Affect Soil Organic Carbon Dynamics Research Articles

Change in Land Use Affects Soil Organic Carbon Dynamics and Distribution in Tropical Systems

Anthropogenic land cover change is directly responsible for the deforestation and degradation of tropical forests. In this context, assessing soil organic carbon (SOC) stocks is key to understanding the impact of anthropogenic activities on SOC so that we can implement management practices that effectively reduce emissions or promote carbon sequestration. Our objective was to assess the effect of land-use change on the dynamics and distribution of SOC in three systems (agriculture, pasture and agroforestry) after 40 years of deforestation in a tropical dry forest in the central–eastern region of Honduras. For this purpose, the bulk density, percentage of coarse fragments (>2 mm) and soil organic carbon content were determined at three depths (0.00–0.10 m, 0.10–0.20 m and 0.20–0.30 m). The results showed an increase in bulk density for all new uses, although soil compaction had not yet occurred. In terms of total soil organic carbon (TOC) stocks, deforestation caused a decrease from 17% to 48% in agricultural and agroforestry soils, respectively; on the other hand, grasslands did not show significant differences compared to tropical dry forest, suggesting that they have a high potential as carbon sinks in deforested tropical areas. However, this did not imply a better state of the system, as the greatest increases in bulk density were found in pastures.

Phosphorus fertilization promotes carbon cycling and negatively affects microbial carbon use efficiency in agricultural soils: Laboratory incubation experiments

Soil organic carbon (SOC) loss from intensive agriculture represents a major global concern. Consequently, strategies to improve soil management to mitigate or abate SOC losses and enhance carbon (C) sequestration are urgently needed. Nutrient availability, especially nitrogen (N) and phosphorus (P), regulates soil C cycling and storage. While N effects are well studied, less is known about how soil P status and different fertilizer types affects SOC dynamics. This laboratory incubation assessed how two common P fertilizers, diammonium phosphate (DAP) and single superphosphate (SSP), affected microbial activity and C immobilization in the zone of soil directly around the fertilizer granule (prillosphere) across three contrasting agricultural soils (Inceptisol, Vertisol, Alfisol). Soils were amended with DAP or SSP granules and C turnover assessed with 14C-labeled glycine, malic acid or glucose, alongside unfertilized controls. After three weeks, soil pH, electrical conductivity (EC), Olsen-P and microbial C use efficiency (CUE) were measured. DAP increased pH in the Inceptisol (acidic soil), while SSP decreased pH in all soils. Both fertilizers increased EC and Olsen-P, but SSP enhanced Olsen-P more than DAP. Cumulative 14CO2 emissions were 19–20 % higher with P fertilizers compared to the control, with DAP stimulating faster initial C mineralization rates than SSP, except in the Alfisol. P addition reduced microbial CUE by 23–34 % across all soils and substrates versus the unfertilized control. We ascribe this reduction in CUE to an alleviation of nutrient limitation or a fertilizer-induced osmotic stress. The co-addition of N either in DAP or glycine did not alter the P-induced CUE response suggesting that P was more important than N in regulating microbial CUE in these soils. We conclude that P fertilization increased short-term C turnover and may lead to reduced C storage in soil, however, further long-term (>1 year) research is needed to identify optimum P management strategies to minimize C losses in agricultural soils.

Contrasting Effects of Nitrogen Deposition and Phosphorus Addition on Soil Organic Carbon in a Subtropical Forest: Physical Protection versus Chemical Stability

Soil organic carbon (SOC) not only contributes to maintain soil health, but is also important in regulating global climate change. How atmospheric nitrogen (N) deposition and phosphorus (P) addition affects SOC dynamics remains unclear, especially in subtropical forests. The response of SOC in three layers to N deposition and P addition in this study is estimated by analyzing the soil aggregates and C chemical stability composition fertilized with N (100 kg N hm−2 a−1) and/or P (50 kg P hm−2 a−1) over 9 years in a Chinese fir (Cunninghamia lanceolata) plantation. Treatments involving N deposition increased the SOC concentration, while P addition alone decreased the SOC concentration in soil layers above 10 cm. The addition of N significantly increased the mean diameter of topsoil aggregates, macroaggregates SOC concentration, and the contribution of N to total SOC. P addition decreased the relative abundances of aromatic and aliphatic functional groups while decreasing the chemical stability of SOC in the topsoil. A structural equation model indicated that N deposition promoted SOC concentration by mainly improving the physical protection of soil aggregates, while P addition reduced SOC sequestration by decreasing the chemical stability of SOC. Our research suggested that elevated N deposition might promote the soil C sink, while P fertilization would not be recommended under increased N deposition to protect soil C storage in subtropical forests.

