The Effects of the Old Acre’s Hill on Its Soil | LSI '23

This post is part of Pete Muhitch’s 2023 O’Donohue Summer Fellowship.

The Yale Farm’s slope uniquely impacts both its above-ground management and the structure and properties of the soil that lies beneath. Along the farm’s hill, are a series of berms running north to south. The berms, consisting of a wonderful variety of perennial herbs and flowers, are in place to mitigate runoff, erosion, and leaching, and carve out a flatter surface for crop production. Pictured below is a map and picture of the farm from the perspective of the path between beds 2U and MAPLE. The yellow lines highlight the elevation change of the land, while the blue lines highlight the berms. 

On its own small scale, the Old Acre slope and its terraces tie the Yale Farm into a global history of farming on hillsides. Indeed numerous societies across the world have employed terracing techniques to transform thin-soiled slopes into soils viable for agriculture. A cursory wikipedia search offers rice farming in mountainous areas of Vietnam as one prime example. 

Topography is a major factor of a given soil’s development. As biological, chemical, and physical processes weather a parent rock (in the case of the Yale Farm, a reddish sandstone called New Haven Arkose) into soil, gravity can transport soil particles depending on an area's topography. Pictured below is a slide adapted from a presentation from Scott Fendorf PhD, a Stanford University soil scientist. This topography principle suggests that soils at the base of a slope tend to be deeper and wetter, as a result of the leaching and accumulation of fine-particle clays from the upper parts of the slopes. Soils on a slope, therefore, will be shallower and more rich in heavier sand particles, and resultantly are well drained. 

With a historic and scientific backdrop of hillside farming, this project aims to study what effects, if any, the slope has yield on the farm’s soil in varying locations. Acknowledging my own lack of expertise in soil science, to the best of my abilities, the goals of this project were to (1) determine the chemical and physical properties of the Yale Farm soil, (2) determine any variance in soil properties versus soil position on the slope, and (3) determine any variance between cultivated and uncultivated soils. In pursuit of accomplishing these goals, I was able to practice soil field analysis techniques, offer scientific suggestions for patterns in the soils, and further inform one thread of the farm’s narrative (its hill!) with data collected. 

A series of four holes were dug to study these thoughts. Though more holes would increase the accuracy of the project, at a certain point too many holes would be beyond the scope of the project (digging is laborious and impractical for the farm). The location of each hole is denoted with an ‘X’ in the map above. Each site was selected to form a line down the hillside, in order to compare the soil at various points along the slope. A hole was additionally dug in field 2M to discover the effects twenty years of agriculture has had on the soil there, compared to the rest of the hill around it. At each site, the soil’s horizons, depth, texture, aggregation, relative wetness, color, and nutrient content was assessed. Texture was determined using the wire method; the Munsell soil color guidebook was used to determine color and aggregation; samples of the near-surface soil of each site were collected and sent to the University of Connecticut soil nutrient laboratory for analysis. Below are the physical results of the project. 

Hill, 41.32041 N, 72.92198 W:

The soil at the hill site consisted of a sandy, well drained, reddish soil (increasing numbers before YR in the color column denotes a change in hue from red to yellow, i.e lower numbers before YR mean a redder hue). After around 26 inches of digging, I reached what I refer to (throughout this project) as the soil’s BC horizon. Though not quite a C horizon of unconsolidated rock, the BC horizon still largely contains soil particles, but is significantly rockier (and more annoying to dig) than the B horizon that lies above. At the risk of oversimplification, I will describe basic soil horizons: an O horizon consists of organic matter and detritus at the surface of the ground; an A horizon is the uppermost soil level, typically high in organic matter and home to plant roots; the B horizon is found below the A, and is lower in organic matter but higher in rock derived nutrients, which are weathered from the C horizon; the C horizon is unconsolidated rock material, just starting to be weathered in soil. Beneath the C horizon is rock. Texture and color changes commonly denote a change in horizon. 

Upper farm, 41.32036 N, 72.92130 W:

The upper farm hole was the most difficult and confusing hole of the project. The soil there is very compacted, sandy (to the point I could not form a ball for the texture test), and shallow. After 28 inches of hard digging, I reached what I believed to be a C layer of solid, impenetrable red rock. This soil presented the same red hue as the hill site.

Field 2M, 41.32036 N, 72.92132 W:

Field 2M yielded a greater clay content than the two higher dig locations. This included a Bt horizon, referring to a translocation, or leaching, of clay to the B horizon of more than 20% increase from the upper horizon. 2M is also deeper (requiring 33 inches of digging before the BC layer was reached) and of a more yellow hue than the upper locations. The relative moisture of this site is altered by the field’s irrigation, resulting in a very dry surface soil, but wetter in the more clay-rich deeper regions. 

