Biochar from Biosolids and Source Separated Human Urine: Soil Health Impacts and Farmer Perspectives

FIELD TRIAL RESULTS - Harvest

Yields ranged between 0.9 and 7.4 dry tons per acre at the NY trial site and 2.7 and 10.4 dry tons per acre in VT over the three year study period. Yields were lower in NY in 2024 and 2025 due to drought.

All fertilized treatments had significantly higher yields (Figure 5), greater ear fill (Figure 6), and greater ear length (Figure 7) compared to the no-fertilizer control treatments in all years at both trial locations (p < .05), with the exception of C + U, which did not show a significantly different yield from the no-fertilizer control treatment in VT in 2025.

None of the yields from fertilized treatments differed significantly from yields of the fertilized control (SN) treatment, indicating that urine may be substituted for urea fertilizer, and that biosolids biochar may be applied with no negative yield effects. 

In 2025, there were two significant differences in yield between C + U and other treatments containing urine; C + U resulted in significantly lower yields than U (NY) and BB + WB + C + U (VT) (p < .05). Such decreased yields resulting from the co-application of urine and compost suggest that nutrients, particularly nitrogen, were not as available during the growing season to promote corn growth as in the other fertilized treatments. 

Similarly, all four treatments containing compost were generally found to have less ear fill and shorter ears than fertilized treatments not receiving compost; C + SN and C + U had significantly lower ear fills than U (NY 2023, VT 2025), SN (VT 2025), WB + U (VT 2025), and BB + WB + U (VT 2025) and significantly shorter ears than U (NY 2025, VT 2025) and SN (VT 2025), and WB + U (VT 2025) (p < .05). 

An analysis of silage crude protein content shows further evidence of lower N availability in compost-containing treatments. Crude protein was significantly lower for all four treatments containing compost than for both WB + U and SN in VT and NY locations in 2025 (p < .05) (Figure 8). Decreased crude protein rates indicate lower plant uptake of nitrogen, and, taken together with yield data, this finding suggests that nutrients were less available for plant uptake in treatments where a fraction of nitrogen was applied in its organic form than in treatments supplying only inorganic nitrogen.

The deficiencies that were observed in treatments containing compost could potentially be corrected by increasing the amount of soluble nitrogen applied. This approach might increase the yield to the same level as the other treatments, while retaining the benefits to soil health that were observed from the compost-containing treatments.

Complete forage results can be viewed here.

FIELD TRIAL RESULTS - Comprehensive Assessment of Soil Health (CASH)

Soil health scores show an improvement in NY soils over the course of the study, from a score of 36 (low) in the 2022 composite baseline test to a range from 45 (medium)–65 (high) in the 2025 subplot-level testing. Varying changes were seen in VT soils, which scored 62 (high) in 2022 and ranged from 54 (medium)–66 (high) in 2025.

For the NY location, overall soil health scores in 2025 were linked to compost applications. Three of the four treatments containing compost (C + SN, C + U, and BB + WB + C + U) showed significantly higher health scores than both the fertilized control (SN) and the no-fertilizer control (p < .05) (Figure 9). This response to compost was not seen in the VT location, however, where there were no significant differences in soil health scores between treatments.

The difference in soil health response between the NY and VT locations may be attributed to differences in baseline soil conditions at each site. In 2022, VT soils were a silt loam (Sand: 27% Silt: 60% Clay: 11%) with “low” to “medium” levels of soil protein, active carbon, and soil respiration, while NY soils were a sandy loam (Sand: 55% Silt: 29% Clay: 14%) with “very low” levels of the same. As compost is known to have positive effects on biological soil health indicators, including soil protein, active carbon, and soil respiration, its application likely had a greater impact in the severely biologically-constrained NY soils than in the moderately-constrained VT soils. 

Unless otherwise noted, the remaining results and discussion of soil health pertain to the NY location.

The best performing treatments for overall soil health were C + U and BB + WB + C + U, with significantly higher scores than SN, U, or the no fertilizer control. Organic carbon from compost applications may underpin the increases in overall soil health scores observed, as it provides habitat, food, and energy resources critical to supporting a healthy soil microbiome.