Soil carbon dynamics in integrated agricultural systems in Minas Gerais state, Brazil: A meta-analysis

The state of Minas Gerais, Brazil, has one of the highest rates of carbon dioxide emission in the country with a large part of these emissions attributed to extensive livestock on degraded pastures. Integrated agricultural production systems are considered a promising strategy to alleviate the negative impacts on soil caused by agriculture (e.g., soil carbon losses via CO2 emissions) while keeping food production. However, the extent to which integrated systems [i.e., integrated crop-livestock (ICL) and integrated crop-livestock-forestry (ICLF)] can contribute to counterbalance soil organic carbon (SOC) losses is limited. Here, through a meta-analysis, we provide a regional-scale assessment of changes in SOC stocks associated with the adoption of ICL and ICLF systems in Minas Gerais state, Brazil. Additionally, we further investigated how SOC dynamics in these systems are affected by distinct soil (e.g., texture, depth) and climatic (e.g., temperature, precipitation) variables. Our results indicate that both ICL and ICLF systems resulted in SOC accrual after their implementation, at average rates of 1.09 and 1.21 Mg ha−1 yr−1, respectivelly. The age of the system affected SOC stocks only in the ICLF system, particularly between 4 and 8 years, in which SOC stocks increased at an average rate of 1.3 Mg ha−1 yr−1. While SOC stocks decreased in clay-sandy soils under ICLF systems, they increased in clay loam soils (1.06 Mg ha−1 yr−1). No clear trend was observed for ICL systems regarding soil texture. Positive effects of precipitation on SOC stocks in ICLF and ICL systems were observed only between 880 and 1000 and 1500–1700 mm, respectively. Clear effects of temperature on SOC stocks were observed only between 22 and 25 °C in ICLF systems. Soil depth had no significant effect on the rate of SOC stock change in the systems evaluated. Although the observed results help to better understand how integrated agricultural systems can affect SOC dynamics, the lack of detailed information in the studies used in our meta-analysis limits statically comparisons. However, our results indicate clear trends that ICLF and ICL systems can contribute to increasing SOC sequestration, and which climate and soil characteristics might be considered to maximize the efficiency of these systems in increasing SOC across Minas Gerais state, Brazil.

Mechanism of polyethylene and biodegradable microplastic aging effects on soil organic carbon fractions in different land-use types

Microplastics (MPs) are widely present in terrestrial ecosystems, but knowledge about the aging characteristics of MPs in different land-use types and their impact on soil organic carbon fractions is still limited. Polyethylene (PE) and biodegradable MPs (Poly propylene carbonate and Polybutylene adipate terephthalate synthetic material (PPC + PBAT, Bio)), at 0 %, 0.03 %, and 0.3 % (w/w) dosages, were added to grassland, farmland, and facility soils for eight-week incubation. The aging degree of MPs was explored by quantifying the carbonyl index (CI). Soil organic C fractions such as SOC, particulate organic carbon (POC), mineral-associated organic carbon (MAOC), and microbial-derived C were analyzed. MPs underwent rapid aging after incubation, and the CI value for 0.03 % PE-MPs increased from 0.05 to 0.27 (farmland) and 0.26 (facility) (p < 0.05). The aging degree of 0.03 % and 0.3 % Bio-MPs was most significant in grassland, with CI decreasing by 46.6 % and 69.0 %, respectively. The CI of MPs were negatively correlated with their dosage. The 0.03 % and 0.3 % PE-MPs decreased soil organic carbon (SOC) content by 7.4 % and 8.2 % in grassland, and 3.0 % and 6.0 % in the facility (p < 0.05). POC content of farmland and facility soil was negatively correlated with PE-MPs' CI (p < 0.05). The 0.03 % PE and Bio-MPs decreased fungal necromass C (FNC) by 0.40 and 0.05 g kg−1 in grassland and 0.48 and 0.21 g kg−1 in farmland. Besides, the dosage of MPs regulated FNC content through soil pH, nutrients, and extracellular enzyme activity, either directly or indirectly, ultimately affecting the soil C pool. Therefore, this study demonstrates that MPs strongly affect SOC dynamics by influencing soil microbial enzyme activity and fungal necromass.

