This post is part of Calista Washburn’s 2023 Lazarus Summer Internship.
For several months this summer, sections of the grassy and peaceful Yale Farm became a muddy and noisy construction zone. As work crews brought in backhoes and dug trenches across the Farm, installing some critical tech infrastructure for the University, the summer farm team grew accustomed to large piles of soil and yellow work machines dotting the landscape. For me, what began as an annoyance became an exciting opportunity to explore the Farm’s soil.
Piles of soil on the southeast side of the Farm, dug up by construction crews in June and July 2023
While all aspects of soil are important to farmers, it is the organic elements—compost and decayed matter, soil carbon and nitrogen—that seem to get center stage time and time again. As the construction crew dug up more and more of this beautiful red, organic-matter-poor soil, I became increasingly curious about those inorganic components we spend less time thinking about.
I’ve loved ceramics and pottery since middle school, and I have spent hours in the Murray Pottery studio coiling sculptures and throwing wobbly saucers on the wheel. I had heard about the process of harvesting wild clay—clay found in the soil all around us—and was eager to try my hand at it. The piles of topsoil lying around the farm presented the perfect opportunity.
Over the course of the summer, I developed a “wet process” method for harvesting usable clay from the mixture of gravel, sand, silt, clay, and organic matter that comprises the Farm’s soil. Iterated steps of adding water, mixing, letting particles settle, and pouring off the still-suspended smaller particles gave me an experiential understanding of the Farm’s soil makeup.
A bin of Yale Farm clay drying in the sun
My firsthand exploration of clay harvesting at the Farm prompted me to learn more about the relationship between ceramics and agriculture, particularly a ceramic-based irrigation method called “pitcher” or “olla” irrigation. The term “olla” can be used to refer to a wide bodied, narrow-necked earthenware pot that is buried and filled with water in order to irrigate the surrounding soil.
Olla irrigation relies on the porosity of low-fired clay to deliver a steady supply of water right to the roots of crops. Instead of water dripping out at a constant rate, as in drip irrigation, water in a buried olla will seep out as a result of negative pressure created by the dryness of the surrounding soil and water tension. Ollas will irrigate soil when it is dry and there is negative pressure, but cease to irrigate when the soil is wet and the pressure gradient evens out. The combination of this intermittent irrigation and the fact that ollas deliver water right to the root zone with little evaporation makes olla irrigation incredibly efficient.
Source: https://www.permaculturenews.org/2022/11/29/irrigation-with-ollas/
Diagram of a buried olla, with a zone of water seepage
Though it can be used in almost all climates, pitcher irrigation has been prevalent in arid and desert agricultural settings for thousands of years. Farmers have used olla irrigation in China, India, Sri Lanka, the Middle East, the southwest United states and Northern Mexico, and large swathes of Africa. In these places, the water savings of pitcher irrigation have made it possible to grow water-intensive crops—even melons—in the most adverse conditions.
Though it is not a recent development, olla irrigation has become a trendy topic in gardening blogs and other small-scale agricultural resources in the past 10 years, and particularly since 2020. Though the scientific community as a whole has given far less attention to pitcher irrigation, the past decade has seen an increase in interest in pitcher irrigation as a remarkably efficient water-saving technology. More and more studies seek to include pitcher irrigation methods and to quantify and optimize their water savings in different agricultural settings. As droughts plague many parts of the U.S. and the world, and as we are increasingly forced to confront the flaws with modern agricultural technology, olla irrigation is hailed as a tried-and-true method with better results than some—if not all—modern technologies.
The trendiness of ollas among gardening blogs, while it remains relatively obscure within mainstream farming wisdom, has helped me reflect on the ways in which traditional knowledge retains legitimacy in modern agricultural spaces. While small-scale farmers and gardeners tend to value tried-and-true, inherited practices, conventional large-scale agriculture focuses much more on cutting-edge technologies and scientifically-proven numerical optimizations.
In my summer of clay exploration at the Yale Farm, I was able to acquaint myself with clay and pottery in a myriad of its forms, from its origins mixed in the soil to an ultimate fate as a vessel centered in cultural, functional, and historical contexts. I am deeply grateful for the Yale Sustainable Food Program and Lazarus Summer Internship team for their enthusiasm about my experimentation.