Loss Of Organic Carbon Research Articles

Influence of land‐use changes on microbial community structure and diversity in a semiarid region

AbstractLand‐use change and the conversion of land into croplands is one of the main drivers of soil degradation and the loss of soil organic carbon. Few studies have evaluated the impact of the expansion of the agricultural frontier on soil microbial communities in the Gran Chaco region in South America; therefore, the objective of this study was to explore how soil microbial communities respond to land‐use changes in a semiarid region of Argentina. The land uses selected were total and selective clearing with livestock (TC‐livestock and SC‐livestock), total clearing with agriculture (TC‐agriculture), and an undisturbed site (R‐Chancaní). Our results suggest that microbial abundances were strongly influenced by seasonal changes. In both seasons, the lowest values of total microbial biomass were observed in TC‐agriculture and TC‐livestock. In the wet season, TC‐agriculture had the lowest fungal abundance, and both total clearing sites (TC‐livestock and TC‐agriculture) had higher bacterial abundance than the other sites. Our data also showed that the Shannon and richness indices were highest at the farming sites, indicating a similar tendency in the diversity indexes in both dry and wet seasons. According to Pearson correlation analysis, humic substance (HS) content was a key driver influencing soil microbial communities, demonstrating that high HS content may significantly increase bacteria, fungi, and total phospholipid fatty acids. Microbial composition highly depended on seasonal changes. Overall, our results suggest that land‐use change altered microbial community structure and bacterial diversity, and that HS content played a crucial role in driving changes in soil microbial composition.

Dynamics of Soil Organic Carbon and CO2 Flux under Cover Crop and No-Till Management in Soybean Cropping Systems of the Mid-South (USA)

The transition of natural landscapes to agricultural uses has resulted in severe loss of soil organic carbon, significantly contributing to CO2 emissions and rising global temperatures. However, soil has the largest store of terrestrial carbon (C), a considerable sink and effective strategy for climate change mitigation if managed properly. Cover crops (CC) and no-till (NT) management are two management strategies that are known to increase percent organic carbon (%OC); however, adoption of these practices has been low in the mid-South due to lack of region-specific research and resistance to unproven practices. Therefore, the purpose of this study was to evaluate the impacts of CC-NT treatments in soybean cropping systems on soil percent organic carbon (%OC) and CO2 flux following long-term implementation. Results showed significantly greater %OC in NT (1.27% ± 0.03) than reduced till (RT; 1.10% ± 0.03; p < 0.001) and greater in both CC (rye: 1.23% ± 0.03, rye + clover: 1.22% ± 0.03) than no cover (1.11% ± 0.03; p < 0.001). Bacterial abundance (p = 0.005) and pH (p = 0.006) were significant predictors of %OC. There was no overall significant difference in CO2 flux between tillage or CC treatments; however, there were significant differences between NT and RT in July of 2020 when %RH increased (p < 0.001). Bacterial abundance negatively impacted CO2 flux (p < 0.05), which contradicts most studies. The rate of proportional change and pattern of variability in C pools suggested loss of %OC in RT treatments that were not apparent when considering %OC alone. The results of this study provide valuable insight into C turnover and the effectiveness of CC use in the Mid-South to increase soil C stocks.

Dynamics of carbon loss from an Arenosol by a forest to vineyard land use change on a centennial scale