Warming inhibits the priming effect of soil organic carbon mineralization: A meta-analysis

Fresh organic carbon (C) input will accelerate or inhibit the mineralization of native soil organic carbon (SOC), which is called positive or negative priming effect (PE), respectively. However, little is known about how warming affects the PE. Here, we adopted a widely-used ratio of SOC mineralization between substrate-added and unadded-control treatments to represent PE intensity and used the PE difference between ambient-control temperature and elevated temperature to indicate the effect of warming on PE (ΔPE). By conducting a meta-analysis of 146 observations from 57 independent soils worldwide, we found that experimental warming significantly decreased the PE by 0.26 (unitless). Among ecosystems, warming significantly suppressed the PE of cropland and grassland soils by 0.43 and 0.21 respectively, but did not change the PE of forest soils. Moreover, we found significant positive correlations of ΔPE with the initial soil C/N ratio and the effect size of warming on microbial biomass. Between substrate types (i.e., containing N or not), warming significantly decreased the PE induced by N-containing substrates. These results suggested that the response of PE to warming is likely regulated by soil N availability and warming-induced changes in microbial biomass. As such, we proposed a conceptual framework—the microbial N mining hypothesis dominates in soils with low C/N ratio where warming inhibits PE by promoting N mineralization, while the stoichiometric decomposition hypothesis dominates in soils with high C/N ratio where warming stimulates PE by promoting N mineralization. Collectively, these findings provide important insights into how warming affects SOC dynamics via inhibiting PE, which may weaken the positive feedback between soil C emission and climate warming.

Cropping systems and agricultural management strategies affect soil organic carbon dynamics in semi-arid regions

IntroductionSoil organic carbon (SOC) dynamic is one of the important factors that directly influence soil properties and quality. In agro-ecosystems, the SOC dynamics are strongly linked to agricultural management practices.MethodsIn this study, we investigated the response of SOC and its fractions to various combination of agricultural management practices based on measurements obtained from an experiment conducted over four growing seasons from 2018 to 2020 in Ahvaz, Iran. The experimental treatments involved three agricultural strategies combined with four crop rotation systems. The agricultural strategies comprised conventional (CON: mineral fertilizer, removal of all crop residues), organic (ORG: organic fertilizer, 30% return of crop residues to the soil), and integrated (INT: mineral/organic fertilizer, 15% return of crop residues) strategies. The crop rotation systems were: fallow-wheat (F-W), corn-wheat (C-W), sesame-wheat (S-W), and mung bean-wheat (B-W). Soil samples were collected from all treatments and SOC, labile-C, and non-labile-C were measured.Results and discussionAfter two years of experiment, no significant improvement was found in SOC of CON strategy (p ≤ 0.05). The ORG and INT strategies contained on average 1.1 and 1.06 times more SOC than the CON strategy, respectively. The value of labile-C was decreased during summer cultivations and increased in the soil samples collected after winter cultivations. However, although the quantity of labile-C in ORG (2 g kg−1) was higher than INT (1.83 g kg−1) and CON (1.87 g kg−1) overall during the experiment time, after the second summer cultivation despite the gradual accumulation of organic matter due to high levels of temperature and humidity, the content in ORG reduced to1.47 g kg−1. In all three agricultural management strategies, the SOC content in the four rotation systems was according to the following descending order B-W (5.7 g kg−1) &amp;gt; C-W (5.29 g kg−1) &amp;gt; S-W (5.23 g kg−1) &amp;gt; F-W (4.52 g kg−1). Therefore, for this region M-W and S-W crop rotation systems are recommended in addition to C-W (which is the most common rotation system). However, crop rotation systems were more beneficial for C-sequestration when combined with organic and inorganic fertilization and crop residue incorporation. This study gives promising results for implementing INT and ORG strategies under long-term cropping systems containing various summer crops in rotation with wheat for improving SOC dynamics in semi-arid regions in Iran.

