中国保护性耕作农田土壤有机碳变化速率研究——基于长期试验点的Meta分析

保护性耕作对于培肥地力、保障粮食安全、缓解气候变化等具有重要意义。本研究搜集了1980～2012年8月有关中国农田保护性耕作的157个试验点的303对田间定位试验数据,采用Meta分析方法定量分析了保护性耕作下我国农田耕层土壤(旱地0～20cm,水田0～15cm)有机碳(SOC)变化特征。结果表明,与传统耕作(CT)相比,传统耕作+秸秆还田(CTS)、免耕(NT)和免耕+秸秆还田(NTS)三种保护性耕作均能显著提高SOC含量,变化速率分别为NTS(0.52 g kg-1a-1)>NT(0.35 g kg-1a-1)>CTS(0.22 g kg-1a-1);三种保护性耕作下SOC变化速率为水田>旱地,一年两熟制>一年一熟制;保护性耕作下,SOC积累与否及其幅度并不完全取决于其初始有机碳含量,短期试验(≤5a)SOC增加速率是长期试验(>5a)的1.75倍,如果仅采用短期试验结果可能高估保护性耕作的固碳潜力。

2000-2007年内蒙古锡林郭勒盟草地土壤有机碳变化估计

以内蒙古锡林郭勒盟历年草地管理面积和不同草地管理下土壤有机碳变化的文献数据为基础，分别采用《2006年IPCC国家温室气体清单指南》Tier2和基于文献数据的转移矩阵方法，估算2000—2007年该盟草地土壤有机碳变化。结果表明，研究期内该盟草地土壤有机碳增加量为20．85～29．80Tg，年均增加量2．61～3．72Tg。其中，东乌珠穆沁旗、西乌珠穆沁旗、苏尼特左旗、苏尼特右旗、阿巴嘎旗和锡林浩特市有机碳增加占全盟总增加量的80％以上。采用IPCC方法2与转移矩阵法估算的土壤有机碳变化量在空间上具有很好的一致性，但前者的估计值比后者约低1／3。用两种方法估算的逐年有机碳变化量在时间序列上不具可比性，IPCC方法2估算的土壤碳贮量前3年增加迅速，转移矩阵法估算的土壤碳贮量后5年增加迅速。

气候智慧型农业措施对中国农田土壤有机碳含量影响的Meta分析

气候智慧型农业(Climate-smart agriculture,CSA)作为一种致力于实现提高农业效率、增强农业适应性和减少温室气体排放三大目标的新型农业,已经在全球农业区得到了广泛实施。本研究旨在探究4种CSA措施——生物炭、免耕、绿肥和秸秆还田对我国农田土壤有机碳(Soil organic carbon,SOC)含量的影响,以期为我国农田SOC管理和CSA的推广提供科学依据。数据来源于CNKI和Web of Science两大文献数据库,共收集了2002—2022年78篇相关的大田试验文献,并摘录470条试验结果和试验背景信息,利用整合分析(Meta-analysis)的方法量化4种CSA措施对我国农田SOC含量的作用效果及作用过程中的外部影响因素。结果表明:相较于传统农业,CSA措施对农田SOC含量具有显著的提升作用,总体可提高18.19%。4种措施的实施效果表现为生物炭>秸秆还田>绿肥>免耕,SOC含量增长率分别为46.67%、17.08%、9.32%、7.34%。区域环境因素(气温、降水、土壤深度、土壤pH、初始SOC含量等)和管理方式(试验持续时长、试验地种植模式)在不同程度上影响4种CSA措施的实施效果,且在我国不同区域实施CSA措施,SOC含量变化差异显著。综上所述,CSA措施对我国农田SOC含量有显著影响,其影响效果与气候、土壤、管理方式、地域等密切相关。在CSA实践中,应综合考虑各因素对实施效果的影响,采取适宜的措施和管理方式,以最大程度促进农田SOC含量的提升。