Abstract. Few studies have focused on Arenosols with regard to soil carbon dynamics despite the fact that they represent 7 % of the world's soils and are present in key areas where food security is a major issue (e.g., in Sahelian regions). As for other soil types, land use changes (from forest or grassland to cropland) lead to a loss of substantial soil organic carbon (SOC) stocks and have a lasting impact on the SOC turnover. Here we quantified long-term variations in carbon stocks and their dynamics in a 80 cm deep Mediterranean Arenosol that had undergone a forest-to-vineyard land use change over a 100 years ago. Paired sites of adjacent plots combined with carbon and nitrogen quantification and natural radiocarbon (14C) abundance analyses revealed a C stock of 53 t ha−1 in the 0–30 cm forest soil horizon, which was reduced to 3 t ha−1 after long-term grape cultivation. Total organic carbon in the vineyard was dramatically low, with around 1 g C kg−1, and there was no vertical gradient as a function of depth. 14C showed that deep plowing (50 cm) in the vineyard plot redistributed the remaining carbon both vertically and horizontally. This remaining carbon was old (compared to that of the forest), which had a C:N ratio characteristic of microbial organic matter and was probably stabilized within organomineral associations. Despite the drastic degradation of the organic matter (OM) pool in this Arenosol, this soil would have a high carbon storage potential if agricultural practices, such as grassing or organic amendment applications, were to be implemented within the framework of the 4 per 1000 initiative.

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.

Drivers of soil respiration across a management intensity gradient in temperate grasslands under drought

Soil respiration is an important pathway of soil organic carbon losses in temperate grasslands; however, it is rarely studied across broad management intensity gradients in a landscape. Using the soda-lime method, we measured in-situ soil CO2 efflux with single measurements of long exposure time (i.e. 3 day long) in 150 grasslands in three German regions in early summer 2018 and 2019. The grasslands ranged from unfertilized and grazed grasslands to intensively fertilized and frequently harvested ones. To assess effects of grazing and fertilization intensities and plant diversity on soil CO2 efflux, we used Structural Equation Modeling to account for direct effects and indirect effects through soil and plant organic matter quantity and quality. Soil CO2 efflux was suppressed by limited water availability caused by naturally occurring droughts in both study years. Under the prevailing environmental conditions, grazing intensity, plant biomass and plant C:N ratio were not related to soil CO2 efflux. In contrast, fertilization intensity was positively associated with soil CO2 efflux (standardized coefficient of net effect: + 0.04 in 2018 and + 0.03 in 2019). This was because fertilization led to lower plant species richness and, thus, to lower C:N ratios in soils, which were associated with higher soil CO2 efflux (plant species richness net effect: −0.09 in 2018 and −0.18 in 2019; soil C:N ratio direct effect: −0.23 in 2018 and −0.33 in 2019). Intensively managed grasslands have higher soil respiration than extensively managed, plant species-rich grasslands even under the extreme conditions of natural droughts.

Litter Inputs Control the Pattern of Soil Aggregate-Associated Organic Carbon and Enzyme Activities in Three Typical Subtropical Forests

Soil extracellular enzyme activities among aggregate fractions are critical to short-term microbial activity and long–term carbon dynamics in forest ecosystems, but little is known regarding the effects of forest types on the soil enzyme activities in different soil aggregate fractions. Three typical subtropical forest types (Broadleaved forest, Moso bamboo forest and Chinese fir forest) were selected, and undisturbed soil samples (0–15 cm) were collected. We investigated the effects of forest types on aggregate stability (mean weight diameter, geometric mean diameter and fractal dimension), aggregate–associated organic carbon (OC) and the functionality of five enzymes (cellobiohydrolase, β-glucosidase, β-xylosidase, N–acetylglucosaminidase, leucine aminopeptidase) of different aggregate fractions (>2 mm, 0.25–2 mm, 0.053–0.25 mm and <0.053 mm). The results showed that the proportion of macro-aggregates, aggregate stability and macro–aggregates associated–carbon content and storage were higher in broadleaved and Moso bamboo forests than in Chinese fir forests, indicating that forest types influence the distribution of total soil OC among aggregate fraction classes and would delay the loss of OC in broadleaved and Moso bamboo forests. We also found that the extracellular enzymes were higher in aggregates of broadleaved forests and Moso bamboo forests. SEM (structural equation model) analysis also supported significantly positive relationships between litter quantity and aggregate enzyme activity, and indirect impact of litter quantity and litter C/N ratio together with soil organic carbon (SOC) and soil aggregate organic C content (SAOCC) on aggregate enzyme activity. The results of this study indicate that forest types showed large impact on aggregate-associated OC and enzyme activities, and the litter input of different forest types is the main control on enzyme activity among different aggregate fractions, and thus may play an important role in adjusting the sink capacity and stability of SOC.

