有机农业发展的低碳机理分析

温室气体排放引起的全球气候变暖是人类关注的环境热点问题之一。本文从农业生态系统影响全球变暖的主要温室气体(CO₂、N₂O 和CH₄)的产生和排放出发, 探讨有机农业在生产减排和土壤固碳方面的机理。研究发现相对于常规农作而言, 有机农业在减排和固碳方面具有很大优势和潜力; 然而, 从长期来看, 通过土壤固碳减少大气温室气体的排放不是无限制的, 到一定程度后会达到一个平衡。因此, 更多的有效固碳途径和管理措施有待于进一步研究。同时, 从低碳理念出发, 强调中国加强有机农业环境效益研究的必要性。     

Soil carbon sequestration in phytoliths

The role of the organic carbon occluded within phytoliths (referred to in this text as ‘PhytOC‘) in carbon sequestration in some soils is examined. The results show that PhytOC can be a substantial component of total organic carbon in soil. PhytOC is highly resistant to decomposition compared to other soil organic carbon components in the soil environments examined accounting for up to 82% of the total carbon in well-drained soils after 1000 years of organic matter decomposition. Estimated PhytOC accumulation rates were between 15 and 37% of the estimated global mean long-term (i.e. on a millenial scale) soil carbon accumulation rate of 2.4 g C m⁻² yr⁻¹ indicating that the accumulation of PhytOC within soil is an important process in the terrestrial sequestration of carbon. The rates of phytolith production and the long-term sequestration of carbon occluded in phytoliths varied according to the overlying plant community. The PhytOC yield of a sugarcane crop was 18.1 g C m⁻² yr⁻¹, an accumulation rate that is sustainable over the long-term (millenia) and yet comparable to the rates of carbon sequestration that are achievable (but only for a few decades) by land use changes such as conversion of cultivated land to forest or grassland, or a change of tillage practices from conventional to no tillage. This process offers the opportunity to use plant species that yield high amounts of PhytOC to enhance terrestrial carbon sequestration.     

低碳农业

农业生产与全球气候变化紧密相关,农业是全球温室气体排放的第二大重要来源,同时,气候变化义影响着农业的发展.面对全球气候变暖,农业作为国民经济的基础产业,在节能减排中应当有所贡献.本文通过农业低碳发展的必然性,提出了低碳农业发展的领域、可能途径以及发展机制,为响应低碳经济,应对全球气候变化提供科学决策,促进现代农业由高碳...     

Organic carbon sequestration in earthworm burrows

Earthworms strongly affect soil organic carbon cycling. The aim of this study was to determine whether deep burrowing anecic earthworms enhance carbon storage in soils and decrease C turnover. Earthworm burrow linings were separated into thin cylindrical sections with different distances from the burrow wall to determine gradients from the burrow wall to the surrounding soil. Organic C, total N, radiocarbon (¹⁴C) concentration, stable isotope values (δ¹³C, δ¹⁵N) and extracellular enzyme activities were measured in these samples. Anecic earthworms increased C stocks by 270 and 310 g m^?2 accumulated in the vertical burrows. C-enrichment of the burrow linings was spatially highly variable within a distance of millimetres around the burrow walls. It was shown that C accumulation in burrows can be fast with C sequestration rates of about 22 g C m^?2 yr^?1 in the burrow linings, but accumulated C in the burrows may be mineralised fast with turnover times of only 3–5 years. Carbon stocks in earthworm burrows strongly depended on the earthworm activity which maintains continuous C input into the burrows. The enhanced extracellular enzyme activity of fresh casts was not persistent, but was 47% lower in inhabited burrows and 62% lower in abandoned burrows. Enzyme activities followed the C concentrations in the burrows and were not further suppressed due to earthworms. Radiocarbon concentrations and stable isotopes in the burrow linings showed an exponential gradient with the youngest and less degraded organic matter in the innermost part of the burrow wall. Carbon accumulation by anecic earthworm is restricted to distinct burrows with less influence to the surrounding soil. Contrary to the initial hypothesis, that organic C is stabilised due to earthworms, relaxation time experiments with nuclear magnetic resonance spectroscopy (NMR) did not reveal any enhanced adsorption of C on iron oxides with C stabilising effect. Our results suggest that earthworm activity does not substantially increase subsoil C stocks but burrows serve as fast ways for fresh C transport into deep soil horizons.     

