两种水分含量下生物质炭对黑土N2O排放及硝化反硝化基因丰度的影响

生物质炭对土壤结构改良、土壤肥力提升和农田温室气体排放具有重要意义。本研究以吉林省梨树县典型黑土为研究对象，通过培育实验，研究不同土壤水分含量（40%WHC和100%WHC）下，生物质炭种类（玉米秸秆生物质炭和稻壳生物质炭）和施加量（0%、1%和4%（w/w））对黑土N2O排放及硝化反硝化功能基因丰度的影响。结果表明，随着秸秆生物质炭施加量的增加，土壤N2O排放呈下降趋势，4%高量秸秆生物质炭添加下，土壤N2O排放量仅为1%低量秸秆生物质炭添加下的33.9%。同时土壤NO- 3-N也表现出一致性规律，4%高量生物质炭添加下土壤NO- 3-N含量显著低于1%低量生物质炭。在100%WHC土壤水分状况下，玉米秸秆生物质炭显著增加了土壤N2O排放，而稻壳生物质炭则显著降低了土壤N2O排放。高土壤水分显著促进了土壤N2O排放，进一步为实时荧光定量PCR结果所证实，高土壤水分通过增加nirS基因丰度进而促进了土壤反硝化作用过程，而4%高量稻壳生物质炭添加下nosZ基因丰度显著高于玉米秸秆生物质炭添加，表现出更强的N2O还原潜力。尽管amoA-AOA基因丰度在不同生物质炭添加量下并未发生显著变化，但amoA-AOB基因丰度在高量玉米秸秆生物质炭添加下显著下降。结果说明，土壤水分和生物质炭通过影响土壤硝化反硝化微生物的营养底物和代谢过程，进而影响土壤N2O排放特征。     

施肥对夏玉米季紫色土N2O排放及反硝化作用的影响

采用原状土柱-乙炔抑制培养法研究了施肥对紫色土玉米生长季土壤N2O排放通量和反硝化作用的影响.结果表明:玉米季施肥显著增加土壤N2O排放和反硝化损失,同时,各施肥处理间N2O排放与反硝化损失量差异显著.猪厩肥、猪厩肥配施氮磷钾肥、氮肥、氮磷钾肥和秸秆配施氮磷钾肥等处理的土壤N,O排放量分别为3.01、2.86、2.51、2.19和1.88 kg hm-2,分别占当季氮肥施用量的1.63％、1.53％、1.30％、1.09％和0.88％,反硝化损失量分别为6.74、6.11、5.23、4.69和4.12 kg hm-2,分别占当季氮肥施用量的3.97％、3.55％、2.97％、2.61％和2.23％,不施肥土壤的N2O排放量和反硝化损失量仅为0.56和0.78 kg hm-2.施肥是紫色土玉米生长前期(2周内)土壤N2O排放和反硝化速率出现高峰的主要驱动因子,土壤铵态氮和硝态氮含量是影响土壤N2O排放、土壤硝化和反硝化作用的限制因子,土壤含水量是重要影响因子,降雨是主要促发因素.土壤N2O排放量与反硝化损失量的比值介于0.45 ～0.72之间,土壤反硝化损失量极显著高于土壤N2O排放量,说明土壤反硝化作用是紫色土玉米生长季氮肥损失的重要途径.     

农田土壤硝化—反硝化作用与N2O的排放

在北京潮土上研究了冬小麦夏玉米轮作体系下土壤硝化反硝化作用以及N2O排放情况。结果表明，小麦生育期土壤温度及含水量降低，无论是反硝化损失氮量还是土壤的N2O生成排放量均不高。土壤的N2O生成排放量与反硝化氮量相当或低于反硝化氮量。玉米生育期土壤温度升高以及孔隙含水量的较大的改善，反硝化损失氮量、N2O生成排放量有明显上升。通常情况下土壤反硝损失氮量与N2O排放氮量基本处于同一水平。在玉米十叶期追肥后的较短时间内，N2O总排放量明显高于反硝化损失氮量，说明至少在这一阶段中，硝化作用在北方旱地土壤N2O的排放中发挥了主要作用。在评价北方旱地农田土壤氮素硝化反硝化损失中，硝化作用的氮素损失是不可忽视的重要方面。     