Soil organic carbon levels were significantly greater in the three treatments containing compost and urine (C + U, WB + C + U, and BB + WB + C + U) than in treatments containing negligible carbon (SN, U, and the no-fertilizer control) (p < .05) (Figure 10). Of these, C + U and BB + WB + C + U also showed significantly improved soil organic matter compared to the same (p < .05) (Figure 11). In contrast, while soil organic carbon and soil organic matter in the C + SN treatment were somewhat higher than the treatments that had negligible organic carbon, this difference was not significant.

Notably, soil organic carbon was significantly higher in the BB + WB + C + U than the C + SN treatment, both of which received the same total carbon amendment in each year.

Indicators associated with healthy soil microbiology were found to be improved from the co-application of compost and urine. Active carbon (Figure 12) and soil respiration (Figure 13) were both significantly greater in C + U than the no-fertilizer control (p < .05). This suggests that both the fraction of soil carbon readily available as food for microbes as well as microbial respiration activity were improved by the co-application of urine and compost, but not by the addition of urine alone or compost with synthetic fertilizers. 

Considering all soil health indicators discussed above, we find C + U to have significantly improved soil organic carbon, organic matter, active carbon, and soil respiration levels compared to the non-fertilized control in NY, whereas treatments containing urine alone or compost with urea (instead of with urine) showed no significant improvements in these indicators from the control (p < .05). Regarding soil organic carbon specifically, all three treatments with compost and urine significantly outperformed U, and all treatments with both compost and urine outperformed C + SN, though only BB + WB + C + Urine was significant (p < .05). This suggests synergistic and positive soil health effects from the co-application of compost and urine.

All four treatments containing compost showed significantly higher soil protein levels than treatments with negligible carbon inputs, including SN, U, and the no-fertilizer control (p < .05) (Figure 14). Given that equal amounts of nitrogen were applied to all fertilized treatments, these findings further support results seen in the harvest data indicating that more nitrogen remained bound in the soil instead of being taken up by the plant when applied in its organic form via compost.

In the VT location, there were no significant differences between the control treatment and all other fertilized treatment groups for any soil health metrics. Despite being no different than the control treatment, C + U showed significantly higher soil respiration than SN (p < .05), suggesting a similar positive and synergistic effect of compost and urine applications on soil microbial activity as was observed in NY. 

Complete CASH results for the NY site can be viewed here.

COMMUNITY RESEARCH RESULTS AND DISCUSSION - Interviews

Here we will not be discussing all the themes or categories coded, but focusing instead on those most salient to the objectives of this project. In our discussion, we use semi-quantitative terms like "a few," "some," "most" or "many." Generally speaking, if more than half the respondents mentioned a certain code, we were comfortable using the term "many." If fewer than five respondents mentioned a code, we used "a few." The other terms fall in between, and we've included specific numbers in many cases for clarification. 

Familiarity: Most respondents were familiar with urine, with only three respondents saying they were not. All but one were familiar with biochar in general, but most were unfamiliar with making biochar from biosolids. When discussing familiarity with biosolids biochar, five respondents expressed confusion around the concept; they seemed to misinterpret and thought we meant biochar from woody debris, or source-separated human solid waste from composting toilets or other means, or biosolids, such as Milorganite. One respondent, when asked about biosolids biochar, said, “Yeah, I somehow have a, have like some inkling that the city of Milwaukee was doing that at one point?” Among the six respondents who were familiar with biosolids biochar, half immediately followed with language such as “I don’t know that much about it” or “I know less about this,” indicating there is minimal knowledge about biosolids biochar even among the few who expressed familiarity. 

Comfort Level: With regard to how "comfortable" respondents felt about potentially using urine-derived fertilizer or biosolids biochar, half of respondents mentioned that they thought "others" would not be comfortable, whereas none mentioned low comfort for themselves. This confirms the importance of education about and demonstration of urine fertilization. Comfort level for biosolids biochar varied. A few respondents had low comfort themselves, and many postulated that others would have a low comfort level. Many respondents changed their minds about biosolids biochar during the interview, identifying various caveats; for example, some – cited high comfort at first, and then indicated a medium level of comfort later in the interview, expressing discomfort with not understanding the production process or the sources used to produce biosolids biochar. One interviewee expressed enthusiasm, but still emphasized a desire for more information about the process. 

