Soil Organic Carbon In Surface Soil Research Articles

Linking soil redistribution to soil organic carbon using 210Pbex along different complex toposequences in a karst region, southwest China

Understanding the magnitudes and patterns of soil and associated soil organic carbon (SOC) redistribution is of great importance for assessing both soil degradation and rocky desertification in fragile karst ecosystems. However, to date reliable information on the application of excess lead-210 (210Pbex) for quantifying dynamics of SOC-soil redistribution relationship is limited on the hillslopes due to the highly heterogeneous landscape after land use change in karst systems. In this study, three typical toposequences (grassland, forests, and agroforestry) were selected in a typical karst graben basin of southwestern China. A total of 229 soil samples were collected along the toposequences to explore the soil redistribution process using a model coupled with measured 210Pbex, and then to ascertain the relationship of discharged 210Pbex to erosion-induced SOC. The results showed that most soil samples were significantly affected by soil erosion (reference value of 210Pbex: 5986 ± 756 Bq m−2). The output of the model demonstrated that the highest estimated net soil flux occurred in agroforestry (21.38 Mg ha−1 yr−1), followed by forests (8.39 Mg ha−1 yr−1) and grassland (−3.54 Mg ha−1 yr−1). Meanwhile, the SOC concentration showed a decreasing order of agroforestry > forest > grassland on the hillslopes, implying that while agroforestry help increase SOC sequestration potential, intensive human intervention also carries a high risk of soil erosion in karst regions. The fitting correlation of 210Pbex and SOC in surface soils displayed the decreasing order of grassland (R2 = 0.80) > forests (R2 = 0.69) > agroforestry (R2 = 0.42), indicating that fallout 210Pbex could be used directly as a tracer to quantify the dynamics of the SOC-soil redistribution relationship in grassland toposequence. Our results provide practical evidence of the potential of 210Pbex for quantifying SOC-soil redistribution along hillslopes with complex toposequences in a karst region.

Long-term effects of NPK fertilizers and organic manures on carbon stabilization and management index under rice-wheat cropping system

The potential of storing carbon (C) in soil and offsetting the atmospheric CO2 depends on the management practices. This study investigated the long-term (15 years) effects of using nitrogen: phosphorous: potassium (NPK) fertilizers with and without organic manures namely farmyard manure (FYM), green manure (GM), and straw incorporation (SI) on soil C stabilization, and C management index (CMI) in intensive rice-wheat system in Typic Ustochrepts soil of a semiarid region in Punjab, India. The long-term effects of different fertilizer treatments as control, NPK, NPK+GM, NPK+SI, and NPK+FYM on soil organic carbon (SOC), labile fractions of SOC (LFSOC), C stabilization, C sequestration, and C management index (CMI) were determined. Prolonged application of NPK fertilizers alone or in combination with organic manures significantly decreased soil bulk density (from 7.3 to 16.6%) and increased total soil porosity of (from 11.7 to 26.2%) as compared to the control in surface soil (0–15cm). Fertilizations had positive and variable effects on different LFSOC, namely water soluble C (WSC), labile carbon (LC), particulate organic C (POC), hot water soluble carbon (HWSC), and total organic carbon (TOC). Long-term intensive cultivation and fertilization significantly increased the SOC in surface soil (0–15cm) up to 5.16gkg−1 as compared with its antecedent value of 2.42gkg−1 in 1999. The sensitivity index indicated that among LFSOC, LC (51–85%), WSC (67–131%), POC (64–159%), and HWSC (38–131%) were more sensitive compared with SOC (29–59%). NPK+SI (5.06MgCha−1) or NPK+FYM (5.31MgCha−1) along with NPK sequestered significantly higher C than the application of NPK (3.57MgCha−1) or NPK+GM (4.10MgCha−1). The fraction of C in stable fractions (Cfrac3+Cfract4) increased from 7 to 29% with application of NPK fertilizers and organic manures compared with that of the control. The CMI indicated that the use of NPK+SI or NPK+FYM was statistically superior to the use of NPK+GM for improving the SOC status. The study concluded that a relatively high sensitivity index of LFSOC may be used as an early indicator for determining the potential of different management practices for improving SOC on short-term basis. The results indicated that the stability of SOC varies with the nature of the added organic manures, suggesting that the selection of organic manure is important for long-term C sequestration.

