Soil Fertility Strategies on Organic Vegetable Farms

Soil Fertility Strategies on Organic Vegetable Farms

Summary

Soil fertility is a top research priority as ranked by organic growers in general—and organic vegetable growers in particular. This project has 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 have participated in all phases of the project, including development, implementation, and evaluation.

Methods have 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.

Objectives/Performance Targets

In this final year of the project (2009) we completed working with the 12 case study farms to collect data, held two on-farm field days, and completed a report summarizing the survey conducted in years 2006 and 2007 as well as highlighting several of the case studies.

Accomplishments/Milestones

The 12 case study farms selected following our survey of organic vegetable farms in Wisconsin and Illinois continued to serve as examples of different fertility management strategies. Additional data and information was collected in 2009 including labor and economic information related to specific fertility management practices and soil test data.

To review, the uploaded file provides an overview of the case study farms in terms of acreage, management category and fertility foci.

The management categories are based on a classification exercise undertaken using the project’s survey data in 2007. This was done in order to get a better sense of how growers are managing fertility. We created four management categories based on the intensity of land use and relative intensity of fertility inputs. The criteria for these management category designations included:

• Ratio of total acres in vegetable operations to total acres in
vegetables and related crops
• Length (duration) of crop rotation
• Use of permanent perennial vegetation in the rotation
• Livestock grazing as part of rotation
• Commercial Fertility Inputs—types and frequency
• Compost—use, frequency, and application rates
• Manure—type, use, and application rates

We then created the following four management categories:

1. Land Intensive, Minimal inputs. This group is characterized by farms that use 75-100% of their land base for vegetables in a given year and use minimal fertility inputs beyond cover cropping.

2. Land Intensive, High inputs. Characterized by farms that use most of their land for vegetable production each year and use significant amounts of nutrient rich inputs such as manure, compost, and high nitrogen fertility products (such as liquid fish, alfalfa meal, soy meal, etc.)

3. Land Extensive, Minimal inputs. This group uses less than 75% of their land for vegetables each year and, most often, less than 50%. They rely on their rotation and cover cropping for the majority of their fertility needs.

4. Land Extensive, High inputs. These farms, again, have ample amounts of land in cover crops each year but also utilize significant N-inputs in the form of manure, compost, and purchased fertilizers and amendments.

In 2009, we replicated the soil test protocol followed in 2008. In the fall, all case study farms were sent a soil test kit. Each farm took soil samples from the same two areas of their farm (reflecting different cropping histories) as in 2008. Duplicate samples were taken in order to send samples to two soil test laboratories (The University of Wisconsin Soil and Plant Analysis Lab and Dr. Michelle Wander’s lab at the University of Illinois at Urbana Champaign). At the University of Wisconsin lab, a standard analysis was conducted, including pH, total phosphorous, and total potassium. Michelle Wander’s lab conducted tests for particulate organic matter and aggregate stability. All twelve farms correctly completed the soil sampling procedure and sent samples to the two labs.

The UW lab completed their tests and analysis and returned results to us in November and December. Michelle Wander’s lab has not completed their testing and reporting. Preliminary observations from the soil tests reveals that many farms have excessive amounts of phosphorous and some also have excessive amounts of potassium. This validates some researchers hypothesis that many vegetable farms can develop excessive soil nutrients given a reliance on composted animal manures, especially poultry litter.

In the fall of 2009 we held field days at Spring Hill Community farm in northwestern Wisconsin and Growing Home CSA in north-central Illinois. We publicized these events to our database of growers, via local newspapers, and grower groups and associations. Attendance at each was good. At Growing Home CSA we had 22 people attend and at Spring Hill 35 people.

As in 2008, these events were contrasts in approach. Spring Hill has been in operation since 1989 and although the growers plead ignorance and confusion about fertility management, they have, over time, developed goals and an action plan to enhance the season-to-season fertility management as well as long-term sustainability. In the early years this farm was an example of the type of farm that imported its fertility in the form of poultry litter–in this case from the nearby turkey industry in the area. These applications were made in a general way rather than linked to specific crop needs or soil tests results. Over time, this simplified strategy has evolved into one where each of the farm’s production areas is monitored closely to follow a rotation and fertility needs are closely monitored by crop and via soil tests. As a result, fertilizer application (now in the form of a pelletized poultry litter fertilizer product with a specific NPK analysis) is more limited and targeted. This farm has always used cover crops but, like most farms, they have improved their integration and utilization of cover crops over time as they become more experienced.

One of the most significant take home messages from this field day was the grower outlining how they have advanced over the years in terms of record-keeping, data collection, and getting expert advice. Soil samples were taken only occasionally in the early years and the grower admitted that he did not know how to interpret or use the results. Crops were always rotated but record keeping and follow-through were not always precise. Now, they test their soil every year, maintain a detailed farm map that tracks what crops are grown where, utilize one of their CSA members who has a soils degree as a consultant, and make more precise fertility management decisions and applications when it comes to applying purchased fertilizers. One way in which the latter is achieved is through the use of a new fertilizer spreader that can be calibrated. This is in contrast to their previous method that involved applying fertilizers by hand.