Motivations/Benefits: A few major themes arose for key motivations and/or benefits of the use of these novel amendments. The most frequently coded motivation was "closing loops," mentioned 64 times by 17 respondents. Respondents were most often motivated to use these novel amendments on certain crop types (crop type was coded 67 times in 17 transcripts) namely non-edible crops, tree crops, nursery crops, and fodder for animal consumption. Urine was seen as safer than other sources by some, compared to biosolids biochar made from the mixture of wastes processed in a municipal wastewater treatment plant. A few respondents thought that if urine was managed locally, and users were aware of what type of pharmaceuticals (if any) were in the collected urine, it would be more acceptable than biosolids biochar, or a good source of fertilizer generally. Access to a local source of either urine or biochar was an important motivation for many. It was mentioned as motivation in 16 out of the 22 interviews. Many interviewees were aware of the benefits of biochar, such as its ability to help build soil over time and retain nutrients, which motivated their potential interest in biosolids biochar (17 out of 22 interviewees). The possibility of using biochar to improve soil health, such as for perennial crops like trees, was mentioned 64 times in 17 transcripts. Several interviewees specially mentioned interest in the potential of pyrolysis to reduce contaminants. 

Concerns and Barriers to Adoption: When asked about concerns with the use of these novel amendments, respondents most often mentioned potential contaminants, specifically PFAS. Concern about contamination was coded 57 times, much more than other codes in the concerns category. Only two respondents did not mention contaminants. Respondents seem to be more concerned about contamination in biosolids biochar (as compared to biochar from woody biomass or urine) because of the mixed-stream production method. One respondent thought that educating the public will be crucial to "have them keep an open mind" and thinks concerns about PFAS will be front of mind for a growing number of people and will need to be addressed. The information provided at the beginning of the interview about PFAS reduction of biosolids through pyrolysis seemed promising to them, though this respondent also wondered about potential PFAS treatment for urine. A few people (6) mentioned "contaminant reduction" as a potential benefit of biosolids biochar, though most wanted more data before feeling comfortable with it. 

When concerns about contamination were mentioned generally, it was often not clear if respondents were concerned about human health impacts or environmental health impacts. These may be perceived as closely linked for many respondents. Another concern was the use of industrial machinery and how it would impact local aesthetics, such as large trucks and tanks, to manage production processes for these amendments at scale. Some respondents thought there were barriers to the application of these amendments for some crop types, such as annual leafy crops like lettuce. 

Another concern and/or barrier to adoption was scale. One respondent saw urine as a useful fertilizer for a variety of non-food crops, such as nursery stock, crops produced in greenhouses, hemp, sod, and golf courses, However, he wondered about the volume of urine that would be available and on how much land it could feasibly be applied. He imagined the scale could grow over time, but considered infrastructure to be the biggest hurdle, along with the costs to collect and transport urine.

Soil Health Indicators: To better understand participants’ thoughts on what mattered to them with regard to soil health, we asked how they determine their fertility and soil health needs. Their own observations of plant and soil characteristics proved to be most significant.  With regard to soil testing, practices varied, with eight respondents answering that they do soil tests regularly, usually every year or two, with one respondent testing weekly. Nutrients, organic matter, and pH were most commonly measured on these tests, with some also looking at microbial life. Six respondents said that they only do soil tests occasionally. Barriers cited include the expense and lack of time to get the results for quick turnaround planting projects. Several perform tests on an as needed basis if they notice problems with plants. A few plan to do more soil testing in the future with greater consistency as their operation grows or they hone in on their practices. Eight respondents do not test their soil, and they usually rely on observations to determine their soil health needs. 

We asked participants what they see as the most important indicators of soil health. Observations of their plants were most frequently mentioned, cited by 17 respondents. They kept an eye on whether plants were productive and growing vigorously or had stunted growth, whether leaves were greening up or yellowing, and whether the plants were healthy and resilient against pests and disease or suffering from infestations. One flower farmer described how observations of plant strength indicated good soil: “We’re just getting to trellising everything… And all of the flowers are really sturdy with thick stems this year. So they’re holding themselves up versus needing to be trellised… which means the roots are able to go deeper and just create a stronger plant structure.” A few observed changes in the flavor of their crops. And a few kept an eye on the richness and variety of plant species in their pasture. 

