Soil Organic Carbon- an Explanation to Soil Health: a review

Soil Organic Carbon- an Explanation to Soil Health: a review

Priyadarshani A. Khambalkar1* , Shashi S. Yadav1 , Akhilesh Singh1 , Sudhir Bhadauria1 , Murlidhar J. Sadawarti2

1Rajmata Vijayaraje Scindia Krishi Viswa Vidyalaya, Gwalior, Madhya Pradesh 4740062, India

2ICAR-Central Potato Research Institute, Regional Station, Gwalior, Madhya Pradesh 474020, India

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Soil organic carbon holds a prominent place among the many indicators of soil quality that are studied concerning soil health. Soil organic carbon (SOC) dynamically impacts soil quality, functionality, and health. Healthy soil is the foundation of the food system. It produces healthy crops that, in turn, nurture people. SOC dynamics is a strong determinant of global food and nutritional security. Organic matter and minerals are two natural sources from which plants obtained nutrients, whereas plant or animal material that returns to the soil; through the decomposition process, they release nutrients in the soil. In addition to providing nutrients and habitat to organisms, organic matter also binds soil particles into aggregates and improves soil’s physical environment. Soil is a living, dynamic ecosystem. Soil organic matter (SOM) is the product of on-site biological decomposition, which affects the chemical and physical properties of the soil and its overall health. Many standard agricultural practices accelerate soil organic matter decomposition and leave the soil susceptible to wind and water erosion. Through combining pasture and fodder species, conservation practices, and manuring with food and fiber crop production, mixed (crop-livestock) systems also enhance soil organic matter, ultimately SOC and soil health. Numerous soil functions and ecosystem services depend on SOC and its dynamics. Improvements in soil health increase soil’s resilience against intensive practices and extreme climatic events (e.g., drought, heatwave).

Akhilesh Singh1, Sudhir Bhadauria1, Murlidhar J. Sadawarti2



Biofertilizers, conservation, integrated nutrient management, organic carbon pools, Soil amendments, Soil health, Soil organic carbon

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Soil is pivotal for the nourishment and endurance of life on earth. The management of SOC (Soil Organic Carbon) is complex, and it is only one factor responsible for the overall maintenance of soil environment and productive capacity. Mankind generally emphasized that food production from limited soil resources creates a load on the soil ecosystem. SOC concentration, along with its quality, mediated territory and created dynamic environments, contributing to the growth and development of plants and another biota. Carbon (C) storage is an important ecosystem function of soils that have gained mounting attention in recent years due to its interactions with the earth’s climate system. Soil is a major C reservoir that holds more carbon than in the atmosphere and terrestrial vegetation combined. All three of these reservoirs are in constant exchange. In many soils, soil organic matter (SOM), which contains roughly 55–60 percent C by mass, comprises most or all of the C stock – referred to as soil organic carbon (SOC) [15].

Soil organic matter content is a function of organic matter inputs (residues and roots) and litter decomposition. It is the product of on-site biological decomposition, which affects the properties of the soil and its overall health. In the presence of climate change, land degradation, and biodiversity loss, soils have become one of the most vulnerable resources in the world. Maintaining soils productivity on a sustainable basis is a big task and can be genuinely managed by SOM. The life-line of soil is SOM, which significantly affects numerous soil properties; viz water holding capacity, cation exchange capacity (CEC), aggregate stability, buffering capacity, salinization, and sodification, acidification, etc. Besides these, it is an essential factor in determining nutrient cycling and its supply to the plants, especially nitrogen, phosphorus, sulphur, and micronutrients [54]. In general, the total organic carbon (OC) is the amount of carbon in the soil related to living organisms or derived from them. Increasing the quantity of OC stored in soil may be one option for decreasing the atmospheric concentration of carbon dioxide (CO2), a significant greenhouse gas. Increasing the amount of OC stored in soil may also improve soil quality as OC contributes beneficial physical, chemical, and biological processes in the soil ecosystem. When OC in the soil is below 1%, soil health is low, and yield potential may be constrained [32].

