**4. Carbon management practices (CMP)**

A 4% increase in global agricultural soil carbon pool up to 1 m depth, 2–3 Gt C can be sequestered annually which would drawdown global anthropogenic GHG emission by 20–35% [15] but practicality has many constraints. For example, in countries with low (inherent) SOC like India, high rate of decomposition due to high temperature and the removal of crop residues does not allow this concept to work well [16]. Due to a greater surface area and charge density, organic matter can react with soil particles to form organo-mineral complexes. The mean residence time of carbon fractions are functions of their turnover rate which is dependent on the degree of protection within soil matrix [17]. Chemical protection involves formation of some recalcitrant compounds [18] like non- acid hydrolysable carbon fraction, aromatic compounds, double chained hydrocarbons and hydrophobic compounds which are not easily decomposed by microorganisms.

Change in soil carbon is a balance sheet of carbon input and output through mineralisation, loss, other emissions etc. [10]. So, the key for sequestering SOC is increasing carbon inputs and reducing carbon outputs. Cropping system biomass productivity has primary control over this carbon input through proper fertiliser, land, water management practices based on exiting soil and climatic condition. Integrated and balanced fertiliser application positively affect both above ground and below ground biomass and crop productivity. This adds more amount of organic matter to the soil directly in the form of straw returns, roots, exudates and organic manures directly. The organic carbon present in soil is very much prone to oxidation if neither biochemically protected (depends on its composition) not physically protected (in soil aggregates). So, researches focus on those practices

*Sustainable Carbon Management Practices (CMP) - A Way Forward in Reducing CO2 Flux DOI: http://dx.doi.org/10.5772/intechopen.97337*

which are helpful to protect pre-existing soil aggregates and/or to promote the genesis of new soil aggregates or to achieve both objectives of CMP.

Important carbon management practices are:


#### **4.1 Conservation Agriculture (CA)**

This is the technology of a set of management practices which aims at conserving the natural resources and biodiversity in the crop land and are characterised by the three principles e.g., i) No/minimum soil disturbance, ii) permanent organic cover or cover crops, and iii) crop diversification. Each principle individually and combinedly contribute towards carbon enrichment in soil. Build-up of carbon in soil can be successful through increased input, reduced decomposition and loss or both. Cultivation of previously uncultivated land can lead to 20%–40% loss in the native carbon in the initial years following initial cultivation [19]. Restoring that carbon in soil through addition and protection can be a potential carbon management practice. Every input like fertiliser, pesticide and irrigation has a carry a 'hidden carbon cost, thus optimising their quantity in a crop management practice should be estimated in the carbon balance sheet [20]. Historically, excessive cultivation operations like tillage can expose SOC for decomposition by microbes which further may cause many land degradation problems such as erosion and soil structural decline. Enhanced soil disturbance triggers carbon losses from soil system via increased decomposition and erosion of SOM. All these ultimately adds to the atmosphere as CO2 fluxes or to the water resource [21]. Soil carbon levels of agricultural soils are lower than corresponding soils under natural vegetation or fallow that indicates the potential for soil carbon storage. In agricultural systems, soil carbon levels tend to be variable and dependent on management practices. Reducing soil disturbance can reduce rate of oxidation of organic matter and provide protection to the microbial habitat. Rate of decomposition can also be reduced by introducing slowly decomposing residues in the rotation. Intensifying crop rotation, legumes and green manure crops in crop cycle, elimination of fallow period, cover crop and residue mulch enhances soil carbon input in the form of both above ground and below ground biomass. The principles of conservation agriculture rotate around the concept of biomass addition and its protection through less soil disturbance. Soil C level and its composition under no-tillage and stubble retention (SOC = 2.5%) was more than the same soil under 3 pass tillage and stubble burning (SOC = 1.5%) after 19 years [4]. Reduced tillage increases the potential of soil c sequestration over conventional tillage practices as described in **Figure 2**. The concept of achieving steady state carbon status in cultivated soil through maximisation of organic input (residues, root biomass, organic amendments) is depicted in **Figure 3**. Conservation agriculture technology can be a potential method for conserving soil moisture, supplying plant nutrient and mitigate pathogen, peat and weed infestation there by cutting off fertiliser, pesticide requirement. Every input like fertiliser, pesticide and irrigation has a carry a 'hidden carbon cost, thus optimising their quantity in a crop management practice should be estimated in the carbon balance sheet [23].

A study conducted by [20] Sapkota et al. (2015) in the Indo-Gangetic region showed that conventional rice- wheat cropping system has 27% higher GHG emission (in terms of CO2 equivalence) as compared to zero tilled rice- wheat crop rotation with residue mulching [23]. Sapkota et al. (2014) found the carbon dioxide efflux so also the global warming potential of wheat (through life cycle analysis) for its unit production under conventional tillage based practice is 10 times higher than no tillage based production. Introduction of legume in crop rotation and residue addition to the soil help reducing fertiliser requirement and energy need in arable systems. Considering the fact that, the annual global fertiliser leads to an annual release of 300 Tg of CO2 into the atmosphere during fertiliser manufacturing process [24], any management practice that will reduce the chemical fertiliser requirement with optimised output is highly environment friendly. They also explained that the release of every 2.6–3.7 kg CO2 per every 1 Kg of synthesised N, is produced from fossil fuel thus causing a net contribution to atmospheric amount of CO2 [24].

While the carbon sequestration in soil will occur at a certain point of time (until saturation) depending upon the soil type, reduction in emission owing to less energy requirement, fossil fuel consumption and machinery use will continue until the practice is carried out [25]. Zero tillage cuts the fuel consumption for land preparation so also CO2 emission. (Erenstein and Laxmi 2008) [26] found that adoption of ZT in wheat- maize system of the IGP could save an average of 36 L diesel ha–1 which is equivalent to a reduction in 93 kg CO2 emission ha−1 yr.−1 Sapkota et al. (2015) [20].

### *4.1.1 Mechanism of soil carbon sequestration in CA system*

The carbon stock–enhancing effect of SOC management practice of conservation is possible due to reduced disturbance which is the prime factor in maintaining

**Figure 2.** *Changes in SOC content in cultivated soil as a result of tillage pattern over years [4].*

**Figure 3.** *Mechanism of achieving steady state SOC through input addition. Adopted from [22].*

soils physical stability. This physical wellness of a soil system has positive effect on microbial habitat, their activities and the natural ecosystem functions of soil like nutrient cycling, buffering capacity, cation exchange etc.

The first principle is no tillage which is growing crops in soil without causing soil disturbance except for sowing or reduced tillage that is significant reduction of soil disturbance through less frequent passes of tillage, tillage in specific portion of the field which is in form of strip or ridge and shallower depth of tillage. Second principle aims at keeping a permanent organic cover on the soil surface in the form of residue mulch, growing cover crops both of which addresses many aspects of soil protection in the form of hindrance towards water, wind erosion, improved soil aggregation, enrichment of substate for microbial growth and functionality and many other chemical properties such as nitrogen fixation, carbon sequestration, etc. the third principle i.e. crop diversification is an essential tool for promoting better soil health as it has a role in allowing nutrient uptake of differently rooted crops from different depths, promoting microbial diversity, reducing disease and pest infestation there by allowing a better plant growth and biomass addition.
