Significant Differences In Soil Organic Carbon Research Articles

Soil Quality Indicators under Different Smallholder Managed Cropping and Landuse Practices in Abuja, Nigeria

There are limited reports about the impacts of smallholder-managed cropping and land-use practices (CLUPs) on soil quality, especially in developing countries. This study investigates the impact of six different Cropping Land Use Practices (CLUPs) on soil quality parameters in Abuja, Nigeria, focusing on sesame mono-cropping (SM), guinea corn mono-cropping (GCM), yam mono-cropping (YM), maize + yam mixed cropping (MYM), maize mono-cropping (MM), and natural forest (NF). The objectives are to determine Soil Organic Carbon (SOC), Total Nitrogen (TN), and pH values in the six CLUPs and assess differences under various CLUPs and soil depths. The study conducted in the University of Abuja Permanent Site, covers 11,000 hectares and analyzes soil samples from three replicate plots per CLUP, considering topsoil (0-15cm) and subsoil (20-30cm). The results indicate slightly acidic soils with low SOC and TN contents. Significant differences in SOC, TN, and C/N ratio are observed among cropping systems, with mixed cropping (MYM) promoting higher SOC. The C/N ratio is consistently low across CLUPs, indicating accelerated decomposition. While intra-plot soil heterogeneity is low, significant declines in soil quality indicators are noted under cropping systems compared to the natural forest. The study recommends site-specific, sustainable land management practices tailored to each cropping system. Encouraging organic matter additions, such as using animal and farmyard manure, is proposed to enhance soil fertility and reverse degradation trends. The findings contribute to understanding how diverse cropping practices impact soil quality, providing valuable insights for sustainable land management in the Abuja region.

Response of soil organic carbon to forested wetlands in East China

Afforestation has been suggested as an ecosystem restoration approach for mitigating carbon loss after land-use changes. Understanding soil organic carbon (SOC) by conversion from abandoned aquaculture ponds to afforestation is crucial. We investigated soil organic carbon from a poplar (Populus spp., 19 years after planting, PS) plantation site with ditches and a pond cypress (Taxodium spp., 4 years after planting, TS) forest with non-ditches on abandoned aquaculture ponds in East China. Soils with three layers (0–10, 10–20, and 20–30 cm) were sampled. The results showed that there were no significant differences in SOC between soil layers for PS with 5.09 ± 2.27, 2.60 ± 0.59, and 6.94 ± 3.56 g kg−1, respectively; compared to TS with 4.16 ± 1.48, 3.31 ± 0.88, and 4.32 ± 1.41 g kg−1, respectively. However, significant differences of soil water contents (SWC) and bulk density (BD) were found between two sampling sites, and both BD and pH had significant negative relationships with SOC. It is suggested that low SWC resulting from the ditch could lead to a potential risk of SOC decomposition and offset the soil carbon sink by afforestation. Additionally, pond cypress might be a preferred species selection for ecosystem restoration in both soil carbon sink and landscape aesthetics.

Limited role of shifting cultivation in soil carbon and nutrients recovery in regenerating tropical secondary forests

Shifting cultivation is a dominant land-use in the tropical forest-agriculture frontier in Southeast Asia and is blamed for much of the environmental degradation in the region. We examined the distribution and availability of four soil macronutrients—i.e., soil organic carbon (SOC), total nitrogen (N), phosphorus (P) and potassium (K), in secondary forests regenerating after shifting cultivation abandonment. Soil samples were collected along an upland fallow gradient on Leyte Island in the Philippines. The effect of site environmental attributes on the availability of SOC and nutrients was investigated using linear mixed-effect models. We found relatively higher concentrations of SOC and P in the oldest fallows and higher N concentration in the youngest fallow secondary forest. There was no significant difference in SOC and other macronutrients within sites of different fallow categories and soil depths, except in the case of soil K, which was highest in our control old-growth forest. Patch size together with slope of the site and fallow age were the most influential factors in explaining the variability in SOC and nutrients availability in secondary forests recovering after shifting cultivation abandonment. Our study suggests that shifting cultivation may not be detrimental to soil quality, at least on the soil parameters and soil type we studied in the Philippines upland.

