Local and regional food systems, soil phosphorus, and resilience in a northeastern regional farmers’ market network

2016 Annual Report for GNE15-105

Project Type: Graduate Student
Funds awarded in 2015: $14,796.00
Projected End Date: 12/31/2017
Grant Recipient: Penn State
Region: Northeast
State: Pennsylvania
Graduate Student:
Faculty Advisor:

Local and regional food systems, soil phosphorus, and resilience in a northeastern regional farmers’ market network


The purpose of this dissertation project is to understand how farmers participating in local/regional food systems (LRFS) manage soil fertility, the many factors that influence those decisions, and soil fertility resilience in a LRFS in the New York City region including parts of the mid-Atlantic and lower New England. These goals will be accomplished through a mixed-methods case study of the New York City

Greenmarket network of farmer’s markets that includes farmer interviews, soil analysis, and nutrient supply mapping. This project will provide a better understanding of the many social and ecological factors that influence soil management decisions, and an assessment of the resilience and sustainability of nutrient supply and soil fertility in this LRFS. These findings have been, and will be made available to farmers through direct feedback, the web, and potential future workshops.

The primary focus of work in 2016 was data collection. Interviews were conducted with all participating farmers (n = 22) during the winter of 2016. Bulk soil was collected from each participating farm field (n = 233) twice during the 2016 growing season for laboratory analysis. Some of this analysis was completed in the spring of 2016, with the remainder scheduled for completion in the winter of 2017. Phosphorus supply data was collected for each farm, and initial network mapping was conducted in the fall of 2016.

Objectives/Performance Targets

The research objectives for this project are as follows:

  1. Assess and describe soil fertility management on farms that participate in the New York City Greenmarket farmers’ markets, which includes:
    1. Documenting all farm management practices each farmer attributes to soil fertility.
    2. Documenting and tracing all input sources and application frequency.
    3. Measuring soil fertility (P (extractable, labile organic), K, Ca, Mg, Zn, Cu, S, pH, cation exchange capacity, soil organic matter, active carbon, and bulk density), microbial activity (phosphatases and microbial biomass).
  2. Explore and document the many factors that influence soil fertility management decisions on these farms, especially the role of participation in the Greenmarket farmers’ markets.

  3. Assess and document soil fertility resilience in the Greenmarket food system.

These objectives changed slightly in 2016 in response to farmer interviews and challenges to field collection of soil. These changes fall under objective 1. Initially, this project intended to include a phosphorus mass balance assessment as part of the soil analysis, but this proved unfeasible as too many participating farmers could not provide accurate data (actual or estimated) on nutrient application rate or harvested biomass. The use of anion exchange resin at 8-week intervals also proved impossible. This was due to inability to locate sites for resin incubation in fields that would not damage crops and also not be disturbed by mechanical cultivation. This method of phosphorus analysis will be replaced with a second extractable phosphorus test with the summer collection of soil to provide a mid-season assessment of available P. Labile organic P and active carbon assessments will also be added to provide a soil health focused approach to soil fertility resilience that will complement the other soil assessments.

Participant retention was a problem during 2016. In early January when farmer interviews began, 31 farms had agreed to participate, and 4 others expressed significant interest. However 9 farms were lost during the phases of data collection. The majority stepped out prior to the interview phase, but several backed out of the project during the spring round of soil collection. This was unfortunate, however, the remaining 22 farms are representative of the demographic variation and soil management practices found in the Greenmarket farmer’s network, and interview analysis suggests robust findings, even with a smaller sample. And with 233 farm fields sampled for analysis, soil data will provide statistically significant findings.


The first round of data collection in 2016 consisted of open-ended, semi-structured interviews with participating farmers. Interviews were conducted using an interview guide to ensure comparability across participants, and to provide specific data on farming practice and experiences managing soil, and participating in a local/regional food system (LRFS). Interviews were conducted in person and via telephone, and recorded for later transcription and analysis. Individual interviews ranged in length from approximately 40 minutes to nearly 2 hours, with most lasting approximately 70 minutes.

Interviews were the primary method used to answer the first two components of objective 1, and objective 2. Soil fertility management among participants fall into four basic approaches: biomass fertility (n = 8), rock mineral (n = 2), synthetic fertility (n = 3), and hybrid fertility (n = 6). Additionally, three participating farms are located in muck soil regions that require no additional fertility.

The four general approaches are defined here as:

  • Biomass Fertility – The application of organic matter to soil to meet plant nutrient needs. Inputs compost (farm-made and purchased), manure (raw, composted, and pelletized), soy meal, fish and kelp emulsions, humates, and cover crops grown as fertility amendments (green manure).
  • Rock Mineral Fertility – The application of crushed, mined, minerals that have not been refined, augmented, or altered with other chemicals to increase solubility.
  • Synthetic Fertility – The application of chemical compounds derived from industrial processes to produce highly soluble and concentrated nutrient fertilizers.
  • Hybrid Fertility – The use of soil amendments that fall in two or more of these three general categories to meet plant nutrient needs.

The presence of a significant number of participants that use hybrid fertility management strategies suggests that these categories might be better thought of as a spectrum of approaches. Most of the hybrid fertility participant use a combination of rock minerals and biomass-based amendments, which is in keeping with certified organic practices (four participant are certified organic and three are certified naturally grown, which has similar restrictions). However, two participants in the hybrid category also use synthetic fertility amendments, which makes it difficult to provide a more precise definition to the category.