A combined GIS and remote sensing approach for monitoring climate change-related land degradation to support landscape preservation and planning tools: the Basilicata case study

Monitoring landscapes in times of climate change patterns is a crucial issue, moreover, in the analyzed Mediterranean area, one of the major global candidates to develop land degradation stresses and consequential desertification phenomena. The research presented here is developed in the Mediterranean Basin, specifically in the Basilicata Region (southern Italy). The region is characterized by a very long history of intensive anthropization endowed by the high diversity of relatively geologically young soil types that consequentially created a vastity of spatial mosaics, which contributed to the composition of its archeolandscapes and endorsed some specific characteristics of the Mediterranean region, that evolved to respond to the human impact, including grazing, cultivation, and fires. Those key elements lead to the crucial issues of the region investigated here as soil erosion, salinization, loss of organic carbon, loss of biodiversity, and landslides, which together with deforestations, depopulation, and wildfires, define the exact framework of degradation and marginality. The evaluation of the sensitivity to degradation was performed (i) firstly at the regional scale, through a MEDALUS (Kosmas et al. 1999) approach, by implementing 6 main indicators (Soil Quality Index, Climate Quality Index, Vegetation Quality Index, Management Quality Index, Landslide Risk Index, Water Availability Index), and (ii) secondly at the mid-regional scale, through remote sensing by evaluation of the NDVI differencing thresholds in time intervals, covering a 20 years’ time span going from 2000 to 2020. The study helped to define the in-progress land degradation trends and scenarios of the region, which must be the evidence-based foundation of integrated landscape planning strategies in marginal territories, implemented through a Decision Support System (DSS) based both on ecological, climate-adaptive, and environmental indicators, and on social, cultural, and economic development co-creation strategies.

Changes in the burial efficiency and composition of terrestrial organic carbon along the Mackenzie Trough in the Beaufort Sea

In this study, we investigated surface sediments collected along a Mackenzie Trough transect during the R/V Araon expeditions (ARA04C, ARA05C, and ARA08C) in the Beaufort Sea in 2013, 2014, and 2017. We applied various inorganic and organic geochemical tools (major elements, carbon and nitrogen contents, stable carbon and radiocarbon isotope compositions, and molecular biomarkers) in combination with sedimentological measurements (mineral surface area (SA) and grain size) to assess the source and burial characteristics of organic carbon (OC). In general, the sediment mean grain size decreased with water depth whereas the SA increased, resulting in a decrease in the OC loading and the burial efficiency of terrestrial OC. The sedimentary OC was further influenced by the loss of terrestrial OC and replacement with marine OC with increasing water depth. Accordingly, our results suggest that hydrodynamic sorting and degradation of terrestrial OC co-occurred together with the enrichment of marine OC with distance offshore. Such processes controlled the burial and reactivity of terrestrial OC along the Mackenzie Trough transect.

Changes in soil free-living diazotrophic community and co-occurrence patterns along desert wetland degradation gradient in the Mu Us Desert, northern China