Soil Organic Carbon and Its Controlling Factors in the Lakeside of West Mauri Lake along the Wetland Vegetation Types

There is a huge carbon pool in the lakeside, which is sensitive to environmental changes and can very easily be transformed into a carbon source as land from the lake is reclaimed. In this paper, West Mauri Lake was employed as a case study to examine soil organic carbon (SOC) and its controlling factors along the lakeside. Four transects of land use (i.e., vegetation) types along the landward lakeside were identified as the fluctuation zone, the beach zone, the mesozoic farmland rewetting zone and the xerophytic farmland rewetting zone. With the increase in soil depth, SOC in the lakeside decreased significantly (p < 0.05). SOC had an obvious seasonal variation (p < 0.001), ranking in order: winter (December) > spring (February) > summer (May). Among the aforementioned transects, SOC density differed significantly (p < 0.05), showing a significant increasing trend. Pearson correlation indicated that most soil physiochemical factors showed a significant correlation with SOC (p < 0.01), except total chromium, total copper, total zinc and total phosphorus. The relationship between SOC density and total nitrogen (N) has an obvious “S” curve, and total N accounts for 81% of the variation of SOC, suggesting that total N is the main controlling factor of SOC in the lakeside. The significant difference in SOC along the different vegetation (land use) types implied that land use affects the SOC in the lakeside. The long-term accumulation of N fertilizer after the man-made reclamation and aquaculture obviously controls SOC in the lakeside of West Mauri Lake.

The effects of plastic film mulching and straw mulching on licorice root yield and soil organic carbon content in a dryland farming

The increasing worldwide demand for traditional herbs has been met by growing cultivated herbs. It is undoubtedly very important to seek a reasonable cultivation mode for the yield, quality and long-term production stability of traditional herbs. In this study, licorice (Glycyrrhiza uralensis Fisch.) was investigated using a field experiment and a process-based model (Denitrification-Decomposition (DNDC) model) to study the effects of mulching methods on root yield and soil organic carbon (SOC) long-term changes. The field experiment contained four treatments: plat planting without mulching (CK), ridge-furrow maize straw mulching (SM), ridge-furrow plastic film mulching (RP), and plat planting with plastic film mulching (FP). Licorice root yield was significantly higher in the SM, RP, and FP than in the CK. SM, RP and FP treatments increased the accumulation of liquiritin and glycyrrhizin in licorice roots. The SM significantly increased SOC content, SOC stocks, SOC sequestration rate, dissolved organic carbon (DOC) content and microbial biomass carbon (MBC) compared to CK, but there was no significant difference in SOC and DOC among CK, RP and FP. The DNDC model was calibrated based on the field test data and showed that under the four CMIP6 SSPs scenarios, the predicted root yield of each treatment was increasing obviously. The production and stability of RP and FP were greater than CK and SM. The SOC under SM showed an increasing trend, whereas it continuously decreased under CK, RP, and FP in the future. The SOC of simulated RS treatment of straw incorporation plus a plastic film mulch was always at the highest value in all the treatments, and its root yield was slightly lower than that of RP and FP, the latter both were very close. Therefore, it is suggested that RS should be adopted to achieve sustained high yield while maintaining a high SOC level.