秸秆生物质炭对稻田土壤剖面N2O和N2浓度的影响*

氧化亚氮（N2O）和氮气（N2）是淹水稻田土壤剖面反硝化过程的重要气态产物,可通过土水界面向大气排放,也可随水向下淋溶。秸秆生物质炭施入稻田后会改变土壤理化及微生物学性质,影响反硝化过程及N2O和N2产排。本研究依托2010年夏建立的连续秸秆生物质炭还田的稻麦轮作农田试验,通过埋设淋溶管收集土壤剖面溶液,采用气相色谱和膜进样质谱分别定量溶液中N2O和exN2（反硝化产生N2量）,观测了2018和2019年水稻季不同秸秆生物质炭施用量（CK：每季0 t·hm-2;1BC：每季2.25 t·hm-2;5BC：每季11.3 t·hm-2;10BC：每季22.5 t·hm-2）下0~1 m土壤剖面溶液中N2O和exN2浓度的时空变化,评估了长期施用秸秆生物质炭对稻田土壤剖面反硝化作用及其主要气态氮产物exN2随水流失的影响。结果表明,两个稻季CK处理N2O浓度以60 cm处较高,exN2浓度则随土壤深度增加呈降低趋势。秸秆生物质炭处理能降低剖面N2O和exN2浓度,以10BC处理最为明显。其中,N2O浓度降低以60 cm处较大,exN2浓度降低随土壤深度增加而加大。施用秸秆生物质炭对土壤剖面溶液无机氮（NO3-+NH4+）含量无明显影响,但5BC和10BC处理增加了可溶性有机碳（DOC）和溶解氧（DO）浓度以及氧化还原电位（Eh）。CK处理下土壤剖面溶液N2O和exN2浓度变化与DOC、硝态氮（NO3-）及DO有关;秸秆生物质炭处理下则主要受DO和Eh控制。exN2淋溶量（按1 m深度计算）CK处理下为2.3 ~5.5 kg·hm-2,相当于无机氮和有机氮（DON）淋溶量的32%~34%,5BC和10BC处理则降低为1.7 ~3.7 kg·hm-2和1.1~1.9 kg·hm-2,上述结果表明,反硝化产生N2随水淋溶量不容忽视,秸秆生物质炭还田可改善淹水稻田土壤剖面的通气状况,增加DO,提高Eh,进而有效减少深层反硝化及其主要气态产物exN2随水流失的风险。     

农田土壤硝化反硝化作用及其对生物炭添加响应的研究进展

氧化亚氮（N2O）是重要的温室气体之一,还会破坏大气臭氧层,影响全球气候变化。农田土壤是N2O最主要的排放源,由微生物主导的硝化和反硝化作用是其最主要的排放途径,因此,土壤的硝化和反硝化作用备受关注。在综合国内外相关研究的基础上,就区分硝化和反硝化作用对N2O排放贡献的研究方法、土壤N2O产生途径及其影响因素以及施用生物炭对N2O排放的影响机理进行归纳总结。结果表明：硝化和反硝化作用对生物炭的响应不同,在N2O减排效应上也存在很大的不确定性,其内在机理尚不明确。在此基础上,提出区分硝化和反硝化作用对N2O排放贡献的最佳研究方法,并就农田土壤硝化反硝化作用的影响因素以及对生物炭的响应机制进行研究展望。     

