Soil Fertility Strategies on Organic Vegetable Farms

Results and discussion is broken down by activity (method), including the survey, case studies, and the advisory board.

Survey Results

After receiving training and approval through the UW-Madison Human Research Protections Program and Institutional Review Board (IRB), the survey was mailed in winter 2005/2006 to 181 organic (certified and un-certified) vegetable growers in Wisconsin and Illinois. The mailing list was a combination of databases from the University of Wisconsin-Madison’s Program on Agricultural Technology Studies (PAST), the Illinois Farm Direct (www.illinoisfarmdirect.org) mailing list, the University of Illinois Agroecology and Sustainable Agriculture program, the Madison Area Community Supported Agriculture Coalition (MACSCAC), the Home Grown Wisconsin marketing cooperative, the Midwest Organic Services Association (MOSA) and the Organic Crop Improvement Association (OCIA). All of these lists were combined and any duplicates and non-vegetable growers were removed.

Given the modest size of the database, we elected to mail surveys to all addresses rather than take a random sample. Surveys were administered during the winter of 2005/2006. After mailing the first round of surveys, a set of reminder postcards was mailed two weeks later. Then a second mailing of surveys was sent out to non-responders followed by a final round of reminder postcards. We received 96 completed surveys. Some of these were eventually discarded because they came from farms that were not organic or did not grow vegetables. We ended up with 88 usable surveys for a response rate of 49%. We believe this high response rate is an indication of the dedication and commitment of organic vegetable growers, good relationships between University personnel and the grower community, and the importance of fertility management as a key challenge facing growers.

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. We used SAS analyses to look at relationships between demographic and response variables. In this analysis, a logistic regression was performed to tease out salient or statistically significant relationships.

To conduct the logistic regression, we needed to create simplified categories for the many questions with multiple response variables. For questions where three or more answers were possible, responses were grouped into more broad categories. For example, the question on organic fertilizers and soil amendments was originally written as a list of specific fertilizers or amendments, then later collapsed into these three categories: 1) Nitrogen rich - soybean meal, kelp meal, blood meal, bone, feather, and fish, 2) Other nutrient source - wood ash, lime, colloidal phosphate, rock phosphate, potassium sulfate, potassium magnesium sulfate, granite dust, and greensand, and 3) Biological - rhizobia, and mycorrizae.

If logistic regression analysis produced at most one statistically significant regressor variable, a 2-way frequency table with a chi-square test was performed. For example, we asked the question “are farmers with an established rotation plan more likely than those farmers without a plan to do soil testing, nutrient budgeting and other more quantitative practices, such as measuring fertilizer, manure or compost application rates or evaluating efficacy of soil amendments.” We were also interested in relating demographic variables that characterized farmer experience with variables characterizing their soil fertility management practices. We used a probability value of 0.05 or less to determine statistical significance.

Farm and Farmer Characteristics
The majority of growers who filled out the survey were highly educated and had more than 10 years of farming experience. In regards to education, 87% of the respondents had had some level of college and/or a college, professional, or graduate degree. The bulk of the respondents were male (70%). The average age of the survey respondents was 46 years old, which is significantly less than the national average age of farm operators. The National Agricultural Statistical Services (NASS) 2007 Census of Agriculture reports that the average age of U.S. farm operators increased from 55.3 in 2002 to 57.1 in 2007. Moreover, the number of operators 75 years and older grew by 20 percent from 2002, while the number of operators under 25 years of age decreased 30 percent (2007 Census of Agriculture). In contrast, the majority of the respondents (68%) in our survey were either between 26-49 (33%) or 50-56 years old (35%). Table 1 (see attached file) summarizes the demographics of the survey respondents.

TABLE 1: Respondent Demographics and Characteristics
[See attached file]

The basic descriptive statistics for farm characteristics show a blend of small, middle and large farms with a similar percentage of farms sized between less than 1 and 6 acres (53%) and farms from 7 to more than 25 acres (47%). See Table 2 in the attached file for a summary of farm scale, income, and soil types. The majority of farms (55%) were generating up to $20,000 from the sale of veggies, melons, herbs and flowers. The majority of farms (60%) are extremely diverse, producing vegetables, livestock, and other additional crops (see Figure 1 in attached file).

