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Comparison of Soils and Plants at Prairie Ridge: % C and % N

Comparison of Soils and Plants at Prairie Ridge: % C and % N. Lori Skidmore. Plant - Soil Interactions. Knops and Tilman (2000) conducted a longterm study of an abandoned agricultural site. Rates of C and N accumulation in soil significantly influenced by plant composition

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Comparison of Soils and Plants at Prairie Ridge: % C and % N

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  1. Comparison of Soils and Plants at Prairie Ridge:% C and % N Lori Skidmore

  2. Plant - Soil Interactions Knops and Tilman (2000) conducted a longterm study of an abandoned agricultural site. • Rates of C and N accumulation in soil significantly influenced by plant composition • C3 grasses and forbs  decreased C and N accumulation rates • C4 grasses • increased the C:N ratio of soil organic matter • increased C accumulation rate • did NOT increase N accumulation rate

  3. Hypothesis • Soil samples collected near C3 grass (fescue) and forbs (ragweed and horsenettle) will have a lower % C than soils collected near C4 grass (bermuda). • %N will be similar in surface soils throughout the plot. • Plant fragments in soils will reflect % C and % N of dominant plant species (bermuda grass) in sample plot. • Do we see this?

  4. Sample Plot N Soil Pit PRS -15 (+2 – 0 cm) PRS -16 (0 – 6 cm bgs) PRS -17 (6 – 11 cm bgs) PRS -18 ( + 11 cm bgs) PRP-9 fescue PRS-5 surface soil PRP-11 bermuda PRP-8 horsenettle PRP-12 fescue PRP-3 ragweed PRP-6 bermuda PRS-7 surface soil PRP-4 ragweed PRP-13 (dead plant matter) PRP-14 bermuda Not to scale

  5. Plant and Soil Data • Calculated average values for replicate analyses of soils and plants. • Excluded questionable analyses. • Calculated “whole soil” compositions from bulk soil and soil plant fragment analyses: whole soil % C = (bulk soil wt * bulk soil %C) + (plant wt * plant %C) bulk soil wt + plant wt whole soil % N = (bulk soil wt * bulk soil %N) + (plant wt * plant %N) bulk soil wt + plant wt

  6. “Corrected” Soil Compositions • Correction for plant fragments picked out changed whole soil composition little. • Plant fragments were only 0.03 – 1.16 % of total sample weight.

  7. Average Soil % C • Bulk soil range was 0.73 - 4.16 % C • Plant fragments range was 18.71 – 41.58 % C • Whole soil range was 0.75 – 4.16 % C

  8. Average Soil % N • Bulk soil range was 0.05 – 0.36 % N • Plant fragments range was 0.56 – 1.93 % N • Whole soil range was 0.05 – 0.36 % N

  9. Transect – NE side of plot Forbs Grasses Horsenettle (C3) Ragweed (C3) Bermuda (C4) Fescue (C3) 43.53 %C 1.79 %N 42.85 %C 3.08 %N 43.56 %C 1.39 %N 46.00 %C 1.73 %N TOTAL 48.27 %C 2.59 %N 40.61 %C 2.57 %N 43.00 %C 1.51 %N 44.98 %C 2.18 %N LEAF 40.19 %C 1.54 %N 41.86 %C 2.17 %N 43.23 %C 1.44 %N 48.06 %C 0.83 %N ROOT PRS-15: 1.90 %C, 0.14 %N PRS-16: 2.35 %C, 0.19 %N PRS-17: 0.82 %C, 0.06 %N PRS-18: 0.75 %C, 0.05 %N PRS-7 3.97 %C 0.36 %N PRS-5 4.16 %C 0.36 %N All soils: 2.32 %C, 0.19 %N NOT TO SCALE

  10. Sample Plot N PRS-15: 1.90 %C, 0.14 %N PRS-16: 2.35 %C, 0.19 %N PRS-17: 0.82 %C, 0.06 %N PRS-18: 0.75 %C, 0.05 %N Fescue C3 PRS-5 4.16 %C 0.36 %N Bermuda C4 Horsenettle C3 Fescue C3 Ragweed C3 Bermuda C4 PRS-7 3.97 %C 0.36 %N Ragweed C3 Bermuda C4 Not to scale

  11. Conclusions • Highest %C and %N in surface soil where bermuda (C4 grass) was dominant • Lower %C and %N in surface soil near forbs (C3) • Lowest %C and %N in soil “pit” beneath large bunch of fescue (C3 grass) • %C pattern consistent with hypothesis, but %N is not

  12. My issues with this data… • Sample depths • Sample distribution in plot • Soil treatments were not the same • Did not get a good density separation • Did not perform grain size analysis • C and N concentrations may be related to percent clay content (Hughes et al., 2002)

  13. References • Knops, J.M.H., and D. Tilman. 2000. Dynamics of soil nitrogen and carbon accumulation for 61 years after agricultural abandonment. Ecology, Vol. 81 (1), pp. 88-98. • Hughes, R.F., J.B. Knuffman, and D.L. Cummings. 2002. Dynamics of aboveground and soil carbon and nitrogen stocks and cycling of available nitrogen along a land-use gradient in Rondonia, Brazil. Ecosystems, Vol. 5, pp. 244-259.

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