Progress report for GNC19-282
Given that 81% of the US population lives in urban areas (2010 census), urban agriculture represents a key sector for increasing food security and improving quality of life for urban communities. However, urban soils often pose issues that limit agricultural productivity: including compaction (~50%), high pH (~8), and contamination with heavy metals (Lead, Arsenic) caused by hotspots of industrial activity and unregulated waste, often at concentrations definitively toxic to humans. This is especially true in Detroit, where, for example, 4 neighboring oil refineries have created the most polluted zip code in Michigan. As a result of uniquely severe soil issues like these, urban farmers, such as those in Detroit, often need to import topsoils and/or compost, which can be prohibitively costly, but is often the sole option for soil remediation due to city-level regulations on maximum urban compost pile sizes. Ultimately, importing organic soils does not represent an ideal nor feasible strategy for the sustainability of crop production by urban farmers. This project addresses urban soil compaction and contamination issues by evaluating the effects of biochar application, alongside legume mixtures, on soil structure, nutrient retention, soil biological activity, and vegetable yield.
To complete this project, we will need to hold training workshops (with participation by at least 10 affiliated farmers, and others welcome) for aggregate mass distribution profile data collection, as well as data collection involving invertebrate identification. These training workshops will be related to general education in local soil ecology, as well as a platform for building community around agriculture. Ultimately, from this project, peer-reviewed publications and educational articles will be written about biochar’s effects on (1) soil aggregate mass distribution scaling parameters in combination with a tailored mechanistic model of soil aggregation, (2) nutrient concentrations in different soil aggregate mass fractions, (3) microbial community composition variation by soil aggregate mass, and (4) invertebrate community composition and diversity in bulk soils. These articles will also be reviewed in part and distributed to local community members, which will serve as lasting material of their own participation in academic research about their community.
To evaluate the impacts of our outreach events, we will conduct post-instructional and data analysis workshop surveys of farmers’ willingness to adopt biochar as a consistent and feasible soil management strategy, as well as synthesize statements on what they learned. In later years, we would also ask previous participants to lead workshops on soil aggregate and invertebrate data analyses for new and returning participants.
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The initial study was conducted on a 50 by 50 ft area of the Michigan State University Detroit Partnership for Food Learning and Innovation. The growing area had been minimally amended since the demolition of the former school on the property in 2017, keeping the soils in need of optimization for plant growth by amendment rather than soil optimized for structural stability for construction. Baseline soil tests for the site show low levels of heavy metals (though nearby areas may have higher levels) and 2-3% organic matter, but high pH and low aggregate stability.
Biochar as an agricultural amendment was chosen because awareness has grown of its role in generating sustainable energy and farming, and has been commercialized, but is also originally an indigenous practice, with archaeological examples in the Amazon region of South American and in Eastern Europe in Ukraine. Using this practice may have variable effects on strict yield measures, but could be a long-term practice focused primarily on soil regeneration and feeding the soil as a reservoir for sustaining future plant growth. Previous studies show effects on soil chemical fertility and microbial abundance and diversity.
The area was rototilled to 4” depth using a shared community rototiller and divided into 64 5 by 5 ft plots. Biochar processed from pine wood was purchased from Wakefield (MO) and added to plots as a 1:1 mixture by volume with compost from a local vendor (Tuthill). The mixture was applied at about 5% by volume (of the prism represented by the 5 x 5 ft plot down to 5 cm depth) and 2 days before seeding.
Before mixing with compost, biochar was sieved with common sieves at 1 mm, to separate different particle sizes. Few previous studies show that particle size and shape, even within such small ranges, can mediate biochar’s effects on plant growth in greenhouses by affecting moisture retention. Given high clay content in these soils, we hypothesized that larger particles would help balance the effective texture and give a loam-like function, including holding slightly less water given clay-tendency to stay wet. However, we acknowledge that compacted soils can likely show complicated water retention, varying between extremely wet and dry conditions.
