Relationship between light and heavy fractions of organic matter for several agricultural soils in China

Although numerous studies about the nature and turnover of soil organic matter（SOM） in light and heavy fractions（ LFOM and HFQM, respectively） have been made, little information is available in relation to the relationship between LFQM and HFOM, and no attempts have been made to quantify a general relationship between LFQM and HFQM for agricultural soils under field condition. Qur hypothesis is there may be an inherent relationship between LFQM and HFQM for agricultural soils under certain unaltered management practices for a long period, to this end, we therefore studied typically soils taken from different parts in China by using a simple density fractionation procedure. The results indicated that LFQM was positively correlated with LFOM/HFOM ratio for three typical soils. This information will be of particular use not only in deepening our understanding of the dynamics of SQM fractions but also in evaluating the potential of agricultural soils to sequestrate C under different management practices in a long term.

Deadwood affects the soil organic matter fractions and enzyme activity of soils in altitude gradient of temperate forests

The main objective of our study has been to determine the role of deadwood in the shaping of the amount of soil organic matter fractions in mountain forest soils.For this purpose,a climosequence approach comprising north(N)and south(S)exposure along the altitudinal gradient(600,800,1000 and 1200 m a.s.l.)was set up.By comparing the properties of decomposing deadwood and those of the soils located directly beneath the decaying wood we drew conclusions about the role of deadwood in the shaping of soil organic matter fractions and soil carbon storage in different climate conditions.The basic properties,enzymatic activity and fractions of soil organic matter(SOM)were determined in deadwood and affected directly by the components released from decaying wood.Heavily decomposed deadwood impacts soil organic matter stabilization more strongly than the less decayed deadwood and the light fraction of SOM is more sensitive to deadwood effects than the heavy fraction regardless of the location in the altitude gradient.Increase in SOM mineral-associated fraction C content is more pronounced in soils under the influence of deadwood located in lower locations of warmer exposure.Nutrients released from decaying wood stimulate the enzymatic activity of soils that are within the range of deadwood influence.

Soil Organic Carbon,Carbon Fractions and Nutrients as Affected by Land Use in Semi-Arid Region of Loess Plateau of China

Cropland (CP),native grassland (NG) and two shrub land treatments which were converted from cropland in 1985:seabuckthorn (Hippophae rhamnoides L.) (ST),and branchytamarisk (Tamarix ramosissima) (BT) were investigated to evaluate effects of land use conversion on soil organic carbon (SOC) and soil nutrients in the semi-arid region of the Loess Plateau of China.Total organic carbon (TOC),light fraction organic carbon (LFOC),heavy fraction organic carbon (HFOC),total N (TN),nitrate nitrogen (NO 3-N) and nitrite nitrogen (NO 2-N),ammonium nitrogen (NH + 4-N),total P,and available P (AP) were measured.The results showed that SOC in NG,ST and BT were 12.7%,27.7% and 34.8% higher than that of the cropland,respectively.LFOC,light fraction (LF) dry matter,ratio of TOC to TN (C/N) and the ratio of TOC to AP (C/P) were higher in the shrub land or native grassland than in the cropland.Cropland had the highest TN,the sum of NO 3-N and NO 2-N,TP and AP due to the use of chemical fertilizers.TOC significantly correlated with LFOC,HFOC and C/N.LFOC significantly correlated with dry matter of the LF and C/N.TN,the sum of NO 3-N and NO 2-N and AP were significantly negatively correlated with TOC and LFOC.Therefore,land use conversion from cropland to shrub land,or maybe grassland,contributed to SOC sequestration and improved soil nutrients stabilization.

