Greater Soil Organic Carbon Stocks Research Articles

Mung Bean Is Better Than Soybean in the Legume–Wheat Rotation System for Soil Carbon and Nitrogen Sequestration in Calcareous Soils of a Semiarid Region

Small changes in soil aggregates-associated organic carbon and soil nitrogen (N) can induce huge fluctuations in greenhouse gas emissions and soil fertility. However, there is a knowledge gap regarding the responses to long-term continuous rotation systems, especially in N-fixing and non-N-fixing crop wheat in terms of the distribution of soil aggregates and the storage of soil carbon (C) and N in aggregates in the semiarid calcareous soil of Central China. This information is critical for advancing knowledge on C and N sequestration of soil aggregates in rainfed crop rotation systems. Our aim was to determine which legume (soybean (Glycine max)– or mung bean (Vigna radiata)–wheat (Triticum aestivum) rotation practice is more conducive to the formation of good soil structure and C and N fixation. A 10-year field experiment, including a soybean (Glycine max)–winter wheat (Triticum aestivum) rotation (SWR) with yield increments of 2020 compared to 2010 achieving 18.28% (soybean) and 26.73% (wheat), respectively, and a mung bean (Vigna radiata)–winter wheat rotation (MWR) achieving 32.66% (mung bean) and 27.38% (wheat), as well as farmland fallow, was conducted in Henan Province, China. The soil organic carbon (SOC), N content in the soil, and the soil aggregates were investigated. Legume–wheat rotation cropping enhanced the proportion of the >2 mm soil fractions and reduced the <0.053 mm silt + clay in the 0–40 cm soil profile. In the 0–30 cm soil layer, the SWR had a greater increment of the >2 mm aggregate fractions than the MWR. Two legume–winter wheat rotations enhanced the C and N sequestration that varied with soil depths and size fractions of the aggregate. In contrast, the MWR had greater SOC stocks in all fractions of all sizes in the 0–40 cm soil layers. In addition, the greater storage of N in the macro-, micro-, and silt + clay fractions was observed in the 0–30 cm layers; the MWR enhanced the C/N ratios in most of the size aggregates compared with the SWR. The MWR cropping system is more beneficial to the formation of good soil structure and the increasement of C and N reserves in soil. Thus, these findings show that mung bean, in contrast with soybean in the legume–wheat rotation system of a semiarid temperate zone, may offer soil quality improvement.

Evaluation of soil organic matter from integrated production systems using laser-induced fluorescence spectroscopy

Agricultural areas under integrated production systems, such as Integrated Crop-Livestock-Forest System (CLFS), have the potential to sequestrate carbon (C) since both Soil Organic Matter (SOM) content and trees biomass increase thus mitigating the emission of greenhouse gases (GHGs) from agriculture. Regarding soil aspects, the C content stands out as the main indicator, but the structural aspect of SOM is also relevant since it plays a key role in the chemical stability of C compounds and the soil lifetime of C compounds. Laser-Induced Fluorescence Spectroscopy (LIFS) is an effective technique to evaluate the SOM humification index (HLIFS) from practically intact whole soil samples under different agricultural systems. Thus, the objective of this study was to analyze the SOM humification index in different integrated systems, such as Integrated Crop-Livestock-Forest System (CLFS), Integrated Livestock-Forest System (LFS), Integrated Crop-Livestock System (CLS), and in references areas, such as Intensive Pasture (INT), Extensive Pasture (EXT) and Native Forest (NF). For this purpose, samples of Red-yellow Latosol (Haplorthox by Soil taxonomy) from the experimental site located at Embrapa Pecuária Sudeste (Southeast of Brazil) were collected five years after the establishment of the integrated systems. Samples were collected at soil depths of 0–5, 5–10, 10–20, 20–30, 30–40, 40–60, 60–80, and 80–100 cm. Pellets of the whole soil samples were prepared for LIFS analysis. In these areas, SOM humification indices (HLIFS) presented the following descending order: CLS > EXT > INT > LFS > CLFS > NF. Previous results have shown a greater soil organic carbon stock in these integrated production systems than in the NF area, suggesting C sequestration in agricultural soil. In the present study, SOM was classified by LIFS as more chemically stable in integrated production systems than in native vegetation. Higher amounts of fluorescent compounds were identified from LIFS data, probably resulting from condensed aromatic groups. SOM with more recalcitrant groups normally has a longer lifetime in the soil, indicating a long-term contribution to mitigating climate change by avoiding fast SOM decomposition and CO2 return to the atmosphere. Also, for the first time, this study was able to identify a positive correlation (R = 0.79) between the SOM humification index (HLIFS) and the Cation Exchange Capacity (CEC)/C content ratio of whole soil samples, another innovative contribution from soil LIFS analyses.

