Aggregate Soil Organic Carbon Research Articles

Impact of Road Construction and Agriculture on Soil Aggregate Stability and Aggregate-Soil Organic Carbon: Ultisols of Derived Savannah

Impact of Road Construction and Agriculture on Soil Aggregate Stability and Aggregate-Soil Organic Carbon: Ultisols of Derived Savannah

Soil aggregate organic carbon and clover root characteristics as affected by earthworms (Metaphire guillelmi)

AbstractSoil aggregate composition is an important factor that affects soil organic carbon (SOC) content. Earthworms can greatly affect soil aggregate composition. However, the effects of earthworms' activities on SOC content in soil aggregates and the stability of these compounds was not clear. To reveal the mechanism of earthworms impacts on soil carbon stock, different earthworms densities were set in soil columns planted with clovers (Trifolium repens L.). We then analyzed the relationship that earthworms had with soil physicochemical properties and clover plant growth. Earthworms increased the large (17.5%–35.6%) and medium aggregate content (0.6%–9.79%) and decreased the microaggregates content (19.8%–29%) of the surface soil. Soil aggregates in medium density treatment were more stable than those in others. Both the mean mass diameter and geometric mean diameter of soil aggregates increased with the densities of earthworms. The average SOC content in large‐, medium‐, and microaggregates were 5.5, 4.2, and 4.2 g kg−1 respectively in soils seeded with earthworms. There was a significant correlation between soil organic carbon content and macroaggregate organic carbon content (R2 = 0.623, p < 0.05). The root characteristic values (root length, surface area, diameter, and biomass) of earthworm‐treated clover‐planted soils were higher than those of control. Clover root indices were positively correlated with the soil organic carbon content and soil aggregates. Earthworms altered the soil aggregate content and enhanced soil organic carbon storage, and thus promoted the development of vegetation roots. This study provides scientific support for a deeper understanding of the mechanisms of earthworms in soil carbon storage.

Effect of Clay Mineralogy and Soil Organic Carbon in Aggregates under Straw Incorporation

The interaction between soil organic carbon (SOC) and clay minerals is a critical mechanism for retaining SOC and protecting soil fertility and long-term agricultural sustainability. The SOC composition and minerals speciation in clay fractions (<2 μm) within soil aggregates under straw removed (T) and straw incorporation (TS) conditions were analyzed by X-ray diffraction, Fourier transform infrared spectra and X-ray photoelectron spectroscopy. The TS treatment promoted enrichment of clay in aggregates. The TS increased the contents of SOC (27.0–86.6%), poorly crystalline Fe oxide (Feo), and activity of Fe oxides (Feo/Fed); whereas, it reduced the concentrations of free Fe oxide (Fed) in the clay fractions within aggregates. Straw incorporation promoted the accumulation of aromatic-C and carboxylic-C in the clay fraction within aggregates. The relative amount of hydroxy-interlayered vermiculite, aliphatic-C, and alcohol-C in the clay fractions within the macroaggregates was higher than that microaggregates, whereas the relative amounts of illite, kaolinite, Fe(III), and aromatic-C had a reverse tendency. The hydroxy-interlayered vermiculite in clay fractions showed positive correlation with the amounts of C–C(H) (r = 0.93) and C–O (r = 0.96 *, p < 0.05). The concentration of Feo and Feo/Fed ratio was positively correlated with the amounts of C=C and C(O)O content in clay within aggregates. Long-term straw incorporation induced transformation of clay minerals and Fe oxide, which was selectively stabilized straw-derived organic compounds in clay fractions within soil aggregates.

