Total Soil Organic Carbon Content Research Articles

Winter tillage impacts on soil organic carbon, aggregation and CO2 emission in a rainfed vegetable cropping system of the mid–Yunnan plateau, China

The mid–Yunnan plateau is one of the major regions for the production of vegetables in China, but intense management practices have led to soil degradation and amplified greenhouse–gas emissions. Understanding management effects on soil organic carbon dynamics and structural stability can aid to improve vegetable cropping systems sustainability in this region. In the present study, we evaluated the effect of seasonal tillage alterations (non–winter–tillage [NWT] and winter–tillage [WT]) on soil (0–10cm) organic carbon (SOC) retention, soil aggregate stability, aggregate–associated C concentrations and CO2 emission in a clay loam soil. Results indicated after 2 years that the plots under NWT had nearly 4% higher total SOC content and 9% higher proportion of large macro-aggregates (>2mm) compared with WT plots in the 0–5cm layer. Greater SOC and labile C within large macro–aggregates in the plots under NWT compared with WT were also observed in the surface layer only. Soil CO2 emission rates were significantly greater in the WT plots than in the NWT plots during the dry season, but did not differ significantly between the WT and NWT plots during the rainy season. Our results demonstrated that the adoption of NWT should be a more sustainable management option than the traditional winter tillage for the maintenance of soil C and reduction of carbon dioxide emission in the rainfed vegetable cropping system of the mid–Yunnan plateau.

Impacts of vegetation type and climatic zone on neutral sugar distribution in natural forest soils

Soil neutral sugars are a significant component of labile soil organic carbon (SOC) and are derived from both plant and microbial biomass. While plants synthesize both pentose and hexose neutral sugars, microbes almost exclusively produce hexoses. Hexose to pentose ratios in soil thus potentially indicate the extent to which microbes process labile SOC. In this study, we used the ratio of galactose + mannose (G+M) to arabinose+xylose (A+X) to estimate the contribution of sugars derived from microbes and plants to SOC in forest ecosystems. We explored how forest type and climatic zone influence soil neutral sugar profiles by studying coniferous and broadleaf forests located in temperate and subtropical regions in China. At each site, neutral sugars from organic (O) and top-layer mineral (A) soil horizons, as well as from freshly-fallen leaf litter, were measured. Total SOC and soil neutral sugar contents were lower in the subtropical region than in the temperate region, with lower levels in the A horizon than in the O horizon. In both climatic zones, litter (G+M)/(A+X) ratios were higher in coniferous forests (1.2±0.3) than in broadleaf forests (0.4±0.1). Differences in the (G+M)/(A+X) ratios between forest types (coniferous and broadleaf) persisted in the O horizon (1.4±0.2>0.9±0.0) and in the A horizon (1.8±0.1>1.3±0.0). Across climate zones and forest types, ratios increased from litter over the O horizon to the A horizon. Contrary to our expectations, climate zone did not affect soil (G+M)/(A+X) ratios. Our findings emphasize the important contribution of microbial biomass to labile SOC pools while revealing that soil neutral sugar profiles do not respond to climatic zone drivers as expected.

Multi-site assessment of the effects of plastic-film mulch on the soil organic carbon balance in semiarid areas of China

Plastic-film mulch is widely used to increase soil temperature and reduce water evaporation in vegetable production. In China, it is also extensively used for growing grain crops, especially in temperature and rainfall limited areas. However, it remains unclear whether the technology is sustainable in terms of maintenance of soil organic carbon (SOC) balance. We assessed the effects of plastic-film mulch on the SOC balance in maize (Zea mays L.) production in a range of cold semiarid environments. We imposed four treatments: (i) no plastic-film mulch or straw incorporation, (ii) plastic-film mulch, (iii) straw incorporation in soil without mulch, and (v) straw incorporation plus mulch, in ridge–furrow prepared fields at five sites along a hydrothermal gradient for up to six years. Maize root biomass across sites increased by 23–38% in mulched plots associated with the increase in aboveground biomass, indicating an increased SOC input, compared to that in non-mulched plots. The plastic-film mulch increased SOC mineralization, indicated by the stimulated decomposition of buried maize straw, and a 4–5% reduction in the concentration of light-fraction SOC (<1.8gcm−3), but the total SOC concentration and stock in the 0–0.15m soil layer did not change relative to no mulch after six years of continuous cropping. Plastic-film mulch did not affect the total non-cellulosic sugar content; however, it significantly increased the contribution of microbial-synthesized sugars to the total non-cellulosic sugars, indicating an intensified microbial action on the SOC pool compared to no mulch. Straw incorporation increased the root biomass, light and total SOC concentrations and non-cellulosic sugars, and changed the non-cellulosic sugar composition. We conclude that the increase in soil temperature and moisture by use of plastic-film mulch enhances productivity, but importantly maintains the SOC level in temperature- and rainfall-limited semiarid regions by balancing the increased SOC mineralization with increased root-derived C input.

