Effect of land management practices on the concentration of dissolved organic matter in soil: A meta-analysis

Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) are important components of dissolved organic matter (DOM) in soil. A change in the concentration of soil DOM leads to changes in the soil carbon (C) and nitrogen (N) pools and the emergence of potential pollution. Many studies have reported that the concentrations of soil DOM could be significantly influenced by land management practices. However, the results obtained from these studies are inconsistent, and the effects of environmental factors on the responses of DOM concentrations to such management practices remain unclear. The aims of this study were to: (1) synthesize the available datasets and elucidate the general patterns of changes in soil DOM concentrations in response to different land management practices; and (2) probe how the responses of DOM concentrations to management practices were affected by environmental factors (e.g., altitude, climate, and soil properties). Data from 942 observations in 184 publications were collected, integrated, and statistically analyzed. The meta-analysis result shows that overall, N fertilization, liming, organic amendment addition, and vegetation cover significantly increased the concentrations of soil DOM, whereas tillage decreased DOC concentrations. The magnitude of all positive and negative effects was driven by implemented management practices. Generally, a threshold range might exist for the application rate and duration of the management measures that could cause significant changes in DOM concentrations. In addition, DOC concentrations were more responsive to N fertilization and liming than were DON concentrations, indicating that the changes in the two variables were not correlated in each management practice. The results also indicate that the responses of DOM concentrations to management practices could be regulated by the altitude, climate (e.g., mean annual temperature and precipitation), and soil property factors (e.g., total C, total N, C:N ratio, clay content, and initial soil pH). In conclusion, our study suggests that in order to maintain proper soil DOM concentrations in an ecosystem, not only the type and implementation of management practices but also the local environmental factors should be considered when proposing a land management plan.