Chemical structure characteristics of organic carbon in saline soil aggregates under straw returning condition

We examined the regularity of distribution and chemical structure characteristics of organic carbon in soda alkaline fluvo-aquic soil aggregates after straw returning. We set up six different straw returning treatments in 2020, including 0 (CK), 2100 (ST1), 4200 (ST2), 6300 (ST3), 8400 (ST4) and 10500 kg·hm-2(full straw returning, ST5). We measured organic carbon (OC) content and infrared spectroscopy characteristics of aggregates and internal different components through physical fractionation method and infrared spectroscopy technology. The results showed that: 1) the OC content of soil and all aggregates increased with the increasing amount of returned straw; 2) different straw returning treatments significantly increased the content of light organic carbon (LOC) in 53-250 μm aggregates. Compared with CK, ST3 and ST4 treatments significantly increased the content of mineral-bound organic carbon (MOC) in 250-2000 μm aggregates and the content of fine particulate organic carbon (fPOC) in 53-250 μm aggregates. The OC content of different components in aggregates followed the order of LOC>MOC>POC. The fPOC content in 250-2000 μm aggregates was higher than that of coarse particulate organic carbon (cPOC); 3) the results of principal component analysis showed that OC chemical structure of different components in aggregates was seldom affected by the straw returning, but was mainly affected by particle size; 4) the OCs in >250 μm aggregates were mainly derived from aromatic carbon and polysaccharides. The OCs in 53-250 μm aggregates were mainly derived from carbohydrates, such as monosaccharides and polysaccharides, while the OC in <53 μm aggregates was mainly derived from aliphatic carbon, alkyl carbon, aromatic carbon and phenolic alcohols. Within different aggregates, LOC was mainly derived from aliphatic carbon, aromatic carbon and phenolic alcohols. Particulate organic carbon (POC) was mainly derived from carbohydrates. MOC was mainly derived from alkyl carbon. In summary, straw returning increased organic carbon content in soil aggregates in short term, but did not alter organic carbon chemical structure. The organic carbon chemical structures of the same particle size fractions in different aggregates were similar. The organic carbon content increased with the decreases of particle size, and the chemical structure tended to be stable. Therefore, straw returning promoted the fixation of organic carbon by saline soil aggregates in short term, but did not change their chemistry structural characteristics, indicating that the location and protection degree of soil organic carbon in aggregates were the main factors affecting the chemical structure of organic carbon.

Dynamics of water-stable aggregates associated organic carbon assessed from delta C-13 changes following temperate natural forest development in China

In the context of global climate change, the preservation of soil productivity and the estimation of carbon budgets and cycles, the quantification of changes in carbon has important significance. In this study, we investigated the dynamics of soil aggregate associated organic carbon (OC) following temperate natural forest development in China. The objectives of this study were to examine the variation of soil aggregate associated OC decomposition rates, quantify the changes in the proportion of new and old soil aggregate OC, and explore the effects of controlling factors on SOC stocks, rate of total SOC increase and decomposition rate constants. The results showed that soil aggregate associated OC sequestration increased in 0−10 cm soil depth, while decreased in 10−30 cm soil depth. However, rate of aggregate associated OC increase, decomposition rate constants, and proportion of new OC increased at the early stage and then decreased along with the natural vegetation restoration. In addition, land use change had an important effect on soil aggregate associated OC dynamics, and soil particles, BD, MWD, C: N, plant diversity also played an important role. Moreover, SOC stocks had a negative relationship with clay and silt, while had a positive relationship with MWD and sandy soils. decomposition rate constants had a negative relationship with plant diversity, silt, and sand, while had a positive relationship with C: N and MWD. The proportions of new SOC had significant positive relationships with C: N, and it had a negative relationship with clay and silt. Therefore, it is necessary to clarify the formation mechanism of soil particles and aggregates, improve plant biodiversity, regulate the soil C: N ratio, and improve soil particle structure to increase soil carbon sequestration.

