李 超, 程凱凱, 廖育林, 郭立君, 文 麗, 唐海明, 湯文光, 汪 柯, 禇 飛, 鐘伶桃, 姜海天, 肖小平**

不同粉碎程度與還田方式對(duì)稻草焚燒特性的影響*

李 超1, 程凱凱1, 廖育林1, 郭立君1, 文 麗1, 唐海明1, 湯文光1, 汪 柯1, 禇 飛1, 鐘伶桃2, 姜海天3, 肖小平1**

(1. 湖南省土壤肥料研究所 長(zhǎng)沙 410125; 2. 寧鄉(xiāng)市農(nóng)業(yè)農(nóng)村局 寧鄉(xiāng) 410699; 3. 寧鄉(xiāng)市農(nóng)資服務(wù)中心 寧鄉(xiāng) 410600)

為從根本上禁止稻草焚燒, 促進(jìn)稻草還田, 本研究依托自主研發(fā)的稻草粉碎均勻拋撒裝置, 通過(guò)大田試驗(yàn)與野外模擬試驗(yàn),以目前水稻收獲的常規(guī)模式稻草不粉碎條帶還田(T1)及中度粉碎條帶還田(T2)為對(duì)照, 設(shè)置稻草粉碎條帶還田模式(T3)及稻草粉碎均勻拋撒還田模式(T4), 研究不同粉碎程度與還田方式對(duì)稻草焚燒特性的影響。結(jié)果表明: 稻草拋撒均勻度及還田密度隨著粉碎程度的增加而顯著增加, 稻草還田厚度則呈顯著減少趨勢(shì)。T4的稻草平均長(zhǎng)度為5.3 cm, 分別僅為T1、T2的13.6%、36.8%; 稻草拋撒均勻度為87.4%, 較T1、T2分別增加49.7個(gè)和42.0個(gè)百分點(diǎn); 稻草還田厚度為2.7 cm, 僅為T1、T2的22.1%、27.8%; 稻草還田密度為17.6 kg?m?3, 較T1、T2分別增加88.3%、17.3%。在稻草條帶還田(T1、T2、T3)模式下, 粉碎程度越高, 含水率下降越慢, 燃燒時(shí)間越長(zhǎng), 燃燒率越低, 燃燒速率越慢, 灰分越高, 燃燒越不充分。T4通過(guò)稻草均勻拋撒雖可加速稻草含水率的下降, 但燃燒時(shí)間、燃燒率及灰分僅分別為0.3 min、6.0%、1.7%, 均顯著低于其他處理, 幾乎未燃燒。表明稻草粉碎均勻拋撒還田條件下無(wú)法燃燒, 有利于從根本上實(shí)現(xiàn)秸稈禁燒。

稻草焚燒; 稻草還田; 稻草粉碎; 均勻拋撒; 燃燒特性; 灰分

我國(guó)農(nóng)作物秸稈年均產(chǎn)量高達(dá)8.02×108t[1], 2010年全國(guó)秸稈露天焚燒比例達(dá)20.8%, 而湖南省秸稈露天焚燒比例高達(dá)43.1%[2], 且主要以水稻()秸稈(稻草)為主。稻草焚燒是中國(guó)秸稈露天焚燒排放的主要貢獻(xiàn)源之一, 其對(duì)各類污染物排放的貢獻(xiàn)率達(dá)27%~51%, 對(duì)PM2.5、BC(黑碳)、SO2和NH3排放的貢獻(xiàn)均超過(guò)40%, 遠(yuǎn)高于玉米()和小麥()秸稈[2], 給周邊城市環(huán)境及居民健康帶來(lái)了巨大壓力。因此, 我國(guó)政府自1999年起, 相繼出臺(tái)了一系列秸稈禁燒文件, 加大秸稈禁燒力度, 提高禁燃監(jiān)管水平, 制止秸稈露天焚燒, 大力推進(jìn)生態(tài)文明建設(shè)[3], 同時(shí)通過(guò)對(duì)秸稈實(shí)行燃料化、飼料化、肥料化、原料化及基料化“五化”處理[1]。近年來(lái), 長(zhǎng)江中下游地區(qū)的秸稈焚燒比例呈下降趨勢(shì), 2017年湖南省的秸稈田間焚燒比例下降至7%[4], 但并未從根本上解決秸稈焚燒這一問(wèn)題。