强酸性茶园土壤中添加不同肥料氮后N2O释放量变化

茶园由于长期偏施氮肥，造成土壤酸化现象严重和 N2O 大量排放。本文对强酸性茶园土壤进行不同氮肥处理试验，结果表明， 通过31 d的好气培养，各施肥处理均显著提高N2O排放， 其中施硝酸钾（KNO3）处理平均每天排放的N2O最高，总排放量为对照（CK）的17倍，其次是硝酸铵（NH4NO3）处理， 尿素［CO（NH2）2］和硫酸铵［（NH4）2SO4］处理虽然能增加N2O 排放，但远远小于硝酸钾处理。对各氮肥处理硝化势的测定表明，尿素、 硫酸铵和硝酸铵处理均明显增加土壤硝化活性，而硝酸钾处理硝化势与对照相比显著降低。强酸性茶园土壤中N2O排放的主要来源是反硝化作用。氧化亚氮还原酶（nosZ）的定量PCR 分析表明，硝酸钾处理的nosZ 基因拷贝数与对照相比显著降低（P0.05）。因此，强酸性土壤中N2O还原酶活性被NO3-抑制是导致高N2O排放的重要原因之一。     

生物质炭对酸性菜地土壤N2O排放及相关功能基因丰度的影响

【目的】 生物质炭显著影响土壤氧化亚氮 (N₂O) 排放,但关于其相关微生物机理的研究相对匮乏,尤其是生物质炭对酸性菜地土壤N₂O排放的微生物作用机理。本文通过研究氮肥配施生物质炭对酸性菜地土壤N₂O排放以及硝化和反硝化过程相关功能基因丰度的影响,探讨酸性菜地土壤N₂O排放与功能基因丰度的关系,阐释生物质炭对酸性菜地土壤试验N₂O排放的微生物作用机理。 【方法】 在田间一次性施入生物质炭 40 t/hm2,试验连续进行了3年,共9茬蔬菜。设置4个处理:对照 (CK)、氮肥 (N)、生物质炭 (Bc) 和氮肥 + 生物质炭 (N + Bc)。在施用后第三年,采集土壤样品进行室内培养,应用荧光定量PCR技术检测硝化过程氨氧化古菌 (AOA)、氨氧化细菌 (AOB) 功能基因amoA和反硝化过程亚硝酸还原酶基因 (nirK、nirS) 以及N₂O还原酶基因 (nosZ) 等相关功能基因丰度,同时监测土壤pH值、无机氮 (铵态氮、硝态氮) 含量及N₂O排放。 【结果】 与CK相比,生物质炭 (Bc) 处理的土壤有机碳 (SOC) 提高了27.1%,总氮 (TN) 提高了8.2%,amoA-AOB基因丰度显著降低了11.0%,nosZ基因丰度增加了21.2% (P < 0.05),N ₂O排放没有显著变化 (P > 0.05)。与CK相比,施用氮肥 (N) 显著降低土壤pH ( P < 0.05),显著增加土壤无机氮含量、 nirK、nirS和nosZ功能基因丰度以及土壤N₂O累积排放量 (P < 0.05)。与N处理相比,生物质炭与氮肥联合施用 (N + Bc) 处理显著增加 amoA-AOA、amoA-AOB、nirK、nirS和nosZ基因丰度,增幅分别为68.1%、39.3%、21.1%、19.8%、48.4% (P < 0.05),但 ( nirK + nirS)/nosZ的比值降低,同时N₂O累积排放量显著降低33.3% (P < 0.05)。室内培养期间N ₂O排放峰出现在1～5 d,N和N+Bc处理排放速率分别为 N 1.70 × 103和1.76 × 103 ng/(kg·h)。相关分析结果显示,N₂O排放速率与氧化亚氮还原酶的标记基因nosZ基因拷贝数 (P < 0.05)、NH ₄+-N含量 (P < 0.01) 呈显著正相关,与pH呈显著负相关 ( P < 0.01)。 【结论】 在菜地生态系统中氮肥和生物质炭联合施用可以有效缓解菜地土壤酸化,减少菜地土壤N₂O排放,主要归因于反硝化作用nosZ基因丰度增加,(nirK + nirS)/nosZ比值降低。      