Agriculture intensification and land-use change from grasslands to croplands are generally known to deplete SOC stocks. The depletion is exacerbated through agricultural practices with the low return of organic material and various mechanisms, such as oxidation/ mineralization, leaching and erosion [51]. Microorganisms accelerate the process of decomposition of SOM, by which losses of OC will occur; this increases surface soil erosion and withdrawal in plant and animal production. The decomposition process is constant; thus without a stable supply of OC, the amount stored in the soil will decrease over time. Losses by erosion may heavily impact the quantity of OC storage and are easily eroded from the surface soil layer. Ingram and Fernandes, (2001) [21] reported that the management practices determine the actual storage of OC in soil by increasing inputs of organic matter via plant production and decreasing losses.

Conventional farming (CONV) refers to residue removal, inversion tillage, and mono-cropping, contributing adverse effects on soil functions and its health. However, there are alternative management practices that enhance soil health and allow sustained agricultural productivity. Conservation agriculture (CA) encompasses a range of such good practices through no-till combined with crop rotation and residue retention [27] as an alternative to optimizing the stipulation of soil functions. In a framework of soil custodianship, CA is practiced to optimize available resources while minimizing external inputs and soil degradation [18]. However, changes in SOM stocks in response to agronomic practices are slow and show years later when it is too late for adjustments in management.

The present review aims to inspect (i) the importance of SOC in the global carbon cycle, the significance of SOC in sustaining soil health, (ii) discuss how the various factors and intensified agricultural practices are degrading SOC, affecting soil health and our future ability to produce food and (iii) how management practices increasing SOC rapidly, and could potentially allow the sustainable usage of soils in intensive agriculture system. A specific focus of the present review is the need to recognize that to reduce the degradation of soil health trough SOC enhancement.


SOC is the main component of soil organic matter (SOM). It is an indicator of soil health. In food production, the contributions of SOC are more important. Also, it helps in mitigation and adaptation to climate change, and the achievement of the Sustainable Development Goals (SDGs). Soil carbon (C) consists of two related but distinct components.  Soil organic C (SOC) comprises plants and animals’ remain at different stages of decomposition and microbial biomass and their by-products. As a component of SOM (45–60%), SOC is a heterogeneous mixture of organic materials, including fresh litter, carbohydrates, simple sugars, complex organic compounds, some inert materials, and pyrogenic compounds.

The SOC is a highly reactive component and is the basis of numerous pedogenic processes. Because of a high surface area and charge density, it reacts with clay and minerals to form organo–mineral complexes. Dungait et al. (2012) [14] stated that the mean residence time (MRT) or its turnover rate depends on the degree of protection within the soil matrix. Among numerous protective mechanisms (physical, chemical, biological, and ecological); physical mechanisms include encapsulation within stable micro aggregates [50], formation of organo–mineral complexes, and transfer deep into the subsoil away from the zone of natural and anthropogenic perturbations. SOM is a key indicator for agricultural productivity and environmental resilience; because SOM is critical for the stabilization of soil structure, retention and release of plant nutrients, and maintenance of water-holding capacity. The decomposition of SOM further releases mineral nutrients, making them available for plant growth (Van der Wal and De Boer, 2017), while better plant growth and higher productivity contribute to ensuring food security  and sustaining soil health.


