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Home  > Question of the Week

Question of the Week

Permalink Why are urea and ammonium sulfate not allowed in organic crop production?

South Dakota

Answer: Urea and ammonium sulfate are prohibited fertilizers in organic production because both are synthetic or artificial commercial fertilizers. As stated in NCAT’s Organic Crops Workbook, on page 15:

Organic agriculture is built around the notion that providing nutritious food and feed is the best way to improve and sustain the health of people and livestock, and that the best way to grow nutritious food is by emulating nature, which begins with feeding the organisms of the soil. Soil micro- and macro-organisms are the external digestive system that processes organic matter, delivering a smorgasbord of minerals, vitamins, and other nutrients to the crop at a metered pace. This is in contrast to the conventional approach where crops are flooded with a limited number of soluble fertilizer nutrients, leading to “luxury consumption,” imbalanced plant nutrition, and a susceptibility to disease and attack by insect pests.

The food that soil organisms need to do their job comes in the form of organic matter, thus composting, manuring, extended crop rotations that include sod crops, green manuring, and similar activities are the standard practices of organic farming.

For the producers of field-scale annual crops, a cropping sequence that includes sod-forming crops is of great value. Sod-forming crops are typically perennial and biennial forage grasses and legumes. Legumes play a special role due to their ability to fix nitrogen…. Additionally, cover crops of annual grasses, small grains, legumes, and other useful plants like buckwheat are inserted into the cropping sequence wherever possible to serve as green manures.


ATTRA publication:
Sustainable Soil Management

Baker, Brian. 2004. Materials used in organic farming. Organic Farming Compliance Handbook. 2 p. (PDF / 103 kb)

Gaskell, Mark, et al. 2000. Soil fertility management for organic crops. University of California – Small Farm Program, Davis. 5 p. (PDF / 123 kb)

Mitchell, Jeff, et al. 2000. Soil management and soil quality for organic crops. University of California – Small Farm Program, Davis. 5 p. (PDF / 112 kb)



Permalink Is there any new information about producer-only farmers' markets that's not in your "Farmers' Markets" publication?


Answer: Although the information in ATTRA's Farmers' Markets is still accurate, interest in farmers' markets has continued to explode around the country, and there are several new resources. A national Farmers' Market Coalition (FMC) has been formed; the University of California has published a direct market training manual that includes material on farmers' markets; and the Farmers' Market Federation of New York, Cornell Cooperative Extension, and NYS Dept. of Ag & Markets have published A Guide to Developing a Community Farmers' Market.

The Farmers' Market Coalition (FMC) was created as a subsidiary of the North American Farmers Direct Market Association (NAFDMA). The FMC elected its first council at the NAFDMA annual conference in mid-February 2005. You can find bylaws, notes from past meetings, and an electronic forum for discussing farmers' market issues at the Web site, . You can also find an overview of federal, state, and non-governmental resources that can assist in development and expansion of farmers' markets across the United States. Several state farmers' market associations are members.

Published in 2005 by the University of California Center for Agroecology & Sustainable Food Systems, Teaching Direct Marketing and Small Farm Viability: Resources for Instructors is organized into six units. Three units focus on marketing, and three cover other topics related to making a small farm economically viable. Included are lessons and resources for organizing and selling at farmers' markets. Although designed as a training manual, the outline provides useful points for any farmers' market member or organizer to consider.

You can download sections or the entire manual from , or you can order hard copy with a 3-ring binder from the Center for Agroecology & Sustainable Food Systems for $25.00 (tax and binder included). Add $4.00 for shipping. To order, send a check made payable to UC Regents to:

CASFS, attn: Direct Marketing Manual
1156 High St.
Santa Cruz, CA 95064

Please be sure to include your mailing address. If you have questions about the resource guide or about ordering, please send e-mail to .

