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Title: Soil Fertility Management Strategies -- Philosophies, Crop Response and Costs

item Karlen, Douglas

Submitted to: Experiment Station Bulletins
Publication Type: Other
Publication Acceptance Date: 10/1/2007
Publication Date: 10/13/2007
Citation: Exner, R., Delate, K., Karlen, D.L. 2007. Soil Fertility Management Strategies -- Philosophies, Crop Response and Costs. Iowa State University - University Extension. p. 2-10.

Interpretive Summary:

Technical Abstract: When it comes to soil fertility, farmers are likely to encounter different “paradigms” or philosophies that ask different questions. This project was designed to document the short- to medium-term outcomes that producers can expect from adopting the SLAN (sufficiency level of available nutrients) or CR (cation ratio) approaches for fertilization and soil fertility management. Soil fertility levels, crop nutrient status, grain quality and yield, weed pressure, and costs were monitored for studies on nine private farms and two Iowa State University research farms during this three-year research project. The most consistent and pronounced treatment effects were in soil and crop tissue, for nutrients that were present in the amendments used. Individual farms sometimes showed differences in other parameters, but they were inconsistent and not strong enough to be considered real treatment effects. Soil fertility treatment did not affect crop yield to the extent of achieving statistical significance. The small yield differences that were observed cannot be positively attributed either to the effectiveness of the CR philosophy or to what the SLAN approach would classify as excessive fertilization. Fertilizer and lime costs averaged $9.27 per acre per year more with the CR approach than for the SLAN, without including application expenses and assuming there were local sources for calcitic limestone. The increased expense outweighed the possible yield advantages at conventional grain prices. Assuming organic premium prices were available, only the soybean crop had a yield increase that could offset the increased input cost. Overall, the three-crop organic system was less profitable using the CR approach than the SLAN.