Potential for carbon sequestration in the drylands

Non-forested drylands occupy 43% of the world's land surface yet they are not currently regarded as important in sequestering carbon due to overuse and poor management. Seventy percent of drylands have already undergone moderate to severe desertification and an additional 3.5% drops out of economic production each year. Reversing the trend towards desertification through cultivation of halophytes on saline lands, revegetation of degraded rangelands and other innovative conservation measures could result in net C sequestration in dryland soils of 0.5–1.0 Gt yr^?1 at a cost of $10–18 t^?1 C, based on a 100 yr scenario. Investment in antidesertification measures in the world's drylands appears to be an economical method to mitigate CO₂ buildup in the atmosphere while accomplishing a major international objective of restoring dryland productivity.     

河北省北部森林植被碳储量和固碳速率研究

为了了解河北省北部森林植被固碳能力,本文以该区域阔叶林、针叶林、混交林、经济林和灌丛为研究对象,基于政府间气候变化专门委员会(IPCC)推荐采用的加拿大林业碳收支模型(CBM-CFS3),利用第7次全国森林资源连续清查数据和野外森林植被调查样地数据,拟合出研究区的蓄积-生物量转换参数和林木器官生物量比例参数,建立研究区内不同森林植被类型的蓄积生长方程、蓄积-干材生物量转换方程、生物量组分比例方程,采用这些方程评估了2010年河北省北部森林生态系统植被碳储量、碳密度和固碳速率。结果表明:拟合的不同森林植被蓄积生长方程的决定系数均大于0.7,蓄积-干材生物量转换方程的决定系数均大于0.8,生物量组分比例方程拟合效果较好,可用于评估该区域森林植被碳汇功能和潜力。2010年河北省北部森林植被碳储量为59.66 Tg(C),平均森林植被碳密度为25.05 Mg(C)×hm~(-2),森林植被固碳速率为0.07~1.87Mg(C)×hm~(-2)×a~(-1);其中阔叶林、针叶林、混交林、经济林碳储量和碳密度分别为30.97 Tg(C)、12.36 Tg(C)、15.73Tg(C)、0.60 Tg(C)和26.09 Mg(C)×hm~(-2)、26.14 Mg(C)×hm~(-2)、24.50 Mg(C)×hm~(-2)、7.53 Mg(C)×hm~(-2)。河北省北部森林植被碳密度与固碳速率均从西北到东南呈升高趋势。造林后森林面积增加6 400 km2,森林植被碳储量增加19.54 Tg(C)(不包括灌丛);林龄结构以中幼龄林为主,未来森林固碳潜力巨大。说明造林在增加森林植被碳储量和提高森林的固碳速率中起到了重要作用。     

不同农业废弃物还田对土壤碳排放及碳固定的影响

在玉米生长季,采用静态箱法,在氮磷钾等养分量(N 240kg/hm~2,P2O5100kg/hm~2,K2O 120kg/hm~2)的条件下,研究秸秆、牛粪、鸡粪与化肥配施还田,对土壤CO_2排放及碳固定的影响。研究结果表明:施肥促进土壤CO_2排放,其中100%秸秆粉碎还田配施化肥(S1)对土壤CO_2排放的促进作用最为明显,平均排放通量达389.0mg/(m~2·h);其次为单施化肥(S4)。S1、S2、S3和S4处理在6,7,8三个月份CO_2平均排放通量表现为S4S1S3S2,分别占整个生长季排放总量的80.1%,78.9%,78.8%和83.7%,表明单施化肥处理(S4)在玉米生长旺季CO_2排放通量最高达624.9mg/(m~2·h)。各施肥处理在玉米生长季出现2个CO_2排放高峰阶段,与2次氮肥(尿素)追施密切相关,2次追施氮肥后CO_2排放通量平均值均表现为S4S1S3S2,表明用农业废弃物中的氮部分代替化肥氮,可减少CO_2排放量。50%牛粪有机氮还田配施50%化肥氮(S2),能明显提高土壤有机碳含量。50%鸡粪有机氮还田配施50%化肥氮(S3)可明显提高玉米各器官及植株含碳量,其中S3处理植株含碳量最高为9.59t/hm~2,促进玉米碳固定;而100%秸秆粉碎还田配施化肥氮(S1),并不能提高玉米各器官及植株含碳量,甚至低于单施化肥(S4)。     

