Beware the Biochar Initiative

Turning bioenergy crops into buried charcoal to sequester carbon does not work, and could plunge the earth into an oxygen crisis towards mass extinction 

~Dr. Mae-Wan Ho
將生物能源作物轉變為埋藏的木炭以固定碳，是行不通的，甚至可能將地球推向氧氣危機，導致大規模滅絕。

~何梅婉博士

原文出處：https://www.i-sis.org.uk/bewareTheBiocharInitiative.php

The story goes that charcoal buried in the soil is stable for thousands if not hundreds of thousands of years and increases crop yields. The proposal to grow crops on hundreds of millions of hectares to be turned into buried ‘biochar’ is therefore widely seen as a “carbon negative” initiative that could save the climate and boost food production.
傳說中，埋藏在土壤中的木炭可以穩定數千甚至數十萬年，並提高作物收成。因此，在數百萬公頃的土地上種植作物，將其轉變為埋藏的「生物炭」的提案，被廣泛視為一項「碳負」計畫，可以拯救氣候並促進食品生產。

That story is fast unravelling. Biochar is not what it is hyped up to be, and implementing the biochar initiative could be dangerous, basically because saving the climate turns out to be not just about curbing the rise of CO₂ in the atmosphere that can be achieved by burying carbon in the soil, it is also about keeping oxygen (O₂) levels up. Keeping O₂ levels up is what only green plants on land and phytoplankton at sea can do, by splitting water to regenerate O₂ while fixing CO₂ to feed the rest of the biosphere [1] (Living with Oxygen, SiS 43).
那個故事正在快速失控。生物炭並不是像宣傳的那樣，而推動生物炭計畫可能會有危險，基本上是因為拯救氣候並不僅僅是透過將碳埋入土壤來抑制大氣中 CO ₂ 的增加，它還必須維持氧氣（O ₂ ）的濃度。維持 O ₂ 濃度只有陸地上的綠色植物和海洋中的浮游植物能做到，它們透過分解水來再生 O ₂ ，同時固定 CO ₂ 以供應其他生物圈[1]（與氧氣共存，SiS 43）。

Climate scientists have only discovered within the past decade that O₂ is depleting faster than the rise in CO₂, both on land and in the sea [2, 3] (O2 Dropping Faster than CO2 Rising, and Warming Oceans Starved of Oxygen, SiS 44). Furthermore, the acceleration of deforestation spurred by the biofuels boom since 2003 appears to coincide with a substantial steepening of the O₂ decline. Turning trees into charcoal in a hurry could be the surest way to precipitate an oxygen crisis from which we may never recover.
氣候科學家僅僅在過去十年內才發現，O ₂ 的消耗速度比 CO ₂ 的增加速度更快，這既發生在陸地上也發生在海洋中[2, 3]（O2 的下降速度快於 CO2 的上升，以及溫暖的海洋缺乏氧氣，SiS 44）。此外，自 2003 年以來由生物燃料浪潮驅動的森林砍伐加速，似乎與 O ₂ 下降的劇烈加劇相吻合。匆忙將樹木轉化為木炭可能是引發氧氣危機的最確定方式，而我們可能永遠無法恢復過去。

Burying charcoal to save the climate
為了拯救氣候而埋藏木炭

The International Biochar Initiative (IBI), according to its website [4], was formed in July 2006 at a side meeting of the World Soil Science Congress at Philadelphia, Pennsylvania, in the United States, by people from academic institutions, commercial ventures, investment banks, non-government organizations and federal agencies around the world, dedicated to research, development, demonstration, deployment, and commercialisation of biochar on a global scale.
國際生物炭倡議組織（IBI），根據其網站[4]所述，於 2006 年 7 月在美国賓夕法尼亞州費城世界土壤科學大會的 side meeting 中成立，由來自全球的學術機構、商業企業、投資銀行、非政府組織及聯邦機構的成員共同組成，致力於全球規模的生物炭研究、開發、示範、推廣及商業化。

IBI has introduced biochar into the 2008 US Farm Bill, so it now counts among a handful of “new, high-priority research and extension areas”. IBI is also working with the United Nations Convention to Combat Desertification to promote biochar in the post-Kyoto climate agreement. And the United Nations Framework Convention on Climate Change has already included biochar in a section entitled: “Enhanced Action on Mitigation” to serve as basis for negotiations during pre-Copenhagen meetings [5].
IBI 已將生物炭納入 2008 年美國農業法案，使其成為少數「新、高優先級研究與推廣領域」之一。IBI 亦與聯合國防治荒漠化公約合作，在京都氣候協議後的框架中推廣生物炭。而聯合國氣候變遷框架公約已將生物炭納入標題為「加強減緩行動」的章節中，作為哥本哈根會議前談判的基礎[5]。

