1. Department of Agronomy
Crop Rotation Diversity to Improve Water Quality and Increase Soil Health
Jordan Kersey, Hanna Poffenbarger, Dan Olk, Antonio Mallarino, Mike Castellano

2. (Russell et al. 2005, Gregorich et al., 2001, Sanford et al., 2012)
Department of Agronomy
Background
Soil organic matter (SOM) helps to maintain good soil health and is essential to the sustainability of Iowa agriculture.
Soil organic matter : C, N, other nutrients
Water-holding capacity
Nutrient supply
Extended rotations found an increase in SOM
(Russell et al. 2005, Gregorich et al., 2001, Sanford et al., 2012)
Reduction of nitrate losses
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3. Biochemical compounds
Department of Agronomy
Biochemical compounds
Phenols (plant lignin)
Fatty acids (microbes and plants)
Cutin (plant shoot-tissue compounds)
Suberin (plant root-tissue compounds)
Cutin:Suberin ratio
Photo source:
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4. What is the biochemical composition of the organic matter?
Department of Agronomy
Research Questions
Do extended rotations increase soil carbon and nitrogen retention in surface and subsoils?
What is the biochemical composition of the organic matter?

5. Department of Agronomy

6. Sampling Methods Samples from two long-term crop rotations
Department of Agronomy
Sampling Methods
Samples from two long-term crop rotations
ISU Northern Research Farm
Fall 2014, both rotations in corn-phase
Four depths
(0-6, 6-12, 12-24, inches)

7. Department of Agronomy
Methods
Samples were dried, ground, and analyzed for total C and N concentrations
Samples were analyzed by pyrolysis-gas-chromatography-mass spectrometry for total phenol and fatty-acid compounds
Identified using a GC-MS library

8. Department of Agronomy
Extended rotations had greater organic soil C % and greater total soil N %

9. Department of Agronomy

10. Department of Agronomy
-The percentage of SOC fatty acid-C increased with increased depth, but did not differ between rotations.
-Fatty acids originate from both plants and microbes. Cutins and suberins are thought to be some of the most recalcitrant plant structures within the soil (Tegelan et al., 1989
), and both tend to have high potential for preservation in soils (Kogel-Krabner et al., 1989).

11. Ongoing research… Cupric-oxide extraction
Department of Agronomy
Ongoing research…
Cupric-oxide extraction
Extension of pyrolysis method
Identifying fatty acid and phenols
Cutin to suberin ratio from biomarkers

12. Department of Agronomy
Conclusions
Crop rotation did not affect the biochemical composition of SOC
C concentration was greater in extended rotations across all depths
Soil organic matter is key
Understanding impacts of crop rotations, important in future of Iowa agriculture

13. Terry Grimard, Kevin Mueller
Department of Agronomy
Acknowledgements
Terry Grimard, Kevin Mueller

14. Questions? Department of Agronomy Tegelan et al., 1989
(Kogel-Krabner et al., 1989)

15. Department of Agronomy
References
Kögel‐Knabner, Ingrid, et al. "Distribution and decomposition pattern of cutin and suberin in forest soils." Zeitschrift für Pflanzenernährung und Bodenkunde (1989):
Mendez-Millan, M., et al. "Molecular dynamics of shoot vs. root biomarkers in an agricultural soil estimated by natural abundance 13 C labelling." Soil Biology and Biochemistry 42.2 (2010):
Olk, Dan C. "Improved analytical techniques for carbohydrates, amino compounds, and phenols: tools for understanding soil processes." Soil Science Society of America Journal 72.6 (2008):
Rasse, Daniel P., Cornelia Rumpel, and Marie-France Dignac. "Is soil carbon mostly root carbon? Mechanisms for a specific stabilisation." Plant and soil (2005):
Weil, R.R. and F. Magdoff Significance of soil organic matter to soil quality and health. pp. 1–43 In Eds. F. Magdoff and R.R. Weil. Soil Organic Matter in Sustainable Agriculture. CRC Press, Boca Raton, FL.
Williams, C.L., M. Liebman, J.W. Edwards, D.E. James, J.W. Singer, R. Arritt, and D. Herzmann Patterns of regional yield stability in association with regional environmental characteristics. Crop Sci. 48: 1545–1559.
Iowa Nutrient Reduction Strategy Iowa Department of Agriculture and Land Stewardship, Iowa Department of Natural Resources, Iowa State University College of Agriculture and Life Sciences.