发展碳汇林业 应对气候变化——中国碳汇林业的实践与管理

 在阐述林业在应对气候变化中的功能与作用,辨析森林碳汇、林业碳汇、碳汇林业的概念和意义的基础上,总结中国碳汇林业的实践。据此,提出加强碳汇林业管理的建议:以实施《应对气候变化林业行动计划》为主线,加强全国森林碳汇计量、监测体系建设和碳汇项目计量队伍资质管理,促进低碳经济林业试点工作。     

Simulating the effect of potassium fertilization on carbon sequestration in soil

The impact of horticultural management on carbon sequestration in soils has been limited so far to tillage and nitrogen fertilization. Our objective was to evaluate by mathematical modeling the effect of potassium fertilization on CO₂ binding in cropland soils. The developed model integrates three subunits: (1) A published simulator of crop dry‐matter (DM) production in response to N, P, K fertilization, but not DM partitioning; (2) a published soil–crop–atmosphere model predicting crop yield and DM partitioning as a function of N but not K fertilization; (3) an original model computing the organic‐inorganic carbon transformations, inorganic‐carbon reactions and transport in soil, CO₂ diffusion, and soil carbon sequestration. The model described the K‐fertilization effect on C binding in soil as a function of the soil pH, the Ca²⁺ concentration in the soil solution, hydraulic properties, air temperature, and crop DM production, and partitioning characteristics. In scenarios of corn (Zea mays L.) growth in clayey soil and wheat (Triticum aestivum L.) in loam soil, the computed K‐induced CO₂ sequestration amounted to ≈ 14.5 and 24 kg CO₂ (kg K)^–1, respectively (0 vs. 100 kg ha^–1 K application). The soil CO₂ sequestration declined by 8% when corn grew in sandy instead of clayey soil and by 20% when the temperature was 10°C higher than the temperature prevailing in mild semiarid zones. All predicted CO₂‐sequestration results were approximately 30‐fold higher than the 0.6 kg CO₂ emitted per kg of K manufactured in industry.     

Agroforestry as a strategy for carbon sequestration

During the past three decades, agroforestry has become recognized the world over as an integrated approach to sustainable land use because of its production and environmental benefits. Its recent recognition as a greenhouse gas–mitigation strategy under the Kyoto Protocol has earned it added attention as a strategy for biological carbon (C) sequestration. The perceived potential is based on the premise that the greater efficiency of integrated systems in resource (nutrients, light, and water) capture and utilization than single‐species systems will result in greater net C sequestration. Available estimates of C‐sequestration potential of agroforestry systems are derived by combining information on the aboveground, time‐averaged C stocks and the soil C values; but they are generally not rigorous. Methodological difficulties in estimating C stock of biomass and the extent of soil C storage under varying conditions are compounded by the lack of reliable estimates of area under agroforestry. We estimate that the area currently under agroforestry worldwide is 1,023 million ha. Additionally, substantial extent of areas of unproductive crop, grass, and forest lands as well as degraded lands could be brought under agroforestry. The extent of C sequestered in any agroforestry system will depend on a number of site‐specific biological, climatic, soil, and management factors. Furthermore, the profitability of C‐sequestration projects will depend on the price of C in the international market, additional income from the sale of products such as timber, and the cost related to C monitoring. Our knowledge on these issues is unfortunately rudimentary. Until such difficulties are surmounted, the low‐cost environmental benefit of agroforestry will continue to be underappreciated and underexploited.     

