1
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2
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- 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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3
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- 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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4
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- 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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5
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- Two forage crops
- Rhizoma perennial peanut (Arachis glabrata)
- Bahiagrass (Paspalum notatum)
- Four temperatures tracking ambient
- Baseline, +1.5, +3.0, and +4.5°C
- Approx +1.5, +3.0,+4.5, +6.0 °C above ambient
- Two CO2 concentrations, 360 and 700 ppm
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6
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- In April 1995, plants established in field soil in Temperature-Gradient Greenhouse
(TGG)
- Fertilized and irrigated well
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7
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- 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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8
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9
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10
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- 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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11
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- 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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12
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- 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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13
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- 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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14
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15
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16
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17
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18
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- 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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19
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20
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21
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22
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- 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
<&>
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23
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24
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25
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26
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- 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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27
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- 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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28
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29
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30
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31
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- 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 <&>
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32
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33
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34
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- 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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35
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- 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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36
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37
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- 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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38
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- 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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39
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40
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41
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42
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- 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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43
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- 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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44
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- 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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45
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