Biochar is just charcoal, produced by burning organic matter such as wood, grasses, crop residues and manure, under conditions of low oxygen (pyrolysis). A number of different pyrolysis techniques exist depending on temperature, speed of heating, and oxygen delivery [6, 7], resulting in different yields of biochar and co-products, “bio-oil” (with energy content value approx 55 percent that of diesel fuel by volume) and “syn-gas” (a mixture of hydrogen, carbon dioxide, carbon monoxide, and hydrocarbons), which can be used to generate electricity, or as low-grade fuel for ships, boilers, aluminium smelter and cooking stoves.
生物炭僅是木炭，透過在低氧條件下（熱解）燃燒有機質如木材、草類、農作物殘留物和糞便製成。存在多種不同的熱解技術，取決於溫度、加熱速度和氧氣供應方式[6, 7]，這些技術會產生不同產量的生物炭和副產品，包括「生物油」（能量含量約為柴油燃料的 55%）和「合成氣」（由氫氣、二氧化碳、一氧化碳和碳氫化合物混合而成），這些副產品可用於發電，或作為低級燃料供船舶、鍋爐、鋁廠和烹飪爐使用。

IBI has encountered strong criticism as a “new threat to people, land and ecosystem” in a declaration signed by more than 155 non-profit organisations worldwide [8]. But patent applications have been made, and companies formed for commercial exploitation of biochar production. Intense lobbying is taking place for biochar to be included in the Kyoto Protocol’s Clean Development Mechanism for mitigating climate change [9, 10], so people implementing that technology would be able to sell certified emission reduction (CER) credits.
國際生物炭研究所（IBI）在一項由全球 155 個以上非營利組織簽署的聲明中被批評為「對人類、土地和生態系統的新威脅」[8]。但已提出專利申請，並成立公司進行生物炭生產的商業開發。為了讓生物炭能包含在《京都議定書》的清潔發展機制中，以減緩氣候變遷[9, 10]，目前正進行激烈的遊說活動，以便實施該技術的人能夠銷售認證減排信用額（CER）。

Things have moved forward so fast with so little public awareness and debate that critics are alarmed, especially over the proposal from some prominent advocates that 500 million hectares or more of ‘spare land’ could be used to grow crops for producing biochar [11, 12], mostly to be found in developing countries; the same as was proposed in the biofuels initiative several years earlier.
事情發展得如此迅速，而公眾的認知和討論卻如此之少，批評者感到驚訝，特別是對於一些知名倡導者提出的方案——即將 500 百萬公頃或更多的「未利用土地」用於種植作物以生產生物炭[11, 12]，這些土地大多位於發展中國家；與幾年前生物燃料倡議中提出的方案相同。

Biofuels proving disastrous
生物燃料證明是災難性的

The biofuels ‘boom’ has already exacerbated climate change by speeding up deforestation and peatland destruction, loss of habitats and biodiversity, depletion of water and soil, and increased the use of agro-chemicals. Above all, it has generated poverty, land grab, land conflicts, human rights abuses, labour abuses, starvation and food insecurity as documented by BiofuelsWatch and 10 other groups [13, 14] (see also [15] (Biofuels: Biodevastation, Hunger & False Carbon Credits, SiS 33). Calls for moratorium on biofuels came from Africa, the US, and the United Nations [16] (UN ‘Right to Food’ Rapporteur Urges 5 Year Moratorium on Biofuels, SiS 36).
生物燃料的「繁荣」已經通過加速森林砍伐和泥炭地破壞，導致棲息地和生物多樣性損失，水資源和土壤資源的枯竭，以及農用化學品的濫用，加劇了氣候變遷。最重要的是，它產生了貧困、土地搶奪、土地衝突、侵犯人權、勞工權益受損、饑餓和糧食不安全，這些都被生物燃料監視組織和其他 10 個團體記錄下來[13, 14]（另見[15]（生物燃料：生物毀滅、饑餓與偽裝碳信用，SiS 33）。要求對生物燃料實施禁令的呼籲來自非洲、美國和聯合國[16]（聯合國「糧食權」專員敦促對生物燃料實施 5 年禁令，SiS 36）。

Biofuel production – mainly bioethanol and biodiesel – more than doubled between 2003 and 2008, driven by rising oil prices; while food prices rose 70 percent between 2005 and 2008 [17], according to data compiled by the international Monetary Fund. The UN declared 2008 the year of the Global Food Crisis (see [18] Food Without Fossil Fuels Now, SiS 39); food riots and fuel protests were rife. UK’s Environment Audit Committee joined the call for moratorium in January 2008 [19], and reiterated it in May 2008 [20].
生物燃料生產——主要為生物乙醇和生物柴油——在 2003 年至 2008 年之間超過倍增，主要受油價上漲的驅動；而根據國際貨幣基金組織編纂的數據，糧食價格在 2005 年至 2008 年之間上漲了 70%[17]；聯合國將 2008 年宣佈為全球糧食危機年（見[18]無化石燃料的糧食，SiS 39）；糧食騷亂和燃料抗議活動頻繁發生。英國環境監察委員會在 2008 年 1 月加入呼籲暫停生產的行列[19]，並在 2008 年 5 月重申此一立場[20]。

