Effects of slow- and controlled-release nitrogen fertilizers on bacterial and fungal community composition in a double-cropping rice system

Slow-and controlled-release (SCR) nitrogen (N) fertilizers improve crop production and N utilization efficiency. However, responses of biological soil characteristics to the long-term application of N fertilizer have received little attention. In this work, a five-year field experiment was performed to assess the influence of different N fertilizer treatments (no N fertilizer application [CK] and applications of polymer-sulfur coated urea [PSCU], conventional prilled urea [PU], and urea-formaldehyde [UF]) on soil microbial communities in yellow clayey paddy soils in southern China. The types of N fertilizers had a stronger impact on soil bacterial diversity and community structure than fungal diversity and community structure. The soil microbial communities of PU and UF treatments did not differ from those of CK regarding alpha diversity indices. However, the PSCU treatment significantly decreased the Shannon index by 2.16% for bacteria but had no significant effect on the Shannon index of fungi. This might be due to the application of PSCU significantly reducing the soil pH by 0.16 units compared to CK and leading to soil acidification. Co-occurrence network analysis determined the keystone species mainly belonging to Proteobacteria and Ascomycota. Notably, these keystone species played an impor-tant role in PSCU-treated soils. Soil Ca2+, Na+, and NH4+ were the main determinants of microbial network stability. These results contribute to our understanding of how SCR-N fertilizers impact soil microorganisms.

Automated summary

Slow and controlled-release nitrogen fertilizers have a positive impact on crop production and nitrogen utilization efficiency. However, little attention has been given to the effects of long-term N fertilizer application on soil microbial communities. In this five-year field experiment, different N fertilizer treatments were applied to yellow clayey paddy soils in southern China, and it was found that the type of N fertilizer had a stronger influence on soil bacterial diversity and community structure compared to fungal diversity and community structure. The application of polymer-sulfur coated urea (PSCU) significantly decreased soil pH and had a significant effect on bacterial diversity indices. Keystone species belonging to Proteobacteria and Ascomycota played an important role in PSCU-treated soils. Soil cations and ammonium were identified as the main determinants of microbial network stability. These findings enhance our understanding of the impact of slow and controlled-release nitrogen fertilizers on soil microorganisms.