The dynamics of SOC is a component of the terrestrial C cycle [29]. The global carbon cycle involves the cycling of carbon through the soil, vegetation, atmosphere, and ocean; here Soil organic carbon (SOC) is one part (Figure 1). The SOC pool stores an estimated 1500 PgC in the first meter of soil, which is more carbon than is contained in the atmosphere (roughly 800 PgC) and terrestrial vegetation (500 PgC) combined [15]. This phenomenal SOC reservoir is not static but is constantly cycling between the different global carbon pools in various molecular forms (Kane, 2015). According to Lal (2004a), the dynamics of soil C pool can strongly impact atmospheric chemistry and the global C cycle. For example, if it were possible to increase soil C pool globally by 4% to 3-m depth, it would cause a drawdown of atmospheric CO2-C by 240 Pg, the amount equivalent to the reduction of >100 ppmv of CO2. However, the logistics of achieving such an increase even over a decadal scale are insurmountable at the present level of scientific advances (Lal 2016). The major carbon-based atmospheric gases are CO2 and CH4 (methane). The autotrophic (mainly plants), photo- and chemo-autotrophic microbes basically synthesize atmospheric CO2 into organic material. The plant residues and exudates are incorporated into the soil by soil fauna, leading to carbon inputs into the soil. Likewise, through the activity, heterotrophic microorganism’s organic material transformed. This process results in the formation of a complex biogeochemical mixture of plant litter compounds and microbial decomposition products in various stages of decomposition [43] that can be associated with soil minerals and occluded within aggregates, enabling SOC persistence in soil for decades, centuries or even millennia.  Microorganisms decomposed SOM and CO2 is emitted back into the atmosphere. The losses of carbon can also be caused by root exudates such as oxalic acid, which liberate organic compounds from protective mineral associations. Finally, carbon is also partly exported from soils to rivers and oceans as dissolved organic carbon (DOC) or as part of erosion material [17].

Figure 1, Global Carbon Cycle Copyright from (FAO, 2017) [17]


SOM contains roughly 55–60 percent C by mass. In many soils, this C comprises most or all of the C stock – referred to as SOC – except where inorganic forms of soil C occur (FAO and ITPS, 2015).SOM can be divided into different pools based on the time needed for full decomposition and the derived residence time of the products in the soil (turnover time) as follows [21]:

Active pools – turnover in months or few years;

Passive pools – turnover in up to thousands of years.

Degens (1997) [9] stated that, the anaerobic conditions such as in peats, incorporation of SOM components into soil aggregates, attachment of organic matter to protective mineral surfaces, the spatial disconnection between SOM and decomposers and the intrinsic biochemical properties of SOM are responsible for long turnover times of organic compounds. Similarly Dexter, (1988) [61] reported that micro aggregates are responsible for the stabilization of the passive pools (permanent stabilizing agents), whereas macroaggregates and clods encapsulating small aggregates and are considered transient stabilizing agents. In addition, such stabilization requires a broad range of microbial enzymes to degrade the insoluble macromolecules that comprise SOM [56].

Similar to SOM, SOC is separated into different pools as a function of its physical and chemical stability [15] as:

  1. Fast pool (labile or active pool) – After the addition of fresh organic carbon to the soil, decomposition results in a large proportion of the initial biomass being lost in 1–2 years.
  2. Intermediate pool – Comprises microbially processed organic carbon that is partially stabilized on mineral surfaces and protected within aggregates, with turnover times in the range of 10-100 years.
  3. Slow pool (refractory or stable pool) – highly stabilized SOC, enters a period of very slow turnover of 100 to >1,000 years. An additional slow SOC pool is pyrogenic SOC, formed from partially carbonized (e.g., pyrolyzed) biomass during wildfires present in many ecosystems [47]. The labile SOC pools serve a better indicator of soil quality to assess variations caused by land-use changes [57], while the non-labile SOC pools add to the total organic carbon stocks [7].

Sahoo et al. (2019) [45] studied the seven different land-use systems of northeast India, which representing the average distribution of organic carbon (0–45 cm) (Figure 2). The SOC stock was distributed with following downward order: Forest > Agroforestry > Wet Rice Cultivation > Plantation > Current Jhum > Grassland > Jhum Fallow. Average fine soil stock (FSS) for 15 cm soil depth and was highest in agroforestry systems (10.09 Mg ha-1) which quantified active and passive carbon pools from total soil organic carbon (TOC). The very labile carbon fraction of TOC was very high (average 40.27%) in all the land use types, implying a constant supply of easily decomposable litter throughout the year in the system. The SOC stock in the former indicates its role in maintaining and sustaining soil health. The study implies how soil carbon build-up could be improved with proper management multidisciplinary and multiregional approaches.