黄土丘陵区县域农田土壤近30年有机碳变化及影响因素研究:以甘肃庄浪县为例

通过采样分析，结合20世纪80年代全国第二次土壤普查土壤有机碳数据，对庄浪县农田耕层（0-20cm）土壤近30年有机碳变化及影响因素进行研究．结果表明：①全国第二次土壤普查时土壤平均有机碳含量为6．80g·kg^-1，2011年为8．90g·kg^-1．近30年有机碳含量增加了30．9％，表现为碳汇效应．有机碳含量增加的农田面积约占庄浪县耕地总面积的90％．②在现有管理措施和农田投入下，黄绵土有机碳的稳定水平约为11．0g·kg^-1．有机碳积累量呈现出离稳定值越远变化越大、离稳定值越近变化越小的规律．③近30年土壤有机碳含量变化受海拔高度、初始有机碳含量和土壤类型等因素的显著影响，其中海拔高度对有机碳变化的影响程度最大，初始有机碳含量、土壤类型、产量及有机肥用量对土壤有机碳变化的影响次之，坡向对有机碳变化的影响最小．

花江小流域石漠化过程中的土壤有机碳氮的变化

以花江峡谷区1.2 km2小流域为研究对象,通过设置不同喀斯特石漠化强度的样地,研究不同等级石漠化样地的土壤有机碳、全氮含量在石漠化过程中的变化。结果表明,喀斯特生境中土壤具有高度异质性,人为干扰方式对土壤有机碳、全氮含量变异性的影响很大;樵采石漠化样地小生境土壤有机碳、全氮含量维持在较高水平,开垦石漠化样地小生境土壤有机碳、全氮含量较低;随着石漠化程度的加剧,樵采和开垦系列样地土壤有机碳、全氮含量呈现不断降低的趋势,这在一定程度上体现了石漠化过程的土壤退化本质。小流域内石漠化成因类型的划分对揭示石漠化过程中的土壤退化是必须的。

驱动因子视域下耕地土壤碳源/汇模型的构建与应用

以闽南地区的厦门市、漳州市和泉州市为研究区,首先利用灰色关联模型探究初选因子对1982—2018年耕地土壤有机碳变化的驱动作用,再基于筛选出的主要驱动因子构建BP神经网络模型模拟预测2019—2055年碳源/汇的变化趋势.研究结果表明:1)土壤本身性质(砂粒含量、黏粒含量、初始有机碳密度等)、外在环境条件(道路通达度、年均温、年降水量等)和农业管理措施(秸秆还田量、耕作强度、有机肥和氮肥施用量等)是过去30多年耕地有机碳变化的主要驱动因子,碳源/汇与这些因素的关联度系数均达0.83以上;2)基于主要驱动因子构建的碳模型能较好地拟合研究区碳源/汇变化,模拟值相对误差和模拟效率分别为1.11%和0.48,均通过验证要求;3)未来30多年研究区耕地有机碳密度均值上升0.15 kg·m^(-2),总体表现为碳汇,但不同区域土壤具有“源”与“汇”双重效应,其中“碳源”土壤面积比例为30.33%,主要分布于平原台地区或为初始有机碳密度较高的耕地,“碳汇”土壤以有机碳密度上升幅度≤1 kg·m^(-2)为主,占“碳汇”土壤总面积的97.10%.因此,未来应重点关注“碳源”耕地,并针对性制定减排措施以期转“源”为“汇”,同时还需进一步提升土壤固碳增汇能力,防止高碳土壤发生碳损失而产生碳源效应.

