Short-Term Effects of Eco-Friendly Fertilizers on a Soil Bacterial Community in the Topsoil and Rhizosphere of an Irrigated Agroecosystem

Fertilizer application to arable soils could be effective for soil nutrients. However, there are many negative effects in croplands with long-term chemical fertilizer application. Whether eco-friendly fertilizer addition could enhance soil quality and soil microbial activity has been investigated before; however, how top- and rhizosphere soil bacterial communities respond to their short-term effects is not well known. Here, we used Illumina MiSeq sequencing to determine the changes of bacterial community structure in both topsoil and rhizoshpere after one month of the addition of three different eco-friendly fertilizers—biochar (B), microbial fertilizer (MF), fertilizer synergist (FS) and selected soil base fertilizer (CK) as a control, in an irrigated agroecosystem of cabbage crop (Brassica oleracea L. var. capitata L.). The results show that three different eco-friendly fertilizers significantly enhanced cabbage growth. The Shannon and Ace indexes of the bacterial community significantly decreased under the FS treatment in both soils, but the total abundance of bacteria was maximal under the FS treatment in the topsoil and the MF treatment in the rhizosphere. The addition of the three fertilizers led to significant differences in the relative abundance of bacteria community at the phylum level, such as Proteobacteria, Acidobacteria, Rokubacteria and Planctomycetes in the topsoil, and Chloroflexi, Actinobacteria, Firmicutes and Rokubacteria in the rhizosphere. The same phylum showed the inconsistent changes under different fertilizer treatments in both topsoil and rhizosphere. The dominant genera, i.e., Nitrosospira and Massilia in the topsoil, and Flavobacterium, Nitrosospira and Pseudomonas in the rhizosphere, were much higher under the FS treatment than others. Redundancy analysis showed that total nitrogen and available phosphorus were the key factors that shaped the bacterial community in this ecosystem. These results highlighted that the short-term addition of eco-friendly fertilizer had an improvement effect on the quality of both topsoil and rhizosphere in croplands with long-term chemical fertilizer application.