TABLE 2: Farm Characteristics
[See attached file]

FIGURE 1: Farm Diversity
[See attached file]

Table 3 helps characterize the respondents in terms of farming practices and operations. Most farms utilize a row crop system (76%) while a significant percentage use a temporary raised beds (37%). Many farms use both. The use of mulch, both natural (straw, hay) and plastic was very commonplace. Almost half the farms reported the practice of multi-cropping—the practice of using a piece of ground for more than one crop in a given year. Obviously, soil fertility management becomes more challenging and important with this type of intensive land and resource use. No-till—a practice currently gaining attention from both growers and researchers—was only reported by 3% of the respondents.

TABLE 3: Practices used in Vegetable Operations
[See attached file]

One question the survey sought to answer was how intensively growers use their land. Our assumption going into the project was that many growers do not have a very large land base and thus cannot rest significant amounts of their land in fallow cover crops. In order to answer this question, we determined the ratio between the total amount of acres used in a grower’s operation and the amount of that land in actually vegetables in a given year.

Nearly 55% of the growers used less than one quarter to three quarters of their available land for vegetables in 2005. Forty percent used half or less of their land for vegetables. About 46% had more than three quarters of their available land in vegetables. We had anticipated more farms to be in position of using three quarters to one hundred percent of the land each year.

TABLE 4: Percent of land used for vegetables each year
[See attached file]

Related to land use intensity is the use of perennial vegetation in the cropping system rotation. Our survey results showed that over half the farms included perennial vegetation for one year or longer into their rotation. Illinois farms were more likely to have perennial vegetation as part of their rotation than Wisconsin farms (Table 6). In contrast to what we hypothesized (growers who had been farming longer might have adopted longer, more diverse rotations, including the use of longer-term perennial cover crops), farmers were less likely to incorporate perennial vegetation in their rotation the longer they resided on their current farm (Table 6). One possible explanation is that longer-term farmers use more of their land to meet increasing production demands, rather than leaving it in perennial cover crops that are less likely to generate income.

Fertility Management
The grower survey explored a wide range of fertility management 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 summarizes some of the results utilizing key questions we had entering the project.

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 (see Table 4).

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

The duration of the respondents’ crop rotation was related to marketing strategy and gross income level. Farms selling mostly to wholesale or processors were more likely to have shorter rotations. Farms with a smaller percent of gross income from vegetables sales were also more likely to have shorter rotations.

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

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.

TABLE 5: Uncomposted Manure Use
[See attached file]

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 (see Table 6). 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%). 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.

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.

TABLE 6: Compost Use
[See attached file]

4) Do growers test their soil regularly and how do the utilize test results?

The majority (82%) of our survey respondents stated they had performed a soil test on their farm (see Table 3). A slightly larger percentage (83%) use soil tests to inform their soil fertility management strategies. Out of those respondents who have performed soil tests, the largest group, 44%, tests their soil every 3-5 years (see Table 7). Curiously, the smaller the farm size (owned + rented), the more likely the farmer was to have soil tests conducted. Farm that were certified organic were more likely to soil test than those that were not certified.

TABLE 7: Soil Testing Practices

Attitudes and Perceptions
Some survey questions were designed to gather opinions, attitudes and perceptions, including research and education needs.

Seventy percent (70%) agree or somewhat agreed with the statement "I believe I rely too heavily on tillage for seed bed preparation, weed management, and/or cover crop incorporation and would like to find ways to reduce the frequency and/or intensity of tillage I use."

With regard to growers’ perceptions of their farm’s nutrient budgets, 47% perceived that micronutrients were in inadequate supply on their farm (compared to 26% for nitrogen (N) and 17% for phosphorous (P) and potassium (K)). Nearly a quarter felt that P and/or K were in excess supply in their soil (compared to only 5% for N and 18% for micronutrients). The fact that only 24% perceived that P is in excess supply, suggests that there might be a need to measure P levels on organic vegetable farms to determine if their perceptions match reality. The amounts of P available to plants in Wisconsin agricultural lands have nearly doubled over a forty-year period (1964 to 2004), due mainly to excess manure and phosphorus fertilizer application (Peters 2005). There is concern that excess soil P concentrations lead to excess P in rivers and lakes, leading to degradation of water quality. It would be important to determine if organic vegetable farms contribute excess soil P to surface waters, particularly relative to other types of farming operations such as livestock production.