国内外土壤侵蚀研究进展

  目的  土壤侵蚀引起的土壤有机碳动态变化对可持续土地利用与管理以及陆地碳收支具有重要意义,为了解该领域的前沿及发展方向,采用文献计量学方法探究近30年来土壤侵蚀与土壤有机碳动态研究进展及热点。  方法  本文基于Web of Science核心数据库和中国知网（CNKI）中文核心期刊数据库,采用CiteSpace软件和文献计量学方法,分析了国内外近30年土壤侵蚀与土壤有机碳动态研究的发展历程、研究热点和趋势。  结果  研究表明欧美国家在该领域的研究发展较早,尤其是美国无论是国际影响力还是国际合作紧密性均处于领先地位,我国虽起步较晚但处于稳步快速发展态势;国际上该领域的研究在1995 ~ 2004年间主要围绕耕作方式和农艺措施对土壤侵蚀与土壤有机碳动态的影响,进而发展为侵蚀条件下土壤微生物及其群落对土壤有机碳的影响;近十年逐渐向基于稳定性同位素技术的土壤侵蚀与土壤有机碳动态定量研究转变,同时土壤侵蚀导致的碳氮流失所造成的面源污染及侵蚀碳在全球碳循环中的作用也是近年来的研究热点。国内于1995 ~ 2004年在本领域的研究主要集中土壤侵蚀所造成的有机碳和养分流失的研究,而后逐渐发展为结合“3S”技术和土壤侵蚀模型,研究人类活动、土地利用及气候变化等因素对土壤侵蚀与土壤有机碳动态的影响。近五年结合核素示踪、光谱等技术,在国家政策引导下该领域逐步发展为从生态综合治理向生态文明建设为核心的问题导向研究。  结论  通过分析对比国内外土壤侵蚀与土壤有机碳动态研究的热点和前沿,提出我国在该领域今后研究的展望。     

Impact of cultivation on soil organic carbon and carbon sequestration potential in semiarid regions of China

Dynamic changes in soil organic carbon (SOC) have become a popular topic in global research on organic carbon as part of the increasing attention being paid to food security and reducing greenhouse gas emissions. In this paper, the semiarid regions of China were selected as a research focus, and SOC data from 1980 to 2015 were analysed using IBM SPSS Statistics 20.0 software. SOC in farmland varied according to cultivated land type, mulching material type and planting method in the studied regions. The SOC content is 10.3–10.8 g kg⁻¹ in supplementally irrigated land and flat dry land, 7.1–8.7 g kg⁻¹ in terraced dry land and river beach land, and 6.2–6.4 g kg⁻¹ in sloping dry land. The SOC content increased to 16.1–17.4 g kg⁻¹ when crop stalks were used as mulch. The increase was only 11.5–13.5 g kg⁻¹ in soils mulched with film or sandstone. The SOC value in wheat, maize and potatoes sown on single or double ridges was 2.4%–3.2%, 35.7%–36.4% and 4.4%–4.8%, respectively, which are higher than the values for wheat, maize and potatoes sown using the flat planting method. The SOC sequestering potential also varied according to the previously noted factors and was improved from 224.1% to 383.8% depending on cultivated land type, from 96.5% to 182.3% depending on mulching material type and from 96.1% to 191.3% depending on planting method. The SOC sequestering potential can be improved by 453.2%–757.4% with the integration of the optimal cultivated land type, mulching material type and planting method. Thus, there is substantial soil carbon sequestration potential in China's semiarid regions.     