Soil microbial life (including species richness, evenness, and abundance) was also important to many, with the health of the soil microbiome cited as a key indicator of soil health by 14 respondents. These farmers saw supporting the soil microbiome as a way to create a healthy and productive system long term.

While some interviewees kept track of microbial populations with soil tests, visual observations of the signs of soil microbial life were frequently relied upon: “I mean, we can tell what a… just sort of a healthy soil system looks like…. And that’s part of the reason we like to grow perennials … we can actually see the mycelium growing underneath…which is just absolutely incredible.” Many farmers described making changes in their practices to support the soil microbiome, including planting perennials, reducing tillage, planting cover crops, or harvesting plants at the base and leaving the roots so as not disturb the soil. The soil microbiome also factored into their choices for amendments, such as using unsulfured blackstrap molasses to feed mycorrhizae, or applying composts: “Microbes. That’s a really big part of compost as opposed to like digestate, just because it’s so active. And I think all of that helps foster plant growth and health long term.” One farmer described how they are starting to pay close attention to how different microbial populations in their compost influence different crops: 

So last year I learned that nightshades, garlic, and onions like higher fungal numbers…and that almost everything else we grow like higher bacterial numbers. So we had been getting our compost very cured so that it was high in fungus. And we were noticing that there was a decrease in production of say, our brassicas and stuff… So now we’re working towards trying to spread some immature compost that hasn’t propagated the amount of fungus yet for the brassicas, lettuce, corn, etc. 

After plant observations and the soil microbiome, nutrient levels as measured on soil tests were the next most important indicator, mentioned by 12 respondents. This was followed by soil organic matter, water-holding capacity, and observations of the soil (including color, smell, or the presence of macrofauna like earthworms) each of which was mentioned by 9 or 10 respondents. Several also cited compaction or drainage as key indicators of soil health. 

Information Needs: Respondents were asked what information would be most helpful for their decisionmaking regarding use of these amendments. Results from experimental trials were mentioned the most, with 17 respondents interested in this information. They would like to see how these amendments are working on other farms, both in terms of yields and improvements in soil health, particularly for biosolids biochar. They would like to see trials done with different crops on farms in a range of soil types and climates. Most people want to see long-term data, the longer the better, with at least two years for yield trials, and at least five years to see soil health changes, including any impacts on soil life and whether contaminants are building up over time or broken down in the soil: 

If we could have a 50-year study and the results were overwhelming that it helps your soil, that would be the biggest help a guy could have. But just what is the analysis when you put it on your soil and then what happens after five years? …Because you would think that within five years you’d either have a buildup or you’d have a change in the soil if there is gonna be one. 

Most respondents also thought an analysis of the presence of contaminants in the amendments themselves before being applied would be helpful, with 16 respondents looking for this data.

There is a significant need for application guidelines, which was mentioned by 16 respondents as well. Some thought urine could fit in well with their current methods and equipment to spread liquids, including fertigation, but wanted to know application rates and techniques to prevent burning crops or runoff into nearby waterways, and were concerned about the effort required to apply enough of it. As one farmer explained: 

I just wonder about how to spread it, I guess. And more of the… technical details of like… how much do I need? Does it need to be concentrated or not? … Because I think there’s a lot of solutions out there for when you want to increase your fertility. And especially for us, and I think a lot of local farmers, it’s more about … what kind of equipment you need and how much time is it going to take you to do it…. I’d be super open to it as long as, you know, it’s not too difficult. 

Farmers were less familiar with what the consistency of biosolids biochar would be like and how it would be spread or incorporated into the soil, and how often it would need to be applied. They also wanted to know more about how it holds onto or releases nutrients in the soil. One explained, “Well, a liquid, obviously, is pretty much gonna be instantly available, and that’s a little easier to use, but as far as a solid goes…obviously, once you plant the field, you can’t get back in there to spread that solid again. So that’s very important to have, you know, [information about] how quickly…it releases.” Additional information on nutrient composition of both amendments, costs per yield achieved compared to other fertilizers, and information or support to obtain the appropriate tools and equipment were also needed, all requested by about half of respondents.

