Farm-scale Urine Fertilizer Implementation: Refining Application Methods, Gathering Buyer and Consumer Perspectives, and Producing Farmer Guide

Drip Fertigation Trial (Results)

Summer 2023: Irrigation trials for the current SARE project began in the summer of 2023. We used the same experimental setup as used previously: a center-fed ½” mainline with ten 10’ foot tapes (Figure 1). Some test runs were done using drip tape with a 0.67 GPM/100’ flow rate, and others with 1 GMP/100’ tape.

We quantified how evenly the urine was distributed during each test run by calculating the distribution uniformity (DU), which is a variability measurement used to quantify evenness of fertilizer delivery in fertigation systems (Coates et al., 2011). During each test run, we set sample collection buckets under the drip tape at even intervals and collected all the fertigation water emitted at the sampling locations over the course of the fertigation run. The electrical conductivity (EC) of each sample was measured using a Hach CDC410 EC probe and Hach HQ440D meter, and the measured EC was used as a proxy for the fertilizer concentration in the sample. For each test run, the conductivity measurements taken at the lowest quartile of sampling locations were averaged, and this average was divided by the average conductivity measurement at all sampling locations, as shown in the following equation:

DU = (Average EC of lowest quartile) / (Average EC of all samples)

A DU of 1 indicates perfect uniformity, and values above 0.85 are considered to be acceptable for drip fertigation (Cahn, 2018). The DU values calculated for all 2023 trials are compiled in Table 1 below.

Two test runs using the 0.67 GPM/100’ drip tape resulted in good DU when drip tapes were in a horizontal position (baseline operation treatment), and when tapes were at a 4% slope (elevation treatment). When the pressure in the irrigation system was allowed to drop for 15 seconds between the initial water injection and the urine injection (fluctuating pressure treatment), the DU suffered and was below 0.85. Because such a pressure drop can be avoided through careful operation, we conducted no further pressure drop tests, but noted the importance of avoiding a pressure drop when transitioning from water to urine.

Testing using the 1 GPM/100’ drip tape had different results. Baseline operation gave poor DU in four test runs, indicating that there was a fundamental problem with distribution, even with tapes in the horizontal position and no pressure fluctuations.

After reviewing available literature, we determined that a too-short advance time (described below) may have been responsible for the poor fertilizer distribution, and we decided to focus on investigating this factor. 

Advance time is the time taken for a drop of liquid to move from the first to the farthest emitter in an irrigation system (da Silva et al, 2022), and in a drip irrigation system it is a characteristic based on drip tape length and water velocity. It can be calculated by injecting dye into the irrigation system, and then measuring the elapsed time between the moments when the dye is observed to begin flowing from the first emitter and from the last emitter.

To promote good fertilizer distribution, the fertilizer should not be injected too quickly, and the duration of the injection period should be at least twice as long as the characteristic advance time of the irrigation system (da Silva et al, 2022).

We calculated the advance time of our test setup by injecting dyed water and measuring the time it took for dye to become visible at the last emitter. We then determined that the duration of the urine injection period was only about ⅔ of the advance time, rather than the recommended 2X. We therefore modified our protocol so that the urine injection period would be 2X the advance time. We did this by diluting the urine prior to injection, in order to increase the volume of fertilizer so that it would be injected over a longer period of time, without changing the total amount of nutrients injected. With the injection duration increased to 2X the advance time, distribution uniformity was excellent (0.95) (Table 1).

Table 1: Distribution Uniformities for varying experimental parameters in 2023 trials. 

The summer 2023 trials found no measurable effect on DU from inclining the drip tapes by 4%, but the tapes were very short, and a larger effect may exist with longer lines. Depressurization of the system while switching from water to urine had a major negative effect on DU, as did the use of a short injection period when using 1 GPM/100’ drip tape. Injection duration in relation to advance time was identified as the most important factor to investigate in 2024.

Summer 2024: In summer 2024 trials, we modified our previous experimental setup to consist of a single 100’ drip tape, rather than ten 10’-foot tapes in parallel, to better approximate a real-world drip irrigation system.