秸秆还田模式对小麦-玉米轮作体系土壤有机碳固存的影响

为解决麦玉轮作体系小麦秸秆直接粉碎还田存在的弊端,基于多年麦玉秸秆还田定位试验,筛选高产-节本-地力提升为一体的还田模式。选择4种还田模式,即小麦玉米秸秆均不还田(WN-MN,CK1)、小麦玉米秸秆均粉碎还田(WC-MC,CK2)、小麦高留茬还田(WH-MN)和小麦高留茬-玉米粉碎还田(WH-MC)为研究对象,比较其产量表现、土壤有机碳贮量盈亏、碳库管理指数等指标,评价将小麦秸秆粉碎还田改成高留茬还田后形成的还田模式与两季秸秆均粉碎还田的优劣。结果表明,与WN-MN相比,WC-MC和WH-MC的土壤碳储量分别增加24.23%和16.05%;与试验开始前土壤有机碳储量相比,4种还田模式的土壤碳固持为–0.83~6.14 Mg·hm^–2;维持土壤初始碳储量水平的最小碳投入量为4.06 Mg·hm^–2·a^–1。各处理不稳定有机碳组分的含量随着土层加深呈下降趋势。与WN-MN相比,WC-MC、WH-MC和WH-MN显著增加了0~20 cm表层不稳定碳组分的含量;WC-MC和WH-MC也显著增加了各土层的碳库管理指数。2015—2016周年产量,WC-MC、WH-MC平均较其他两个处理分别增加了34.5%、20.1%;2016—2017周年产量,以WH-MC最高,较其他处理平均高出11.1%。小麦高留茬-玉米粉碎还田模式下土壤有机碳储量、不稳定有机碳组分、碳库管理指数和作物产量均较高,且节本增效,表明该模式有利于关中平原麦玉轮作体系粮食生产可持续发展。     

耕作方式对华北农田土壤固碳效应的影响

研究不同耕作方式对华北农田土壤固碳及碳库管理指数的影响,可为探寻有利于农田固碳的耕作方式提供科学依据。该研究在中国农业大学吴桥实验站进行,试验于2008年设置了免耕秸秆不还田(NT0)、翻耕秸秆不还田(CT0)、免耕秸秆还田(NT)、翻耕秸秆还田(CT)和旋耕秸秆还田(RT)5个处理。研究测定分析了土壤容重、有机碳、易氧化有机碳含量及不同耕作方式下的碳库管理指数。通过对不同耕作方式下0～110cm土壤的分析,结果表明,随着土层的加深,土壤有机碳含量不断下降,NT显著增加了表层(0～10cm)土壤有机碳含量,而>10～50cm有机碳含量较其他处理(NT0除外)有所下降,深层(>50～110cm)处理间差异不明显;土壤容重与有机碳含量呈显著的负相关关系(P<0.01);0～30cm土层有机碳储量以NT最高,CT与其无明显差异,二者较CT0分别高出13.1%和11.0%,而至0～50cm土层,CT的碳储量最高,但与NT无显著差异(P<0.05);与CT0相比,NT0降低了各层土壤易氧化有机碳含量,而NT则在0～10cm土层表现为增加;RT、CT分别显著增加了0～10、>10～30cm土层的碳库管理指数。结果表明,秸秆还田可改善土壤质量,提高农田碳库管理指数,同时碳库管理指数受耕作方式的影响也较大,尤其是CT和RT;NT通过减少土壤扰动、增加有机质的输入,可提高上层土壤有机碳的储量。     