An important information need revealed by respondents would be to help farmers understand what biosolids biochar really is, as it's not intuitive to most. One requested a diagram that would help to clarify the product: 

I think it would just help me to have… even just like a very basic diagram of like, here’s how your biochar got to be in its current form… just like a little super for dummies diagram of the steps. So that I can have an image of what happened. Because I have images now of just like this gross, sludgy poop thing. And then getting like dried down into something that can be burned. So it’s kind of just like this powdered poop [laughs].... But…I think there are probably ways that that’s not accurate, you know.

Terminology for biosolids biochar may need to change, given the confusion that arose in several interviews, between biosolids biochar and other amendments. As one respondent put it, “I think that if they’re too similarly named, like saying biochar versus the other one that starts with bio [referring to biochar from wood biomass], I think, because like I’m already getting confused in this conversation…. I think having two distinct words for it is going to be the best.” 

Education Recommendations: The need for more education on these amendments for farmers, their customers, and the broader public emerged as another significant concern. Most respondents, especially those doing direct-to-consumer sales, were already involved in education about farming practices and philosophy. Some considered it a key component of their role, either as an educational farm offering public workshops and tours, or through work with agricultural extension, or as a part of other agriculture-related committees and professional organizations. 

Reflecting on these experiences, all of our respondents had recommendations for what educational methods and content they believed would be most effective in addressing concerns around these amendments and encourage broader acceptance and adoption. Most frequently, respondents described a science-based approach, with educational materials focused on sharing research results, particularly on the safety and any social or environmental benefits of using these amendments. Several respondents commented positively on the introductory material provided at the beginning of the interview, which compared contaminants taken up by crops fertilized with urine to levels found in crops grown with other amendments they may currently use, such as animal manures. They found this information surprising and helpful for their own decision making and something that would be useful to pass along to customers. One respondent explained: 

Our minds first go to well, what about like peeing out pharmaceuticals, but then you were mentioning that they are found in other [fertilizer and amendment] sources. So I think that is a really powerful point to make. And especially if the point is that they’re actually lower in this source than others, if that shows up to be true. 

Some respondents thought a chart comparing the levels of contaminants found in a range of amendments would be an effective way to present this information. One respondent stressed how important such information on contaminants will be for growers heading into the future, especially for vegetable producers who are starting to get pressure from retailers asking them to sign liability documents stating that if any problems with PFAS come up in the vegetables, the retailer will not be liable. They explained that many producers are starting to be concerned about this pressure from their markets. A few respondents mentioned wanting printed materials like pamphlets to have available for their customers that would provide short, easy-to-digest information, but would also have links to websites to explore the deeper research on safety. 

In addition to educational materials on safety, resources that helped to explain the source materials and process for creating these amendments were also frequently mentioned, especially for biosolids biochar, which respondents were less familiar with. Farmers were interested in this information both for their own understanding and to share with their customers, who they thought would be more comfortable if they knew the level of processing. As one respondent put it, “really like hammering home that this isn’t raw sewage. This is a very different thing that has undergone X, Y and Z process to become this thing, and it’s not just poop.” 

Diagrams, infographics, photographs, videos and other visual media were frequently mentioned as helpful ways to illustrate the processing and application methods for these amendments, along with in-person demonstrations. One respondent suggested an interactive map could be created showing farms already using these amendments, which users could then select to see photographs and hear interviews from the farmers themselves on their results. They thought these testimonials would normalize the practice by explaining how “this makes sense.” Pushing back against the label of “novel” amendments, some respondents also thought educational materials should point out the long history of reusing human waste in agriculture, highlighting that “this is what’s been going on for thousands of years.” 

Some respondents mentioned how they would want to take on the responsibility of showing the breadth of “places where it’s working well” by modeling the practices on their own farm and putting information on their website or social media. One respondent, who heads an educational farm, described how they already bring everyone on farm tours to their composting toilet, and most visitors have a positive experience, with some commenting that their expectations about the smell and cleanliness were changed after using it. To further the farm’s educational goals, they would want to share information about using urine or biosolids biochar: “I feel like we’re very transparent with like how we live, how we manage. We have …very detailed stuff on our website…We would say this is how we do it, just to educate people too.”