Biomass accumulation and carbon sequestration in an age-sequence of Zanthoxylum bungeanum plantations under the Grain for Green Program in karst regions, Guizhou province

Ensuring ecological security in the environmental degradation has always been a top priority in China. Under the Grain for Green Program (GGP), millions of hectares of farmland in the karst region of Guizhou province have been converted into Zanthoxylum bungeanum plantations in order to arrest and reverse “rocky desertification”. The aim of this study was to estimate biomass increment and carbon accumulation in four different aged (1-, 4-, 7- and 10-year-old) Z. bungeanum stands, as well as the distribution of carbon stock among the various biomass components and soil depths. The total plant biomass measured for the four stands of different ages was 0.05, 6.76, 12.22, and 16.71Mgha−1, respectively. Compared with other plant species in the region, Z. bungeanum plantations has a larger capacity for accumulating biomass. The C content in components of Z. bungeanum tree ranged from 40.47% to 48.64% with the mean value of 44.67%. The use of the standard coefficient (50%) in converting biomass into C storage results in 10% overestimation. Soil organic carbon (SOC) storage at the top soil (0–30cm) increased from 75.22MgCha−1 in 1-year-old stand to 80.06MgCha−1 in 10-year-old stand, and decreased with increasing soil depth for each stand age. Total ecosystem C storage increased with plantation age, averaging 75.24, 79.79, 84.43, and 87.62MgCha−1, respectively, of which more than 90% was stored in the soil. Our study suggests that the protection of SOC in surface soils during plantation management practices plays a crucial role in improving the C sequestration. Data of plantation area and annual biomass C accumulation rate (under the GGP in Guizhou province) indicate a net C sink of 6.35×106Mg in 2010, corresponding to a 4.92% compensation of C emission from energy consumption in that year. Besides increasing C storage over time, the large-scale planting of Z. bungeanum has the potential of restoring severely degraded soils in the karst region of SW China.

高寒草原土壤有机碳及土壤碳库管理指数变化研究

The alpine steppe plays a vital role in the stability of alpine ecosystem. To understand the variation of soil organic carbon( SOC) and active soil organic carbon( ASOC) in alpine steppe,and the influence of grassland degradation on soil carbon pool,We initially investigated the SOC and ASOC in the surface soil( 0—10 cm) and subsurface soil( 0— 20 cm) in normal steppe,light degraded steppe,severely degraded steppe in The Northern Tibet Plateau. The results showed that:( 1) The SOC and ASOC all declined with different degree in each layer soil in mildly degraded steppe and severely degraded steppe. The decline of SOC in surface soil were much higher than that in subsurface soil in these degraded steppe,and the decline of SOC in each layer soil decreased with the steppe degradation.. But the decline of ASOC in surface soil was much lower than subsurface soil,and which in severely degraded steppe was much higher than that in mildly degraded steppe.( 2) The distribution ratio of ASOC in surface soil in normal steppe,mildly degraded steppe and severely degraded steppe were 16. 8%,21. 3% and 16. 6%,respectively,and which in the subsurface were 21. 8%, 18. 1 and 16. 0%,respectively. Besides that,the variation tendencies of soil carbon pool activities were consistent with the distribution ratio of ASOC. So that,the SOC in the surface soil in the mildly degraded steppe is unstable.( 3) The soil carbon management index( CMI) in the surface soil and subsurface soil all significantly declined in degraded steppe,the decline of CMI in surface soil much lower than subsurface soil. The CMI in each layer soil of mildly degraded steppe were much higher compared to severely degraded steppe.( 4) The negative correlation was observed between SOC and ASOC in each layer soils in normal steppe,mildly degrade steppe and severely degraded steppe in alpine grassland. This result suggests that the effects of soil microorganism on SOC,ASOC might be different.