黄河三角洲湿地退化和恢复对柽柳土壤有机碳含量及红外碳组分的影响

  目的  湿地生态系统在土壤碳循环过程中起着至关重要的作用。通过分析退化和自然湿地下0 ~ 100 cm的土壤理化性质、土壤无机碳含量及其储量的变化,探究土壤无机碳储量与土壤和植物性质之间的关系。  方法  以黄河三角洲盐生植物（柽柳）的退化和自然湿地为研究对象,利用全自动土壤无机碳分析仪测定土壤无机碳含量;基于土壤容重、无机碳含量和土壤深度来估算土壤无机碳储量。  结果  相比较自然湿地,退化湿地具有较低的交换性钙、镁离子含量和碳酸盐相对含量,而土壤容重和pH的差异不大。退化湿地显著降低了土壤无机碳含量和储量,表明湿地退化不利于无机碳在土壤中的固持。通过分析各个土壤深度无机碳储量与土壤理化性质的相关性,指出土壤无机碳储量与土壤容重、含水量、交换性钙和镁离子含量、土壤无机碳含量和地上植物生物量显著正相关,而与土壤电导率负相关。逐步回归分析表明土壤容重、含水量和阳离子含量是导致 0 ~ 100 cm 土壤无机碳储量变化的主要因素。另外,深层土壤无机碳（40 ~ 100 cm）大约贡献了0 ~ 100 cm 总土壤无机碳储量的60%,表明深层土壤对无机碳库的固持发挥着重要作用。  结论  湿地退化增加了土壤无机碳的损失,保护和恢复湿地有利于土壤无机碳的存储。因此,通过阐释黄河三角洲退化和自然湿地下土壤无机碳储量的变化,可以从无机碳的角度提高湿地土壤碳汇能力,为实现碳中和目标提供科学依据。     

农田土壤固碳作用对温室气体减排的影响

温室气体排放引起的全球气候变暖和平流层臭氧空洞已成为当前人们关注的环境问题之一。土壤碳库作为地表生态系统中最活跃的碳库之一,是甲烷、二氧化碳、一氧化二氮等温室气体的重要释放源,也是重要的吸收汇。因此,寻找农田土壤系统碳管理的有效方法已经成为缓解温室效应的重要科学问题。西方发达国家已将固碳农业作为环境管理的重要导向,应用颗粒分组13CNMR或CPMAS-NMR技术对土壤碳固定的机制研究指出微团聚体与矿物-粘粒复合体的相互作用是土壤有机碳稳定存在的主要方式,揭示了土壤有机碳的腐殖质转化及其与土壤矿物、金属氧化物结合的微观水平,且从土壤物理结构、化学组成和生物学特性等多学科交叉研究土壤有机碳的固定机理及其稳定机制。长期传统的土地利用方式和管理措施所导致的土壤有机碳含量、密度及垂直分布的变化是造成土壤碳库损失的主要原因,为了增加农业生态系统土壤有机碳的含量,土地利用方式和农业管理措施应该从增加有机碳输入量和减少有机碳矿化两方面着手,加强对农业土壤固碳潜力和土壤碳库稳定性影响因素的多角度研究。     

施肥对喀斯特地区植草土壤活性有机碳组分和牧草固碳的影响

通过盆栽试验,研究施肥对喀斯特地区植草土壤不同活性有机碳组分和牧草固碳的影响。试验处理包括CK（不施肥）、 N1 （N 150 mg/kg）、 N2 （N 250 mg/kg）、 N1P1 （P2O5100 mg/kg）、 N2P2 （P2O5150 mg/kg）、 N1P1K1 （K2O 70 mg/kg）、 N1P1K2 （K2O 105 mg/kg）和N2P2K1和N2P2K2。结果表明,与对照（不施肥）相比,施肥处理增加植草土壤有机碳、 微生物量碳和易氧化碳,有机碳日矿化量和累积矿化量以及牧草固碳量。其中N1P1K1处理土壤有机碳和易氧化碳最高,N1P1处理土壤微生物量碳最高,N2P2K1处理土壤可溶性碳最高,N2P2K2处理牧草地上部及根系固碳量、 有机碳日矿化量和累积矿化量均最高。综上,低量氮磷钾肥配施有利于土壤活性有机碳的积累,高量氮磷钾平衡配施牧草固碳效果最佳。     

