為15 t?hm-2、30 t?hm-2和45 t?hm-2; SNPK為秸稈還田處理。CK is the control; C15, C30 and C45 are biochar application treatments with biochar rate of 15 t?hm-2, 30 t?hm-2and 45 t?hm-2, respectively; SNPK is treatment of corn straw incorporation.

2.5 生物炭對(duì)玉米農(nóng)田土壤溫室氣體綜合排放的影響

與CK相比, 處理C15、C30、C45和SNPK分別增加玉米產(chǎn)量4.41%、5.07%、9.20%和4.28%, 且不同生物炭及秸稈處理間及其與CK間差異顯著(<0.05), 隨生物炭施入量增加玉米產(chǎn)量顯著提高, 處理C45的玉米產(chǎn)量最高, 處理C15與SNPK相近。與CK相比, 處理C15、C30、C45和SNPK的玉米生長(zhǎng)季CO2累積排放量分別減少21.18%、13.86%、16.61%和19.76%, N2O累積排放量分別減少25.44%、57.43%、86.40%和29.22%, 且差異顯著(<0.05), 說(shuō)明施用一定量的生物炭對(duì)土壤CO2和N2O的排放具有抑制作用(表3)。處理C15、C30和SNPK的CH4累計(jì)吸收量比CK分別增加57.43%、32.76%和41.10%, 處理C45則降低83.04%, 且差異顯著(<0.05)。玉米生長(zhǎng)季CH4通量表現(xiàn)為負(fù)值, 即為土壤對(duì)CH4進(jìn)行吸收, 處理C15、C30和SNPK對(duì)土壤CH4的吸收具有一定促進(jìn)作用, 而處理C45則抑制了土壤對(duì)CH4的吸收, 因此說(shuō)明適量施用生物炭對(duì)土壤吸收CH4具有顯著促進(jìn)效果(表3)。整個(gè)生長(zhǎng)季處理C15與SNPK溫室氣體通量變化相近。施入生物炭顯著降低了玉米農(nóng)田的GWP和GHGI, 其中C15對(duì)降低GWP和GHGI貢獻(xiàn)最大, 處理SNPK與處理C15相近。作為重要的溫室氣體, 在100年尺度上CH4和N2O的全球增溫潛勢(shì)分別是CO2的25倍和298倍。本研究表明施入生物炭有效降低了溫室氣體的GWP, 其中處理C15的GHGI最小。

3 討論

本文研究發(fā)現(xiàn)在土壤中添加生物炭及秸稈還田均會(huì)抑制土壤CO2的累積排放, 這個(gè)結(jié)果與非干旱區(qū)小麥-玉米輪作農(nóng)田規(guī)律相反[22], 與內(nèi)蒙古河套區(qū)玉米農(nóng)田結(jié)果相同[23]。本研究區(qū)為干旱區(qū), 土壤含水率較低, 微生物活性對(duì)土壤含水率的變化較為敏感[24], 因此生長(zhǎng)季CO2通量與土壤含水率呈顯著正相關(guān), 同時(shí)較低的土壤含水率會(huì)限制微生物對(duì)生物炭的分解利用能力[21]。有研究表明當(dāng)施入生物炭較多時(shí), 反而會(huì)降低生物炭中不穩(wěn)定碳組分被微生物降解的表觀呼吸率[25], 從而使施入生物炭對(duì)干旱區(qū)與非干旱地區(qū)土壤CO2通量產(chǎn)生不同的影響。生長(zhǎng)季初期(播種后)各處理CO2排放均高于對(duì)照CK, 其原因可能是由于生物炭中含有大量易被微生物吸收利用的有機(jī)質(zhì), 促進(jìn)了土壤中微生物的呼吸作用[26],且生物炭的裂解溫度較低時(shí)會(huì)產(chǎn)生較多轉(zhuǎn)化不完全的糖類(lèi)物質(zhì), 從而使土壤微生物活性增強(qiáng), 降低了土壤的固碳能力[27]。7月6日后CK的CO2排放明顯高于其他處理, 此時(shí)生物炭對(duì)土壤CO2通量表現(xiàn)為明顯的抑制作用, 并在生長(zhǎng)季整體體現(xiàn)為對(duì)CO2排放的抑制, 是因?yàn)檗r(nóng)田中微生物和玉米經(jīng)過(guò)一段時(shí)間的生長(zhǎng)發(fā)育后, 簡(jiǎn)單易吸收的有機(jī)質(zhì)已經(jīng)被吸收殆盡, 并且生物炭會(huì)促進(jìn)土壤中難以被微生物分解吸收的大分子物質(zhì)(腐殖質(zhì)、芳烴及碳水化合物等)的形成[28], 從而降低了微生物對(duì)土壤中碳的吸收和利用[29], 減小土壤碳的礦化速度[30], 最終呈現(xiàn)出對(duì)土壤CO2排放的抑制。生物炭對(duì)農(nóng)田土壤CO2通量的影響是貫穿整個(gè)生長(zhǎng)季的長(zhǎng)期過(guò)程, 添加生物炭對(duì)土壤理化性質(zhì)有所改變進(jìn)而影響CO2通量[31]。