Figure 2. Distribution of soil carbon pools at three soil depths in different land-use systems of northeast India.

Khambalkar et al. (2013a) [33] concluded under long term fertility experiment of pearlmillet- mustard cropping system that; the biomass production was increased through the optimal application dose of fertilizer in combination with FYM or biofertilizers and superoptimal dose of chemical fertilizers, which was led to an additional buildup of SOC. The study indicated that even if a small portion of biomass could be recycled to soil then only crop production itself can enrich SOC content and stop its further deterioration.

Lal (2004b) [38] summarized the results of a number of studies and concluded that improved fertility management could enhance the SOC content at the rate of 0.05 to 0.15 Mg ha-1year-1 to the soil through only crop roots. Gregorich et al. (2001) [22] observed that the use of organic manure and compost enhances the SOC pool more than the application of the same amount of nutrients as inorganic fertilizers. Similarly, the adequate supply of nutrients in the soil and long-term manure application can enhance biomass production and TOC content [34]. Agricultural management practices increase SOC stock is thus may have profound effects on climate mitigation. Additional benefits include higher soil fertility since increased SOC stocks improve the physical and biological properties of the soil [51].


The soil organic matter is a central constituent of soil health. “Soil health is the condition of the soil concerning its inherent (or potential) capability to sustain biological productivity, maintain environmental quality, and promote plant and animal health. Healthy soil is productive, sustainable and profitable”. The primary attributes of soil are (1) physical for provisioning of air, water, and gaseous exchange and habitat; (2) chemical for moderating soil reaction and availability and transformation of nutrients; (3) biological for the source of energy and food and nutrient cycling; and (4) ecological for hydrological and energy budget, and landscape processes. These attributes, individually and through interaction, make environments favorable to life, and vice versa [39]. Indirectly, all these attributes build soil health and improve its quality and functionality (Figure, 3).

Higher SOC concentration improves microbial activity and a better physical environment in soil, thus ensures better health of the soil. Soil organic carbon has profound effects on soil’s physical, chemical, and biological properties [23]. Conservation agriculture practices has been shown to sustain soil health by improving soil properties, thereby enhancing water transmission, water retention, and crop yield in many parts of the world. The pressure on the management of soil organic matter is increasing as costs of inputs for agriculture increase, and the capacity and ability to overcome soils in poor condition by adding more fertilizer, adding one more cultivation, adding one more irrigation or adding another input are diminished.

Agronomic productivity affected by abundant soil-related constraints (Figure 4) may be reduced through enhancement and sustainable management of the SOC pool. More frequent constraints are as follows: (1) endogenous soil properties related to the parent materials and soil formation; (2) exogenous factors related to climate, landscape, and other biotic and abiotic factors; (3) water-related issues which influence the drought-flood syndrome; and (4) the human extent that affect availability and access to inputs, along with social, cultural, and environmental issues. These issues can be addressed by exploit improvement in soil health through SOC enhancement. Similar to soil quality, soil health also cannot be measured directly. Thus, key soil attributes can be used as surrogates to develop soil health indicators [39].

Figure 3. Soil attributes as indicators of soil health (AWC – available water capacity; SOC -soil organic C; CEC – cation exchange capacity; EC – electrical conductivity; MBC -microbial biomass; MRT – mean residence time), (source, Lal, 2016)[39]

Figure 4. Global soil-related constraints to agronomic productivity (source, Lal, 2016) [39]


The environmental and edaphic factors control the activity of soil biota and thus sustain the balance between accumulation and decomposition of organic matter in the soil. There are various factors that influence the SOC build-up and its sequestration discussed as under:

  1. Decrease in biomass production, decrease in organic matter supply, and increased decomposition rates affect the native SOC.
  2. Replacement of mixed vegetation with the monoculture of crops; pastures clearance of primary forests often leads to rapid mineralization of organic matter.
  3. High harvest index: the green revolution was replaced indigenous varieties of species with high-yielding varieties (HYVs). These HYVs often produce more grain and less straw than locally developed varieties; the harvest index of the crop (ratio of grain to total plant mass aboveground) is increased. This reduced amount of crop residues remain after harvest for soil cover and organic matter or for grazing of livestock (which results in manure). Moreover, where animals graze the residues, even less remains for conservation purposes, decline SOC and soil health.
  4. Use of bare fallow: Some farmers use bare fallow to regenerate their lands. However, apart from spontaneous weed growth, there is no energy source for the soil biota present on the land. Instead of recovering the soil food web, the soil organic matter is degraded further, and the lack of cover can result in severe erosion and runoff when the rains start after the dry season.
  5. Burning of natural vegetation and crop residues: This is a common practice for clearing land, both in slash-and-burn systems and in more intensive agricultural production systems
  6. Overgrazing and crop residues removal:  Overgrazing destroys the most palatable and useful species in the plant mixture and reduces the density of the plant cover. Continue residue removal diminishes the inert SOC level, thereby increasing the erosion hazard and reducing the land’s nutritive value and nutrient recycling capacity.
  7. Tillage practices: Tillage enhances decomposition rate and results in the formation of less stable humus and an increased liberation of CO2 to the atmosphere, thus reducing organic matter and SOC. In terms of short-term organic matter loss, the more soil is tilled, the more the organic matter is broken down (Table 3). There are also longer-term losses attributed to repeated, annual cultivation. Cropping systems that return the little residue to the soil accelerates this decline. Many modern cropping systems combine frequent tillage with small amounts of rubble, with resultant reductions in the organic matter content of many soils.

Table 3: Tillage induced flush of decomposition of organic matter (source: Glanz, 1995) [20]

Type of tillageOrganic matter lost in 19 days (kg/ha)
Mouldboard plough + disc harrow (2x) Mouldboard plough Disc harrow Chisel plough Direct seeding4 300 2 230 1 840 1 720 860
  1. Drainage: Decomposition of organic matter occurs more slowly in poorly aerated soils, where oxygen is limiting or absent, compared with well-aerated soils. Soil drainage is determined strongly by topography – soils in depressions at the bottom of hills tend to remain wet for extended periods because they receive water (and sediments) from upslope having a slow rate of organic matter decomposition. Where soils are drained artificially for agricultural or other uses, the soil organic matter decomposes rapidly.
  2. Fertilizer and pesticide use: Initially, fertilizer and pesticides enhance crop development and thus production of biomass (especially important on depleted soils). However, the use of some fertilizers, especially N fertilizers, and pesticides can boost micro-organism activity and thus decomposition of organic matter. The chemicals provide the microorganisms with easy-to-use N components. This is especially important where the C:N ratio of the soil organic matter is high, and thus decomposition is slowed by a lack of N.


Various types of human activity decrease soil organic matter contents and biological activity. However, increasing the organic matter content of soils or even maintaining good levels requires a sustained effort that includes returning organic materials to soils and rotations with high-residue crops and deep- or dense-rooting crops. Different approaches are needed for various soil and climate conditions [16]. The activities like conservation tillage, cover crops/green manure crops, crop rotation, agroforestry integrated nutrient management, biofertilizer and composting, etc., assist in creating a new equilibrium in the agro-ecosystem increase of SOM and sustaining soil health through SOC build-up.

The greater association between CEC and pH was reported in earlier and has revealed a significant role of organic matter in enhancing CEC [25]. It is well established that SOC plays a crucial role in the maintenance of the majority of soil properties for better crop production and soil health. SOM significantly affects water-holding capacity, aggregate stability, and compaction and strength characteristics of soils. It also improves aggregate stability and tends to reduce water erosion. As the size of the aggregates reduces to less than 850 they become more susceptible to erosion caused by wind and water. Researchers have reported a negative relationship between organic matter content and bulk density of soils, which is helpful in crop production [46]. Bandyopadhyay et al., (2010)[2] reported that the use of organic matter (FYM @ 4 t ha–1) in combination with recommended levels of inorganic fertilizers resulted in a decrease in bulk density (9.3%), soil penetration resistance (42.6%) and an increase in hydraulic conductivity (95.8%), size of water-stable aggregates (13.8%) and SOC (45.2%) compared to control. It has been shown that thermal heat properties of soil-related to storage and heat flow through it are also influenced by SOM [1].