The grower admitted that they still have significant improvements and changes to make, however. Chief among this is evolving toward a system where they are only using half their land each year and are allowing half their land to rest under season-long, sod-forming cover crops. This will be a challenge for them as they are already currently using most of their tillable land.

The Growing Home CSA field day in Illinois featured a farm that integrates livestock into their operation and rotation. This farm raises pastured poultry in addition to vegetables. Vegetable crops are grown in rotation following a fallow period when pastured poultry is grazed using movable pens. This farm also utilizes cover crops, mostly in an opportunistic way as windows are open during their vegetable cropping sequences.

This farm works with volunteers and is managed by a relatively new manager. Impressions from the field day suggest that this farm was where many other farms were when they began their operations: still learning and working to develop a coherent and effective system to manage fertility. Interviews with other growers suggest that fertility management often takes a back seat to the day-to-day pressures to plant, cultivate, harvest, and market on a highly diversified market farm. The many crops and frenetic pace of a market farm often mean that the best laid plans are abandoned. The complexity of market farms and their 30 to 50 crops also means that even developing a plan is a challenging task.

Field Day evaluations were conducted and were positive. Satisfaction responses were similar from the two field days in 2008 with 70% of people rating the events “very useful” and 30% “moderately useful.” No one rated the events as “not very useful” or “not useful at all.” As in 2008, participants ranged from experienced vegetable growers to beginners. The vibrant “roundtable” conversations that took place during the field days suggest that similar field days would be popular and worthwhile to continue in the future. Having university or extension personnel on hand to answer questions AND hear the perspectives of growers makes these events even more beneficial.

• Case Study Farm Table

Impacts and Contributions/Outcomes

We were pleased with the turnout at our two fall field days and the interaction among growers and university personnel. Based on our experience over the course of this project, fertility management remains a topic of great interest as well as uncertainty. Based on comments and questions at the field days, growers hear confusing and sometimes conflicting information and need help sorting out what practices will help them achieve the goals they set for their farm in terms of soil management.

The participants in the 2009 field days learned a great deal and seemed keenly motivated to learn via “real case examples” of how farms build and maintain soil fertility. The case study approach followed in our project seems to fit well with a grower audience, who are hungry for more than isolated recommendations and field trial data. Growers want to see and learn from working farms both in terms of understanding a other growers’ overall goals and perspective (philosophy, if you will) and the gritty details in terms of how the work gets accomplished, what tools are used, costs, labor demands, and results. Case studies lend themselves to capturing both the big picture perspective as well as in-the-field realities.

Unfortunately, not everyone seems to recognize the utility and validity of a case study approach to documenting and evaluating soil fertility management strategies and practices. A 25-page manuscript prepared by the organizers of this research project was rejected by university and Extension colleagues. While reviewers had many constructive and helpful comments and editorial suggestions, there appears to be a fundamental disconnect between the kind of reporting and publications deemed appropriate and useful by university personnel and growers. For example, university reviewers deemed to report to be “unfriendly” for a grower audience. Ironically, comments from the growers that reviewed the report conveyed the opposite.

The final impacts and contributions of this project will be determined, in part, on the ability of the project organizers to successfully negotiate the gap between university reviewers and the intended grower audience.

As mentioned in the 2008 report, the soil test results from our case study farms suggested a need to educate growers and to recommend adjustments to fertility management practices so that excessive levels of phosphorous can be avoided and potential leaching issues can be mitigated. The 2009 field days provide one opportunity to highlight the phosphorous overload issue, particularly at Spring Hill, where—although the growers most likely inherited a phosphorous overload problem—they have nonetheless recognized the issue and taken specific steps to reduce their fertilizer applications. It is hoped that the case studies can eventually be published so that a wider group of growers can be made aware of this important issue as well as appropriate steps to address this challenge.

Efforts to integrate grower knowledge and perspectives into programming at both the University of Wisconsin and the University of Illinois continued and culminated with a webinar led be Illinois collaborator Michelle Wander and her staff who plan to utilize the baseline case study data and the relationships formed with growers in ongoing work to improve and enhance soil fertility management research and education. At the University of Wisconsin, several of the original grower advisory panel members (and case study growers) are now involved in various research and Extension efforts including being feature in a forthcoming SARE cover crop case study.

Through the grower survey and case studies completed through this project, we have provided a unique and useful examination of the fertility practices common on vegetable farms in Wisconsin and Illinois. In so doing, we have advanced the collective understanding of fertility management options and impacts. In addition, by building a better understanding of fertility management practices and long-term strategies, we have helped direct and focus university research in ways that best meet the needs of organic vegetable growers.

Collaborators: