Survey of the Nutrient Status of Organic Vegetable Farms

Final Report for LNE01-144

Project Type: Research and Education
Funds awarded in 2001: $35,397.00
Projected End Date: 12/31/2004
Matching Non-Federal Funds: $8,975.00
Region: Northeast
State: Connecticut
Project Leader:
Thomas Morris
University of Connecticut
Expand All

Project Information

Summary:

(Note to the reader: Tables referenced in the report are available from Northeast SARE. Send a request for a hard copy final report to nesare@uvm.edu and reference LNE01-144 as the project report you need.)

This project is a survey of the nutrient status of organic vegetable fields in the Northeast US. The objective is to document the nutrient status of organic vegetable fields. We are documenting the nutrient status by collecting soil samples from fields of organic growers at two times during the year. Samples were collected in June and in November. The samples in June documented the nitrogen fertility of the fields by measuring the soil nitrate concentration of the soil in the surface foot of soil. The samples collected in November documented the pH, macronutrient fertility (Ca, Mg, P, and K), and the nitrogen fertility. Two soil samples were collected in the fall: one for pH and macronutrient fertility from the surface 6-inch layer of soil, the other for nitrogen fertility from the surface 12-inch layer of soil.

Field information about the history of nutrient applications, tillage and cropping pattern were collected from each grower. The field information was used to place the fields into categories based on the length of time in organic production, type of nutrients, amount of nutrient application, and cropping pattern. One of our hypotheses is that we will be able to classify the soil fertility based on the history of nutrient applications on the field. The soil test results allow us to objectively test our hypothesis.

We plan to use the results of the survey to develop an educational program about soil fertility for organic growers. Results from the two year’s survey indicate that organic growers need much education. Many fields have soil test results in the below-optimum category and many other fields have soil test results in the above optimum category. Only a small percentage of the fields have soil test results in the optimum category.

Introduction:

Most organic vegetable producers use composts and manures to maintain the fertility and tilth of their soil. Composts and most manures are known to slowly release a good portion of their nitrogen (N) and phosphorus (P) during the year of application and for a number of years after application. This slow release of nutrients is thought to provide a steady supply of nutrients for optimum crop growth. Many organic growers believe that the slow-release nature of organic amendments, especially compost, minimizes or eliminates the problem of nutrients escaping their fields in leachate or runoff.

Unfortunately, preliminary results from research performed at the Rodale Research Institute and from soil samples collected from compost-amended farmer’s fields suggest that only small amounts of compost can cause excessive amounts of extractable P and possibly soil nitrate. We believe N can be excessively available on some organic fields because the N mineralization potential of the soil is greatly enhanced by large compost additions. Phosphorus accumulates because only a small amount of P is exported from the field compared with the amount of P applied to the field. Pollution of the environment by nonpoint sources, which include leachate and runoff from farm fields, is of concern to the US EPA, and such pollution is not in the best interests of society or organic vegetable producers. Organic growers, organic growers’ associations like the Northeast Organic Farmers Associations, and scientists at the Rodale Research Institute are concerned about the accumulation of nutrients on organic fields. We surveyed the N and P status of a total of 176 organic vegetable fields across at least 30 farms in the five states in the Northeast. We measured soil nitrate concentrations and extractable P concentrations for two years. The results indicate that organic vegetable fields are not being managed properly. Only a small percentage of fields (22%) were in the optimum range for P. Over half (53%) tested above optimum and 25% were below optimum. Similar results were seen for the other mineral nutrients. Due to heavy rain in the spring of both testing years nitrate was low. We feel that in a normal year NO3 would also test high. These results indicate that organic farms need education on fertility management to better balance nutrient loading into the environment. Many farms use good practices and can be tapped as informational resources for the entire region.

Performance Target:
  1. 1. Each state will obtain permission from at least 3 organic vegetable farms to perform the survey of the nutrient status of their fields.

    2. Each state will collect soil samples in late-spring and late-fall from at least 20 fields in 2002 and 2003.

    3. Growers will complete a questionnaire about historical use of nutrients on their farm.

Cooperators

Click linked name(s) to expand
  • George Hamilton
  • Stefan Seiter
  • Eric Sideman

Research

Materials and methods:

This project was designed to evaluate the current status of soil nutrients in organic vegetable fields in the northeast. Most organic growers base there fertility management on the addition of compost or raw manure. We are determining if there is an elevation of nutrients, specifically N and P, from this practice as has been seen in continuously manured conventional corn fields. By correlating the management survey with the soil test results we can determine which practices are most environmentally sound while still maintaining yields.

In the summer of 2002, farmers from five states were asked to participate in the survey. Contact was made by letter and follow-up phone call. Upon agreeing to participate growers were asked to complete a survey of their current and past nutrient management as well as providing copies of past soil test results. The survey was either completed and returned by the grower or by interview.

Soil samples were taken in early summer and fall of 2002 and 2003. The summer samples followed the procedure of the Pre-Sidedress Nitrogen Test (PSNT). Samples were taken to a depth of 12 inches. They were spread and air dried within 24 hours or kept cold if drying could not be done within 24 hours. Two separate samples were taken in the fall, one for nitrogen following the procedure above and one for mineral nutrients, pH and organic matter. The mineral nutrient test was the Modified Morgan procedure. The organic matter was determined by loss on ignition.

Research results and discussion:

In 2002 we collected soil samples from 31 farms. This is 16 farms greater than required by our milestones. The number of farms sampled in each state ranged from 5 to 7. We were required to sample only 3 farms per state. We collected samples from 153 fields, which is much greater than the 125 fields noted in our milestones. We also collected 6 soil samples from tunnel greenhouses. We collected data on the historical use of nutrients on the farms and obtained photocopies or digital images of past soil test results.

