garden ecology lab

garden ecology lab

Urban agriculture has received a lot of attention over the past decade, as more folks are looking to localize their food supply, reduce food miles, and/or exert greater control over their food. Urban agriculture, however, brings a distinct set of challenges from farm systems in more rural regions. For example, urban farms tend to be relatively small and diverse (which can make it challenging to rotate crops), and are often close to neighborhoods and housing developments (which may make urban farms more prone to nuisance complaints). Urban farmers tend to be younger and to have less experience in agriculture, compared to rural farmers, and in need to high levels of technical assistance from Extension and other providers (Oberholtzer et al. 2014). However, many of the resources that Extension has to offer are focused on traditional growers, rather than new urban farmers.

Our lab group wanted to examine an issue that is specific to urban growers, and for which we could find very little information: urban agricultural soils. Soil scientists have prioritized research on urban agricultural soils as a key priority for the 21st century (Adewopo et al. 2014). Yet for his thesis work, Mykl Nelson could only find 17 academic papers that looked at urban agricultural soils in the United States. Most of these studies focused on

residential-scale or community-scale urban agriculture (in home or community gardens). Only one paper looked at soils on an urban farm.

Still, residential- and community-scale gardening is an important type of urban agriculture. In Portland, a conservative count of 3,000 home gardens collectively covers more than 20 acres of land (McClintock et al. 2013). In Chicago, residential food gardens cover 29 acres of land, and represent 89% of all urban agriculture (Taylor and Lovell 2012). In Madison, WI, more than 45,000 food gardens cover more than 121 acres of land (Smith et al. 2013).

For Mykl’s thesis, he looked at urban soils from 27 Master Gardener-tended gardens, in Portland and Corvallis, OR. Even though all gardens were tended by OSU Extension trained Master Gardeners, they were incredibly diverse: 74 different annual crops, and 58 different perennial crops were grown across these gardens. Unique crops included kalettes, papalo, thistle, savory, paw paw, quince, sea berry, and service berry, among others.

In terms of the soils, Mykl found that soils were within the recommended range for physical parameters, such as bulk density, wet aggregate stability, and soil compaction. However, home garden soils tended to be over-enriched in soil organic matter. Growers generally aim to foster soils that are between 3-6% organic matter. However, Mykl’s tested soils were on average 13% organic matter! Raised beds were on average 15% organic matter. In ground beds were a bit better: 10% organic matter, on average. So to put this another way, Master Gardener vegetable garden soils had 2-5X the recommended level of organic matter for productive agricultural soils. We suspect that Master Gardeners were annually adding organic matter to their soils, without necessarily knowing the baseline levels in their soils. Adding more organic matter, without knowing where you’re starting from, encourages over-applications.

Does that matter? Afterall, for years, we have been preaching that if you have sub-par soils, ‘just add organic matter’. Biological activity in these soils was great! But, the excess in organic matter promoted excess in several soil nutrients. Garden soils were over-enriched in phosphorus (mean phosphorus across all gardens was 2-3X recommended levels. Potassium in some gardens was 5X recommended levels! Gardens were over-enriched in magnesium and manganese, too. Nutrient excess was worse in raised beds, compared to in-ground gardens.

Unexpectedly, Mylk found the highest lead levels in raised beds. Often, we tell gardeners to grow their food in raised beds, to avoid heavy metal contaminants. Why would there be high lead in raised beds, if we weren’t finding elevated lead levels in nearby in-ground beds? We suspect that the lead might be coming in from compost waste that can be purchased on the retail market. If a compost product makes no nutritional claim, then it is exempt from analysis and contamination limits.

We can’t wait to finalize this work for publication. In the meantime, I wanted to share a brief update on this work.

Mykl will be defending his thesis on May 31st. We’re trying to arrange an online broadcast of the public portion of his thesis defense (1pm-2pm, May 31st). I will update this post, if we are able to get an online link for his presentation.

It’s been a busy month in the Garden Ecology Lab.

  • Gail’s manuscript on bees in home and community gardens has been published in Acta Hort. Briefly, the results of this literature review are that: 213 species of bee have been collected from a garden habitat; gardens have fewer spring-flying and fewer ground-nesting bees, compared to non-garden sites; I suspect that over-mulching might be cutting out habitat for ground-nesting bees in gardens.
  • Aaron presented his first Extension talk to the Marion County Master Gardeners. This 90-minute talk was an overview of using native plants in home gardens.
  • The entire lab is getting ready to present their research results at the 2018 Urban Ecology Research Consortium annual conference, to be held in Portland on February 5th. A few highlights of our presentations, can be found below.

Gail’s Poster on Urban Bees: we sampled bees from 24 gardens in the Portland Metro area (co-authored with Isabella and Lucas)

  • Langellotto and Messer UERC 2018 Poster: click to see preliminary results
  • Most of the bees that we collected await identification. We did find a moderate relationship between lot size and bee abundance: larger yards hosted more bees. But, we also found evidence that suggests that intentional design can influence bee abundance: one of our smallest gardens (site 56 = 0.1 acre), located in the Portland urban core (surrounded by lots of urban development) had the second largest number of bees (42), of the 24 gardens sampled. This garden was focused, first and foremost, on gardening for pollinators. The plant list for this garden (photos, below) includes: borage, big-leaf maple, anise hyssop, globe thistle, California poppy, nodding onion, yarrow, fescue, goldenrod, Phacelia, Douglas aster, lupine, mallow, columbine, meadow foam, yellow-eyed grass, blue-eyed grass, coreopsis, snowberry, Oregon grape, trillium, mock orange, pearly-everlasting, serviceberry, coneflower, blue elderberry, currant, milkweed, dogwood, shore pine, crabapple, cinquefoil.