不同酸碱性紫色土的硝化活性及微生物群落组成

为研究紫色土中的硝化作用、总微生物和硝化微生物的群落结构,以重庆永川的酸性紫色土(p H=5.3)和中性紫色土(p H=7.2)以及四川盐亭的石灰性紫色土(p H=8.5)为研究对象,采用稳定性同位素标记技术进行培养实验,并通过Miseq测序对三种紫色土微生物群落结构进行分析。每种土样共设有三种处理,包括~(13)CO_2标记处理、~(12)CO_2对照处理和~(13)CO_2+C_2H_2对照处理。结果表明,中性紫色土(p H=7.2)和石灰性紫色土(p H=8.5)经过56 d的培养后发生了强烈的硝化作用,而酸性紫色土(p H=5.3)中未发生明显的硝化作用,并且硝化作用类型都以自养硝化为主。三种紫色土中都存在着变形菌门(Proteobacteria)、酸杆菌门(Acidobacteria)、厚壁菌门(Firmicutes)、绿弯菌门(Chloroflexi)、放线菌门(Actinobacteria)、拟杆菌门(Bacteroidetes)和芽单胞菌门(Gemmatimonadetes),其中变形菌门在三种紫色土中都大约占有20%的比例。中性紫色土和石灰性紫色土各处理中硝化螺旋菌门(Nitrospirae)百分比大于酸性紫色土各处理。三种紫色土各处理中的氨氧化细菌(Ammonia-oxidizing bacteria,AOB)主要以亚硝化螺菌属(Nitrosospira)为主,亚硝酸氧化细菌(Nitrite-oxidizing bacteria,NOB)主要以硝化螺菌属(Nitrospira)为主。且NOB/AOB的值在三种紫色土各处理中最高可达到13,这意味着全程氨氧化细菌(Comammox)可能在紫色土的硝化作用中占据重要贡献。     

短期培养下抑制剂烯丙基硫脲对土壤硝化作用及微生物的影响

硝化抑制剂烯丙基硫脲（ATU）对土壤硝化作用及温室效应的影响及机理尚不清楚。本研究采集典型旱地土壤,进行21天室内微宇宙培养,探究了氮肥与不同剂量ATU（分别为氮素用量的1%, 5%, 10%, 15%和20%）配施对土壤硝化作用及N2O和CO2排放通量的影响,并通过实时荧光定量PCR和高通量测序16S rRNA基因技术监测硝化微生物群落变化,同时与传统硝化抑制剂双氰胺（DCD）进行了保氮减排效果的对比。结果表明,与未施加氮肥的对照相比（CK）,单施氮肥（N）显著提高了土壤硝化强度并促进了N2O排放。DCD能显著抑制硝态氮和N2O的积累,抑制效率分别为68.6%和93.3%。而低浓度ATU对土壤硝化作用无影响,仅在高浓度具有抑制效应,且抑制效率最高仅为14.7%。所有ATU处理N2O排放量均显著降低,降幅为60.3～68.2%,仍远高于DCD处理。处理间N2O和CO2的综合温室效应强弱顺序为N>ATU+N>DCD+N≈CK,且不同ATU施用量处理之间差异不显著。相关分析发现氨氧化细菌（AOB）,而不是氨氧化古菌（AOA）和全程氨氧化细菌（Comammox）,与土壤硝态氮积累和N2O排放显著正相关,与土壤pH显著负相关。高通量测序结果表明Nitrosovibrio tenuis类型AOB对氮肥诱导的硝化过程起主导作用。除此之外,ATU和DCD还能显著提高Cupriavidus,并降低Patulibacter、Aeromicrobium、Actinomycetospora、Defluviicoccus和Acidipila等微生物属在群落中的相对丰度。该研究为深化土壤碳氮循环理论,合理使用硝化抑制剂以及减缓温室气体排放提供科学依据。     