Native soil labile organic matter influences soil priming effects

The input of exogenous labile carbon into the soil is an important factor affecting soil organic carbon dynamics by accelerating or inhibiting the decomposition of native soil organic matter, known as the priming effect. Many factors affect the priming effect, including biological factors, such as soil microorganisms, plants, and soil fauna, as well as, abiotic factors, such as soil structure, nutrients, water, and temperature. Although the mechanisms responsible for the occurrence and maintenance of priming effects are well-understood, most previous studies only considered the impact of input of exogenous available organic carbon on priming effects. How the native soil labile organic matter (LOM) affects the direction and magnitude of the priming effect remains unclear. In this study, mineral layer soil was collected from a Chinese fir plantation in Qianyanzhou, Jiangxi. Native LOM concentrations in the soil were adjusted using vacuum soil solution extraction. The priming effect was quantified by adding 13C-labeled glucose at two different concentrations. Changes in the concentration of native LOM affected the native microbial biomass in the soil, in turn altering the response of soil microorganisms to exogenous available organic carbon. In the absence of glucose, soil with a high concentration of native LOM contained high levels of soil microbial biomass carbon. After adding glucose, soil microbial biomass increased, which promoted the decomposition of soil organic carbon and produced a positive priming effect. At two glucose addition levels, soil with the native LOM concentration of 50 % showed a significantly lower priming effect with values of 1.00 ± 3.10 and 0.69 ± 2.99 mg C g−1 SOC at 5 % and 20 % MBC, respectively. The priming effects did not significantly differ between the other native available organic matter concentration treatments. Thus, the influence of the native LOM concentration on the soil priming effect may be much more complex than previously considered.

Land-use-driven change in soil labile carbon affects microbial community composition and function

The conversion of natural forests to plantations can lead to a substantial loss of soil organic carbon (SOC) and threaten the function of soil microbial communities. However, the effect of forest conversion on the relationship between SOC dynamics and shifts in the composition and function of the microbial community remain poorly understood, although such information is critical for predicting the long-term effect of land-use change on global SOC dynamics and storage. To fill this knowledge gap, our study investigated the influence of two decades of converting natural forest to a tea plantation on SOC storage, microbial community composition, C-degrading enzyme activity and the abundance of C-degrading microbial functional genes in a subtropical region in China. Two decades after converting natural forest to tea plantation, SOC storage decreased by 30%, and labile SOC [including easily mineralized C (Cmin), readily oxidizable C (ROC), dissolved organic C (DOC), and microbial biomass C (MBC)] decreased by 21–71%. Land-use change decreased the relative abundance of copiotrophic bacteria but increased the relative abundance of oligotrophic bacteria and lignin-degrading fungi. This resulted in a decrease in cellulase activity and cbhI gene abundance involved in cellulose degradation and conversely an increase in ligninase activity involved in lignin degradation after the conversion. Such shifts in microbial community composition and function associated with land-use change were mediated by the decrease in the labile C pool rather than the total SOC. Our study provided new insights into not only shifts in microbial communities but also specific C functional genes and related enzymes after forest conversion. These findings highlight that labile SOC, as an important functional soil component for microbial communities, significantly affects SOC dynamics and storage.

Agricultural Management Practices and Decision-Making in View of Soil Organic Matter in the Urbanizing Region of Bangalore

Rapid urbanization and agricultural intensification are currently impacting the soils of many tropical countries. Bangalore is a growing megacity experiencing both issues and their derived ecological and socio-economic effects. This paper seeks to understand how the socio-economic effects of urbanization are affecting soil organic carbon (SOC) in Bangalore’s rural–urban interface. We first compiled information on how management practices affect SOC dynamics and specifically evaluated the effects of fertilization practices on SOC levels in major cropping systems. We then used interview data from farmers’ households across an urbanity gradient in Bangalore to test the association between urbanization as well as related socio-economic drivers and farming practices. We found that fertilization increases SOC concentrations, especially when mineral fertilizer is combined with additional farmyard manure. Single mineral fertilizer and a combination of mineral fertilizer and farmyard manure are commonly applied in Bangalore. Conservation practices, such as reduced tillage and mulching, are applied by 48% and 16% of households, respectively. Farm and household characteristics, including market integration, are the most important determinants of management decisions that affect SOC. Our study shows that improving farm and household conditions and opportunities, independently of the degree of urbanity, is necessary for implementing agricultural practices that can benefit SOC in Bangalore.