Short- and long-term effects of animal manures and mineral fertilizer on carbon stocks in subtropical soil under no-tillage

Establishing the long-term effects of different types of animal manures on soil organic carbon (SOC) stocks has both agronomic and environmental implications. However, only a few studies have analyzed the effects of the types of animal manure on SOC storage in subsurface soil layers. Furthermore, the effect of animal manure on labile and stable soil organic matter (SOM) fractions has been scarcely reported for subtropical no-till soils. We evaluated the effect of animal manure application in the short and long term (4 and 12 years) on SOC storage at different depths throughout a 0–70 cm soil profile and on the physical fractions of SOM in the 0–20 cm layer of a sandy Alfisol cropped under no-tillage. The study involved five treatments: pig deep-litter (PDL), cattle slurry (CS), pig slurry (PS), mineral fertilizer (MF) and a control without fertilization (CL). The SOC stock in the soil profile (0–70 cm) was influenced by manure application in only the long term, which was due to high SOC accumulation in the surface (0–20 cm) in the short-and long-term. The PDL and CS applications resulted in 16% (8.6 Mg ha−1) and 10% (5.2 Mg ha−1) increases in the SOC stock, respectively, compared with those in the CL, but only PDL resulted in greater SOC stocks than MF. These results are related to the greater C addition and higher SOC retention coefficient with the PDL application (17%) than with the CS (15%) and PS (7%) applications. Most of the manure-induced changes were observed in the silt plus clay-sized heavy fraction (SCHF), with PDL and CS being more efficient at increasing SOC storage as organic-mineral complexes than PS or MF in the 0–20 cm soil layer. However, in the subsurface layer (20–70 cm), manure caused a decrease in SOC compared with that in the CL, resulting in negative SOC storage rates in this layer, which partially or completely neutralized the SOC storage rates observed in the surface layer (0–20 cm). In the long term, this condition resulted in SOC storage rates in the 0–70 cm soil profile of 0.48 Mg ha−1 year−1 for PDL, 0.21 Mg ha−1 year−1 for CS, −0.03 Mg ha−1 year−1 for PS and 0.01 Mg ha−1 year−1 for MF. These results indicate that PDL and CS are suitable alternatives to MF for increasing the SOC stock and that the SOC retention is greater with solid manure than with liquid manure (PDL vs CS and PS) and with CS than with PS. Moreover, the results reveal the importance of monitoring SOC changes in the long term and within deep soil layers to better quantify the effects of successive applications of animal manure on SOC storage potential in subtropical sandy soils under no-tillage.

Effect of Fast-Growing Trees on Soil Properties and Carbon Storage in an Afforested Coal Mine Land (India)

Surface coal mining activities have numerous consequences on terrestrial ecosystems. Loss of soil and biomass carbon pool due to mining activities is a serious concern in the rapidly changing environment. We investigated the effect of fast-growing trees (Albizia lebbeck, Albizia procera, and Dalbergia sissoo) on soil fertility and ecosystem carbon pool after eight years of afforestation in the post-mining land of Jharia coalfield, India, and compared with the adjacent natural forest site. Significant differences in soil organic carbon (SOC) and total nitrogen (TN) stocks in afforested mine soil and natural forest soils were observed. Greater SOC stock was found under D. sissoo (30.17 Mg·C·ha−1) while total N stock was highest under A. lebbeck (4.16 Mg·N·ha−1) plantation. Plant biomass accumulated 85% of the natural forest carbon pool after eight years of afforestation. The study concluded that planting fast-growing trees in post-mining lands could produce a promising effect on mine soil fertility and greater carbon storage in a short period.

Bioenergy crop induced changes in soil properties: A case study on Miscanthus fields in the Upper Rhine Region.

