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INTRODUCTION
Current agriculture relies heavily on the excessive mineral fertilizer application, which have severely degraded 40% of the world's agricultural soil (Zhang et al., 2017). To tackle this issue, modern agriculture is confronted with the task of identifying alternative strategies to traditional mineral fertilization, which allow its reduction or replacement. Among these alternatives, Plant Growth Promoters (PGP)-based biostimulants are gaining attention, since they have proven effective in enhancing soil microbial activity (Kumar and Verma, 2019) and can increase crop yield by different mechanisms, including nutrient solubilization, nitrogen fixation or phytohormone secretion (du Jardin, 2015). The aim of this study was to determine the effect of reducing the mineral fertilization rate together with the application of a PGP-based biostimulant on rice yield, plant biometric and physiological parameters, as well as on the rice rhizosphere-associated microbiome.
MATERIALS, METHODS
A field experiment with rice (Oryza sativa var Hispagran) was carried out in Isla Mayor (Sevilla, Spain). The treatments tested consisted of the application of a conventional rate (C) of 150 kg N ha-1 and half of conventional rate (½C) 75 of kg N ha-1. These two rates were either applied alone or combined with the biostimulant (BS) Sullicab® (Corteva AgriSciencesTM), consisting in a four Bacillus strain cocktail (40% B. licheniformis, 20% B. safensis, 30% B. pumilus and 10% B. velezensis). Fertilization was applied in one amendment before sowing. At the end of the crop cycle plant biometric and physiological parameters were determined prior to grain yield determination. Rice rhizosphere samples of C, ½ C and ½ C-BS were also taken to determine the microbial diversity by bacterial 16S rRNA and fungal ITS1 amplicon sequencing.
RESULTS
The application of ½C fertilizer rate induced a decrease of 35% (down to 5.638 kg ha-1) in grain yield with respect to the C rate (8.735 kg ha-1). The addition of BS to the C fertilizer rate did not exert any effect in terms of grain yield. However, when BS was supplemented to the ½C fertilizer rate, this decrease was recovered by 61%, obtaining a yield of 7.516 kg ha-1. Besides, the application of BS significantly increased root development (both in terms of volume and dry matter), the flag leaf area and its total chlorophyll and carotenoid contents.
Regarding the rhizosphere bacterial communities, differences in terms of alpha diversity were observed between the C and ½C in richness and evenness, and between ½C-BS and C just in evenness; being diversity in C lower than in the other treatments. No differences were observed in fungal alpha diversity. The changes observed in bacterial community composition were explained by 25% due to BS application, and by 37% due to the fertilizer rate. The fungal community composition was influenced by both BS and fertilizer rate, in 19% and 17%, respectively.
DISCUSSION
The amendment of BS together with reducing fertilizer application resulted in a promising strategy, as BS was able to recover about 61% of the yield lost due to the fertilizer rate reduction. In line with the fact that the fertilization impacts community structures, leading to a decrease in bacterial alpha diversity in the root environment (Reid et al., 2021), in this trial the bacterial diversity was more significantly influenced by the fertilizer rate than by the application of the BS, which agrees with the greater effect of the fertilizer rate on grain yield.
REFERENCES
du Jardin, P. (2015). Plant biostimulants: definition, concept, main categories and regulation. Sci. Hortic. 196 3–14. 10.1016/j.scienta.2015.09.021
Kumar, A., Verma, J.P. (2019). Ecological wisdom inspired restoration engineering. Springer Singapore.
Reid, T. E., et al. (2021). Inorganic chemical fertilizer application to wheat reduces the abundance of putative plant growth-promoting rhizobacteria. Front. Microbiol., 12. https://doi.org/10.3389/fmicb.2021.642587
Zhang, H., et al. (2017). Microbial taxa and functional genes shift in degraded soil with bacterial wilt. Sci. Rep., 7. https://doi.org/10.1038/srep39911
ACKNOWLEDGEMENTS
Spanish Government (Grant PID2021-128273OB-I00 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”), Basque Government (IT1560 22) and AvanzaBio Agro S.L. M.M. is holder of an IKERTALENT2022 Fellowship funded by the Basque Government and M.J.M. is holder of the contract PRE2022 102053 funded by MCIN/AEI/10.13039/501100011033 and FSE+. Z.S.S. received a grant from the Regional Government of Castilla y León and a grant co-financed by the European NextGenerationEU.
| Keywords | efficient microorganisms; microbial diversity; yield; sustainable agriculture |
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