Long-term unregulated mining of ion-adsorption clays (IAC) in China has resulted in severe ecological destruction and created large areas of wasteland in dire need of rehabilitation. Soil amendment and revegetation are two important means of rehabilitation of IAC mining wasteland. In this study, we used sludge biochar prepared by pyrolysis of municipal sewage sludge as a soil ameliorant, selected alfalfa as a revegetation plant, and conducted pot trials in a climate-controlled chamber. We investigated the effects of alfalfa revegetation, sludge biochar amendment, and their combined amendment on soil physicochemical properties in soil from an IAC mining wasteland as well as the impact of sludge biochar on plant growth. At the same time, we also assessed the impacts of these amendments on the soil microbial community by means of the Illumina Miseq sequences method. Results showed that alfalfa revegetation and sludge biochar both improved soil physicochemical properties and microbial community structure. When alfalfa revegetation and sludge biochar amendment were combined, we detected additive effects on the improvement of soil physicochemical properties as well as increases in the richness and diversity of bacterial and fungal communities. Redundancy analyses suggested that alfalfa revegetation and sludge biochar amendment significantly affected soil microbial community structure. Critical environmental factors consisted of soil available K, pH, organic matter, carbon–nitrogen ratio, bulk density, and total porosity. Sludge biochar amendment significantly promoted the growth of alfalfa and changed its root morphology. Combining alfalfa the revegetation with sludge biochar amendment may serve to not only achieve the revegetation of IAC mining wasteland, but also address the challenge of municipal sludge disposal by making the waste profitable.

Potted rice seedlings independently treated with N, P, and NP were continuously ¹³ CO2 labeled to investigated the influence of N and P application on the contribution of photosynthesized C to the rhizosphere versus bulk soil and particulate organic matter (POM) versus mineral fraction (MIN). N and NP enhanced net assimilated ¹³ C on day 14 (D14), with maximum C assimilation occurring on day 22 (D22) under NP. Aboveground biomass retained more ¹³ C than belowground biomass for all treatments. 13C incorporation into the rhizosphere exceeded that in bulk soil, with the maximum (6–10%) found under N addition. Newly assimilated ¹³ C incorporated into POM increased in the rhizosphere under N and NP conditions, whereas MIN remained largely unaffected. ¹³ C-MBC proportion in the total microbial biomass C (MBC) pool revealed that N and NP stimulated microbial activity to a greater degree than P. The main portion of ¹³ C in the rhizosphere and bulk soil was found in POM on D14, which decreased over time due to microbial utilization. Contrastingly, root-derived ¹³ C in the MIN remained unchanged between sampling days, which indicates that the stabilization of rhizodeposits in this fraction might be the potential mechanism underlying SOM sequestration in paddy soils.