Soil Fertility Strategies on Organic Vegetable Farms

2007 Annual Report for LNC05-258

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

Soil Fertility Strategies on Organic Vegetable Farms


Organic growers in general—and organic vegetable growers in particular—rank soil fertility as a top research priority. This project is documenting the soil fertility practices employed by organic vegetable growers in Wisconsin and Illinois, gathering specific grower information needs and research questions, generating a set of cases studies highlighting contrasting fertility management strategies, and providing a framework for instituting organic research plots on University of Wisconsin and University of Illinois research farms. Growers are participants in all phases of the project, including development, implementation, and evaluation.

Methods include a survey, case studies, and the development of an advisory panel to interact with University researchers. Publications, field days, and workshops are being used to communicate results and solicit feedback.

Outcomes will include 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 increasing organic research acreage on University research farms.

Objectives/Performance Targets

In this year of the project (2007), 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.


Statistical analysis of the survey data began with simple frequencies, averages, medians, and ranges. Following that, a 2-way frequency table with a chi-square test was used. If several variables were thought to influence certain answers, a logistic regression was performed.

Based on this statistical analysis the following preliminary findings and observations were made:

1. As percentages of farm income from vegetable sales increased, farms were more likely to use compost and less likely to use manure.

2. Farms with sandy or sandy loam soils were more likely to use uncomposted manure than farms with loam or clay textured soils.

3. The number of years farming was the only variable that influenced how farmers determined compost application rates. The more years farming made it more likely that personal experience and compost test results determined application rates. Farmers were more likely to rely on “wild guess” and/or compost test results with fewer years experience.

4. The duration of a farms crop rotation was influenced by marketing strategy and gross income level. Farms selling mostly to wholesale or processors were more likely to have shorter rotations. Farms with a smaller % of gross income from vegetables sales were also more likely to have shorter rotations.

5. Farms were more likely to incorporate perennial vegetation as part of their rotation with larger farm size (owned + rented)

6. Illinois farms were more likely to have perennial vegetation as part of their rotation than Wisconsin farms

7. The longer the time on the current farm, the less likely growers were to incorporate permanent perennial vegetation in their rotation.

8. The smaller the farm size (owned + rented), the more likely the farmer was to have soil tests conducted.

9. Farm that were certified organic were more likely to soil test.

Initial Questions and Selected Findings

The grower survey explored several issues including:
1) composting and compost use,
2) other inputs (including manure, organic fertilizers and soil amendments,
3) intensity of land use and rotations, and
4) tillage. This section details some key issues probing each via corresponding responses produced from the grower survey.

1) Do most vegetable growers farm intensively on smaller acreages without much land to rotate crops?

While 36% of our respondents farm less than 3 acres and 53% farm less than 6 acres of vegetables, there 47% are above 7 acres with 19% farming over 25 acres. Although nearly 46% of farms used 75 to 100% of their land for vegetables, a robust 55% used less than 75% and an impressive 40% used less than half their land.

Those at a smaller scale tended to have less land available for cover cropping and crop rotations, however. Sixty eight (68) percent of farms less than 3 acres and fifty three (53) percent of farms between 3 and 6 acres used 75% to 100% of their land for vegetables in a given year. In contrast, larger farms frequently had ample land for rotation and cover cropping. Thirty seven percent of farms above 7 acres used less than 50% of their land for vegetables in a given year.

Additionally over half the farms incorporated permanent perennial vegetation that stays in place for more than a year into their rotation. Smaller farms were just as likely to maintain land in perennial cover as part of their rotation as larger farms. The length of growers’ rotation plan was also not significantly affected by farm size.

2) Is raw manure use as prevalent as some detractors of organic farming assume?

Use of uncomposted manure was reported by almost 50 percent of farms. In contrast, nearly 70 percent reported using compost. The most frequent time for manure application is in the fall, a practice that helps farms comply with the strict rules about manure use on organic farms. Sixty one percent of farms keep livestock themselves and 29% utilize livestock grazing as part of their larger crop rotation meaning that the manure is applied directly to fields in perennial cover by the animals themselves.

3) How extensive is compost use and how have the USDA Organic standards influenced its production and use?

Compost use was reported on 69% of the farms. Many farms (70% of compost users in our survey) use compost as an ingredient in a greenhouse potting soil mix. However, an even greater number of farms (77%) apply compost to their fields. The most common rate of application was 1 to 5 tons per acre (65%) and the most common frequency was every year (48%).

An impressive 82% make some compost on their farm although 47% buy compost from commercial sources. Farms were more likely to use compost and less likely to use manure as the percent of farm income from the sale of vegetables increased.

