Soil Fertility Strategies on Organic Vegetable Farms

Project Overview

Project Type: Research and Education
Funds awarded in 2005: $72,056.00
Projected End Date: 12/31/2009
Region: North Central
State: Wisconsin
Project Coordinator:
John Hendrickson
CIAS, UW-Madison

Annual Reports


  • Agronomic: potatoes
  • Fruits: melons
  • Animal Products: dairy


  • Education and Training: workshop
  • Farm Business Management: budgets/cost and returns
  • Production Systems: organic agriculture
  • Soil Management: soil analysis, soil quality/health


    Soil fertility is a top research priority as ranked by organic growers in general—and organic vegetable growers in particular. This project documented the soil fertility practices employed by organic vegetable growers in Wisconsin and Illinois, gathered grower information needs and research questions, generated a set of cases studies highlighting contrasting fertility management strategies, and has helped provide baseline data for ongoing organic research and outreach programming at the University of Wisconsin and University of Illinois. Growers participated in all phases of the project, including development, implementation, and evaluation.

    Methods included a survey, case studies, and facilitating interaction and communication between growers and university researchers. Publications, field days, and workshops have been used to communicate results and solicit feedback. Outcomes include an increased knowledge base among growers and university specialists, changes in grower practices based on an increased understanding of soil fertility management options and their cost and impacts, and expanded organic research programming at universities.

    In addition, this project identified a need to conduct further education and outreach on the following specific issues:

    1. Helping growers understand the value and utility of regular soil tests to monitor nutrient levels, pH, organic matter, and aggregate stability scores. Many growers reported not understanding soil test results or struggling to put recommendations into practice. Others mistrusted the information because it is not geared specifically to their organic farming practices and principles.

    2. Working with soil testing laboratories to better communicate soil test results and recommendations to serve the needs of organic growers.

    3. Managing soil phosphorous inputs to reduce the excessive P loads common on many Wisconsin farms with a livestock (dairy) history. Some farms may be contributing to excessive phosphorous levels through their use of poultry based fertilizers and manure based composts.


    Organic growers in general—and organic vegetable growers in particular—have consistently ranked soil fertility as a top research priority. This project documented the soil fertility practices employed by organic vegetable growers in Wisconsin and Illinois, gathered specific grower information needs and research questions, generated a set of cases studies highlighting contrasting fertility management strategies, and has helped influence the development and advancement of organic research plots and research programming at the University of Wisconsin and University of Illinois. Methods included a survey, case studies, and field days. Publications, field days, and web videos were and are being used to communicate results and solicit feedback.

    Outcomes have included increasing the knowledge base of growers and University specialists, changes in grower practices based on an increased understanding of soil fertility management options and their cost and impacts, and advancing organic research programming at universities and their respective research farms.

    The vegetable industry in the North Central Region features both significant processing vegetable acreage and a large and growing fresh market industry dominated by many small farms. This project focused on the latter group but results are relevant for many different types of farms. In Wisconsin, in 2007, there were 2,145 farms that produced vegetables, potatoes and melons (USDA, 2007). Illinois’s fresh market industry was about half that size, with 1,047 farms. In terms of acreage, Wisconsin had roughly three times as many acres in vegetables, potatoes and melons in 2007 with 55,764 acres compared to Illinois with 17,670. Organic farms and acreage comprise a much more significant sector in Wisconsin than Illinois. Based on 2008 data, Wisconsin had 254 farms producing certified organic vegetables and Illinois had 68 and the acreage figures were 1,749 and 230 respectively.

    Organic vegetable growers face a common challenge regardless of specific crops grown, farm scale, or marketing strategy. Vegetable growers export significant amounts of biomass and nutrients off their farms each year. To maintain or improve crop yields and quality—and uphold the soil building tenets of organic farming—organic growers endeavor to improve soil health and supply nutrients through a wide variety of strategies. These include short-term cover cropping, spreading compost or manure, rotating cash crops with long-term (sod) cover crops, and applying various approved fertility amendments.

    Prior to the project, direct personal communication between the project coordinators and growers indicated that growers questioned how well their cover cropping schemes provide fertility for subsequent crops and whether they were making sufficient progress toward improved soil health (such as increases in both biologically active and stable organic matter pools). Many growers also aspired to implement longer-term rotations but lacked sufficient land or proof that such rotations were economical.

