**4.3 Crop diversification or rotation**

Monoculture is a technique that favour strong outbreak of diseases and pests. Again, due to same root architecture in every season, plants access nutrient from a specific depth. These affect plant growth and production. On the other hand, the stratified root architecture associated with crop diversification allows plants to uptake nutrients from various depths of the soil. Rhizosphere provides suitable environment for microbial diversity and proliferation in different level of the soil. Crop diversification has been shown to reduce the emergence and damage of such pests and diseases. This promotes better above ground as well as below ground biomass production in crop plant by which crop diversification directly contributes to carbon enrichment in soil. Crop rotation or mixed cultivar use instead of single genotype are found to improve resilience towards climate change extremities, pest, disease occurrence, enhance yield stability and reduce fertiliser footprint which ultimately cuts contribution of crop production towards CO2 emission. A study conducted by Hu et al. (2016) [42] showed that there is 46% less soil respiration and 10% less emission in wheat- maize intercropping as compared to maize monoculture in north-west China. In case of intensive cropping systems, minimum one legume crop is necessary for soil carbon stabilisation along with other soil quality benefits. Legume plants are characterised by deeper root system, high leaf shedding, higher root exudates accelerate rhizospheric activity [43]. The quality and quantity of both root exudates and microbial polysaccharides (rich in lignopolyphenol complexes) promote macro and meso aggregate associated carbon storage in "rotation with legume" system than "cereal- cereal" system which is a good indicator of carbon sequestration [44, 45]. A life cycle-assessment (LCA) review conducted by Clune et al. (2017) [46] from 2000 to 2015 around the world highlighted that pulses have a very low Global Warming Potential (GWP) values (0.50–0.51 kg CO2 eq kg−1 which makes inclusion of a pulse crop in crop rotation, a win-win situation.

Pulse cultivation has other beneficial effect on soil environment viz.; pulses during summer can conserve moisture because soil covering through litterfall protects soil surface from atmospheric temperature. Not only the exudate or biomass quality but the management practices associated with crop rotation (irrigation, fertiliser dose, nitrogen fixation, amount of residue recycled for different crop rotations) cause variation on biomass input into a system. Legume crops acquire their N from biological nitrogen fixation (except for starter dose of nitrogen fertiliser) rather than from the soil as nitrate a slight decrease in pH of soil occurs. The reduction in soil pH in neutral and alkaline soil environments promote microbial activity in root zone and increase the nutrient availability [45]. Therefore, pulse in rotation enhances the macroaggregates rather than cereal- cereal system. Though the results of legume in rotation are strong for higher carbon management, a cereal- cereal rotation improve the passive carbon pool because higher carbon: nitrogen ratio of such crop residues [45]. Cereal in a rotation has also found to be important in environmental aspect as per a study conducted by Senbayram et al. (2016) [47] who found that monocropped faba beans lead to three times higher cumulative N2O emissions than that of unfertilized wheat whereas faba bean wheat intercropping could lower the cumulative N2O emissions by 31% as compared to N-fertilised wheat.

Proliferated root condition under diversified cropping system supports a hierarchy of aggregate formation (macroaggregates followed by microaggregates within macroaggregates). Plant roots are residues bind the individual soil particles together to form macroaggregates then fine root hairs grow into these aggregates. The organic acids, enzymes, and other C-rich compounds exuded by these roots support higher microbial populations and act as the nucleation centre for microaggregate formation [48, 49]. The microbially altered organic compounds get polymerised and are then strongly bound to finer particles (silt & clay) inside of the macroaggregates. These newly formed occluded microaggregates are C and N enriched [48, 49].

### **4.4 Integrated and balanced nutrient management**

With increase in demand of food per capita per unit land area, farmers are adopting higher fertiliser application in hope of getting higher yield. But in contrast the expectation, over use of chemical fertiliser result in severe soil degradation which is a major contributor towards soil carbon loss and higher GHG emission. As a correction measure to such issue, many scient have looked for the role of integrated (chemical+ organic) and balanced fertilisation on GHG emission reduction and soil carbon enrichment. As per a study conducted in subtropical north-western states of India, application of organics along with chemical fertilisers reduces the gaseous N losses as compared to fertiliser nitrogen alone in rice-wheat system [50]. Addition of organics no doubt acted as the primary source of denitrification, but the carbon balance was still positive. The higher yielding cropping systems created a scenario of higher CO2-C consumed by crops for photosynthesis than the total flux of CO2-C from rice-wheat system even with the use of organics thus making it a sink of atmospheric CO2-C [50].