表3 不同生物炭處理下溫室氣體通量累積排放量、玉米產(chǎn)量、綜合增溫潛勢(shì)(GWP)及溫室的氣體排放強(qiáng)度(GHGI)

CK為空白對(duì)照; C15、C30和C45為施用生物炭處理, 施用量分別為15 t?hm-2、30 t?hm-2和45 t?hm-2; SNPK為秸稈還田處理。同列不同小寫(xiě)字母表示不同處理間在0.05水平差異顯著。CK is the control; C15, C30 and C45 are biochar application treatments with biochar rate of 15 t?hm-2, 30 t?hm-2and 45 t?hm-2, respectively; SNPK is treatment of corn straw incorporation. Different lowercase letters indicate significant differences among treatments at 0.05 level.

本研究發(fā)現(xiàn)在農(nóng)田土壤中添加生物炭對(duì)土壤N2O排放有抑制作用, 這與大量研究結(jié)果相同[36-37,39]。經(jīng)相關(guān)分析表明(表2), 處理CK、C15和SNPK生長(zhǎng)季土壤N2O通量與淺層土壤溫濕度呈顯著正相關(guān)(<0.05), 而處理C30和C45土壤N2O通量與表層土壤溫濕度(10 cm處)無(wú)顯著相關(guān)性, 其原因可能是由于本試驗(yàn)區(qū)生長(zhǎng)季土壤溫度均處于硝化反應(yīng)和反硝化反應(yīng)的適宜溫度, 也有可能是由于土壤N2O通量的影響掩蓋了土壤含水率對(duì)土壤N2O通量的影響所致。本研究發(fā)現(xiàn)隨著施入生物炭量的增加, 生物炭對(duì)土壤N2O排放的抑制效果逐漸增強(qiáng), 這與其他地區(qū)的研究結(jié)果相同[40-42]。一方面生物炭會(huì)大量吸收土壤中的N2O[40], 另一方面生物炭對(duì)土壤氮素轉(zhuǎn)化具有一定影響作用[25], 且生物炭本身具有較高的C/N比, 隨著大量生物炭的施入, 土壤的通透性和保水持水能力得到了增強(qiáng), 對(duì)硝化作用和反硝化作用起到了一定程度上的抑制, 從而增加了土壤的固氮作用[41,43]。本文中處理SNPK與C15效果相近, 均對(duì)生長(zhǎng)季土壤N2O的排放具有一定的抑制作用, 這與山東小麥-玉米輪作模式下秸稈還田的規(guī)律不同[22], 這可能是由于土地利用方式、氣候差異以及土壤理化性質(zhì)的不同造成的。

屈忠義等[23]、李露等[42]和李秀云等[44]發(fā)現(xiàn)施入生物炭后整體提升了玉米產(chǎn)量, 這與本文研究結(jié)果一致, 生物炭施入土壤后有效改善土壤理化性質(zhì)并提升作物對(duì)營(yíng)養(yǎng)物質(zhì)的吸收利用, 從而提升作物產(chǎn)量。但本研究施入生物炭后玉米產(chǎn)量的提升與其他研究者得出的結(jié)果相比較低, 可能是本研究區(qū)作為干旱區(qū)降水較少, 對(duì)玉米的生長(zhǎng)有一定程度上的限制作用[24]。