Organic carbon characteristics in Swedish forest soil trace post‐depositional carbon dynamics

SummaryWe investigated soil organic carbon (SOC) characteristics in three forests along a north–south transect in Sweden where these forest types cover about 69% of the landscape. There was variation in 14C ages, and the median ages ranged from about 25 to &gt; 2500 cal BP in SOC. Although total SOC and nitrogen (N) contents decreased, stable carbon isotope and humification indices increased with depth. These progressive changes with depth and age were related to degradation. The δ13C values and specific biomarkers indicated that organic carbon was primarily from C3 plants. Biomarkers were effective in distinguishing OC input from specific sources (i.e. angiosperms, gymnosperms and grasses). A sharp decrease in biomarkers with depth indicated degradation of OC in the upper soil horizon, and limited contribution in the subsoil towards the stabilization of SOC. The sharp decrease in carbon stocks and 14C age in the soil OC pool with increasing soil depth, and quite large values for the percentage of modern carbon, suggested a decrease in SOC pools. Overall, these results showed that carbon sequestration in high latitude forests was small, and their role as potential carbon sinks needs to be reassessed.Highlights We studied soil organic carbon (SOC) characteristics in Swedish boreal and temperate forests. The decline of SOC with depth contributes little to carbon sequestration in deeper soil horizons. Soil degradation causes a decline in total carbon, nitrogen, alkanes and lignin with depth and age. The role of these forests as carbon sinks needs to be reassessed because of degradation of SOC.

Stabilization of new carbon inputs rather than old carbon decomposition determines soil organic carbon shifts following woody or herbaceous vegetation transitions

Although numerous studies have quantified the effects of land-use changes on soil organic carbon (SOC) stocks, few have examined simultaneously the weight of carbon (C) inputs vs. outputs in shaping these changes. We quantified the relative importance of soil C inputs and outputs in determining SOC changes following the conversion of natural ecosystems to pastures or tree plantations, and evaluated them in light of variations in biomass production, its quality (C:N) and above/belowground allocation patterns. We sampled soils up to one-meter depth under native grasslands or forests and compared them to adjacent sites with pastures or plantations to estimate the proportion of new SOC (SOCnew) retained in the soil and the decomposition rates of old SOC (k SOC-old ) based on δ 13C shifts. We also analyzed these changes in the particulate organic matter fraction (POM) and estimated above and belowground net primary production (ANPP and BNPP) from satellite images, as well as changes in vegetation and soil’s C:N ratios. The conversion of grasslands to tree plantations decreased total SOC contents while the conversion of forests to pastures increased SOC contents in the topsoil but decreased them in deep layers, maintaining similar soil stocks up to 1 m. Changes in POM were less important and occurred only in the topsoil after cultivating pastures, following SOC changes. Surprisingly, both land-use trajectories showed similar decomposition rates in the topsoil and therefore overall SOC changes were not correlated with C outputs (k SOC-old ) but were significantly correlated with C inputs and their stabilization as SOCnew (similar results were obtained for the POM fraction). Pastures although decreased ANPP (as compared to forest) they increased belowground allocation and C:N ratios of their inputs to the soil, probably favoring the retention and stabilization of their new C inputs. In contrast, tree plantations increased ANPP but decreased BNPP (as compared to grasslands) and scarcely accumulated SOCnew probably as a result of the high C retention in standing biomass. Our results suggest that SOC changes are mainly controlled by the quantity and quality of C inputs and their retention in the soil, rather than by C outputs in these perennial subtropical ecosystems.