Climate change and human activities have led to the degradation of desert wetlands. Free-living diazotrophs are vital to soil nitrogen input. However, a comprehensive understanding of how soil free-living diazotrophic community and co-occurrence patterns respond to desert wetland degradation is lacking. Here, quantitative polymerase chain reaction (qPCR) and amplicon sequencing targeted on nitrogenase ( nifH ) genes and network analysis were used to investigate soil free-living diazotrophic abundance, diversity and composition and co-occurrence patterns along the wetland degradation gradient [non-degraded (ND), lightly degraded (LD), moderately degraded (MD), and severely degraded (SD) wetlands] in the southeastern of Mu Us Desert, northern China. Results showed the abundance, Shannon, Simpson, Chao1 and Ace indexes decreased ( P < 0.05) by 14.6%, 20.7%, 2.1%, 46.5% and 45.0% at SD, respectively, whereas no significant difference ( P > 0.05) was observed between ND and LD. The relative abundance of Proteobacteria generally decreased across the degradation (53.5%–19.7%), while the variation was opposite for Cyanobacteria from ND to MD (6.2%–40.1%). Soil organic carbon had the strongest linkage with abundance, diversity and composition, followed by total nitrogen, moisture and pH. The lowest network nodes, edges and density were observed at MD and SD, indicating the complexity of free-living diazotrophic networks was reduced by continued degeneration. Overall, severe desert wetland degradation more negatively affects soil free-living diazotrophic abundance, diversity and network complexity than light degradation. The degradation promotes the growth of autotrophic diazotrophs, inhibiting heterotrophic diazotrophs. These changes are mostly related to the loss of soil organic carbon.

No-till farming: prospects, challenges – productivity, soil health, and ecosystem services

Globally, declining soil quality due to soil degradation is of great concern, and directly affects crop production, soil health and sustainability of natural resources. In conventional farming practices, the loss of fertile topsoil via runoff and erosion from arable land is a big concern. In addition, changes in land use and management practices result in loss of soil organic carbon (SOC) stock by −10–59%. The change from conventional till (CT) with residue burning/removal to no-till (NT) farming with residue retention/conservation agriculture (CA) practices have been recognised as important soil management practices for sustaining soil health and reversing land degradation. Worldwide, NT/CA practices are now being adopted on about 180 million ha (i.e. ∼14% of arable land). CA practices promote soil health by increasing organic carbon, and soil aggregation, thus improving infiltration and minimising erosion losses. In addition, CA has the potential to increase SOC sequestration, reduce greenhouse gas (GHG) emissions and help to mitigate global climate change. Among sustainable food production systems, CA is often advocated with a view to increase food production while conserving natural resources and SOC. This special issue ‘No-till farming: prospects, challenges – productivity, soil health, and ecosystem services’ addresses and critically reviews these important issues and aims to foster awareness of NT farming. The collection of 15 papers lucidly covers various facets of NT farming. A summary and salient findings of these papers are provided in this Editorial. NT farming is a promising practice, which not only improves soil physical, chemical and biological health but also enhances carbon sequestration, crop productivity and mitigates GHG emissions through appropriate crop residue and nutrient management strategies. The adage says ‘one size won’t fit all’ or ‘a single recipe will not solve all problem/challenges’, so we need to adopt site-specific NT systems for higher benefits and productivity and sustaining soil health.

Soil carbon, nutrients and their stoichiometry decrement in relation to paddy field degradation: Investigation in a subtropical region

Owing to intensive cultivation, paddy fields suffer from varying degrees of degradation and loss of soil organic carbon (SOC), consequently jeopardizing the industry’s future sustainability. Accurate assessment of soil nutrient loss and SOC stability is not only indispensable for developing measures to arrest and counter this problem but to also gauge the impact of degraded soils in paddy fields towards the global carbon budget. Herein, we examine soil nutrients, their stoichiometric ratios, and carbon pool management index (CPMI) across 26 paddy fields in a subtropical region under three degraded levels – namely, low-risk degradation, high-risk degradation, and severe degradation. Our results showed a 23% likelihood of severe degradation in sampled paddy fields of southeastern China. Compared with low-risk degradation soils, the severe degradation soils had significantly lower concentrations of total nitrogen (N) (31%), labile organic carbon (C) (50%), total phosphorus (P), and available P concentrations, while the iron (Fe) and available N tended to increase. Compared to low-risk degradation, C:N, C:P, N:P ratios were 25, 50, and 30%, respectively, lower in severe degradation plots. Low CPMI values were associated with soils that are at high-risk for degradation and severe degradation, indicating that C pools in degraded paddy soils were gradually deteriorating. Moreover, soil stoichiometric ratio and nutrients were significantly affected by soil pH, Fe3+, sand, and electrical conductivity, and there were significant and positive correlations between CPMI and soil C, N and LOC concentrations. Based on the above results, our work provided evidence that paddy degradation led to a greater loss of soil carbon and nitrogen than phosphorus, reducing the soil’s potential for C sequestration. Therefore, adopting proper agricultural practices whilst minimizing the cultivation of exhaustive crops could mitigate further soil degradation and assist in restoring soil fertility and C sequestration in paddy fields of Southeastern China.