Most farms (73%) indicated that the USDA standards for certified organic compost have not affected their production. Anecdotal evidence suggests that farms still making compost often treat it as they would manure because they are not following the USDA standards. Only 7 farms (12%) indicated that they used to make compost but no longer do so. The challenges associated with following the USDA NOP standards for compost was the most frequently cited as a reason for no longer making compost.

Fertility Management Matrix

In order to get a better sense of how growers are managing fertility and analyze the survey results, we created four management categories based on the intensity of land use and use of fertility inputs. The criteria for management category designations included:
• Ratio of total vegetable acres/total acres in veggies 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, application rates
• Manure—type, use, 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 inputs such as manure, compost, N-rich fertility products (such as liquid fish, alfalfa 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.

Heading into this SARE project, published and anecdotal evidence suggested that many organic farms use land intensely and use large amounts of off-farm fertility inputs, often in the form of poultry litter. In this initial plotting, it is interesting, therefore, to see that many farms have relatively ample land in which to rotate crops and that many farms reply on cover crops and on-farm manure or compost for fertility.

Farm Fertility Management Matrix
(figure would not paste into on-line reporting webpage)

Some patterns that stand out in this matrix include:

1. The tendency for farms in the Land Extensive, Minimal Input category to use more inputs as the percentage of their land base devoted to vegetable crops each year increases from left to right.

2. A significant number of farms that have ample land to rotate crop still use relatively large amounts of fertility inputs. It is worth noting that a number of farms in this category have animals integrated into their vegetable rotation (noted by blue numbers). Our assumption going into the project was that many growers farm relatively small acreages rather intensively and that the integration of livestock is relatively rare.

3. It appears that some of the farms in the lower left area of the Land Intensive, Minimal Input quadrant (based on information from the surveys only), were potentially in danger of mining their soils given the lack of fertility inputs used.

The case study farms are intended to afford an in-depth look at overall strategies and specific fertility management practices over a 3-year period. By showcasing various practices and host field days, we hope to educate organic growers about soil fertility management and encourage them to develop long-term, sustainable approaches that promote soil health. We originally planned to identify 8 farms the represent a mix of approaches such as farms that integrate animals and their manure, farms that make and use compost, farms that rely heavily on cover crops. We also wanted the case study farms to represent a range in terms of the intensity of their land use (i.e. the length of their rotation).

Given the decision to postpone the case study portion of the project, we were able to expand the number of case study farms from eight to twelve. The farms were selected so that we have farms representing each quadrant of our soil fertility management matrix. Furthermore, we have three farms that raise livestock and incorporate animal grazing into their vegetable operation. Some farms focus on cover crops, some on compost, others on commercial fertilizer products. Four farms are in Illinois and 8 are in Wisconsin.

Initial farm visits to collect background data and update information from the mailed survey are planned for early 2008. Soil sampling will begin in 2008 as well. Two field days will be conducted (one in Wisconsin and one in Illinois) in both 2008 and 2009.

(note: to view figures from this report, contact the NCR-SARE office at [email protected])

Impacts and Contributions/Outcomes

A workshop and a poster on our survey results were presented at two conferences in early 2008: the Upper Midwest Organic Farming Conference and the Illinois Organic Production Conference. Attendance was strong and growers are clearly interested and motivated to improve their understanding of soil fertility management. Additional conference presentation opportunities are being pursued. Furthermore, we are drafting a paper for publication in a peer reviewed journal that will contribute to the collective understanding of organic fertility management.

Working with University researchers is especially promising. Since this grant was written, more efforts are underway to investigate organic vegetable cropping systems at both the University of Wisconsin and the University of Illinois.
A series of meetings are underway to facilitate interaction between project participants (growers and organizers) and University researchers.

The picture of soil fertility management on organic vegetable farms gathered via our survey is one of diversity, complexity, and uncertainty. There are clearly many, many approaches and a multitude of interacting factors to consider (scale, farm diversity, rotation, tillage, inputs, etc.).

As we delve into the case study farms, we intend for this project to highlight various types of “best management practices.” There are certainly many viable strategies depending on soil type, access to materials, land availability, and other factors that will allow growers to improve soil tilth, adopt cost-effective means of supply fertility to crops, and reduce or eliminate practices that foster soil erosion, compaction, the excessive build-up and leaching of macro nutrients, and overall sustainability.


John Henrickson

[email protected]
University of Wisconsin-Madison
1450 Linden Dr
Madison, WI 53706
Office Phone: 9209277362