Case Study 2: Application of biofertilizers based on engineered rhizobia to corn fields in the American Midwest.

Engineering Biology for Climate & Sustainability

Case Study 2: Application of biofertilizers based on engineered rhizobia to corn fields in the American Midwest.

Introduction

The application of fertilizers to agricultural fields enables more crops for food or fiber to be produced on a given area of land. Globally, the use of nitrogen fertilizers has increased about 800% since 1961, which has contributed to a 30% increase in food supply per capita.¹ The production of synthetic nitrogen fertilizers uses the energy intensive Haber-Bosch process, accounting for around 2-3% of the world’s energy supply.² Nitrogen fertilizers can leach out of the soil into waterways, causing ecological problems such as eutrophication,³^,⁴ and they release nitrous oxide, a problematic greenhouse gas.⁵ Non-synthetic (“organic”) fertilizers work well in many agro-systems but generally contain lower concentrations of nitrogen which often is not in a bioavailable form.

This case study considers how the beneficial relationships that plants such as legumes share with rhizobia can be extended to widely grown, nitrogen-intensive crops such as corn. It is likely that both the plant and bacteria would need to be engineered to support symbiosis, but because the nontechnical dimensions of plant engineering are well-explored elsewhere (e.g., Helliwell et al., 2019⁶), we focus here on engineered rhizobia. Engineered rhizobia could reduce (or perhaps eliminate) the need for Haber-Bosch-derived fertilizers for growing corn, and potentially many other crops, as the key determinants of plant-rhizobia symbioses become fully elucidated. Then, such symbioses could be engineered to support the growth of other crops as well. Biofertilizers could further reduce agricultural emissions if they could be applied in the field at the same time as planting, for example as a seed coating for a symbiotic crop. Use in corn fields in the American Midwest could minimize nitrogen run-off and its downstream effects, such as toxic bacteria and algae growth impacting waters in the Gulf of Mexico. However, this might mean that more energy-intensive synthetic fertilizers no longer used in the Midwest might be sold and used elsewhere in the world. As a result, greenhouse gas emissions would not actually decrease, and those new markets might see higher food security coupled to negative environmental impacts. For maximal impact, engineered biofertilizers would need to be internationally available and economically competitive with synthetic fertilizers. If less expensive than synthetic fertilizers, it could additionally support global food security as an option for growers who cannot afford synthetic fertilizers.

Nontechnical considerations and social dimensions

Solutions landscape:

Ethical / societal – This approach assumes that fertilizers for corn are necessary; are there farming practices or other advances in soil ecology that could minimize or eliminate the need for fertilizers?
- What, if any, impacts would greater adoption of such practices (e.g., crop rotations, rotational livestock grazing to restore soil nutrients) have on the food supply chain and cost?
Ethical / societal – Can other approaches, such as new chemistries for ammonia production or real-time sensing for precision fertilizer application, mitigate the energy-intensity and run-off challenges of synthetic nitrogen fertilizers?

Feasibility:

Economic – Will biofertilizers be available and financially accessible to different types of farmers (large vs. small scale) in disparate international locations? Would incentives (and what kinds of incentives) increase uptake?
Economic – Where can the biofertilizer be produced, and how expensive will it be? If it were only financially available in wealthier countries, would it still make an impact? What long term prospects might there be for lowering costs and distributing globally?

Benefits and consequences:

Ethical / societal – Soil systems and microbial communities can vary greatly; is it possible to understand the impacts of engineered microbes in advance of applications in all these different environments?
- Is a single engineered strain sufficient or would the solution require a community of engineered organisms for effective colonization and nitrogen fixation? If multiple strains are required, are all considerations compounded?
Ethical / societal – What impacts (positive, negative, or neutral) might biofertilizers have on ecosystems? What might the impacts be on the micro- and macro-biomes where it is applied and where it may eventually move/be transported to?
Ethical / societal – How do potential environmental risks of deployment compare to the better understood challenges of continued reliance on fertilizers made through the Haber-Bosch process?

