Soil Fertility Paradigms Evaluated through Collaboration On-Farm and On-Station

1998 Annual Report for LNC98-138

Project Type: Research and Education
Funds awarded in 1998: $59,027.00
Projected End Date: 12/31/2002
Matching Federal Funds: $40,300.00
Matching Non-Federal Funds: $25,956.00
Region: North Central
State: Iowa
Project Coordinator:
Dr. Rick Exner
Practical Farmers of iowa

Soil Fertility Paradigms Evaluated through Collaboration On-Farm and On-Station


Within sustainable agriculture, two contradictory approaches to soil fertility uneasily coexist – the cation ratio paradigm (CR) and the one referred to as “sufficient level of available nutrients” (SLAN). There is little communication between the two camps because they use different terms and conceptualize fertility differently. SLAN proponents, and this now includes all of the U.S. land grant universities, concern themselves with whether the soil contains enough of each nutrient in forms that are available to the crop. In contrast, the CR approach looks not at the gross amounts of available nutrients but the proportions in which they are represented on the soil cation exchange. It is the farmer who is forced to integrate these two information streams and make the financial judgements required in farm management. Sustainable agriculture must deal constructively with this schism if it is to grow in credibility and relevance.

We have initiated a process, one involving stakeholders on both sides of the question, to compare the economic and agronomic consequences of these two philosophies. We have implemented a series of side-by-side comparisons of the two management styles. Both approaches are accurately and credibly represented.

Research sites consist of two Iowa State University experiment stations and six farms: two organic, two transitional-to-organic and two farms that use synthetic production inputs in a sustainable manner. Project collaborators include the two primary sustainable agriculture organizations in Iowa: Practical Farmers of Iowa (PFI) and the Organic Crop Improvement Association (OCIA). Based on the two approaches to fertility, two sets of recommendations have been generated for each site, with materials applied accordingly in replicated plots, six replications per site. The project focuses on selected crop and soil parameters chosen to reflect impacts of the two systems on grain quality, soil quality and soil biological activity. Crop production and profitability are monitored for each site and for the study overall, as are crop quality and soil physical, chemical and biological indicators. After each cropping year, farmer-scientist roundtables will take place in producer meetings to discuss findings and their significance.

The project monitors the following crop and soil quality parameters in the two comparison systems: grain yields and moisture, population, grain crude protein, ADF, TDN, net energy, 10 minerals (grain), soil aggregate stability, bulk density, soil particulate organic matter and microbial biomass, soil P1, P2, K, Mg, Ca, S, Zn, Mn, Fe, Cu, B, OM, pH, buffer pH, and corn nitrogen status through the late spring soil nitrate test and end-of-season stalk nitrate test. Indicators beyond gross yield are sometimes diagnostic of hidden problems, especially in the CR approach. Further, they may be indicative of soil quality benefits that are not reflected in crop yields or profits, at least in the short term.


Douglas Karlen

[email protected]
National Soil Tilth Laboratory
314 USDA National Soil Tilth Laboratory
Iowa State University
Ames, IA 50011
Office Phone: 5152943336
Richard Thompson

Practical Farmers of IA
IA 50036
Kathleen Delate

[email protected]
Organic Cropping Specialist
Department of Horticulture
147 Horticulture Hall
Iowa State University
Ames, IA 50011
Office Phone: 5152947069