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

Hypothesis

We hypothesize that there are positive effects on soil health and crop yield through using biochar and soluble fertilizer combinations in comparison to their use alone. We anticipate that these benefits can be achieved using two recycled amendments: source-separated urine and biosolids biochar. Our project will evaluate the potential for adoption of these novel human waste-derived soil amendments through investigating: 

1. How urine, biomass biochar, and biosolids biochar affect soil health, compared to currently-used conventional and organic amendments.
2. The questions, concerns, and recommendations of farmers, including specific indicators of soil health they consider important with respect to the tested amendments.

Materials & Methods

SOIL HEALTH

Field trials are being conducted: 1) on a commercial farm, in Brattleboro, VT,  and 2) at the Cornell University Long Island Horticultural Research and Extension Center in Riverhead, NY. Urine used in the study is pasteurized to meet Class A biosolid standards and sourced from near Brattleboro, VT. The urine used for the NY trials was shipped from Vermont.  

We originally intended to begin the field trials in 2022, but due to the short period of time between funding of the grant and the beginning of the field season, we determined that was not feasible. We therefore focused on planning and procurement of materials in 2022, and began the field trials in 2023. Baseline soil health samples were collected in late winter/early spring 2022.

Treatments

Nine treatments were selected to include a range of soluble and organic forms of nitrogen, along with labile (quick-to-decompose) organic carbon, recalcitrant (slow-to-decompose) organic carbon, or negligible levels of organic carbon. The treatments are listed below, and then in a table to show their distribution along two axes representing different forms of carbon and nitrogen:

Treatment

1. Control (no amendments)
2. Urea
3. Urine
4. Compost
5. Compost + urine
6. Biomass biochar + urine
7. Biosolids biochar + biomass biochar + urine
8. Biomass biochar + compost + urine
9. Biosolids biochar + biomass biochar + compost + urine

This design allows evaluation of the multi-year effect of applying labile carbon paired with organic nitrogen (N), compared to primarily recalcitrant carbon paired with soluble N. Intermediate treatments contain a combination of both types of N and carbon, to examine synergistic effects. The two low-to-no-carbon fertilizers and the control offer fertilized and unfertilized comparisons to the high-carbon treatments. The experiment also directly compares biomass biochar and biosolids biochar.

Amendment application rates for all treatments (except the control) are calculated to meet the agronomic N needs of silage corn. Supplemental phosphorus (P) and potassium (K) will be added if needed as indicated by soil tests. The treatments where both urine and compost are applied receive compost to meet all carbon requirements and urine to meet remaining N requirements. Compost (sourced from Vermont Compost Co.) was broadcast applied before tilling. Urine and urea were split between a planting application and mid-season sidedress, and applied in a band 2-3” below the soil surface and 4-6” away from the corn row.

Biomass biochar was produced from Southern Yellow Pine pyrolyzed at 800°C, and biosolids biochar was pyrolyzed at 600°C. Biochar was charged by mixing with compost or urine 1-2 weeks before surface application in Year 1. For the biochar treatments, biochar was mixed with urine and broadcast applied before tilling. Biochar application rates were chosen in consultation with project Advisory Committee members.

Methods

Two field experiments were established, one on Long Island and one in Vermont, both using a randomized complete block design. Each field location contains 45 subplots, to accommodate five replicates of nine treatments. Subplots measure 20’ long and contain four rows of silage corn. Subplot width is 12’ in VT and 11.3’ in LI due to the different spacing of the corn planting machines at the two locations. Harvest sampling occurred within the center 16’ of the middle two rows.

At both field trial locations:

Before season 1:

Baseline soil health and nutrient samples were collected and sent to the Cornell Soil Health Lab for the Comprehensive Assessment of Soil Health (CASH) standard analysis.