我国地膜覆盖和残留污染特点与防控技术

  目的  探明全生物降解地膜覆盖对土壤有机碳库及团聚体的影响,为改善土壤质量和实现普通塑料地膜减量替代提供理论依据。  方法  基于2021年10月至2022年6月在江苏邳州大蒜地开展的大田定位试验,采用随机区组设计,设置无地膜覆盖（CK）、普通聚乙烯地膜覆盖（PM）和全生物降解地膜覆盖（BM）3个处理,探究0 ~ 20 cm耕作层土壤活性有机碳库和不同粒级水稳性团聚体有机碳含量的变化特征。  结果  相较于CK,PM和BM处理对土壤总有机碳含量的影响均不显著,相较于PM,BM处理能显著增加土壤水溶性有机碳和易氧化有机碳的含量,但显著降低了微生物生物量碳的含量。不同处理下各粒径水稳性团聚体质量占比均以 > 5 mm粒径最大,占比为33.65% ~ 37.85%;相较于CK,PM和BM处理均显著提高了团聚体的平均重量直径和几何平均直径,而对团聚体破碎率影响不显著。不同处理下土壤水稳性团聚体有机碳含量均以0.5 ~ 1 mm粒径中为最高;除 > 5 mm和3 ~ 5 mm粒径的水稳性团聚体外,其他粒径水稳性团聚体有机碳含量在BM处理下均显著高于CK或PM。  结论  全生物降解地膜覆盖能改善蒜地土壤结构,增加土壤活性有机碳组分和 > 0.25 mm水稳性团聚体有机碳含量,有助于土壤质量的提升。     

Long-term effects of agronomic practices on the soil organic carbon sequestration in Chernozem

The study was based on data from selected long-term field trials established at the Experimental Fields of the Institute of Field and Vegetable Crops, Novi Sad (Serbia). The effect of tillage systems on SOC concentration and SOC stock was most pronounced at 0–10 cm depth. In a 0–40 cm soil layer, in a 7-year period, no-till (NT) sequestrated 863 kg SOC ha^?1 yr^?1 more compared to moldboard plow tillage (PT), while the effects of disc tillage (DT) and chisel tillage (CT) were not significantly different. Unfertilized three-crop rotation (CSW) compared to two-crop rotation (CW) enhanced SOC storage in a 0–30 cm soil layer by 151 kg C ha^?1 yr^?1 in a 56-year period. Within fertilized treatments, SOC concentration was highest under continuous corn (CC). Mineral fertilization (F) non-significantly increased the SOC stock compared to no fertilization in corn monoculture in a 32-year period. The incorporation of mineral fertilizers and harvest residues (F + HR) and mineral fertilizers and farmyard manure (F + FYM) sequestered 195 and 435 kg C ha^?1 yr^?1 more than the unfertilized plot, respectively, in a 0–30 cm soil layer, in a 35-year period. Irrigation did not significantly affect SOC sequestration.     

Use of models to evaluate carbon sequestration in agricultural soils

ABSTRACT

The Rothamsted Carbon (RothC) model, which is one of widely used soil carbon (C) models, was validated against long-term experimental datasets in Japan and modified to suit Andosols and paddy soils reflecting unique soil C turnover mechanisms in these soils. Nationwide soil C calculation system was developed by combining these modified models and spatial model input data such as weather, soil type, land use, and agricultural activities. The model was validated in China and Thailand by using long-term field experimental datasets, too. Further studies especially in tropical Asia will be needed. Matching conceptual model C pools with measurable fractions have been big challenges. Using various plant materials, two conceptual pools of plant litter, decomposable plant material (DPM) and resistant plant material (RPM), in the RothC were successfully identified. It was achieved by comparing the default proportions of DPM and RPM pools in the RothC and proportions in plant material fractions determined by two-step acid hydrolysis with H₂SO₄. The trial to match all of five C pools in the model, however, remains unachieved though a study was conducted comparing not only the size of C pools but mean residence time of the pools. A web-based decision support tool called ‘Visualization of CO₂ absorption by soils’ was developed. This allows users to easily calculate changes in soil C, CH₄ and N₂O emissions, and fossil fuel consumption. With this tool, farmers can see how to improve the environmental sustainability of their products and this tool may help spread mitigation options widely. Soil C sequestration can help achieve climate change mitigation and sustainable agricultural production. Importance of long-term field observations should be more highlighted because long-term experiments have supported the development of modeling approaches. I hope models will be more widely used by decision makers. Collaboration between modeling and monitoring studies is important.