**5. Increasing organic carbon stocks in agricultural soils**

Agricultural systems are dependent on maintenance of four major functions; nutrients cycling, carbon transformations, soil structure maintenance, and regulation of pests and diseases [14]. Increasing SOM in agricultural soils contribute to food security and adaptation to climate change as well as mitigation of climate change [12]. SOM has a major role in soil fertility and water retention [47]. Therefore, SOM indirectly contributes to agricultural productivity and consequently to food security [12]. Management practices can influence SOC stocks by either decreasing SOC losses or increasing C inputs to soils. When OC input to a soil is larger than the OC outputs by mineralization or erosion, the SOC increases [12]. Below are technological options to manage SOC in agricultural ecosystem.

#### **5.1 No-tillage and conservation agriculture**

Soil organic matter is considered an important indicator of soil quality and health, which can be impacted by crop production practices such as tillage [48]. Tillage has the potential to increase the rate of C mineralization through breaking larger macro aggregates, mixing crop residues and exposing protected SOC in the aggregates to soil microorganisms [5, 6, 49, 50]. In general, tillage is considered to increase SOC mineralization as a result of mechanical and rain induced disruption of soil aggregates and the consequent release of CO2. Hence, conservation tillage/no-tillage has been considered as a suitable practice to maintain or increase SOC stocks compared to conventional tillage [12, 51, 52]. Conservation tillage practices such as no till can enhance assimilation of SOC by decreasing soil disturbance and increasing crop residue accumulation in comparison to conventional tillage [12, 25, 48, 53]. For example; Blanco-Canqui and Lal [54] indicated an increase in SOC with increasing crop residue retention, whereby 16.0 t C ha−1 of SOC was reported without straw additions, 25.3 t SOC ha−1 with 8 t ha−1 of straw added and 104.9 t C ha−1 with 16 t ha−1 of straw added.

Global meta-analyses and reviews have recently confirmed that SOC stock increases in the upper soil layers (0–15 or 0–20 cm) under no tillage, but generally has low to non-significant effects on SOC stocks over 30 cm depth or deeper [51, 55–58] (**Figure 4**). In addition to carbon sequestration, conservation tillage can reduce CO2 emissions [60]. Accumulation of SOC exhibit a positive correlation with the sequestration of atmospheric CO2, while oxidation of SOC, as a result of practices such as tillage, can contribute to CO2 emission from agricultural fields [48]. For example, CO2 emission in conventional tillage was 29% greater than in no till in a loamy soil as reported by Bista et al. [61].

#### **5.2 Irrigation**

Irrigation may have similar effects on SOC decomposition in varying scenarios, but, its effects on primary production are likely to be much higher in arid and semi-arid areas compared to humid regions with dry summers [62]. It is reported that irrigation exhibited strong positive effects on SOC stocks in desert soils,

#### *Land Use Change Affects Soil Organic Carbon: An Indicator of Soil Health DOI: http://dx.doi.org/10.5772/intechopen.95764*

positive effects in semi-arid areas, but no consistent trend was observed in humid areas [12, 62]. Further, it is emphasized that SOC stocks are dependent on climate and initial SOC content [62].