  • Conservation agriculture involves minimal soil disturbance, a permanent soil cover, and ecologically viable crop rotations. Through the use of cover crops and crop residue mulch retention, a permanent soil cover combined with reduced-tillage could be the best management practice for SOM restoration and control of erosion [27]. A conservation tillage system is an ecological approach to soil surface management as it conserves soil organic matter, maintains physical properties, minimizes soil erosion risks but on the other hand, increases surface bulk density and, overall, enhances soil health. Kumar et al., (2018) [36] concluded in his study that adoption of zero tillage (ZT), residue (R) incorporation and integration of weed management practice, optimize the oxidizable organic carbon pool, active and passive pools, SOC, maintain the soil structure by providing greater stability to soil aggregates MWD>125 μm and increase total aggregates percentage and reduce surface soil temperature over conventional tillage and residue incorporation treatments compared to the conventional tillage followed by conventional tillage system.

Soil service (2012) [52] reviewed the soil organic matter (SOM) content, which is closely linked to SOC, in conventional and organic farming, respectively. The conventional farming areas included management regimes with mineral fertilizer and pesticide application, whereas organic fields included management types with organic fertilizer and no pesticides. The results indicated a positive effect of organic fertilizers and no pesticides on SOM content (Figure 5).

Figure: 5, Forest plots of the effect sizes (Hedges’s g) of 29 studies on the effect of conventional vs. organic farming on SOM [52].

Mandiringana et al., (2005) [41] studied the relationship between total above-ground biomass input and SOM under long-term continuous tillage in maize mono-cropping and crop residue removal. The results concluded that soils in the low input smallholder systems depleted the SOM to levels below 1% at 0–5 cm soil depth. Surface SOM is essential to erosion control, water infiltration, and conservation of nutrients [19]. Dube (2012) [13] reported a strong positive linear relationship between nitrogen fertilizer input and SOM. The N fertilization increased the biomass production for oat and vetch due to N fixation and building SOM at 0–5 cm on a loamy sand soil in South Africa.

The various studies examine combination of reduced tillage and increased residue return [36] through appropriate cover crop species [45] selection and astute fertilizer application [33] present opportunity for SOM build up and effects on SOM pools. The accumulation rate of SOM, its fractions, and its fractions depend on soil texture, precipitation, and temperature [6]. On a local scale, microenvironmental conditions that depend on factors such as microtopography, surface cover components, and land management dictate spatial differences in SOM [ 49, 11].

  • Integrated nutrient management

The importance of integrated nutrient management has been well-documented by Katyal [31], with continuous application of chemical fertilizers to virgin soil, SOC remained stable for 10 years, while in manure and fertilizer (integrated nutrient management) practices, it was stable for 25 years. This indicated that the combined use of organic and inorganic fertilizers played an essential role in stabilizing and maintaining SOC in cropping systems and ensuring sustainability. Long-term application of chemical fertilizers could not maintain optimum soil carbon content and crop productivity [35, 53]. On the other hand, the sole use of organic fertilizers also could not maintain the desired agronomic productivity due to the inherently low nutrient status of soils. Therefore, the application of a recommended dose of the chemical fertilizer coupled with organic fertilizer is essential [44].