Conventional tillage improves the storage of soil organic carbon in heavy fractions in the Loess Plateau, China

Soil labile organic carbon （C） plays an important role in improving soil quality. The relatively stable fractions of soil organic C （SOC） represent the bulk of SOC, and are also the primary determinant of the long-term C balance of terrestrial ecosystems. Different land use types can influence the distribution patterns of different SOC fractions. However, the underlying mechanisms are not well understood. In the present study, different fractions of SOC were determined in two land use types： a grazed grassland （established on previously cultivated cropland 25 years ago, GG） and a long-term cultivated millet cropland （MC）. The results showed that C concentration and C storage of light fractions （LF） and heavy fractions （HF） presented different patterns along the soil profiles in the two sites. More plant residues in GG resulted in 91.9% higher LF storage at the 0-10 cm soil depth, further contributed to 21.9% higher SOC storage at this soil depth; SOC storage at 20-60 cm soil depth in MC was 98.8% higher than that in GG, which could be mainly attributed to the HF storage 104.5% higher than in GG. This might be caused by the long-term application of organic manure, as well as the protection from plough pan and silt- and clay-sized particles. The study indicated that different soil management practices in this region can greatly influence the variations of different SOC fractions, while the conventional tillage can greatly improve the storage of SOC by in- creasing heavy fractions.

Effects of Caragana microphylla plantations on organic carbon sequestration in total and labile soil organic carbon fractions in the Horqin Sandy Land, northern China

Afforestation is conducive to soil carbon（C） sequestration in semi-arid regions. However, little is known about the effects of afforestation on sequestrations of total and labile soil organic carbon（SOC） fractions in semi-arid sandy lands. In the present study, we examined the effects of Caragana microphylla Lam. plantations with different ages（12-and 25-year-old） on sequestrations of total SOC as well as labile SOC fractions such as light fraction organic carbon（LFOC） and microbial biomass carbon（MBC）. The analyzed samples were taken from soil depths of 0–5 and 5–15 cm under two shrub-related scenarios： under shrubs and between shrubs with moving sand dunes as control sites in the Horqin Sandy Land of northern China. The results showed that the concentrations and storages of total SOC at soil depths of 0–5 and 5–15 cm were higher in 12-and 25-year-old C. microphylla plantations than in moving sand dunes（i.e., control sites）, with the highest value observed under shrubs in 25-year-old C. microphylla plantations. Furthermore, the concentrations and storages of LFOC and MBC showed similar patterns with those of total SOC at the same soil depth. The 12-year-old C. microphylla plantations had higher percentages of LFOC concentration to SOC concentration and MBC concentration to SOC concentration than the 25-year-old C. microphylla plantations and moving sand dunes at both soil depths. A significant positive correlation existed among SOC, LFOC, and MBC, implying that restoring the total and labile SOC fractions is possible by afforestation with C. microphylla shrubs in the Horqin Sandy Land. At soil depth of 0–15 cm, the accumulation rate of total SOC under shrubs was higher in young C. microphylla plantations（18.53 g C/（m^2·a）; 0–12 years） than in old C. microphylla plantations（16.24 g C/（m^2·a）; 12–25 years）, and the accumulation rates of LFOC and MBC under shrubs and between shrubs were also higher in young C. microphylla plantations than in old C. microphylla plantations. It can be concluded that the establishment of C. microphylla in the Horqin Sandy Land may be a good mitigation strategy for SOC sequestration in the surface soils.

Changes of Organic Carbon in Soil under Different Land Use Patterns in Alpine Agricultural Region of Qinghai

Using organic carbon density grouping method,the change trends of soil total organic carbon(SOC),light fraction content and light fraction organic carbon under 4 land use patterns of returning cultivated land to forest(cropland,artificial forest,inter-cropping of forest and grassland and original sample plot)in alpine agricultural region of Qinghai were studied.The content of SOC was in order:intercropping of forest and grassland > original sample plot > artificial forest > cropland.There was signi...

Long-term effects of gravel―sand mulch on soil organic carbon and nitrogen in the Loess Plateau of northwestern China