Temporal persistence and stability of soil water storage after rainfall on terrace land

The “Grain for Green” Project on the Loess Plateau of China has converted a large area of cultivated slope farmland to terraces to reduce soil erosion and improve the ecological environment. The area of terraced land on the Loess Plateau was 32,600 km2 in 2010. Knowledge of the behavior of soil water storage (SWS) and its spatiotemporal distribution provides essential information concerning hydrological and ecological processes. This study aimed to analyze the temporal stability of SWS after rainfall for different time periods on terraces planted with jujube trees (Ziziphus jujuba Mill.). The SWS of 21 locations was obtained from July 19 to September 3 in 2014 and from August 01 to August 31 in 2015. Relative difference analysis and the nonparametric Spearman rank correlation test were used to check the temporal stability of SWS. The SWS on terraces was normally distributed and demonstrated moderate spatial variability. The SWS at three soil depths all showed strong temporal stability with stability in the order of 0–0.6 < 0–1.0 < 0–1.6 m. Rainfall significantly affected the temporal stability of SWS in the depth of 0–0.6 m. The number of representative locations of SWS was not constant. The best representative locations were not identical for different soil depths; however, a common representative location did exist for the different depths and periods. Moreover, the mean SWS generally increased from the upper to lower slope. The temporal stability of SWS was not significantly affected by rainfall but was significantly negatively correlated with sand content. The total root length and soil organic carbon content did not show any obvious correlations with mean SWS. It was feasible to use the representative locations of SWS to represent the mean SWS over a period of time. However, the cumulative absolute error increased with cumulative days. In conclusion, SWS in the deeper soil depths indicated greater temporal stability than that in shallow soil depth during wet period. The best representative locations for SWS were depth and time dependent.

Soil physicochemical properties impact more strongly on bacteria and fungi than conversion of grassland to oil palm

The conversion of grassland to oil palm is expected to increase throughout tropical regions where oil palm grows. Given the extent of land use change, there are concerns associated with impacts on ecosystem function and nutrient cycling. For this work, soil samples were collected in Papua New Guinea from 15 sites with oil palm (planted on grassland) and adjacent remnant grassland. Using DNA-based approaches, bacterial and fungal community composition was assessed in each sample, along with abundance of genes involved in key nitrogen cycling steps: nitrification (bacterial and archaeal amoA genes), nitrite reduction (nirS gene), and nitrous oxide reduction (nosZ gene). Across all microbial properties measured, variation among sites was greater than variation due to land use change. This was driven by among-site variation in soil physicochemical properties, particularly total soil organic carbon content and δ13C, electrical conductivity, exchangeable calcium, potassium and magnesium content, and extractable phosphorus content. The results suggest that in this environment, routinely measured soil properties such as soil pH, organic carbon, and exchangeable cation contents may serve as indicators for the effects of land use and management on soil microbial community composition and functioning.

Soil organic carbon content affects the stability of biochar in paddy soil

Recalcitrant biochar application appears to be a promising method to decelerate global warming through increasing long-term carbon sequestration in soil. Stability of biochar carbon (C), which is the major determining factor of C sequestration effect, depends mainly on biochar physiochemical characteristics and soil properties. However, little is known about biochar C stability in paddy soil. In this study, 13C labeled rice straw (RS) biochar produced at 500°C was incubated with five types of paddy soils to determine the key soil characteristics involved in biochar-C stability. Results showed that cumulative mineralization rates of RS biochar-C incubated with different paddy soils were relatively low (0.17–0.28%) during 390days of incubation. The cumulative mineralization rates of RS biochar-C increased with the increasing native soil total organic carbon (TOC) content. The estimated mean residence time (MRT) of stable C components of RS biochar in paddy soil, varying from 617 to 2829 years, decreased with the increase of soil TOC content. In addition, greater atomic O/C ratio and oxygen-containing functional groups were observed in biochar samples incubated in paddy soils with higher TOC content. These results suggest that RS biochar application could be an effective method for C sequestration in paddy soil. However, the stability of RS biochar in paddy soil would be significantly impacted by soil TOC content. From the perspective of long-term C sequestration, RS biochar is more suitable for applying in paddy soils with lower TOC content.

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 were different with the changes of SOC (p<0.05), meanwhile, both LFOC and POC were related to total SOC (p<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.