Biochar is widely seen as the successor to biofuels on grounds that it will sequester carbon and improve soil fertility while also producing energy. Biochar is not just carbon neutral; it is “carbon negative”, according to its proponents, because buried biochar is stable for thousands, if not hundreds of thousands of years.
生物炭被廣泛視為生物燃料的後繼者，因其能固碳並改善土壤肥力，同時也能產生能源。生物炭不僅是碳中和，據其支持者所言，更是「碳負」，因為埋藏的生物炭能穩定數千，甚至數萬年。

A lifecycle analysis published in 2008 [21] by John Gaunt and Johannes Lehmann, principal biochar proponent at Cornell University, New York, in the United States, considered both purpose grown bioenergy crops (BEC) and crop wastes (CW) as feedstock. The BEC scenario involves a change from growing winter wheat to miscanthus, switchgrass, and corn as bioenergy crops. The CW scenario considers both corn stover and winter wheat straw as feedstock. The energy balance is much more favourable than the production of biofuels such as ethanol from corn. The avoided emissions are between 2 and 5 times greater when biochar is applied to agricultural land than used solely for energy in fossil energy offsets. Some 41–64 percent of emission reductions are related to the retention of C in buried biochar (so the stability of biochar is important), the rest due to offsetting fossil fuel use for energy, fertilizer savings, and avoided soil emissions of N₂O and CH₄, as additional effects of biochar. Unfortunately, the analysis is largely based on assumptions. Biochar is now found to be not quite as stable as claimed and can speed up litter decomposition in the soil (see below). The energy balance of pyrolysis is taken as that reported by one company; and there is lack of conclusive evidence in support of the supposed significant N₂O reduction for at least ten years [6, 11]..
2008 年發表的一篇生命週期分析[21]，由約翰·高恩（John Gaunt）與喬治亞·萊曼（Johannes Lehmann）撰寫，他們是美國紐約康乃爾大學的生質炭主要推動者，該分析將專門種植的生質能源作物（BEC）與農作物廢棄物（CW）視為原料。BEC 情境涉及從種植冬小麦改為種植芒草、鐵線草和玉米作為生質能源作物。CW 情境則考慮了玉米殘體和冬小麦秸秆作為原料。與從玉米生產乙醇等生物燃料相比，能量平衡顯得更加有利。當生質炭應用於農田時，與僅用於化石能源抵銷的能源相比，避免排放量高達 2 至 5 倍。約 41–64%的排放減少量與埋藏生質炭中碳的保持有關（因此生質炭的穩定性很重要），其餘則由於抵銷化石燃料用於能源、肥料節省，以及避免土壤排放的 N ₂ O 和 CH ₄ ，作為生質炭的額外效果。不幸的是，該分析主要基於假設。現已發現生質炭的穩定性並不如宣稱的那般穩定，且會加速土壤中凋落物的分解（見下文）。 熱解的能量平衡採用一家公司所報告的數據；且至少十年來，缺乏支持所謂顯著的 N ₂ O 減少的確鑿證據[6, 11]。

Biochar is not ‘terra preta’
生物炭不是「黑土」

The biochar initiative was inspired by the discovery of ‘terra preta’ (black earth) in the Amazon basin [22, 23], at sites of pre-Columbian settlements (between 450BC and 950AD), made by adding charcoal, bone, and manure to the soil over many, many years (see Fig. 1). Besides charcoal, it contains abundant pottery shards, plant residues, animal faeces, fish and animal bones. The soil’s depth can reach 2 metres, and is reported capable of regenerating itself at the rate of about 1 cm a year. Similar sites are found in Benin and Liberia in West Africa, in the South African savannahs, and even in Roman Britain. According to local farmers in the Amazon, productivity on the terra preta is much higher than surrounding soils.
生物炭推動計畫受到在亞馬遜盆地發現「黑土」（terra preta）的啟發[22, 23]，位於前哥倫布時期聚落（西元前 450 年至西元 950 年）的地點，通過在許多年（見圖 1）裡將木炭、骨頭和糞便添加到土壤中製成。除了木炭外，它還含有豐富的陶器碎片、植物殘留物、動物糞便、魚和動物骨頭。土壤深度可達 2 公尺，據報導每年約能以 1 公分的速度自我再生。類似的地點在西非的貝寧和利比里亞、南非的草原以及甚至羅馬不列顛都發現過。根據亞馬遜當地農民的說法，黑土上的生產力遠高於周圍的土壤。

