Assessing soil quality of gleyed paddy soils with different productivities in subtropical China

Gleyed paddy soil is a typical soil with low productivity, and gleization of paddy soil is a serious issue in subtropical China. A systematic evaluation of soil quality can facilitate improvements in soil fertility and productivity. However, research data on soil quality assessment of gleyed paddy soils remain limited. Our study was to quantify soil quality and assess the constraints limiting rice productivity of gleyed paddy fields.Based on the mean annual rice yield, gleyed paddy soils were divided into high (HPGS, >13,500kgha−1), medium (MPGS, 11,250–13,500kgha−1), and low productivity (LPGS, >11,250kgha−1). Eighty-four soil samples were collected and analyzed for 28 soil parameters including physical, chemical, and biological properties. The 17 variables showing significant differences (P≤0.05) among HPGS, MPGS and LPGS were selected for principal component analysis.A minimum data set (MDS) was established with total nitrogen (TN), available K (AK), microbial biomass C, β-glucosidase, total bacteria and arbuscular mycorrhizal fungi, accounting for 88.0% of the quality variation among soils. Soil quality index (SQI) was also developed based on the MDS method, and HPGS, MPGS and LPGS received mean SQI scores of 0.87±0.05, 0.73±0.04, and 0.64±0.05, respectively, thus ranking as HPGS>MPGS>LPGS.Overall, HPGS showed relatively good soil quality and was characterized by high levels of nutrient availability, and enzymatic and microbial activities, but the opposite was true of LPGS. Lower levels of TN, AK and biological activities were considered as the major constraints limiting rice production in LPGS compared with HPGS. Our study area was seriously deficient in AK limiting crop production. Significant correlation between SQI and rice yield suggested that SQI may be a promising tool to integrate soil information and indicate the degree of soil quality for gleyed paddy soil in subtropical China and other paddy areas with similar soils.