How effective are soil and water conservation measures (SWCMs) in reducing soil and water losses in the red soil hilly region of China? A meta-analysis of field plot data.

Anthropogenic pressure coupled with high rainfall and diverse heterogeneous landscapes (e.g., land use and topography) has resulted in severe water erosion in the red soil hilly region (RSHR) of China. Soil and water conservation measures (SWCMs) have been extensively implemented, and their effects on runoff and sediment control have been widely tested at plot scales. However, it is difficult to gain an overview of the efficiency of SWCMs due to the difficulty of directly upscaling field observations to regional scales. We conducted a meta-analysis of 498 field plots covering 53 sites in the RSHR to evaluate the efficiency of different SWCMs and identify optimal conservation practices. The results were as follows: (i) SWCMs involving erosion control (92%) had a greater efficiency than those focusing on runoff reduction (73%). (ii) The implementation of combined measures was more effective than single measures for reducing runoff and soil loss. (iii) All thirty SWCMs showed a significant effect with respect to runoff and sediment control, except for contour tillage effect on reduction of soil loss. (iv) The maximum and minimum ratios between runoff and sediment reduction were found in orchard and cropland, respectively. (v) Six measures, mulching, tree crop + grass, tree crop + hedgerows, tree crop + grass cover + terrace, tree crop + hedgerows + terrace and hedgerows + contour tillage, can be recommended as high effective SWCMs in the RSHR. This study provides a systematic overview quantifying the factors controlling the effectiveness of SWCMs in the RSHR and can serve as a scientific foundation enabling decision makers to implement suitable SWCMs in mitigating land degradation due to water erosion.