南京土壤研究所常熟站物质循环过程与调控团队在秸秆炭化还田研究方面取得进展

(1)提出以沼气为稳定热源热解秸秆制备生物质炭的理念和方法(附件1),设计了隧道窑秸秆炭化系统(附件2~3),可实现秸秆生物质炭专门批量生产,将利用秸秆 农业/养殖废弃物生产沼气与秸秆炭化还田有效衔接,增加秸秆利用链条。通过与木质源生物质炭比较,发现秸秆生物质炭具有较高的灰分和吸附固持能力及碳稳定性(附件4)。

(2)通过土壤培养、土柱模拟淋溶试验发现秸秆生物质炭:①促进酸性土壤外源氨硝化,增加氨氧化菌数量,改变其群落结构和优势种群逐渐与碱性土壤趋同。土壤初始pH及NH4 , TN 和C/N比是驱动群落组成变化的主因(附件5~7)。铵态或酰胺态氮肥持续施用下,生物质炭促进硝化的致酸作用对其土壤酸度改良效果长期影响须予以关注。②减少氮淋溶,但土壤固持氮量增加不是其减少氮淋溶的唯一原因,生物质炭短期大量添加也有增加氮素气态损失风险(附件8)。③减少硝化、反硝化过程N2O排放,提高土壤氮吸附固持,好气下加速NH4 硝化避免NO2-累积,和厌氧下促进N2O还原酶nosZ活性(附件9~10)。④短期添加和长期施用对土壤反硝化影响不同。短期添加促进硝态氮还原,增加反硝化N2产生,长期处理则降低硝态氮还原及反硝化N2量。短期添加通过快速提高土壤DOC、有效元素含量和pH值等改善土壤环境和提高微生物菌群的硝化、反硝化性能。长期处理土壤硝态氮还原能力降低则与随生物质炭老化,土壤DOC和氮有效性下降有关(附件10)。长期处理也改善淹水稻田土壤剖面通气状况,减少深层反硝化及其主要气态产物exN2随水流失风险(附件11)。因此,基于一次性、大剂量生物质炭添加方式研究氮转化响应可能导致认识偏差,应加强生物质炭长期施用效应研究。

(3)建立盆栽、土柱和田间秸秆炭化还田试验,连续多年观测水旱、旱旱及不同作物轮作下作物生长、土壤性质、土壤碳库、温室气体排放和氮素利用及损失的影响,发现长期施用生物质炭:①对作物生长促进作用:红壤>酸性水稻土>潮土>碱性水稻土。红壤上主要通过消减酸度,增加团聚体稳定性和水分/养分有效性来提高土壤肥力和养分吸收(附件12~13)。潮土中更依赖于其带入灰分使有效磷、钾等含量提高以及持水性的增加(附件14~16)。酸碱性水稻土作物生长效应则与pH值有关(附件17~19);②增加红壤和潮土氨挥发,主要是酸性土壤pH提高与土壤容重降低和通气性增加所致(附件8、附件16);对水稻土影响则与水旱作物季有关,稻季淹水利于NH3/NH4 吸附,但随累积用量增加和通透性持续改善,又增加氨挥发(附件18);③迅速提升土壤稳定性碳库,N2O减排旱地高于水稻土,固碳和甲烷减排则以水稻土较好(附件19)。53~500 um细颗粒有机碳组分增加,及无定形铁含量增加促进的土壤有机-矿物化学保护作用是水稻土固碳效应较好的重要原因(附件20;附件22)。上述结果明确了秸秆炭化还田固碳减排和土壤改良的潜在作用及土壤差异;秸秆炭化还田因明显扰动土壤性质进而影响氮素迁移转化,应关注其对肥料氮利用与损失及氮盈亏的长期影响。

(4)通过碳足迹、生态系统净环境经济效益(NEEB)方法,分析了长期秸秆炭化还田的农学、环境和经济效益(附件19、21),发现:①秸秆炭化还田显著降低农田净综合温室效应和增加碳汇,但目前较低的CO2交易价格决定了其净固碳效益远低于生物质炭成本投入而导致NEEB降低;②生物质炭投入成本和作物增收是决定NEEB的重要因素。生物质炭在酸性红壤增产明显,可维持和提高NEEB;石灰性潮土及水稻土上,其增产增收作用较小,难以平衡生物质炭投入成本。本研究试验条件下,秸秆炭化还田用量为每季7~8 ton/ha,且红壤、潮土和水稻土施用生物质炭成本须分别低于1.8元/kg、0.2元/kg和0.9元/kg时才可保证NEEB不降低。因此,优化秸秆炭化工艺及还田方法,显著降低成本也是探讨秸秆炭化还田技术推广应用的必要前提。