Investigations in the laboratory revealed that terra preta soils are rich in nutrients such as nitrogen, phosphorus, calcium, zinc, and manganese, and have high levels of microbial activities. Terra preta contains up to 70 times more black carbon (BC) than the surrounding soils. Due to its polycyclic aromatic structure, black carbon is believed to be chemically and microbiologically inert (but see later) and persists in the soil for centuries, if not thousands of years. During this time, oxidation produces carboxylic groups increasing its nutrient-holding capacity. Bruno Glaser and colleagues at the University of Bayreuth concluded that [24] “black carbon can act as a significant carbon sink and is a key factor for sustainable and fertile soils, especially in the humid tropics.”
實驗室調查顯示，黑土（terra preta）土壤富含氮、磷、鈣、鋅和錳等營養素，並具有高水平的微生物活動。黑土的黑碳（BC）含量比周圍土壤高達 70 倍。由於其多環芳香結構，黑碳被認為在化學和微生物學上是惰性的（但見後文），並能在土壤中持續數百年，甚至數千年。在此期間，氧化作用產生羧基，增加其養分保持能力。拜羅伊特大學的布魯諾·格拉斯爾（Bruno Glaser）及其同事結論認為[24]「黑碳可以作為重要的碳庫，並是維持土壤永續和肥沃的關鍵因素，尤其是在濕潤熱帶地區。」

Similarly, BC derived from terra preta sites in central Amazon differing in age from 600 to 8 700 years were chemically, biologically and spectroscopically indistinguishable, as consistent with their “extremely slow” rate of decomposition [25].
類似地，來自亞馬遜中部不同年代（600 至 8,700 年）的土壌黑炭，在化學、生物學和光譜學上無法區分，與其「極度緩慢」的分解速率[25]相符。

However, BC collected from 11 historical charcoal blast furnace sites from Quebec Canada to Georgia USA, were quite different from BC newly produced using rebuilt historical kilns [26]. The historical BC samples were substantially oxidized after 130 years in soils compared to the new BC, or new BC incubated for one year at 30 C or 70 C. The major alterations were an increase in oxygen from 7.2 percent in new BC to 24.8 percent in historical BC; a decrease in carbon from 90.8 percent to 70.5 percent; formation of oxygen-containing function groups, particularly carboxylic acid and phenolic functional groups; and disappearance of surface positive charge, to be replaced entirely by negative charges. New BC incubated at 30 C or 70 C for 12 months increased in oxygen concentrations to 9.2 and 10.6 percent respectively; and also had complete replacement of surface positive charges by negative charges.
然而，從加拿大魁北克到美國喬治亞的 11 個歷史性木炭風爐採集的 BC，與使用重建的歷史性窯爐新製造的 BC [26] 相比，顯得相當不同。歷史性 BC 樣本在土壤中經過 130 年後，相較於新 BC，或新 BC 在 30°C 或 70°C 下孵育一年，已大幅氧化。主要的變化包括氧氣從新 BC 的 7.2%增加到歷史 BC 的 24.8%；碳從 90.8%減少到 70.5%；形成含氧官能基團，特別是羧酸和酚類官能基團；以及表面正電荷的消失，完全被負電荷取代。在 30°C 或 70°C 下孵育 12 個月的新 BC，氧氣濃度分別增加到 9.2%和 10.6%；同時表面正電荷也完全被負電荷取代。

These findings show that BC is a substantial oxygen sink, and could deplete atmospheric O₂ fairly rapidly if massive amounts are produced in a hurry!
這些發現顯示，生物炭是一個顯著的氧氣吸收體，如果在短時間內大量生產，可能會相當快速地耗盡大氣中的氧氣！

The main factor accounting for the changes was mean annual temperature, which was highly correlated with degree of oxidation. BC oxidation was increased by 87 nmoles/kg C / degree Celsius increase in mean annual temperature. BC oxidation to carboxylic groups accounts for the high cation exchange capacity of natural BC in the soil that the authors suggest is the basis of the enhancement in soil fertility.
導致變化的主要因素是年平均溫度，它與氧化程度高度相關。BC 的氧化程度隨年平均溫度每增加 1 攝氏度而增加 87 nmoles/kg C。BC 氧化成羧基解釋了自然土壤中 BC 的高陽離子交換容量，作者建議這是土壤肥力提升的基礎。

So charcoal is not the same as terra preta that has been created over thousands of years by human intervention and natural geochemistry. The claim that biochar is a “stable carbon pool” in the soil that does not degrade for thousands of years is not borne out by the study, nor by a number of other studies (see below).
所以木炭並不等同於由人類干預和自然地球化學在數千年前所創造的陶土黑。研究並未證實生物炭是土壤中「穩定的碳庫」，在數千年内不會分解，這一說法也未被其他多項研究（見下文）所支持。