南京郊区番茄地中氮肥的气态氮损失

采用田间试验研究了番茄地施用化学氮肥后的氨挥发、反硝化损失和N2O排放及其影响因素。氨挥发采用通气密闭室法测定，反硝化损失（N2＋N2O）采用乙炔抑制-土柱培养法测定，不加乙炔测定N2O排放。结果表明，番茄生长期间全部处理均未检测到氨挥发，其原因是土表氨分压低于检测灵敏度，较低的氨分压是由于表层土壤的铵态氮浓度和pH都不高所致。在番茄生长期间，对照区即来自有机肥和土壤本身的反硝化损失和N2O℃排放量相当高，反硝化损失总量高达N29．6kghm^-2，N2O排放量为N7．76kghm^-2。施用化学氮肥显著增加了反硝化损失和N2O排放，3个施用化学氮肥处理的反硝化损失变化在N40．8～46．1kghm^-2之间，占施入化肥氮量的5．50％～6．01％；N2O排放量为N13．6～17．6kghm^-2，占施入化肥氮量的2．62％～4．92％；与尿素相比，包衣尿素未能显著减低反硝化损失和N2O排放。施用尿素的处理在每次追肥后，耕层土壤均会出现NO3^--N高峰，继之的反硝化和N2O排放高峰。反硝化速率与土壤含水量呈极显著正相关。总的看来，番茄生长期间没有氨挥发，而硝化反硝化是氮素损失的重要途径之一。     

Effects of biochar amendment on greenhouse gas emissions,net ecosystem carbon budget and properties of an acidic soil under intensive vegetable production

Biochar addition to soils has been frequently proposed as a means to increase soil fertility and carbon (C) sequestration. However, the effect of biochar addition on greenhouse gas emissions from intensively managed soils under vegetable production at the field scale is poorly understood. The effects of wheat straw biochar amendment with mineral fertilizer or an enhanced‐efficiency fertilizer (mixture of urea and nitrapyrin) on N₂O efflux and the net ecosystem C budget were investigated for an acidic soil in southeast China over a 1‐yr period. Biochar addition did not affect the annual N₂O emissions (26–28 kg N/ha), but reduced seasonal N₂O emissions during the cold period. Biochar increased soil organic C and CO₂ efflux on average by 61 and 19%, respectively. Biochar addition greatly increased C gain in the acidic soil (average 11.1 Mg C/ha) compared with treatments without biochar addition (average ?2.2 Mg C/ha). Biochar amendment did not increase yield‐scaled N₂O emissions after application of mineral fertilizer, but it decreased yield‐scaled N₂O by 15% after nitrapyrin addition. Our results suggest that biochar amendment of acidic soil under intensive vegetable cultivation contributes to soil C sequestration, but has only small effects on both plant growth and greenhouse gas emissions.     

Wheat straw and its biochar had contrasting effects on soil C and N cycling two growing seasons after addition to a Black Chernozemic soil planted to barley

Application of crop residues and its biochar produced through slow pyrolysis can potentially increase carbon (C) sequestration in agricultural production systems. The impact of crop residue and its biochar addition on greenhouse gas emission rates and the associated changes of soil gross N transformation rates in agricultural soils are poorly understood. We evaluated the effect of wheat straw and its biochar applied to a Black Chernozemic soil planted to barley, two growing seasons or 15 months (at the full-bloom stage of barley in the second growing season) after their field application, on CO₂ and N₂O emission rates, soil inorganic N and soil gross N transformation rates in a laboratory incubation experiment. Gross N transformation rates were studied using the ¹⁵N isotope pool dilution method. The field experiment included four treatments: control, addition of wheat straw (30 t ha^?1), addition of biochar pyrolyzed from wheat straw (20 t ha^?1), and addition of wheat straw plus its biochar (30 t ha^?1 wheat straw + 20 t ha^?1 biochar). Fifteen months after their application, wheat straw and its biochar addition increased soil total organic C concentrations (p?=?0.039 and <0.001, respectively) but did not affect soil dissolved organic C, total N and NH₄ ⁺-N concentrations, and soil pH. Biochar addition increased soil NO₃ ^?-N concentrations (p?=?0.004). Soil CO₂ and N₂O emission rates were increased by 40 (p?p?=?0.03), respectively, after wheat straw addition, but were not affected by biochar application. Straw and its biochar addition did not affect gross and net N mineralization rates or net nitrification rates. However, biochar addition doubled gross nitrification rates relative to the control (p?2 and N₂O emissions and enhance soil C sequestration. However, the implications of the increased soil gross nitrification rate and NO₃ ^?-N in the biochar addition treatment for long-term NO₃ ^?-N dynamics and N₂O emissions need to be further studied.     