Gravel-sand mulch has been used for centuries to conserve water in the Loess Plateau of north- western China. In this study, we assessed the influence of long-term （1996-2012） gravel-sand mulching of cultiv- ated soils on total organic carbon （TOC）, light fraction organic carbon （LFOC）, microbial biomass carbon （MBC）, total organic nitrogen （TON）, particulate organic carbon （POC）, mineral-associated organic carbon （MOC）, perma- nganate-oxidizable carbon （KMnO4-C）, and non-KMnO4-C at 0-60 cm depths. Mulching durations were 7, 11 and 16 years, with a non-mulched control. Compared to the control, there was no significant and consistently positive effect of the mulch on TOC, POC, MOC, KMnO4-C and non-KMnO4-C before 11 years of mulching, and these organic C fractions generally decreased significantly by 16 years. LFOC, TON and MBC to at a 0-20 cm depth in- creased with increasing mulching duration until 11 years, and then these fractions decreased significantly between 11 and 16 years, reaching values comparable to or lower than those in the control. KMnO4-C was most strongly correlated with the labile soil C fractions. Our findings suggest that although gravel-sand mulch may conserve soil moisture, it may also lead to long-term decreases in labile soil organic C fractions and total organic N in the study area. The addition of manure or composted manure would be a good choice to reverse the soil deterioration that occurs after 11 years by increasing the inputs of organic matter.

Effect of fire intensity on active organic and total soil carbon in a Larix gmelinii forest in the Daxing'anling Mountains,Northeastern China

Studying contents and seasonal dynamics of active organic carbon in the soil is an important method for revealing the turnover and regulation mechanism of soil carbon pool. Through 3 years of field sampling and lab analysis, we studied the seasonal variations, content differences, and interrelationships of total organic carbon （TOC）, light fraction organic carbon （LFOC）, and particulate organic carbon （POC） of the soil in the forest areas burned with different fire intensities in the Daxing＇anling Mountains. The mean TOC content in the low-intensity burned area was greater than that in the unburned area, moderate-intensity, and high-intensity burned areas in June and November （P 〈 0.05）. LFOC and POC in the low-intensity burned area were greater than that in either moderate-intensity or high-intensity burned areas, with significant differences in LFOC in September and November （P 〈 0.05）. A significant difference in LFOC between the unburned and burned areas was only found in July （P 〈 0.05）. However, the differences in POC between the unburned and burned areas were not significant in all the whole seasons （P 〉 0.05）. Soil LFOC and POC varied significantly with the seasons （P 〈 0.05） in the Daxing＇anling Mountains. Significant linear relationships were observed between soil TOC, LFOC, and POC, which were positively correlated with soil nitrogen and negatively correlated with soil temperature in the Daxing＇anling Mountains.

Soil Organic Matter Fractions under Different Vegetation Types in Permafrost Regions along the Qinghai-Tibet Highway, North of Kunlun Mountains, China

As a key attribute of soil quality, soil organic matter(SOM) and its different fractions play an important role in regulating soil nutrient cycling and soil properties.This study evaluated the soil carbon(C) and nitrogen(N) concentrations in different SOM fractions(light– and heavy fractions,microbial biomass) under different vegetation types and analyzed their influencing factors in continuous permafrost regions along the Qinghai-Tibet Highway in the North of Kunlun Mountains, China.Soil samples were collected in pits under four vegetation types — Alpine swamp meadow(ASM), Alpine meadow(AM), Alpine steppe(AS) and Alpine desert(AD) — at the depth of 0-50 cm.The vegetation coverage was the highest at ASM and AM, followed byAS and AD.The results indicated that the concentrations of light fraction carbon(LFC) and nitrogen(LFN), and microbial biomass carbon(MBC)and nitrogen(MBN) decreased as follows: ASM > AM >AS > AD, with the relatively stronger decrease of LFC,whereas the heavy fraction carbon(HFC) and nitrogen(HFN) concentrations were lower in AS soils than in the AD soils.The relatively higher proportions of LFC/SOC and MBC/SOC in the 0-10 cm depth under the ASM soils are mainly resulted from its higher substrate input and soil moisture content.Correlation analysis demonstrated that aboveground biomass, soil moisture content, soil organic carbon(SOC) and total nitrogen(TN) positively correlated to LFC, LFN, HFC, HFN, MBC and MBN, while p H negatively correlated to LFC, LFN, HFC, HFN, MBC and MBN.There was no relationship between active layer thickness and SOM fractions, except for the LFC.Results suggested that vegetation cover, soil moisture content, and SOC and TN concentrations were significantly correlated with the amount and availability of SOM fractions, while permafrost had less impact on SOM fractions in permafrost regions of the central Qinghai–Tibet Plateau.

