Next issue will be posted August 9 . Read previous issues through our calendar of issues.

This article explains why and how you might use nematodes to understand how your soil is functioning. The influence of nematodes on decomposition, soil nutrient supply and population development of other biota has attracted interest in their use as indicators of soil condition. You've likely been told that the success of organic farming depends upon the adequate management of soil properties achieved through the enhancement of soil organic matter. No doubt you know that soil organic matter can be improved through the use of cover crops, rotations and the incorporation of composts, animal and green manures, and that soil organic matter contains nutrients, including N, that are not released until microbes colonize materials and convert organic structures into mineral forms that are plant available. You know microbes use the soil organic matter as substrate to satisfy their nutritional requirements. What you might not know is that other organisms in the soil food web can determine whether the N contained in the microbial biomass (bacteria and fungi) is made available for plant use.

Nematodes, which are the second largest contributors to N mineralization after bacteria (Hunt et al., 1987), exert their influence by controlling the base of the food web. The most abundant nematodes in agricultural soils are the bacterial feeders. Their abundance increases rapidly after organic matter incorporation and increases in bacterial growth. Bacterial feeding nematodes contribute to the inorganic N supply by releasing N in the form of ammonium (NH 4 +) that is readily available for plant uptake. Without the presence of nematodes in soil, mineralization is much slower and N can remain immobilized or sequestered in the microbial biomass for longer periods of time.

The basics of nematode feeding and N mineralization
The contribution of bacterial-feeding nematodes to soil N supply depends on the quality and quantity of soil organic matter fueling the system. Net nitrogen mineralization takes place when the carbon/nitrogen (C/N) ratio of organic residue is below 20. When the C/N ratio is higher than 30, the rates of mineralization decrease because microbes need N to meet their nutritional requirements. In this situation, N is immobilized within the microbial biomass. Incorporation of manure, compost and cover crops with intermediate C/N ratios (ranging from 10-18) can supply soil microbes with the nutrition they need. This results in bacterial growth that provides food for bacterial feeding nematodes and ultimately results in increased soil N supply to plants.

Figure 1 is a conceptual representation of how the food web is affected when N rich organic matter is incorporated into the system. The increase in bacterial growth (shown in heavier boxes) could be associated with higher populations of bacterial feeding nematodes and protozoa. Population increases of these nematodes and protozoa accelerate N availability.

Figure 1. Simplified food web illustrating food web connectedness of organisms and contribution of organic inputs to soil organic matter and soil biota (represented in the black arrows). Contributions of soil biota to soil organic matter decomposition and inorganic N supply are represented in red arrows. Shifting the food web towards bacterial dominance might increase N availability.

Changes in nematodes and soil food webs can happen fast
Changes in nematode populations were apparent during the first year of the Windsor Organic Research on Transition (WORT) project in Illinois (See the June 24, 2004 New Ag Network article at http://www.new-ag.msu.edu/issues04/06-24.htm#3 by Catherine Eastman). Bacterial feeding nematodes were the most abundant of all types of nematodes and their relative proportion was greatest in treatments where soil N availability (determined using the Illinois Soil N Test) was highest (Figures 2 and 3). Soil food webs were shifted toward bacterial dominance in soils that had received recent manure additions. The influences of manure were initially greater than was the affect of cropping system (Figure 3). Ongoing work will determine whether crop mix and tillage ultimately change the foodweb structure and how N is supplied to plants or retained within soils. If successful, this approach would allow us to use nematodes as indicators to understand whether a system is being managed under optimum conditions where populations of soil biota are in balance and the nutrient supply is adequate but not in excess.

Figure 2. Seasonal average of plant available N during the 2004 growing season in three farming/management intensities and three organic inputs.
Figure 3. Seasonal means of nematode trophic abundance in three farming intensities and three different organic inputs.

Philosophies of soil management

Michelle Wander (mwander@uiuc.edu) Natural Resources and Environmental Sciences,
University of Illinois

How can you tell if you are “building” your soil?
Organic certification standards suggest organic transition practices should “build” soils in a manner that enhances their biological and physical condition to increase nutrient and water use efficiency, suppress plant diseases, and resist erosion or compaction. No one testing method or assessment tool is going to help you keep track of all of these goals. Conventional soil testing seeks to determine the proper fertilization for plants to be grown while nutrient management plans are a conservation planning tool with the intent to "integrate ecological (natural resource), economic and production considerations in meeting both the owner's/operator's objectives and the public's natural resource protection needs.” The NRCS' soil conditioning index estimates soil organic matter in the surface depth as a function of inputs, tillage and soil type. If and when you figure out how to monitor success in your system using any or all of these tools, you might find that balancing your goals is an even more difficult challenge.