Soil carbon stocks and dynamics of different land uses in Italy using the LUCAS soil database

In terrestrial biosphere, soil represents the largest organic carbon pool, and a small change of soil organic carbon (SOC) can significantly affect the global carbon cycle and climate. Land use change (LUC) and soil management practices coupled with climate variables can significantly influence the soil organic carbon stocks (SOC–S) and its dynamics; however, our understanding about the responses of SOC in different LUC's (e.g., cropland, grassland and forest land) to mitigate climate change is quite limited at country level like Italy. Thus, the aims of this study were which factors are affecting SOC dynamics in three LUC's over time across Italy; and their relevance in terms of SOC–S in the superficial layer of soil that significantly contributes to the climate change mitigation, using LUCAS soil database. To calculate the SOC–S, it is necessary to have soil bulk density (BD) which is not present in the LUCAS database. Thus, we estimate the soil BD using the pedotransfer function (PTFs); and results shows that the soil BD obtained from fitting of the PTFs were reasonable to estimate the SOC–S for different land use types (R2 ≥ 0.75). Overall, results showed that LUC's and soil management practices can significantly (p < 0.001) influences SOC dynamics and SOC storage from the soil and varied among LUC's but not for over time except grassland. Spatially, the mean SOC–S storage of the different LUC's was in the following order: forest land > grassland > cropland for both years 2009 and 2015. On the other hand, the SOC–S storage increased by 8.33% for cropland, 13.56% for forest land, and 29.79% for grassland during the year of 2009–2015, while SOC–S storage increased significantly (p < 0.001) in grassland over time but not for cropland and forest land which also follow the increasing trend but insignificantly. Our results also reveal that the SOC dynamics negatively correlated with MAT, and positively correlated with MAP for all land uses except forest land. Thus, this research indicates that LUC's and soil management practices coupled with climate variables can significantly influence SOC storage and its dynamics in the superficial layer of soil which have the potential capacity to mitigate climate change.

High microbial diversity stabilizes the responses of soil organic carbon decomposition to warming in the subsoil on the Tibetan Plateau

Soil microbes are directly involved in soil organic carbon (SOC) decomposition, yet the importance of microbial biodiversity in regulating the temperature sensitivity of SOC decomposition remains elusive, particularly in alpine regions where climate change is predicted to strongly affect SOC dynamics and ecosystem stability. Here we collected topsoil and subsoil samples along an elevational gradient on the southeastern Tibetan Plateau to explore the temperature sensitivity (Q10 ) of SOC decomposition in relation to changes in microbial communities. Specifically, we tested whether the decomposition of SOC would be more sensitive to warming when microbial diversity is low. The estimated Q10 value ranged from 1.28 to 1.68, and 1.80 to 2.10 in the topsoil and subsoil, respectively. The highest Q10 value was observed at the lowest altitude of forests in the topsoil, and at the highest altitude of alpine meadow in the subsoil. Variations in Q10 were closely related to changes in microbial properties. In the topsoil the ratio of gram-positive to gram-negative bacteria (G+:G-) was the predominant factor associated with the altitudinal variations in Q10 . In the subsoil, SOC decomposition showed more resilience to warming when the diversity of soil bacteria (both whole community and major groups) and fungi was higher. Our results partly support the positive biodiversity-ecosystem stability hypothesis. Structural equation modeling further indicates that variations in Q10 in the subsoil were directly related to changes in microbial diversity and community composition, which were affected by soil pH. Collectively our results provide compelling evidence that microbial biodiversity plays an important role in stabilizing SOC decomposition in the subsoil of alpine montane ecosystems. Conservation of belowground biodiversity is therefore of great importance in maintaining the stability of ecosystem processes under climate change in high-elevation regions of the Tibetan Plateau.