Lower farm, 41.32036 N, 72.92133 W:

The most clay rich soil was found at the lowest dig site, which aligns with the topography principle of soil formation. This hole had the same yellow-ish hue of 2M, but required more than 43 inches of digging before any semblance of a BC horizon was reached. As a result of its clay content, it was the moistest soil of the project as well. 

Overall physical results: 

**relative wetness affected by irrigation schedules 

The principle of topography and resulting soil properties largely hold true on the old acre. Lower dig sites tended to yield wetter, deeper, more clay rich soils, while the upper two sites were sandier, shallower, and drier. The upper farm site does preclude the farm from perfectly following the topography principle, with abnormally shallow and coarse for its slope position. This could be due to leaching from the slope it is on, but also could be a result of other factors, such as the berm lying above it trapping erosion from the upper slope, or the many tree roots that surround it. Another perennial possibility is that the land was altered by unbeknownst human activity. Upper soils also tended to be redder. I offer the following explanation: soil color is largely determined by the predominant oxidation state of the soil’s iron. Given the difference in moisture and other physical properties of the upper and lower dig sites, the iron oxidation could be likewise different, explaining the color difference. 

The topography principle also has implications for a soil’s nutrient content. Nutrient leaching will often occur on slopes as a result of runoff, causing nutrients to settle at the bottom of a hill. Moreover, clays and organic matter, also more abundant at a hill’s base, generally have a greater capacity to hold nutrients due to greater particle surface area.

Hill: 

Upper Farm:

2M:

Lower Farm:

Overall there does appear to be a greater concentration of nutrients, and a higher pH, at the base of the hill on the farm. While it is possible that this is due in part to topography and the accumulation of clay there, it is likely because the soils of the farm have been affected by 20 years of fertilization and lime application. It is therefore clear that years of farming has drastically increased the soil’s fertility and improved its pH. These improvements appear to not be limited to the field 2M, the only site currently being cultivated, but extend to the other on-farm sites (upper and lower farm holes). This could be a result of leaching of fertilizer, or due to an accumulation of nutrients at the base of the steeped part of the hill. Regardless, the data shows a greater nutrient content, pH, cation exchange capacity, and base saturation in the three on-farm soils tested in contrast to the hill site. 

Revisiting the goals of the project, the four holes dug largely appear to uphold the topography principle of soil formation, as the project does show a trend of deeper, more clay rich and fertile soils at the base of the hill. Cultivated soils also tend to be more fertile and higher in pH, but this does not appear to be localized to beds that are currently being cultivated. Personally, it was great fun to get dirty, dig some holes, and practice some soil science techniques while investigating this unique characteristic of the Yale farm. 

Soil Health Policy Guidebook with Abbey Warner YSE '22 and Darya Watnick YSE '22

This November, the Yale Center for Business and the Environment’s Regenerative Agriculture Initiative published the Soil Health Policy guidebook. The report, written by Abbey Warner YSE ’22 and Darya Watnick YSE ’22, offers recommendations for creating community-driven, state-level soil health policy and programs. YSFP communications team member Kapp Singer ’23 sat down with Warner and Watnick to learn a little more about the goals of and approaches to creating the guidebook.

This interview has been edited lightly for length and clarity.

Abbey Warner YSE ‘22 (left) and Darya Watnick YSE ‘22, the authors of the Soil Health Policy guidebook.

Kapp Singer: Why is soil health so important?

Darya Watnick: Soil health is the basis for anything that you're growing because all of the nutrients live in the soil. Soil holds water, so thinking about the soil health as a baseline means that anything else growing in the soil is going to have better yields, better health, and better nutritional value in some cases. The better your soil, the more resilient your crops are going to be to droughts or pests. There are just so many benefits to thinking about farming through the lens of soil.

Abbey Warner: The only other thing I would add is the importance of having a broader view of soils—how are they also relevant to people who aren’t farmers or thinking about food systems? Soil provides a range of ecosystem services, from water filtration, to nutrient cycling, to food provisioning, which are all really critical to how we grow our food and our fiber. It’s also really important for other benefits related to water pollution or the ability to withstand drought and have more healthy ecosystems.

KS: What motivated you to create the Soil Health Policy guidebook?