Solubility and Leaching Risks of Organic Carbon in Paddy Soils as Affected by Irrigation Managements

Influence of nonflooding controlled irrigation (NFI) on solubility and leaching risk of soil organic carbon (SOC) were investigated. Compared with flooding irrigation (FI) paddies, soil water extractable organic carbon (WEOC) and dissolved organic carbon (DOC) in NFI paddies increased in surface soil but decreased in deep soil. The DOC leaching loss in NFI field was 63.3 kg C ha−1, reduced by 46.4% than in the FI fields. It indicated that multi-wet-dry cycles in NFI paddies enhanced the decomposition of SOC in surface soils, and less carbon moved downward to deep soils due to less percolation. That also led to lower SOC in surface soils in NFI paddies than in FI paddies, which implied that more carbon was released into the atmosphere from the surface soil in NFI paddies. Change of solubility of SOC in NFI paddies might lead to potential change in soil fertility and sustainability, greenhouse gas emission, and bioavailability of trace metals or organic pollutants.

Land use and management influences on surface soil organic carbon in Tasmania

The effects of environmental parameters, land-use history, and management practices on soil organic carbon (SOC) concentrations, nitrogen, and bulk density were determined in agricultural soils of four soil types in Tasmania. The sites sampled were Dermosols, Vertosols, Ferrosols, and a group of texture-contrast soils (Chromosol and Sodosol) each with a 10-year management history ranging from permanent perennial pasture to continuous cropping. Rainfall, Soil Order, and land use were all strong explanatory variables for differences in SOC, soil carbon stock, total nitrogen, and bulk density. Cropping sites had 29–35% less SOC in surface soils (0–0.1 m) than pasture sites as well as greater bulk densities. Clay-rich soils contained the greatest carbon stocks to 0.3 m depth under pasture, with Ferrosols containing a mean of 158 Mg C ha–1, Vertosols 112 Mg C ha–1, and Dermosols 107 Mg C ha–1. Texture-contrast soils with sandier textured topsoils under pasture had a mean of 69 Mg C ha–1. The range of values in soil carbon stocks indicates considerable uncertainty in baseline values for use in soil carbon accounting. Farmers can influence SOC more by their choice of land use than their day-to-day soil management. Although the influence of management is not as great as other inherent site variables, farmers can still select practices for their ability to retain more SOC.

논 토양의 유기탄소 변동에 관한 비료와 개량제의 장기연용 효과

The changes of soil organic carbon (SOC) content in paddy soils (sandy loam) were assessed from data of the 59 years fertilization plots in which the continuous rice cropping experiment started in 1954. The treatments were no fertilization(no fert.), NPK fertilization (N, NPK), NPK plus rice straw compost (NPK+C), and NPK plus rice straw compost, silicate fertilizer and lime (NPK+CLS). After 41 years, SOC content in NPK+C and NPK+CLS treatment in surface soils (0~15 cm) reached at the highest, followed by maintaining a plateau level for 8 years. After 51 years, they showed a tendency to decrease. Peak concentrations of soil organic carbon were in NPK+CLS, in NPK+C, in NPK, in N, and in control. Dissolved organic carbon(DOC) contents in surface soil solution were about 2.3 times higher in NPK+C than that in NPK+CLS. Therefore, SOC in subsurface soil(15~30 cm) was greater in NPK+C than the other treatments. These results indicate that continuous application of rice straw compost and silicate fertilizer affected significantly on the level of SOC in surface soils, subsurface soils, and soil solutions. Thus, the combined applications of NPK fertilizers with organic compost and silicate as a soil amendment are recommended as the best fertilization practice for soil carbon accumulation, environment conservation, and enhancement of soil fertility status in the continuous rice cropping system.