 

 

 

 

 

 

 

 

Mykl’s Poster on Urban Soils: we sampled soils from 33 vegetable beds across Corvallis and in Portland (co-authored with Gail)

  • All gardens were tended by OSU Extension Master Gardeners.
  • Gardens were over-enriched in several soil nutrients. For example, the recommended range for Phosphorus (ppm in soil) is 20-100 ppm. Garden soils averaged 227 ppm. The recommended range for Calcium is 1,000-2,000 ppm, but the mean value for sampled beds was 4,344 ppm.
  • Recommended ranges gleaned from OSU Extension Publication EC1478.
  • There was a tendency for soils in raised beds to be over-enriched, compared to vegetables grown on in-ground beds.
  • Data suggests that gardeners are annually adding additional soil amendments or compost, and that there has a build up of certain elements in the soil.

Aaron’s Talk on Native Plants: measured bee visitation to 23 species of native and 4 species of non-native garden plants (co-authored with Lucas)

  • Field plots established at the North Willamette Research and Extension Center
  • In the first year of establishment, of the 27 flowering plants that were the focus of this study, seven natives (lotus, milkweed, camas, strawberry, iris, sedum, blue-eyed grass) one non-native (Lavender) did not bloom, or else did not establish
  • Several natives attracted more bees than even the most attractive non-native (Nepeta cataria, or catmint). These include:
    • Gilia capitata: Globe Gilia
    • Madia elegans: Common Madia
    • Aster subspicatus: Douglas’ Aster
    • Solidago candensis: Goldenrod

 

A soil pit is used to understand the nature of subsoil strata.
The Benton County Master Gardener demonstration garden was one of our soil test sites. This site had vegetables growing in raised beds, and in in-ground beds.
The Benton County Master Gardener demonstration garden used intercropping techniques to suppress weed growth in their beds.

This post is modified from a submission from Michael Nelson. It details lessons learned from his survey of garden soils, across Corvallis, Oregon, and the Portland Metropolitan area.  In September 2017, Michael sampled soils from about 25 gardens. These gardens used raised beds and/or in ground gardens to grow a variety of vegetables, herbs, and fruits. We wanted to study urban garden soils ~ and soils in raised beds versus in ground beds ~ for a few reasons. Specifically, we wanted to look at a few different questions:

  1. Do raised bed gardens offer greater protection from soil contaminants than in-ground gardens? In the Master Gardener Program, we recommend raised beds as a way to work around soils that may have heavy metal contaminants. However, heavy metals can become airborne, and deposited on soils from industrial emissions, traffic, and re-suspension of road dust. If this is the case, then gardening in raised beds might offer a false sense of comfort. We thus chose to sample gardens that are close to, versus further from, major roadways and traffic.
  2. Are garden soils deficient in some nutrients (such as nitrogen), but over-enriched in others (such as phosphorus)? With enthusiasm surrounding organic gardening and composting, we are wondering if repeated applications of compost might be contributing to nitrogen deficiencies, phosphorus leaching, or other soil nutrient issues.
  3. What is the general state of urban garden soils in Oregon? If we had to ‘grade’ soil health, by looking at soil structure, tilth, nutrients, and other biological, chemical, and physical characteristics of soils ~ what would that grade look like?

I asked Michael to write up a short report on his summer work. What did he observe in the gardens? What did he hear from gardeners? Are there initial findings or impressions he could share?  His report is below.

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We began this project to examine differences between raised and in-ground garden beds in urban areas. We conducted a short survey of each site, where we noted weed pressure, garden area (in meters squared), and crops grown. We also noted any concerns voiced by the gardeners, about their vegetable production site. We sampled garden beds and kept samples separate depending on the type of bed (in ground versus raised-bed). We are now processing the soil samples in the Central Analytical Laboratory of OSU, so that we can determine the chemical, physical, and biological characteristics of our garden soil samples.

A few initial observations:

  • The most common complaint we heard from gardeners was a lack of space to properly rotate their crops. For example, nearly every site had tomatoes, but many did not have the space to avoid planting in the same ground as the previous season.
  • In the lab, our initial findings are that garden soils do not fit well with traditional soil testing methods. The very high content of organic matter and low incidence of rocks brings immediate problems to the lab testing process. The first step taken when a lab receives a soil sample is to pass the sample media through a sieve. The larger pieces are lightly ground and sieved again. The aim is to isolate the soil from non-soil matter in order to restrict laboratory tests to just the soil content itself. The organic matter is often shredded by this process, which can alter the results of the laboratory tests. The primary problem here is that the organic material in our sampled garden soils is mostly forest by-products: timber waste. This material is generally inert in the garden setting and not accessible to plants. When this organic matter is included in a soils analysis, the organic matter compounds are incorporated into the test results and  skew the report away from the actual state of the garden’s soil.

The next steps in understanding garden soils are in research and application. In research, soil testing should be reconsidered with gardens in mind. There may be alternative processing techniques to reduce variability between test results and garden soil content. Theoretical models may be able to produce a metric which could be used to adjust the results of a standard soil test to reflect garden conditions more accurately.

In application, greater precision of terminology would allow for a more refined view and management of garden systems. In particular, bed-types should be grouped by their method of establishment (i.e. was soil transported to the garden, or not), rather than the presence or lack of a garden border. Additionally, organic mulches and compost should be considered in finer detail. The source of the product is important to determine what chemical content is being applied to the soil top. The physical structure of the product is important to relay the extent to which the mulch content will likely be incorporated into the soil, itself.

We’re still actively working to process and test samples. We look forward to sharing more results, in the near future.