Integrated nutrient management (INM) technology improves the physical, chemical and biological activity of the soil, which leads to a healthy plant population and higher yield. Organic treatments like FYM, sulphitation press mud (SPM), green gram residue (GR) and rice-wheat crop residues (CR) may consistently increase biomass yields and increase C inputs in soil. The strong influence from increasing C stock through long-term balanced fertilisation under rice–wheat cropping system was found by Nayak et al., 2012 [51]. Organic material incorporation improved soil aggregation and structural stability and resulted in higher C content in macroaggregates, thereby improved C sequestration potential in soils. However, the C accumulation in aggregates may determine by the kind and source of organic inputs. Thus, study by Das *et al*. (2014) [52] found that a combination of GR in rice and FYM in wheat significantly improved C content in macroaggregates, 100% N application through inorganic fertiliser. However, CR incorporation enhances coarse particulate organic matter (>0.25 mm) which substantially increase C content within macroaggregates. Intensive rice–wheat system through combination of inorganic and organic fertilisers and crop residues increases C content in microaggregates- within-macroaggregates [53] indicating higher potential of C stabilisation in soil.

Organic amendment like FYM, vermicompost, biochar etc. have higher humification rate constant but less decomposition rate thus, improve the amount and stability of SOC through their addition. An incubation study by Naher et al., 2020 [54] described that carbon mineralisation rate was 0.011 tonne year−1 for INM followed by balanced fertiliser and control which in turn enhance the scope for SOC sequestration in soil for sustainable rice production.

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


#### **Table 5.**

*Effect of INM on emission and yield.*


#### **Table 6.**

*Effect of INM on various soil properties for better soil health and crop production.*

A study conducted by Bharali et al. (2018) [55] in the north-eastern India showed that addition of organics (Azolla compost or green manure) along with chemical fertilisers resulted in higher emission worth of higher global warming potential however, the carbon efficiency ratio and amount of fixed carbon in terms of grain yield was found to be higher and lower in case of Azolla compost as compared to chemical fertiliser alone. Likewise, in case of NPK + green manure, there is 64% higher emission over the control, a lower carbon efficiency ratio but higher total C fixed in a form of grain carbon (**Table 5**). Though INM is not a direct solution for reducing C efflux, the extra organics added may result in more emission as compared to sole chemical fertiliser addition, it also contributes to sufficiently higher C fixation in the form of grain C which ultimately shows to have a positive carbon balance due to INM.

A review done by Wu and Ma (2015) [56] shows the effect on INM on different soil properties and crop growth in countries of Asia is summarised in **Table 6**.

A meta-analysis conducted by Waqas et al. (2020) [57] all over China to study the effect of balanced, imbalanced, integrated, sole fertilisation and their combinations on yield sustainability (YSI), yield variability index (YVI) suggest that balanced and integrated fertilisation has highest YSI and lowest YVI and balanced chemical fertilisation has less YVI as compared to sole organics addition or imbalanced chemical fertilisation. The result supports the fact that integrated and balanced fertilisation supports carbon addition through higher above ground and below ground biomass production. Even imbalanced+ organic fertilisation and organic fertilisation alone can increase SOC due to direct addition of stabilised carbon through organic amendments. Organic amendments are also supply additional nutrients (N, P, S, etc.) into the soil which are responsible for production of fine

fraction of soil organic matter [58]. The direct and indirect carbon input through integrated fertiliser management is a great adoptive measure as carbon management practice. In general, cold temperature promotes carbon sequestration due to low rate of organic matter decomposition but in higher temperature region with higher productivity and consequently increased biomass carbon input into soil [59], SOC can be improved through stable aggregate formation.

Sole and continuous use of chemical fertilisers inhibit the micro-organisms and their biochemical compositions, which reduced the aggregate formation. But the fresh organic matter added through organic amendments supply promote microbial polysaccharide formation (water soluble and hydrolysable substrate) that also promote aggregate formation. In completely no fertiliser condition, higher root extraction causes shattering of macroaggregates and breaking up soil structure [60].

Biochar as an organic amendment is also a great choice because the carbon-rich material has many organic functional groups to which act as bridge to form strong complexes with soil and is also helpful to increase soil aggregation through charged surface, porous structure and high cation exchange capacity [61].

Biochar amendments has two mechanisms of improving SOC dynamics (1) promoting soil aggregation thereby physical protection of bound SOC (2) Negative priming by means of higher recalcitrant organic substrate pool having low decomposition rate [62] (**Tables 7** and **8**).


**Table 7.**

*Carbon sequestration in soil with rice–rice–fallow cropping sequence for 10 years [54].*


#### **Table 8.**

*Total organic carbon (TOC) content under INM and chemical fertilisation practice in various regions of Asia (TOC given in g/kg).*