Is that huge dark green broccoli head evidence of success?
To satisfy organic principles you can't just try to maximize your yields. Ideally fertilizers and organic amendments should be managed so that nutrient stocks are neither depleted nor accumulated in excess. Amendments should be added as needed to maintain appropriate crop yields and to minimize or prevent nutrient losses to the environment. Yield expectations should be tailored to suit the cropping system and environment. Both amendment type and application strategy (timing and rate) should be considered as should the influence of practices on soil's biology and physical fertility.

Conceptual framework
To figure out how to tackle this problem in management terms it might help if first we consider the theory behind biologically based fertility that promises high or stable productivity without causing harm to the soil or environment. Figure 1 might help. This is adapted from a paper by Schimel and Bennet (2004) who were studying the different nitrogen (N) uptake mechanisms used by plants in nature.

Figure 1. Adapted from Schimel and Bennett, 2004

Based on this figure, I'd argue that organic growers committed to biologically-based fertility want to shift plant N uptake mechanisms to the left. You are going to need to think more like an ecologist than an agronomist to work through this with me. Agronomic systems tend to be type 'A' in that they are managed intentionally to add inorganic N directly and/or force N mineralization by aerating soils to oxidize organic N and ammonium to nitrate. By adding N or promoting N mineralization (moving from the C to B or the B to A sectors) we aid plants in their competition with microbes for N. This works well for the plant but; unfortunately, has undesirable environmental consequences. Intensive farming systems and well drained-coarse textured soils have type A tendencies. Precision farming and careful management of N to synchronize its addition with plant demand are essential to maintain yields and avoid environmental loss.

Management for the B or C type scenarios might be more appropriate for most organic growers. Plants grow perfectly well and acquire N even though net N mineralization seldom occurs. Plants do this by either competing well for N and other nutrients or by cooperating with microbes. Symbiotic nitrogen fixation and mycorrhizal associations can both help plants acquire N. Mycorrhizal associations can also enhance plant water and phosphorus uptake. Microbial partnering becomes increasingly important as plant available N becomes increasingly scarce and is less important, or is even suppressed, when inorganic nutrient levels are high. So, to satisfy adherents to original organic principles, fertility recommendations have to guide management of biology to leverage nutrients instead of just metering out amendments. How will we do this?

B). You might increase overall yield and possibly achieve higher yields with lesser inputs if enhanced soil condition increased the crop's ability to acquire nutrients either by increasing root health, increasing plant available water, and/or the volume of soil explored. Alternatively, if you transition a soil that has never been plowed that is in good condition you are likely to move from a curve C to a curve B or even to an A type situation unless you are a very good steward. Managing soils to maintain a C type yield curve is conceptually challenging and, if Figure 1 is correct, could require an entirely different approach to soil testing.

Figure 2. Yield response curves for soils where (A) yield potential and input use efficiency are low, (B) yield potential is low but input use efficiency is high, and (C) both yield potential and input use efficiency are high.

Soil building workshop offered in Michigan – August 23

Vicki Morrone, Mott Group for Sustainable Food Systems, Michigan State University

Farmers and consultants interested in gaining a better understanding of living soils are invited to attend a workshop about building soil for improved crops and identifying organic markets. The workshop, “Building Soils and Markets for Organic and
Biological Systems” targets the needs of organic and transitioning farmers. It will take place on August 23 at Morgan Compost, Inc. in Sears, Michigan (west of Clare). The guest speaker is from Midwest Bio Systems in Illinois, Roger Kropf. He will discuss building soil fertility with integration of compost, cover crops and soil amendments.

For more information and registration information please visit the Mott group web site: www.mottgroup.msu.edu At this site you will find a flyer with directions to the venue.

Maps of Minnesota organic farms and processing facilities now on the Internet

The University of Minnesota is offering maps showing county-by-county locations of certified organic farms and processing facilities in Minnesota on the University’s organic website, www.organicecology.umn.edu

The Minnesota Department of Agriculture recently compiled the maps which indicate there are currently 507 certified organic farms and 137 certified organic processing facilities in the state. Counties with the largest numbers of organic farms are Stearns, Winona, Fillmore, Goodhue, Houston and Otter Tail. Counties with the most organic processors are Hennepin, Ramsey, Polk, LeSueur, Goodhue and Winona.

The University of Minnesota has the largest certified organic acreage at any land grant university in the country, and the Minnesota Department of Agriculture has been quite supportive of the growth of the organic sector in the state. For more information on the University of Minnesota’s organic agriculture research and outreach programs, visit the website, or contact Jim Riddle, 31762 Wiscoy Ridge Road, Winona, MN. Phone 507-454-8310. Cell – 507-429-7959.

