Soil Microbial Co-Occurrence Patterns under Controlled-Release Urea and Fulvic Acid Applications

Abstract

The increasing amount of agricultural applications of controlled-release urea (CRU) and fulvic acids (FA) demands a better understanding of FA's effects on microbially mediated nitrogen (N) nutrient cycling. Herein, a 0-60 day laboratory experiment and a consecutive pot experiment (2016-2018) were carried out to reveal the effects of using CRU on soil microbial N-cycling processes and soil fertility, with and without the application of FA. Compared to the CRU treatment, the CRU+FA treatment boosted wheat yield by 22.1%. To reveal the mechanism of CRU+FA affecting the soil fertility, soil nutrient supply and microbial community were assessed and contrasted in this research. From 0-60 days, compared with the CRU treatment, leaching NO₃^--N content of CRU+FA was dramatically decreased by 12.7-84.2% in the 20 cm depth of soil column. Different fertilizers and the day of fertilization both have an impact on the soil microbiota. The most dominant bacterial phyla <i>Actinobacteria</i> and <i>Proteobacteria</i> were increased with CRU+FA treatment during 0-60 days. Network analysis revealed that microbial co-occurrence grew more intensive during the CRU+FA treatment, and the environmental change enhanced the microbial community. The CRU+FA treatment, in particular, significantly decreased the relative abundance of <i>Sphingomonas</i>, <i>Lysobacter</i> and <i>Nitrospira</i> associated with nitrification reactions, <i>Nocardioides</i> and <i>Gaiella</i> related to denitrification reactions. Meanwhile, the CRU+FA treatment grew the relative abundance of <i>Ensifer</i>, <i>Blastococcus</i>, and <i>Pseudolabrys</i> that function in N fixation, and then could reduce NH₄⁺-N and NO₃^--N leaching and improve the soil nutrient supply. In conclusion, the synergistic effects of slow nutrition release of CRU and growth promoting of FA could improve the soil microbial community of N cycle, reduce the loss of nutrients, and increase the wheat yield.