  • Green manuring and Cover crops

The incorporation of green manuring crops biomass in the soil enhances the SOC and other nutrients, especially nitrogen, irrespective of the cropping system under different climatic conditions [48]. There was a tremendous potential to increase SOC content and improve other associated soil functions using different green manuring crops, particularly dhaincha and sun hemp. Some studies have indicated considerable improvement in the activities of various enzymes (dehydrogenase and phosphatase activity) with green manuring using sunhemp, green gram, and cowpea crops compared to control. A significant build-up of N, P, and K was also observed with green manuring crops. Several other studies have indicated the benefit of green manuring in rainfed regions [61].  The autumn and spring crops are grown as cover crops, when incorporated in the soil, can help in building or maintaining SOM. The best results of raising these crops can be achieved if other remedial practices such as in situ moisture conservation are also adopted. Results of the long term experiments in rainfed agroecology suggested that in situ incorporations of fresh biomass of horse gram (Macrotyloma uniflorum) with different levels of fertilizers over a period 10 years, increased the organic carbon and microbial biomass carbon by 24% and 28%, respectively, compared to fallow plots. These practices also helped in improving soil fertility and its health [54].

  • Biofertilizers, composting and organic amendments

The proper use of biofertilizers in agricultural system could be a viable approach to increase crop yield and improve soil health. Microbial biofertilizers have long been recognized as effective means of fertilization [4] that exert a range of beneficial effects in enhancing plant growth by an array of activities, including N2-fixation, decomposition of organic materials, increasing the availability of macro and micronutrients in the soil, phytostimulation, suppression of plant diseases, synthesis of antibiotics, production of phytohormones, build-up of soil fertility and structure in the long run etc. [59]. Biofertilizers are low-cost, and eco-friendly over chemical fertilizers while retaining the correct balance between enhanced crop production, soil health and conserved environment, thus ensuring environmental and economic sustainability [42].

Compost is a stabilized and sanitized product, which has undergone decomposition through the process of humification [5]. Composts not only supply plant nutrients, organic matter, inhibit root pathogens/soil borne plant diseases but also enhancing crop production. Moreover, it can be used as a soil conditioner which improves soil physical, chemical, and biological properties [55] which are significant for continuing the soil as a vital living system and improve its health [8]. The functions occurred in healthy soil will sustain biological productivity, the quality of surrounding air and water, as well as promote plant, animal, and human health [12]. Regular applications of different organic sources to the soil help progressively enhance the soil’s organic matter status and supply essential nutrients to plants.

There are various options available for on-farm generation of organic sources of crop and weed residues and their composting, vermicomposting, green manuring through crops, tree-based green leaf manuring, tank silt application, application of FYM, poultry manure, and sheep and goat manuring to increase SOC content and crop productivity. Some off-farm sources such as treated sewage sludge, biochar, and agro-industries waste (baggessage, coir pith, groundnut shell, poultry manure, sheep penning, press mud, seri waste, etc.) can also be used as sources of the organic matter. Over the years, organic amendments have become the critical factors for maintaining soil health and crop productivity of soil [54].


Soil organic carbon is an integral component of soil organic matter and has a close relationship with soil health and crop production. Hayne (1940) [23] stated that, “if we feed the soil, it will feed us,” and that “only productive soil can support a prosperous people.” Thus, for prolong human health; maintaining soil health is mandatory because ecosystem functions and nature conservancy were achieved through ultimate soil health. The global carbon cycle involves the cycling of C through the soil, vegetation, atmosphere, and ocean. The build-up of SOC assists in mitigating the impact of climate change and ultimately sustain soil health. Soil health is coupled with different attributes and affected by various constraints. The environmental consequence of soil health is also determined by the SOC pool, its dynamics and the turnover time. Soil OM is in a constant state of turnover, where it is decomposed and replaced by new organic material. Therefore the balance between inputs and the rate of loss will determine the relative flux in SOM content. Various management practices include conservation agriculture, integrated nutrient management, the addition of organic amendments, compost, biofertilizers, cover crops, the biomass of green manuring crops, etc., which can help in increasing organic matter status in soils and enhance soil health.If these practices are followed systematically, the organic matter status of soils can be enhanced on a long-term basis, and overall soil health (functionality) can be significantly improved.


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