4 結(jié)論

添加生物炭有效降低了科爾沁地區(qū)玉米生長(zhǎng)季農(nóng)田土壤CO2和N2O的累計(jì)排放量, 并對(duì)土壤吸收CH4有一定的促進(jìn)作用, 其中施用15 t?hm-2生物炭對(duì)CO2和CH4的減排效果最好; 過(guò)多添加生物炭(45 t?hm-2)抑制了整個(gè)生長(zhǎng)季土壤對(duì)CH4的吸收, 說(shuō)明只有適量地施入生物炭才能夠有效減排。隨著施入生物炭含量的增大, 生物炭對(duì)土壤N2O的減排效果逐漸提升, 其中施用45 t?hm-2生物炭N2O的減排效果最好。秸稈還田與施用15 t?hm-2生物炭的效果相近, 對(duì)CO2、CH4和N2O均有減排效果。從GWP上來(lái)看, 施用15 t?hm-2生物炭對(duì)溫室氣體減排的整體效果最好。施用生物炭及秸稈還田均有效提高了科爾沁地區(qū)的玉米產(chǎn)量, 且玉米產(chǎn)量隨著施入生物炭含量的增大而提升。從GHGI來(lái)看, 施用生物炭及秸稈還田均具有一定的經(jīng)濟(jì)效益和減排意義, 其中施用15 t?hm-2生物炭的綜合效益最高。因此綜合經(jīng)濟(jì)效益與環(huán)境因素, 建議科爾沁地區(qū)農(nóng)田在種植玉米時(shí)添加15 t?hm-2生物炭, 并在不具備購(gòu)買(mǎi)生物炭條件時(shí)可以考慮以秸稈還田作為對(duì)廢棄秸稈的處理手段。

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Effects of biochar and straw on greenhouse gas fluxes of corn fields in arid regions*

CHENG Gong1,3, LIU Tingxi1,2**, LI Dongfang1,2, DUAN Limin1,2, WANG Guanli1,2

(1. Water Conservancy and Civil Engineering College, Inner Mongolia Agricultural University, Hohhot 010018, China; 2. Key Laboratory of Water Resource Protection and Utilization of Inner Mongolia Autonomous Region, Hohhot 010018, China; 3. Nanjing Water Conservancy Planning Design Institute Corp. Ltd, Nanjing 210000, China)