Stover management modifies soil organic carbon dynamics in the short-term under semiarid continuous maize

In croplands, the adoption of certain management practices may increase soil organic carbon (SOC) levels. In this study, we evaluated the short-term impact of crop stover management and the interaction between crop stover and irrigation method on SOC change in a continuous maize (Zea mays L.) system in Spain. Four years after the beginning of the experiment, total SOC and C fractions (particulate organic matter carbon, POM-C; and mineral-associated organic matter carbon, Min-C) contents, SOC stocks and SOC stock changes were measured in four different soil layers (0−5, 5−10, 10−25 and 25−50 cm) in an experiment with two irrigation methods (sprinkler and flood) and three stover management systems (conventional tillage with all the stover incorporated, CT; no-tillage maintaining the stover, NTr; and no-tillage removing the stover, NT). Stover management resulted in significant differences in SOC and POM-C but not in Min-C. In particular, NT reduced SOC and POM-C contents compared with CT and NTr (about 10 and 60 %, respectively). After 4 years, SOC change was not affected by the interaction between stover management and irrigation. Concurrently, both CT and NT showed SOC losses, reaching 0.11 and 1.22 Mg ha−1 yr−1 in CT and NT, respectively. However, NTr showed SOC gains at a rate of 0.09 Mg ha−1 yr−1. Consequently, the removal of crop stover has been demonstrated as a detrimental strategy to store SOC in the short-term in irrigated continuous maize systems.

Deciphering the Effects of Waste Amendments on Particulate Organic Carbon and Soil C-Mineralization Dynamics

It is important to understand the dynamics of soil carbon to study the effects of waste amendment inputs on soil organic carbon decomposition. The aim of this study was to evaluate the effect of waste amendment carbon input on the soil organic carbon (SOC) content, soil particulate organic carbon (POC) content and soil organic carbon mineralization rate dynamics. A 60-day experiment was carried out in the laboratory. The following treatments were compared: (1) CK: soil without amendments; (2) FW1: soil with food waste compost (soil/food waste compost = 100:1); (3) FW2: soil with food waste compost (soil/food waste compost = 100:2); (4) GW1: soil with garden waste compost (soil/garden waste compost = 100:0.84); (5) GW2: soil with garden waste compost (soil/garden waste compost = 100:1.67); (6) FGW1: soil amendments mixture (soil/food waste compost/garden waste compost = 100:0.5:0.42); (7) FGW2: soil amendments mixture (soil/food waste compost/garden waste compost = 100:1:0.84); the inputs of amendment carbon to FW1, GW1 and FGW1 were 2.92 g kg−1, the inputs of amendment carbon to FW2, GW2 and FGW2 were 5.84 g kg−1. The results showed that the addition of waste amendments increased the amount of cumulative mineralization from 95% to 262% and accelerated the rate of soil mineralization. After adding organic materials, the change in the soil organic carbon mineralization rate could be divided into two stages: the fast stage and the slow stage. The dividing point of the two stages was approximately 10 days. When equal amounts of waste amendment carbon were input to the soil, there was no significant difference in SOC between food waste and garden waste. However, SOC increased with the amount of amendment addition. However, for POC, there was no significant difference between the different amounts of carbon input to the garden waste compost treatments. SOC and POC were significantly correlated with the cumulative emissions of CO2.

Soil quality assessment based on soil organic matter pools under long‐term tillage systems and following tillage conversion in a semi‐humid region

AbstractA field study was conducted to assess the long‐term effects of no‐tillage (NT) and conventional tillage (CT), and the short‐term effects following tillage conversion from CT to NT (NTn) and from NT to CT (CTn) on soil quality (SQ) indicators in a semi‐humid climate. First, plots of a long‐term tillage experiment on a Luvic Phaeozem initiated in 1986 were split into two subplots in 2012, yielding four treatments: NT, CT, NTn and CTn. In 2015, composite soil samples were collected from each treatment and from a natural site (Ref) at depths 0–5, 5–10, 10–20 and 0–20 cm. Several indicators were determined: soil organic carbon (SOC) and nitrogen (SON); particulate organic C (POM‐C) and N (POM‐N); potential N mineralization (PMN) and soil respiration (Rs). Moreover, bulk density was determined in long‐term tillage systems. Different ratios between indicators were calculated, with emphasis on its function in the agroecosystem, that is functional indicators. Significant differences in SOC, SON and PMN were found between CT and NT at most depths. In contrast, 3 years after tillage conversion, only a part of the SQ indicators studied were modified mainly at the 0–10 cm depth. The functional indicators showed differences between tillage systems in the long‐term and after short‐term tillage conversion depending on the depth; however, the PMN/SON ratio demonstrated differences at all depths. Under these conditions, this ratio‐related to easily mineralizable N fraction proved to be a promising indicator for assessing SQ under contrasting tillage systems regardless of the sampling depth.

