8
Going Forward
Viewed simply as a medium for growing food, soil in the United States has and will continue to contribute to the production of abundant food because of the expanse of agricultural land and the availability of nutrient, pest management, and water inputs. This prediction is agnostic to the associated costs, monetary or environmental, that such a view may entail. Food prices may be higher in the future if the cost of inputs rise or if the same unit of input or unit of land is less effective or productive in the future due to soil degradation. Food may also be more expensive if the amount of agricultural land declines because of conversion to other land uses or because its productivity is lost to changes in climate. Water bodies may be further degraded from sedimentation and excess nutrients, adversely affecting aquatic life, drinking water, and recreational activities. Aquifers may be depleted, and soil biodiversity may be lost. Nevertheless, given the size of the country, the United States will continue to produce a substantial amount of food.
If soil is instead viewed as a living system that supports not only food production but also clean water and air, contaminant degradation, and climate regulation and that serves as a reservoir of genetic resources yet to be discovered, then the rationale for considering soil as simply a medium is not only weak but misguided. The concept of One Health posits that soil should be valued as an ecosystem that, when healthy, contributes to the health of other ecosystems, plants, humans, and other animals and that contains a microbiome that connects not only to plants but also likely to people. Therefore, the way soil is tended to must be altered from that of a widget in a production system to that of a component in a holistic system that includes but extends far beyond agriculture.
This latter view requires a shift in approach not only for common agricultural management practices but also for land management in general. As this report recommends, a greater awareness of the importance of soil health to all citizens, not just those involved in agriculture, will be needed. Those responsible for land management will
have to prioritize the preservation of soil habitat and biodiversity, the increase of organic matter content where possible, and the optimization of nutrient use, including waste products. Such priorities will likely entail an increase in the complexity of management systems, for which a diverse set of tools needs to be available. Some tools exist, such as cover or perennial crops, but have not received the research investment needed to demonstrate their effectiveness and to make their adoption attractive in all environments. Other tools, such as soil sensors and biochar, are not yet widely affordable, user-friendly options for maximizing the efficient use of resources with minimal environmental trade-offs. The benefits that may come from better evidence of microbiome connectivity between soils and humans require adequate funding, standardized approaches, and infrastructure development for researchers to collect, share, and analyze data across microbiomes. The development and deployment of all these tools would be advanced by collaboration within and across disciplines, whether in the field or in the laboratory.
MONITORING AND MANAGING DATA
Preservation of soil biodiversity would ideally be accompanied with ways not only to account for what is in the soil but also to identify function. In the case of microorganisms, function would include that of the species as well as the community. Understanding function would open possibilities for manipulating and enhancing soil health, soil-derived Nature’s Contributions to People, and ultimately human health.
Tools for monitoring soil physical and chemical properties, soil microbial communities and their activity, and the soil processes influencing local- to global-scale biogeochemical cycles exist or are in development. Support from the U.S. Department of Agriculture and other funding agencies to develop and deploy these technologies at price-points that are feasible for researchers and producers to use will advance understanding of regulating ecosystem services, which can in turn inform management practices that promote such services. Similarly, efforts to map high-risk areas for chemical contamination can inform decisions about how to mitigate the bioavailability and bioaccessibility of contaminants in crops grown in those locations or whether crops should be grown at all.
Investing in data collection is not enough. To make the most use of these data, a data management system is needed that is accessible and catalogued with metadata for other researchers to query. Systematic, repeated monitoring efforts that are stored properly will eventually enable comparisons of management practices, climate conditions, and other environmental variables on soil health and ecosystem services.
Microbiome researchers have similar needs. Given the potential that microbiomes have in modulating soil, plant, and human health, adequate infrastructure is needed to store and make use of microbiome data from all these systems. Such data infrastructure would enable predictive understanding of these microbiomes and facilitate exploration of the existence of the microbiome continuum spanning soils to human health. The achievement of these objectives would be greatly assisted by an improvement in
the rigor of sampling designs to capture the heterogeneity of microbiomes, enhanced universal methodologies for microbiome analysis, and funding to support the metadata information and infrastructure necessary for microbiome scientists to access data, regardless of field.
FROM WASTES TO RESOURCES
Soil is a natural vehicle for recycling wastes, including animal excreta and food waste, into nutrients that support plant growth. There is no lack of underutilized material available today that can be used as soil organic amendments for agricultural soils, whether it be manure, food waste, or human excreta. The issue is that many of these waste streams may contain levels of heavy metals, plastics, per- and polyfluoroalkyl substances (PFAS), and other contaminants that adversely affect soil physical, chemical, and biological properties and can harm human health through food consumption and have detrimental effects on other soil-derived Nature’s Contributions to People.
