**2.2 Effect of agronomic management on soils microbiome and CO2 balance in soils**

Agronomic management involves a combination of soil and crop management practices that when appropriately applied will improve soil performance and nutrient availability, and contribute to better growth and higher crop yield [24]. These management practices can be further categorized into an untargeted approach based on common agricultural practices, or targeted approaches based on specific interactions between soil and plant. Targeted approaches often involve biotechnological applications such as biofertilizers and biostimulants. Regardless of the type of approach, the soil microbiome will be affected either directly or indirectly. Considering that the soil microbiome is regarded as the primary organism that may influence the overall plant health due to its close interaction with plant roots, applying the right management practice is crucial toward achieving the goal of food security for the growing global population [25]. Therefore, soil microbiome must not be overlooked in agronomic management practice especially when SOM is concerned due to its major role in soil C pool. For instance, additional OM applications may result in increased decomposition and reduced C storage due to reduced microbial C use efficiency, positive priming effect from enhanced mineralization of SOM, as well as increased C skimming due to accumulation of microbial products and residues, or necromass over time [26].

SOC is known to be directly influenced by the stabilization and decomposition of SOM. Therefore, agronomic management that boosts SOM such as fertilization, conservation tillage, cover cropping, and crop rotation will also affect SOC [27]. More importantly, soil biotic and abiotic factors such as texture, moisture, C/N ratio, SOC content, pH, climate, vegetation, and land use also affect the persistence of SOM, and ultimately the C pools [28]. It is due to the complex interactions of these various factors that it is uncommon for an ecosystem to change from a net C source to a C sink in a relatively short time [29]. Thus, agronomic management practice must take into account the most appropriate way to minimize its impact on climate change [27].

Crop management refers to a collection of agricultural activities aimed at enhancing crop growth, development, and production. It starts with seedbed preparation, seed sowing, and crop maintenance and concludes with crop harvest, storage, and commercialization. Although fertilization not only improves soil fertility and quality but also crop production, it causes soil pollution, soil hardness, organic matter mineralization, increased nitrous oxide emissions, and nitrate leaching into groundwater and surface waters [30]. Fertilizer application considerably affected the soil C/N ratio. When Liu et al. [30] analyzed chemical and organic fertilizers, they discovered that chemical fertilizer (NPK) treatment lowers soil pH, and when combined with organic fertilizer, it lowers the soil pH even more. Furthermore, the relative populations of microbiome components varied after organic waste (straw) treatment due to changes in ammonium nitrogen (NH4 + -N) and nitrate nitrogen (NO3 + -N).

Bhattacharyya et al. [26] reported that the influence of organic matter accessibility on the significance of SMC to soil C control can be explained in numerous ways:


The interrelationship between nutrients, roots, water, and SOM is another component that influences SOM to build up in more complex cropping systems. In the surface soil layer, available nutrients are dynamic; they may be reduced by net microbial immobilization during heavy litter intake times and abundant during times of net mineralization. Microorganisms regulate root proliferation through their effects on nutrient availability and water, while roots influence microbial activity through their effects on nutrient availability. Increased litter inputs encourage competition for nutrients between microorganisms. When litter and organic matter pool sizes increase over longer periods, mechanisms favoring C sequestration are reinforced such as improved plant water availability, stronger nutrient recycling capacity, and reduction of nutrient leakage. Since microbial and plant respiratory processes are dominated by nutrient availability, cover crops that increase CO2 and N2O fluxes would have a good impact on soil respiration.

The pH of the soil influences microbial activity. As a result, soil management activities such as liming have an impact on soil emissions as additional carbonate can be emitted as CO2. Soil emissions are reduced when the soil is acidic. The ideal pH

*Regenerating Soil Microbiome: Balancing Microbial CO2 Sequestration and Emission DOI: http://dx.doi.org/10.5772/intechopen.104740*

for methanogenesis (CH4 generation) is found between pH 4 and 7. CO2 emissions are at their highest when the pH levels are neutral. Under acidic soil conditions, N2O emissions are reduced. Because the balance between NH3 and NO3 flips to ammonia at higher pH values, nitrification rises. However, there was no evidence of a link between NO and N2O emissions and pH. Denitrification produces NO emissions under acidic soil conditions, whereas nitrification produces NO emissions under alkaline soil conditions.

Crop rotation (CR) changes soil microbial profiles toward microorganisms with C-sequestering characteristics. According to Venter et al. [31], microbial diversity and richness can be increased by 15 and 3.4%, respectively, using CR. Different crop rotation practices may cause variations in soil C storage and SMC use. After a long-term CR practice involving legumes, SOC stock, MBC, and soil enzymatic activity (acid/ alkaline phosphatase, beta-glucosidase, and arylsulfatase) may rise. The presence of legumes in CR may help to protect the SMC in general.