Large catchment-scale spatiotemporal distribution of soil organic carbon

There are a dearth of studies globally examining soil organic carbon (SOC) at large catchment scales. Here we assess the catchment scale climate and geomorphic controls on SOC. The study was conducted on the east coast of New South Wales, Australia and focussed on a 562 km2 (Krui River) catchment sampled in 2006 and 2015 and a 606 km2 (Merriwa River) catchment sampled in 2015. Both catchments have similar soils, topography and landuse. There was no significant difference in SOC between 2006 and 2014 data sets, indicating that SOC was temporally stable over the intervening 8 years (Krui catchment), despite the seasonal variability in climate such as rainfall. SOC concentration was also shown to have no significant difference between Krui catchment and Merriwa catchment, indicating that SOC is spatially stable for catchments of similar land-use, climate and geomorphology. SOC concentrations from all three data sets were compared to a range of terrain attributes. Similar with other studies, elevation, as a surrogate for orographic rainfall, was found to have the strongest significant control on SOC % at the large catchment scale. Confirmation of the use of elevation as a surrogate for rainfall was made by comparing SOC with rainfall obtained from a network of weather stations across the study sites. Relationships between SOC and other terrain attributes found inconsistent relationships. The findings demonstrate that for catchments with similar soils, topography and climate that SOC can be reliably predicted using simple topographic variables. The methods here provide a robust tool which can be used for SOC assessment at other sites as well as assist in understanding SOC distribution and controls for longer term and regional scales.

Does maize and legume crop residue mulch matter in soil organic carbon sequestration?

Soil management techniques, such as mulching, are used to enhance soil organic carbon sequestration. However, we demonstrate that the potential of crop residue mulching to increase soil organic carbon (SOC) sequestration varies by cropping system and soil type in Austrian agricultural soils. Effects of mulch (as harvested crop residues applied at 1.0 t C ha−1) on soil and microbial carbon (C) and nitrogen (N) and soil δ13C were measured in an Austrian Cambisol field experiment with sole maize or vetch or vetch-maize rotation cropping systems after five years with or without mulching to elucidate how SOC is affected. The direct role of mulch on SOC in different soil types was also investigated in a similar greenhouse mesocosm study with controlled moisture using the same Cambisols and an Austrian agricultural Chernozem. Only sole maize cropping in the field experiment resulted in higher SOC with mulching and when legumes were included in a legume-maize rotation SOC did not improve. Mulching in the field experiment only resulted in higher SOC in the top 0–5 cm of soils with sole maize cropping (by 22%) compared to soils without mulch. Although mulch did not increase SOC in vetch-maize rotation, the δ13C of SOC was less negative with mulch indicating larger C contribution from maize than vetch mulch. After four years of annual soybean-maize rotation in the mesocosm experiment, no significant differences in SOC were observed in Cambisols with or without mulch. Again, δ13C of both soil types was less negative with mulching indicating a larger C contribution from maize than soybean mulch. No relationships between microbial biomass C and N and SOC were observed in either experiment and only soil N concentration was positively correlated with SOC. Together these studies indicate that maize can increase SOC when crop residues are applied in Austrian Cambisols but that inclusion of legume production and legume mulch in rotation can mute these benefits.

Spatial pattern of soil organic carbon and total nitrogen, and analysis of related factors in an agro-pastoral zone in Northern China.