Other farmers had some skepticism about how transparent they could be and weren’t sure if they would highlight their use of these amendments with customers. One respondent noted that even though their customers may have had positive experiences with using the composting toilet at a nearby educational farm, they would still be hesitant to tell customers about using these amendments because they didn’t think those good feelings would necessarily translate over when those customers would have to confront the topic more directly and think about these amendments being used on their food: “They’ll get down with a… composting toilet thing at like, the nonprofit farm, but… I think it’s like a little too much for people sometimes. Like if we were like, ‘Yeah, we’re using urine and humanure at our farm,’ that could– just confuse people ‘cause it’s too close to home.”

When it comes to customers who may be uncomfortable or have many concerns, some respondents doubted how effective education could be. As one respondent put it: 

They come in already believing what they believe… So I don’t really think that there is something like information on our website or whatever that could change anyone’s mind…at all. Like I think the people who that appealed to would have to already be kind of open-minded to it. 

Others echoed this sentiment about following a kind of path of least resistance when it comes to education, and focusing on those who are already exhibiting curiosity. Many respondents mentioned that their customer base tends to be open-minded in general and receptive to the “language of research,” but also stressed that information shouldn’t be dry and inaccessible. One respondent thought it would be helpful to initially draw people in with humor: “You can move away from the potential squeamishness by kind of like almost making fun of it.” Another described how they would use popular culture to ease uncomfortable customers by referencing the main character in The Martian growing potatoes with his own poop. 

Regulation: We did not use sub-codes for specific ideas about regulation, but each respondent was asked how they thought these amendments should be regulated and by whom. The results indicated considerable confusion and uncertainty. Many respondents mentioned that they are not sure whom they can trust to regulate or provide certification in a transparent and credible way. On the other hand, many feel some type of regulation would be important. For example, one said:

I think there is importance to regulation, [but] …sometimes I wish it were done with a more like, I don't know, more rational way. But I think there is importance to regulation because then we know that a product is, we hope to know that a product is doing what it says it's going to be doing and it's helped with those standards. And that if we're buying it from a source that is regulated versus a source that's sort of flying under the radar, then we're at least given that information to make those choices and take that risk….

Several cited the current government priorities as affecting their thinking about the credibility of the regulatory role of government agencies. Others mentioned what they felt was unnecessary bureaucracy, and regulators not really understanding farmers' needs. Some indicated prior negative experiences in this regard. When asked whether they would prefer state versus federal regulation, again, most respondents were unsure. For example, a typical response went something like this:

Yeah, good question. I don't know. I mean, yeah, I guess when I originally interpreted your question, I was like, universities should be doing, you know, should be running the tests. But yeah, I don't, I don't really have an answer for that. I mean, I think some sort of independent or, I don't know, I don't know, I wish everybody like… [trails off]. I trust, I trust a lot. But I think that some people aren't trustworthy, I guess, I'm learning in my old age [laughs]. So yeah, unfortunately… maybe it is university… independent, like, you know, that go out there and get paid to, you know… I don't know, I don't know. I don't know!

Generally speaking, however, most respondents seemed to lean toward some sort of independent body providing regulation and/or certification for these products. There was some movement away from, or less emphasis on, the value of organic certification than might have been expected. Many interviewees had experienced financial and logistical barriers with organic certification and think these amendments might need to be regulated through a separate entity.

Community Research Results and Discussion - Surveys

Below are results from the quantitative survey questions from the combined Vermont and Long Island surveys, including both dialogue group participants and those who did not participate. Some differences between the latter groups are noted in the discussion. Thirteen participants from the Brattleboro field day, ten participants from the Long Island Field day, and four more from each site who participated in a dialogue group filled out surveys. The survey addressed the participants’ most important indicators of soil health, most important factors when choosing a soil amendment, and finally their acceptance and ranking of using synthetic fertilizers, compost, urine, biochar from woody biomass, biochar from biosolids, and biosolids as a soil amendment.