事实上,未来秸秆炭化还田能否作为农田固碳减排和土壤改良及秸秆资源化利用的关键技术所面临的问题并不仅在于其效应及机理研究本身,须从农田生态系统生产、经济、生态等可持续性方面进行综合权衡。应加强长期秸秆炭化还田对氮循环、土壤生产力及其稳定性影响等方面研究,有助于多角度科学论证主要农区秸秆炭化还田可行性。

上述研究得到国家自然科学基金(41001147、41271312、41771338)、中科院青促会以及土壤与农业可持续发展国家重点实验室资助。

附件1:

Large-scale biochar production from crop residue: a new idea and the biogas-energy pyrolysis system, BioResources, 2013

附件2:

秸秆炭化装置及秸秆炭化的方法2012.7.31, 中国, ZL 2012 1 0267771. 8

附件3:

秸秆炭化装置2012.7.31 中国, ZL201220374239.1

附件4:

Comparisons of Biochar Properties from Wood Material and Crop Residues at Different Temperatures and Residence Times, Energy & Fuels, 2013

附件5:

Nitrification, acidification, and nitrogen leaching from subtropical cropland soils as affected by rice straw-based biochar: laboratory incubation and column leaching studies, Journal of Soils and Sediments, 2014

附件6:

Comparison of straw-biochar-mediated changes in nitrification and ammonia oxidizers in agricultural oxisols and cambosols: Biology and Fertility of Soils, 2016

附件7:

Population and community structure shifts of ammonia oxidizers after four-year successive biochar application to agricultural acidic and alkaline soils, Science of The Total Environment, 2018

附件8:

Effects of the addition of rice-straw-based biochar on leaching and retention of fertilizer N in highly fertilized cropland soils, Soil Science and Plant Nutrition, 2013

附件9:

The effects of rice-straw biochar addition on nitrification activity and nitrous oxide emissions in two Oxisols, Soil and Tillage Research, 2016

附件10:
Variable responses of nitrification and denitrification in a paddy soil to long-term biochar amendment and short-term biochar addition. Chemosphere, 2019

附件11:

秸秆生物质炭对稻田土壤剖面N2O和N2浓度的影响,土壤学报,2020

附件12:

Effects of crop-straw biochar on crop growth and soil fertility over a wheat-millet rotation in soils of China, Soil Use and Management, 2014

附件13:

Successive biochar amendment improves soil productivity and aggregate microstructure of a red soil in a five-year wheat-millet rotation pot trial. Geoderma, 2020

附件14:

秸秆生物炭对潮土作物产量和土壤性状的影响, 土壤学报, 2015

附件15:

潮土长期施用生物炭提高小麦产量及氮素利用率. 农业工程学报, 2018

附件16:

长期秸秆黑炭施加对石灰性潮土肥力、固碳及氨挥发的影响, 应用生态学报, 2018

附件17:

秸秆源黑炭还田对水稻土生产力和固碳的影响, 环境科学研究, 2013

附件18:

Successive straw biochar application as a strategy to sequester carbon and improve fertility: A pot experiment with two rice/wheat rotations in paddy soil, Plant Soil, 2014

附件19:

Assessing the viability of soil successive straw biochar amendment based on a five-year column trial with six different soils: Views from crop production, carbon sequestration and net ecosystem economic benefits. Journal of Environmental Management, 2019

附件20:

Structural and microbial evidence for different soil carbon sequestration after four-year successive biochar application in two different paddy soils,Chemosphere, 2020

附件21:

Successive straw biochar amendments reduce nitrous oxide emissions but do not improve the net ecosystem economic benefit in an alkaline sandy loam under a wheat-maize cropping system. Land Degradation & Development, 2019

附件22:

Accumulation of organic compounds in paddy soils after biochar application is controlled by iron hydroxides. Science of the Total Environment, 2020

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