The spatial pattern of soil organic carbon (SOC) and total nitrogen (TN) densities plays a profound important role in estimating carbon and nitrogen budgets. Naiman Banner located in northern China was chosen as research site, a total of 332 soil samples were taken in a depth of 100 cm from the low hilly land in the southern part, sandy land in the middle part and an alluvial plain in the northern part of the county. The results showed that SOC and TN density initially decreased and then increased from the north to the south, The highest densities, were generally in the south, with the lowest generally in the middle part. The SOC and TN densities in cropland were significantly greater than those in woodland and grassland in the alluvial plains and for Naiman as a whole. The woodland SOC and TN density were higher than those of grassland in the low hilly land, and higher densities of SOC and TN in grassland than woodland in the sandy land and low hilly land. There were significant differences in SOC and TN densities among the five soil types of Cambisols, Arenosols, Gleysols, Argosols, and Kastanozems. In addition, SOC and TN contents generally decreased with increasing soil depth, but increased below a depth of 40 cm in the Cambisols and became roughly constant at this depth in the Kastanozems. There is considerable potential to sequester carbon and nitrogen in the soil via the conversion of degraded sandy land into woodland and grassland in alluvial plain, and more grassland should be established in sandy land and low hilly land.

Perennial Grass Bioenergy Cropping on Wet Marginal Land: Impacts on Soil Properties, Soil Organic Carbon, and Biomass During Initial Establishment

The control of soil moisture, vegetation type, and prior land use on soil health parameters of perennial grass cropping systems on marginal lands is not well known. A fallow wetness-prone marginal site in New York (USA) was converted to perennial grass bioenergy feedstock production. Quadruplicate treatments were fallow control, reed canarygrass (Phalaris arundinaceae L. Bellevue) with nitrogen (N) fertilizer (75 kg N ha−1), switchgrass (Panicum virgatum L. Shawnee), and switchgrass with N fertilizer (75 kg N ha−1). Based on periodic soil water measurements, permanent sampling locations were assigned to various wetness groups. Surface (0–15 cm) soil organic carbon (SOC), active carbon, wet aggregate stability, pH, total nitrogen (TN), root biomass, and harvested aboveground biomass were measured annually (2011–2014). Multi-year decreases in SOC, wet aggregate stability, and pH followed plowing in 2011. For all years, wettest soils had the greatest SOC and active carbon, while driest soils had the greatest wet aggregate stability and lowest pH. In 2014, wettest soils had significantly (p < 0.0001) greater SOC and TN than drier soils, and fallow soils had 14 to 20% greater SOC than soils of reed canarygrass + N, switchgrass, and switchgrass + N. Crop type and N fertilization did not result in significant differences in SOC, active carbon, or wet aggregate stability. Cumulative 3-year aboveground biomass yields of driest switchgrass + N soils (18.8 Mg ha−1) were 121% greater than the three wettest switchgrass (no N) treatments. Overall, soil moisture status must be accounted for when assessing soil dynamics during feedstock establishment.

On-farm comparisons of soil organic carbon under no-tillage and chisel-plow systems

ABSTRACTPurpose: Role of no-tillage (NT) in soil conservation has been already established but its influence on soil organic carbon (SOC) is still under debate.Materials and methods: Three paired sites, with NT and chisel-plow (CT) fields adjacent to each other were selected for this study. Fields were under the same tillage practices for more than 20 years. Fields were sampled up to 90 cm depth to determine SOC and different C pools based on soil CO2 flux during 86 d of incubation.Results and conclusion: Significant differences in SOC and its pools were limited within the surface 0–15 cm depth only. Profile SOC did not vary between NT and CT. Tillage had a significant influence on soil C pools but the effect was not consistent across sites.