15N示踪法研究生物炭施用对油菜氮素吸收和转运的影响

以棕壤为供试土壤,采用15 N示踪法研究水稻稻壳制成的生物炭在不同用量(0,0.5%,1%,2%)下对连续种植两季油菜的土壤中氮含量、油菜产量、油菜地上及地下部分的吸氮量以及N2O气体损失的影响,并计算肥料氮的氮素利用率及其不同去向所占比例,探明生物炭施用对油菜肥料氮吸收及转运的影响。结果表明:(1)施加生物炭显著提高了第1季、第2季油菜的产量。(2)0.5%生物炭用量与对照相比,第1季油菜吸收土壤氮素的比例提高了2.0%;0.5%,1%,2%生物炭用量使第2季油菜吸收土壤氮素的比例分别提高了0.8%,2.4%,3.2%。第1季、第2季油菜叶和根对氮素的吸收随生物炭施用量的增加而增加。(3)与对照相比,施加生物炭处理显著降低了两季油菜N2O气体排放,2%生物炭用量使第1季、第2季N2O气体排放分别减少了0.30,0.10mg/kg。(4)2%生物炭用量处理与对照相比,第1季氮素利用率提高了16.3%;两季氮素利用率的结果显示,0.5%,1%,2%处理分别比对照提高了0.4%,0.7%,5.3%,其中以2%生物炭施用量效果最佳。     

肥料添加剂降低N2O排放的效果与机理

如何降低氮肥施入农田后的N2O排放,实现氮肥增产效应的同时降低其对环境的负面影响是全球集约化农业生产中重要的科学问题,氮肥添加剂是有效途径之一。本研究采用室内静态培养法,在调节土壤水分含量和温度等环境因素的条件下,研究不同肥料添加剂对华北平原典型农田土壤N2O排放的影响及其机制。结果表明,N2O排放通量的峰值大约出现在施氮后的第24 d,肥料混施较肥料表施的出峰时间提前。与单施尿素处理相比,添加硝化抑制剂DMPP或DCD能分别降低N2O排放总量99.2%和97.1%; 添加硫酸铜对N2O排放的抑制作用不显著; 添加秸秆会增加N2O排放总量60.7%,而在添加秸秆的土壤中施加硝化抑制剂DMPP能够显著降低N2O排放量至无肥对照水平。说明华北平原农田土壤中N2O的产生主要是由硝化作用驱动,同时也可看出,添加硝化抑制剂是N2O减排的有效措施。     

Contrasting effects of wheat straw and its biochar on greenhouse gas emissions and enzyme activities in a Chernozemic soil

Biochar produced from plant biomass through pyrolysis has been shown to be much more resistant to biodegradation in the soil as compared with the raw biomass, such as cereal straw that is routinely shredded and discharged on to farm fields in large amounts. Biochar application to soil has also been reported to decrease greenhouse gas (GHG) emissions, although the mechanisms are not fully understood. In this study, the emissions of three main GHGs (CO₂, CH₄, and N₂O) and enzyme activities (urease, β-glycosidase, and dehydrogenase) were measured during a 100-day laboratory incubation of a Chernozemic soil amended with either straw or its biochar at rates of 0.67 and 1.68 % (based on the amount of C added) for the low and high rates, respectively. The biochar application dramatically reduced N₂O emissions, but CO₂ or CH₄ emissions were not different, as compared with the un-amended soil. At the same C equivalent application rate, CO₂ and N₂O emission rates were greater while CH₄ emission rates were lower in straw than in biochar application treatments. The activities of both the dehydrogenase and β-glycosidase significantly declined while that of urease significantly increased with the biochar as compared with the straw treatment. We conclude that pyrolysis of cereal straw prior to land application would significantly reduce CO₂ and N₂O emissions, in association with changed enzyme activities, while increasing the soil C pool through the addition of stable C in the form of biochar.     