Organic Carbon Stored in the Aerial Phytomass of Fire-threatened Andean Grassland Species

The practice of burning Andean grasslands in uncontrolled conditions and dry seasonal periods affects the sustainability of the ecosystem with the loss of native grasslands species with superficial roots, the volatilization of organic matter and superficial soil nitrogen, and greater susceptibility to wind and rain erosion, which affects the forage supply of grazing areas that affect the economy of the cattle rancher in addition to emitting abundant CO₂ into the atmosphere. The objective was to quantify the loss of organic carbon contained in the aerial phytomass of burned grasslands and the dynamics of recovery of their shoots, for which seven grasslands with different dominant species and the exclusion of grazing were chosen from five plots of 900 m² with five subplots of 64 m², whose aerial phytomass was harvested, and the shoots were measured in their leaf height for nine months. As a result, variable amounts of carbon were obtained according to dominant grassland species for p: 0.001 from 5.02±1.05 to 20.02±0.95 t/ha, equivalent from 22.09 to 73.47 t.CO₂/ha. The recovery of shoot phytomass barely reached 37.32% to 55.94% concerning the initial amount obtained in the mother plants. It was concluded that each grassland has its performance of storage and recovery of stored carbon and the findings should be cause for reflection and be the basis for public policies to promote the protection of grasslands.

Soil Respiration in Planted and Naturally Regenerated Castanopis carelesii Forests during Three Years Post-Establishment

Reforestation through assisted natural regeneration usually accumulates more biomass carbon than through tree planting, but its effects on soil respiration (Rs) and its components, autotrophic respiration (Ra) and heterotrophic respiration (Rh), are poorly understood despite the importance in forest carbon cycling. In this study, we clear-cut part of a 35-year-old secondary Castanopsis carelesii (C. carelesii) forest and reforested the logged land with C. carelesii via two approaches—active tree planting and assisted natural regeneration—and measured Rs, Ra, and Rh as well as soil temperature and moisture in these forests. In the first two years following reforestation, Rs, Ra and Rh rates were mostly reduced in the two young forests compared to the secondary forest, likely due to reduced photosynthate production and thus carbon substrate input associated with the clear-cut. However, the Rh:Rs ratio was significantly greater in the young plantation than in the other two forests in the first two years, suggesting a greater loss of soil organic carbon from the young plantation. In the third year, the mean Rs, Rh, and Ra rates of the young forest established via assisted natural regeneration were similar to those of the secondary forest, but significantly greater than those of the young plantation. The rates of Rs, Rh, and Ra mostly increased exponentially with increasing soil temperature in all forests, but mostly lack significant relationships with soil moisture. These findings indicate that, compared with reforestation via tree plantation, assisted natural regeneration not only reduced the loss of soil organic carbon via soil respiration, but also had a more rapid recovery of soil respiration to the level of the secondary forest. Our study highlights that, in addition to temperature, carbon substrate availability is also important in regulating soil respiration following reforestation.