土壤碳库及其变化研究进展

土壤碳库变化对于全球温室效应、全球碳循环有重大的影响,土地利用方式变化而致的土壤碳库亏缺是大气CO2浓度升高的主要原因之一,发挥土壤碳汇效应已成为降低大气温室气体浓度、减缓全球温室效应的简便有效方法。综述了土壤碳库变化与全球温室效应的关系,详细介绍了当前国内外土壤碳库储量与分布以及土壤有机碳库变化动态与潜力研究的现状,并重点分析国内已有研究中存在的问题,最后提出开展土壤碳库及其变化研究的必要性与可能性,指出未来研究方向。

基于土壤有机碳密度变化率的畜禽粪便农田承载力估算

为完善面向土壤固碳的畜禽粪便承载力估算方法研究,以北大荒集团和新疆生产建设兵团种养业生产系统为研究对象,根据种养业生产现状与农田土壤固碳机制,以静稳态模型为基础,构建基于土壤有机碳密度变化率的畜禽粪便农田承载力模型;设定土壤有机碳密度变化率目标值,估算每hm^(2)农田适宜施用畜禽粪便有机肥量与畜禽承载量。结果表明:1)当农田土壤有机碳密度维持当前水平,北大荒集团和新疆生产建设兵团农田可承载的畜禽养殖量以猪当量计分别为180.5~832.1和14.7~327.6头/hm^(2)。2)考虑土壤固碳需求,两地畜禽养殖业未来发展潜力大。本研究成果可为区域种养结合与绿色低碳发展提供参考资料。

施用生物炭和秸秆还田对农田温室气体排放及增温潜势的影响

【目的】农业生态系统增温潜势是影响全球气候变化的重要部分。本研究通过田间试验明确施用生物炭和秸秆还田对农田增温潜势的影响,以期为减缓气候变化和农业废弃物资源化利用提供理论依据。【方法】在山东省桓台县农业生态系统试验站的冬小麦-夏玉米轮作农田中开展了3年田间定位试验,试验共设置4个处理:①对照(CK);②施用生物炭9.0t·hm^(-2)·a^(-1)(C);③全量秸秆还田(S);④秸秆还田配施9.0 t·hm^(-2)·a^(-1)生物炭(CS)。4个处理均施等量的氮磷钾化肥,其中氮肥为尿素,用量为200 kg·hm^(-2)·a^(-1),磷肥为过磷酸钙,用量为55 kg·hm^(-2)·a^(-1),钾肥为硫酸钾,用量为40 kg·hm^(-2)·a^(-1)。采用静态暗箱-气相色谱法测定各处理温室气体(CO_(2)、N_(2)O和CH_4)的排放通量并计算净全球增温潜势(NGWP)和温室气体排放强度(GHGI),分析连续施用生物炭和秸秆还田对农田温室气体排放及增温潜势的影响。【结果】(1)综合3年的温室气体排放情况,与CK处理相比,S和CS处理的年平均生态呼吸排放量(Re)分别增加了47.8%和67.9%(P<0.05);C处理的年平均N_(2)O累积排放量降低了20.3%(P<0.05),而S和CS处理的N_(2)O年平均累积排放量分别增加了23.6%和41.4%(P<0.05)。(2)与CK处理相比,C、S和CS处理的土壤有机碳年平均变化量(ΔSOC)均有显著增加,其中CS处理增幅最大,增加了150.6%(P<0.05)。与第1年相比,C、S和CS处理第3年的ΔSOC均有显著增加(P<0.05),分别增加了21.7%、20.8%和17.8%。各处理的NGWP和GHGI均存在显著差异,与CK相比,C、S和CS处理的年平均NGWP分别降低了163.5%、171.7%和273.0%(P<0.05),与第1年相比,C、S和CS处理第3年的NGWP均有显著降低(P<0.05),分别降低了73.4%、58.8%和54.7%。与CK相比,C、S和CS处理的年平均GHGI分别降低了236.2%、253.3%和388.9%(P<0.05),C、S和CS处理第3年的GHGI较第1年分别降低了126.3%、98.2%和108.6%(P<0.05)。就产量而言,C、S和CS处理的作物产量保持相对稳定,有轻微增长,但与CK相比无显著差异。【结论】与单施化肥相比,在施化肥的基础上添加生物炭、秸秆还田、秸秆还田配施生物炭的措施均能够在不影响作物产量的前提下抑制增温潜势,其中秸秆还田配施生物炭能够最大程度地降低农田增温潜势,因此秸秆还田配施生物炭是增加农田固碳、缓解气候变化的一项有效措施。