Results:

What are your most important indicators of soil health? (Check all that apply):

Notes: The most important indicator by a wide margin was plant health based on observations, followed by soil fertility based on soil tests and soil texture or tilth based on observations; microbial activity and soil color showed less importance. This was consistent throughout at both sites and among those who participated dialogue groups and those who did not. 

What are the most important factors when you choose a soil amendment?

Notes: Soil amendment cost and effects on soil health emerged as the most important factor; organic certification was less important. This was consistent at both locations and whether or not respondents participated in a dialogue group.

Add any other thoughts on questions 2 or 3? (Optional)

• “Do you need certain machines to use urine? Are all the study/tests that have been done on tilled soil?”
• “I prefer amending soil with as local and natural and resourceful sources as possible, e.g. urine, ash, burnt bones, compost.”
• “Preferably sources that are close to the farm - local sources of compost that is processed appropriately would be best.”

After what you have learned today, would you consider using the following amendments in your soil amendment program?

Notes: Every respondent concluded that they would consider using compost as a soil amendment: urine and biochar from wood biomass were both well accepted; synthetic fertilizers and biosolids were met with the least acceptance: biosolids and biochar from biosolids were met with the most uncertainty.

Please rank amendments in order of your personal interest in using them in your soil health program (not considering cost and availability).

Notes: Compost had the most acceptance, biochar from wood biomass and urine next; biosolids biochar in the middle; synthetic fertilizers and biosolids last.  

Do you think biosolids biochar should be encouraged as a soil amendment (regardless of whether you would use it personally)?

Notes: While not everyone might want to use biosolids biochar as a soil amendment themselves, they still encourage the use of it. This may reflect an understanding of its potential usefulness after more testing. A large portion of respondents, however, remain uncertain. 

Add any other thoughts on questions 4, 5 or 6 (optional):

• “But not sure about biochar from woody material. I'm not sure we should be making biochar at the expense of compost, chips, mulch, etc. (These feed the soil, which seems to me more important overall.) I think of perhaps using biochar in small quantities on a farm in potting mixes maybe as a fertilizer converter. But I acknowledge I still have questions and I am not an expert on it.”
• “I would most likely look for a mix of them, except biosolids.”

Discussion:

Survey respondents overwhelmingly identified plant health based on observations as the most important indicator of soil health, followed by soil fertility based on tests and soil texture or tilth based on observations. Indicators like soil organic matter and soil life held moderate importance, while soil color and microbial activity were seen as less critical. These preferences were consistent across both geographic locations and whether or not respondents participated in dialogue groups, suggesting shared priorities in soil assessment practices among participants in these field days. 

Importantly, while participants did not emphasize soil color and microbial activity in the surveys, these are closely tied to soil organic matter and cation exchange capacity (CEC). For instance, higher organic matter levels usually darken soil color and increase CEC, which in turn affects nutrient retention and pH stability. Soils with lower CEC tend to be more prone to nutrient leaching and pH fluctuations. (The in-depth interviews, in contrast, revealed significant interest in microbial activity, with some farmers making considerable effort to learn more about this in recent years, and many interviewees also indicated their observations of soil color was important.)

When it came to selecting soil amendments, the two most important factors for survey respondents were clearly effects on soil health and cost, with over 87% of participants selecting these. Other considerations like the source of the amendment were moderately valued, while organic certification was deemed relatively unimportant. Actual performance and affordability were prioritized over certification labels. This may reflect uncertainty about certification and regulation as reflected in the in-depth interviews.

In terms of willingness to use specific amendments, compost stood out with 100% acceptance. Biochar from woody biomass (93.55%) and urine (80.65%) were also widely accepted. However, biosolids and biochar from biosolids were met with lower acceptance and higher levels of uncertainty, and synthetic fertilizers received the least support. Despite the tentative responses, a majority (nearly 70%) agreed that biosolids biochar should be encouraged as a soil amendment option, suggesting an understanding of its potential benefits even while there may be uncertainty about its sources and an interest in further data. Personal ranking data echoed these trends: compost was by far the most preferred amendment, followed by biochar from woody biomass and urine. Synthetic fertilizers and biosolids consistently ranked lowest. 

