Passive Carbon Pools Research Articles

Early-stage soil organic carbon stabilization in conservation agriculture-based cereal systems

In South Asia, the sustainability of conventional tillage and input-intensive cereal-based cropping systems (such as rice-rice and rice-wheat) is under scrutiny due to soil organic carbon depletion, stagnant productivity, and adverse environmental impacts stemming from greenhouse gas emissions (N2O, CH4, and CO2). Against this backdrop, a long-term field experiment was initiated in 2009 at three sites in India (Karnal, Patna, and Aduthurai) and one site in Bangladesh (Gazipur) to assess four scenarios (S) reflecting current and future diversified crop rotations and conservation agriculture (CA) practices: S1 - double cereal rotation with conventional practices; S2 - double cereal plus legume rotation with partial CA; S3 - double cereal plus legume rotation with full CA; and S4 - futuristic diversified cereal-legume rotations with full CA. This study delved into the dynamics and stabilization of soil organic carbon across all scenarios and sites. Replicated soil samples were collected from depths of 0–15 cm and 15–30 cm after two crop cycles. We analyzed Walkley-Black carbon (WBC), total organic carbon (TOC), and various carbon pools with different oxidizability, determining the amount of carbon stabilized under CA-based scenarios and identifying optimal systems for carbon economy in South Asia. On average, active and passive carbon pools, TOC, and WBC stocks followed the order: S4 > S3 > S2 > S1 at all sites, except Gazipur, where the order was S3 > S4 > S2 > S1. CA practices stabilized applied carbon inputs to soil organic carbon at an annual rate of 1.7 %, with greater stabilization observed under S4 (11.7 %) > S3 (10.6 %) > S2 (7.8 %), regardless of location. Rice-rice sites exhibited a higher carbon stabilization rate (13.4 %) compared to rice-wheat sites (6.7 %). A significant proportion of stabilized carbon (63 %) was allocated to passive pools in soils under S2, S3, and S4, highlighting CA's potential to enhance carbon stability. Using a linear indexing technique, we identified that both S3 and S4 are conducive to better carbon stabilization, yield sustainability, and environmental co-benefits. Consequently, full CA systems with best management practices (S3) and best management practices with crop diversification (S4) are recommended for sustainable crop production in the major double cereal growing regions of South Asia, including India and Bangladesh.

Unlocking the Secrets of Soil Health: Exploring the Influence of Natural and Synthetic Nutrients on Soil Organic Carbon and Active & Passive Carbon Pool in Vertisols

The experiment carried out in this field study was between 2022 and 2023 at the (AICRP) research farm in the outward-bound farm of the College of Agriculture, Indore. Indore is a small city in the western part of Madhya Pradesh, Central India, situated on the Malwa Plateau. An experiment was conducted with three replication by using different combination of N, P levels and crop residues in RBD design. Experiment field was medium to black soil with pH of 7.63 and medium in organic carbon 0.58%. The soil was low in available nitrogen (208.0 kg/ha) medium in available phosphorus (21.0 kg/ha) and high in potassium (585 kg/ha) and divided into gross plot size of 10 x 7.2 m2 and a net plot size of 9 x 6.4 m2, respectively. During crop harvest four different depths were used to gather the soil samples: 0–10, 10–20, 20–30, and 30–40 cm. All the collected samples are examined separated for soil organic carbon, active (highly labile, labile SOC), and passive (non-labile, less labile SOC) carbon pools. The finding showed that maximum soil organic carbon (%) was observed with the application of treatment T6 treatment (FYM 6 t ha-1 + N20 P13. Similar trend was found with active (very labile, labile) and passive carbon (less labile, non-labile) pools of soil.