Biochar suppresses N2O emissions while maintaining N availability in a sandy loam soil

Nitrous oxide (N₂O) from agricultural soil is a significant source of greenhouse gas emissions. Biochar amendment can contribute to climate change mitigation by suppressing emissions of N₂O from soil, although the mechanisms underlying this effect are poorly understood. We investigated the effect of biochar on soil N₂O emissions and N cycling processes by quantifying soil N immobilisation, denitrification, nitrification and mineralisation rates using ¹⁵N pool dilution techniques and the FLUAZ numerical calculation model. We then examined whether biochar amendment affected N₂O emissions and the availability and transformations of N in soils.Our results show that biochar suppressed cumulative soil N₂O production by 91% in near-saturated, fertilised soils. Cumulative denitrification was reduced by 37%, which accounted for 85–95 % of soil N₂O emissions. We also found that physical/chemical and biological ammonium (NH₄⁺) immobilisation increased with biochar amendment but that nitrate (NO₃⁻) immobilisation decreased. We concluded that this immobilisation was insignificant compared to total soil inorganic N content. In contrast, soil N mineralisation significantly increased by 269% and nitrification by 34% in biochar-amended soil.These findings demonstrate that biochar amendment did not limit inorganic N availability to nitrifiers and denitrifiers, therefore limitations in soil NH₄⁺ and NO₃⁻ supply cannot explain the suppression of N₂O emissions. These results support the concept that biochar application to soil could significantly mitigate agricultural N₂O emissions through altering N transformations, and underpin efforts to develop climate-friendly agricultural management techniques.     

N2O emission mitigation and microbial activity after Biochar and Cao application in a flooded nitrate-rich vegetable soil

Adding easily decomposable organic materials into flooded nitrate-rich soils can effectively decrease the soil nitrate concentration and repair nitrate-rich soil. However, nitrate reduction is usually accompanied with an increase in N₂O emission. This study was conducted to reduce N₂O emission in a nitrate-rich vegetable soil flooded for remediation and amended with biochar. Nitrate-rich vegetable soil was placed in five treatment groups: flooding (F); flooding with rice straw (F?+?RS); flooding with rice straw and 1% biochar (F?+?RS?+?1% biochar); flooding with rice straw and 3% biochar (F?+?RS?+?3% biochar); flooding with rice straw and CaO (F?+?RS?+?CaO). Biochar and CaO reduced the N₂O emission levels relative to the F?+?RS group, with the former being more effective than the latter, achieving reduction of 40.70% (3% biochar) and 17.35% (CaO) of cumulative N₂O emission. The 3% biochar was more effective than the 1% biochar. Regression analysis showed a positive correlation between the abundance of NO reductase gene (norB) and soil N₂O emission flux. In general, biochar and CaO could effectively reduce N₂O emissions from a nitrate-rich vegetable soil during flooding remediation, duo to elevating soil pH and altering denitrifying activity. The norB gene was the most important denitrifying gene driving soil N₂O emission in the remediation.     

Effects of biochar addition on greenhouse gas emissions during freeze–thaw cycles in a black soil region,Northeast China

