Soil Organic Carbon and Nitrogen Accumulation of Rhizoma Perennial Peanut and Bahiagrass Grown under Elevated CO2 and Temperature

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Soil Organic Carbon and Nitrogen Accumulation of
Rhizoma Perennial Peanut and Bahiagrass Grown
under Elevated CO2 and Temperature
Leon H. Allen,ARS-FL Stephan L. Albrecht,ARS-OR
Kenneth J. Boote,UF Jean M.G. Thomas,UF and
Katherine Skirvin ARS-OR USDA-ARS and University
of Florida
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Introduction

• More work has been done on carbon accumulation in
  forests and natural grasslands than in managed
  grasslands, especially in the Southeastern USA

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Hypotheses

• 1. Shift from cultivated land to forage crops
  will increase soil organic carbon (SOC) and
  nitrogen (SON).
• 2. Accumulation of SOC and SON will be enhanced
  by elevated CO2 and diminished by elevated
  temperatures.
• 3. Forage species will affect SOC and SON
  responses.

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Objectives

• Measure SOC and SON accumulation of two
  contrasting perennial forage species, rhizoma
  perennial peanut (PP), C3 legume, and bahiagrass
  (BG), C4 grass to test hypotheses.

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Materials and Methods-1

• Two forage crops
• Rhizoma perennial peanut (Arachis glabrata)
• Bahiagrass (Paspalum notatum)
• Four temperatures tracking ambient
• Baseline, 1.5, 3.0, and 4.5C
• Approx 1.5, 3.0,4.5, 6.0 C above ambient
• Two CO2 concentrations, 360 and 700 ppm

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Materials and Methods-2

• In April 1995, plants established in field soil
  in Temperature-Gradient Greenhouse (TGG)
• Fertilized and irrigated well

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Materials and Methods-3

• Temperature gradients of 4.5 Celsius were
  maintained with variable speed ventilation fans
  and on-off heaters.
• CO2 was controlled with injection of gas and
  measurement of concentrations down wind in the
  TGGs for feedback control.

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CONTROLLED VENTILLATION FAN
BG
PP
CELL 4 WARM
B 4.5C
PP
BG
B 3.0C
CELL 3
PP
BG
PLOTS ARE 5 m x 2 m
B 1.5C
CELL 2
PP
BG
AIR FLOW DIRECTION
Baseline, B
CELL 1 BASELINE AMBIENT
AIR INTAKE
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Materials and Methods-4

• Herbage was harvested four times each year
  (Boote et al., 1999 Fritschi et al., 1999a,
  1999b Newman et al., 2001, 2005).
• In 1996 and 1997, measurements of biomass of
  belowground components were made.

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Materials and Methods-5

• Four replicated soil samples were collected from
  the top 20 cm of each plot in Feb. 1995 and each
  year thereafter.
• Soil samples were dried and plant fragments were
  separated using a 2.2-mm sieve.

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Materials and Methods-6

• Total C and N were determined at Pendleton Oregon
  with a Thermo-Finnigan Flash EA 1112 CNS analyzer
  at 1800 Celsius

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Materials and Methods-7

• Data from the beginning and the end of the
  experiment analyzed by SAS ANOVA to determine
  overall effects of conversion from cropped land
  to forages on SOC and SON.
• Differences of SOC and SON between final and
  initial years were analyzed by SAS ANOVA to
  determine the effects of CO2, temperature, and
  forage species on 6-year increments of SOC and
  SON

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Results and Conclusions
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1. Overall Effect of Forage on SOC and SON
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Overall Effect of Forage on SOC and SONAcross
the whole 6-year period

• Overall SOC increased 1.08 g/kg (26)
• Overall SON increased 0.095 g/kg (34)
• Hypothesis that conversion from cultivated land
  to forages will enhance SOC and SON is supported

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2. Species Effect on Increase of SOC and SON
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Species Effect on Increase of SOC and SON

• SOC increased by 0.75 g/kg for PP
• SOC increased by 1.40 g/kg for BG
• BG/PP ratio 1.87 for SOC
• BG/PP ratio 1.46 for SON
• Conclusion Growth of BG promotes more SOC
  accumulation than PP, but with relatively less
  SON accumulation ltgt

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3. CO2 Effect on Increase of SOC and SON
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CO2 Effect on Increase of SOC and SON

• SOC increase 0.94 g/kg for 360 ppm
• SOC increase 1.20 g/kg for 700 ppm
• SON increase 0.084 g/kg for 360 ppm
• SON increase 0.112 g/kg for 700 ppm

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CO2 Effect on Increase of SOC and SON

• 700/330 ratio 1.27 for SOC
• 700/330 ratio 1.13 for SON
• Conclusion Elevated CO2 promotes relatively
  more SOC accumulation than SON