Intake and fixation of organic carbon in grain agrophytocenosis of Western Siberia

In nature, carbon plays an important role in the circulation of organic matter in the soil-plant-atmosphere system. To understand the full picture of the farming system impact on carbon dioxide emissions, long-term stationary experiments are needed, which will reduce the influence of weather conditions on changes in organic carbon stocks in soils and develop an optimal model of the crop cultivation system considering the positive balance of organic carbon in soils. The research was carried out from 1995 to 2020 in the grain crop rotation at the station of the Department of Soil Science and Agrochemistry of the SAU of the Northern Trans-Urals, near vil. Utyashevo in the Tyumen region. Purpose. The purpose of the research was to establish the effect of increasing doses of mineral fertilizers on the intake and fixation of organic carbon with plant residues in the grain agrophytocenosis in the conditions of the forest-steppe zone of the Trans-Urals. The refusal to use mineral fertilizers leads to annual losses of organic carbon in the form of CO2 up to 0.6 t/ha. The use of high doses of mineral fertilizers for the planned yield of 5.0 and 6.0 t/ha of grain annually increases the emission of CO2 by 0.4-0.6 t/ha per year. In these variants, the carbon received from plant residues is not fixed in the soil. A positive balance of organic carbon is provided only by the use of doses of mineral fertilizers for the planned yield of 3.0 and 4.0 t/ha of grain, which annually increases the carbon stock in the soil by 0.4-0.6 t/ha, and up to 14-21% is fixed from the incoming organic carbon in the form of plant residues in the soil.

Prospects of Biochar for Sustainable Agriculture and Carbon Sequestration: An Overview for Eastern Himalayas

The net arable land area is declining worldwide rapidly due to soil erosion, drought, loss of soil organic carbon, and other forms of degradation. Intense rainfall, cultivation along steep slopes, unscientific land-use changes, shifting cultivation, soil acidity, and nutrient mining in hills and mountains make agriculture unsustainable and less profitable. Hills and mountain ecosystems of the Eastern Himalayan Region (EHR) are further prone to the impact of climate change posing a serious threat to agricultural production and the environment. Increasing soil carbon reserves contributes to multiple ecosystem services, improves soil nutrient and water-holding capacities, and advances climate-resilient agriculture. Thus, carbon sequestration is increasingly becoming an important aspect of farming among researchers in the region. The EHR predominantly practices shifting cultivation that degrades the ecosystem and promotes land degradation and biodiversity loss. Leaching of exchangeable bases is highly favored due to excess rainfall which in turn creates an acidic soil accounting for &gt;84% of the region. Application of lime to raise the soil acidity for the cultivation of crops did not get adequate acceptance among the farming community due to multiple issues such as cost involvement, non-availability in time and place, and transportation issues. The application of biochar as soil amendments is widely known to improve soil’s physical, chemical, and biological properties. Biochar has also emerged as a potential candidate for long-term carbon sequestration due to its inbuilt structure and higher stability. Shift from traditional “slash and burn” culture to “slash and char” might lead to the sequestration of carbon from the atmosphere. Around 0.21 Pg of carbon (12% of the total anthropogenic carbon emissions by land-use change) can be sequestered in the soil if the traditional “slash and burnt” practice is converted to “slash and char”. The objective of this review is to provide detailed information about the role of biochar in altering the soil properties for sustaining agriculture and carbon sequestration, especially for hills and mountain ecosystems.

Effect of selected bioengineering measures on runoff, soil loss, and cotton (Gossypium hirsutum L.) productivity in the semi-arid region of western India

Soil erosion and associated loss of soil nutrients and organic carbon are one of the major reasons for low crop productivity in major cotton (Gossypium hirsutum L.) growing areas of India. This calls for designing acceptable and low-cost bioengineering measures to enhance system productivity and soil health. Thus, a field study was conducted at Vasad, Gujarat, India from 2014 to 2017 to evaluate the efficacy of selected bioengineering treatments on cotton crop production and runoff and soil loss. The eight experimental treatments consisted of bio-filters of three grass species, viz.Para (Brachiaria mutica), Guinea (Megathyrsus maximus),and Napier (Pennisetum purpureum) at two strip widths (1 m and 2 m), field bund, and the conventional system as practiced by the farmers of the region. The treatments were tested in 45 × 10 m plots having the gauging facility for recording runoff and soil loss data. Rainfall, runoff, sediment concentration, soil loss, organic carbon, nutrient loss, and growth and yield parameters of grass barrier species and the cotton crop were recorded and analysed. The filter strip of Guinea sp. at 2 m width was most effective, reducing runoff by 30%, soil loss by 66%, nutrients loss by 69%, sediment concentration to 1/3rd, and soil organic carbon loss by 65%. The lowest runoff coefficient value of 0.209 observed among the filter strips in this treatment, indicated about 79% of rainwater was conserved in situ. The available soil nutrients increased by up to 42% and SOC concentration by 61%, and cotton equivalent yield by 25% than that of the conventional system. We concluded that Guinea grass filter strips of 2 m width planted at 45 m spacing in cultivable lands having 2% slope minimized runoff, soil loss, nutrient loss, improved soil fertility and enhanced cotton productivity.