A Guide to Developing a Community Farmers' Market addresses a number of issues involved in establishing a farmers' market, from building interest in a market to organizational structure and evaluation. It also includes sample surveys, rules and regulations, and membership application. The 48-page spiral bound booklet is available from:

Farmers' Market Federation of NY
2100 Park St.
Syracuse, NY 13208

Contact Diane Eggert at the Federation office at 315-475-1101 or for more information

Another resource that you might find useful is U.S. Farmers' Markets 2000: A Study of Emerging Trends from the Agricultural Marketing Service, U.S. Department of Agriculture. This 40-page document provides detailed farmers' market information, including market management structure, total number of vendors, and average customer spending. You can download the publication from the Web site



Permalink What’s the background on using black medic as a legume cover crop, and where can I get seed?


Answer: The University of California Sustainable Agriculture Research and Education Program has compiled extensive information on black medic for their on-line Cover Crop database. See Resources, below.

Black medic (Medicago lupulina L.) is a non-native plant that has become naturalized in some western states in the U.S. In 1987, four Montana farmers formed Timeless Seeds, a company set up specifically to develop from several wild strains and market an improved black medic (‘George’), in addition to other soil-building crops, as an alternative to cultivated fallow. Research was conducted in collaboration with Jim Sims, former Montana State University agronomist.

Oklahoma State University (OSU) has investigated a number of the annual Medicago spp.—including black medic—as cool-season annual forages and concluded they can make a “small, but significant contribution to forage production programs.” OSU Extension notes that commercial seed for annual medic species is

…difficult to find, and the plant is seldom intentionally sown. The seed may lie dormant in the soil for many years; but, when the medics do appear, they produce excellent forage for grazing and may produce an abundant seed crop.

Besides Timeless Seeds, Valley Seed Service, Fresno, CA, is a “weed seed supplier for research purposes.” (See Resources, below.)

Most of the World Wide Web articles that turned up in a search using the term “black medic” seed were about weed eradication from lawns and golf courses. Once sown, seed of this species can remain dormant for years, but when plants become established, they produce abundant seed. Since some of the research has been done in Oklahoma, it might be wise to consult with your state forage Extension specialist regarding your specific needs.

Black medic is in the same genus as alfalfa (Medicagosativa L.). When plans were announced to develop a GMO alfalfa there were immediate concerns about spread of GMO material to established wild populations of black medic and related leguminous species. More recently, concerns have been expressed because black medic is one of the hosts of soybean rust.


Country Pride staff. 2004. Asian Soybean Rust Detected in U.S. Country Pride Services Co-op Newsletter. Fall. p. 1.

Staff. [n.d.] Black medic. UC SAREP Online Cover Crop Database.

Timeless Seeds & Specialty Food Products

Valley Seed Service



Permalink Are there any organic controls for poison hemlock in pastures?


Answer: Several western states have excellent publications on poison hemlock, Conium maculatum. The Montana publication (see Resources, below) includes distinguishing characteristics so that you can positively identify the weed and tell it from similar plants. Note the sections on managing the weed population, including mechanical and biological control methods.

Another fact sheet from Arizona contains a few more bits of information about the plant and its control. This fact sheet doesn’t mention the hemlock moth, Agonopterix alstroemeriana (Clerck), which offers some, though not always excellent, control. There are two sources of the moth listed below, if you decide to purchase some as a part of your organic control program.

You may also want to see the ATTRA publications on flame weeding. This is another type of mechanical control that should prove effective if well-timed and consistently used.


Diver, Steve. 2002. Flame Weeding for Vegetable Crops. ATTRA Publication. National Center for Appropriate Technology, Fayetteville, AR. 16 p.

Moser, L., and D. Crisp. No date. Poison Hemlock: Conium maculatum. San Francisco Peaks Weed Management Area fact sheet. Coconino National Forest. 2 p. (PDF / 161 kb)

Pokorny, Monica L., and Roger L. Sheley. 2000. Poison Hemlock. Montguide MT 2000-13. Montana State University Extension Service, Bozeman, MT. 4 p.

Sullivan, Preston. 2001. Flame Weeding for Agronomic Crops. ATTRA Publication. National Center for Appropriate Technology, Fayetteville, AR. 2 p.

Sources of hemlock moth Agonopterix alstroemeriana (Clerck):

Integrated Weed Control

Biological Control of Weeds, Inc.



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