Biochar refers to a kind of stable and carbon-rich solid matter, generally composed of biomass and fertilizers, such as litter and crop straw, which have been pyrolyzed and carbonized under high temperatures in either a completely anaerobic or partially anoxic state. To explore the effects of biochar and straw returning on the greenhouse gas fluxes of corn fields in arid areas, an experiment was conducted on a corn field in the Horqin District, Inner Mongolia. A static chamber-gas chromatography (GC) technique was used to conduct in situ observations on greenhouse gas (CO2, CH4, and N2O) fluxes under different experimental treatments. These treatments included different application rates of biochar: 0 (CK), 15 (C15), 30 (C30), and 45 t?hm-2(C45); and straw returning (SNPK). For the experiments, the global warming potential (GWP) and greenhouse gas intensity (GHGI) during the growing season were estimated. The results showed that the addition of biochar could significantly reduce the soil CO2and N2O emissions. During the growing season, the CO2fluxes in the C15, C30, C45, and SNPK treatments decreased by 21.16%, 14.34%, 17.02%, and 19.93%, respectively. Among these treatments, C15 exhibited the best emission reduction effect. Compared with CK, the N2O fluxes of C15, C30, C45, and SNPK reduced by 24.42%, 56.83%, 86.25%, and 28.28%, respectively. With the increase in biochar rates, the inhibition effect on N2O emissions increased. Among the treatments, C45 provided the greatest reduction in emissions. Appropriate addition of biochar could promote the soil to absorb CH4. Compared with CK, the soil CH4absorption of C15, C30, and SNPK increased by 56.62%, 32.05%, and 40.35%, respectively. The CH4absorption of C45 decreased by 81.36% compared with CK. Excessive biochar could cause less CH4absorption in the soil. There was a positive correlation between soil CO2flux, temperature, and moisture during the growing season. The CH4and N2O fluxes of CK, C15, and SNPK were significantly correlated with the soil temperature and moisture during the growing season. However, the CH4and N2O fluxes of C30 and C45 did not exhibit a significant correlation with the soil temperature or moisture during the growing season. The addition of biochar and straw returning to the field had a significant effect on increasing the corn yield and reducing the GWP and GHGI in the farmlands. Biochar and straw returning both effectively increased the corn yield in the Horqin District. The corn yield increased as the amount of biochar increased. From the perspective of the GWP, a biochar rate of 15 t?hm-2had the best overall effect on reducing greenhouse gas emissions, similar to the SNPK treatment. From the perspective of the GHGI, biochar and straw returning had certain economic benefits and significant reducing-effects of greenhouse gas emissions. Among the different treatments investigated, 15 t?hm-2of biochar had the highest comprehensive benefits, and the C45 and SNPK treatments were slightly inferior to C15, but higher than C30. Therefore, from the perspectives of comprehensive economic benefits and environmental factors, it was suggested that 15 t?hm-2of biochar should be added to the farmlands in Horqin when growing corn. If biochar was not available, straw returning can also be considered to achieve an increase in corn yields and decrease in greenhouse gas emissions.

Biochar; Corn; Farmland; Greenhouse gas; Straw returning; Arid region

, E-mail: txliu1966@163.com

Jan. 3, 2019;

Mar. 14, 2019

S154.1

2096-6237(2019)07-1004-11

10.13930/j.cnki.cjea.190008

程功, 劉廷璽, 李東方, 段利民, 王冠麗. 生物炭和秸稈還田對(duì)干旱區(qū)玉米農(nóng)田土壤溫室氣體通量的影響[J]. 中國(guó)生態(tài)農(nóng)業(yè)學(xué)報(bào)(中英文), 2019, 27(7): 1004-1014

CHENG G, LIU T X, LI D F, DUAN L M, WANG G L.Effects of biochar and straw on greenhouse gas fluxes of corn fields in arid regions[J]. Chinese Journal of Eco-Agriculture, 2019, 27(7): 1004-1014

* 國(guó)家自然科學(xué)基金項(xiàng)目(51620105003, 51139002, 51769020)、內(nèi)蒙古自然科學(xué)基金重點(diǎn)項(xiàng)目(2018ZD05)、教育部科技創(chuàng)新團(tuán)隊(duì)滾動(dòng)發(fā)展計(jì)劃(IRT_17R60)、科技部重點(diǎn)領(lǐng)域創(chuàng)新團(tuán)隊(duì)(2015RA4013)、內(nèi)蒙古自治區(qū)草原英才創(chuàng)業(yè)創(chuàng)新人才團(tuán)隊(duì)、內(nèi)蒙古農(nóng)業(yè)大學(xué)寒旱區(qū)水資源利用創(chuàng)新團(tuán)隊(duì)(NDTD2010-6)和內(nèi)蒙古自治區(qū)高等學(xué)?！扒嗄昕萍加⒉胖С钟?jì)劃”項(xiàng)目(NJYT-18-B11)資助

劉廷璽, 主要研究方向?yàn)樯鷳B(tài)水文。E-mail: txliu1966@163.com

程功, 研究方向?yàn)闇厥覛怏w通量。E-mail: 18645979803@163.com

2019-01-03

2019-03-14

* The study was supported by the National Natural Science Foundation of China (51620105003, 51139002 and 51769020), the Natural Science Foundation of Inner Mongolia (2018ZD05), the Innovative Research Team of Ministry of Education of China (IRT_17R60), the Innovative Research Team in Priority Areas of Ministry of Science and Technology of China (2015RA4013), the Innovative Research Team of Inner Mongolia Agricultural University (NDTD2010-6) and the Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region (NJYT-18-B11).