Implication of Macroalgal Bloom to Soil Organic Carbon Stock in Seagrass Meadows - A Case Study in South Hainan, China

The adverse impact of macroalgal blooms associated with nutrient enrichment on seagrass habitats and carbon storage potential is an ecological concern. In the present study, the soil carbon stock and sources were compared between a seagrass meadow where a serious macroalgal bloom occurred (site M) and an adjacent site without apparent macroalgae (site R) in a nutrient-enriched lagoon in South Hainan Island, China, to test whether macroalgal blooms associated with nutrient enrichment would impact the soil carbon in seagrass meadows. The soil organic carbon (OC) and total nitrogen contents in the top 30 cm at site M were significantly lower than those at site R. The soil OC stocks (top 30 cm) were 3.4 and 5.4 Mg C ha-1 at site M and site R, respectively, and no difference was observed between sampling stations with different distances offshore at either site. Soil δ13C was more enriched and closer to the δ13C of seagrass tissues at site R than at site M. Bayesian stable isotope mixing model analyses suggested that seagrass-derived material contributed ~50% to soil OC at site R, while at site M, the contribution was reduced to ~25%. The results suggested that macroalgal blooms associated with nutrient enrichment could drive the loss of seagrass-derived OC and the OC stock in the soil, which is worthy of full attention for blue carbon conservation.

Soil organic carbon accrual due to more efficient microbial utilization of plant inputs at greater long-term soil moisture

High long-term soil moisture may either stimulate or inhibit soil organic carbon (SOC) losses through changes to mineral and chemical composition, and resultant organo-mineral interactions. Yet, the trade-off between mineralization and accrual of SOC under long-term variation in unsaturated soil moisture remains uncertain. We tested the underexplored relationships between long-term soil moisture and organo-mineral chemical composition and its implications for SOC persistence in an experimental field in New York, USA, with differences in long-term mean soil volumetric water content (0–0.15 m depth) ranging from 0.40 to 0.63 (v/v) during the growing season. Long-term soil moisture across 20 subplots on four fallow plots were positively correlated with SOC (R2 = 0.23; P = 0.019, n = 20), mineral-associated organic matter (MAOM) content (g fraction/g soil) (R2 = 0.44; P = 0.001; n = 20) and occluded particulate organic matter (oPOM) content (R2 = 0.18; P = 0.033; n = 20). Higher long-term soil moisture was associated with a decrease in the relative content of sodium pyrophosphate extractable Fe (R2 = 0.33; P < 0.005; n = 20), an increase in sodium dithionite extractable Fe (R2 = 0.44; P < 0.001; n = 20), and an increase in SOC retention by non-crystalline Al pools (R2 = 0.51; P = 0.0002 for sodium pyrophosphate extracts, R2 = 0.41; P = 0.0014 for hydroxylamine hydrochloride extracts; n = 20 for both). Increasing long-term soil moisture was associated with a four-fold increase in microbial biomass C (per unit SOC) and lower metabolic quotient (R2 = 0.56, P < 0.001). MAOM fractions of high-moisture soils had lower C:N (from C:N 9.5 to 9.0, R2 = 0.27, P = 0.011, n = 20). Consistent with decreasing C:N, increasing decomposition with increasing moisture was reflected by a 15% and 10% greater proportion of oxidized carboxylic-C to aromatic-C and O-alkyl C, respectively, as measured with 13C NMR, and a more pronounced FTIR signature of N-containing proteinaceous compounds in high-moisture MAOM fractions, indicative of microbial metabolites and transformation products. A partial least squares regression showed that SOC content increased with greater long-term moisture (P = 0.019), pyrophosphate-extractable Al (P = 0.0001), and exchangeable Ca (P = 0.013). Taken together, our results show that higher long-term soil moisture resulted in SOC accrual by enhancing conversion of plant inputs into microbial biomass that interacts with reactive minerals.

