Effects of controlled-release fertilizer residual coat accumulation on soil microbial communities

To explore the effect of controlled-release fertilizer residual coat accumulation on soil microbial communities, pot experiments were conducted with five treatments of 3.60–4.00 mm polyurethane addition (residues of controlled-release fertilizer coat), namely no residual coat (CK), 140 kg∙hm⁻² polyurethane addition (CR1), 280 kg∙hm⁻² polyurethane addition (CR2), 560 kg∙hm⁻² polyurethane addition (CR3), and 1400 kg∙hm⁻² polyurethane addition (CR4). Illumina MiSeq high-throughput sequencing technology was used to analyze the differences in soil bacterial and fungal community composition and diversity under different treatments. The results revealed that the contents of soil dissolved organic carbon (DOC), soil moisture (SM), and belowground biomass of maize (BGB) in CR4 treatment and NO₃⁻-N in CR3 treatment were significantly increased compared with those in CK; however, the soil pH and contents of available potassium, total nitrogen (TN), available phosphorus (AP), and NH₄⁺-N did not significantly change in all treatments. The operational taxonomic units of bacteria and fungi, the diversity index (Shannon), and the richness indexes (Ace and Chao) of the soil bacterial community increased as the polyurethane addition rate increased, and the difference between CR4 and CK was significant; however, the diversity and richness indexes of the soil fungal community did not significantly change under different treatments. The relative abundance of the soil bacterial and fungal communities at the phylum and genus levels changed as the polyurethane residual coat increased. The relative abundance of Proteobacteria, Bacteroidetes, and Burkholderia increased with the accumulation of the residual coat; however, the relative abundance of Acidobacteria and Sphingomonas showed the opposite pattern, and the difference was significant between treatments CR4 and CK. Compared with CK, treatment CR3 improved the relative abundance of Ascomycota significantly, treatment CR4 increased the relative abundances of Glomeromycota and Mortierella significantly. The Mantel test showed that soil DOC, AP, SM, and maize BGB were the key factors affecting the bacterial community structure, whereas soil DOC, TN, and SM were the key factors affecting the fungal community structure. Therefore, polyurethane residual coat addition can directly or indirectly improve the diversity of bacterial communities and affect the composition of bacterial and fungal communities in the short term by changing the soil DOC, SM and maize BGB, and other factors.