Biological conservation measures are better than engineering conservation measures in improving soil quality of eroded orchards in southern China

Both biological and engineering measures have proven to be effective soil and water conservation practices for eroded environments, whereas how the soil quality varies with them remains unclear. In this study, we measured soil properties in the 0-to-100-cm soil layer of eroded orchards in southern China after 17-yr of application of different conservation measures. The purpose of the experiment was to examine the effect of biological (grass planting, intercropping) and engineering measures (terrace) on the soil quality of eroded orchards. We selected an orchard plot with traditional clean-tillage as control. In comparison, soil pH, organic carbon, total phosphorus, microbial carbon, available potassium, and available micro-elements contents increased significantly in orchards with biological measures, and the improvements were more dramatic in orchards planting grass in strips. However, biological measures significantly reduced the mean weight diameter of aggregates. Engineering measures significantly increased the soil pH of orchards but decreased the contents of available iron and available manganese. The soil quality index (SQI) was 4-55% higher in the biological treatment than in the control. Moreover, higher SQIs were found in the orchards with grass planting than that with intercropping, and this effect was greater in the topsoil than in deeper soils. On the contrary, engineering measures had similar SQI with clean tillage. These results suggest that biological measures are more effective than engineering measures in maintaining soil quality and nutrient content in eroded orchards in southern China.