Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: September 6, 2004
Publication Date: March 1, 2005
Citation: Pikul Jr, J.L., Johnson, J.M., Wright, S.E., Caesar, T., Ellsbury, M.M. 2005. Soil organic matter and aggregate stability affected by tillage. E.A. Ghabbour and G. Davies (eds) Humic Substances: Molecular Details and Applications in Land and Water Conservation. Taylor and Francis, Inc. New York. p. 243-258. Interpretive Summary: In northern sub-humid regions of the Great Plains, wind and water erosion are persistent problems. Soil conservation practices that improve soil aggregate stability also help to retard soil loss by maintaining surface conditions resistant to the weather vagaries. Long term field experiments on comparable soil located in close proximity provide a unique and valuable opportunity to compare divergent management strategies. The adjacent farm fields used in this study were under two different tillage management strategies for ten years and were in the same rotation phase. We think that improved soil aggregation and increased surface cover of NT compared to CT will help to keep top soil in place. The multifaceted approach to characterizing SOM as it relates to soil aggregate formation helped to identify how different components of SOM interact to improve soil aggregation. Differences in properties among aggregates show that organic cementing agents (humic materials or microbial exudates) are not uniformly distributed among aggregate groups. Our results show improved soil aggregation as a consequence of no tillage farming, when compared to tillage.
Technical Abstract: Soil organic matter (SOM) is important to soil function and productivity. Increased tillage intensity has been implicated in the loss of SOM. Objectives were to determine effect of tillage on components of SOM and stability of soil aggregates. Measurements were made on adjacent farms in eastern South Dakota. One farm used no tillage (NT) and the other used chisel tillage (CT). Soil is a clay loam. A rotary sieve was used to separate 10 kg-soil-samples into 6 size groups. Group 1 was soil <0.4 mm, group 2 was 0.4-0.8 mm, group 3 was 0.8-2.0 mm, group 4 was 2.0-6.0 mm, group 5 was 6.0-19.0 mm, and group 6 was >19.0 mm. Water stability of aggregates from groups 3, 4, and 5 was measured by wet-sieving. Humic acid (HA) was extracted from soil with 0.5 M NaOH. Total carbon (C) and nitrogen (N) of soil and HA were measured by combustion. Immunoreactive total glomalin (IRTG) and soil aggregating basidiomycete fungi (BF) were measured using enzyme-linked immunosorbent assay (ELISA). Particulate soil organic matter (POM) was isolated by sieving. Soil C was greater (p=0.001) under NT, compared with CT, in aggregate groups 1-6. Basidiomycete population and IRTG were greater (average of size groups, p=0.003) under NT. There was a difference (p=0.01) in C:N of HA between NT and CT. Fine POM and water stability of aggregates were greater (p=0.001) under NT, compared with CT, in aggregate groups 3-5. Multiple regression identified that fine POM, C:N of HA, and BF accounted for 63% (p<0.001) of the variability in water stability of dry aggregates. Differences in properties among aggregates show that organic cementing agents (humic materials or microbial exudates) are not uniformly distributed among aggregate groups. Results show improved soil aggregation under no tillage is due to increased organic matter.