Comprehensive evaluation of effects of various carbon-rich amendments on overall soil quality and crop productivity in degraded soils

Abstract

Soil degradation is a global menace to agricultural crop production. Since loss of soil organic carbon (SOC) is a significant characteristic of soil degradation and since SOC underpins nearly all critical soil functions, a broad range of C-rich amendments (CRAs) have been applied to avoid soil degradation. However, little information is available regarding how various CRAs influence overall soil quality. Here, we conducted experimental trials under field conditions simultaneously at two sites (Beijing and Ningxia; the nutrient-holding capacity was much higher in the Beijing soil than in the Ningxia soil) over two consecutive years, to investigate effects of various CRAs (i.e. straw-C, composted straw-C, and humic acid-C) on overall soil quality and tomato yields. The overall soil quality was expressed by the soil quality index (SQI) covering a wide range of soil physical, chemical and microbial properties. In general, straw-C addition enhanced SQI mainly at Beijing site through increasing soil water content and plant beneficial bacterium Myxococcota, and decreasing soil pH (alleviating alkalization). Composted straw-C addition increased SQI primarily at Ningxia site by enhancing soil porosity, nutrient availability and plant beneficial bacterium Firmicutes, and reducing soil pH, harsh environment-adapted bacteria Methylomirabilota and Gemmatimonadota, and plant fungal pathogen Basidiomycota. However, humic acid-C addition had no effect on SQI at any experimental site. The SQI showed a significant positive correlation with either root biomass or tomato yields at both sites. Together, our results demonstrate that straw-C addition is an effective method for enhancing overall soil quality and crop productivity in soils having a high nutrient-holding capacity (Beijing), while composted straw-C addition is beneficial to soils having a low nutrient-holding capacity (Ningxia).