Naturally occurring black carbon has a far more complex relationship with the soil and the earth as a whole, as recent research is revealing. Moreover, black carbon pollution from fossil fuel and biomass burning associated with deforestation contribute as much to global warming as CO₂, and climate scientist are proposing a reduction of black carbon emissions as a way of cooling the planet [27] (see Black Carbon Warms the Planet Second Only to CO₂, SiS 44). That’s another reason the biochar initiative will spoil the climate, by increasing BC emissions.
自然產生的黑色碳與土壤以及整個地球之間的關係遠比想像中更複雜，正如近年來的研究所揭示。此外，來自化石燃料和生物質燃燒所產生的黑色碳污染，與森林砍伐相關，對全球暖化所做出的貢獻與 CO2 相當，氣候科學家正建議將黑色碳排放減少作為一種使地球降溫的方式[27]（見黑色碳暖化地球僅次於 CO2，SiS 44）。這是另一個原因，為何生物炭計畫會破壞氣候，因為它會增加 BC 排放。

Biochar increases loss of organic carbon from humus
生物炭增加從腐殖質中流失的有机碳

A ten-year trial in Swedish forests showed that buried charcoal appear to promote the breakdown of humus, the decomposing plant matter on the forest floor [28], thus completely offsetting the carbon sequestered in the charcoal.
在瑞典森林進行的十年試驗顯示，埋藏的木炭似乎會促進腐殖質的分解，腐殖質是森林地表層分解的植物質[28]，從而完全抵銷了木炭中封存的碳。

David Wardle and colleagues at Umeå University started their experiment to investigate the effect of forest fires on soil ecology. They buried hundreds of litter bags containing humus, charcoal, or a 50–50 mixture of the two in several sites in the Swedish boreal forest.
David Wardle 與烏梅大學的同事們開始了他們的實驗，旨在調查森林火對土壤生態的影響。他們在瑞典的泰加林區多個地點埋葬了包含腐植質、木炭或兩者 50–50 混合物的數百個廢棄袋。

Periodically, they weighed the bags and measured the concentration of carbon and nitrogen. After just one year, they began to see an unexpectedly large decrease in mass from the bags containing the humus–charcoal mixture: 17 percent (the expected was 9 percent), compared to 18 percent in the bags with only humus and 2.5 percent in the bags with only charcoal Over ten years, the bags with mixed humus and charcoal released just as much carbon as did those containing only humus (130 mg per g initial mass), instead of only half as much as would be expected if charcoal had no effect on the loss of carbon from humus. The bags with charcoal had lost a small amount of its carbon (less than 5 mg per g initial mass) but gained about the same in nitrogen and microbial activity. The mixture did not gain or lose any nitrogen while humus released 2 mg N per g initial mass.
他們定期稱量袋子並測量碳和氮的濃度。僅僅一年後，他們開始注意到包含腐植質–木炭混合物的袋子出現了出乎意料的巨大質量減少：17%（預期為 9%），而只有腐植質的袋子減少了 18%，只有木炭的袋子減少了 2.5%。在十年內，混合腐植質和木炭的袋子釋放的碳量與僅含腐植質的袋子一樣多（每克初始質量 130 毫克），而不是預期中如果木炭對腐植質的碳損失沒有影響，只會釋放一半。含木炭的袋子損失了少量碳（每克初始質量少於 5 毫克），但同時獲得了約相等的氮和微生物活性。混合物沒有增減任何氮，而腐植質釋放了每克初始質量 2 毫克的氮。

The results show that burying charcoal can speed up the decomposition of forest humus during the first decade, thus offsetting nearly all of the carbon sequestered in the charcoal itself.
結果顯示，埋藏木炭可以在第一個十年內加速森林腐植質的分解，從而抵銷了木炭本身所固碳的幾乎全部碳。

Biochar may not be a stable carbon pool
木炭可能不是一個穩定的碳庫

Caroline Masiello, marine chemist at Rice University Houston, Texas, in the United States, pointed to apparent discrepancy in the production and deposition of of BC on both sea sediment and on land [29]. BC production globally was previously estimated at 0.05 to 0.27 Gt/y [30], representing 1.4 to 1.7 percent carbon exposed to fire that’s converted to BC. The only documented loss process for BC is deposition in ocean sediments. However, the rate of total organic carbon deposited on the seafloor is only 0.16 Gt/y. Even assuming the lower end of the BC production rate, 0.05 Gt/y, would mean that BC should be 30 percent of ocean sediment organic carbon; but the actual measured amount is 3-10 percent.
來自美國德克薩斯州休斯頓稻米大學的海洋化學家卡羅琳·瑪西埃洛指出，海床沉積物和陸地上的生物炭生產與沉積之間存在明顯的差異[29]。全球生物炭的生產量先前估計為每年 0.05 至 0.27 Gt[30]，代表 1.4 至 1.7%的暴露於火災中的碳被轉化為生物炭。生物炭的唯一記錄在案的損失過程是沉積在海洋沉積物中。然而，沉積在海床上的總有機碳速率僅為每年 0.16 Gt。即使假設生物炭生產率的較低端，0.05 Gt/年，也意味著生物炭應該佔海洋沉積物有機碳的 30%；但實際測量的數量僅為 3-10%。