Impact of ridge tillage on soil organic carbon and selected physical properties of a clay loam in southwestern Ontario

Ridge tillage (RT) creates a distinctly different soil environment relative to no-tillage (NT) and mouldboard plow tillage (MP), which may in turn affect soil properties. In this study, the impacts of long-term (29 years) RT on soil organic carbon (SOC), water content, bulk density and penetration resistance were compared with NT and MP tillage on a clay loam soil under a corn (Zea mays L.)–soybean (Glycine max L. Merr.) rotation. The ridges in RT were formed at 76-cm spacing and corn was planted in the center of the ridges whereas soybean was planted in the shoulders of the ridges at 38-cm spacing. Soil samples were collected from the ridge crest (i.e. corn row), from the two ridge shoulder positions and from the interrow (furrow) positions of the ridges to evaluate both the spatial and profile distributions of the selected soil properties under RT relative to NT and MP. Ridge tillage produced low SOC in the interrows, high SOC in the crests and medium SOC in the shoulders relative to MP and NT. Soil water content was higher in the interrows than in the crests of the ridges, while soil penetration resistance followed the reverse trend. No-tillage resulted in a distinct SOC stratification with significantly higher SOC in surface soil and slightly lower SOC in subsurface soil while a uniform distribution of SOC was observed in the plow layer of MP soil. Hence, RT produced different SOC, water content, bulk density and penetration resistance distributions than NT and MP. Twenty-nine years of RT management resulted in improved soil physical conditions in the plow layer for crop root growth relative to NT and greater SOC stocks within the plow layer compared to MP.

Effect of tillage, rotation and crop residues on wheat crop productivity, fertilizer nitrogen and water use efficiency and soil organic carbon status in dry area (rainfed) of north-west Pakistan

Crop productivity, soil organic carbon (SOC), fertilizer nitrogen and water use ef- ficiency (WUE) in rainfed dry area is influenced by tillage, rotation and crop resi- dues management. Field experiments were conducted during 2004-09 to study the effect of tillage, rotation and crop residues on wheat yield, nitrogen fertilizer and water use efficiency and SOC under semi-arid condition in north-west Pakistan. The treatments consisted of three rotations: i) Wheat-fallow-wheat (farmers' practice) ii) Wheat- summer legume-wheat and iii) Wheat-summer cereal-wheat with two tillage and crop residues management treatments: i) Tillage (crop residues removed) and Tillage (crop residues retained) and ii) No-tillage (crop residues removed) and No-tillage (crop residues retained). Basal doses of N 60 : P 60 (kg ha -1 ) to wheat, N 90 : to wheat as an aqueous solution in micro plot within each treatment plot. Changes in soil water storage were monitored with neutron moisture probe for calculation of WUE. The results revealed that the wheat grain and straw yield was not increased by the tillage treatment. Crop residues retention significantly enhanced the wheat grain and straw yield. Crop residues with no-tillage resulted in 520 kg ha -1 greater wheat grain yield than residues removed treatment. Similarly WUE, N yield and fertilizer N utilization by wheat was increased significantly by crop residues under no-tillage compared to the tillage treatment. Maximum N fertilizer utilization 24.1 %, 62.7 % and 38.0 % in wheat were obtained under no-tillage + residues treatment during 2006, 2007 and 2008 respectively. The SOC in surface soil (0-15 cm) was higher in wheat-fallow-wheat and wheat-legume-wheat rotation under no-tillage + residues treatment. The results showed that no-tillage + crop residues and legume based rota- tion treatment were beneficial under the rainfed (dry) conditions.

Landuse impacts on SOC fractions and aggregate stability in typic ustochrepts of Northwest India