A significant finding from the survey data, also reflected in the interviews, is that most participants were unsure about both biosolids and biosolids-based biochar, and their opinions didn’t change, even after receiving more information through information sheets or dialogue groups. Given that most still felt biosolids biochar should be encouraged as a soil amendment, this suggests that their uncertainty primarily reflects the need for more information and data, rather than rejection of the concept of biosolids biochar. The types of data participants would like to see is reflected in this comment from one dialogue group participant:

[I would] like to feel confident that looking at the indicators on a test is actually backed up by much more detailed research looking at a wider array of things that actually like track the fate of what happens to them in the soil. Like do they run off as water infiltrates? Do they get bonded to like parts of the biochar and just stay there in soil? How much, what do the plants, different types of plants uptake? Like can bioconcentration be a risk for any contaminants? Just all the possible complicated things that can happen.

In the interviews, during which participants had more opportunity to explain their thinking, various concerns were elaborated as described earlier. Nonetheless, most respondents were intrigued by the concept and eager to learn more as more data becomes available. 

More education and exposure may help people feel more comfortable with the idea of using biochar made from biosolids. At the same time, the dialogue group results show that more information can also make people more cautious, not necessarily more accepting. During the dialogue groups, respondents gained more clarity about what biosolids biochar is, and these may have affected these results. Further research, some of which will be conducted in the next two years through the FFAR study, may help elucidate the impact of educational materials and additional data on acceptance. For example, one dialogue group participant said they might use biosolids biochar on any crop, "once I understand it a little bit better.… I think that the making it into a biochar will make it safe…. But I really want like an independent study done that shows me exactly what's in it, exactly what the risks are." Nonetheless, unknowns about sources of biosolids biochar remained a concern for some participants: "I mean, certain places though, like industrial cities, like they've been pumping heavy metals out of their smoke stacks for years and like all of the ground is, like… it's completely covered in heavy metals." 

Interestingly, among field day participants, synthetic fertilizers were generally viewed just as negatively as biosolids, indicating a clear preference for more natural or local soil inputs in this group. Some respondents were unsure about biochar from other biomass including wood, but noted in their comments that this might have more to do with the idea of making biochar at the expense of compost, rather than direct concern about the biochar as an amendment.

Some differences between dialogue/no dialogue and Vermont/Long Island surveys

Comparing responses at the two sites, there was a higher rate of acceptance of urine among those who had taken part of the dialogue group compared to those who had not. The dialogue group responses ranked using urine as a soil amendment as a 2.38 on average (with 1 being the highest and 6 being the lowest), putting it in second place after compost and tied with biochar from woody biomass. Among those who did not participate in a dialogue group, the surveys from the Vermont field day still showed a high acceptance of urine with an average of 2.84, still in second place. Long Island surveys indicated less comfort with urine, as their average rating was 3.98, behind compost and biochar from woody biomass.

When looking at the acceptance of biosolids biochar and biosolids, the least acceptance was among those who took part in a dialogue group (at both sites) followed by the Long Island non-dialogue group surveys. The highest acceptance of biosolids biochar was among non-dialogue group participant respondents in Vermont. These results could be due to current understanding and knowledge among Vermont participants who potentially were more familiar with the work of Rich Earth Institute. The field day in Vermont also focused primarily on the results of this study, while the Long Island field day also included focus on several other soil health studies, potentially affecting responses.

Dialogue groups provided opportunities for further discussion of biosolids biochar including current "unknowns" regarding sources of inputs. This may have influenced outcomes. Given the relatively small number of dialogue group participants (4 at each site) results could also be reflective of individual differences and dynamics within the groups. For example, in the Vermont dialogue group, one participant expressed significant doubts, saying: 

I'm not even looking for this product [because I already have the amendments I need] but I can tell you, I'll never even consider it unless it has very clear markings that it's safe and what it's going to add to my soil and the benefits of it… like NPK, micronutrients, and like, definitely like low or no heavy metals, all that kind of stuff. In terms of labeling.

While this individual's concerns may have affected fellow participants' survey responses (i.e. increasing uncertainty about biosolids biochar), the advocacy for safety and nutrient information and labeling was shared by many interviewees as well, including those with more favorable responses.