我國(guó)稻草資源總量達(dá)1.77×108t[5], 稻草富含作物生長(zhǎng)所需的各種養(yǎng)分元素。在農(nóng)村勞動(dòng)力緊缺日益突出及化肥減施背景下, 稻草將是今后水稻生產(chǎn)中最主要的有機(jī)肥來(lái)源。其養(yǎng)分釋放及產(chǎn)生的后效性要優(yōu)于焚燒還田[6-7], 養(yǎng)分殘效的連續(xù)疊加, 使得土壤在氮磷鉀等養(yǎng)分供應(yīng)上更具漸進(jìn)性和持久性[8], 從而可直接替代約20%化學(xué)氮肥、5.0%化學(xué)磷肥和50.0%化學(xué)鉀肥[6,9]; 且顯著增加土壤穩(wěn)定性大團(tuán)聚體、有機(jī)碳含量及其庫(kù)容量[10-11], 還可增加土壤腐殖質(zhì)含量, 改善腐殖質(zhì)品質(zhì)及土壤通氣孔隙, 改善土壤結(jié)構(gòu)[12], 最終可增產(chǎn)2.9%~12.3%[6,13-14]。但稻草以上培肥功能的發(fā)揮需建立在稻草還田的基礎(chǔ)上,而水稻生產(chǎn)中由于水稻收割機(jī)的不配套, 稻草粉碎程度及拋撒均勻度低, 尤其是雙季稻區(qū), 易導(dǎo)致耕作質(zhì)量差、晚稻少免耕操作難及晚稻生長(zhǎng)緩慢等問(wèn)題; 同時(shí), 稻草焚燒便于晚稻農(nóng)事操作的開(kāi)展, 還可降低病蟲草害[15], 相比稻草還田, 農(nóng)戶更青睞稻草直接焚燒。因此, 如何從根本上破解稻草焚燒, 已成為水稻生產(chǎn)向資源節(jié)約型與環(huán)境友好型方向轉(zhuǎn)型的關(guān)鍵問(wèn)題之一。近年來(lái), 水稻收割機(jī)均配套了稻草粉碎裝置, 但存在粉碎程度不夠及拋撒不勻等問(wèn)題, 收割后的稻草曬干后依然可以直接焚燒。本研究基于課題組研發(fā)的與水稻收割機(jī)進(jìn)行組裝配套的稻草粉碎均勻拋撒裝置[16-17], 以目前水稻生產(chǎn)中的常用收割機(jī)收獲后的稻草粉碎及還田方式為對(duì)照, 開(kāi)展不同粉碎程度及還田方式對(duì)早稻草焚燒的影響研究, 以期為稻草禁燒及促進(jìn)稻草還田提供一定理論及技術(shù)支撐。

1 材料與方法

1.1 試驗(yàn)設(shè)計(jì)

供試水稻品種為早稻‘湘早秈45號(hào)’, 2020年7月14日收獲。為更好地還原生產(chǎn)實(shí)際, 采用大田試驗(yàn)與野外模擬試驗(yàn)相結(jié)合。試驗(yàn)以目前水稻生產(chǎn)中的常規(guī)收獲模式稻草不粉碎條帶還田(T1)、中度粉碎條帶還田(T2)為對(duì)照; 依托自主研發(fā)的稻草粉碎均勻拋撒裝置, 設(shè)置稻草粉碎條帶還田(T3)及稻草粉碎均勻還田(T4), 共4個(gè)處理, 每個(gè)處理3次重復(fù)。收獲前, 將目標(biāo)田塊平分為12個(gè)200 m2的小區(qū)(20 m×10 m), 小區(qū)之間間隔0.5 m作隔離帶, 并按隨機(jī)區(qū)組法進(jìn)行編號(hào)。然后對(duì)T1采用未配套稻草粉碎裝置的全喂入聯(lián)合收割機(jī)(星光4LZ-4.2Z)進(jìn)行收獲; T2采用配套稻草粉碎裝置的全喂入聯(lián)合收割機(jī)(雷沃4LZ-5G)進(jìn)行收獲; T4采用配套自主研發(fā)的稻草粉碎均勻拋撒裝置的全喂入聯(lián)合收割機(jī)(沃得4LZ-4.0E)進(jìn)行收獲, 該裝置的碎草原理及應(yīng)用效果見(jiàn)廖育林等[16-17]的研究成果; T3為模擬試驗(yàn)時(shí)增加的處理, 水稻田間收獲時(shí)無(wú)此模式, 故此處未列出, 其稻草粉碎程度同T4。水稻收獲時(shí)留樁高度為30 cm左右。收獲后調(diào)查各小區(qū)的稻草拋撒均勻度及稻草還田厚度, 同時(shí)按五點(diǎn)取樣法取鮮草2000 g左右, 塑料袋密封帶回實(shí)驗(yàn)室用于稻草長(zhǎng)度、含水率及失水速率等相關(guān)測(cè)量及檢測(cè)。