Effect of deforestation on soil organic carbon fate and pool, a case study in Mazandaran, Iran

Deforestation and agricultural operations greatly impact soil organic carbon (SOC) and its fractions. In order to decrease carbon dioxide emissions, prevent threats to ecosystem stability, and apply efficient land use planning for sustainable soil management, it is essential to have a deep understanding of variations in soil organic carbon pools and their fractions. Soil samples were collected from six land uses of the undisturbed forest, pasture, orchard, and agricultural lands (cultivated with Oat, Maize, and three-carbon plants including wheat and soybean, which are indicated by the plant names of Oat, Maize + C3, and Maize + C3 (R) (R = rotationally)) with three replications at 0–30, 30–60, and 60–100 cm depths. The objective of this study was to evaluate the effect of land use on SOC, active carbon (AC), passive carbon (PC), dissolved organic carbon (DOC) content and pools, its fractions, carbon management index (CMI), soil respiration (SR), soil microbial biomass carbon (MBC), invertase (INV), and cellulase (CEL) enzymes activities in Dasht-e Naz region of northern Iran. Results illustrated that the different forms of organic carbon and enzyme activities were sensitive to land use change. The highest values of SOC (167.197, 39.179, 33.211 Mg ha−1), AC (24.596, 1.955, 1.637 Mg ha−1), and PC (142.6, 37.224, 31.575 Mg ha−1) pools were observed in the pasture land at all three depths. the highest value of DOC was seen in the pasture land at 0–30 and 60–100 depths and in the orchard at 30–60 cm depth. The values of SR (1.001 mg CO2 g dry soil−1 week−1), MBC (1367.7 µg organic carbon g soil−1), and CEL enzyme activity (648.04 µg glucose g dry soil−1 24 h−1) in the undisturbed forest were significantly greater relative to other land uses in 0–30 cm depth, along with significantly higher INV enzyme activity in the pasture and the orchard lands. The largest amount of SOC in 2–4.75 and 0.053–0.25 mm aggregates in all depths was related to the pasture and Maize + C3 land use, respectively. The concept of physical protection confirms the importance of aggregation in the stabilization processes of soil organic carbon, as a physical shield against microorganism attacks. The results of CMI demonstrated that the carbon storage capacity decreased due to the agricultural and orchard lands establishment in the region. Also, the change of land use towards pasture land increased the amount of organic carbon, preventing soil degradation.

Projected soil carbon loss with warming in constrained Earth system models

The soil carbon-climate feedback is currently the least constrained component of global warming projections, and the major source of uncertainties stems from a poor understanding of soil carbon turnover processes. Here, we assemble data from long-term temperature-controlled soil incubation studies to show that the arctic and boreal region has the shortest intrinsic soil carbon turnover time while tropical forests have the longest one, and current Earth system models overestimate intrinsic turnover time by 30 percent across active, slow and passive carbon pools. Our constraint suggests that the global soils will switch from carbon sink to source, with a loss of 0.22–0.53 petagrams of carbon per year until the end of this century from strong mitigation to worst emission scenarios, suggesting that global soils will provide a strong positive carbon feedback on warming. Such a reversal of global soil carbon balance would lead to a reduction of 66% and 15% in the current estimated remaining carbon budget for limiting global warming well below 1.5 °C and 2 °C, respectively, rendering climate mitigation much more difficult.

Long-term warming altered soil physical structure and soil organic carbon pools in wheatland field

Summary The impacts of long-term warming on soil physical structure and soil organic carbon (SOC) pools are currently disputed and uncertain. We conducted an eleven-year warming experiment in wheatland field in Henan, China. We found that long-term warming significantly increased soil bulk density by 4.5%, and significantly decreased total porosity and non-capillary porosity by 3.4% and 5.0%, respectively. Besides, long-term warming decreased the >2 mm fraction proportion and increased <0.053 mm fraction proportion of dry and wet aggregates. The mean weight diameter value for dry and wet aggregates in long-term warming treatment was significantly decreased by 7.0% and 6.7%, respectively. Moreover, long-term warming significantly decreased the total SOC, very labile pool (F1) and labile pool (F2) content by 10.6%, 30.6%, and 43.6%, and significantly increased the less labile pool (F3) and non-labile pool (F4) content by 94.2% and 21.1%, respectively. Long-term warming increased the passive carbon pool percentage but decreased the active carbon pool (ACP) percentage. Our results suggest that long-term warming negatively affected the soil's physical structure and impaired soil ACP accumulation. The findings of this study help improve our understanding of the response of farmland soils in northern China to climate change and provide scientific basis for establishing carbon management measures in farmland.

