# A Review on Carbon Source and Sink in Arabic Land Ecosystems
## 4 Main Factors Affecting the Dynamics of Carbon Sources and Sinks in Arable Land Ecosystems
### Impact of Human Management Measures on Arable Land Carbon
#### 4.2.3 Irrigation Measures  
Irrigation and its scheduling affect soil and crop water status, thereby affecting microbial function and greenhouse gas emissions [111]. Proper soil moisture would enhance root respiration and microbial activities, accelerate the decomposition of SOM and increase CO\({}_{2}\) emission [104]. However, high humidity reduces soil aeration and inhibits soil respiration and CO\({}_{2}\) emissions [112]. The effect of irrigation on carbon sequestration appear to be highly dependent on location/conditions [72]. In arid areas or soil with low initial carbon content, irrigation can increase the content of SOC [16; 113]. Wetting the soil with irrigation  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Agricultural Management Practices** & **Carbon Sequestration Potential** \\  & **(Tg C Year\({}^{-1}\))** \\ \hline Straw return & 23.2–57.1 [99] \\ Conservation tillage & 21.5–43.0 [99] \\ Saline soil improvement & 20–40 [100] \\ Agroforestry & \(1.2\times 10^{3}\)–\(2.2\times 10^{3}\)[101] \\ Organic fertilizer & 5.5–42.2 [102] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Estimation of potentials for agricultural carbon sequestration by different management practices.  
after drought could release the accumulated SOM during drought periods and produce a large amount of nutrients and organic carbon [114]. In desert areas, due to large soil pores, the infiltration of moisture can transport SOM and fine particles to deep layers [20]. However, in areas with humid climate and high initial SOC content, irrigation might lead to a decrease in SOC [115].  
The commonly used irrigation methods in arable land include border irrigation, sprinkler irrigation and drip irrigation, which may cause different effects on arable land carbon. In southwestern Nebraska, [PERSON] et al. [16] compared the carbon stocks between irrigation and dryland management treatment, it was found that the carbon stocks of irrigation were 25% higher than that of dryland cultivation, and the carbon input of crop residue under drip irrigation was estimated to be 2.5 times higher than that under drought. However, it was found that increasing carbon input under irrigation could not improve the level of large aggregates and the greater carbon stock was mainly due to the higher carbon sequestration in micro aggregates. The impact of tillage damage on the overall level was greater than the increased residue input under irrigation [16]. [PERSON] et al. [111] concluded the CO\({}_{2}\) flux and cumulative emission of drip irrigation plot were significantly higher than that of border irrigation plot. The increase of CO\({}_{2}\) emission of drip irrigation might due to the better water and soil environment created by irrigation, resulting in higher plant root respiration and stronger microbial activity. However, there were no unified conclusions on the impacts of irrigation method on CO\({}_{2}\) emission. [PERSON] et al. [116] reported that under the condition of film covering, the CO\({}_{2}\) emission of drip irrigation in clay loam was lower than that of flood irrigation. Therefore, information on different management practices and other irrigation systems in different regions is needed to more accurately understand the overall impact of irrigation on soil carbon storage.