Soil C:N:P stoichiometry in plantations of N-fixing black locust and indigenous pine, and secondary oak forests in Northwest China

Soil nutrient concentrations and stoichiometry are important indicators of plant growth, terrestrial productivity, and ecosystem functioning. Nevertheless, little is known about the vertical distribution and the environmental factors influencing the spatial patterns of different forest types under the “Grain for Green” program and the “Natural Forest Resources Protection” project in Northwest of China. We collected 114 soil profile samples within a 0–100-cm depth from black locust and Chinese pine plantations, and secondary oak forests. We determined the vertical distributions of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and their ratios along environmental gradients in Shaanxi Province, Northwest China. The results showed that both SOC and TN concentrations decreased exponentially within the soil profiles of the three forest types, but there was minimal change in TP. Significant differences in SOC, TN, and TP were found in the surface soil layers among the forest types. Both SOC and TN were relatively low in the N-fixing black locust plantations and TP was comparatively low in the Chinese pine plantations. The C:N:P ratios decreased with increasing soil depth for the three forest types. These ratios were comparatively high in the Chinese pine plantations, relatively low in the black locust plantations, and moderate in the oak forests. The differences in the ratios among the three forest types were more significant in surface soil than in deep soil. Precipitation was positively correlated with the concentrations of SOC and TN and the ratios of C:N:P. Temperature was negatively correlated with concentrations of SOC and TN and the ratios of C:N:P across all soil depths. A log-transformed linear C-N relationship was found for all three forest types, suggesting a well-constrained coupling between the levels of the two elements. Our results demonstrated the effect of different tree species on soil C:N:P ratios and their controlling factors within soil profiles along environmental gradients. The secondary oak forest accumulated soil C and N more effectively than the plantations. The Chinese pine plantations were relatively more susceptible to P limitation. Therefore, the mechanism of different plant species on soil biogeochemical processes at the whole soil profile level must be considered when developing forest management strategies and implementing vegetation restoration projects.

Biochemical proxies indicate differences in soil C cycling induced by long-term tillage and residue management in a tropical agroecosystem

A potential benefit of conservation agriculture (CA) is soil organic carbon (SOC) accrual, yet recent studies indicate limited or no impact of CA on total SOC in tropical agroecosystems. We evaluated biochemical indicators of soil C cycling after 9 years (18 seasons) of contrasting tillage with and without maize residue retention in western Kenya. Potential activities of C-cycling enzymes (β-glucosidase, GLU; β-galactosidase, GAL; glucosaminidase, GLM; cellobiohydrolase, CEL), permanganate-oxidizable C (POXC), and soil organic matter (SOM) composition (by infrared spectroscopy) were measured. POXC tended to be greater under reduced tillage and residue retention, but did not significantly differ among treatments (≤ 2% of SOC). Despite no significant differences in SOC concentrations or stocks, activities of all 4 C-cycling enzymes responded strongly to tillage, and to a lesser extent to residue management. Activities of GLU, GAL, and GLM were greatest under the combination of reduced tillage and residue retention relative to other treatments. Reduced tillage produced an enrichment in carboxyl C = O (+6%) and decreased polysaccharide C-O (−3.5%) relative to conventional tillage irrespective of residue management. Though enzyme activities and POXC are typically associated with SOC accrual, changes in soil C cycling at this site have not translated into significant differences in SOC after 9 years. Elevated enzyme activities may have offset potential SOC accumulation under CA. However, the ratio of C-cycling enzyme activities to SOC was higher under reduced tillage and residue retention relative to other treatments, indicating that stoichiometric scaling of SOC and enzyme activities does not explain absence of significant differences in SOC among tillage and residue managements. Potential factors that may explain the low SOC accrual rates in this tropical agroecosystem included the low, albeit realistic, levels of residue retention, nutrient limitations, and high temperatures favoring decomposition.