Furthermore, isotope studies of highly refractory BC detected ¹⁴C graphite BC in sediment from the Northeast Pacific coastal transept. This was not a product of fossil fuel combustion but the result of erosion of very old graphite from rocks and deposited into the ocean, which is at least in part derived from petrogenic graphite. If BC deposited in ocean sediments comes both from biomass burning and from recycled petrogenic graphite, even less of the annually produced BC can be accounted for in ocean sediments. So where does the rest of the earth’s annually produced BC go?
此外，針對高難燒燬性的生物炭進行同位素研究，在北太平洋沿岸橫斷面的沉積物中檢測到 ¹⁴ C 石墨生物炭。這並非來自化石燃料燃燒，而是由岩石中非常古老的石墨侵蝕後沉積到海洋中，至少部分來源於石油成因石墨。如果沉積在海洋沉積物中的生物炭既來自生物質燃燒，也來自再循環的石油成因石墨，那麼每年產生的生物炭中，能夠在海洋沉積物中計算到的比例就更少了。那麼，地球每年產生的其他生物炭去哪兒了呢？

The same applies to BC on land. If BC has been produced since the last glacial maximum from biomass burning at the same rate as it is now produced, and if it is as stable as assume, it should account for 25 – 125 percent of total soil organic carbon pool. Instead, only a few measurements of BC or soil organic carbon ever reach 25 percent. A study of BC production during Siberian boreal forest fires made clear that not enough BC remains even after 250 years to account for all the BC produced during a fire [31] – estimated at 0.7 -0.8 percent of organic carbon – due to a combination of in situ erosion and translocation within the soil profile, with in situ degradation being the most likely.
同樣適用於陸地上的生物炭。如果生物炭是從上次冰期以來，以現在的產生速率由生物質燃燒製造的，且如果它像假設的那樣穩定，它應該佔總土壤有機碳庫的 25 – 125%。然而，只有少數測量生物炭或土壤有機碳的數值達到 25%。一項關於西伯利亞泰加林野火期間生物炭產生的研究清楚地顯示，即使過了 250 年，仍然沒有足夠的生物炭來解釋野火期間產生的所有生物炭[31] – 估計佔有機碳的 0.7 -0.8% – 這是因為原地侵蝕和土壤剖面內的遷移共同作用，而原地降解是最可能的。

In a later study, the amount of BC in organic carbon was compared in soils of three Siberian Scots pine forests with frequent, moderately frequent, and infrequent fires [32]. The researchers concluded that BC did not significantly contribute to the storage of organic matter, most likely because it is consumed by intense fires. They found 99 percent of BC in the organic layer, with a maximum stock of 72 g/m². Less intense fires consumed only parts of the organic layer and converted some organic matter to BC, whereas more intense fires consumed almost the entire organic layer.
在一項後續研究中，比較了三個西伯利亞松樹林土壤中 BC 在有機碳中的含量，這些林分分別經歷頻繁、中等地頻繁和罕見的火災[32]。研究人員結論認為，BC 並未顯著貢獻於有機質的儲存，最可能的原因是它被強烈的火災消耗了。他們發現有機層中有 99%的 BC，最大儲存量為 72 g/m²。較不激烈的火災僅消耗了部分有機層，並將部分有機質轉化為 BC，而更激烈的火災則消耗了幾乎整個有機層。

But appreciable degradation of BC can also occur in the absence of fires, by microbial action or photo-degradation. The stability of BC was investigated in a sandy savannah soil at Matopos in Zimbabwe, where some soil plots have been protected from fire for the past 50 years [33]. The abundance of BC in these plots was compared to plots that have continued to be burnt. The plots protected from fire had 2.0+5 mg/cm² BC, about half of the 3.8+0.5 mg/cm² found in plots burnt every 1-5 years. The half-life of BC at a depth of 0-5 cm of the soil protected from fire was estimated at < 100 years, and that of large particles <50 years. The results suggest that in well-aerated tropical soil environments, charcoal and other BC can be significantly degraded in decades to a hundred years.
但在沒有火災的情況下，生物炭（BC）也可能因微生物作用或光降解而發生顯著降解。在津巴布韋的馬托波斯地區的沙質稀樹草原土壤中，研究了生物炭的穩定性，其中一些土壤區域在過去 50 年來受到保護，免於火災侵襲[33]。這些受保護區域的生物炭豐度，與持續被燒燬的區域進行了比較。受火災保護的區域含有 2.0±5 mg/cm ² 的生物炭，約為每 1-5 年燒燬區域中 3.8±0.5 mg/cm ² 的一半。在受火災保護的土壤 0-5 公分深度，生物炭的半衰期估計為小於 100 年，而大顆粒則小於 50 年。研究結果顯示，在通氣良好的熱帶土壤環境中，木炭和其他生物炭在數十年至一百年內可以被顯著降解。

