Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: September 26, 2005
Publication Date: September 28, 2005
Citation: Jaynes, D.B., Karlen, D.L. 2005. Sustaining soil resources while managing nutrients. In: Final Report: Gulf Hypoxia and Local Water Quality Concerns Workshop, September 26-28, 2005, Ames, Iowa. p. 149-158. Technical Abstract: Effects of nutrient management practices need to be evaluated against not only economics and water quality, but also against long-term soil productivity to ensure a profitable and environmentally sustainable agricultural production system within the Corn and Soybean Belt. Soil organic matter is an important indicator of soil productivity and soil tilth as many of the biological, chemical, and physical properties of a soil that are important for crop production in the Corn and Soybean Belt are strongly influenced by SOM levels. In the examples used here, the negative N mass balances for the 1X treatment in Table 1 and the corn/soybean rotation under liquid manure application in Table 3, are equivalent to about a 0.2% yr**-1 loss in SOM from the top 20 cm of the profile. Conversely, the positive N balances for the cover crop in Table 2 and the continuous corn with liquid manure application in Table 3, represent increases in SOM of about 0.2% and 0.9 % yr**-1, respectively. While small in terms of our current ability to directly measure, these changes represent about a 5% loss in SOM over 30 yr for the first two, and a gain of 5% and 26% in 30 yr for the latter two. The losses may be even more important for soil function, as these losses are primarily from the labile pool, which is the most chemically, biologically, and physically active SOM pool. Thus, nutrient management practices need to be assessed for their ability to enhance or maintain SOM content in addition to their impact on yield and profit. Just as nutrient management studies are incomplete if they consider only yield and ignore water quality, water quality studies evaluating nutrient practices that neglect the long-term effects on the soil resource are also incomplete. Future nutrient management studies must be designed to measure impacts on soil and water resources as well the economics of various practices.