Soil nitrogen mineralization in a wind-disturbed area on Changbai Mountain after 30 years of vegetation restoration

Wind-disturbed (1986) and undisturbed primary forest areas (controls) on Changbai Mountain (China) were studied to compare levels of soil nitrogen mineralization. Soil samples were collected at 0–10cm (topsoil) and 10–20cm (subsoil) depths from the vegetation zones of a broadleaf Korean pine forest (BKPF), spruce-fir forest (SFF), and an Erman's birch forest (EBF) at different altitudes. Nitrogen status and mineralization characteristics were studied in the soil samples from a wind-disturbed area where vegetation cover has been restored after 30years of regrowth. Soil organic carbon (SOC) and total nitrogen (TN) contents in the topsoil layer of the three vegetation types were significantly higher than in the subsoil layer. SOC and TN contents in the topsoil layer increased, and soil C/N ratio significantly decreased with increasing altitude. No significant differences in SOC, TN or pH were detected in the wind-disturbed and control area soils of BKPF and EBF. SOC and TN levels in the subsoil layer of SFF were significantly higher in wind-disturbed than in control areas. The topsoil C/N ratios of BKPF and SFF were significantly higher in the control area vs. the wind-disturbed area. After 21d incubation, inorganic nitrogen contents (ammonium nitrogen NH4+-N and nitrate nitrogen NO3−-N) in the soils of BKPF, SFF and EBF increased in both the wind-disturbed and control areas. Ammonium nitrogen (NH4+-N) was the primary inorganic form of nitrogen. The changes in the amount of NH4+-N formed from ammonification contributed to the 57.1–76.2% total amount of nitrogen mineralized (net nitrogen mineralization) and the net nitrogen mineralization rate. The nitrogen mineralization process was mainly the result of net ammonification. Correlation analysis on the soil nitrogen mineralization rate and chemical properties showed that the ammonification rate had strong positive correlation with SOC and the C/N ratio. Nitrification rate was highly correlated with SOC and TN contents, as well as soil pH. Net nitrogen mineralization rate was significantly correlated with SOC and TN contents, C/N ratio, and soil pH. Multiple comparisons analysis of variance (ANOVA) demonstrated that soil nitrogen mineralization was greatly influenced by vegetation type, soil depth, and wind disturbance in the forest soils at different altitudes. Net ammonification and net nitrogen mineralization were significantly affected by wind disturbance. The vegetation cover has undergone restoration for nearly 30years in the wind-disturbed area on Changbai Mountain, but our data demonstrate that differences in soil quality between primary forest and wind-disturbed areas remain significant due to the different vegetation types.

Fire and Tillage as Degrading Factors of Soil Structure in Northern Zagros Oak Forest, West Iran

AbstractThe effects of fire and the conversion to vineyard on soil organic carbon (SOC), and soil aggregate size distribution and stability were studied in a forest of Iran. For this purpose, topsoil was sampled in an unburned area, a portion of the forest burned three years earlier, and a vineyard, all three contiguous and showing similar topographic features. In the burned forest, soil was sampled in areas undergone high, moderate, or low severity. Air‐dried soil samples were sieved to obtain four aggregate size classes, which were subsequently wet sieved. Soil aggregate distribution index, mean weight diameter, geometric mean diameter, and aggregate stability index were determined on both dry and wet specimens. No significant differences in SOC between burned and unburned forest were found, most probably because of the supply of charred biomass to soil, while in the vineyard thirty years of cultivation had removed half of initial SOC. Both severe fire and cultivation had decreased the stability of aggregates and the relative amount of the biggest ones (8 to 2‐cm diameter). However, aggregate stability was significantly lower in the vineyard than in the burned forest, which points out to a stronger impact of prolonged cultivation than a single fire, although severe. Cultivation and severe fire had decreased the proportion of C in macroaggregates, to the advantage of meso (1 to 0.25 mm) and micro (&lt;0.25 mm) aggregates. A hierarchical cluster analysis of all investigated properties and indices demonstrated that cultivation and highly severe fire both were causes of soil degradation. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Distribution characteristics of soil organic carbon of burned area under different restorations.