Stability of organic carbon pools and sequestration potential as affected under different agroforestry systems

There are few data on the possibility of soil organic carbon sequestration for agroforestry systems (AFSs). Rarely are the effects of AFSs established for the regeneration of carbon in degraded soils of the Indian North Eastern Himalayas (susceptible to soil erosion, carbon and nutrient loss) examined. The effects of five different AFSs on the stability of organic carbon pools and sequestration potential were evaluated at the ICAR-Sikkim Centre. Black gram + mandarin + Alnus nepalensis had the lowest bulk density at all depths. The highest oxidizable carbon was observed in the black gram + mandarin + Alnus nepalensis system, followed by soybean + Ficus hookerii + guava, maize + Schima wallichii, and soybean + Ficus hookerii + guava, followed by Napier. Regardless of soil depth, the buckwheat + mandarin system had a noticeably lower SOC than the other systems. The total soil organic carbon gradually decreased with increasing depth of the soil profile. According to the results, there was little difference in the total active carbon pool in the 0–90 cm depth among the various systems; however, when compared with Buckwheat + Mandarin, it varied significantly (P ≤ 0.05). The mean passive carbon pool in soils ranged from 22.4 to 25.1 Mg ha−1 across the land use in the 0–90 cm depth. The least soil microbial biomass carbon (MBC) was observed during the winter season in all systems at different soil depths. The maximum MBC was recorded at 0 to 15 cm depth (476.2 – 302.5 µg dry soil−1). By simultaneously cultivating kinds of trees with several uses and agri-horticultural crops, a large-scale adoption of AFSs may replace carbon lost via the development of the crop in degraded soils and offer a viable choice for livelihood.

Exploration of microbial signature and carbon footprints of the Nilgiri Hill Region in the Western Ghats global biodiversity hotspot of India

Land use change (LUC), alters the multifarious biodiversity hotspots directly and indirectly through the loss of soil quality. A comparative study on soil carbon status and soil microbiome in undisturbed natural forest ecosystems with that of other land uses which gradually altered over time can serve as a suitable indicator for understanding LUC impact on carbon cycles. With this aim, the current investigation was initiated to infer the cyclic effects of LUC on the soil carbon status under six major ecosystems viz., cropland (CL), deciduous forest (DF), evergreen forest (EF), forest plantation (FP), scrubland (SL) and tea plantation (TP) of the Nilgiri Hill Region (NHR) (India's first biosphere reserve). The total organic carbon (TOC) and carbon stocks were highest in evergreen forest (10.25 %, 322.06 t ha−1) and they decreased with increasing depth of the soil profile across the pools of varying carbon lability. The proportion of active carbon pools (AP) in total carbon was higher in crop land and tea plantation (57.47 %, 58.38 %), however, in the case of evergreen forest, deciduous forest, forest plantation and scrub land the passive carbon pools (PP) (54.99 %, 61.28 %, 59.43 % and 60.70 %) was higher. We discovered LUC has altered the proportion of soil carbon pools, and the efficiency of soil microbiome and has resulted in higher carbon dioxide (CO2) emissions in tea plantation (71.87 t ha−1) and crop land (82.39 t ha−1). However, the native ecosystems (evergreen forest and deciduous forest) with higher recalcitrant carbon pools (46.96 g kg−1 and 34.89 g kg−1) prevent such carbon degradation and thereby hinder the soil carbon emissions as recorded in evergreen forest (48.43 t ha−1) and deciduous forest (56.47 t ha−1). Conclusively, our study demonstrates that LUC has substantially influenced the carbon cycle by altering the carbon stocks and CO2 emissions in relation to soil microbes. Henceforth, in order to maintain carbon footprints and attain carbon net neutrality under the current climate change scenario, suitable carbon management measures must be implemented in carbon-degraded ecosystems (crop land and tea plantation) of NHR.

Sowing carbon solutions: Decoding soil characteristics and carbon fluxes in maize-dominated cropping systems of Tamil Nadu, India