Long‐term, amplified responses of soil organic carbon to nitrogen addition worldwide

Soil organic carbon (SOC) is the largest carbon sink in terrestrial ecosystems and plays a critical role in mitigating climate change. Increasing reactive nitrogen (N) in ecosystems caused by anthropogenic N input substantially affects SOC dynamics. However, uncertainties remain concerning the effects of N addition on SOC in both organic and mineral soil layers over time at the global scale. Here, we analysed a large empirical data set spanning 60years across 369 sites worldwide to explore the temporal dynamics of SOC to N addition. We found that N addition significantly increased SOC across the globe by 4.2% (2.7%-5.8%). SOC increases were amplified from short- to long-term N addition durations in both organic and mineral soil layers. The positive effects of N addition on SOC were independent of ecosystem types, mean annual temperature and precipitation. Our findings suggest that SOC increases largely resulted from the enhanced plant C input to soils coupled with reduced C loss from decomposition and amplification was associated with reduced microbial biomass and respiration under long-term N addition. Our study suggests that N addition will enhance SOC sequestration over time and contribute to future climate change mitigation.

Effects of different fertilization managements on microbial necromass and plant lignin accumulation in a Mollisol

Fertilization is an effective management to maintain and increase soil organic carbon (SOC) level in agroecosystems. Both microbial metabolism and plant component retention control SOC sequestration. Here, we used amino sugars and lignin as biomarkers to investigate the responses of distribution of microbial necromass and plant debris in a long-term cultivated soil (30 years) and SOC accumulation to different fertilization regime. The results showed that, compared with unfertilized treatment, inorganic fertilizer application (N fertilizer-only or the combination of organic or inorganic fertilizers) increased crop production and soil amino sugar accumulation, but did not affect the concentrations of lignin and SOC, indicating that inorganic fertilizer stimulated the assimilation of microbial substrate and accelerated the turnover of SOC and lignin in the plough layer. Compared with inorganic fertilizer treatment, long-term organic fertilizer application promoted SOC accumulation (38.3%), but did not affect amino sugar concentration in SOC, which indicated that soil could reach a 'saturation' state with respect to microbial residue accumulation. In contrast, the application of organic fertilizer increased the proportion of lignin in SOC,indicating that the contribution of plant residues to SOC persistence was enhanced. Compared with the manure-only treatment, organic-inorganic combined application mainly increased the contribution of amino sugar to SOC accumulation. Our findings indicated that long-term fertilization could affect SOC dynamics through modulating the accumulation processes of microbial necromass and plant debris.

Soil Organic Carbon in Sandy Paddy Fields of Northeast Thailand: A Review

Soil organic carbon (SOC) improvement has become a sustainable strategy for enhancing soil resilience and reducing greenhouse gas (GHG) emissions in the rice cropping system. For tropical soils, the SOC accumulation was limited by the unfavorable environment, likely the sandy soil area in Northeast (NE) Thailand. This review aims to quantify and understand SOC in sandy paddy fields of NE Thailand. The existing research gap for alternative management practices is also highlighted to increase ecological and agronomic values. We review previous studies to determine the factors affecting SOC dynamics in sandy paddy fields, in order to enhance SOC and sustain rice yields. High sand content, up to 50% sand, was found in 70.7% of the observations. SOC content has ranged from 0.34 to 31.2 g kg−1 for the past four decades in paddy rice soil of NE Thailand. The conventional and alternative practice managements were chosen based on either increasing rice crop yield or improving soil fertility. The lack of irrigation water during the mild dry season would physically affect carbon sequestration as the soil erosion accelerates. Meanwhile, soil chemical and microbial activity, which directly affect SOC accumulation, would be influenced by nutrient and crop residue management, including chemical fertilizer, manure and green manure, unburned rice straw, and biochar application. Increasing SOC content by 1 g kg−1 can increase rice yield by 302 kg ha−1. The predicted carbon saturation varied tremendously, from 4.1% to 140.6% (52% in average), indicating that the sandy soil in this region has the potential for greater SOC sequestration. Our review also suggests that broadening the research of rice production influenced by sandy soil is still required to implement adaptive management for sustainable agriculture and future food security.