由于田間禁止焚燒稻草, 同時(shí)為便于對(duì)各處理稻草的燃燒特性進(jìn)行統(tǒng)計(jì)觀察, 以及便于后續(xù)采樣, 于2020年7月16日開(kāi)展不同稻草粉碎程度及還田方式下的野外模擬燃燒試驗(yàn)。選擇一土面緊實(shí)濕潤(rùn)且表面平整的泥土地, 將其表層的泥沙等雜物清理干凈, 然后各處理取等量烘干后的稻草220 g (基于田間調(diào)查所得收割后稻草干重3060 kg?hm?2, 不包括稻茬), 其中, T1、T2、T3處理的烘干稻草樣置于90 cm×40 cm的樣方內(nèi), 代表稻草條帶還田, T4處理置于90 cm×80 cm樣方內(nèi), 代表稻草均勻還田。燃燒開(kāi)始后記錄燃燒開(kāi)始時(shí)間及結(jié)束時(shí)間, 有無(wú)明火, 燃燒結(jié)束后稱量剩余稻草干重及灰渣量。

1.2 檢測(cè)項(xiàng)目與方法

稻草粉碎程度: 即水稻收獲后不同長(zhǎng)度稻草的占比情況, 長(zhǎng)度較短的稻草占比越大代表粉碎程度越高。早稻采用不同機(jī)型收割機(jī)收獲后, 按五點(diǎn)取樣法取鮮稻草100 g, 帶回室內(nèi)用直尺測(cè)量稻草長(zhǎng)度,統(tǒng)計(jì)0~5 cm、5~10 cm、10~20 cm、20~30 cm及>30 cm的稻草占比, 并計(jì)算稻草平均長(zhǎng)度。

稻草還田厚度(cm): 收割機(jī)收獲后沿著收割方向, 在田塊中間收割寬幅內(nèi)的稻草覆蓋區(qū)域隨機(jī)選擇10個(gè)橫截面, 每個(gè)橫截面等距離選擇5個(gè)點(diǎn)測(cè)量稻草覆蓋厚度并取平均值。

稻草還田密度(kg?m?3): 將各收割模式下的稻草按五點(diǎn)取樣法取稻草1000 g左右, 3個(gè)重復(fù), 帶回實(shí)驗(yàn)室80 ℃烘干至恒重, 充分混勻后選取部分稻草, 以自然松散狀態(tài)填滿泡沫盒(長(zhǎng)35 cm×寬18 cm×高15 cm)稱重, 稻草還田密度=稻草干重/稻草體積。

稻草拋撒均勻度(%): 指在聯(lián)合收割機(jī)作業(yè)幅寬內(nèi), 作業(yè)后的稻草沿幅寬橫向分布的均勻性, 即100%?拋撒不均勻度[18]。

稻草含水率(%)及失水速率(%?h?1): 收割機(jī)收獲后, 各處理按五點(diǎn)取樣法取1000 g鮮稻草, 3個(gè)重復(fù), 置于恒溫電熱鼓風(fēng)干燥箱中, 溫度設(shè)置50 ℃, 每2 h測(cè)量一次稻草重量直至恒重。稻草含水率(%)=(稻草鮮重?稻草干重)×100/稻草鮮重; 失水速率(%?h?1)=?含水率/(2?1), ?含水率表示相鄰時(shí)間點(diǎn)1至2的稻草含水量降幅。