Cover cropping sequences and rotations, and strategies for building and maintaining organic matter were the two issues that respondents rated as the most important research topics for universities. There was also a strong interest in research focused on the interactions between soil fertility practices and weed, insect and disease pressures. Other soil fertility management issues that were highlighted as being important included: 1) the influence of different practices on amount and timing of nitrogen availability, 2) on-farm composting and use, 3) managing carbon: nitrogen ratios in crop residue and influence on nutrient availability, and 4) the influence of practices on phosphorous and potassium levels/run-off/leaching.

Fertility Management Matrix

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 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, 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.

The matrix below represents our plotting of each survey respondent based on the above criteria. Each number corresponds to a farm that returned the survey. The different colored numbers indicate the primary source of fertility inputs (green= cover crops; brown=manure/compost; orange=commercial fertilizer inputs) where this was possible to determine (some surveys provided far more complete and detailed information than others). The blue numbers indicate farms that have livestock integrated into their vegetable operation.

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 fertility management plotting, it is interesting, therefore, to see that many farms have relatively ample land in which to rotate crops and that many farms rely on cover crops and on-farm manure or compost for fertility.

FIGURE 2: Farm Fertility Management Matrix
[see attached file]

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 (depleting) their soils given the lack of fertility inputs used.

Case Study Results

The case study farms were intended to afford a more in-depth look at overall strategies and specific fertility management practices over time. By showcasing various practices we hope to educate organic growers about soil fertility management and encourage them to develop long-term, sustainable approaches that promote soil health. As stated above, 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, and 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 until survey results were analyzed, we were able to expand the number of case study farms from eight to twelve. The farms were selected to have farms representing each quadrant of the soil fertility management matrix developed as part of the survey analysis (see Figure 2, above). Given the number of farms that raise livestock and incorporate animal grazing into their vegetable operation among the survey respondents we selected 3 farms from utilize this approach. Among all the farms, some focus on cover crops, some on compost, and some on commercial fertilizer products. Four farms were chosen from Illinois and eight from Wisconsin.

In order to capture the spectrum of management styles existing in our survey sample, we selected farms in order to have examples in each category. Given that a land intensive, Minimal input (LIMI) approach was uncommon in the sample (and unlikely to be sustainable in terms of yields and profitability) we emphasized the other categories in terms of case-study farm selection. Indeed, as we began to collect addition information from the two farms that were in the LIMI category, we found that these growers had made changes to their operation that would reclassify them as land intensive, high inputs. As a result, we ended up with four farms in each of the LIHI, LEHI, and LEMI categories.

Our case study farms range in scale from 8 to 138 total acres (owned plus rented) with between 2 and 25 acres in vegetables in a given year. Table provides an overview of the farms in terms of scale, fertility management category, and fertility management focus.

TABLE 8: Case Study Farm Overview
[see attached file]

Initial farm visits to collect background data and update information from the mailed survey were conducted in 2008. Soil sampling began as well in the fall of 2008. The farm visits and interviews were made during the spring and early summer. Information from these interviews was added to over time through additional visits as well as email and phone communication.

We formulated a soil test protocol and made arrangements with 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) to analyze duplicate soil samples from each farm. In the fall, all case study farms were sent a soil test kit including a bulb planter, plastic containers and plastic bags, soil test paperwork, detailed sampling procedures, labeling instructions, and return mailing envelopes. Each farm was directed to take soil samples from two different areas of their farm (reflecting different cropping histories). Duplicate samples were taken in order to send samples to the two labs. At the University of Wisconsin lab, a standard analysis was conducted, including pH, total phosphorous, and total potassium. At Michelle Wander’s lab, the samples were tested for particulate organic matter and aggregate stability. Eleven of the farms correctly completed the soil sampling procedure and sent samples to the two labs in 2008 and all 12 completed the process in 2009.

The most immediately obvious results of the soil tests is that many farms have excessive amounts of phosphorous and some also have excessive amounts of potassium. This lends credence to some researchers’ previous hypotheses that vegetable farms can develop excessive soil nutrients given a reliance on composted animal manures, especially poultry litter. However, many of the farms in this sample likely inherited this problem as the majority farm on former dairy operations. In at least some cases, however, it appears that growers may be continuing or exacerbating high P and K levels through their use of high P poultry fertilizer products and, in one case, high volumes of nutrient rich compost.

Examples of the case study summaries that were completed can be found in the attached document titled “Soil Fertility Management on the Intensive Market Farm.” This document also summarized the survey results.

