Coated controlled-release fertilizers (CRFs) have been widely applied in agriculture due to their increased efficiency. However, the widespread and a lot of coated CRFs application may leave undesired coating residues in the soil due to their slow degradation. Limited information is available on the effects of substantial residual coatings on the soil bacterial community. By adding 0, 5, 10, 20, and 50 times quantities of residual coating from conventional application amount of resin and water-soluble coated CRFs, we studied the responses of soil properties and bacterial community composition to these two residual coatings in black soil. The results showed that the resin and water-soluble coatings did not essentially alter the properties of black soil or cause dramatic changes to bacterial diversity within the test concentration range. The residual resin and water-soluble coatings also did not distinctly alter the relative abundance of the top ten bacteria at phylum level. Heatmap results suggested that the treatments were basically clustered into two groups by concentration rather than types of coating material. Pearson correlation analysis showed that the Simpson’s diversity index of the bacterial community was significantly correlated with microbial biomass carbon (MBC, r=0.394, P<0.05), and the richness index abundance-based coverage estimator (ACE) of the bacterial community was significantly correlated with microbial biomass nitrogen (MBN, r=0.407, P<0.05). Overall, results of this study suggested that substantial residual resin and water-soluble coatings with 0–50 times quantities of residual coating from conventional application amount of coated CRFs did not generate obviously negative impacts on the bacterial community in black soil.

Rational application of nitrogen (N) fertilizers is an important measure to raise N fertilizer recovery rate and reduce N loss.A two-year field experiment of rice-wheat rotation was employed to study the effects of N fertilization modes including aN fertilizer reduction and an organic manure replacement on crop yield, nutrient uptake, soil enzyme activity, and numberof microbes as well as diversity of microbes. The result showed that 20% reduction of traditional N fertilizer dose of localfarmers did not significantly change crop yield, N uptake, soil enzyme activity, and the number of microbes (bacteria,actinomycetes, and fungi). On the basis of 20% reduction of N fertilizer, 50% replacement of N fertilizer by organic manureincreased the activity of sucrose, protease, urease, and phosphatase by 46-62, 27-89, 33-46, and 35-74%, respectively, andthe number of microbes, i.e., bacteria, actinomycetes, and fungi by 36-150, 11-153, and 43-56%, respectively. Further,organic fertilizer replacement had a Shannon’s diversity index (H) of 2.18, which was higher than that of other modes ofsingle N fertilizer application. The results suggested that reducing N fertilizer by 20% and applying organic manure in theexperimental areas could effectively lower the production costs and significantly improve soil fertility and biologicalproperties.