Response of bacterial compositions to the use of slow-release fertilizers with long-acting agents and synergists

Slow-release fertilizer (SRF) is a new type of fertilizer, which is consistent with the physiological nutrient requirements of crops, but can also improve fertilizer utilization by reducing the total amount of fertilizers and the number of applications. However, its effects on soil fertility and bacteria in sugarcane fields are not clear. This study investigated the proper usage of SRF and the long-term application of SRF on soil fertility and health in sugarcane fields, seven fertilization treatments were set up as follows: SRF + 125 g/t long-acting agent (A), SRF +150 g/t long-acting agent (B), SRF + 235 g/t long-acting agent (C), SRF + 3 kg/t synergists (D), SRF + 8 kg/t synergists (E), SRF + 18 kg/t synergists (F) and traditional fertilization (CK). Traditional and Illumina HiSeq high-throughput sequencing technologies were used to compare and analyze soil enzyme activity, microbial biomass, and other biological traits and bacterial diversity. The results showed that sugarcane yields could be significantly increased by the application of SRFs. Meanwhile, soil fertility, which was represented by the content of total organic matter, nitrogen, phosphorus, and potassium, or the available nitrogen, phosphorus, and potassium, were all significantly improved or similar to those of CK. Moreover, the bioindicators of soil fertility, such as the activities of soil enzymes (β-Glucosidase, aminopeptidase, and phosphatase) and soil microbial biomass (carbon, nitrogen, and phosphorous), were also significantly increased or similar to those of CK in most of the SRFs treatments. In comparison with CK, soil microbial diversity, richness, and soil bacterial community structures were not significantly altered in sugarcane fields under different SRFs applications. In addition, although unclassified_f__Acetobacteraceae, Humibacter, and norank_f__Caulobacteraceae were the unique dominant bacterial genera in CK, some soil bacterial genera, such as unclassified__Subgroup_6, unclassified__Subgroup_2 and unclassified__IMCC26256 were also enriched as the special soil dominant bacterial genera in all or parts of the SRFs treatments. i.e., soil bacterial community structures also were not destroyed by SRFs application which compared to CK. In comparison to CK, cane yields increased significantly over three years, but soil fertility and health in sugarcane fields could also be improved or maintained by SRFs applications. All of the above results indicate that the traditional fertilization method for sugarcane production can be completely replaced by SRFs application. Furthermore, based on the cane yields and the prices of sugarcane and fertilizers in the local area, the treatment C can be concluded as the most cost-effective SRFs usage among the six SRFs treatments: A to F.