Effects of vegetation restoration on the aggregate stability and distribution of aggregate-associated organic carbon in a typical karst gorge region

Abstract. Land use changes have a major impact on soil structure and soil nutrients. The influences of vegetation restoration on aggregate stability and soil carbon storage have been studied extensively, but the distribution of aggregate-associated carbon is not yet understood. The objective of this work was to study the influences of vegetation restoration on aggregate stability and distribution of soil organic carbon (SOC) associated with water-stable aggregates (WSAs) in a karst gorge region. The experiment was carried out in 2012 and included four land use types: bare land (BL), grassland (GL), shrubland (SL), and woodland (WL). Soil samples were collected from the 0–20, 20–40, and 40–60 cm depths, and aggregates were separated by a wet-sieving method. Aggregate stability and aggregated-associated SOC were determined, and the relationships between water-stable aggregation with SOC were examined. The results showed that total SOC and SOC associated with WSAs of various sizes were the highest at a soil depth of 0–20 cm. In addition, the SOC contents of the WSAs increased as the soil aggregate sizes decreased. The SOC contents of the WSAs &lt; 0.25 mm were highest except in the bare land, and the SOC contents of the aggregates &lt; 0.25 mm comprised the majority of the total aggregate SOC contents. The aggregates were dominated by particles with sizes &gt; 5 mm under dry-sieving treatment, while aggregates were predominantly comprised of WSAs &lt; 0.25 mm under wet-sieving treatment. At a soil depth of 0–60 cm, the mean weight diameter (MWD), geometrical mean diameter (GMD), and fractal dimensions (D) of the dry aggregates and water-stable aggregates in the different types of land were ranked, in descending order, as WL &gt; GL &gt; SL &gt; BL. The contents of WSAs &gt; 0.25 mm, MWD, and GMD increased significantly, in that order, and the percentage of aggregate destruction (PAD) and fractal dimensions decreased significantly as the soil aggregate stability improved. SOC contents increased after vegetation restoration, and the average SOC content of WL was 2.35, 1.37, and 1.26 times greater than that in the BL, GL, and SL, respectively. We conclude that woodland and grassland facilitated WSA stability and SOC protection; thus, promoting the natural restoration of vegetation by reducing artificial disturbances could effectively restore the ecology and prevent soil erosion in karst regions.

Biochar addition drives soil aggregation and carbon sequestration in aggregate fractions from an intensive agricultural system

Biochar application is deemed to modify soil properties, but current research has been mostly conducted on the degraded land in tropical regions. Using six consecutive years of biochar field trial, we investigated effects of biochar on soil aggregates, structural stability, and soil organic carbon (SOC) and black C (BC) concentrations in aggregate fractions. The findings have important implications in managing soil structure and SOC sequestration in high fertility soils of the temperate areas. The study had four treatments: control; biochar rate at 4.5 (B4.5) and biochar rate at 9.0 t ha−1 year−1 (B9.0); and straw return (SR). Soil samples were collected from 0–10-cm layer, and aggregate size distribution was determined with the wet-sieving method. Then, the mean weight diameter (MWD) of aggregates and the aggregate ratio (AR), i.e., the ratio of the >250 μm to the 53–250 μm size were calculated to assess the structural stability. Total SOC and BC concentrations in bulk soil ( 2000, 250–2000, 53–250, and 2000, 250–2000, and 53–250 μm) and BC in extracted fractions under biochar soils were observed. These results implied that biochar addition enhanced both native SOC and BC physical protection by aggregation. Biochar application is effective in mediating soil aggregation, and thus improves both native SOC and BC stabilization in an intensive cropping system of North China.