The soil organic carbon (SOC) and its fractions are good indicators of soil quality and environmental stability. Among the factors affecting SOC pool and fluxes in a watershed, land use changes and soil erosion are factors of importance. The differences in SOC and its fractions among different land uses can help understand the process of soil carbon dynamics. A study was conducted in Typic Ustochrepts of Northwest India to understand the impact of forest, grassland, agricultural and eroded lands on aggregate stability and SOC fractions. The undisturbed soil aggregates were sampled from different land uses in a watershed in Shiwaliks of lower Himalayas. The aggregate stability was determined by shaking the pre-saturated aggregates under water and by single simulated raindrop technique. The SOC, labile carbon, hot-water soluble carbon, particulate organic carbon and aggregate associated organic carbon were determined in aggregates of different sizes as well as in the bulk soils. The water stability of aggregates expressed as mean weight diameter (MWD) and stability index (SISRT) was highest in surface soils (0–15 cm) of grasslands followed by forest, agricultural and eroded lands. The WSA > 2 mm (water stable aggregates > 2 mm) were highest (17.3%) in grasslands and lowest (0.85%) in eroded lands. The eroded soils had 2.2, 7.4 and 3.4 times higher amount of micro-aggregates (WSA < 0.25 mm) than agricultural, forest and grassland soils, respectively. The SOC in surface soils significantly decreased by 27% in forest and 45% in agricultural land from that in grassland soils. In subsoil (15–30 cm), the SOC in eroded, agricultural and grasslands was statistically similar. The SOC stock in the subsoil (15–100 cm) was of significance. The grassland soils could store 41 Mg ha-1 SOC stock compared to 31 Mg ha-1 in the subsurface layer. This difference widened in forestland, where subsoil contained 73.4% of total SOC stock in 100 cm soil profile. Among all the SOC fractions studied, labile carbon was mostly affected by erosion and was 91.6% lower in eroded than in grassland soils. The magnitude of aggregate associated organic carbon decreased with aggregate size in all the land uses. Among the SOC fractions, the aggregate stability under simulated raindrop impact could better be explained (R2 = 0.78) by hot water soluble carbon whereas the water stability of aggregate could better be explained (R2 = 0.69) by particulate organic carbon.

Spatial Variability of Soil Organic Carbon Under Maize Monoculture in the Song-Nen Plain, Northeast China

Soil organic carbon (SOC) and its relationship with landscape attributes are important for evaluating current regional, continental, and global carbon stores. Data of SOC in surface soils (0–20 cm) of four main soils, Cambisol, Arenosol, Phaeozem, and Chernozem, were collected at 451 locations in Nongan County under maize monoculture in the Song-Nen Plain, Northeast China. The spatial characteristics of soil organic carbon were studied, using geographic information systems (GIS) and geostatistics. Effects of other soil physical and chemical properties, elevation, slope, and soil type on SOC were explored. SOC concentrations followed a normal distribution, with an arithmetic mean of 14.91 g kg −1. The experimental variogram of SOC was fitted with a spherical model. There were significant correlations between soil organic carbon and bulk density ( r = −0.374**), pH ( r = 0.549**), total nitrogen ( r = 0.781**), extractable phosphorus ( r = −0.109*), exchangeable potassium ( r = 0.565**), and cation exchange capacity ( r = 0.313**). Generally, lower SOC concentrations were significantly associated with high elevation ( r = −0.429**). Soil organic carbon was significantly negatively correlated with slope gradient ( r = −0.195**). Samples of the Cambisol statistically had the highest SOC concentrations, and samples of the Arenosol had the lowest SOC value.

Spatial Variability of Soil Organic Carbon in Relation to Environmental Factors of a Typical Small Watershed in the Black Soil Region, Northeast China

A total of 292 soil samples were taken from surface soil (0-20 cm) of a typical small watershed-Tongshuang in the black soil region of Heilongjiang province, northeast China in June 2005 for examining the concentration of soil organic carbon (SOC). Spatial variability of SOC in relation to topography and land use was evaluated using classical statistics, geostatistics and geographic information system (GIS) analyses. The objective of this study was to provide a scientific basis for land management targeting at improving soil quality in this region. Classical statistical analysis results indicated that the variability of SOC was moderate (C (V) = 0.30). Slope position and land use types were discriminating factors for its spatial variability. Geostatistics analyses showed that SOC had a strong spatial autocorrelation, which was mainly induced by structural factors. Mean concentration of SOC in surface soil was 2.27% in this watershed, which was a very low level in the northern black soil region of northeast China. In this small watershed, present soil and water conservation measures played an important role in controlling soil loss. But SOC's restoration was unsatisfactory. Nearly three-quarters of the area had worrisome productivity. How to improve SOC concentration targeting at soil fertility is a pressing need in the future.