This study on soil carbon dynamics provides valuable insights for sustainable agricultural practices, optimizing crop productivity and environmental sustainability in maize-based cropping systems. The present study aimed to find out the soil characteristics and carbon dynamics in maize-based cropping systems in the Western zone of Tamil Nadu, India. Soil samples from six cropping systems were analyzed for bulk density, sand, silt, clay content, pH, available nutrients (N, P, K, Zn), total organic carbon (TOC), oxidizable organic carbon fractions, microbial biomass carbon (MBC), and carbon pools. The distribution of oxidizable organic carbon fractions varied among cropping systems and soil depths. The easily decomposable and moderately labile fractions were highest in the maize-black gram system, while the recalcitrant fraction showed variations across cropping systems. The active carbon pool (Cf1 + Cf2) was highest at 2.53 g kg-1 in the maize-blackgram system, while the passive carbon pool (Cf3 + Cf4) was also highest at 3.79 g kg-1 in this system. The study also assessed the carbon stock and microbial biomass carbon. TOC content decreased with depth, with the highest values observed in the topsoil. The maize-black gram system had the highest TOC content at all depths. MBC content followed a similar pattern, with the highest values in the topsoil and the maize-black gram system. These findings provided insights into the soil characteristics and carbon dynamics in maize-based cropping systems in the study area. The long-term integration of maize cultivation with blackgram demonstrated significant enhancements in organic carbon levels, TOC content, microbial biomass carbon (MBC), and both passive and active carbon pools characterized by rapid turnover rates.

Land-use change affects carbon storage and lability in tropical soil of India

Soils are storehouse of organic carbon that is amenable to different degrees of degradation. But, information on the impact of land use change on carbon storage and lability in tropical soil is scarce. The present investigation aimed to study the carbon fractionation of tropical soils concerning their accumulation based on differential chemical oxidation involving potassium dichromate and sulphuric acid. The work was carried out in a tropical forest and pasture lands (located at a mean distance of 60 m from each other) in India. The readily oxidizable carbon (active carbon pool) dominated both the studied land uses (forest and pasture) more than the less oxidizable fraction (passive carbon pool). The carbon pool index and the carbon management index computed from the results of the two carbon pools favored the forest land for long-term carbon sequestration and were significantly correlated with the active carbon pool (p < 0.05). The results further showed a significant variation in the cumulative soil organic carbon stock of the forest (248.92 t/ha) and the pasture (184.21 t/ha) land (p < 0.05). Soil depth did not show any impact on the carbon fraction distribution. It can, thus be, concluded that land use change alters the stability and lability of organic carbon and its storage in tropical soils. Therefore, regular evaluation of carbon pools and subsequent carbon management can enhance the prospects of the long-term stay of carbon in the soil.

Active and Passive Soil Organic Carbon Pools as Affected by Different Land Use Patterns in Red Soils of Vikarabad District, Telangana, India

A survey was conducted in the years (2019-20 and 2020-21) in red soils of Vikarabad district covering eight mandals and soil samples were collected from four predominant land use patterns at two depths (0-15 and 15-30cm). Land use patterns studied included cultivated land with different cropping intensity i.e., 100% cropping intensity (redgram-fallow), 200% cropping intensity (rice-rice) and two from natural conditions i.e., forest land and fallow land to assess the impact of these land uses on various pools of SOC viz., total organic carbon (TOC), oxidizable organic carbon and its pools. The SOC content of forest land recorded the highest mean value (7.30 g kg-1) and that of fallow land recorded the lowest value (2.24 g kg-1).The mean SOC stock was highest in forest land (13.92 Mg Cha-1) and that of fallow land was the lowest (5.64 Mg C =ha-1). The highest accumulation of mean TOC was observed in forest (26.28 Mg ha-1). The per cent contribution active carbon pools to TOC was highest forest land (54.33 %) followed by redgram-fallow 53.16 %, suggesting that the accumulated carbon could be easily lost following the land use change. Contrarily, the per cent distribution of TOC to passive carbon pool was highest under fallow land (54.96 %) and rice-rice cropping system (52.00%) indicating more stable nature of the accumulated organic matter.

Long term impact of different tillage systems on carbon pools and stocks, soil bulk density, aggregation and nutrients: A field meta-analysis

