# Impacts of Land-Use Change from Primary Forest to Farmland on the Storage of Soil Organic Carbon
## 4 Discussion
### Effects of Tillage and No-Tillage on SOC Reserves in Cultivated Land  
When the virgin forest was converted to cultivated land system, soil organic carbon decreased rapidly, partly due to the low proportion of insoluble substances in the easily decomposed crop residues. Cultivated soil enhances the mineralization of SOC through cultivation and releases CO\({}_{2}\) into the atmosphere. Tillage requires periodic mixing of the soil, which destroys soil aggregates and produces carbon compounds that cannot be decomposed by microorganisms. Incineration of crop residues is also a major cause of the reduction of SOC storage, especially in tropical regions. Incineration of crop residues is a common management measure of cultivated land systems. This process emits various greenhouse gases into the atmosphere, leaving inert components such as charcoal as residual substances in the soil. [PERSON] et al. (2002) [30] reported that, in fire-prone ecosystems, charcoal produced by incomplete biomass combustion may account for about 35% of the total organic carbon. The study of [PERSON] et al. (2001) [31] also showed that an important reason for the reduction of SOC storage caused by crop cultivation in cultivated soil is that incineration measures separate a large number of soil organic carbon components from the organic carbon pool into intractable carbon, which accounts for a very large proportion of the total organic carbon pool in the soil. Tillage is a major soil management practice that alters soil structure, leading to the destruction of soil aggregates, increasing soil compaction, and disrupting soil plant and animal communities. Soil structure is defined as the size, shape, and arrangement of solids and voids. Void and pore spaces in turn regulate the flow of fluids in the soil and the growth and development of plant roots. Intensive tillage alters soil structure and affects soil organic carbon. Tillage promotes the mineralization of organic carbon, and the optimal soil moisture conditions for mineralization allow organic residues to be fully exposed to microorganisms, exposing the encapsulated carbon to degrading enzymes. There is also a strong interaction between tillage and drainage, both of which reduce soil moisture and increase soil temperature, thereby reducing SOC mineralization rates. [PERSON] et al. (2000) [32] found that the timing and intensity of tillage determined the extent of its impact on SOC. Compared with intensive tillage, no-till crop management systems have relatively more macropores, biological pathways, stable soil aggregates, and more SOC sequestration. The positive effects of no-till or disturbance-reduced tillage on soil sequestration depend on the specific soil and location, for example, in poorly drained soils and fine-textured soils, which are inconsistent with the general increase in SOC. In contrast, studies in North America, Brazil, Argentina, and Europe have reported high levels of carbon sequestration in soils under conservation tillage. Tillage systems with low disturbance usually result in the release of easily degraded organic matter substrates. [PERSON] et al. (2004) [33] reported that conservation or no-till soils provided morephysical protection of carbon components than intensively tilted soils, thereby promoting carbon accumulation. [PERSON] (1986) [26] proposed that macroscale polymers (particle size > 250 \(\upmu\)m) contain more unstable SOC, which his research found was easily lost under high disturbance. [PERSON] et al. (1998) [34] estimated that conservation tillage could sequester about 43 tons of carbon per year in the soils of cultivated systems in the EU, and they proposed a shift to no-till for all tillage practices to offset all fossil fuel carbon emissions from European agriculture. Similar to tillage, crop residue management and mulching change soil structure through a variety of processes and methods. Adding residues and mulch can reduce erosion and evaporation, protect soil from rainwater, and improve the stability of soil aggregates.