Implementation:

Policy / regulatory – Would the use of fertilizer composed of engineered microbes exclude a crop from organic certification? If not, how many years after application could the land be certified for organic production? Would there need to be testing to show no genetically engineered microbes remained?
- At present, synthetic fertilizers cannot be used in organic farming; would such a fertilizer be considered “synthetic” because of the specific microbes used?
Security, Policy / regulatory – What level of containment (if any) at the sequence and/or the organism level would be necessary? How would containment be demonstrated to regulators?
Policy / regulatory, Ethical / societal – Will microbes used in biofertilizers be protected Intellectual Property (IP)? If so, will farmers be subject to legal action if protected microbes are found on their property?
- Could the microbes be developed within an Open Source framework that allows for more equitable distribution?
- What reasons might there be to have IP be open here?
Security – If engineered organisms are sold as protected IP and are distributed in live culture, what measures protect from IP “theft” (i.e., reculturing and propagating engineered microbes)?
Ethical / societal, Economic – Can technical decisions be made that ultimately increase biofertilizer accessibility globally?
- How can biofertilizers be made accessible to small-holder farmers to avoid contributing to the growing gap between small and large farming operations?

Micro-level impacts:

Economic – Given potential persistence (or lack of persistence), would biofertilizers affect other environmentally-beneficial farming practices such as crop rotation?
Ethical / societal – Where were the wild type microbes originally identified? Is there a historical context for the cultivation of these microbes in symbiosis with agricultural plants? Who benefits from their use? What measures need to be established to ensure benefits sharing and prevent biopiracy?

Macro-level impacts:

Ethical / societal – Would engineered microbes be present in run-off and downstream waterways?
Security – Could dependence on well-defined strains open up vulnerability to the evolution (or targeted attack) of neutralizing microbes (or plasmids, antibiotics)?

Competing values and priorities:

Ethical / societal – If biofertilizers both meaningfully reduce the need for synthetic fertilizers and significantly alter soil ecology in the regions where they are applied, how should those benefits and costs be weighted?
- Could metrics be developed by regulators and made available for public comment before implementation? What would be measured and where would that information be available?
Economic – How might early research choices influence the industrial and economic models used later for commercialization?
- Might linkage of engineered microbes to complementary engineered plants lock farmers into buying one (or few) plant varieties?
- Would farmers need to reapply biofertilizers each season, or would microbes persist to recolonize roots in subsequent growing seasons?
Policy / regulatory – The scale of biofertilizer production necessary to make a difference in the use of synthetic fertilizers would be significant; production and distribution on such scales is likely to be more feasible for large corporate actors. Should the economic beneficiaries of such technologies be a consideration in their development?

Footnotes

Mbow, C., C. Rosenzweig, L.G. Barioni, T.G. Benton, M. Herrero, M. Krishnapillai, E. Liwenga, P. Pradhan, M.G. Rivera-Ferre, T. Sapkota, F.N. Tubiello, Y. Xu. (2019). Food Security. In: Climate Change and Land: an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems. Retrieved from https://www.ipcc.ch/site/assets/uploads/sites/4/2021/02/08_Chapter-5_3.pdf
DeLisi, C., Patrinos, A., MacCracken, M., Drell, D., Annas, G., Arkin, A., Church, G., Cook-Deegan, R., Jacoby, H., Lidstrom, M., Melillo, J., Milo, R., Paustian, K., Reilly, J., Roberts, R. J., Segrè, D., Solomon, S., Woolf, D., Wullschleger, S. D., & Yang, X. (2020). The Role of Synthetic Biology in Atmospheric Greenhouse Gas Reduction: Prospects and Challenges. BioDesign Research, 2020, 1–8. https://doi.org/10.34133/2020/1016207
Howarth, R. W. (2008). Coastal nitrogen pollution: A review of sources and trends globally and regionally. Harmful Algae, 8(1), 14–20. https://doi.org/10.1016/j.hal.2008.08.015
Bijay-Singh, & Craswell, E. (2021). Fertilizers and nitrate pollution of surface and ground water: An increasingly pervasive global problem. SN Applied Sciences, 3(4), 518. https://doi.org/10.1007/s42452-021-04521-8
Schwenke, G. D., Herridge, D. F., Scheer, C., Rowlings, D. W., Haigh, B. M., & McMullen, K. G. (2015). Soil N2O emissions under N2-fixing legumes and N-fertilised canola: A reappraisal of emissions factor calculations. Agriculture, Ecosystems & Environment, 202, 232–242. https://doi.org/10.1016/j.agee.2015.01.017
Helliwell, R., Hartley, S., & Pearce, W. (2019). NGO perspectives on the social and ethical dimensions of plant genome-editing. Agriculture and Human Values, 36(4), 779–791. https://doi.org/10.1007/s10460-019-09956-9