Daycent模型模拟不同农作管理措施下华北地区土壤有机碳的变化

基于华北地区3个长期定位试验站点(河南郑州、山东禹城和河北曲周)的试验数据,用站点实测作物产量和土壤有机碳(SOC)双标准对Daycent模型进行校验和验证.结果表明:模型参数组合对作物产量和SOC的长期变化动态拟合效果良好,表明Daycent模型可较好地模拟作物产量和SOC的动态变化.用校验和验证了的模型对3个站点在气候情景RCP 4.5下4种不同管理措施(单施化肥NPK、化肥+有机肥MNPK、秸秆还田SNPK、免耕+秸秆NT)下SOC的变化动态进行模拟.结果表明:郑州站点NPK、MNPK、SNPK处理中,MNPK处理的SOC相对年平均增幅最高,2001—2050年间的SOC年增幅达1.7%,其次为SNPK处理(年均增幅为1.3%)和NPK处理(年均增幅为0.8%),从长远角度看,增施有机肥对灌溉轻壤土有机碳的增加有明显效果.在禹城站点,研究期间,MNPK处理的SOC年均增幅(0.4%)高于NPK处理(0.3%),由于该站点土壤有轻度盐化特征,因此各措施下SOC的增幅较低.在曲周站点,NT处理更有利于SOC的增加,研究期间的SOC年均增幅达1.3%,远高于SNPK处理(0.7%)和NPK处理(0.4%).华北地区气温适宜、灌溉条件好、具备秸秆还田及免耕机械条件,免耕+秸秆还田是该地区增加SOC的较好农作管理措施.

不同包装材料的注射用水总有机碳含量的长期稳定性研究

目的:考察不同包装材料对注射用水中总有机碳含量的影响。方法:采用薄膜电导法测定不同包装材料包装的注射用水在12个月内电导率及总有机碳含量的变化,对结果进行相关性分析及偏相关性分析。结果:采用不同包装材料的包装的注射用水的总有机碳在12个月内变化非常明显,不同包装之间总有机碳的变化存在明显差异,总有机碳与电导率值不存在相关性(p>0.05)。结论:包装材料对注射用水中总有机碳含量的增加有非常显著的影响。

Soil Organic Carbon Content and Distribution in a Small Landscape of Dongguan, South China

Global warming has become an increasing concern, and using soil as a carbon sink to sequester carbon dioxide has attracted much attention in recent years. In this study, soil organic carbon (SOC) content and organic carbon density were estimated based on a soil survey of a small landscape in Dongguan, South China, with spatial heterogeneity of SOC distribution and the impacts of land-use patterns on soil organic carbon content assessed. Field sampling was carried out based on a 150 m×150 m grid system overlaid on the topographic map of the study area and samples were collected in three 20-cm layers to a depth of 60 cm. Spatial variability in the distribution of SOC was assessed using the Kruskal-Wallis test. Results showed that SOC in the topsoil layer (0-20 cm) was not much higher or even lower in some sites than the underlying layers, and except for the two sites covered with natural woodland, it did not exhibit a pronounced vertical gradient. The difference in both horizontal and vertical distribution of SOC was not statistically significant. However, in the topsoil layer among land-use/land-cover patterns, significant differences (P≤0.05) in SOC distribution existed, indicating that management practices had great impact on SOC content. SOC storage in the study area to a depth of 20, 40, and 60 cm was estimated as 2.13×106 kg, 3.46×106 kg, and 4.61×106 kg, respectively.