Intensive tillage frequently has adverse impact on soil physical quality and soil organic carbon stocks in temperate regions. A consequence of this has been a reduction in crop production over the years demonstrating the necessity of effective and sustainable agriculture. This study aimed to evaluate soil organic carbon (SOC) storage and pools, soil bulk density, aggregation and nutrient availability under different tillage systems (no-tillage, chisel and conventional tillage), based on a long field experiment. After 10 years of crop rotation, in 0–30 cm soil depth, no-tillage system had higher total organic carbon over conventional tillage treatment. Plots under no-till and chisel treatments in 0–10 cm depth, had 7–13%, 34–35% and 9–15% higher non-labile fraction (Cfrac4), very-labile fraction (Cfrac1) and total organic carbon (TOC), respectively compared to that of conventional ones. Also, no-till system had higher passive carbon pool and carbon management index than conventional system. In addition, the conservative tillage, reduced soil bulk density compared with conventional tillage in the surface layer. The stability of slow-wetting and room storage aggregates from conservative tillage were significantly higher (p < 0.05) than conventional tillage. Overall, stability of soil aggregates is improved under conservative tillage. Tillage system, crop rotation and residues, increased soil available nutrients N, P and K in the 0–10 cm depth, with the highest values in no-tillage system. Therefore, conservation tillage could be recommended as a tillage practices that improve fertility soil characteristics and production sustainability.

Changes in soil organic carbon lability along the altitudinal variations in three land use types of Meghalaya, India

Assessment of soil organic carbon (SOC) in different land use systems is very important, due to the tremendous potential of terrestrial ecosystems in carbon (C) sequestration. Moreover, its dynamic nature and vulnerability to land use change, makes SOC an important indicator of soil health. In order to elucidate the effects of different land uses on total SOC content and labile C pools, soil samples were collected from forest, rubber plantations and cultivated fields (30 cm depth from three elevation zones). Total SOC was significantly higher in forest soils (1.81%), while plantation and cultivated fields had statistically similar values. The higher value of very labile carbon (CVL) pool (12.09 mg g−1) was also recorded in forest soils and was significantly affected by land uses. However, the values of less labile carbon (CLL) and non-labile carbon (CNL) were highest under rubber plantation. In all the studied land uses, active carbon pool (ACP) was higher in comparison to passive carbon pool (PCP). Correlation study demonstrated that total SOC content mainly depends on the CVL and labile C (CL) pool. CVL and ACP were significantly influenced by the studied land uses at the considered elevations and their content increases with the elevation. These results suggest forest soil C is more vulnerable, if converted to other land uses, while rubber plantations have potential to store C in long term, by conserving CLL and CNL pools. In addition, there is need to study the relationship between soil moisture, C supply, soil microbial and enzymatic actives, which can modify labile C pools in different land uses at different elevations.

Temperature sensitivity of soil carbon decomposition due to shifts in soil extracellular enzymes after afforestation

Afforestation of arable land has been proposed as one of the most effective strategies for climate change mitigation. However, the effects of afforestation on soil CO2 emissions have not been well investigated due to a lack of information on the capacity of carbon pools to sequester CO2 over the long term. In this study, we conducted a 414-day incubation experiment to monitor changes in CO2 emission, soil extracellular enzymes, and microbial biomass at soils collected from a site afforested with R. pseudoacacia L and an adjacent cropland system under 15 °C and 25 °C constant temperatures. The study was to reveal how soil organic carbon decomposed under different temperatures during incubation along an afforestation gradient. Our results showed that: 1) after warming, active pool respiration increased from 0.64% to 12.57%, passive pool respiration increased from 20.62% to 46.77%, and slow pool respiration decreased from 21.27% to 59.35% for cropland to afforested land; 2) active and slow carbon pool increased in young and middle-aged afforested lands while the passive carbon pool increased in the late stage; and 3) microbial biomass and enzyme activities affected the respiration rate and the fraction of respiration during warming, especially enzyme affected active and slow pools. Our findings indicate that the temperature sensitivity of soil organic carbon decomposition changed mainly due to shifts of soil extracellular enzymes after afforestation, and provides insight into how SOC decomposition in afforested ecosystems may respond to future changes in climate.

Studying the relationship between total organic carbon and soil carbon pools under different land management systems of Garo hills, Meghalaya

The contribution of land uses in sequestering soil carbon (C) is a key question of research in tropical regions, where C emissions due to land use changes, extreme rainfall events and high temperatures can aggravate the global issue of climate change. In the present study, different pools of soil organic C were assessed, from shifting cultivation lands (jhum), rubber, tea garden and coffee plantations of Tura district in Meghalaya, which is located in Northeastern region (NER) of India. To achieve this goal, different parameters such as bulk density (BD), total organic carbon (TOC) and C pools, viz., very labile (CVL), labile (CL), less labile (CLL) and non-labile (CNL) were analyzed. The results indicated significant correlations among TOC and C pools in most land uses, except for CNL pool. Tea gardens showed the highest value of TOC stock (62.75 ± 1.47 t C ha−1) while the lowest was found in the jhum lands (33.34 ± 5.04 t C ha−1). Similarly, both the active (12.03 mg g−1) and passive (4.60 mg g−1) C pools were highest under tea gardens. CVL was found to be positively correlated with TOC and active carbon pool (ACP), while CLL was also positively correlated with passive carbon pool (PCP). This study indicates the potential of tea gardens as a promising C sequestering land use, which can be promoted in jhum lands to mitigate the negative impacts of climate change.