燃燒率(%): 燃燒結(jié)束后, 將剩余稻草帶回實(shí)驗(yàn)室80 ℃烘干至恒重并稱重, 燃燒率=100%?燃燒后剩余稻草干重×100%/燃燒前稻草干重, 即已燃燒稻草干重占總稻草干重的百分比。

燃燒時(shí)間(min): 稻草開(kāi)始燃燒至結(jié)束燃燒的時(shí)間, 采用秒表進(jìn)行記錄。

燃燒速率(%?min?1): 燃燒速率=燃燒率/燃燒時(shí)間, 即單位時(shí)間內(nèi)稻草干重的燃燒百分比。

灰分(%): 燃燒結(jié)束后, 收集灰渣, 帶回實(shí)驗(yàn)室80 ℃烘干至恒重并稱重, 灰分=燃燒后灰渣量×100/燃燒前稻草干重, 即燃燒后灰渣量占燃燒前稻草干重的比值。

1.3 數(shù)據(jù)處理

運(yùn)用SPSS Statistics 21、Excel 2007實(shí)用數(shù)據(jù)分析軟件對(duì)試驗(yàn)數(shù)據(jù)進(jìn)行統(tǒng)計(jì)分析和作圖。

2 結(jié)果與分析

2.1 還田稻草的田間特征

表1表明: T1模式下的稻草長(zhǎng)度主要以20~ 30 cm及>30 cm為主, T2模式主要以5~10 cm及10~20 cm為主, T4主要以0~5 cm和5~10 cm為主, 其中0~5 cm占比高達(dá)70.5%。稻草粉碎(T4)處理的稻草平均長(zhǎng)度僅分別為稻草不粉碎(T1)及一般粉碎(T2)處理的13.6%和36.8%。稻草還田厚度隨粉碎程度的增加而顯著降低, T4的稻草還田厚度僅分別為T1、T2的22.1%、27.8%。稻草還田密度隨粉碎程度的增加而顯著增加, T4的稻草還田密度分別為T1、T2的1.8倍、1.2倍。稻草拋撒均勻度隨粉碎程度的增加而顯著增加, T4的稻草拋撒均勻度較T1、T2分別增加49.7個(gè)、42.0個(gè)百分點(diǎn)。這表明稻草粉碎程度越高, 還田厚度越低, 拋撒均勻度越高, 還田密度越大。

表1 不同粉碎與還田方式下稻草的田間特征

T1: 稻草不粉碎條帶還田; T2: 稻草中度粉碎條帶還田; T4: 稻草粉碎均勻還田。同列不同小寫字母表示處理間差異顯著(<0.05)。T1: rice straw was not crushed and returned to field in a belt; T2: rice straw was moderately crushed and returned to field in a belt; T4: rice straw was crushed and evenly returned to field. Different lowercase letters in the same column mean significant differences at<0.05 level.

2.2 還田稻草的水分蒸發(fā)動(dòng)態(tài)

各烘干時(shí)間點(diǎn)的稻草含水率均表現(xiàn)為T4T1>T2>T3(圖1B), 其中T4的平均失水速率為8.4%?h?1, 分別是T1、T2、T3的1.8倍、1.9倍、2.4倍, 10 h后下降為零。而T1、T2、T3的稻草失水速率表現(xiàn)出先增加后降低的趨勢(shì), 其平均失水速率較T4分別降低28.9%、37.4%、34.6%。表明在稻草條帶還田下, 粉碎程度越高, 含水率下降越慢, 但通過(guò)稻草均勻拋撒可明顯加速稻草水分的下降。

T1: 稻草不粉碎條帶還田; T2: 稻草中度粉碎條帶還田; T3: 稻草粉碎條帶還田; T4 : 稻草粉碎均勻還田。T1: rice straw was not crushed and returned to field in a strip shape; T2: rice straw was moderately crushed and returned to field in a belt; T3: rice straw was crushed and returned to field in a belt; T4: rice straw was crushed and evenly returned to field.