Mean Residence Time of Soil Organic Carbon in Aggregates Under Contrasting Land Uses Based on Radiocarbon Measurements

Radiocarbon is a useful tool for studying carbon dynamics in soil aggregates. The objective of the current study was to determine the mean residence time (MRT) of soil organic carbon (SOC) in macroaggregates and microaggregates under contrasting land uses. Contrasting land uses investigated at Alfisol (equivalent to Dermosol in Australian Soil Classification) sites were native pasture (NP), crop-pasture rotation (CP), and Eucalypt woodland (WL), whereas in Oxisol (Ferrosol in Australian Soil Classification) sites, land uses comprised improved pasture (IP), cropping (CR), and forest (FR). Soil aggregates were separated into macroaggregates (250–2000 μm) and microaggregates (53–250 μm) by wet-sieving, and their14C signatures were determined by accelerator mass spectrometry (AMS). The14C activity in both macro- and microaggregates was &amp;gt;100 pMC, indicating the presence of post-bomb carbon in the soil. The mean residence time (MRT) of SOC in macro- and microaggregates (MRTagg) was on average 68 yr longer in the Oxisol compared with that in the Alfisol. The MRTaggin microaggregates was 10 yr longer than that of macroaggregates in the Alfisol. However, the MRTaggin microaggregates was 50 yr shorter compared to macroaggregates in the Oxisol.The MRT of macro- and microaggregates can be separated into active, slow, and stable SOC pools. Among the 3 SOC pools, the MRT of the stable pool is of higher significance in terms of SOC stabilization in soil aggregates because of its longer MRT. However, isolation and direct MRT estimation of the stable SOC pool is difficult. The MRT of active and slow SOC pools associated with macro- and microaggregates was measured using a SOC mineralization experiment to estimate the MRT of the stable SOC pool under contrasting land uses by applying a mass balance criterion. The MRT of active (MRTA) and slow (MRTS) SOC pools in macro- and microaggregates varied between 1–50 days and 13–38 yr, respectively. The estimated MRT of the stable pool carbon (MRTP) in microaggregates was 897 yr longer compared to that of macroaggregates in the Alfisol. However, in the Oxisol, MRTPin microaggregates was 568 yr shorter than that of macroaggregates. Among the land uses, WL in Alfisol and CR in Oxisol had longer MRTaggand MRTPcompared to other land uses.

Mean Residence Time of Soil Organic Carbon in Aggregates Under Contrasting Land Uses Based on Radiocarbon Measurements

Radiocarbon is a useful tool for studying carbon dynamics in soil aggregates. The objective of the current study was to determine the mean residence time (MRT) of soil organic carbon (SOC) in macroaggregates and microaggregates under contrasting land uses. Contrasting land uses investigated at Alfisol (equivalent to Dermosol in Australian Soil Classification) sites were native pasture (NP), crop-pasture rotation (CP), and Eucalypt woodland (WL), whereas in Oxisol (Ferrosol in Australian Soil Classification) sites, land uses comprised improved pasture (IP), cropping (CR), and forest (FR). Soil aggregates were separated into macroaggregates (250–2000 μm) and microaggregates (53–250 μm) by wet-sieving, and their 14C signatures were determined by accelerator mass spectrometry (AMS). The 14C activity in both macro- and microaggregates was &gt;100 pMC, indicating the presence of post-bomb carbon in the soil. The mean residence time (MRT) of SOC in macro- and microaggregates (MRTagg) was on average 68 yr longer in the Oxisol compared with that in the Alfisol. The MRTagg in microaggregates was 10 yr longer than that of macroaggregates in the Alfisol. However, the MRTagg in microaggregates was 50 yr shorter compared to macroaggregates in the Oxisol.The MRT of macro- and microaggregates can be separated into active, slow, and stable SOC pools. Among the 3 SOC pools, the MRT of the stable pool is of higher significance in terms of SOC stabilization in soil aggregates because of its longer MRT. However, isolation and direct MRT estimation of the stable SOC pool is difficult. The MRT of active and slow SOC pools associated with macro- and microaggregates was measured using a SOC mineralization experiment to estimate the MRT of the stable SOC pool under contrasting land uses by applying a mass balance criterion. The MRT of active (MRTA) and slow (MRTS) SOC pools in macro- and microaggregates varied between 1–50 days and 13–38 yr, respectively. The estimated MRT of the stable pool carbon (MRTP) in microaggregates was 897 yr longer compared to that of macroaggregates in the Alfisol. However, in the Oxisol, MRTP in microaggregates was 568 yr shorter than that of macroaggregates. Among the land uses, WL in Alfisol and CR in Oxisol had longer MRTagg and MRTP compared to other land uses.