Active and passive soil organic carbon pools as affected by different land use types in Mizoram, Northeast India.

Soil organic carbon plays an important role in the stability and fertility of soil and is influenced by different management practice. We quantified active and passive carbon pools from total soil organic carbon (TOC) in seven different land use systems of northeast India. TOC was highest (2.75%) in natural forest and lowest in grassland (1.31%) and it decreased with increasing depth in different pools of lability. Very Labile Carbon (VLC) fraction ranged from 36.11 to 42.74% of TOC across different land use system. Active carbon (AC) pool was highest in Wet Rice Cultivation (61.64%) and lowest (58.71%) in natural forest. Higher AC pools (VLC and less labile) in most land use systems barring natural forests suggest that the land use systems in the region are vulnerable to land use change and must adopt suitable management practice to harness carbon sequestration.

Diversification of maize-wheat cropping system with legumes and integrated nutrient management increases soil aggregation and carbon sequestration

Retention of carbon in arable soils has been recommended as an important mechanism to mitigate the climate change and sustainability of the agro-ecosystems. We reasoned that legume-inclusive crop rotations and integrated nutrient management would promote higher soil aggregation and carbon sequestration compared with continuous cereal-cereal [maize (Zea mays L.) – wheat (Triticum aestivum L.)] rotation and chemical fertilization. To test the hypothesis, we used a long-term field experiment (13 years) in Typic Ustochrept soil of Kanpur, India. The field experiment was undertaken in split-plot design comprised of four crop rotations: maize–wheat (MW), maize–wheat–mungbean (Vigna radiata L.) (MWMb), maize–wheat–maize–chickpea (Cicer arietinum L.) (MWMC) (2 years rotation), pigeonpea (Cajanus cajan L.)-wheat (PW) in main plot, and three nutrient management treatments: without fertilization (CT), recommended dose of inorganic fertilizers in the region (NPKSZnB), and integrated nutrient management (INM) in sub-plot. Water stable macroaggregates (>0.25 mm), aggregate ratio, mean weight diameter, and geometric mean diameter followed the order of PW > MWMb > MWMC > MW (p < 0.05) for crop rotations, and INM > NPKSZnB > CT (p < 0.05) for nutrient management practices. The PW rotation and INM practice retained higher coarse macroaggregated- and ‘silt + clay’-carbon compared with MW and NPKSZnB treatments. The PW and MWMb rotations allocated 69.7 and 65.7% carbon in macroaggregates, respectively. While, MW rotation allocated higher carbon in microaggregates (55%). The PW and MWMb rotations significantly enhanced the active (very labile + labile) and passive (less labile + non labile) carbon pools compared with that of MW rotation. The PW stabilized 15% higher carbon in less labile fraction (Cfrac3) over the MW (p < 0.05). It indicated that higher passive carbon pool and its stabilization in PW and MWMb rotations could promote the carbon sequestration. Therefore, MWMb and PW systems had 14.7 and 3.9% higher carbon management index than that of MW rotation (p < 0.05). Among nutrient management treatments, INM resulted in higher active (26%) and passive (8%) carbon pools compared with that of NPKSZnB. Further, INM increased carbon management index by 29 and 16% (p < 0.05) compared with those of CT and NPKSZnB, respectively. Principal component analysis indicated that PW(INM) and MWMb(INM) distinctly situated from MW(CT) and MW(NPKSZnB) in coordinates. Thus, PW and MWMb rotations with INM practice can enhance the soil aggregation and carbon sequestration in long-run. The research findings can be extrapolated in the South Asian and other countries, where continuous cereal-cereal induced soil health issues are a pervasive problem.