Soil organic carbon pool along different altitudinal level in the Sygera Mountains, Tibetan Plateau

Labile organic carbon（LOC） is one of the most important indicators of soil organic matter quality and dynamics elevation and plays important function in the Tibetan Plateau climate. However, it is unknown what the sources and causes of LOC contamination are. In this study, soil organic carbon（SOC）, total nitrogen（TN）, microbial biomass carbon（MBC）, microbial biomass nitrogen（MBN） and LOC were analyzed based on different soil horizons and elevations using turnover time in an experimental site（3700 m to 4300 m area） in Sygera. SOC and LOC in higher-elevation vegetation types were higher than that of in lower-elevation vegetation types. Our results presented that the soil microbial biomass carbon（SMBC） and soil microbial biomass nitrogen（SMBN）were positively correlated with SOC. The content of easily oxidized carbon（EOC）, particulate organic carbon（POC） and light fraction organic carbon（LFOC） decreased with depth increasing and the content were the lowest in the 60 cm to 100 cm depth.The total SOC, ROC and POC contents decreased with increasing soil horizons. The SOC, TN, MBC and MBN contents increased with increasing altitude in the Sygera Mountains. The MBC and MBN contents weredifferent with the changes of SOC（p＆lt;0.05）,meanwhile, both LFOC and POC were related to total SOC（p＆lt;0.05）. The physical and chemical properties of soil, including temperature, humidity, and altitude,were involved in the regulation of SOC, TN, MBC,MBN and LFOC contents in the Sygera Mountains,Tibetan Plateau.

辽河口湿地土壤有机碳组分特征及其影响因素

湿地生态系统碳汇潜力巨大,但不同的气候条件及植被类型,导致湿地土壤有机碳库组分有较大的差异,进而导致不同类型的湿地土壤有机碳受土壤理化性质的影响也有差异。深入了解土壤有机碳组分特征对滨海湿地生态系统开发及保护具有重要意义。以辽河口湿地为对象,选取5种土地覆盖类型(翅碱蓬群落、芦苇群落、光滩裸地、油井区和农耕区),分析不同土地覆盖类型下土壤有机碳组分及土壤基本理化性质,对所得数据进行相关性和差异性分析,以期探明辽河口湿地土壤有机碳组分特征,并确定土壤理化性质对辽河口湿地有机碳储量的影响。结果表明:辽河口湿地在不同土地利用类型下土壤总有机碳(Soil organic carbon,SOC)含量差异显著,其中芦苇群落碳储量最丰富,达(52.6±3.80) g·kg^(-1),光滩裸地碳储量最少,为(28.2±7.05) g·kg^(-1);在植物覆盖下土壤有充沛的碳输入而有利于土壤有机碳的固定,这一现象随土层深度的加深而减弱。轻组分有机碳(Light fraction organic carbon,LFOC)、重组分有机碳(Heavy fraction organic carbon,HFOC)和易氧化有机碳(Easily oxidized organic carbon,EOC)均与SOC含量具有显著的相关性(P<0.05),相关性大小为EOC>HFOC>LFOC。SOC含量与pH值、阳离子交换量呈显著正相关,而受含水率、总可溶性固体的影响不显著,这一现象可能与有机碳组分特征有关。辽河口湿地土壤碳库中HFOC占比最大,EOC占比最小,碳库结构较为稳定。pH值、阳离子交换量主要通过影响HFOC积累速率来影响SOC含量。因此,提高湿地土壤中较为稳定的HFOC储量,有助于提升湿地土壤的固碳能力。研究结果可为滨海湿地生态系统保护与碳汇功能提升提供参考。