    There has been some speculation about nutrient imbalances on organic farms but a lack of soil test data to confirm or refute the build up of available nutrients on organic farms, particularly those that might impair water quality (N and P). It is possible that few organic farmers test their soil because soil testing and interpretation of test results are geared toward conventional farmers. There is a clear need to document the use of soil testing in soil fertility management and to help organic growers interpret and take advantage of soil test results.

    Another question relates to the use of un-composted manure. Critics of organic farming often site the health risks associated with using animal manure but there is no specific documentation indicating how prevalent the use of un-composted manure really is and, if it is used, how and when.

    Another question posed by the research team was to learn whether the USDA National Organic Program (NOP) has influenced compost use. Although NOP created a compost task force to develop new guidelines for producers and certifiers that make composting easier to achieve on organic farms (,
    some growers may no longer compost on farm or import compost from off farm.

    The rationale behind this project was that an important first step in documenting and understanding the impacts and benefits of various fertility strategies is a close examination of the current practices used by growers while simultaneously gathering information from growers about research needs and priorities.

    Literature Review

    The general benefits of cover crops and compost are well-documented (SAN; Hendrickson[1]; Magdoff and van Es) and most organic vegetable growers are committed to their use and show great skill and ingenuity in incorporating these soil enhancing practices into their farming systems. Numerous SARE and Organic Farming Research Foundation projects have investigated related issues, such as optimizing specific cover cropping schemes for fertility, weed suppression, or reduced tillage often for a specific vegetable crop (e.g. Weller; Gallandt; Scholberg). However, there have been no comprehensive and detailed studies that document current fertility practices in use or comparisons of fertility strategies across farms.

    A study by Fernandez-Cornejo, et al. reports that organic vegetable growers rely primarily on traditional organic processes such as green manuring, animal manuring, composting, and crop rotation to supply crop nutrients. According to their survey, animal meal, fish products, and lime are the most frequently reported supplemental nutrient sources with 14, 20 and 28% of organic growers, respectively, reporting that they use these materials. Details about these fertility management practices were not gathered, however, nor was there any assessment of their costs and benefits.

    Organic growers in general—and organic vegetable growers in particular—historically rank soil fertility as a top research priority (Walz). An Organic Farming Research Foundation national survey found that fertility management issues are a high research priority for organic growers. Three different fertility management topics were ranked 2nd, 5th, and 6th out of a list of thirty-two other research topics by all organic growers while these same fertility topics were ranked 1st, 2nd, and 6th by vegetable growers (Walz).

    No one knows how prevalent various soil fertility practices are within the organic vegetable grower community. Literature and communication with growers suggests that many growers rely on off-farm sources of manure, especially poultry litter. Some have questioned the sustainability of this practice and new phosphorous management standards may prevent growers from applying enough manure to supply crop nitrogen needs. A study titled "Contradictions in Organic soil management practices: evidence from 31 farms in Maine" which was presented at the 2nd International IFOAM (International Federation of Organic Agriculture Movements) Conference in Montreal, CA in October 1978, found that the great majority of organic farms in Maine utilized a very simplified fertility regime that relied minimally on on-farm fertility management such as legume rotations and cover crops and instead relied primarily on cheap off-farm chicken manure. The authors express concern that with the Maine poultry industry in decline, most of the organic farmers in Maine were in a very economically vulnerable partnership. The authors were also concerned about the ecological consequences of most of Maine's organic farmers depending on heavy annual applications of poorly composted poultry manure.

    Organic agriculture has come along way since 1978 but it may still be true that many organic vegetable farmers are still dependent on off-farm sources of manure. A 1993 survey of organic vegetable growers in Florida revealed that over 70% of growers relied on chicken manure or bagged organic fertilizer (also based primarily on poultry manure) for plant nutrients. The latest Organic Farming Research Foundation survey ranks fertility practices by frequency (cover crops ranked first followed by compost applications) but there is no detail and no breakdown of the data by type of farm or crop (Walz). Similarly, a study by the USDA Economic Research Service in 1994 concluded that 77% of vegetable growers use legume cover crops, 78% apply manure, and 61% apply compost but there is no further breakdown or definition of these practices (such as the source and quality of the manure or compost).