To continue research into the effect of urine injection duration on distribution uniformity, we conducted test runs with fertilizer injection durations equal to approximately 1X, 2X, and 3X of the advance time (which we determined by dye injection to be 1.87 minutes).

By coincidence, because this system had an advance time of 1.87 minutes and a flow rate of 1 GPM, the time taken to inject the experimentally specified 2 gallons of urine (2 minutes) was very close to the advance time of this system (1.87 minutes). As a result, injecting 2 gallons of undiluted urine resulted in an injection duration equal to 1.07X the advance time. We therefore specified that each experimental dilution would contain 2 gallons of pure urine, with 0, 2, or 4 gallons of water added for the three injection duration treatments, which were nominally 1X, 2X, and 3X the advance time, respectively. (In actuality, the injection durations were approximately 7% longer than their nominal duration, because the undiluted treatment had an injection duration of 1.07, and injection duration could be lengthened by dilution but not shortened.)

Test runs for each injection duration were conducted in triplicate. Injection of the urine (or diluted urine) was preceded by two gallons of pre-injection water to fill and pressurize the system, and followed by 16 gallons of post-injection water to flush the remaining urine from the drip tape. Samples were collected every 10’ along the 100’ drip tape, and temperature, electrical conductivity, and volume of each sample were recorded.

Distribution uniformity was excellent across all three injection duration treatments. The raw data is shown in Figure 2 below. Even the shortest injection duration tested (1X advance time) had an excellent DU value, in contrast to the 0.67X advance time injection duration measured in 2023. This could indicate that there is a major DU performance transition between 0.67 and 1X advance time, but it is important to be aware that the physical configuration of the irrigation systems were very different in 2023 and 2024. Therefore we cannot draw this conclusion, and can only state that injection times between 1X and 3X advance time provided excellent distribution uniformity using a single 100’ length of drip tape with a flow rate of 1 GMP/100’.

Table 2: Average distribution uniformity (DU) values for injection

durations of 1X, 2X, and 3X advance time in 2024 trials.

We also conducted limited runs to test whether temperature differences between cold urine and warm irrigation water could affect the DU, due to colder and denser urine moving along the bottom of the irrigation lines or preferentially pooling in dips in the drip tapes. However, preliminary testing conducted at 1X advance time with large temperature differences between urine and water showed similar results compared to other trials where such a temperature difference was not enforced. Results can be found in Supporting-Information-Drip-Fertigation-Trials.

Our conclusion is that plug-flow injection of urine fertilizer is an effective method for delivering urine fertilizer to crops using a drip irrigation system. Care should be given to maintain constant pressure within the irrigation system when switching between urine and water, and the duration of urine injection should be at least 1X the irrigation system’s characteristic advance time. Although we did not observe this in our experiment, literature suggests that injection durations of at least 2X the advance time may sometimes be needed to achieve good distribution uniformity. Achieving injection durations of 2X or more requires dilution of the urine fertilizer with water, but doing so could involve trade-offs for growers using very hard water due to greater risk of clogging.

The next step in the study of this topic should be testing plug-flow injection of urine into a real-world drip irrigation system on a farm and documenting the distribution uniformity and any issues with clogging.

Pete's Stand: Fertilizing Annual Row Crops (Results)

Sweet Corn Trial: The use of concentrated urine fertilizer enabled Janiszyn to fertilize about three times more acreage between tank refills, compared with using standard urine, reducing application labor. This was the first field crop farm trial of urine concentrate fertilizer, a novel product produced using freeze concentration technology developed by Brightwater Tools LCC (a spin-off of the Rich Earth Institute).

The increased ammonia concentration required immediate incorporation into the soil in order to prevent ammonia volatilization. Urine concentrate was applied through a hose running from the applicator tank to a spot in the air right above where the corn was being hilled, and the spider wheel hillers were effective in burying the urine in the soil with no apparent wet spots at the surface. Odors were limited, indicating minimized ammonia losses (Figures 3 and 4).