Accumulation of soil organic carbon in aggregates after afforestation on abandoned farmland

To understand how organic C (OC) accumulates in afforested soils and to quantify the contribution of aggregate-associated OC to OC accumulation, we investigated the changes in soil structure, total soil OC, and aggregate-associated OC from 0- to 10- and 10- to 20-cm depths in afforested forests and adjacent farmlands of northwestern China. We assessed the contribution of macroaggregate-associated OC increase to total soil OC accumulation. Afforestation increased macroaggregate amount, mean weight diameter, and mean geometric diameter but decreased the amount of microaggregate and silt + clay-sized fractions. The improvement of soil structure was greater in surface than subsurface soils and was greater in soils afforested with white birch than in soils afforested with other tree species. Fifty years after afforestation, total soil OC concentrations and stocks and aggregate-associated OC concentrations increased depending on soil depth and tree species. Afforestation increased macroaggregate-associated OC stocks but decreased microaggregate- and silt + clay-associated OC stocks. Soil OC stocks and changes in OC stocks after afforestation mainly depended on macroaggregate-associated OC stocks and their changes. The results from this study suggest that OC accumulation in afforested soils is due to the accumulation of OC in macroaggregates and the redistribution of OC from fine particles to coarser fractions.

Effects of agricultural management systems on soil organic carbon in aggregates of Ustolls and Usterts

Soil erosion contributes to the removal and redistribution of soil organic C from cultivated fields. The soil organic C content of wind erodible and water unstable aggregates is an important factor in determining the amount of carbon loss occurring in erosion processes. The relative distribution of organic carbon among aggregate size fractions may also affect the response of soils to erosion. Soil organic C distribution is dependent on the chosen management system. The effects of no-till, till, and grassland management systems on organic C content of erodible and non-erodible aggregates were examined in six Ustolls and two Usterts of central South Dakota. Organic C contents were related to dry- and wet-sieving to represent the potential influence of wind and water erosion on C loss in the absence of vegetative cover. Loss of aggregate stability in cultivated soils was associated with organic C loss. Most structural characteristics developed under tilled systems persisted after 6–16 years of no-till. Changes in distribution of organic C due to management systems were most evident in Ustolls where cultivation resulted in net soil C losses. Soil organic C was not significantly increased by the no-tillage practices applied in this on-farm study (in Ustolls 49 Mg ha −1 in no-till versus 41 Mg ha −1 in till, for 0–0.20 m depth). Soil properties of Usterts were less affected by land use and management practices due to the high shrink swell action and self-mixing. In both soil orders the greater concentration of organic C in the wind erodible (<1 mm) dry aggregate size fraction implies a high potential for organic C loss by erosion in addition to organic C loss from mineralization after tillage. Grassland when compared to cultivated topsoil showed the largest amounts of organic carbon stored and the minimal potential for erosion loss of soil organic C.

The physical protection of soil organic carbon in aggregates: a mechanism of carbon storage in a Vertisol under pasture and market gardening (Martinique, West Indies)

Abstract Soil aggregation can influence the storage of carbon in soil. The role of soil structure on soil respiration was investigated by destructive treatment (crushing, dry–wetting events). The soil was a Vertisol under market gardening, a 5-year-old pasture and a long-term pasture. When the soil structure was affected by crushing, soil respiration increase from 1 to 3.4 times. This increase, which represented the amount of protected soil organic carbon (SOC), was much higher in soil under pasture than under market gardening cultivation. There was a positive correlation between the amount of protected SOC and total SOC content. The rate of decay of the protected SOC seemed to be slightly higher than the rate of decay of the unprotected SOC. Because Vertisol is a clayey soil dominated by 2/1 clays, it showed a high capacity to protect mineralisable SOC from mineralisation in macro-aggregates compared with literature results. Even if the protected SOC in aggregates amounted to less than 10% of the total SOC, it represented more than 50% of the mineralisable SOC of a pasture soil. This mechanism seemed then to be an important factor to understand SOC storage in soil under pasture.