During each of the three growing seasons:

1. Terminate winter rye cover crop using herbicide. On April 8, 2023 herbicide (glyphosate) was applied to terminate the winter rye cover crop prior to trial establishment at the Long Island site. No herbicide was applied in 2024 to terminate the cover crop at the LI trial location and instead a lite disking was to terminate the cover crop. No herbicide was applied at the VT trial location prior to planting.
2. Surface-apply compost and charge biochar to appropriate treatments. Surface-apply supplemental phosphorus and potassium to appropriate treatments.
3. Till the entire field. 
4. Plant silage corn.
5. Apply synthetic fertilizer and urine treatments using standard practices: band applied 2-3” below the soil and 4-6” away from each row.
6. Apply herbicide (VT). At the Long Island trial location, herbicide (glyphosate) was applied on June 9 and 26, 2023, to manage weeds and on June 12, in 2024. At the VT location, herbicide (glyphosate) was applied to terminate weeds post-planting.
7. At mid-season, test leaf chlorophyll levels using a SPAD meter, and sample soil for pre-sidedress nitrogen testing (PSNT) on all subplots
8. Side-dress corn with the remaining N using appropriate fertilizer sources for that treatment. (We did not use the PSNT or SPAD results to determine sidedress N rates but instead just applied the remaining N as determined by the treatment.)
9. Collect yield data: biomass and forage analysis.
10. Collect soil nutrient samples (years 1 & 3 only) (A composite field sample was taken in year 1, subplot samples will be taken in year 3.)

After season 3:

Collect soil health samples from each subplot in Fall 2025.

Soil health testing will be done again using the CASH test. Soil health samples provide information on a soil’s physical, chemical, and biological properties, allowing for more holistic or systems thinking approaches to management. Through separate funding, longer-term  microbial analyses will be conducted concurrently from samples collected in spring 2023 and 2027.

Lysimeters were installed in year 1 at the Long Island Trial site to collect data on nitrogen leaching from the different treatments. Leachate was collected at various times throughout the study from the lysimeters but unfortunately, we were unable to collect samples from several of the lysimeters in the trial despite multiple attempts. Due to variability in performance of the lysimeters over the course of the season and the lack of samples to perform statistical analysis of the data, it was decided to forgo the lysimeter component of the project moving forward.

For years 1 and 2 data, an analysis of variance (ANOVA) was used to determine significant differences between treatments at each location (p < .05). The analysis included the main effects of treatment, location, and year. A Tukey HSD test (p < .05) was performed to determine pairwise significance between treatments at each location and year. All data analyses were performed in R Version 4.2.1 (R Core Team, 2022). Results will be disseminated through the final report, farmer field days, conferences, and at least one article for the peer reviewed literature and one for trade literature. (See "Farmer Outreach" section for specific journals to be targeted.)

Seasons 1&2 Update: 

In mid-April, 2023, baseline soil samples were collected from each of 45 subplots in both VT and LI plots and submitted for amplicon sequencing (Cornell University, NY) and phospholipid fatty acid (PLFA) analysis (Soil Health Assessment Center, Columbia, MO). This was done using funding from the Foundation for Food & Agriculture Research for conducting an add-on component to this study examining impacts of the treatments on soil microbiology.

In the spring of  both 2023 and 2024 seasons, compost, biochar amendments, and triple superphosphate (TSP) and potassium chloride (KCl) fertilizer supplements were applied to subplots according to the treatments detailed above. Compost was distributed evenly from a 5-gallon bucket to each plot, the boundaries of which were marked with a 20’ x 12’ subplot grid (Figure 1). Biochar amendments were weighed into 5-gallon buckets and mixed with urine in a 1:1 ratio to “charge” the biochar one week prior to application. Charged biochar was applied to field plots by evenly dispersing it from the 5-gallon buckets over the subplot grid. TSP and KCl amendments were applied to subplots using a hand-pushed fertilizer cart (VT site) and by hand (LI site).

The field was tilled and planted with corn in May. When seedlings emerged in late May, the first of two applications of urine and synthetic urea amendments were applied to their respective treatments. Both urine and urea were applied to furrows (2” deep and 2” from seedlings) and covered with a rake following application. Urine was applied evenly to each furrow using a hand-held applicator which was similar to a watering can. Urea was applied by shaking pellets evenly into furrows from a hand-held container (Figure 2). 