Effect of Management Practices on Seasonal Dynamics of Organic Carbon in Soils Under Bamboo Plantations

Soil samples for conventional management (CM) and intensive management (IM) practices were taken over a year at 2-month intervals to determine the effect of management practices on soil organic carbon (SOC) and to quantify seasonal dynamics in SOC for bamboo (Phyllostachys pubescens Mazel ex H. de Lehaie) stands. The results with IM compared to CM showed large decreases in total organic carbon (TOC), microbial biomass carbon (MBC), water-soluble organic carbon (WSOC), and the MBC/TOC ratio in the soils. With all IM plots in the 0-20 cm depth across sampling periods, average decreases compared with CM were: TOC, 12.1%; MBC, 26.1%; WSOC, 29.3%; the MBC/TOC ratio, 16.1%; and the WSOC/TOC ratio, 20.0%. Due to seasonal changes of climate, seasonal variations were observed in MBC and WSOC. Soil MBC in the 0-20 cm depth in September compared to May were 122.9% greater for CM and 57.6% greater for IM. However, due primarily to soil temperature, soil MBC was higher during the July to November period, whereas because of soil moisture, WSOC was lower in July and January. This study revealed that intensive management in bamboo plantations depleted the soil C pool; therefore, soil quality with IM should be improved through application of organic manures.

Spatial-Temporal Changes of Soil Organic Carbon During Vegetation Recovery at Ziwuling, China

To probe the processes and mechanisms of soil organic carbon (SOC) changes during forest recovery, a 150-yearchronosequence study on SOC was conducted for various vegetation succession stages at the Ziwuling area, in the centralpart of the Loess Plateau, China. Results showed that during the 150 years of local vegetation rehabilitation SOC increasedsignificantly (P < 0.05) over time in the initial period of 55-59 years, but slightly decreased afterwards. Average SOCdensities for the 0-100 cm layer of farmland, grassland, shrubland and forest were 4.46, 5.05, 9.95, and 7.49 kg C m-3,respectively. The decrease in SOC from 60 to 150 years of abandonment implied that the soil carbon pool was a sink forCO2 before the shrubland stage and became a source in the later period. This change resulted from the spatially variedcomposition and structure of the vegetation. Vegetation recovery had a maximum effect on the surface (0-20 cm) SOCpool. It. was concluded that vegetation recovery on the Loess Plateau could result in significantly increased sequestrationof atmospheric CO2 in soil and vegetation, which was ecologically important for mitigating the increase of atmosphericconcentration of CO2 and for ameliorating the local eco-environment.

The Effects of Estuarine Processes on the Fluxes of Inorganic and Organic Carbon in the Yellow River Estuary

Riverine carbon flux is an important component of the global carbon cycle. The spatial and temporal variations of organic and inorganic carbon were examined during both dry and wet seasons in the Yellow River estuary. Concentrations of dissolved organic carbon （DOC） and dissolved inorganic carbon （DIC） in the Yellow River during dry seasons were higher than those during wet seasons. The effective concentrations of DOC （CDOC＊） were higher than the observed DOC at zero salinity. This input of DOC in the Yellow River estuary was due to sediment desorption processes in low salinity regions. In contrast to DOC, the effective concen- trations of DIC were 10% lower than the DIC measured at freshwater end, and the loss of DIC was caused by CaCO3 precipitation in low salinity region, Particulate organic carbon （POC） and particulate inorganic carbon （PIC） contents of the particles stabilized to constant values （0.5%：t：0.05% and 1.8%--0.2%, respectively） within the turbidity maximum zone （TMZ） and showed no noticeable seasonal variations. A rapid drop of PIC and rise of POC occurred simultaneously outside the TMZ due to an intense dilution of riv- erine inorganic-rich particles being transported into a pool of aquatic organic-poor particles outside the TMZ. Annually, the Yellow River transported 6.95× 10^5 t of DIC, 0.64× 10^5 t of DOC, 78.58× 10^5 t of PIC and 2.29× 10^5 t of POC to the sea.