As global warming intensifies, the soil environment in middle to high latitudes will undergo more extensive and frequent freeze–thaw cycles (FTCs), which will significantly affect the carbon and nitrogen cycles of soil ecosystems and aggravate greenhouse gas (GHG) emissions. Biochar can increase soil organic carbon storage and mitigate climate change. To effectively control GHG emissions, soil supplemented with biochar at different application rates (0%, 2%, 4% and 6% [w/w]) under different numbers of FTCs (0, 3, 6, 9, and 12) was selected as the research object. The soil GHG emission characteristics in different experimental treatments and their relationships with soil physical and chemical properties were determined. Our results showed that N₂O and CO₂ emissions were promoted during FTCs, with values of 3.13–50.37 and 16.22–135.50 μg m⁻² h⁻¹, respectively. The order of N₂O and CO₂ emissions with respect to biochar application rate was as follows: 2% > 0% > 4% > 6%. CH₄ emissions were negative during FTCs, varying from −1.62 to −10.59 μg m⁻² h⁻¹, and negative CH₄ emissions were promoted by biochar. Correlation analysis showed that N₂O, CO₂ and CH₄ emissions were significantly correlated with pH, soil moisture and soil organic matter (SOM), total nitrogen (TN) and ${\mathrm{NH}}_4^{+}$–N contents (p < .01). The conceptual path model demonstrated that GHG emissions were significantly influenced by FTCs, moisture, SOM and biochar application rate. Our results indicate that the effects of FTCs on GHG emissions were greater than those of biochar application. Biochar application rates of 4% or 6% should be considered in the future to reduce soil GHG emissions in the black soil region of Northeast China. Our results can help provide a theoretical basis and effective strategy to reduce soil GHG emissions during FTCs in seasonally frozen regions.     

Impact of fresh and aged palm shell biochar on N2O emissions,soil properties,nutrient content and yield of Komatsuna (Brassica rapa var. perviridis) under sandy soil conditions

ABSTRACT

Biochar can reduce N₂O emissions and it can be added to the soil once, whereas fertilizers are often applied every cultivation season. The aging of biochar in soil affects its functioning but it is unclear whether palm shell biochar (PSB) could still mitigate N₂O emissions even when additional basal N fertilizers are applied 1 year after the initial biochar application. We studied the impact of fresh and aged PSB (0%, 6%, 12%, and 18% w/w of dry soil) on N₂O emissions, soil properties, nutrient content and yield of Komatsuna (Brassica rapa var. perviridis) under sandy soil conditions. The aged PSB non-significantly reduced N₂O emissions but significantly offset soil acidification, and maintained a high soil nutrient status. Biochar application with fertilizer significantly increased plant tissue K and Ca content but decreased N, P and Mg content compared to the treatments without biochar. At higher application rates, biochar had negative effects on crop yield but as it aged, the negative effects were offset as a result of the similar variation in plant N uptake. Since seasonal N fertilizer application seems to be inevitable in Komatsuna cultivation, addition of biochar could be a possible way of counteracting the effects of excessive fertilizer use. Further research is needed to assess the feasible biochar application rates for Komatsuna fields in various soil types under field conditions.     

The effects of rice (Oryza sativa L. ssp. japonica) husk biochar on nitrogen dynamics during the decomposition of hairy vetch in two soils under high-soil moisture condition

ABSTRACT

Legumes, including hairy vetch (Vicia villosa Roth), are widely used as green manures. They fix nitrogen (N) and provide the N to other crops when they decompose, and thus are considered alternatives for chemical N fertilizers. However, N-rich plant residues, including hairy vetch, are also sources of soil nitrous oxide (N₂O) emissions, a greenhouse gas. On one hand, rice (Oryza sativa L. ssp. japonica) husk biochar is widely used as a soil conditioner in Japan and has been reported as a tool to mitigate soil N₂O emissions. We conducted a soil core incubation experiment (1.5 months) to compare the N₂O emissions during the decomposition of surface-applied hairy vetch (0.8 kg dried hairy vetch m^?2 soil) under semi-saturated soil moisture conditions (~100% water-filled pore space (WFPS)), using two soil types, namely Andosol and Fluvisol. Throughout the incubation period, the use of biochar suppressed soil NH₄⁺-N concentrations in Andosol, whereas the effect of biochar on NH₄⁺-N was not clear in Fluvisol. Biochar increased the nitrate (NO₃^?-N) levels both in Andosol and Fluvisol, suggesting a negative influence on denitrification and/or a positive influence on nitrification. Biochar application did not influence the cumulative N₂O emissions. Our study suggests that rice husk biochar is not a good option to mitigate N₂O emissions during the decomposition of surface-applied hairy vetch, although this study was performed under laboratory conditions without plants. However, the trends of the inorganic-N concentration changes followed by the addition of hairy vetch and biochar were markedly different between the two soil types. Thus, factors behind the differences need to be further studied.