干旱区典型盐生植物群落土壤团聚体组成及有机碳分布

PDF HTML阅读 XML下载 导出引用 引用提醒 干旱区典型盐生植物群落土壤团聚体组成及有机碳分布 DOI: 10.5846/stxb201405221057 作者: 作者单位: 石河子大学 石河子,石河子大学 石河子 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(U1203282, 31360320); 教育部科学技术研究项目(213039A) Distribution of soil aggregates and aggregate-associated organic carbon from typical halophyte community in arid region Author: Affiliation: Shihezi University,Shihezi University;China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以干旱区玛纳斯河流域扇缘带为研究区,分析了花花柴(Karelinia caspia)、雾冰藜(Bassia dasyphylla)、梭梭(Haloxylon ammodendron)和柽柳(Tamarix ramosissima)4个典型盐生植物群落土壤团聚体的组成及有机碳分布。研究表明:不同植物群落土壤团聚体均以0.25-0.053 mm粒径为主,占了46.7%-74.6%,且与其他粒径差异显著(P < 0.05), > 0.25 mm和 < 0.053 mm粒径土壤团聚体含量较少,仅占7.8%-43%。梭梭群落 > 0.25 mm团聚体平均含量较高,达32%。不同植被群落土壤总有机碳介于2.01-8.73 g/kg之间,不同粒径团聚体有机碳介于1.70-13.68 g/kg之间。不同群落之间,梭梭和柽柳群落总有机碳和团聚体有机碳含量均相对较高,且随着土层深度下降而下降。不同粒径之间,有机碳含量在0.25-0.053 mm粒径最低,在 > 0.25 mm和 < 0.053 mm粒径中最高,呈现"V"型分布且差异显著(P < 0.05)。0.25-0.053 mm团聚体中有机碳含量的贡献率最高,达43.43%,而 < 0.053 mm粒级贡献率较低,但有机碳含量较高,说明了小粒径团聚体对有机碳保护能力较强。土壤有机碳含量与0.25-0.053 mm团聚体含量呈显著负相关(P < 0.05)。而从整体来看,梭梭群落 > 0.25 mm团聚体比例较高,且土壤有机碳和团聚体有机碳含量也较高,说明了在该研究区,梭梭群落聚集土壤养分能力较强,相对其他群落更有利于土壤有机碳的积累。 Abstract:Soil aggregates are organic-inorganic complexes and the basic unit of soil structure. Their formation and stability are closely related to soil organic carbon content. The distribution of aggregate-associated organic carbon determines the capacity for soil organic carbon storage and retention. Currently, research on soil aggregate-associated organic carbon mainly focuses on agricultural and artificial ecosystems; relatively few studies have focused on natural ecosystems. In particular, little is known about distribution of aggregate-associated organic carbon in halophyte communities in Xinjiang. In light of this, a field experiment was conducted on an alluvial fan in the Manasi River Basin to quantify changes in soil aggregation and aggregated-associated soil organic carbon associated with four halophytes (Karelinia caspia, Bassia dasyphylla, Haloxylon ammodendron, and Tamarix ramosissima). Our objective was to determine 1) the particle size that is most conducive to carbon retention and 2) which of the four halophytes is associated with the accumulation of the most soil organic carbon. The results showed: 1) 46.7% to 74.6% of the total soil mass comprised particles of intermediate diameter (0.25-0.053 mm). This was significantly greater (P < 0.05) than the other two classes of particle size defined in this study ( > 0.25 mm and < 0.053 mm). The > 0.25 mm or < 0.053 mm classes only comprised 7.8% to 43% of soil mass. The > 0.25 mm class was most abundant in the Haloxylon ammodendron community, accounting for 32% of soil mass. 2) Soil total organic carbon content was 2.01-8.73 g/kg, and aggregate-associated soil organic carbon content varied from 1.70 to 13.68 g/kg among communities. Total organic carbon and aggregate-associated organic carbon were greater in the Haloxylon ammodendron and Tamarix ramosissima communities than in the other communities studied. These measures decreased in all communities with depth. 3) The aggregate-associated organic carbon content was lowest in the 0.25-0.053 mm class, and significantly higher (P < 0.05) in the >0.25 mm and < 0.053 mm classes. 4) Because the 0.25-0.053 mm class was the most abundant, aggregate-associated organic carbon in this fraction contributed more to soil total organic carbon contained 43.43%. There was more aggregate-associated organic carbon in the < 0.053 mm class, but this contributed less to total soil organic carbon, indicating that these micro-aggregates have the greatest potential to retain soil organic carbon. There was a significant negative relationship between the abundance of 0.25-0.053 mm soil aggregate particles and soil organic carbon content.Total soil organic carbon, aggregate-associated soil organic carbon and abundance of >0.25 mm aggregate particles were highest in the Haloxylon ammodendron community, which implies that this community has the greatest potential to gather soil nutrients of the four communities studies, could be useful for accumulating soil organic carbon in arid areas. 参考文献 相似文献 引证文献

Glomalin‐related Soil Protein Response to Heating Temperature: A Laboratory Approach