Effects of land use change on soil carbon and nitrogen in purple paddy soil

Rural land use patterns in southern China centered on household grain crop production have observed significant changes in the past few decades, profoundly affecting the release and fixation of carbon and nitrogen in the paddy soil of the region. This study selected different land use patterns developed in purple paddy soil on a decadal time scale, examined the changing rate of soil carbon and nitrogen of the purple paddy soil after abandonment, dry-farming, and fish-farming, and revealed the impact of land use changes on the balance of soil carbon and nitrogen. Results showed that the loss rates of soil organic carbon, readily oxidizable organic carbon and total nitrogen at the initial stage of dry-farming were most considerable, followed by abandonment and fish-farming. An average of 11.95–13.94 g kg−1 soil organic carbon loss and 0.90–1.03 g kg−1 total nitrogen loss of the cultivation horizon were observed when purple paddy soil was abandoned and dry farmed. In comparison, the net release of soil organic carbon and total nitrogen after fish-farming were 6.64 and −0.23 g kg−1. The changes of land use of rural area driven by rising labor cost and market demand have been inducing a continuous decline in soil C:N and significantly reducing the purple paddy soil's carbon sequestration ability. The promotion of no-tillage management, increase of organic manure application, and avoidance of over-use of nitrogen fertilizer in dryland farming need to be further considered to meet the dual pressures of China's resource constraints and carbon neutrality goals. A regression model may predict the changes in soil carbon after the change of paddy soil utilization, which provides a pathway for predicting changes in farmland carbon sequestration potential and carbon storage caused by changes in paddy soil utilization in the future.

Prediction of soil organic carbon in mining areas

Coal mining activities have destroyed natural landscapes and surface vegetation, resulting in a large loss of soil organic carbon (SOC) storage in farmlands. Therefore, farmland SOC mapping in mining areas is of great significance to low-carbon reclamation and ecological compensation. Natural factors such as topography, climate, vegetation, and soil properties are key variables for SOC mapping. Human activities, including crop rotation and farmland damage caused by coal mining, also severely interfere with farmland SOC in mining areas. Here, we use take mining areas of the Changhe watershed as a case study to explore the effects of these activities on farmland SOC storage. Farmland damage was quantified using mining area geological hazard data, and four random forest (RF) models were constructed to predict SOC content based on natural variables alone (RF-N), natural variables + crop rotation (RF-C), natural variables + farmland damage (RF-F), and natural variables + crop rotation + farmland damage (RF-A). We found that: (1) the RF-A model most accurately captured SOC spatial differentiation information (followed by RF-C, RF-F, and RF-N). (2) There were significant differences in the SOC of different crop rotation areas and between low and high damage farmlands; specifically, the SOC content of wheat-corn rotations (one-year two cropping system) was higher than wheat-soybean-corn rotations (two-year three cropping system) and wheat (one-year one cropping system), and the SOC of high damage farmlands was lower than that of low damage farmlands. (3) Variable importance analysis showed that crop rotation and farmland damage were the two most important variables for predicting SOC in mining areas—demonstrating the effectiveness of common farming practices in predicting SOC in mining areas. Our results provide a scientific basis for land reclamation, soil carbon input, and land remediation planning in mining areas.