Three fertilizer treatments (urine, urine concentrate, and urea) and a non-fertilized control were applied to rows of corn at Janisyn’s farm. Composite leaf tissue samples of the ear leaf were taken at fruiting time and analyzed by Spectrum Analytics (Table 3). Nitrogen levels were comparable across all fertilized treatments, which were substantially higher than the unfertilized control. Other nutrient levels in all treatments (including the unfertilized control) were within or above the normal range for all nutrients except for boron, which was below the normal range for all treatment groups. Manganese and zinc levels were higher in the two urine treatments than the urea and unfertilized treatments, suggesting that urine fertilization may increase the uptake of these nutrients, yet these results are not conclusive as only one sample per treatment was analyzed. Notably, sodium content did not differ substantially between fertilization treatments, despite the known high salt content of urine.

Table 3: Leaf tissue nutrient content of four treatment groups, performed by Spectrum Analytics.

Pumpkin Trial: Pumpkin trials served to pilot an innovative application method that Janiszyn was quite excited about (Figure 5). We found this novel application method to be manageable and streamlined, as it did not require any extra passes through the field with the tractor. We feel there is more work to be done on refining the method for best results with different crops, but this method shows great promise because of its ease of execution and ability to quickly bury the urine in the soil, preventing ammonia loss.

Regarding crop health, Janiszyn reported that the pumpkin seedlings showed some leaf browning and curling initially, but appeared healthy and robust later in the season. This could have been the result of receiving too much nitrogen, and poses a question for further investigation.

Qualitative observations: With regard to the application methods with sweet corn, John Janiszyn observed that the mounded soil effectively covered the urine at all the tractor speeds trialed, and could go a little faster with the concentrated urine. He noted that the odor was "not too smelly, so that was nice." The reduced odor as compared to Janiszyn's previous trials with urine (Noe-Hays, 2022) was likely due to the addition of a lid to cover the opening at the top of the urine tank. 

The side-dressing was done on a late-seeded crop, in August, at 6 -8 leaf stage. At the time of the interview, in October, the corn was still not fully mature. At that time, Janiszyn did not find significant overall performance differences between the conventional and urine side-dressed corn, though it appeared that the conventional urea treated ears were more fully developed. The urine treated corn was doing better than the control, and the unconcentrated urine was doing better (taller, greener) than the corn treated with the concentrated urine. Janiszyn speculated that extreme rain during the growing season, and topography issues (places where water could pool) may have affected nutrient uptake. Also, Janiszyn noted that he may have gone a little too fast with the concentrate, and so provided a lower rate of application than with the unconcentrated urine. However, he felt that all the corn would produce saleable ears at maturity. He'd consider applying a higher dose of urine in the future: "I’d be curious to see what that would look like if I even went 50% more or even, or even doubled it just to see how the plants would react to that in the short term and the long term."

Janiszyn commented that there are advantages to a liquid fertilizer over a granular one in terms of ease of application, so his experience with this project, and talking to another farmer who had switched from a granular to a liquid fertilizer for corn, led directly to Janiszyn's decision to partner again with Rich Earth on a follow-up project. 

With regard to pest and disease pressure, no significant differences were observed, although there was somewhat less pest pressure (corn earworm) in the urine-treated rows than in the controls. Janiszyn speculated this was more likely due to a confounding factor (sun exposure) than the urine treatment. 

Based on Janiszyn’s positive experience, and the lack of any obvious problems, it would be useful to next conduct a rigorous controlled experiment with randomized replicates in order to better quantify the effects of urine fertilizer and concentrated urine fertilizer.

Yellowbud Farm: Fertilizing Nursery Trees (Results)

Chestnut trials: Farmer Jesse Marksohn reported that a commercial mycorrhizal inoculum was applied to the seedlings just prior to the urine fertilization. He noted exceptional results in seedling health and in mycorrhizal colonization of tree seedling plant roots, despite his prior understanding that mycorrhizal colonization rates would be higher in lower fertility conditions. He plans to do additional research to more precisely tailor species and timing of inoculation in the future.