    Personal communication with growers in Wisconsin prior to this project suggested that poultry litter is a common source of nutrients (Hendrickson) combined with various annual cover crops. Furthermore, on-farm integration of crops and livestock and complex rotations that include both row (cash-) crops and sod crops was perceived by the research team to be uncommon on the vast majority of organic vegetable farms in Wisconsin and Illinois.

    In regards to the criticism that organic farms pose a threat to human health due to the potential presence of pathogens in manures applied as fertilizer, there seems to be no precise data about the prevalence or timing of manure applications on organic vegetable farms. The Organic Farming Research Foundation survey found that the use of raw manure was only used “frequently or regularly” on 22% of all farms (OFRF, 1) but it would be useful and important to know more, especially in regard to fresh market vegetable farms that sell raw products directly to consumers. Of course, the USDA organic rule contains specific guidelines for how and when manure can be used and organic farms are inspected to make sure such practices are followed (a safeguard not in place for both “uncertified organic” farms or non-organic farms).

    The Organic Farming Research Foundation’s State of the States report criticizes many Land Grant Colleges for the lack of research and infrastructure to support organic farming through scientific inquiry (Sooby). This project hoped to address this critique by providing a framework to establish organic plots at University of Wisconsin research farms and expanding work underway at the University of Illinois to document soil fertility changes under various organic transition approaches (Eastman).

    Project objectives:

    This project sought to document the soil fertility practices employed by organic vegetable growers in Wisconsin and Illinois, gather grower information needs and research questions, generate a set of cases studies highlighting contrasting fertility management strategies, and provide input into organic research programming on University of Wisconsin and University of Illinois research farms. Short-term outcome goals included:

    • Increase the knowledge base of growers and University specialists on the range of soil fertility strategies employed by organic vegetable growers and
    • Increase awareness among organic growers of soil fertility options available to them and the cost and benefits of different practices and strategies.

    Intermediate-term outcome goals included:

    • Changes in grower practices based on an increased understanding of soil fertility management options and their impacts and
    • Increasing organic acreage on University research farms

    Long-term outcome goals included:

    • Enhancing the sustainability of organic farming and
    • Engendering future organic research and programming at Land Grant Universities.

    Progress and analysis on these outcomes is reported in the Results and Discussion section below.

    In terms of the completion of objectives and performance targets, the following is a year-by-year summary.

    We began the process of conducting a grower survey to quantify the types and prevalence of different soil fertility practices. A database of growers was created by using lists from organic certifiers, grower groups and networks, and existing databases managed by project collaborators.

    Following our project methods, we also initiated a pre-test of the survey among a group of University colleagues as well as organic farmers serving as advisors to the project.

    2005 was also when we original planned to select a group of case study farms for a more in-depth look at specific soil fertility management approaches and practices. We changed our plans, however, because we decided it would be better to utilize the survey data to identify common and intriguing management practices as well as broaden the potential pool of case study candidates beyond the farms with which the project coordinators were already familiar.

    Activities in 2006 included the completion and analysis of the mailed survey, and select the case study farms.

    Drafting the survey with input from several collaborators and then pre-testing it with our grower advisory group was completed in early 2006. Surveys were then sent to a database originally containing 385 growers. We learned later that this list contained a large number of organic farms that do not produce vegetables and this prompted a database cleaning process in order to determine our actual population size and response rate. After cleaning, the database shrank to 181 growers.

    In this year of the project, the main goal was to complete the analysis of the mailed survey, communicate results, select the case study farms, and begin collecting data on those case study farms. In addition, we planned to produce various outreach materials (presentations, poster) and begin sharing results with interested stakeholders. These activities were accomplished with the change that we decided to select 12 case study farms rather than 8. This decision was based on the desire to include a wider representation of dominant management practices and facilitate better opportunities for comparisons across farms. This was possible financially because we shortened the length of the case studies to two years from the original three years.

    In 2008 we continued to work with the 12 case study farms to collect data, held two on-farm field days, and prepared a report on the results of the grower survey (completed in 2006/2007). In addition, we pursued opportunities to integrate the information we learned and the direct perspectives of growers into the ongoing programming at both the University of Wisconsin and the University of Illinois.

    A second year of data collection on the case study farms was completed and another set of field days were held in Wisconsin and Illinois. Year 2 soil samples were collected and analyzed by the University of Wisconsin and University of Illinois laboratories. A webinar was held with case study participants reviewing some of the soil test data as well as looking at opportunities for future investigations and activities.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.