An Unintentional Experiment in Soil Genesis: the Lysimeter Soils at the San Dimas Experimental Forest Soil Genesis Studies S = f (cl,o,r,p,t) S: cl: o: r: p: t: soil formation climate organisms relief parent material time Hans Jenny Soil Genesis Study: Biosequence S = f (organisms)cl,r,p,t Vegetation monocultures Soil Genesis Study: Biosequence S = f (organisms)cl,r,p,t Confined lysimeters 1987 Unconfined lysimeters 17 m x 24 m Soil Genesis Study: Biosequence S = f (organisms)cl,r,p,t cl: r: p: t: o: mesic, xeric (MAP = 710 mm) toeslope (5% slope, south facing) diorite-derived material time 0 = 1946 Quercus dumosa (“oak”) or Pinus coulteri (“pine”) 1934 5.3 m x 5.3 m x 2.1 m 1937 ~1937 ~1937 1937 Lysimeter fill material (“p”) Samples archived in 1937 Fine sandy loam 7.5 YR 4/4 moist San Dimas Lysimeters Chronology 1934 Construction begins 1937 Lysimeters filled 1946 Wildland species planted; Time = 0 yrs 1987 Soils sampled for Graham (1991, 1995), Tice (1995), Ulrey (1995), Quideau (1998); Time = 41 yrs 1996 Soils sampled for Johnson-Maynard (2002, 2004), Quideau (2000,2001, 2003); Time = 50 yrs 1940 1946: Time = 0 1987: Time = 41 years 1987 Oi Oe A Oi A BAt AC Bt OAK PINE Typic Xerorthent Horizon Depth (cm) Oi 7-0 A 0 – 7.5 AC C Horizon Depth (cm) Oi to Oe 10 - 0 10 YR 3/3 A 0-1 10 YR 4/3 7.5 - 20 7.5 YR 4/4 BAt 1 – 10 7.5 YR 4/4 20 - 65 7.5 YR 4/4 Bt 10 – 20 7.5 YR 4/4 C 35 - 65 7.5 YR 4/4 Parent Material Moist Color Typic Haploxeralf 7.5 YR 4/4 Moist Color 7.5 YR 4/4 Oi Oe A Oi A BAt AC Bt OAK 300 earthworms m-2 PINE no earthworms Oi Oe A Oi A BAt AC Bt OAK 300 earthworms m-2 PINE no earthworms Oi Oe A Oi A BAt AC OAK OC, g kg-1 Depth, cm Bt PINE Oi Oe A Oi A BAt AC OAK Clay, % Bt PINE A A Bt Depth, cm AC C C Initial Conclusions • Biotic factor determines direction and rate of soil formation • Biotic factor = plants + animals • Earthworms impact: – Clay distribution – Biocycling – Clay mineralogy – Organic matter decomposition Lysimeter fill material archived 1937 1987: Time = 41 years • Soils sampled in 1937. • Litter and A horizon material sampled in 1987. • 14C content measured in the 1937 and 1987 samples by Accelerator Mass Spectrometry. 14CO 2 “Bomb” 14C is used as a tracer for organic carbon cycling as long as pre-1960’s archived soils exist Measured litter fall (g m-2 yr-1) 1997-1998 225 135 Oi Oe A Oi A BAt AC OAK Bt PINE Measured litter fall (g m-2 yr-1) 1997-1998 225 135 Oi 226 A 12.7 BAt AC OAK Oi Oe A Bt PINE Estimated carbon inputs from leaves and roots into soil A horizon (g m-2 yr-1 ) No earthworms 300 earthworms m-2 OAK 1.8 Oi 12.5 A 1.9 – 3.7 Oi 33 Oe A 25 AC Bt BAt PINE Estimated turnover rates of organic C (years) Conclusion: “…the model results demonstrate distinctly different SOM dynamics under different tree species which implies that similar differences exist among shrubs and herbs” San Dimas Lysimeters Soils Research Paul Zinke Hutch Wood Bob Graham Oliver Chadwick Kathy Rose Jodi Johnson-Maynard April Ulery Sylvie Quideau Paul Hendrix Louise Egerton-Warburton Paul Sternberg Pete Shouse Jack Jobes Xiahong Feng • USFS Pacific Southwest Experiment Station Mike Oxford, Pete Wohlgemuth, Dave Larson • National Science Foundation • Kearney Foundation of Soil Science • National Commision on Science for Sustainable Forestry OAK pH Depth, cm PINE