The urine was applied just before rain to avoid nitrogen loss from volatilization (Figures 6 and 7). (It was noted that this was a very very wet year, which was fortuitous in this case; in a drier season, they might have wanted to irrigate first, so that soil would be moist during fertilization.) Fellow farmer Eric Cornell noted, with regard to odor, that "when you walk[ed] right next to the bed, you know, you can notice that pee was just applied, but it's not like extreme, it's not extremely offensive and it was gone…by the next day." Though some of the urine hit the seedling foliage during application, no burning of leaves was observed. Marksohn and Cornell want to use urine fertilizer in subsequent years, and noted that they believe the nursery stock could benefit from higher rates of urine application. They would like to explore the upper limits of how much urine could be applied without becoming detrimental.

Hickory Trials: Our analysis found urine fertilization to increase both root diameter and stem diameter in bitternut hickory seedlings (see Figure 8 for a photo of data collection). The average stem diameter and root diameters were greatest in the high treatment group (stem: 3.00 ± 0.05mm; root: 6.33 ± .25mm), followed by the low treatment group (stem: 2.78 ± .05mm; root: 5.86 ± .08mm), and narrowest in the control group (stem: 2.65 ± 0.05mm; root: 5.74 ± 0.07mm) (Figure 9). Differences in stem and root diameter between fertilization treatments were significant (p < .05), and the high treatment group had significantly greater stem and root diameters than the control treatment group (Tukey’s HSD p < .05). This increase in stem and root growth may indicate greater overall seedling health, as larger seedling stem diameters have been linked to increased seedling survival in both nursery-grown yellow poplar (Liriodendron tulipifera) (Dierauf and Garner, 1996) and ground-planted shortleaf pine (pinus echinata) (Kabrick et al. 2015). 

Seedling height and mass also increased with higher levels of urine fertilization: the average seedling dry masses were 3.34g, 3.05g, and 2.6g, and average wet masses were 11.92 ± .89g, 10.60 ± .74g, and 9.98 ± .73g for the high, low, and control treatment groups, respectively (Figure 10). The average stem height was greatest in the high treatment group (9.90 ± .46cm), followed by the low treatment group (9.14 ± .27cm), and shortest for controls (8.72 ± .29cm) (Figure 9). A larger sample size may enable us to determine whether these positive trends are significant. The more prominent effect of urine fertilization on stem diameter than on stem height observed in this experiment may reflect differences in tree growth patterns, given that nitrogen, the most abundant nutrient in urine, was found to be more closely associated with stem ground diameter than to stem height in container-grown hickory seedlings (Carya cathayensis) (Wang et al. 2012). Marksohn and Cornell also noted that Hickories are slow growing trees, and direct more energy towards root growth than shoot growth in their first year. 

This quantitative assessment is in agreement with the practical results observed by farmer-partners. Marksohn and Cornell were encouraged by the quality of seedlings grown under the high urine fertilization treatment, noting that about half of the seedlings from this group were worthy of sale while only a handful of trees from the control and low treatment groups were of saleable quality. As in the chestnut trials, they felt that the dose of urine could be increased above what was applied in the high treatment group to further increase the proportion of saleable seedlings and to better characterize the relationship between seedling growth and fertilizer rate.

Buyer & Consumer Perspectives (Results)

Buyers

Initial Reactions: Familiarity with the concept of urine diversion and re-use varied, from very little prior knowledge to one person who was very familiar and already diverted urine for fertilization personally. Perceptions varied, but a common theme was that if urine based fertilizers were readily available, were regulated in some way (i.e. such as by being permitted for use as a fertilize by a government agency), and were applied appropriately, they would be comfortable with this use, and it might in fact be preferable to synthetic fertilizers. One commented, "it makes so much sense to use what we do, what we need to do, many times each day," and wants to support local farmers who keep nutrients out of the waste stream.

Concerns: One of the buyers felt that, as their organization supplied produce to "vulnerable populations" including medical institutions and K-12 students, it was likely that these customers would be uncomfortable with urine fertilization until it became more of a norm, although this buyer did feel that with sufficient education about the steps that are taken to maintain food safety when processing or applying urine fertilizer, this discomfort could be overcome. This buyer also indicated some concerns about potential pharmaceutical microcontaminants in urine and would like to see results of any research on mitigation. 