In late June, PSNT and SPAD testing was performed in each subplot. PSNT soil samples were sent to DairyOne Labs for analysis, and results from both PSNT and SPAD analysis indicated low nitrate availability. Sidedress urine and urea applications were applied to respective treatments using the methods from the prior application, with furrows (2” deep and 6” from plants) on both sides of a corn row to account for the greater volume of urine applied at this time (Figure 3).

In mid-September, the corn of each subplot was harvested and the wet weight recorded. A subsample of shredded stalk and leaf material was sent to DairyOne Labs for forage analysis (Figure 4). For eight ears in each subplot, variables of 1) ear length, 2) length of ear with developed kernels, and 3) the number of kernel rows were measured and recorded. Corn kernel measurements were not taken at the LI field location in 2024 due to heavy bird damage of corn ears.

SOCIAL RESEARCH

Our social research aims to understand farmer perspectives on the novel amendments studied in this project. We are analyzing farmers' questions and concerns, and identifying opportunities for and barriers to adoption (including economic factors) to inform our research and education strategies. We are also identifying specific indicators of soil health that are most important to farmers. To accomplish this, we are utilizing an iterative farmer engagement process, creating opportunities for participation through interviews, small dialogue groups at field days, and a regional survey.

Years 1 & 2

Interviews are being conducted with 20 farmers in New England and on Long Island in NY, to identify opportunities for implementation and future research needs. With Advisory Committee help, we are selecting farmers representing a diversity of operations, with specific effort to include farmers who currently use biochar or biosolids (or have demonstrated interest in such use), as well as BIPOC and women-owned enterprises. Interviews include current nutrient management practices; decision making about farm/soil management; ideas/concerns about the novel amendments of this study; suggestions for both consumer oriented and farmer-to-farmer educational materials; and soil health information needs. Interviews are being recorded, transcribed and coded for analysis, using standard triangulation protocols for qualitative research (Saldana, 2016). Results from our interview analysis will be used to inform the ongoing research plan.  

Year 3 

A farmer survey will be disseminated to farmers across the Northeast region through networks identified in the Farmer Engagement section above. The survey will be used to gather perspectives on the potential adoption of the tested amendments, including barriers, opportunities, and outstanding questions. The survey will introduce preliminary results compiled from field trials and interviews, and solicit additional recommendations for educational materials. 

We will also host a field day at each test site (one in NY and one in VT) to share study results with farmers, agricultural educators, and others and gather participants' feedback, questions and concerns. We will provide educational materials to share with farmers, informed by prior social and technical results, and facilitate break-out groups to discuss and evaluate the educational materials and their potential adaptation for different purposes. (See Steps to Adoption section above).

Data from the interviews, survey, and the small group conversations will be analyzed for dissemination via conferences, the final report, and articles for both trade literature and peer-reviewed journals. (See "Farmer Outreach" section above for specific journals.)

Year 1 & 2 Social Research Update:

We have identified a range of potential interviewees in Vermont and on Cape Cod and Nantucket in Massachusetts and Long Island in NY and continue to seek additional interviewees to ensure a diverse sample. We are behind in our goal of completing 20 interviews in Years 1 and 2, but the initial interviews represent diverse crops (e.g. ornamental shrubs, hemp, tomatoes, flowers) management history, scale of operation and farm types. We have expanded our thinking about the type of land managers to engage to include not only farms per se, but greenhouse operators and community gardeners, and some individuals involved with technical support for farmers. We anticipate completing the 20 planned interviews by March, 2025. We have developed analysis protocols, and are currently engaged in coding and analysis of the first group of interviews, which will inform our upcoming interviews as well as our Year 3 survey and field day dialogue.

Farmer Engagement 

We received IRB approval through Cornell University for the social research component of the project. During Years 1 and 2 of the project, we identified a range of farmers to interview and with whom to conduct site visits in New England and New York. We decided to expand the range of potential interviewees to include farmers on Cape Cod, given Rich Earth's complimentary work with a range of actors in that region interested in reducing nitrogen effluent into waterways.  We developed interview protocols (and revised these based on initial interview responses) and have been conducting interviews, but are currently behind in our goal of 20 interviews in Years 1 and 2. We intend to complete the remaining interviews in Jan - March of 2025.  

SARE 2022 farmer interview guide revised 7.29.24