In 2003 we collected soil samples from 30 farms. This is 15 farms greater than required by our milestones. The number of farms sampled in each state ranged from 5 to 7. We were required to sample only 3 farms per state. We collected samples from 176 fields, which is much greater than the 125 fields noted in our milestones. We also collected 4 soil samples from tunnel greenhouses. We tabulated the survey information began to develop models for the results.
In 2004 we collected samples from selected fields during the summer for the PSNT. Forty-three samples were taken from nine farms. These were duplicate fields from 2002 so a comparison could be made between them. We did this to show that, in a dry year, fields have the potential to generate excess NO3.

In 2002, 18% of the fields tested optimum while 18% were deficient of P, measuring below 10 pounds per acre (Table 3). 31% of the fields exceeded optimum, with results over 40 pounds per acre, twice the optimum amount. In 2003, 25% of the fields were below optimum while 53% were above optimum (Table 6). Only 22% of the fields tested in the optimum range. This is a strong indication that P levels are building in organic vegetable fields. But it may be that this is occurring on only a small number of farms. In both years the mean for P was high, 80 lb/A in 2002 and 73 lb/A in 2003. This is nearly four times the optimum. Yet the median was 24 in 2002 and 20 in 2003, very close to optimum. We found that a small number of farms had extremely high P levels, several over 500 lb/A. This is a major contributor to the high average.

Soil test results can be correlated with farming practices to determine if any trends emerge. When comparing the number of years organic (Table 7) we find that P increased as does other minerals, while organic matter and NO3 remained the same. When comparing farm size (Table 8) P, NO3 and organic matter all decrease as the size of the farm increases. Most participants said they did not use raw manures so different compost ingredients were compared (Table 9). The types of compost were: (1) chicken, cow, horse, mixed barnyard, (2) vegetative and (3) compost from a mushroom operation. There were large P differences between the composts but not for NO3 or soil organic matter. Mushroom and horse had the highest P while dairy and no compost had P levels near optimum. Farms that apply no compost had comparable organic matter with those that did. The survey indicated that only about 40% of the fields are managed with a season-long cover crop (Table 10). There was very little difference in P, NO3 or organic matter between fields that used season-long covers and those that did not. Fifty-six percent of the fields received a blended fertilizer as part of the fertility management (Table 11). The fields that use blended fertilizers had a lower P, NO3 and organic matter than the fields with no fertilizer.

Nitrogen levels showed similar trends though rain in the early summer of both 2002 and 2003 reduced soluble NO3. In summer 2002 only 14% of fields were in the optimum range while 58% were below optimum and 28% were above optimum (Table 1). In summer 2003, 17% were optimum while 34% were below optimum and 49% were above optimum (Table 4). Fall nitrate levels are a concern because excess NO3 in late fall will leach into groundwater. In 2002, 92% of fields were below 20 ppm (Table 2) and in 2003 96% of fields were below this mark (Table 5).

The spring of 2004 was drier than the previous two springs and we wanted to determine if there would be differences between years because of reduced leaching of nitrate. We collected 43 samples from fields we collected from in 2002. May and June had a rainfall total of 10.3 inches in 2002 and a total of 5.7 inches in 2004. Based on a t-test, a significant difference was found between these fields from 2002 and 2004. The there was an average increase of 11 ppm, representing a 44% increase in NO3 between years. In 2004, 58% of fields were above optimum, compared to 28% in 2002. This indicates long-term additions of compost can create excess NO3.

Participation Summary

Education

Educational approach:

Title: Nutrient status of organic vegetable fields in the Northeast
Audience: Certified Crop Advisor Re-Certification Program
Location: Portsmouth, NH
Date: February 6, 2003
Attendance: 50 people

Title: Organic Fertilizers and Soil Amendments
Audience: Northeast Organic Farmer Association of Massachusetts Short Course on Organic Land Care
Location: New Haven, CT
Date: February 11, 2003
Attendance: 45 people

Title: Organic Fertilizers and Soil Amendments
Audience: Northeast Organic Farmer Association of Massachusetts Short Course on Organic Land Care
Location: Boylston, MA
Date: January 22, 2003
Attendance: 45 people

Title: How manage nutrients on organic vegetable farms
Audience: Certified Crop Advisors Workshop
Location: Portsmouth, NH
Date: February 4, 2004
Attendance: 62 people

Title: Nutrient status of organic vegetable fields in the Northeast
Audience: NOFA Summer Conference
Location: Hampshire College, Amherst, MA
Date: August 10, 2003
Attendance: 32 people

Title: Nutrient status of organic vegetable fields in the Northeast
Audience: New England Vegetable Conference
Location: Manchester, NH
Date: December 16, 2003
Attendance: 200 people

No milestones

Additional Project Outcomes

Project outcomes:

Impacts of Results/Outcomes

The impact of these results will be the knowledge that work needs to be done in implementing organic fertility management practices. Organic growers strive to reduce the environmental impact of their farming practices. For years it has been professed that organic matter has a great deal of beneficial qualities for vegetable production and this undoubtedly is true. But, continuous heavy applications of organic matter can have a negative environmental impact and this is not within organic principles. This project was not designed to change farm practices but to determine if changes may be necessary.

Economic Analysis

There was no economic analysis component to the project.

Farmer Adoption

Farmer adoption was not one of our performance targets.

Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

This research indicates that some organic farms are having problems maintaining optimum nutrient levels. Some are in excess and some are under. Additional study into the best nutrient management practices for organic farmers is needed. This should include an educational component that will increase adoption of these practices.

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.