填闲作物还田方式对烟田土壤轻重组有机碳的影响

为了提高多年连作烟田的土壤肥力,改善土壤生态环境,在烤烟冬闲期种植油菜、冬牧70、光叶紫花苕等3种作物,同时以冬季空闲不种植任何作物为对照,采取2种方式(掩青和收割)进行处理,通过测定不同处理不同土层的土壤轻、重组有机碳含量、比例及储量,探讨填闲作物收割和掩青处理对烟田土壤轻重组有机碳的影响。结果表明,不同填闲作物和不同还田方式下土壤总有机碳、重组有机碳、轻组有机碳含量均随着土壤深度的增加而降低。与对照相比,填闲作物掩青处理能够显著增加土壤总有机碳、重组有机碳、轻组有机碳含量,尤其是冬牧70在20~40 cm土层增加比较显著,分别增加了22.3%、21.98%、27.78%;填闲作物收割处理会降低土壤轻组有机碳比例和土壤轻组有机碳储量,而掩青处理则会增加土壤轻组有机碳比例和轻组有机碳储量,其中冬牧70掩青在0~20 cm土层增加比较明显,分别增加了18.14%、40.03%。填闲作物掩青处理增加了烟田土壤的含水量和持水量、降低了土壤容重以及增加土壤轻重组有机碳储量。综合来看,冬牧70掩青处理效果最好,能显著增加土壤总有机碳和轻重组有机碳含量,油菜次之。

坡面片蚀泥沙有机碳组分及^(13)C同位素不均匀富集对水动力学参数的响应

[目的]探究片蚀泥沙轻组有机碳(LF_(OC))和重组有机碳(HF_(OC))不均匀富集的水动力学和碳同位素特征,为正确理解水蚀作用下土壤有机碳库变化提供理论与技术支撑。[方法]以陕西省咸阳市杨凌区土为研究对象,采用改进“三区”移动式变坡钢制土槽,结合人工模拟降雨技术,测定径流水动力学参数和泥沙各粒径团聚体有机碳组成及其δ^(13)C值,并辅以棕壤侵蚀泥沙有机碳δ^(13)C值和水力参数,验证土试验结果的准确性。[结果]①雨强和坡度较小时,侵蚀泥沙LF_(OC)和HF_(OC)易发生富集,且相较黏粉粒和微团聚体,大团聚体LF_(OC)与HF_(OC)含量受雨强和坡度的影响更大;②侵蚀泥沙黏粉粒中有机碳δ^(13)C值与其有机碳活跃分数(λ)呈负相关,而其他粒径团聚体有机碳δ^(13)C值与其λ呈显著正相关(p<0.05);③流速与黏粉粒λ显著正相关(p<0.05),雷诺数与各粒径团聚体有机碳δ^(13)C值均呈显著负相关(p<0.01),片蚀过程中流速越大,黏粉粒中LF_(OC)越易于优先输移,而紊流加剧则促进低δ^(13)C值团聚体有机碳的优先输移;④对于侵蚀泥沙黏粉粒,流速和雷诺数越大,其有机碳δ^(13)C值越小,λ越大;对于微团聚体和大团聚体,雷诺数越小,其有机碳δ^(13)C值与λ越大。[结论]片蚀过程中轻重组有机碳流失与流速和雷诺数密切相关。并进一步验证了^(13)C同位素对侵蚀泥沙有机碳示踪的有效性。

Molecular composition and structure of organic matter in density fractions of soils amended with corn straw for five years

Corn straw is an important source of carbon(C),and when applied to soil,it alters the accumulation and distribution of organic C.However,the mechanistic pathways by which newly added C is stored and stabilized in soil remain a subject of interest and debate among scholars.In this study,we investigated the chemistry of organic matter in different density fractions of Haplic Cambisol(sandy clay loam)in a field experiment with corn straw at8900 kg ha^(-1)year^(-1)under no tillage(NT),minimum tillage(MT),and conventional tillage(CT).After five years of corn(Zea mays L.)monocropping,soils were collected from the 0-20 and 20-40 cm depths and processed to obtain the organic matter in light fraction(LFOM),occluded particulate(oPOM),and heavy fraction(HFOM)in the order.The results showed that compared with conventional tillage without corn straw return(CT0),corn straw return(i.e.,NT,MT,and CT)increased soil organic C content by 11.55%-16.58%.Thermogravimetric and Fourier transform infrared analyses demonstrated that the HFOM was characterized by a greater proportion of easily biodegradable substances,which may be due to the deposition of microbially processed materials on the surface of soil minerals.The LFOM and o POM were distinguished by greater phenolic,aromatic C,and thermally stable compounds.Compared with CT0,the NT and MT fields showed higher abundances of hydrophobic,aliphatic,and thermally unstable organic compounds,which increased soil C content and stability in the HFOM.Therefore,NT and MT may be ideal practices to increase soil organic C content.