AbstractForest fires are a recurrent natural phenomenon in the Mediterranean basin. Fires can affect physical, chemical and biological soil properties. The effects on soil properties are closely controlled by fire severity, which is a consequence of temperatures reached and the length of residence of heat in the soil. In this study, the response of glomalin‐related soil protein (GRSP) − a glycoprotein produced by arbuscular mycorrhizal fungi − to heating temperature has been studied. Laboratory heating treatments were carried out at 180°C, 200°C, 250°C, 300°C, 400°C and 500°C in soil samples from eight different sites in SE Spain. The sites selected had mainly different soil characteristics. The results of heating on soil water repellency and soil organic carbon (SOC) were also included in the study. GRSP response to temperature was different between sites. Redundancy analyses divided sandy soils from the rest of soil types. Total content of aggregates, SOC and clay and sand content were the most significant properties explaining the response of GRSP to heating treatments. Results showed that GRSP was affected even at low temperature. SOC response to temperature was very similar between sites. Soil water repellency did not appear after heating in wettable soils and disappeared in water‐repellent ones at temperatures over 200°C. Our results indicate that GRSP could provide relevant information about fire severity. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Soil-nitrogen net mineralization increased after nearly six years of continuous nitrogen additions in a subtropical bamboo ecosystem

In order to understand the effects of increasing atmospheric nitrogen (N) deposition on the subtropical bamboo ecosystem, a nearly six-year field experiment was conducted in a Pleioblastus amarus plantation in the rainy region of SW China, near the western edge of Sichuan Basin. Four N treatment levels—control (no N added), low-N (50 kg N ha−1 a−1), medium-N (150 kg N ha−1 a−1), and high-N (300 kg N ha−1 a−1)—were applied monthly in the P. amarus plantation starting in November 2007. In June 2012, we collected intact soil cores in the bamboo plantation and conducted a 30-day laboratory incubation experiment. The results showed that the soil N net mineralization rate was 0.96 ± 0.10 mg N kg−1 day−1, under control treatment. N additions stimulated the soil N net mineralization, and the high-N treatment significantly increased the soil N net mineralization rate compared with the control. Moreover, the soil N net mineralization rate was significantly and positively correlated with the fine root biomass, the soil microbial biomass nitrogen content and the soil initial inorganic N content, respectively, whereas it was negatively correlated with the soil pH value. There were no significant relationships between the soil N net mineralization rate and the soil total nitrogen (TN) content and the soil total organic carbon content and the soil C/N ratio and the soil microbial biomass carbon content, respectively. These results suggest that N additions would improve the mineral N availability in the topsoil of the P. amarus plantation through the effects of N additions on soil chemical and physical characteristics and fine-root biomass.

Soil organic matter quality and weed diversity in coffee plantation area submitted to weed control and cover crops management

Soil organic matter (SOM) plays an important role for soil quality and productivity maintenance, acting as energy source, promoting biological diversity, enhancing terrestrial ecosystems composition. This study assessed the effects of long-term weed control and cover crops between coffee rows on SOM quality in a very clayey (80dagkg−1 of clay) Typic Haplorthox (Dystroferric Red Latosol) from State of Paraná, Southern Brazil. Seven weed control and cover crops were assessed between coffee rows: (i) hand weeding—HAWE; (ii) portable mechanical mower—PMOW; (iii) pré+post-emergence herbicides—HERB; (iv) peanut horse (Arachis hypogeae) cover crop—GMAY; (v) dwarf mucuna (Mucuna deeringiana) cover crop—GMMA; (vi) no-weed control between coffee row—SCAP; (vii) weed check—CONT. Soil samples were collected in the center of the inter-rows between coffee trees at four depths: 0–10cm, 10–20cm, 20–30cm, and 30–40cm. SOM quality assessment included total soil organic carbon (SOC) content and organic matter humification degree (HFIL) by laser-induced fluorescence spectroscopy (LIFS). C content was up to 26% higher for SCAP and CONT samples, compared to the other field conditions, denoting influence of plant material accumulation at top soil (0–10cm). Higher HFIL results (up to 47%) were observed at deeper layers, inferring incidence of less humified/labile structures at top soil, and condensed/recalcitrant character for organic matter at depth, regardless of cover crops and weed control method considered. In terms of weed density it was observed a higher negative impact on weed growth in areas under GMMA cover crop (decrease of 90.8% in weed density). The behavior may be attributed to the chemical composition of the species, ultimately leading to possible occurrence of allelopathic phenomenon.

