Bioorganic–Mineral Fertilizer Can Remediate Chemical Fertilizer-Oversupplied Soil: Purslane Planting as an Example

Chemical fertilizer (CF)-oversupplied soils in intensive agricultural systems are typically abandoned due to loss of fertility and productivity. In this study, we investigated the potential of organic-mineral fertilizer (OMF), produced by a combination of organic matter, potassium (K)-feldspar powder and microbial fermentation, to alleviate the same in purslane cultivation. A gradient dose of OMF was applied to CF-oversupplied soils and purslane was grown in it and the alterations in soil physic-chemical parameters and enzyme activities along with purslane nutritional traits were analysed after 80 days. From the results, soil with excessive CF exhibited a sharp decrease in pH and increased electrical conductivity (EC); further, the activities of enzymes, such as urease, alkaline phosphatase and carbonic anhydrase (CA), showed an abrupt decrease. When a gradient dose of OMF (67, 134 and 200 g kg−1 soil based on the previous research in the lab) was applied to the CF-oversupplied soil, their available K content was significantly higher than the CF-oversupplied treatment and control. Additionally, the contents of total carbon and active organic carbon (AOC) were highest in treatment group OMF3 + CF (200 g of OMF kg−1 soil). The nutritive contents of purslane, such as soluble sugar and total flavonoids, and relative contents of ω-3 polyunsaturated fatty acid (PUFA) etc. showed a significant increase when compared with control, while the anti-nutritive compounds, such as nitrates and soluble oxalic acid, decreased. The positive effects on the soil quality traits and purslane growth and nutritive quality suggest the OMF treatment might be a promising approach for sustainable crop production and soil remediation in CF-oversupplied soil.