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4. Temperature Effect on Increase of SOC and SON
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Temperature Effect on Increase of SOC and SON

• SOC increased 1.12, 1.21, 0.97, and 0.92 g/kg at
  the increasing temperatures
• SON increased 0.104, 0.106, 0.087, and 0.079 g/kg
  at the increasing temperatures
• Conclusion Accumulation of SOC and SON
  decreases with increasing temperature only at 1.5
  to 3 Celsius above Gainesville ambient ltgt

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5. Species X CO2 Interaction on Increase of SOC
and SON
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Species X CO2 Interaction on Increase of SOC and
SON

• SOC increase 0.54 g/kg for PP at 360
• SOC increase 0.95 g/kg for PP at 700
• SOC increase 1.34 g/kg for BG at 360
• SOC increase 1.45 g/kg for BG at 700
• Conclusion 1 Increase of SOC was greater for
  BG than PP

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Species X CO2 Interaction on Increase of SOC and
SON

• SOC ratio of PP 700/360 1.74
• SOC ratio of BG 700/360 1.10
• Conclusion 2 Elevated CO2 caused much greater
  increase of SOC for PP than BG

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Species X CO2 Interaction on Increase of SOC and
SON

• SON increase 0.0655 g/kg for PP at 360
• SON increase 0.0875 g/kg for PP at 700
• SON increase 0.112 g/kg for BG at 360
• SON increase 0.112 g/kg for BG at 700
• Conclusion 1 Increase of SON was somewhat
  greater for BG than PP

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Species X CO2 Interaction on Increase of SOC and
SON

• SON ratio of PP 700/360 1.34
• SON ratio of BG 700/360 1.00
• Conclusion 2 Elevated CO2 caused no increase
  of SON for BG
• Conclusion 3 Elevated CO2 caused less increase
  of SON than of SOC for PP

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Comparisons of Belowground Biomass with SOC
Accumulation
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BELOWGROUND BIOMASS of PP and BG vs.
CO2 ----------------------------------------------
--------------------------------------------------
--------- VARIABLE PERENNIAL PEANUT
BAHIAGRASS 360 ppm 700 ppm 360 ppm
700 ppm ------------------------------------------
--------------------------------------------------
------------- - - - - - - - - - - - - - -
Biomass, g m-2 - - - - - - - - - - - - - Rhizome
or Stolon 1996 697 893
1066 1178 1997 1097
1326 1537 1727 Root 1996
73 71 622 593
1997 100 86 692
674 Total belowground 1996 770
964 (1.25) 1688 1771 (1.05)
1997 1197 1412 (1.18) 2229
2401 (1.08) Belowground ratio, BG/PP, at
360 and 700 ppm 1996
2.19 1.84 1997
1.86 1.70 -----------------------------
--------------------------------------------------
-------------------------- Adapted from Boote et
al. (1999). Data in parenthesis are 700/360
ratios.
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ANNUAL HERBAGE YIELD of PP and BG vs.
CO2 ----------------------------------------------
--------------------------------------------------
------------- VARIABLE PERENNIAL PEANUT
BAHIAGRASS 360 PPM 700 PPM 360 PPM 700
PPM ----------------------------------------------
--------------------------------------------------
------------- - - - - - - - - - - - - - -
Biomass, g m-2 - - - - - - - - - - - - - Total
herbage biomass 1996 1320 1680
(1.27) 880 1020 (1.16) 1997
1460 1870 (1.28) 740 910
(1.23) 1998 1850 2280 (1.23)
710 780 (1.10) Ratio, BG/PP, at 360
and 700 ppm 1996 0.67 0.61
1997 0.51 0.50 1998
0.38 0.34 --------------------------------
--------------------------------------------------
-------------- Adapted from Boote et al. (1999)
and Newman et al. (2001). Data in parenthesis are
700/360 ratios.
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Comparisons of Belowground Biomass with SOC
Accumulation

• Herbage Yields were greater for PP than for BG.
• However, both belowground biomass and SOC
  accumulation were greater for BG than for PP.

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Conclusions

• Conversion of cultivated land to forage crops
  could sequester more SOC.
• BG has the potential to sequester more carbon
  than PP.
• C/N ratio appears to be higher in BG than PP
• PP, a C3 legume, responds more to CO2 than BG in
  SOC accumulation and herbage yield.

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Comparisons with other data

• SOC accumulation 540 kg/ha per year
• Without CO2 effect 425 kg/ha per year
• Albrecht (1938) 380 kg/ha per year
• Potter et al. (1999) 450 kg/ha year
• Allen Nelson 370 kg/ha per year for PP, which
  is lower than for grasslands.

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END