Soil organic carbon fractions and sequestration across a 150-yr secondary forest chronosequence on the Loess Plateau, China

Restoration of natural vegetation is recommended as an effective approach to restore soil function and rebuild degraded ecosystems. Information is lacking about the long-term results of secondary forest succession on the Loess Plateau with respect to soil organic carbon (SOC) fractions and sequestration in the root-zone soil profile. We investigated the differences in SOC fractions down to 100cm depths along a 150-yr chronosequence, including cropland (control) and five successional stages (pioneer weeds, herbage, shrub, early forest, and climax forest). Total, labile, and non-labile SOC concentrations increased rapidly at early successional stages (before shrub, <50-yr) and then gradually leveled off. Total SOC stock was highest at the climax forest stage (64.3Mgha−1) and lowest in cropland (39.9Mgha−1). Nearly half (~44.8%) of total SOC stock was stored in surface soils (0–20cm) and the majority (76.4%) existed in the non-labile fraction. The ratio of labile to non-labile fraction decreased with depth but remained stable across successional stages. The mean SOC sequestration potential and rate relative to cropland were 20.5Mgha−1 and 0.73Mgha−1yr−1, respectively. Although the SOC sequestration potential decreased with depth (64.7% for 0–20cm vs. 35.3% for 20–100cm), it decreased by 3.1Mgha−1 in the surface and increased by 3.4Mgha−1 in the subsurface from herbage to climax forest stage. This study indicated that long-term secondary forest succession played a positive role in SOC sequestration on the Loess Plateau, especially in the subsurface soil layers.

Exogenous application of EE-GRSP and changes in citrus rhizosphere properties

Mycorrhization-induced secretion of glomalin-related soil protein (GRSP) is known to contribute in improving soil fertility and aggregate stability. But, there is hardly any evidence that exogenous GRSP could produce the similar type of response. The present study was, therefore, carried out to extract easily extractable GRSP (EE-GRSP) from citrus rhizosphere soils and evaluate the response at 1/4, 1/2 and full strength EE-GRSP solutions watered into the rhizosphere of 27-year-old Satsuma mandarin (Citrus unshiu) grafted on the rootstock of Poncirus trifoliata. After ~5 months, exogenous EE-GRSP treatments produced significantly positive responses on endogenous EE-GRSP, difficultly-extractable GRSP (DE-GRSP), total GRSP production and soil organic carbon (SOC) content. A significantly positive correlation of these endogenous GRSP fractions with SOC indicated an active participation of GRSP on soil C pool. Exogenous GRSP showed a key role in binding water-stable aggregate (WSA) at 2–4, 1–2, 0.5–1, and 0.25– 0.5 mm size and enhancing WSA stability through changes in mean weight diameter (MWD). A stronger correlation of EE-GRSP and total GRSP with MWD was observed than DE-GRSP fraction. On the other hand, exogenous EEGRSP showed a positive effect on soil phosphatase activity, and soil endogenous EE-GRSP was significantly and positively correlated only with neutral phosphatase. Our studies suggest that exogenous EE-GRSP could be used as an effective regulator to affect soil fertility and soil structure within citrus rhizosphere.

Fine-root distribution, production, decomposition, and effect on soil organic carbon of three revegetation shrub species in northwest China

Revegetation with xerophilous shrubs is an effective approach to combat desertification in northwestern China; however, evaluation studies on fine-root properties of shrubs and soil organic carbon are limited. To gain a better understanding of revegetation practices, we investigated the vertical distribution of fine-root biomass, necromass, production, and effect on soil organic carbon (SOC) content in three shrub species (Salix psammophila, Hedysarum mongolicum, and Artemisia ordosica). In addition, we also estimated the fine root decomposition rate with litterbag techniques. The results showed that revegetation practices resulted in a significant increase in SOC content. Over a 10year period of revegetation, the SOC content in S. psammophila, H. mongolicum, and A. ordosica plots increased by 0.87, 1.07, and 1.82 times, respectively, more than that in bare-land plot. Increase in total SOC content was mainly due to increase in light-fraction SOC, except for the A. ordosica plot. Variations in the short-term increase of SOC content after revegetations with the three shrubs on sand land might be explained by fine root decomposition rates, at least in part. A. ordosica may be a better species for SOC accumulation and sequestration in the study site. Additionally, fine-root biomass and production were not associated with more SOC content increase in shrub plots. The results suggest the mechanism of SOC accumulation and sequestration differed among shrub plots and highlight the effectiveness of different shrub species as revegetation materials in terms of SOC accumulation and sequestration.