典型黑土的黑度与土壤有机质组分关系研究

土壤颜色作为土壤的一项重要物理指标,被广泛应用于土壤诊断、分类以及土壤性质判断。在矿物成分大致相同条件下,土壤有机质(SOM)是控制土壤变黑的重要因素。采用基于CIE L*a*b*颜色分析系统的分光测色仪,并结合土壤物理分组方法,对30个典型黑土及其物理组分(轻组、粗颗粒、细颗粒和矿质结合态有机质)的黑度进行了分析,旨在明确黑土SOM含量与其黑度间的定量关系,揭示不同物理组分对土壤黑度的贡献。结果表明:黑土的黑度与SOM、以及各物理组分的黑度与相应组分的有机碳含量之间,均呈显著正相关关系。而且随着组分稳定程度的增加,这种相关性逐渐增强。从不同组分看,轻组和粗颗粒组分的黑度值大于细颗粒和矿质结合态组分,但相关分析表明,轻组和粗颗粒组分的黑度与原土黑度无显著相关关系,二者对土壤黑度的贡献率仅为2.6%。而矿质结合态组分作为土壤腐殖质的主要储存位置,其对土壤的黑度贡献率达81%以上,是黑土呈现黑色的决定性因素。

黔中不同发育阶段马尾松人工林土壤有机碳组分变化特征

为探究马尾松人工林发育对土壤不同活性有机碳组分的影响,采用时空替代法,选取黔中地区不同发育阶段的马尾松人工林为研究对象,研究马尾松人工林发育过程中土壤总有机碳(TOC)、重组有机碳(HFOC)和轻组有机碳(LFOC)含量、比例的变化及相互关系。结果显示:(1)不同发育阶段0~80 cm土层内重组质量分数的范围为83%~91%,轻组为9%~17%,重组中有机碳的含量为1.53~33.07 g/kg,轻组为8.20~119.10 g/kg;(2)通过对土层容重和相应有机碳含量进行加权,得出5个发育阶段TOC、HFOC和LFOC的平均值为11.62~18.83 g/kg、7.52~12.05 g/kg、4.10~7.33 g/kg,TOC和HFOC在幼龄林至近熟林阶段逐渐升高,在成熟至过熟林阶段降低,LFOC随发育阶段呈降低-升高-降低-升高变化趋势;3种有机碳含量均随土层加深而降低,且表层多显著(P<0.05)高于其他土层;(3)不同发育阶段0~80 cm土层内HFOC/TOC、LFOC/TOC的范围分别为32%~80%、20%~68%,但在发育阶段和土层深度间的变化趋势不明显;(4)3种有机碳组分两两之间均为正相关,TOC与HFOC之间相关性最强(R 2=0.92)。研究结果表明:黔中马尾松人工林发育的后期,土壤对TOC和HFOC固持的能力下降,需进行合适的人工管理,以加强马尾松人工林的地力维持。

不同恢复模式对退化高寒沼泽湿地土壤轻重组有机碳的影响

以若尔盖县麦溪乡已实施多年水位提升和植被恢复工程的高寒沼泽湿地为研究对象,分别采集重度退化(HD)湿地、未退化(UD)湿地以及不同恢复模式下湿地各土层(0—20 cm、20—40 cm、40—60 cm、60—80 cm)土壤样品,分析土壤有机碳轻重组分的变化及其与土壤因子的关系。结果表明:不同恢复措施均能造成退化湿地土壤总有机碳含量在各土层之间的空间分异,但补播草种措施不能显著提升各土层总有机碳含量;恢复措施对退化湿地土壤中重组分有机碳和轻组分有机碳含量提升效果不显著。综合RDA分析来看,单一补播草种措施短期内不能根本改善湿地退化状况,水位提升措施能使土壤碳组分结构趋近于未退化湿地,土壤TN是影响土壤有机碳组分的最关键因子,可作为反映高寒沼泽湿地恢复的关键指标。