A total of four field days were conducted; one in Wisconsin and one in Illinois in both 2008 and 2009. In the fall of 2008 the host farms were Henry’s Farm in Congerville, IL and Tipi Produce in Evansville, WI. We publicized these events to our database of growers, local newspapers, and grower groups and associations. Attendance at each was exceptional. At Henry’s Farm in central Illinois we had 30 people attend and at Tipi Produce over 60 people came.

Henry Brockman of Henry’s Farm detailed his rotation in which he keeps land fallow in hay for two year before using that land for vegetable production for two years. The fallow/hay land produces mulch for his vegetable crops, hay for livestock, and paddock space for grazing. He seeds a mixture of alfalfa, red clover and orchard grass for the two year fallow part of the cycle. During the two years of vegetable production he makes extensive use of wheat and vetch cover crops in the fall. He does not use any supplemental fertilizers and accomplishes his fertility management strategy with a minimal amount of equipment and purchased inputs. It should be noted that his fields lie, for the most part, on rich bottom land along a creek, where the topsoil is deep. A more detailed synopsis of his rotation plan is part of the case study report completed in 2009.

The field day at Tipi Produce was a great contrast to the one at Henry’s Farm. Steve Pincus and Beth Kazmar led a tour of their operation and described the many different inputs and strategies they employ based on individual crops, availability of nutrients and materials, and yield expectations. They place an emphasis on adding bulky organic materials such as plowed down cover crops, leaf compost, and chopped alfalfa. They also use some concentrated materials such as soybean meal if crops needs them. Their stated goal is to increase biological activity in their soils rather than a sharp focus on supplying NPK. In contract to Henry’s Farm, their approach relied on many more types of off-farm inputs and also required different types of machinery (fertilizer side dressers, side and rear-discharge spreaders, front end loaders, etc.).

In 2009 we held the field days at Spring Hill Community farm in northwestern Wisconsin and Growing Home CSA in north-central Illinois. These events were, again, contrasts in approach. Spring Hill has been in operation since 1989 and although the growers pleads 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 from the nearby turkey industry in the area. These applications were made in a general 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 more closely monitored by crop and via soil tests. As a result, fertilizer application (still in the form of composted poultry litter but now a bagged product with a specific NPK rating) 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. Thirty people attended the field day at Spring Hill.

The Growing Home CSA field day in Illinois featured a farm that integrates livestock into their operation and rotation. Twenty people attended the field day at Growing Home. 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 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 very positive. Satisfaction responses were similar from the two field days with 73% of people rating the events “very useful” and 27% “moderately useful.” No one rated the events as “not very useful” or “not useful at all.” Participants ranged from experienced vegetable growers to beginners to university students to extension or other agricultural professionals.

We utilized the field day evaluations to gather some information and opinions on soil fertility management. We asked participants at the events about the challenges facing them in managing fertility for organic vegetables. The following is a ranking of fertility management challenges from most significant to least significant:

1-Lack of time during busy growing season
2-Rotation planning and execution
3-Uncertainty about crop needs
4-Information about amendments (tied with)
4-lack of access to equipment
5-Access to land (for longer rotations)
6-Information on cover crops
7-Interpreting soil tests
8-Access to compost
9-Access to manure
10-Access to cover crop seed
11-Access to knowledgeable people

Beginning growers were more likely to rank access to equipment and uncertainty about crop fertility needs as major challenges.

Advisory Board Results

Ongoing partnerships between growers and university researchers are 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. In practice, the advisory board was one of the more challenging aspects of this project to manage given time, distance, and expectations. A formal advisory board failed to coalesce into a permanent structure but individual growers and research have had increased, positive, and on-going interactions as a results of this project. For example, researchers in the department of Horticulture at the University of Wisconsin have broadened and deepened their pool of contacts to include small, more diversified growers in addition to the large processing conning vegetable with whom they have traditionally worked with and relied upon for input. As another example, researchers in Illinois now have access and relationships with the pool of case study farms and are in the process of developing programs and projects to build upon this initial, foundation research.

We are confident that our survey results and case studies will continue to yield valuable impacts as they are utilized for information and collaborative research/outreach partnerships. Furthermore, our case study approach appears to fit well with related and parallel efforts by others including Wisconsin SARE coordinator Diane Mayerfeld and the Midwest Cover Crops Council.

• Table 8
• Tables 1 through 7
• Figures 1 and 2
• Survey Summary and Case Study Report