Assessment of soil organic carbon stocks and fractions under different agroforestry systems in subtropical hill agroecosystems of north-east India

Soil total organic carbon (TOC) is not sensitive enough to measure the short and medium term changes due to land use change practices, and thus meaningful fractions of soil organic carbon (SOC) should be measured. The objective of this study was to evaluate four agroforestry systems (AFSs) in order to test the hypothesis that agroforestry systems promote an increase in the soil organic carbon stocks and fractions, thus improving soil quality. For this, four 26 years old agroforestry systems consisting of multipurpose tree species (MPTs) (Michelia oblonga Wall, Parkia roxburghii G. Don, Alnus nepalensis D. Don, and Pinus kesiya Royle ex- Gordon) maintained at ICAR Research Complex, Umiam, Meghalaya, India were tested and compared with control plot for SOC stocks, microbial biomass carbon (MBC), readily oxidizable carbon (ROC), non-labile carbon (CNL), particulate organic carbon (POC), and carbon management index (CMI). The soil samples were collected at five depths: 0–15, 15–30, 30–45, 45–60, and 60–75 cm. The TOC, POC, ROC, CNL and MBC in soils of agroforestry land use, on average, increased significantly by 26.3, 60.1, 27.1, 46.4 and 34 %, respectively in relative to control plot. However, the AFS consisting A. nepalensis recorded the highest mean SOC stocks (60.2 Mg ha−1), TOC (3.60 g 100 g−1), POC (5.42 g kg−1), ROC (10.16 g kg−1) and MBC (548 mg kg−1) than other AFSs. Furthermore, the CMI was highest under A. nepalensis (129.6) followed by M. oblonga (119.4), whereas P. kesiya showed the lowest value (91.1). The SOC stocks and fractions were, on average, 35.3 and 70 %, respectively higher in upper soil layer (0–15 cm) compared to subsurface soil layers (15–75 cm) in all the AFSs. The strong and positive correlation (P < 0.05) between labile soil carbon fractions with TOC (r = 0.680** for POC; r = 0.683** for ROC and r = 0.758** for MBC) indicates that the changes in TOC content of soils is mainly influenced by the labile C pools and are the sensitive indicators of soil quality improvements. The AFSs, A. nepalensis in particular, can, therefore, be recommended as an alternative soil management strategy for food production, and for the maintenance of soil quality and agricultural sustainability through increased SOC sequestration in the highly fragile agro-ecosystems of northeast India.

Impacts of farmland conversion to apple (Malus domestica) orchard on soil organic carbon stocks and enzyme activities in a semiarid loess region

AbstractLand‐use change often affects the sizes of soil organic carbon (SOC) stocks and the activities of soil enzymes. Responses of relevant soil quality indices caused by farmland conversion to orchard are largely unknown in the semiarid loess regions. This study was conducted at orchard sites, which have been under very intensive cultivation, to evaluate the impacts of farmland conversion to apple (Malus domestica) orchard on SOC stocks and soil enzyme activities in the semiarid loess region of Weibei, Shaanxi province, China. The spatial and temporal changes in a variety of soil quality indices were measured for the 0–100 cm soil profile in apple orchards of three age groups (&lt; 10 y, juvenile; 10–15 y, mature; &gt; 15 y, over‐mature) and adjacent farmlands (control). After farmland conversion, total SOC (TOC) content and density and soil alkaline phosphatase activity significantly decreased, while soil catalase activity increased for the 0–100 cm soil profile. The labile SOC (LOC) content, its proportion to TOC content, and carbon management index (CMI, changes in the total content and lability of SOC) significantly increased in the 0–40 cm soil layer, whereas soil urease and invertase activities only increased in the 0–20 cm layer (P &lt; 0.05). With increasing age of apple orchards, SOC stocks significantly increased after 10 y, being more than 10% larger in mature and over mature orchards than in adjacent farmlands. The LOC content and CMI value also had an increasing trend, while soil enzyme activities showed different response patterns. There were significant correlations between soil enzyme activities, SOC fractions, and CMI value (P &lt; 0.05). We concluded that farmland conversion to apple orchard affected soil quality by reducing SOC stocks in the soil profile and changing SOC content as well as soil enzyme activities at various depth intervals. Long‐term apple cultivation was effective to restore SOC stocks, although it took over a decade to rebuild a new increasing trend after farmland conversion.