Influence of Agricultural Land Use on Soil Organic Carbon Fractions in an Arid Ecosystem

This study aims to determine the effect of land-use systems on soil organic carbon (SOC) and its fractions in an arid agro-ecosystem (Kachchh District, Gujarat). SOC fractions (very labile, labile, less labile, and non-labile) and pools (active and passive) from six pedons (two each from mango orchards, sorghum, and cotton cultivated fields) were estimated. The results showed that SOC and its fractions, except the labile fraction, were significantly affected by land-use up to 20 cm depth. Further, land use significantly affected the absolute content of active carbon pool at 0-10 and 10-20 cm (p&lt;0.05) depth, whereas the effect was significant at 20-50 cm depth at p&lt;0.1. The higher passive carbon pool under the mango plantations indicates plantation crops’ potential to increase the carbon sequestration in the soils. The soils under sorghum with higher passive carbon pool suggest that high-root density crops can increase the carbon storage in the arid regions.

Impact of zero-till residue management and crop diversification with legumes on soil aggregation and carbon sequestration

We evaluated the long-term impact of zero tillage (ZT) in post–rainy seasons (winter and summer) crop/s, crop residue management, and crop diversification on soil aggregation and carbon sequestration. The field experiment (started in 2009) was undertaken in split-plot design for seven consecutive years on a sandy loam soil of Kanpur, India. The experiment comprised of four tillage and crop residue management treatments: PTR – conventional tillage (CT) without crop residue (PTR–CT), PTR – ZT without crop residue (PTR–ZT–R), PTR – CT with crop residue incorporation (PTR–CT+R), and PTR – ZT with surface crop residue retention (PTR–ZT + R) in main plot, and three cropping systems: rice–wheat (RW), rice–chickpea (RC), and rice–chickpea–mungbean (RCMb) in subplot. Treatment PTR–ZT + R resulted in 13% (p < 0.05) higher water stable macroaggregate over the PTR–CT. Meantime, PTR–ZT+R increased carbon content in macro- aggregate (28%) and meso-aggregate (39%) over the PTR–CT, because of added carbon through the surface-laden crop residue. The tillage and crop residue management followed the sequence of PTR–ZT+R > PTR–ZT–R > PTR–CT+R > PTR–CT (p < 0.05) across the soil depths for active and passive carbon pools. After seven years, PTR–ZT+R enhanced soil microbial biomass carbon (SMBC) and particulate organic carbon (POC) by 70 and 56% over PTR–CT, respectively. The RCMb and RC rotations increased (p < 0.05) the macro– and meso– aggregates, and aggregate mean weight diameter compared to the RW rotation in both soil depths. Crop rotations had the following trend: RCMb > RC > RW (p < 0.05) for SMBC and POC. Notably, treatment PTR–ZT+R with RCMb or RC rotations largely increased the carbon management index compared to the PTR–CT and RW systems. The structural indices and soil carbon parameters were significantly correlated to the rice grain yield, except microaggregated carbon. Thus, crop diversification with grain legume/s, zero tillage in post rainy season crop/s, and crop residue retention provided not only higher soil aggregation but also increased carbon sequestration in Inceptisol of subtropical humid climate.

Including grain legume in rice–wheat cropping system improves soil organic carbon pools over time

Deterioration of soil physical quality and depletion of soil organic carbon (SOC) are widespread challenges in tropical rice–wheat growing regions. Consequently, soil productive capacity, production sustainability, and resource use efficiency have declined in this agro-ecosystem. Ecological engineering approach such as legume inclusion in cropping system offers several ecosystem services, and thus, may serve an important role in the restoration of soil health. Given that, a long-term (2003–2015) field experiment was conducted to assess the impact of four rice-based crop rotation treatments [rice–wheat, rice–chickpea, rice–wheat–mungbean, rice–wheat–rice–chickpea] each with three levels of nutrient management treatments [control, integrated nutrient management, chemical fertilizers] on soil aggregation, soil carbon pools, and carbon stabilization. Legume inclusive rotations increased water stable macro-aggregates (WSMA) over rice–wheat rotation in both surface (0–0.2 m) and subsurface (0.2–0.4 m) soil depths. In surface soil, WSMA was the highest in rice–wheat–mungbean rotation (65%) followed by rice–chickpea rotation (57%) and was the least in rice–wheat rotation (50%). Subsequently, grain legume inclusive rotations had the higher aggregate ratio and mean weight diameter over rice–wheat rotation, being the highest in rice–wheat–mungbean rotation. Rice–wheat–mungbean and rice–chickpea rotations had higher carbon concentration in coarse macro-aggregates, meso-aggregates, and coarse micro-aggregates as compared with rice–wheat rotation. Grain legume inclusive rotations increased active carbon pool (9–18%), SOC (6–17%), and carbon management index (5–7%) over rice–wheat rotation, and the order was rice–wheat–mungbean > rice–chickpea ≥ rice–wheat–rice–chickpea > rice–wheat. Integrated nutrient management treatment resulted in higher macro-aggregate (7%), mean weight diameter (6%), active carbon pool (22%), passive carbon pool (16%), SOC (20%), and carbon management index (22%) over the chemical fertilizer treatment. Thus, it is concluded that inclusion of grain legume in lowland rice-based rotation and integrated nutrient management could improve soil aggregation, carbon concentration in aggregates, and soil carbon pools in the tropical soils. The study highlights the prospects of strategic designing of legume inclusive rotation/s for rice agro-ecosystem health and its sustainability.

