# 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
#### 4.2.2 Fertilization Measures  
The impacts of fertilization on carbon source and sink of arable land ecosystems are mainly reflected in two aspects [19; 80]. First, it improves the vegetative environment for plant growth and increases biomass, so as to increase the input of soil organic residues and promote the accumulation of organic carbon. Second, by affecting the population, quantity and activity of soil microorganisms, it has an impact on soil respiration. Many researchers have reported positive effects on SOC sequestration due to increased fertilizer and organic inputs. [PERSON] et al. [103] found that after 15 years of application of mineral nitrogen, the amount of carbon retained in the soil increased due to the increase of crop residue production. [PERSON] et al. [104] concluded that the combination of irrigation and fertilization may lead to a significant increase in SOC content, especially in light soil with low initial organic carbon content. [PERSON] et al. [15] showed in a meta-analysis that nitrogen application significantly increased the total carbon storage of soil by 5.82%, and increased the carbon content of aboveground and underground parts of plants by 25.65% and 15.93% respectively. Globally, nitrogen addition significantly increased aboveground net primary productivity by 52.38%, indicating that with the increase of nitrogen deposition, terrestrial ecosystems may be enhanced as carbon sinks. [PERSON] et al. [105] observed that the SOC accumulation effects of farmyard manure (FYM) and FYM + NPK (N: nitrogen; P: phosphorus; K: potassium) treatments were better than that of NPK alone.  
In intensive agriculture, production depended on the extensive use of synthetic fertilizers, especially nitrogen fertilizer [106]. Some studies found that nitrogen addition was considered to be the largest contributor to the impact of different management practices on carbon emissions, the emissions caused by nitrogen fertilizer exceed 50% of the total emissions [107; 108]. Due to the decline of nutrient use efficiency, the use of chemical fertilizer to maintain crop yield has been increasing, which leads to higher direct emissions of greenhouse gases from soil [109]. The mechanism of nitrogen fertilizer affecting CO\({}_{2}\) emission is that nitrogen application promotes microbial growth and soil respiration that depends on the SOM content. When the soil carbon source is sufficient, applying N fertilizer will promote soil respiration and increase CO\({}_{2}\) emission, while when the carbon source is insufficient, soil respiration is inhibited [110]. [PERSON] et al. [107] found that increasing the amount of nitrogen application could improve rice yield, but when the amount of nitrogen application exceeded 225 kg N ha\({}^{-1}\), it had little impacts on rice yield and even caused some adverse effects. This highlights the importance of improving nitrogen management practices, preventing economic losses to crop producers, thus achieving a balance between reducing carbon emissions and expanding net carbon sinks in arable land ecosystems.