The present study investigated the interactions among nitrogen transformation and soil bacteria along the direction of diffusion of hole-applied urea. To this end, a lab incubation trial was conducted on sandy loam and silty loam soils. Soil bacterial communities were analyzed via 16S rRNA high-throughput sequencing, and soil chemical properties were measured at 8, 20, and 60 d after urea application. The treatments were the fertilizer point and 0–4 cm, 4–8 cm, 8–12 cm, and 12–16 cm horizontally distant from the fertilization point. They were designated FP, 0–4, 4–8, 8–12, and 12–16, respectively. The pre-culture and pre-incubation soil sample was used as a control. Soil NH₄⁺ concentration was the key factor influencing the soil bacterial community. For the sandy loam, the FP and 0–4 treatments reduced the putative abundance of amoA by 38.9–83.4% and 40.7–67.6%, amoB by 38.9–83.4% and 40.6–67.6%, and amoC by 41.1–84.1% and 43.6–69.9%, respectively, compared with the control group. For the silty loam, the FP and 0–4 treatments reduced the putative abundance of amoA by 85.0–87.3% and 28.9–82.6%, amoB by 84.6–87.2% and 29.1–82.5%, and amoC by 81.9–87.1% and 27.5–82.7%, respectively, compared with the control group. The fertilizer core region was 60 d, which strongly inhibited nitrification. Overall, the fertilizer core region slowly released nitrogen and inhibited nitrification. For these reasons, hole application of urea may serve as a long-acting nitrogen fertilizer.

Organic amendments application has been proposed as an efficient method for remediation of heavy metals-contaminated soils. This study evaluated the performance of the water-insoluble organic material polyvinylpolypyrrolidone on decontaminating water and soil polluted by heavy metals Cu, Cd and Zn via batch trials, soil incubation and pot experiments with oilseed rape. The adsorption process of Cu, Cd and Zn by polyvinylpolypyrrolidone included a rapid step which achieved 92%, 76% and 87% of adsorption capacities within 10 min, followed with a slow step before reaching equilibrium which varied from 4 to 24 h among the three heavy metals. The maximum adsorption capacities were 327, 330 and 186 mg g⁻¹ for Cu, Cd and Zn, respectively. With application doses of polyvinylpolypyrrolidone ranging from 10 to 60 g kg⁻¹, the DTPA-extracted Cu, Cd and Zn showed 59–96%, 27–93% and 13–83% reduction compared to no addition. Moreover, the uptake of Cu, Cd and Zn by oilseed rape were significantly inhibited with polyvinylpolypyrrolidone amendments, and the effects improved with the accrual of polyvinylpolypyrrolidone. Intriguingly, the application of polyvinylpolypyrrolidone showed insignificant influences on nutrients taken up by oilseed rape. Results of the present study indicated that polyvinylpolypyrrolidone is a promising organic amendment for heavy metal (Cu, Cd and Zn) stabilization in polluted water and soil.