Biomass as a renewable energy source has become increasingly prevalent in Europe to comply with greenhouse gas emission targets. As one of the most efficient perennial bioenergy crops, there is great potential in the Upper Rhine Region to explore biomass utilization of Miscanthus to confront climate change and land use demand in the future. Yet, the impacts of Miscanthus cultivation on soil quality have not been adequately explored. This study investigated the soil profiles of five- and 20-year-old Miscanthus fields (1 m depth) as well as grassland for reference in eastern France and Switzerland. The soil organic carbon (SOC) concentrations and δ13C compositions of four soil layers (0–10 cm, 10–40 cm, 40–70 cm and 70–100 cm) were determined. The CO2 emission rates of the topsoil were monitored for 42 days. Our results showed that Miscanthus, in general, could increase the SOC stocks compared to grassland, but the benefits of SOC sequestration were constrained to the surface soil. Isotopically, the Miscanthus-derived SOC ranged from 69% in the top 10 cm of soil down to only 7% in the 70 cm to 100 cm layer. This result raises the risk of overestimating the total net benefits of Miscanthus cultivation, when simply using the greater SOC stocks near the surface soil to represent the SOC-depleted deep soil layers. The Miscanthus fields had greater CO2 emissions, implying that the Miscanthus fields generated greater ecosystem respiration, rather than larger net ecosystem exchanges. Compared to the grassland soils, the surface soils of the Miscanthus fields tended to have a risk of acidification while having higher concentrations of phosphorus and potassium, calling for the inclusion of soil characteristics and SOC stability when evaluating the impacts of long-term Miscanthus cultivation on both current and future land use changes.

Soil organic carbon stocks in three Canadian agroforestry systems: From surface organic to deeper mineral soils

Our understanding of the effect of agroforestry systems on soil organic carbon (SOC) is largely limited to the upper layer of the mineral soil, while LFH (litter, partially decomposed litter and humus) and deeper soil layers are poorly studied. In this study, the effects of three different agroforestry systems (hedgerow, shelterbelt, and silvopasture) and their component land-cover types (treed area and adjacent herbland) on SOC stock in LFH and mineral soil layers (0–75 cm) were investigated across 36 sites in central Alberta, Canada. The SOC stock of mineral soil (0–75 cm) was not affected by agroforestry systems but by land-cover type. The treed area had greater (p < 0.001) SOC in the 0–75 cm mineral soil (25.5 kg C m−2) than the herbland (19.4 kg C m−2), driven by the greater (p < 0.001) SOC level in the top 0–30 cm rather than that in the deeper layers (30–75 cm). Within the treed area, the silvopasture system that was dominated by broad-leaf deciduous trees had 56–70% more SOC in the 0–10 cm soil than in the hedgerow and shelterbelt systems. The SOC stock in the 0–10 cm layer was positively (p = 0.025) related to the C stock of the overlying LFH layer in the silvopasture system. These results together with the 22–24% higher dissolved organic carbon (DOC) concentration in the silvopasture than in the other systems suggest that the greater SOC stock in the 0–10 cm mineral soil could be attributed to the higher rates of translocation of DOC from the LFH in the silvopasture than that in shelterbelt or hedgerow. We conclude that SOC stock in the top mineral soil (e.g., 0–30 cm) is more responsive to changes in land-cover type and the LFH layer plays an important role in increasing SOC stock in the surface mineral soil of the agroforestry systems in central Alberta.

Soil organic carbon and nitrogen sequestration and turnover in aggregates under subtropical leucaena–grass pastures

Stabilisation and protection of soil organic carbon (SOC) in macroaggregates and microaggregates represents an important mechanism for the sequestration of SOC. Legume-based grass pastures have the potential to contribute to aggregate formation and stabilisation, thereby leading to SOC sequestration. However, there is limited research on the C and N dynamics of soil organic matter (SOM) fractions in deep-rooted legume leucaena (Leucaena leucocephala)–grass pastures. We assessed the potential of leucaena to sequester carbon (C) and nitrogen (N) in soil aggregates by estimating the origin, quantity and distribution in the soil profile. We utilised a chronosequence (0–40 years) of seasonally grazed leucaena stands (3–6 m rows), which were sampled to a depth of 0.3 m at 0.1-m intervals. The soil was wet-sieved for different aggregate sizes (large macroaggregates, &gt;2000 µm; small macroaggregates, 250–2000 µm; microaggregates, 53–250 µm; and &lt;53 µm), including occluded particulate organic matter (oPOM) within macroaggregates (&gt;250 µm), and then analysed for organic C, N and δ13C and δ15N. Leucaena promoted aggregation, which increased with the age of the leucaena stands, and in particular the formation of large macroaggregates compared with grass in the upper 0.2 m. Macroaggregates contained a greater SOC stock than microaggregates, principally as a function of the soil mass distribution. The oPOM-C and -N concentrations were highest in macroaggregates at all depths. The acid nonhydrolysable C and N distribution (recalcitrant SOM) provided no clear distinction in stabilisation of SOM between pastures. Leucaena- and possibly other legume-based grass pastures have potential to sequester SOC through stabilisation and protection of oPOM within macroaggregates in soil.