2.3 還田稻草的燃燒特征

2.3.1 燃燒率

圖2A表明, 各處理間的稻草燃燒率表現(xiàn)為T4

2.3.2 燃燒時(shí)間

圖2B表明, 各處理間的稻草燃燒時(shí)間達(dá)顯著差異(0.05), 稻草均勻還田T4處理的燃燒時(shí)間僅為0.3 min, 顯著低于條帶還田處理(T1、T2、T3)。條帶還田處理的燃燒時(shí)間在2.1~16.2 min, 表現(xiàn)為T1

2.3.3 燃燒速率

圖2C表明, 條帶還田條件下, T1、T2、T3之間的燃燒速率達(dá)顯著差異, 表現(xiàn)出T1>T2>T3, T1的燃燒速率分別為T2、T3的2.5倍、8.6倍, 這表明條帶還田條件下稻草的燃燒速率隨粉碎程度的增加而顯著降低。T4處理的燃燒速率雖然與T2接近, 但由于燃燒率最低及燃燒時(shí)間最短, 幾乎未燃燒, 故不參與比較。

T1: 稻草不粉碎條帶還田; T2: 稻草中度粉碎條帶還田; T3: 稻草粉碎條帶還田; T4: 稻草粉碎均勻還田。不同小寫字母表示各處理間在<0.05水平差異顯著。T1: rice straw was not crushed and returned to field in a strip shape; T2: rice straw was moderately crushed and returned to field in a belt; T3: rice straw was crushed and returned to field in a belt; T4: rice straw was crushed and evenly returned to field. Different lowercase letters indicate significant differences among different treatments at<0.05 level.

2.3.4 灰分

表2表明: 各處理間的出灰率表現(xiàn)為T4

表2 不同粉碎與還田方式下稻草燃燒的出灰率

T1: 稻草不粉碎條帶還田; T2: 稻草中度粉碎條帶還田; T3: 稻草粉碎條帶還田; T4: 稻草粉碎均勻還田。同列不同小寫字母表示各處理間在<0.05水平差異顯著。T1: rice straw was not crushed and returned to field in a strip shape; T2: rice straw was moderately crushed and returned to field in a belt; T3: rice straw was crushed and returned to field in a belt; T4: rice straw was crushed and evenly returned to field. Different lowercase letters in the same column indicate significant differences among different treatments at<0.05 level.

3 討論與結(jié)論

秸稈燃燒特征與秸稈含水率、受熱溫度、顆粒大小及外界氧氣濃度等密切相關(guān)[19-20]。馬增益等[21]和Simmons等[22]發(fā)現(xiàn), 木屑或小木塊在不同含水率條件下, 燃燒速率隨著含水率的增加而減少。秸稈升溫速率越快, 最大燃燒速率越大, 平均燃燒失重速率增加, 且升溫速率越快, 揮發(fā)分更易析出, 燃燒性能越好, 燃燒更穩(wěn)定[20]。外界氧濃度的增加有利于揮發(fā)分的析出, 秸稈燃盡所需要的時(shí)間縮短, 燃盡溫度降低, 最大燃燒速率增加, 平均燃燒失重速率也會(huì)相應(yīng)增加, 秸稈燃燒的穩(wěn)定性提高[20]。本研究表明: 條帶還田模式下, 秸稈粉碎程度越高, 鮮稻草的水分散發(fā)越慢, 變?yōu)楦傻静莺蟮娜紵龝r(shí)間越長(zhǎng), 燃燒率越低, 燃燒速率越慢, 這主要是由于粉碎程度越高, 密度越大, 相互填充能力越強(qiáng), 秸稈間的空隙度及空隙量越小[19], 從而不利于稻草水分的散失, 這在一定程度上可抑制稻草的焚燒。同時(shí)粉碎程度越高, 秸稈間的氧濃度也相應(yīng)降低, 不利于傳熱傳質(zhì)的進(jìn)行, 揮發(fā)分的析出峰值時(shí)間滯后, 揮發(fā)分不易析出, 析出過(guò)程較為平穩(wěn), 導(dǎo)致燃燒時(shí)間越長(zhǎng), 燃燒速率越慢[23]。而本研究在稻草粉碎均勻拋撒還田模式下, 稻草的水分散失最快, 但稻草幾乎未燃燒, 這主要是由于稻草的覆蓋厚度低, 分布散, 導(dǎo)致稻草間的熱能傳遞效率差而無(wú)法燃燒。