Cowpea and Buckwheat seeds were received by donation from the well-known local urban agriculture organization Keep Growing Detroit, and they source their seeds from Johnny’s Selected Seeds provider (based in ME). Two alternating rows of each species were seeded with a hand hoe. These cover crops were chosen for a few reasons. Cowpea, as a plant in the legume family, was chosen because many previous studies have shown that biochar, which is a relatively decay-resistant form of carbon, is most useful when added together with nitrogen, such as from the bacteria inside the root nodules of a legume species (or urea, used by smaller farms in the tropics). Furthermore, within the many leguminous plant species, cowpea was likely to do well in the region, and also has African origins, thereby supporting planting and agriculture as a cultural endeavor, especially when practicing in service to communities of color, which dominate Detroit. (Specifically, the Brightmoor neighborhood has experienced effects of food apartheid, or food “desert”, given that large grocery stores are rare, at least 1 mile away, ref. USDA Food Access Atlas). Buckwheat was chosen for its ability to grow quickly, scavenge soil phosphorus, and attract pollinators via high floral density (SARE cover crop guide).
Plants grew from July to October. Similar to recommended urban farm system checks on a subset of growing spaces, data was observed and recorded regularly throughout the growing season. Specifically, observations were recorded of field soil moisture and soil invertebrate diversity, with soil samples extracted with a sand hammered and bulk density cylinder for future processing. These current data apply to objective #4, and future data collection will address objectives #1-3.
Field soil moisture within the top 5 cm was measured using an analog hygrometer and then validated with an electric sensor. Readings were recorded 2-3 times a week for about 3 months. This schedule was chosen to capture natural fluctuations in soil moisture, and use this temporal resolution to check if different amendment effects appeared at the direst or wettest extremes. Previous studies have shown that soil binds water with varying strength depending on the direction of phase change (i.e. wetting or drying), thereby making the water more or less available for roots to absorb, and potentially affecting plant growth. Furthermore, compacted clay soils likely show extremes in moisture during the summer.
Soil invertebrates (insects plus relevant non-insects, like springtails and mites) were surveyed using pitfall traps, which were wide plastic cups filled with some alcohol and covered with propped paper plates to block sun but allow crawlers to continue foraging and fall in. Each plot had 1 trap in the center and they were left out for about a week without heavy rain. Cups were then collected, sealed, and the invertebrates compiled into a smaller vial filled with alcohol to preserve them. Each individual was then tallied and identified under a microscope down to taxon order and morphologically distinguishable species. This required much time post-harvest to analyze. We hypothesized that invertebrates would be positively affected because of biochar reported benefits to microorganisms, and that this would outweigh the potentially negative effects of toxicity of small dissolved mutagenic byproduct molecules resulting from the burned carbon (which similarly explain the harm of oil spills on sea life).
Additional data were collected on oven dry crop biomass, yield, soil pH, pollinator visitation, and buckwheat flower number and fruit set, all mostly taken on a few separate days a few weeks before the end of the growing season.
To test for biochar effects numerically and uncover likely amendment effects compared to effects of natural variation in the recorded measurements, statistical analyses were done. All data was organized and entered continuously in Excel (Google Suite for collaboration), and subjected to computing functions available in the public and open-source coding software R. More specifically, the most recent “rstatix”, “lmerTest”, “vegan” and “tidyverse” packages were used for running generalized linear mixed effects models and plotting.
Initial results reported help address objective #4; other objectives involving additional data remain in progress.
Overall, biochar had a significant positive effect on average soil moisture and significant yet slight negative effects on invertebrate biomass and diversity, but no detectable response of other measured variables after the first 3 months. Soil moisture was 2% higher in soils with unsieved biochar particles (Mixed, including those > 2 mm), and most of this effect appeared to come from the smallest (< 1 mm) particles (S). Larger (> 1 mm) biochar particles (L) appeared to perhaps reduce soil moisture on average, as hypothesized, but this was not detectable as statistically significantly different from control (None, N) plots, given natural variations among plots of the same treatment.
Soil invertebrate biomass was significantly lower in soils amended with small particles, and invertebrate diversity (alpha / richness) was significantly lower in the soils with unsieved (Mixed, standard) biochar applied. Though effects came from different treatments here, they make sense given that most of the effects, e.g. on moisture, appear to come from smaller particles (S, < 1 mm), which presumably have more surface area (biochar already has a lot) and uniform shape compared to larger particles (L, > 1 mm). The loss in invertebrate biomass and richness could be due specifically to fewer ground beetles, which have thicker exoskeletons, or using a bit more inference based on the results of a few other studies, due to negative effects of biochar on the reproductive rates of springtails, which are one of the most abundant groups of soil invertebrates, and a weaker effect of some relatively positive (i.e. less negative) biochar effects on younger invertebrate life forms due to more moist soil environments.