Initial interview analysis suggests that the primary influence on soil fertility management strategy is a participant’s formative experiences as farmers. Nearly all participating farmers manage soil fertility (and many other environmental aspects of farming) in a manner that is consistent with the way they learned to farm – whether that be through apprenticeship, experiences as in an intergenerational family farm, or through reading and self-education. Geographic location also seems to be an important factor that not only controls soil type (and thus native fertility), but also access to resources – especially raw materials for biomass amendments.

Interview analysis reveals a complex relationship between farmer’s market participation and soil fertility management. Direct interactions with consumers in the context of the market do not seem to have a direct influence on soil management, however this is likely due in part to the fact that very few consumers ask questions about soil management. There is frequent producer-consumer dialogue about other environmental aspects of farm management, such as the use of pesticides, and interview analysis suggests that over time, farmers do begin to adopt different approaches to pest and disease management that are more environmentally friendly. In terms of soil, the farms that use synthetic fertility are beginning to change, or rethink, their approaches to soil fertility, and this does seem to be indirectly related to participating in the Greenmarket farmer’s markets. However, it is also very common for producer-consumer interactions to reinforce current practice rather than induce changes. This is because farmers are often able to effectively explain their practices and assuage the concerns of potential customers. And the establishment of long-term relationships with repeat customers only seems to bolster this effect.

Soil was collected from the upper 20cm of soil in each participating farm field during the March and June of 2016. Soil collected in March was analyzed for baseline fertility and soil organic matter, and soil collected in June will be analyzed for microbial activity, labile organic phosphorus, and active carbon.

Results from baseline fertility analysis find that 85% of sampled fields have excessive levels extractable phosphorus, with 12.8% in the optimal range, and only 1.7% showing P deficiency. There is no significant correlation between management type and extractable P levels. After controlling for soil types with very high levels of soil organic matter (SOM), the average level of SOM is 2.3%, with no significant correlation between SOM level and management type. There is some indication that the number of years a field has been in production is a significant factor in both SOM and extractable P, but since many of these fields were in production prior to being managed by participating farmers, it is not possible to reliably test this hypothesis with the given data.

Analysis of soil samples collected in June was scheduled for the summer and fall of 2016, but this was delayed by lab renovations and other logistical issues. The work will begin in January of 2017, and when completed will provide a more holistic picture of soil phosphorus management and resilience on participating farms. However, the soil analysis completed thus far indicates that the majority of fields have extractable phosphorus levels that present high potential for nutrient loading and eutrophication in connected ecosystems. Furthermore, all but one participant typically adds additional phosphorus to all fields under production on an annual basis. This compounds the problem of nutrient transfer, and suggests that are not utilizing the phosphorus resources present in the soil, which can decrease resilience in the system.

As expected, initial phosphorus supply mapping indicates that the flow of P through this LRFS is almost completely linear. In other words, none of the phosphorus that is exported from farms in the form of food is returned to the fields for recycling. This is due to the fact that New York City does not supply biosolids for fertilizer production, and municipal food waste recycling for compost generation in the city has only recently begun on a small scale.

The phosphorus supply for all participating farms links to non-renewable phosphate rock, largely mined in the state of Florida (some is sourced from South Carolina and Morocco). The length of these links varies significantly, however, with management type. Synthetic fertility links directly to mined phosphorus through the fertilizer supplier. This is also true of rock mineral fertility, though one supplier used by numerous participating farms has recently transitioned to using bone char for all phosphorus inputs, and this recycling of poultry bones is adds a node to the supply chain. Biomass fertility is generated entirely from recycled plant material and manure, and these farms link to mined phosphorus through the animal feed provided to the animals that created the manure. None of the farms that produced their own manure use organic feed (due to supply and cost issues), and purchased manure products are likewise not generated from organic animal operations. Given the cost constraints of animal feed production, it is likely that the majority of non-organic feed used in this LRFS is produced using synthetic fertility that links directly to mined minerals. The bulk of plant waste used in farm-made compost comes from municipal leaves and wood chips. Three farms generate all or nearly all of their own plant waste through crop waste recycling and, in one case, the mowing of permanent fallows. While no farm is able to fully close the phosphorus cycle, the recycling utilized by biomass based fertility significantly lengthens the supply chain and increases soil fertility resilience.

Impacts and Contributions/Outcomes

Results of the baseline soil fertility assessments were compiled and returned to farmers prior to field planting to assist in their soil management decisions for the 2016 growing season. In addition to the results, farmers were provided with recommendations for fertility management including phosphorus, pH, and organic matter. All participating farmers found this quite useful, and were able to make adjustments to their soil management to improve performance during the growing season. In several cases, the test results and consultation with farmers lead to significant reductions in phosphorus fertilizer use which over the course of years, will reduce the risk of nutrient loading and lower farmer spending on inputs.

Participating farmers are significantly interested in the soil health assessments, and the nutrient supply mapping, and this information will be provided to farmers in the first half of 2017. This information, along with additional consultation, will aim to assist farmers in identifying accessible methods of improving soil fertility resilience and improving the long-term sustainability of their farms.


Dr. Karl Zimmerer

Professor of Geography
Penn State
302 Walker Building
University Park, PA 16802
Office Phone: 8148653433