秸稈主要由纖維素、半纖維素及木質(zhì)素組成[24]。秸稈的燃燒失重過(guò)程分3個(gè)溫度階段: 第1個(gè)溫度階段(室溫~200 ℃), 失重由秸稈中的吸附水蒸發(fā)及揮發(fā)性氣體析出引起; 第2個(gè)溫度階段(200~350 ℃), 失重由半纖維素、纖維素以及部分木質(zhì)素的熱解和揮發(fā)分的燃燒引起; 第3個(gè)溫度階段(350~600 ℃), 失重由剩余的木質(zhì)素?zé)峤饧敖固咳紵餥25]。稻草的纖維素、半纖維素及木質(zhì)素含量分別為28.4%、27.9%和14.2%[24], 半纖維素最易熱解, 纖維素次之, 木質(zhì)素最難熱解且持續(xù)時(shí)間最長(zhǎng), 半纖維素、纖維素?zé)崃呀夂蟮闹饕龀龀煞譃閾]發(fā)分, 而木質(zhì)素?zé)岱纸夂笾饕商糩26], 這與本研究中稻草條帶還田下燃燒后14.7%~15.3%的灰分結(jié)果吻合。秸稈半纖維素及纖維素?zé)峤馕龀鰮]發(fā)分的同時(shí), 在溫度及氧氣濃度達(dá)到一定程度時(shí)揮發(fā)分才能著火燃燒, 揮發(fā)分燃燒釋放的熱量為后續(xù)揮發(fā)分的析出及著火提供了條件[27]。本研究中, 條帶還田模式下, 粉碎程度越高, 灰分越大, 這可能主要是由于在稻草初始燃燒的低溫段, 粉碎程度越高, 稻草間的孔隙及氧氣濃度越低, 導(dǎo)致稻草的升溫速率越慢, 平均燃燒失重速率降低, 揮發(fā)分更難析出, 且不利于后續(xù)揮發(fā)分的析出, 導(dǎo)致焚燒的損失量低, 灰渣量大, 從而使灰分增大[20,28]。隨著溫度繼續(xù)升高, 反應(yīng)的速度主要決定于氧氣濃度, 前期纖維素?zé)岱纸夂笕紵傻幕野Ｓ嗄举|(zhì)素, 阻礙了氧氣與焦碳的接觸, 雖然溫度達(dá)到了焦炭的著火點(diǎn), 但是其燃燒速度依然較慢[27,29], 這進(jìn)一步增加灰渣量, 導(dǎo)致灰分增加。

本研究中, 在條帶還田模式下, 稻草均能燃燒, 燃燒率為86.3%~96.8%, 但燃燒率及燃燒速率均伴隨粉碎程度的增加而降低, 不粉碎處理的燃燒速率分別為中度粉碎及粉碎處理的2.5倍、8.6倍。稻草粉碎均勻拋撒還田模式下, 其稻草拋撒均勻度較不粉碎條帶還田模式及中度粉碎條帶還田模式分別顯著增加49.7個(gè)和42.0個(gè)百分點(diǎn), 顯著降低了稻草還田厚度及燃燒率, 導(dǎo)致稻草無(wú)法燃燒, 從而從根本上破解了稻草焚燒這一難題。因此, 當(dāng)?shù)卣毮懿块T只需對(duì)聯(lián)合收割機(jī)強(qiáng)制安裝稻草粉碎均勻拋撒裝置, 則可從源頭上徹底禁止稻草焚燒, 這極大地降低了農(nóng)業(yè)執(zhí)法部門執(zhí)行秸稈禁燒政策的執(zhí)法難度及成本, 提高了執(zhí)法效率, 對(duì)于打贏藍(lán)天保衛(wèi)戰(zhàn)及緩解氣候變暖具有重要意義。但本文僅研究了不同粉碎程度及還田方式下的稻草焚燒特性, 而稻草焚燒后的養(yǎng)分損失特征, 稻草還田后的腐解特性、養(yǎng)分釋放規(guī)律及對(duì)土壤養(yǎng)分等的影響, 均有待進(jìn)一步深入研究。

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Effect of crushing degree and returning method on straw combustion*

LI Chao1, CHENG Kaikai1, LIAO Yulin1, GUO Lijun1, WEN Li1, TANG Haiming1, TANG Wenguang1, WANG Ke1, CHU Fei1, ZHONG Lingtao2, JIANG Haitian3, XIAO Xiaoping1**