Soil property and soil organic carbon pools and stocks of soil under oases in arid regions of Tunisia

In Tunisia, the lowest soil organic carbon stocks are attributed to arid soils. This study was conducted to assess and to quantify soil organic carbon (SOC) stocks and pools under oases agrosystems in arid regions of Tunisia. Soil samples were collected from 0- to 5-cm and from 0- to 30-cm layer depth from two principal types of soils (Lithosols and Solonchaks) under three oases. Total SOC, particulate organic carbon (POC) and SOC < 50 µm content and stocks were calculated. The results showed that Lithosols contain the highest SOC content (1.11%). However, Solonchaks accumulate the highest POC. Both Lithosols and Solonchaks store large amount of SOC < 50 µm. Particularly in 0–5-cm layer, negative and significant correlation was found between POC and bulk density (BD) in Lithosols but in Solonchaks POC was positively correlated with BD. On average SOC stocks in Lithosols in 0–5-cm layer are above those calculated for Solonchaks and not exceed 0.81 kg C/m2. The greater SOC stocks in 0–30 cm depth characterize Lithosols (4.33 kg C/m2). SOC stocks for Solonchaks were below 3.19 kg C/m2. Otherwise, differences in POC stocks were observed in 0–30-cm layer between soils. Solonchaks store between 0.98 and 1.24 kg C/m2 of POC. The proportion of POC stocks relative to the total SOC stock is <25% in two types of soil. Organic carbon stocks are mostly stable, as SOC < 50 µm stocks reached over 70% of SOC. We can suggest that arid soils have high capacity to store organic carbon under oasis agrosystems.

Grazing land intensification effects on soil C dynamics in aggregate size fractions of a Spodosol

Impacts of land intensification on soil organic carbon (SOC) responses are important components of sustainable management evaluation. Because of poor aggregation often associated with coarse-textured soils and the limited potential for chemical and physical protection of SOC, we hypothesized that the fine aggregate fraction (<53μm) represents an important sink for SOC stabilization in sandy soils. We investigated the impacts of converting native rangeland ecosystems into intensively managed pastures on SOC stocks and the distribution and decomposition rates of C associated with aggregate size fractions in a Coastal Plain Spodosol. Experimental sites consisted of three grazing land biomes: native rangelands, pine (Pinus elliottii Engelm)–bahiagrass (Paspalum notatum Fluegge) silvopasture, and improved pastures under similar soil and climate conditions, but subjected to different management intensities. As grazing land intensification increased, SOC stock (0- to 20-cm depth) increased. Greater SOC stock was associated with improved pasture and silvopasture (53Mg C ha−1) as compared to the native rangeland ecosystem (35Mg C ha−1). This response was due the introduction of more productive plant species (i.e., warm-season C4 grass) augmented by N fertilization. δ13C signature of the improved pasture (−14.7‰ to −18.8‰) reflected the influence of introduced C4 pasture grass, while the native rangeland and silvopasture showed more negative δ13C values (−20.3‰ to −22.7‰). Grazing land intensification affected C associated with the <53-μm aggregate size fraction, representing clay- and silt-protected SOC. Unlike previous studies that indicated that C associated with fine aggregate size represents a resistant C pool, our data suggested the <53-μm fraction of a Spodooil is dynamic and is susceptible to changes in response to land use intensification.

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

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

Carbon input differences as the main factor explaining the variability in soil organic C storage in no-tilled compared to inversion tilled agrosystems

Conversion to no-till (NT) is usually associated to increased soil organic carbon (SOC) stocks in comparison to inversion tillage (IT). However, an important and unexplained variability in the changes in SOC with NT adoption exists, which impedes accurate prediction of its potential for C sequestration. We performed a meta-analysis with pedo-climatic and crop factors observed to influence SOC storage under NT at local and regional scales, in order to determine those better explaining this variability at a global scale. We studied SOC stocks (0–30 cm) in an equivalent soil mass, climatic and soil characteristics in 92 NT–IT paired cases. A sub-base with the 35 pairs providing C inputs was used to test their effect. Greater SOC stocks were observed with NT, with a smaller difference than often described (6.7%, i.e. 3.4 Mg C ha−1). Crop C inputs differences was the only factor significantly and positively related to SOC stock differences between NT and IT, explaining 30% of their variability. The variability in SOC storage induced by NT conversion seems largely related to the variability of the crop production response. Changes at the agro-ecosystem level, not only in soil, should be considered when assessing the potential of NT for C sequestration.