The distribution characteristics of soil organic carbon (SOC), soil dissolved organic carbon (DOC) and soil microbial biomass carbon (MBC) under different restorations were studied in Larix gmelinii plantation, Pinus sylvestris var. mongolica plantation, artificial promotion poplar-birch forest and the natural secondary poplar-birch forest restored from burned area after the severe fire of Greater Xing' an Mountains in 1987. The results showed that the variations in SOC, DOC and MBC ranged from 9.63 to 79.72 g·kg-1, from 33.21 to 186.30 mg·kg-1 and from 200.85 to 1755.63 mg·kg-1, respectively, which decreased with soil depth increasing. There was significant diffe-rence in SOC, DOC and MBC among different restorations, with the maximum carbon contents for artificial promotion poplar-birch forest, followed by L. gmelinii plantation, natural secondary poplar-birch forest and P. sylvestris var. mongolica plantation successively. The soil microbial quotient va-ried from 1.1% under P. sylvestris var. mongolica plantation to 2.3% under artificial promotion poplar-birch forest, and its vertical distributions were different in the four restoration forests. Correlation analysis indicated that MBC had a significant positive correlation with SOC and DOC, respectively. The activity of soil organic carbon in artificial promotion poplar-birch forest was higher than in other forest stands, suggesting a stronger capacity of the soil carbon cycle through natural regeneration with artificial promotion on burned area in Greater Xing'an Mountains.

Spatial variability of soil magnetic susceptibility, organic carbon and total nitrogen from farmland in northern China

Spatial variability of magnetic susceptibility (χ), soil organic carbon (SOC) and total nitrogen (TN) concentrations were analyzed using geostatistics method in different soil horizons from farmland in the North China. Results showed that a significant difference in SOC and TN contents, while no significant difference in χ was observed at two soil horizons using the t-test. The average values of χ 93.0×10−8m3kg−1, SOC 11.25gkg−1 and TN 1.03gkg−1 were higher at the 0–20cm than those measured at the 20–40cm depth, respectively. The value of frequency dependent susceptibility (χfd) was greater than 6% indicated the formation of superparamagnetic particles through pedogenesis and/or human activities. The isotropic semivariogram models of χ, SOC and TN were fitted to spherical model. A clear variogram of soil properties with a medium spatial dependent was observed. The range of spatial correlations was determined to be approximately12km, which seemed to be characteristic for a regional scale. The kriging interpolated maps provided information for soil monitoring and management. Geometric and small spherical magnetic particles were identified by microscopy. Vertical distributions of soil properties proved that soil magnetic signature mainly originated from lithogenic and anthropogenic contribution.

Differences in soil organic carbon and total nitrogen and their impact factors under different restoration patterns in the Loess Plateau.

Knowledge of the effect of different vegetation restoration measures on soil organic carbon (SOC) and total soil nitrogen (TN) is of importance to better understand carbon and nitrogen cycling in terrestrial ecosystems and deal with the global greenhouse effect. The differences in SOC and TN content in 0-100 cm soil profile between different restoration measures and their impact factors were investigated in the Loess Plateau. The results showed that artificial vegetation restoration led to a significant increase in both SOC and TN content in the 0-100 cm soil profile compared with that of cropland. The highest increase in average SOC content was observed in the artificial woodland(1.43 times that of the cropland), followed by the artificial shrubland (1.36 times) and artificial grassland (1.21 times); whereas the highest increase in average TN content was observed in the artificial woodland (1.30 times that of the cropland), followed by the artificial grassland (1.21 times) and artificial shrubland (1.13 times). Compared with the cropland, there was a significant difference in SOC and TN content and fine root density up to a maximum depth of >100 cm in the artificial woodland and shrubland, but about 60 cm in the artificial grassland. The fine root density, soil C:N ratio and aboveground litter production of artificial woodland, shrubland and grassland were significantly higher than that of cropland, and fine root density was significantly linearly correlated with SOC and TN (P<0.01). The quantity and quality of fine root and litter biomass might be the dominant factors contributing to the observed difference in SOC and TN contents between the different artificial vegetation types in the Loess Plateau.