Reasons for support: The idea of a locally available source of nutrients, utilizing a material that is currently being wasted, and mitigating greenhouse gas emissions and energy cost of synthetic fertilizer production, were the most salient potential benefits of urine-derived fertilizer for the buyers interviewed. One buyer concluded, "I don’t see any reason not to keep going forward with it… like why not, you gotta start somewhere, because what we have been doing [with regard to how we are managing human waste] isn’t working!”  

Transparency and Education: With regard to whether farmers should disclose their use of urine fertilizer, while transparency was valued, buyers did not feel farmers should be required to disclose use of urine fertilizer, as long as it was being used under some type of state or federal permitting or regulation. The food coop buyer noted, however, that having information about the positive things farmers are doing to steward the land and protect waterways is an incentive for customers' purchases, so having information, (either in the store or on farmers' websites) that farmers were using urine fertilizer and it was working well, would generate support for those farmers. All but one of the buyers interviewed had some concerns about the perceptions of their customers, but felt that with education, these perceptions could be addressed. The two "farm-to-institution" buyers both felt that having educational materials they could provide to their customers would be helpful [such as a brochure with "FAQ" about urine safety, etc. One commented, "[To be] armed with the knowledge so I could pass it on to the customer… that would be awesome – minds would change." They felt that providing such information was part of their responsibility in their roles at their agencies. One buyer also wanted to ensure that the farmers they bought produce from had received adequate education concerning appropriate application guidance. However, given that this buyer prioritizes buying from farms that use ecological growing methods, the concept of using urine fertilizer was appealing. 

Certification and Regulation: A buyer for a food coop that prioritizes purchasing local and organic produce felt that organic certification of urine fertilizer would be very helpful. Without that, he would want information about when and how the material was applied on any edible crops (such as time from application to harvest.) He would have fewer concerns for non-edible crops like flowers or animal feed. Another buyer also felt that approval from Vermont Organic Farmers would help to achieve more widespread acceptance. One felt that as long as the material complied with state regulations for other fertilizer use, they were comfortable.

Labeling: With regard to labeling at the point of sale, opinions were mixed. While not all buyers felt that labeling was necessary, there was the sense that labeling, or having educational material available to customers, could be a way of introducing the concept, potentially leading to wider acceptance. One buyer thought, "It would be new and kind of groundbreaking…. it would be a process obviously, but I think with a little marketing, it would definitely be readily accepted… I’m torn! I want the consumer to know what they’re getting, but in the beginning it would be a hard sell." Similarly, another thought that "It would be great to be much more vocal about the benefits of this work," but worried about misinformation or misperceptions until the practice becomes more widespread and/or has received organic certification. With regard to terminology, most of the buyers felt an acronym (such as UDF for "urine-derived fertilizer") would be best. "Urine-derived" was also noted as conveying the idea that some sort of processing or treatment (such as sanitization) had occurred which would be seen as positive by customers. 

Produce Customers

Initial reactions to the idea of fertilizing crops with urine was generally positive. "Excited," "really interesting," and "curious" were common words used. As one participant put it, "learning of urine separation, and its being decoupled from industrial processes and industrial fertilizer, that seemed amazing that we weren’t already doing it on a much larger scale!" Another said, "It’s closing a circle, completing the cycle, that’s the way of planet earth, so let’s do it.” Another commented, “I love the idea of being more eco-friendly and economical and if we can use a resource like that effectively, I think that makes complete sense.”

Reasons for Support: When asked which of the potential benefits of urine diversion and its re-use as fertilizer was most salient to their thinking, participants frequently noted the nutrient make-up of urine, something most participants were unfamiliar with previously. However, the other potential benefits (water conservation, less use of synthetic fertilizers, reduced greenhouse gas emissions) were all cited as "most important" by various of the participants. For example, one said, "What I know about the world of synthetic fertilizer is just that it's like… one of the most energy intensive processes you could find… it's a big part of our carbon footprint." If urine derived fertilizer could be less expensive than synthetic fertilizers, that was also considered important. Overall, participant motivations could be summarized by the comment, "Sounds great compared to all the other things we could be doing with it."