Soil Organic Carbon and Labile Carbon Along a Precipitation Gradient and Their Responses to Some Environmental Changes

Based on data from a field survey in 2001 along the Northeast China transect (NECT), a precipitation gradient,and a short-term simulation experiment under ambient CO2 of 350 μmol mol-1 and doubled CO2 of 700 μmol mol-1with different soil moisture contents of 30%-45%, 45%-60%, and 60%-80% soil water holding capacity, the distributionof soil organic carbon and labile carbon along the NECT, their relationships with precipitation and their responses toCO2 enrichment and soil moisture changes were analyzed. The results indicated that the soil labile carbon along thegradient was significantly related to soil organic carbon (r = 0.993, P < 0.001). The soil labile carbon decreased morerapidly with depth than organic carbon. The soil organic and labile carbon along the gradient decreased with decrease inlongitude in both the topsoils and subsoils, and the coefficient of variation for the labile carbon was greater than that forthe organic carbon. Both the soil organic carbon and labile carbon had significant linear relationships with precipitation,with the correlation coefficient of soil organic carbon being lower (0.677 at P < 0.001) than that of soil labile carbon(0.712 at P < 0.001). In the simulation experiment with doubled and ambient CO2 and different moisture contents, thecoefficient of variation for soil organic carbon was only 1.3%, while for soil labile carbon it was 29.7%. With doubled CO2concentration (700 μmol mol-1), soil labile carbon decreased significantly at 45% to 60% of soil moisture content. Theseindicated that soil labile carbon was relatively more sensitive to environmental changes than soil organic carbon.

Land Use Effects on Soil Organic Carbon, Microbial Biomass and Microbial Activity in Changbai Mountains of Northeast China

Land use changes are known to alter soil organic carbon （SOC） and microbial properties, however, information about how conversion of natural forest to agricultural land use as well as plantations affects SOC and microbial properties in the Changbai Moun- tains of Northeast China is meager. Soil carbon content, microbial biomass carbon （MBC）, basal respiration and soil carbon mineraliza- tion were studied in five selected types of land use： natural old-growth broad-leaved Korean pine mixed forest （NF）; spruce plantation （SP） established following clear-cutting of NF; cropland （CL）; ginseng farmland （GF） previously under NF; and a five-year Mongolian oak young forest （YF） reforested on an abandoned GF, in the Changbai Mountains of Northeast China in 2011. Results showed that SOC content was significantly lower in SP, CL, GF, and YF than in NF. MBC ranged from 304.4 mg/kg in CL to 1350.3 mg/kg in NF, which was significantly higher in the soil of NF than any soil of the other four land use types. The SOC and MBC contents were higher in SP soil than in CL, GF, and YF soils, yielding a significant difference between SP and CL. The value of basal respiration was also higher in NF than in SP, CL, GF, and YF. Simultaneously, higher values of the metabolic quotient were detected in CL, GF, and YF soils, indicat- ing low substrate utilization of the soil microbial community compared with that in NF and SP soil. The values of cumulative mineral- ized carbon and potentially mineralized carbon （Co） in NF were significantly higher than those in CL and GF, while no significant dif- ference was observed between NF and SP. In addition, YF had higher values of Co and C mineralization rate compared with GF. The results indicate that conversion from NF into agricultural land （CL and GF） uses and plantation may lead to a reduction in soil nutrients （SOC and MBC） and substrate utilization efficiency of the microbial community. By contrast, soils below SP were more conducive to the preservation of soil organic matter, which was reflected in the comparison of microbial indicators among CL, GF, and YF land uses. This study can provide data for evaluating soils nutrients under different land use types, and serve as references for the rational land use of natural forest in the study area.

Changes of Labile Organic Carbon Fractions in Soils Under Different Rotation Systems