Additionally, the replacement of animal waste with excessive use of synthetic fertilizer as the primary source of nutrients—though beneficial for crop yields—has led to nitrogen pollution that harms aquatic life, contaminates drinking water, and contributes to global warming. The production and use of synthetic fertilizers are also associated with high levels of energy consumption and greenhouse gas production.
The committee is not suggesting the abandonment of synthetic fertilizer. As discussed in Chapter 4, when applied at appropriate levels, synthetic fertilizers can increase microbial biomass and soil organic matter through the promotion of plant growth and rhizodeposition. Nor is it proposing to abandon the use of waste material as organic amendments because of contamination concerns; landfilling all waste presents its own environmental problems. What is needed is investment in technologies that can facilitate the use of organic amendments to substitute for some of the use of synthetic fertilizers in crop production. Such technologies would provide producers with better information about the nutrient and carbon content of the organic amendments they are applying as well as remove contaminants in the amendments below a threshold of concern. Investment in the affordable production of biochar would be one option to pursue to help address contaminants that are particularly persistent, such as PFAS. Additionally, if safely managed and appropriately processed (e.g., through thermochemical transformation), soil organic amendments can be used to remediate soil contamination (e.g., heavy metals and perhaps PFAS) while improving soil health. Combined with precision agriculture technologies to improve the targeted use of nitrogen (whether in the form of synthetic fertilizer or organic amendments), these efforts for waste reuse would increase soil organic matter content and mitigate pressure on planetary boundaries for chemical contaminants and nitrogen flows.
COMPLEXITY AND COLLABORATION
Many benefits can be achieved by incorporating cover crops, perennial crops, or crops bred specifically for root system development or rhizosphere interactions with soil biota into planting rotations. By promoting root biomass, these approaches increase belowground biomass, which can reduce erosion, mitigate nitrogen pollution, and increase organic matter content. More research and development will be needed to make these crops viable choices in the diverse soils and climates of the United States. On-farm research that involves scientists, producers, and industry will help identify crops that work in all field conditions. Similarly, collaborative research approaches can be used to assess which biostimulants (under what conditions) promote soil health, nutrient uptake, or yield and how they interact with indigenous soil microbiomes. Practices that seek to replace tillage or herbicides as weed management strategies would also garner the best results when conducted as real-world field trials so they can be tailored to specific climate, soil, and crop parameters.
Shifting to an approach in agriculture that places a high level of emphasis on soil health, at times at the expense of yield maximization, is not a small undertaking and should not be placed solely on the backs of producers. Producers are parts of systems, too, which often involve leases, subsidies, loans, and insurance policies that constrain choices. Prioritizing soil health will require incentives for producers, and land managers more generally, to transition to more complex systems and economic structures that recognize the value of soil health in underpinning system resilience.
Translational research that identifies how different agricultural management practices, environmental conditions, and food-processing techniques influence the nutrient and bioactive density of food crops is also fraught with complexity. While it may be difficult to tease out the degree to which each variable affects nutrient and health-beneficial bioactive density, collaborative research across disciplines and with industry can support the breeding of crops and the development of food-processing technologies that enhance the profile of desirable nutrients and bioactive compounds without sacrificing consumer acceptability.
Support for collaboration is also needed to advance microbiome science. Within disciplines, research funding across different areas of soil science, for example, would help to integrate methodologies for composition and functional assessments of soil microbiomes. Across disciplines, supporting collaboration among researchers from different fields would advance what is known about the connectivity of soil, plant, and human microbiomes.
Bringing together the report’s recommendations in order to leverage data, reduce and reuse waste streams, increase complexity in agricultural systems, and promote collaboration across disciplines will improve soil health and advance microbiome science, both of which will contribute positively to human health. These pursuits will also help address additional grand and interwoven challenges, namely, climate change, food security, and environmental contamination. Although investment in research and practices that improve soil health and advance microbiome science will not solve
these grand challenges singlehandedly, it will expand options to reduce agricultural contributions to global warming, sequester carbon, and degrade contaminants while producing food more sustainably. Furthermore, pursuing the recommendations in this report will fill many knowledge gaps in the soil and microbiome sciences, such as the mechanistic links underlying microbiota composition and function, soil health, and human health and how to interrogate data across microbiomes. It will identify means by which trade-offs between food production and other benefits that people derive from soils can be quantified and minimized and answer questions about the effects of agricultural management practices on the nutrient and phytochemical density of crops. Finally, it will bolster what should be evident: that through myriad direct and indirect linkages, healthier soil contributes to healthier people.