DW: I had a summer internship in the summer of 2020 working with some folks who were starting a community group to launch a bill that would hopefully create a soil health program for the state of Colorado, run through the state’s Department of Agriculture. I have continued working for them since that summer—it’s almost been a year and a half at this point—and the program is now in place in Colorado, which is very exciting. I’d been talking to my supervisor about how we learned so much through that process, and how there are other states that are interested in following this same path. We came to the conclusion that we should write it down so that people don’t have to reinvent the wheel. There’s an initiative at the Center for Business and the Environment at Yale (CBEY) called the Regenerative Agriculture Initiative (RAI) that provides funding for student projects related to regenerative agriculture, and I thought this would be a cool opportunity.

AW: Darya and I were chatting about what to do for RAI and because she had already come up with a great idea, I was super on board. I had also been working in Colorado that summer and was really interested in the farming challenges there—ideas around soil health and water management. We ended up getting funding through RAI to create a guidebook that would collect all of these lessons learned from Colorado and also from other states that had passed soil health bills or programs, including California and New Mexico. We interviewed over 30 stakeholders from those states and also from other states that were in the process of working on soil health legislation or coalition-building to try to understand both the lessons learned and the needs of groups not as far along in the process. We were trying to strike a balance between providing concrete recommendations that are practical, but not overly prescriptive, because each state has a very different context around soil health.

KS: Your report outlines that a community-based approach is key to tackling issues of soil health. What kind of results or outcomes become possible when the whole community is involved?

AW: At its most basic level, having community involvement in soil health policy-building is really the only way to get these sorts of policies and programs passed. With every natural resource issue that you’re working on, there’s always going to be different sides to issues. There’s also a lot of very real concerns that different stakeholders have about how agricultural policy is made, how environmental policy is made, and the repercussions those policies could have for certain communities. It was really interesting hearing about how in some cases, it wasn’t even necessary to organize for the support of certain stakeholder groups—like commodity crop organizations—but to organize to the point that they wouldn’t actively oppose a certain policy.

DW: Community-building also helps bring farmers or ranchers—whoever is going to be implementing the practices—to the table, because they’re the ones who are going to be doing this work on their fields. You could have the greatest program, but if they don’t feel like it’s actually valuable to them in any way or worth their time to implement, then obviously you’re not going to have a good result or make a real impact. 

KS: Tell me about your approach to creating this guidebook. Are there any notable parts of the process you’d like to share?”

AW: Darya and I came in with a really concrete idea about what we wanted to do, which was helpful in keeping focused throughout the process. The first semester we were working on this mainly involved background research, outlining the project, and getting the Institutional Review Board (IRB) exemption so we could interview people. Then, in January of last year, we started our interview process, and that was when we interviewed over 30 different stakeholders. That was my favorite part of the process—it was really interesting to talk to all these people and get to ask them questions about what sort of lessons they wanted to share with other people, or what sorts of things they were curious about in soil health policy-making. We were able to tap into this wide network of people from different worlds, but who are all really coming together on soil health. I felt so lucky to get to talk to all of those folks. Then, at the end of the spring semester, we started our writing process. We outlined and drafted the guidebook and then edited it throughout the summer and into the fall, and then we worked with a design team to help us format it so that it would look fun and exciting to read instead of looking like a typical research paper.

DW: We split up the sections and did a little writing retreat—we went to an AirBnB for a weekend and spent hours writing. This was a huge part of how it got done—just sitting down and forcing ourselves to write.

Soil Health Policy: Developing Community-Driven State Soil Health Policy and Programs (November 2021). Click here to read the full report.

KS: Now that the report has been published, whose hands do you hope it will end up in? Who do you think would benefit most from reading through the Soil Health Policy guidebook?

AW: We’re really hoping it ends up in the hands of either already established groups that are hoping to drive soil health policy-building in their state, or maybe in the hands of state agency staffers or legislative staffers who are already thinking about soil health and other environmental issues.

DW: We wrote it for a very specific audience—the groups Abbey just mentioned—so hopefully it finds its way to that audience. 

AW: And that could also include people at nonprofits, or really anyone who is interested in soil health, which is cool. There are definitely states that are already interested in this work, like Montana, Nebraska, and Virginia. There are lots of different people who are already thinking about this all over the nation. Hopefully they can pick the report up wherever they are in that process and find something useful to them.

KS: Is there anything else you’d like people to know about the guidebook that I haven’t asked about?

AW: We’ve gotten some feedback from some people that this toolkit could be helpful for other natural resource issues like urban greening. Since a lot of the tips we were trying to give are very practical, and not necessarily exclusively related to soil health, anyone who is trying to build a coalition around a natural resource issue may find something useful in it.

KS: Thank you both so much.