In the present times, long-lasting ecological equilibriums are challenged by human activities at a global scale. With world population expected to grow 25% in the next 20 years, it is likely that the environmental pressure that we exert would also increase. If we want to avoid the uncertainties derived from a climate changing scenario, matching economic growth to sustainability is arguably the most important challenge needs tackling. On the other hand, more and better food will be required in the coming years, putting farming practices in a hotspot for building up a sustainable future [1].

The agricultural sector, with few notable exceptions like the slash-and-burn method or the dairy/meat industry, does not contribute strongly to greenhouse gas emissions, due to the balancing effect of the carbon sequestered during plants’ growth and fructification. Nonetheless, farming in its present, conventional form, is considered unsustainable, as it heavily depends on external inputs, mostly synthetic fertilizers [2]. Although industrial nitrogen forms are mostly responsible for the increased agricultural productivity over the last few decades, its pervasive use came with various negative environmental implications. Firstly, nitrogen fertilizers are produced starting with the Haber-Bosch process, an energy intensive chemical transformation that burns non-renewable gas resources to fix molecular nitrogen into ammonia. With an estimated annual production of 450 million tons of nitrogen fertilizers, this process alone is responsible for as much as 5% of the total use of extracted methane [3]. Furthermore, leaching of nitrogen fertilizers from the fields negatively impacts water bodies causing eutrophication, a phenomena that has many times led to massive death of fishes and other aquatic animals [4]. Nonetheless, in the authors’ view, one of the worst aspects related with the effectiveness of fertilizers is a cultural one: it has allowed farmers to start viewing the plant as a simple mean of production, totally dissociated to the natural cycles that so heavily depends on. As a consequence, promoting farmers’ adoption of sustainable practices, often based on a system view of the plant-soil interactions, will not be trivial.

References

1. Ramankutty N., et al. “Trends in Global Agricultural Land Use: Implications for Environmental Health and Food Security”. Annual Review of Plant Biology 69 (2018): 789-815. 
2. Pretty J., et al. “Global assessment of agricultural system redesign for sustainable intensification”. Nature Sustainability 1 (2018): 441-446.
3. “Fertilisers in the EU”. EU Agricultural Markets Briefs (2019).
4. Padilla FM., et al. “Global trends in nitrate leaching research in the 1960-2017 period”. Science of The Total Environment 643 (2018): 400-413.
5. West TO and Post WM. “Soil Organic Carbon Sequestration Rates by Tillage and Crop Rotation”. Soil Science Society of America Journal 66.6 (2002): 1930-1946.
6. Pywell RF., et al. “Wildlife-Friendly Farming Increases Crop Yield: Evidence for Ecological Intensification”. Proceedings of the Royal Society B: Biological Sciences 282 (2015).
7. Letourneau DK., et al. “Does Plant Diversity Benefit Agroecosystems? A Synthetic Review”. Ecological Applications 21 (2011): 9-21.
8. Blanco-Canqui H., et al. “Cover Crops and Ecosystem Services: Insights from Studies in Temperate Soils”. Agronomy Journal 107.6 (2015): 2449-2474.
9. Kleijn D., et al. “Ecological Intensification: Bridging the Gap between Science and Practice”. Trends in Ecology and Evolution 34 (2019): 154-166.
10. Bender SF., et al. “An Underground Revolution: Biodiversity and Soil Ecological Engineering for Agricultural Sustainability”. Trends in Ecology and Evolution 31 (2016): 440-452.
11. Sahu PK., et al. “Connecting microbial capabilities with the soil and plant health: Options for agricultural sustainability”. Ecological Indicators 105 (2019): 601-612.
12. Pii Y., et al. “Microbial Interactions in the Rhizosphere: Beneficial Influences of Plant Growth-Promoting Rhizobacteria on Nutrient Acquisition Process. A Review”. Biology and Fertility of Soils 51.4 (2015): 403-415.
13. Ruzzi M and Aroca R. “Plant growth-promoting rhizobacteria act as biostimulants in horticulture”. Biostimulants in Horticulture 196 (2015): 124-134.
14. Zhang R., et al. “The unseen rhizosphere root-soil-microbe interactions for crop production”. Environmental Microbiology 37 (2017): 8-14.
15. Heijden van der MGA., et al. “The Unseen Majority: Soil Microbes as Drivers of Plant Diversity and Productivity in Terrestrial Ecosystems”. Ecology Letters 11 (2008): 296-310.
16. Desbrosses GJ and Stougaard J. “Root Nodulation: A Paradigm for How Plant-Microbe Symbiosis Influences Host Developmental Pathways”. Cell Host and Microbe 10 (2011): 348-358.
17. Vessey JK. “Plant growth promoting rhizobacteria as biofertilizers”. Plant and Soil 255.2 (2003): 571-586.
18. Mehnaz S. “An Overview of Globally Available Bioformulations”. Bioformulations: For Sustainable Agriculture, edited by Naveen Kumar Arora, et al. New Delhi: Springer India (2016).
19. Bhatti TM and Yawar W. “Bacterial solubilization of phosphorus from phosphate rock containing sulfur-mud”. Hydrometallurgy 103.1-4 (2010): 54-59.
20. Hafeez FY., et al. “Plant Growth-Promoting Rhizobacteria as Zinc Mobilizers: A Promising Approach for Cereals Biofortification”. Bacteria in Agrobiology: Crop Productivity, edited by Dinesh K. Maheshwari, et al. Springer Berlin Heidelberg (2013).
21. Gupta G., et al. “Plant Growth Promoting Rhizobacteria (PGPR): Current and Future Prospects for Development of Sustainable Agriculture”. Journal of Microbial and Biochemical Technology 7 (2015).
22. Backer R., et al. “Plant Growth-Promoting Rhizobacteria: Context, Mechanisms of Action, and Roadmap to Commercialization of Biostimulants for Sustainable Agriculture”. Frontiers in Plant Science 9 (2018): 1473.