Concerns: The most significant concern mentioned was "safety," with regard to either human health or soil health over time. Participants wanted to be sure that "sanitization" reduced any potential human health risk, and wondered whether treatment processes included pharmaceutical residues. (Among pharmaceuticals, potential presence of hormone residues seemed to generate most concern.) However, participants noted that they have little knowledge about the likely presence of these constituents in the composts, manures, and other fertilizers farmers use. Most emphasized their trust in farmers they knew, whom they believed were doing the right thing with regard to environmental stewardship. They also felt confident in the researchers currently working on urine diversion and re-use. There was some concern that if urine recycling became more widespread, some of this local accountability could be undermined. Questions were also raised about the energy costs of treatment. Some would like to see a life cycle analyses of the energy and transportation costs of these systems, and wondered "Are we doing the right thing in order to do the right thing?" 

Which crops? Participants were generally most comfortable with the use of urine on non-edible crops (flowers, ornamental plants, animal forage), and on fruits and berries, as opposed to leafy greens, although this varied, with some unconcerned about urine use on any crops, as long as appropriate application methods were followed. 

Labeling: Perspectives varied considerably. Some participants would very much like labeling at the point of sale and/or on farmers' websites. Others felt that this was unnecessary, and could be confusing or off-putting. For others, the idea of farmers being able to tout the environmental benefits of UDF [urine-derived fertilizer] was seen as potentially very positive, and could help to "de-stigmatize" the concept of urine fertilizer. One said, "Being able to say '....as a UDF farm, we have prevented x amount of the bad stuff going into the watershed,’ I love that.'" When asked what criteria participants found most important in making their purchasing decisions, "local'" and knowing their farmer/s and their practices were key to many, so having fertilization information available was desirable. With regard to terminology, many liked the term "urine-derived fertilizer" or "UDF" as sounding more "professional" than "peecycling," and noted that “'urine derived fertilizer'....talks about the pathway through which it becomes something that can be applied…that seems easier to accept," although some thought "peecycling" was "catchy" and appealing. Many participants liked "urine recycling" because, as they noted, people often feel positive about "recycling" in general and thus can easily grasp the extension of the concept to the beneficial use of urine.

Key Takeaways: Results from buyer and consumer interviews will be helpful to us in our future communication and education efforts, to farmers with whom we share the guide, and those who read this report. Key among these insights were the following: 

1. Buyers want educational materials to share with both the farmers they buy from and the institutions they sell to.
2. Buyers feel that some type of certification would help achieve more widespread acceptance among the farmers they buy from. Approval by VOF was seen as likely to be very helpful. 
3. Buyers and consumers both indicated food safety concerns, but generally felt these concerns could be alleviated with education about treatment methods.
4. Both buyers and consumers were generally supportive of the use of urine fertilizer for a range of reasons. As one buyer put it, "I find it to be really important to use what we have and what we produce everyday so that it doesn't have to go through waste water treatment. Then it can be utilized instead of end up in waterways inevitably…. So it, it makes so much sense to take care of what we do, what we need to do everyday, many times a day, in a more useful sense." 
5. A key motivation for consumers was learning about the nutrient value of urine, something many were unfamiliar with prior to these conversations.
6. Participants were generally most comfortable with the use of urine on non-edible crops (flowers, ornamental plants, animal forage), and on fruits and berries, as opposed to leafy greens.
7. While ideas about where and how urine-fertilized crops should be labeled varied, both buyers and consumers felt that transparency was important. They would like access to information about what amendments and fertilizers are used by farmers, while acknowledging that information about currently used fertilizers is not always readily available.

Co-developing Guide (Results)

A copy of the Farmer Guide to Fertilizing with Urine can be found on Rich Earth's website, and a pdf version is attached to this report (see Information Products).