The effects of biochar found here may be slightly negative more directly on soil fauna, but the short-term positive effects on soil moisture may help save water for irrigation. The later benefits to crop growth and yield may be more variable as they depend on the the quantity and frequency of rainfall in the season, especially for soils with low organic matter. However, biochar application, which was of comparable cost to compost in this study and could be cheaper if sourced locally, could be an option to withstand variable rain and save money on irrigation, which can be expensive for home-owning urban growers in cities like Detroit.
Educational & Outreach Activities
Engagement was limited this year due to Michigan universities’ pandemic policies, but we participated in a promotional video for the site and connected with several interested neighbors and informally with some local growers on several days while gathering data, since the site is relatively new, and is aiming for acceptance by the most immediate neighbors of practice of the broader mission, which needs building after leasing of the site. We also produced a short internal report about the project, connected with local agricultural non-profits, and made slides as part of a resulting thesis presentation. We aim to host broader online workshops about soil health that are unique from the efforts of other groups, such as presenting to the local public interesting and relevant conceptual frameworks about soil food web dynamics, microbiology, and soil nutrient cycling that may be a bit less practical, to highlight our more direct connections to local basic academic research.
Improving urban soil health is still likely to benefit urban growers. While biochar may still likely be an external input, it should be most sustainable when made or purchased from wood as local as possible, and mixed with compost and a legume crop so as not to bind and make nutrients less accessible to plants. It may be a long-term practice for improving soil quality over initial years rather than immediately increasing short-term yields. Future analyses for additional objectives will reveal how different dimensions of soil health respond specifically to biochar. Overall, the current site used has certainly been a place of exchange of ideas among nearby farmers and sustainable agriculture practitioners, and is of much benefit to re-orient and innovate perspectives, paradigms, and norms of academic research.
Working with the Detroit Partnership for Food, Learning, and Innovation has put into perspective the kind of research that is most useful to farmers, and that academic research often asks related but separate and more conceptual questions. Areas of land, as the most fundamentally valuable assets in society (e.g. the source of the majority of inter-generational wealth) might be ideally used for setting up plots that mimic what small-scale, rather than industrial or entrepreneurial scale, urban farmers do in practice (including vested interests in specific crops with more local vs. regional or national markets). Additionally, conceptual studies can be paired and done in smaller and more controlled settings. Furthermore, data collection could be more targeted to mimic what farmers would typically collect data on when doing an intensive survey of some fraction of a production system each year, as is recommended. Then, much of the conceptual aspects of how nature is functioning in the agricultural system can be teased apart analytically, such as with qualitative comparison to simple (parsimonious) model representation and simulation, rather than relying on strict independent manipulation. The latter may usually weigh the most as quality of evidence for constructing or deducing knowledge, but this is worth discussing different ways of knowing, and validating how different strategies of approaching research questions match the breadth of societal problem or specific research question or concept being investigated. Ultimately, we explored more deeply and concretely (vs. typical formal education credits) the ways that academic researchers should best serve in service to farmers and the public.
We have had several fruitful discussions about how urban agriculture ought to look with growers and students of nearby universities, further revealing the nuances and philosophical diversity of doing ecological and agricultural research depending on the community of assumed beneficiaries, be them other researchers, practitioners, suburban entrepreneurial growers, or younger urban growers with unique experiences. For example, one volunteer generated an idea for resourceful drip-line systems using recycled unused hoses that are still usable with little repair as a way of innovating urban growing with minimal input cost, and a communal outlook. Similar ideas are already implemented, such as a shared tool shed. Finally, individuals have shown consistent interest in the specifics of how biochar works while visiting, highlighting a role for future organized group discussions.
By holding more water, biochar can be useful for mitigating effects of drought on soils and plants, and reducing irrigation, which can be expensive, and may have separate issues with systemic contamination such as in Flint, MI. There also may be a trade-off with invertebrate diversity (as predators), even with positive effects on microbial diversity (as prey). There remain only a handful of studies considering the invertebrate diversity of agricultural soils, and to our knowledge none to date in response to biochar use in urban systems, so future efforts should continue to monitor invertebrate activity to better understand the full complex ecology of soil food webs and how they respond to agricultural management. Specifically, biochar may have positive effects on some aspects of soil health, but the specific and net effects on food webs requires more research by engaged practitioners.