(1. Institute of Soil Fertility Research in Hunan Province, Changsha 410125, China; 2. Ningxiang Agriculture and Rural Bureau, Ningxiang 410699, China; 3. Ningxiang Agricultural Materials Service Center, Ningxiang 410600, China)

Rice straw burning is a major source of pollutants emissions in China. Its contribution to the emission of various pollutants is much higher than that of corn and wheat straws, which has resulted in tremendous pressure on the surrounding urban environment and residents’ health. Simultaneously, rice straw will become the most important source of organic fertilizer for rice production in the future. To fundamentally forbid rice straw burning and promote rice straw return to the field, in this study, we set the current conventional mode of rice harvest, including rice straw stripped to the field without crush (T1) and with moderate crush (T2) as controls, and crushed rice straw stripped to the field (T3) and evenly returned to the field (T4) as the treatments. The treatments relied on a self-invented device that crushed and homogeneously scattered the rice straw in field tests. The field simulation tests aimed to study the influence of different crushing degrees and returning methods on the rice straw combustion characteristics. The results showed that the scattering homogeneity and returning density of rice straw increased significantly with increased crushing degree, but the returning thickness of rice straw significantly decreased. The rice straw average length of T4 was 5.3 cm, which was only 13.6% and 36.8% of T1 and T2, respectively. The scattering homogeneity of T4 was 87.4%, which was 49.7% and 42.0% higher than that of T1 and T2, respectively. The thickness of rice straw returned to the field of T4 was 2.7 cm, which was only 22.1% and 27.8% of T1 and T2, respectively. The density of rice straw returned to the field of T4 was 17.6 kg?m?3, which was 88.3% and 17.3% higher than that of T1 and T2, respectively. Under the rice straw strip-returning modes (T1, T2, T3), the higher the degree of rice straw crushing, the slower the decline in moisture content, the longer the combustion time, the lower the combustion rate, the slower the combustion speed, the higher the ash content, and the less sufficient the combustion. Although T4 can accelerate the decrease in rice straw moisture content by homogeneous scattering, the combustion time, combustion speed, and ash content were only 0.3%, 6.0%, and 1.7%, respectively. This was significantly lower than those in the other treatments, indicating that the rice straw was almost unburned. These results indicate that the rice straw could not be burned when crushed and evenly thrown to the field, which was beneficial for achieving a ban on rice straw combustion. Therefore, local government functional departments need only to compulsorily install the devices for crushing and homogeneously scattering rice straw with the combine harvester, which will completely prohibit the burning of rice straw. This will promote the fertilization of paddy soil and greatly reduce the difficulty and costs of agricultural law agencies enforcing rice straw burning bans.

Rice straw combustion; Rice straw returning; Rice straw crush; Homogeneously scattering; Combustion characteristics; Ash content

10.13930/j.cnki.cjea.200668

李超, 程凱凱, 廖育林, 郭立君, 文麗, 唐海明, 湯文光, 汪柯, 禇飛, 鐘伶桃, 姜海天, 肖小平. 不同粉碎程度與還田方式對(duì)稻草焚燒特性的影響[J]. 中國(guó)生態(tài)農(nóng)業(yè)學(xué)報(bào)(中英文), 2021, 29(5): 922-928

LI C, CHENG K K, LIAO Y L, GUO L J, WEN L, TANG H M, TANG W G, WANG K, CHU F, ZHONG L T, JIANG H T, XIAO X P. Effect of crushing degree and returning method on straw combustion[J]. Chinese Journal of Eco-Agriculture, 2021, 29(5): 922-928

S225.4; X513

* 國(guó)家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(2016YFD0300906)和湖南省農(nóng)業(yè)科技創(chuàng)新資金項(xiàng)目(2019LS03-1)資助

肖小平, 主要從事稻田培肥及農(nóng)作制研究。E-mail: hntfsxxping@163.com

李超, 主要從事稻田培肥與耕作生態(tài)研究。E-mail: hnchaoli0419@163.com

2020-08-12

2020-09-23

* This study was supported by the National Key Research and Development Program of China (2016YFD0300906) and Hunan Agricultural Science and Technology Innovation Fund Program (2019LS03-1).

, E-mail: hntfsxxping@163.com

Aug. 12, 2020;

Sep. 23, 2020