BC is best understood as a continuum of combustion products, ranging from slightly charred, degradable biomass to highly condensed refractory soot [28]. All components of this continuum are high in carbon content, chemically heterogeneous and dominated by aromatic structures. The reactivity of BC also varies along the combustion continuum. Charcoal decomposes much more rapidly than soot when exposed to chemical oxidants, such as acid dichromate, in the lab [33].
BC 最好被理解為一種燃燒產物的連續體，從略顯焦炭狀、可降解的生物质到高度凝聚的耐火烟灰[28]。這種連續體的所有成分都富含碳，化學性質異質，並以芳香結構為主。BC 的活性也隨著燃燒連續體而變化。在實驗室中，當暴露於化學氧化劑，如酸式重铬酸時，木炭的分解速度遠比烟灰快[33]。

The results are also complicated by the different ways of producing charcoal and different methods of quantifying BC [28]. In studies on the National Institute of Standards and Technology reference materials, the values varied by a factor of 500, depending only on the method used in quantification.
結果也因為製造木炭的不同方式以及量化 BC 的不同方法而變得複雜[28]。在國家標準技術研究所參考材料的研究中，僅僅取決於所使用的量化方法，其值變化達到 500 倍。

Research in the atmospheric chemistry community has shown that even soot, the most inert part of the combustion spectrum, can be chemically altered on a very short timescale through reaction with atmospheric oxidants. Reaction with ozone and other atmospheric oxidants create hydrophilic carboxylic acid groups on its exterior These reactions are so rapid that solubilisation of soot particles can occur in 30 min in the presence of 50 ppb (parts per billion) ozone, making it possible to dissolve soot in a solution of distilled water. Ozone concentration in rural air in the US ranges diurnally from 20 to 70 ppb. So soot can enter some of the Earth’s dissolved organic carbon pools.
氣象化學界的研究顯示，即使是燃燒譜中最惰性的黑煙，也能在非常短的時間尺度內，透過與大氣氧化劑反應而化學改變。與臭氧和其他大氣氧化劑的反應會在其表面形成親水性羧酸基團。這些反應速度非常快，在 50 ppb（十億分之五十）臭氧存在下，黑煙顆粒可在 30 分鐘內溶解析出，使其有可能在蒸餾水中溶解黑煙。美國鄉村空氣中的臭氧濃度在白天範圍從 20 至 70 ppb。因此，黑煙可以進入地球某些溶解有機碳庫中。

BC has been measured by thermal techniques to be 5 to 12 percent of dissolved organic carbon in Chesapeake Bay, the Delaware Bay, and in adjacent Atlantic Margin. Another electrospray ionization with high resolution mass spectrometry applied to dissolved organic matter from a small stream in New Jersey and Rio Negro detected BC degradation products that were assigned chemical structures.
透過熱分析方法測量，黑煙（BC）在切薩皮克灣、特拉華灣及其相鄰的大西洋邊緣的溶解有機碳中佔 5 至 12%。另一項應用於新澤西州一條小溪和黑河溶解有機物的電噴霧化高解析質譜法，檢測到黑煙降解產物，並分配了其化學結構。

Biochar effects on soil fertility not always positive
生物炭對土壤肥力的影響不總是正面的

Experiments carried out so far have yielded equivocal results on the ability of biochar to increase productivity. There have been positive effects claimed, at least in the short term, but also some negative impacts, at least partly due to nitrogen limitation [34]. In a small scale lab experiment, biochar appeared to increase nitrogen fixation by legumes, principally by increasing the availability of trace elements boron (B) and molybdenum (Mo), and to a lesser extent, K, Ca, and P, while lowering N availability and Al saturation. The results on productivity were not statistically significant, however.
至今為止所進行的實驗，對於生物炭能否提升產量的能力，結果並不一致。雖然有人聲稱在短期內有正面效果，但也存在一些負面影響，至少部分是因為氮素限制[34]。在一個小規模的實驗室實驗中，生物炭似乎能增加豆科植物的固氮作用，主要是透過增加微量元素硼（B）和鎂（Mo）的可利用性，以及相對較小的程度增加 K、Ca 和 P，同時降低氮素的可利用性和鋁飽和度。然而，對於產量的影響並沒有統計上的顯著性。

A report published in 2007 presented results on crop yields over four seasons [35]. Researchers at the University of Bayreuth in Germany, and EMBRAPA Amazonia Occidental Manaus in Brazil carried out a field trial near Manaus on cleared secondary forest with 15 different amendment combinations of chicken manure (CM), compost (CO), forest litter, chemical fertilizer (F), and charcoal (CC) applied once on rice and sorghum, and followed over four cropping cycles (see Fig. 2).
一份於 2007 年發表的報告呈現了四個季節的作物產量結果[35]。德國拜羅伊特大學以及巴西 EMBRAPA 亞馬遜西部馬瑙斯研究單位在馬瑙斯附近進行了一項田野試驗，在清理過的次生林區進行試驗，使用雞糞(CM)、堆肥(CO)、森林落葉、化學肥料(F)和木炭(CC)組合了 15 種不同的改良組合，分別在水稻和小米上施用一次，並追蹤了四個耕作週期（見圖 2）。