Soil labile (biologically active) organic carbon fractions under different crop rotation systems in Jiangsu Province, China, were investigated after 10 years of rotation. The rotation systems, including green manurerice-rice (GmRR), wheat-rice-rice (WRR), wheat-rice (WR) and wheat/corn intercrop-rice (WCR) rotations,were established on paddy soils using a randomized complete block design with three replicates. The total organic carbon (TOC), total nitrogen (TN) and water-soluble organic carbon (WSOC) in the soils under different systems were greater in the GmRR and WRR than in the WR and WCR rotation systems because the soils under triple cropping often received more crop residues than the soils under double cropping. Both the WSOC and the microbial biomass carbon (MBC) contents in the soils of the GmRR rotation system were significantly greater than those in the other crop rotation systems, which was due to the return of green manure to the fields of the GmRR rotation system. The results of a 13C nuclear magnetic resonance (13C-NMR) analysis indicated that the structural characteristics of soil WSOC were similar under the four crop rotation systems with carbohydrates and long-chain aliphatics being the major components. Correlation analysis showed that the content of the WSOC was positively correlated with that of the MBC (P ＜0.01),and all had significantly positive correlations with TOC and TN. The coefficients of variation (CVs) for WSOC and WSOC/TOC were greater than the other indices (e.g, MBC, TOC and TN), suggesting that WSOC in the soils was more sensitive to these rotation systems. The results above indicated that the soil amended with green manure could not only increase the usable C source for soil microorganisms, but could also enhance soil organic matter content; hence, rotation with green manure would be a good strategy for sustainable agriculture.

Emission and Fixation of CO_2 from Soil System as Influenced by Long-Term Application of Organic Manure in Paddy Soils

The observations of 25-yr long-term experiment in Zhejiang paddy soils showed that the soil organic matter could increase continuously with applying organic manure, and the increase in rate enhanced along with the application rates of organic manure. By mathematical modeling, the soil organic matter increased by 22 kg when 1 t of fresh FYM was applied. The CO2 emission resulting from the mineralization of soil organic matter increased with the increase in the application rate of the organic manure as well as the increase in the root residues. It is expected that the CO2 emission will be at 10.04-21.61 t ha-1 yr-1 when 16.5-49.5 t ha-1 yr-1 of fresh FYM is applied. The soil organic carbon from mineralization and release of applied organic carbon (fresh FYM and root residues) will affect the CO2 concentration in the atmosphere. So, the higher the application rate of organic manure, the more is the fixed organic carbon. The CO2 fixation will be at 1.885-3.463 t ha-1 yr-1 when 16.5-49.5 t ha-1 yr-1 of fresh FYM is applied. Thus, the CO2 fixation will increase by 46.7 kg by applying 1 t fresh FYM. To apply organic manure continuously in rice fields may reduce the contribution to the increase of CO2 concentration in the atmosphere.

Soil Organic Carbon Pools in Particle-Size Fractions as Affected by Slope Gradient and Land Use Change in Hilly Regions,Western Iran

This study was conducted to explore the effects of topography and land use changes on particulate organic carbon(POC),particulate total nitrogen(PTN),organic carbon(OC) and total nitrogen(TN) associated with different size primary particle fractions in hilly regions of western Iran.Three popular land uses in the selected site including natural forest(NF),disturbed forest(DF) and cultivated land(CL) and three slope gradients(0-10 %,S1,10-30 %,S2,and 30-50%,S3) were employed as the basis of soil sampling.A total of 99 soil samples were taken from the 0-10 cm surface layer in the whole studied hilly region studied.The results showed that the POC in the forest land use in all slope gradients was considerably more than the deforested and cultivated lands and the highest value was observed at NF-S1 treatment with 9.13%.The values of PTN were significantly higher in the forest land use and in the down slopes(0.5%) than in the deforested and cultivated counterparts and steep slopes(0.09%) except for the CL land use.The C:N ratios in POC fraction were around 17-18 in the forest land and around 23 in the cultivated land.In forest land,the silt-associated OC was highest among the primary particles.The enrichment factor of SOC,EC,was the highest for POC.For the primary particles,EC of both primary fractions of silt and clay showed following trend for selected land uses and slope gradients:CL> DF> NF and S3 > S2> S1.Slope gradient of landscape significantly affected the OC and TN contents associated with the silt and clay particles,whereas higher OC and TN contents were observed in lower positions and the lowest value was measured in the steep slopes.Overall,the results showed that native forest land improves soil organic carbon storage and can reduce the carbon emission and soil erosion especially in the mountainous regions with high rainfall in west of Iran.