Soil organic carbon storage varies with stand ages and soil depths following afforestation

Soil organic carbon (SOC) is the largest component of the terrestrial biosphere carbon pool. Afforestation is an effective solution to mitigate Carbon (C) emission and sequester C into soils. However, how and to which extent afforestation influences SOC stock changes are not well understood. This study conducts a quantitative review that synthesizes 544 data points from 261 sites from 90 papers, to examine the impact of afforestation on SOC changes in three soil layers (0-20 cm, 20-40 cm and 40-60 cm). 212 data points are obtained by standardization and/or extrapolationwith high reliability. The results indicate that stand age has significant effects on the SOC stock dynamics under different conditions of previous land use types, plant functional types, temperature or precipitation. The effect is greatest at the topsoil layer of 0-20 cm. Previous land use types significantly influence SOC accumulations, but these effects are not significant in the first 10 years or after 30 years of afforestation. Besides, afforestation on grassland seems to sequester more SOC than that of cropland in the long term. Plant functional types also significantly affect SOC dynamics, with deciduous hardwood reporting a continuous increase of SOC contents at soil depth of 0-60 cm during the whole afforestation period. On the other hand, the accumulation of SOC in evergreen hardwood and evergreen softwood start from the third decades. Higher SOC accumulation rates are observed under evergreen hardwood but no significant differences were found between deciduous hardwood and evergreen softwood for the longer period after afforestation (>20 years). Mean annual temperature and precipitation negatively affect SOC accumulation in the first two decades of afforestation, however, the effects become positive in the later years.We also found that initial SOC stocks did not play a major role in SOC sequestration. In other words, lower SOC soils could also sequestrate a significant amount of SOC after reforestation.

Simulation of Soil Organic Carbon Effects on Long-Term Winter Wheat (Triticum aestivum) Production Under Varying Fertilizer Inputs.

Soil organic carbon (SOC) has a vital role to enhance agricultural productivity and for mitigation of climate change. To quantify SOC effects on productivity, process models serve as a robust tool to keep track of multiple plant and soil factors and their interactions affecting SOC dynamics. We used soil-plant-atmospheric model viz. DAISY, to assess effects of SOC on nitrogen (N) supply and plant available water (PAW) under varying N fertilizer rates in winter wheat (Triticum aestivum) in Denmark. The study objective was assessment of SOC effects on winter wheat grain and aboveground biomass accumulation at three SOC levels (low: 0.7% SOC; reference: 1.3% SOC; and high: 2% SOC) with five nitrogen rates (0–200 kg N ha-1) and PAW at low, reference, and high SOC levels. The three SOC levels had significant effects on grain yields and aboveground biomass accumulation at only 0–100 kg N ha-1 and the SOC effects decreased with increasing N rates until no effects at 150–200 kg N ha-1. PAW had significant positive correlation with SOC content, with high SOC retaining higher PAW compared to low and reference SOC. The mean PAW and SOC correlation was given by PAW% = 1.0073 × SOC% + 15.641. For the 0.7–2% SOC range, the PAW increase was small with no significant effects on grain yields and aboveground biomass accumulation. The higher winter wheat grain and aboveground biomass was attributed to higher N supply in N deficient wheat production system. Our study suggested that building SOC enhances agronomic productivity at only 0–100 kg N ha-1. Maintenance of SOC stock will require regular replenishment of SOC, to compensate for the mineralization process degrading SOC over time. Hence, management can maximize realization of SOC benefits by building up SOC and maintaining N rates in the range 0–100 kg N ha-1, to reduce the off-farm N losses depending on the environmental zones, land use and the production system.