A Long-Term Impacts of Planted Fodder Grasses on Soil Quality and Organic Carbon Fraction Pools

Different fractions of soil organic carbon (SOC) act as a major source and sink for atmospheric carbon (C). Thus, understanding SOC dynamics and its allocation into various resistance organic C pools especially in grassland ecosystem may have a greater role in environmental stability. A perennial grass block with three fodder species namely hybrid Napier (Pennisetum glaucum × P. purpureum), Congo signal (Brachieria rosenesis) and combo Napier (P. purpureum) were established at ICAR Research Complex for NEH Region, Tripura centre in 2003 to study the impact of grasses on SOC dynamics and its distribution into different organic C pools in comparison to a natural mixed-grass soil [grasses, those were grown naturally without any management and might be an admixture of non-legume and legume species suitable for this region for example bermuda grass (Cynodon dactylon), buffalo grass (Bouteloua dactyloides), crab grass (Digitaria sanguinalis), green fingers (Lotrochota birotulata), para grass (Brachiaria mutica), rhodes grass (Chloris gayana), crown grass (Paspalum scrobiculatum), Mimosa (Mimosa diplotricha), Euphorbia hirta, Cassia tora, Vicia hirsuta, V. sativa, Melilotus indica etc.]. Water holding capacity (WHC) and field capacity (FC) of different soils under three fodder species of hybrid Napier, Congo signal and combo Napier ranged between 40.65–59% and 28.62–46.84%, respectively. The soils under natural mixed grasses had the highest WHC. Bulk density was the lowest in soils under hybrid Napier. Available nitrogen and potassium were the highest in soils under hybrid Napier, however, available phosphorus was the highest in soils under Congo signal. Total pool of Walkley and Black carbon (WBC) and total carbon (TC) in top 1 m soil profile ranged from 59.7 to 86.3 Mg/ha and 74.8 to 112.6 Mg/ha, respectively, across the treatments. However, TC pools in soils under mixed grasses were 50.4, 22.1 and 28.6% higher than those in soil under hybrid Napier (74.8 Mg/ha), Congo signal (92.2 Mg/ha) and combo Napier (87.5 Mg/ha), respectively. The most important aspect of the study is that about 62.9–65.5% WBC pool and 64.4–66.8% TC pools lied below 30 cm depth across the grasses. Although soils under combo Napier had higher AC pools by 26.4, 28.2 and 57.1% over those of soils under hybrid Napier (49.4 Mg/ha), Congo signal (48.7 Mg/ha) and mixed natural grasses (62.4 Mg/ha), respectively. The PC pools were higher in soils under mixed natural grasses by 99.5, 16.4 and 6.2% over the soils under three fodder species, that is, hybrid Napier (25.4 Mg/ha), Congo signal (43.4 Mg/ha) and combo Napier (47.3 Mg/ha), respectively. Thus, study suggests that the restoration of low carbon degraded land through establishment of mixed grasses is a feasible option in northeastern Indian Himalayan region as grasses have high potential for allocation of SOC into passive carbon (PC) pool (recalcitrant pool). However, among the perennial grasses, combo Napier maintained more of PC pool in soil, thus, it has potential to increase the stable SOC pools in degraded lands and mitigate the changing climate.