Pesticide-free and organic farming on the Allison Farm

In 1989, David Johnston, an assistant professor of the Western Illinois University (WIU) Agriculture Department, located a historically pesticide‑free, limited‑fertilizer, 80‑acre farm located near WIU. The farm had been owned and operated by the same couple, Mr. and Mrs. Allison, since 1953. Prior to that time, it was farmed by Mrs. Allison's parents. In 1989 Department Chair Dr. Gerald Carlson contacted the Allisons, and obtained permission to conduct research studies on this land. With the cooperation of the owners and scientists from the USDA Soil Tilth Lab in Ames, Iowa, the WIU Department of Agriculture initiated systematic sampling and characterization of the soil chemical, physical and biological properties of these Sable-Muscatine soils.

The owners continued to operate the entire farm themselves through 1991. In 1992, 20 acres of the farm were leased to WIU and in 1993, with the passing away of Mr. Allison, the entire farm was leased by WIU and a cooperating farmer. An effort has been made to maintain this benchmark farm in a pesticide-free condition to serve as an agricultural scientific reserve for the purpose of conducting research related to soil health and sustainability.From 1989 through 1997 the following studies were conducted:

• Completed a systematic sampling and characterization of the chemical, physical and biological properties of these Sable‑Muscatine soils;
• Completed a characterization of soil invertebrates;
• Established research to evaluate tillage and cropping practices to control weeds; and
• Initiated research to determine the optimum environment (date‑of‑planting) for controlling weeds in food grade soybeans grown to meet quality and certification standards of alternative markets for organic crops.

Federal research funds provided to WIU were used to initiate these studies in 1991. As the USDA funds ran out in 1997, funds from C‑FAR (Illinois Council for Food and Agriculture Research) were combined with financial and technical support from the McDonough and Warren Co. Soil and Water Conservation Districts for the agriculture industry and local area cooperating farmers to continue this project. Funds for 2002–04 were obtained through a grant from the Conservation 2000 Sustainable Agriculture Grant Program of the Illinois Department of Agriculture.

The basic objectives of this project are: (1) to develop alternative soil and crop management strategies for pesticide‑free farming systems and to study the feasibility of alternative crops for west central Illinois, and (2) To evaluate the impact of alternative farming systems on long-term soil productivity, including chemical (nutritional), physical (tilth) and biological (biotic activity and diversity) soil characteristics.

Since 1997, our studies have focused on ways to control weeds and pests, evaluate cropping and tillage practices, and determine the economic feasibility of pesticide-free and organic crops. We have continued to involve local farmers and members of the agricultural industry in identifying research needs, as well as planning, conducting and supporting this research. For more information, contact ourwebsite: www.wiu.edu/ag/stuorg/organicfarm/ or phone: 309-298-1172.

Allison Organic Farm field day –August 10

The marketing of organic products and organic farming methods will be featured at the annual Western Illinois University Allison Farm Field Day beginning at noon on Thursday, August 10 at the WIU Agriculture Department's 80-acre pesticide-free and organic Allison Research and Demonstration Farm located in southern Warren County, seven miles north of Sciota (view more details and directions). Samples of organic foods and drink, such as organic chocolate and vanilla ice cream, organic pop and other organic foods will be available for tasting.

Field day presentations will begin after a complimentary noon lunch. Presentations include:

• A representative from Wal-Mart will describe the Organic Marketing Program that is expanding in Wal-Mart stores.

• Bruce Black from Hy-Vee will describe the organic food offerings in Hv-Vee grocery stores.
• Roger Hendricker, manager, Clarkson Grain, Beardstown, IL, will present marketing opportunities for organic soybeans and corn.
• A representative from Midwest Organic Farmers Coop will present opportunities for marketing organic crops by means of a Midwestern Coop.
• Karl Dallefeld of MidWestern Bio-Ag will describe biological farming.

• Maury Johnson of Blue River Hybrids will present seed production for organic crops.
• Jerry Vigue, WIU agriculture professor and coordinator of the field day, will present field testing organic soybean varieties and corn hybrids.

Event co-sponsors are the McDonough Co. and Warren Co. Soil and Water Conservation Districts and the WIU Agriculture Department. The field day is open free to the public, but advance registration is required for the lunch. To register, contact the WIU Agriculture Department at 309-298-1080 by noon on Tuesday, August 8. For more information, contact Jerry Vigue or Andrew Clayton at 309-298-1172. The website describing the WIU Organic Program can be found at: www.wiu.edu/ag/stuorg/organicfarm.