Chicken manure gave by far the highest yield over the four cycles (12.4 tonne/ha). Compost application came second at about half the yield, but was still four times higher than chemical fertilizer. The control, leaf litter (burnt and fresh), and charcoal treatments gave no grain yields after the second season, and were discontinued.
雞糞在四個循環中產量遠高於其他處理（12.4 公噸/公頃）。堆肥施用次之，產量約為一半，但仍高於化學肥料四倍。對照組、葉片落葉（燒過與新鮮）、以及木炭處理在第二個季節後無法產生穀物收穫，因此停止實驗。

In combination with compost, charcoal amendment decreased yield by about 40 percent compared to compost alone, and only improved yield in combination with chemical fertilizer. The charcoal was derived from secondary forest wood bought from a local distributor, and applied at the rate of 11 tonne/ha. This corresponded to the amount of charcoal C that could be produced by a single slash-and-char event in a typical secondary forest on the dry iron-rich soil of central Amazonia.
與堆肥結合時，木炭改良劑使產量比單獨使用堆肥減少了約 40%，且僅在與化學肥料結合時才能提高產量。這些木炭來自當地供應商購買的次生林木材，施用量為 11 公噸/公頃。這相當於在亞馬遜中部乾燥鐵質土壤的典型次生林中，單次刈割燒炭活動所能產生的木炭 C 量。

The highest yields for all treatments were obtained at the first harvest, and except for chicken manure, yields declined rather sharply by the second harvest.
所有處理方式中，最高收穫量是在第一次收穫時獲得，除了鴨糞之外，第二次收穫時收穫量都明顯下降。

A second fertilization with chemicals was applied after the second harvest to all remaining treatments, but that did not improve the yields.
在第二次收穫後，對所有剩下的處理方式進行了第二次化學肥料施肥，但這並沒有提高收穫量。

Plants fertilized with chicken manure had the highest nutrient contents followed by plants that received compost and/or chemical fertilizer. Chicken manure significantly improved the K and P nutrition compared to all other treatments, while charcoal applications did not show a significant effect on nutrient levels. Most importantly, surface soil pH, phosphorus, calcium and magnesium were significantly enhanced by chicken manure. Plots fertilized by chicken manure had pH higher than 5.5 and increased cation exchange capacity.
使用雞糞施肥的植物具有最高的養分含量，其次是使用堆肥和/或化學肥料施肥的植物。與其他處理方式相比，雞糞顯著提升了 K 和 P 養分，而木炭施用對養分水平沒有顯著影響。最重要的是，雞糞顯著提升了表面土壤的 pH 值、磷、鈣和鎂含量。使用雞糞施肥的區域，其 pH 值高於 5.5，並增加了陽離子交換容量。

These results are disappointing for those looking to promote ‘biochar’ as a means of improving the yield of crops at the same time as sequestering carbon, which also turns out to be illusory.
這些結果對於那些希望將「生物炭」作為提高作物產量的同時進行碳封存的方法來推廣的人來說，是令人失望的，而且這一點也證明是虛幻的。

The potential for an oxygen crisis is real
氧氣危機的潛在可能性是確實的

It is clear that biochar has not lived up to its promises as a stable C repository or enhancer of crop yields. On the other hand, the risk of oxygen depletion is real [1-3]. Biochar itself is an oxygen sink in the course of degrading in the soil [24. 32]; adding to the depletion of oxygen that cannot be regenerated because trees have been turned into biochar for burial. And worse, as in the biofuels boom that has already apparently speeded up deforestation and oxygen depletion since 2003 [2], if biochar is promoted under the Clean Development Mechanism, it will almost certainly further accelerate deforestation and destruction of other natural ecosystems (identified as ‘spare land’) for planting biochar feedstock, and swing the oxygen downtrend that much closer towards mass extinction.
很明顯，生物炭未能實現其作為穩定碳庫或提高作物產量的承諾。另一方面，缺氧的風險是確實存在的[1-3]。生物炭本身在土壤中降解過程中是氧氣的吸收源[24. 32]；加上因為樹木被轉化為生物炭進行埋藏，導致氧氣無法再生，進一步加劇了缺氧問題。更糟的是，正如自 2003 年起已經明顯加速了森林砍伐和缺氧的生物燃料風潮一樣[2]，如果生物炭在潔淨發展機制下被推廣，幾乎可以肯定將會進一步加速森林砍伐和破壞其他自然生態系統（被識別為「剩餘土地」）以種植生物炭原料，並將氧氣下降趨勢推至大規模物種滅絕的邊緣。

Article first published 07/09/09

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