洞庭湖湿地有机碳垂直分布与组成特征

以洞庭湖3类湿地的9个典型剖面为代表,研究了洞庭湖湿地有机碳垂直分布和组成特征.结果表明,湖草滩地表层(0～1 0cm)有机碳含量(>4 0g/kg)明显高于芦苇滩地(2 0±2 . 8) g/kg和垦殖水田(2 8±8 . 6 ) g/kg .0～30cm内,湖草和芦苇滩地有机碳含量随深度的增加而下降,30cm以下有机碳含量基本稳定.垦殖水田的3个剖面间有机碳含量存在较大变异.湖草滩地表层0～1 0cm轻组碳占总有机碳的2 0 %以上,而芦苇滩地和垦殖水田表层0～1 0cm的有机碳以稳定的重组碳为主(>90 %) .同一类型湿地垂直方向上,受有机碳来源复杂性的影响,轻组碳占总有机碳的比例具有明显的层次性.分组试验还表明,重组碳与总有机碳、容重与总有机碳、重组碳与重组氮之间具有极显著的相关关系(p <0 . 0 1 ) .

桃园生草对土壤有机碳及活性碳库组分的影响

果园生草是解决传统清耕引起的水土流失、土壤有机质减少、土壤肥力下降和果品品质变劣的果园地面管理措施之一。阐明不同牧草种类对土壤有机碳及其活性组分的影响是实现果园土壤生态管理、促进有机果品生产技术体系完善和果园土壤质量提高过程中亟待解决的问题。通过研究桃园人工种植黑麦草和毛苕子对土壤总有机碳(TOC)及其活性组分(微生物量碳(MBC)、水溶性有机碳(WSOC)、轻组有机碳(LFOC)、重组有机碳(HFOC)以及团聚体有机碳)的影响,探明豆科牧草与禾本科牧草种植对桃园土壤有机碳及其组分的影响及其差异。结果表明:与清耕对照(CK)相比,种植黑麦草后土壤TOC、MBC和WSOC分别提高了5.13%、76.4%和18.1%,种植毛苕子土壤LFOC提高了11.3%,土壤HFOC降低了13.2%,但对土壤TOC、MBC和WSOC未产生显著影响。此外,黑麦草显著提高土壤较大粒级(>74μm)团聚体有机碳含量,而毛苕子则显著降低土壤较小粒级(<2000μm)团聚体有机碳含量。对提高TOC而言,在桃园种植禾本科牧草黑麦草优于豆科牧草毛苕子。土壤MBC、WSOC、LFOC以及HFOC可以作为指示桃园土壤质量提高与否、表征土壤有机碳变化的敏感指标。

垦殖对新疆绿洲农田土壤有机碳组分及团聚体稳定性的影响

土壤有机碳是土壤质量变化的重要指标,土壤活性有机碳组分在土壤质量变化方面发挥重要作用。采用有机碳分组技术,研究了干旱荒漠区自然土壤开垦对绿洲农田土壤有机碳活性组分及团聚体稳定性的影响。结果表明:低有机碳含量的自然土壤垦殖后,有利于干旱荒漠区绿洲棉田土壤有机碳的积累,且垦殖(0-5a)增加显著,年均增加在0.65gkg-1以上,上升幅度为76%-286%,5a后维持在相对平衡的水平;土壤活性有机碳、轻组有机碳在垦殖0-5a显著增加,平均增加72%和99%,5a后下降;颗粒有机碳则表现出垦殖0-10a明显增加,增加在275%以上,10a后下降;土壤水稳性团聚体含量随垦殖年限的延长显著增加,0-20a内较自然土壤提高了75%。垦殖可能是干旱区绿洲农田潜在碳汇的重要影响因素;但随垦殖年限延长,土壤有机碳活性组分下降,土壤质量又存在一定的退化风险。