A historical perspective on soil organic carbon in Mediterranean cropland (Spain, 1900–2008)

Soil organic carbon (SOC) management is key for soil fertility and for mitigation and adaptation to climate change, particularly in desertification-prone areas such as Mediterranean croplands. Industrialization and global change processes affect SOC dynamics in multiple, often opposing, ways. Here we present a detailed SOC balance in Spanish cropland from 1900 to 2008, as a model of a Mediterranean, industrialized agriculture. Net Primary Productivity (NPP) and soil C inputs were estimated based on yield and management data. Changes in SOC stocks were modeled using HSOC, a simple model with one inert and two active C pools, which combines RothC model parameters with humification coefficients. Crop yields increased by 227% during the studied period, but total C exported from the agroecosystem only increased by 73%, total NPP by 30%, and soil C inputs by 20%. There was a continued decline in SOC during the 20th century, and cropland SOC levels in 2008 were 17% below their 1933 peak. SOC trends were driven by historical changes in land uses, management practices and climate. Cropland expansion was the main driver of SOC loss until mid-20th century, followed by the decline in soil C inputs during the fast agricultural industrialization starting in the 1950s, which reduced harvest indices and weed biomass production, particularly in woody cropping systems. C inputs started recovering in the 1980s, mainly through increasing crop residue return. The upward trend in SOC mineralization rates was an increasingly important driver of SOC losses, triggered by irrigation expansion, soil cover loss and climate change-driven temperature rise.

Long-term effects of management history on carbon dynamics in agricultural soils in Northwest China

Human activities and climate change have substantial effects on soil ecosystems. The historical variations in soil organic carbon (SOC) in Northwest China were investigated in this paper. Using an agro-ecosystems database, a process-based model, Denitrification-Decomposition (DNDC), was used to support a regional SOC simulation. Over the 1980s and 1990s, the SOC storage (0–50 cm) reduced slightly from 1.25 PgC (pentagrams of carbon, 1 PgC = 1015 gC) and stabilized at 1.23 PgC. SOC significantly differed in Northwest China farmland both temporally and spatially. Climatic variability magnified the response of the spatially heterogeneous region to climate and greatly influenced the vegetation and soil. The SOC increase appeared in areas with a mild and humid climate in the east, including Shaanxi, Gansu, Ningxia and south Xinjiang. Management practices greatly affect SOC dynamics through straw C input, increased 46.31 % C budget and 20.52 % total SOC (TSOC) through 60 % crop residue incorporation. Reducing human disturbance to the surface soil through conservative tillage and improving soil fertility through reasonable nutrient input and water-use efficiency have important implications for C sequestration, emission reduction and soil productivity improvement in arid or semiarid agricultural farmland regions.

Conversion of cropland to Chinese prickly ash orchard affects soil organic carbon dynamics in a karst region of southwest China

Knowledge about the effect of land use conversion on soil organic carbon (SOC) due to Grain-for-Green Program in karst regions is needed to assess carbon cycles in karst ecosystems. In order to evaluate the effects of land conversion, soil sampling was performed in a revegetation sequence down to 0–0.3 m, which included the conversion of cropland to Chinese prickly ash orchard (Zanthoxylumbungeanum Maxim.) for 7, 14, and 35 years, in a karst region of southwest China. The soil samples were fractioned into three aggregate-size classes: macroaggregate (250–2000 μm), microaggregate (53–250 μm), and silt + clay fraction (<53 μm). Results indicated that SOC concentrations and stocks increased after the conversion of cropland to Chinese prickly ash orchard. The highest SOC concentrations and stocks were all found during the 14 years land use conversion at both the 0–0.15 and 0.15–0.3 m depths. However, the SOC concentrations and stocks showed a decrease trend after 14 years land conversion at both soil depths. For all land use types, the macroaggregate-size class was the dominant fraction in storing SOC, followed by silt + clay fraction and microaggregate. In this study, the increases in macroaggregate-associated SOC stocks were due to increases in both macroaggregation and macroaggregate-associated SOC concentrations, especially dominant by increases in macroaggregate-associated SOC concentrations. However, the increases in microaggregate- and silt + clay-associated SOC stocks were only due to increases in amount of the microaggregates and silt + clay fractions, respectively, after conversion from cropland to Chinese prickly ash orchard. The results suggest that conversion of cropland to Chinese prickly ash orchard can play an important role in SOC sequestration. Nevertheless, for long-term Chinese prickly ash orchard plantation, some appropriate management practices should be implemented to prevent SOC losses in karst region of southwest China.