Silveira solutions to new challenges

Challenges and Opportunities for Soil Carbon Sequestration in Grazing land Ecosystems

Maria L. SilveiraAssociate Professor, Soil and Water Science

University of Florida – Range Cattle Research and Education Center

• Globally, grazing lands (rangelands and pasture) cover ~ 3.5 billion ha (26% world land area and 70% world agricultural area). In the USA, rangelands account for ~ 20-23% of total land area, while pasturelands represent ~ 8-11%

• Carbon stored in grazing lands represents 10 to 30% of world’s soil C stocks (Eswaran et al., 1993)

• Increase (or loss) of 1% of SOC sequestered in the top 10 cm of grazing land soils is equivalent to the total US agriculture emissions (Follett, 2001)

Importance

Maria Silveira, Soil and Water Science, UF/IFAS Range Cattle REC

• ~ 60% of the rangeland area in the western USA is degraded

• Significant proportion of grazing land area is being replaced

Limitations



520,000

540,000

560,000

580,000

600,000

620,000

640,000

660,000

680,000

1945 1949 1954 1959 1964 1969 1974 1978 1982 1987 1992 1997 2002 2007

US Grassland Pasture and Range Acres, 48 States, 1945-2007

US 48 StatesAcres in 1,000's

Source: Grassland and other non-forested pasture and range based on National Resources Inventory, USDA, National Resources Conservation Service, 2009

• ~ 60% of the rangeland area in the western USA is degraded

• Significant proportion of grazing land area is being replaced

• The warm climate of the Southeastern USA offers great potential for photosynthetic fixation of C; however, SOC decomposition rates are also high

• Lack of policies to encourage SOC sequestration by agriculture

• Projections of temperature and precipitation across the USA during the next 50 yr anticipate a 1.5 to 2oC warming and slight increase in precipitation (Izaurralde et al., 2011)

Limitations


SOC for improved vs. unimproved pastures, SOC for grassland vs. cultivated fields, SOC for grasslands vs. native vegetation

SOC stocks increased by an average of 31% (4-76%)

Source: Conant et al. (2001)


Fertilization

Improve above- and below-ground production

Change species composition and C input quantity and quality

Climatic regime

Priming effect

N2O emissions and nutrient losses


Long-term SOC responses (0 to 20 cm) to different tall fescue (Festuca arundinacea Schreb.) fertilization strategies1

Fertilization SOC Particulate organic C

__________ g m-2__________

Low fertilization(13.4-1.5-5.6 g N-P-K m-2 yr-1)

3759 b 1393 b

High fertilization(33.6-3.7-13.9 g N-P-K m-2 yr-1)

4034 a 1553 a

1Source: Franzluebbers and Stuedemann (2005).


Fig. 2 Mean SOC and soil N concentration (0-15 cm) as affected by N fertilization and harvest regimen (Billings et al., 2006)

13.5% increase in SOC during a 5-yr period; however, soil C accumulation in response to N fertilization was present in readily available forms


Urea fertilization impact on SOC mineralization in tropical pastures1

Soil Depth Days Control 150 kg N ha-1 Priming Effect

SOC mineralization (CO2-C µg g-1) %0 – 5 cm 1 106 116 +10

2 195 225 +164 396 446 +1314 1469 1570 +728 3136 3225 NS

5 - 10 cm 1 28 40 +432 55 69 +254 149 170 +1414 335 372 +1128 595 658 NS

1Source: Hamer et al. (2009).

Shifts in microbial community towards a higher relative abundance of fungi and Gram-negative

bacteria

Management practices that improve SOC

1. Fertilization

2. Sowing improved grass or legume species


0

10

20

30

40

50

60

70

80

90

100

Rangeland Silvopasture Improved Pasture

Soil

C s

tock

(Mg

ha-1

)

50-100

30-50

20-30

10-20

0-10

b

a

a

Long-term (>25 yr) impacts of grazing land intensification on SOC stocks (0-100 cm)1


1Source: Adewopo, et al., 2014


Management practices that improve SOC

1. Fertilization

2. Sowing improved grass or legume species

3. Grazing management• Positive : Derner et al., (1997); Schuman et al.,

(2001); Franzluebbers and Stuedemann (2003); Franzluebbers et al., (2012)• Negative : Bauer et al. (1987); Derner et al. (1997); April and Bucher (1999); Conant and Paustian (2002) • Neutral: Milchunas and Laurenroth (1993); Manley et al., (2005)


SOC stocks for soils from exclosed (EX), continuously, light grazed (CL), and continuously, heavy grazed (CH) (1982-2003) northern-mixed rangeland (Ingram et al., 2008)

Soil Depth (cm) EX CL CH_____________ SOC (Mg ha-1) _____________

0-5 10.8 b 13.8 a 10.9 a5-15 16.5 18.1 15.1 NS

15-30 20.0 a 22.2 a 16.6 b30-60 33.2 38.3 28.0 NS

0-15 27.3 b 32.0 a 26.0 b0-30 47.3 b 54.2 a 42.5 b0-60 80.5 b 92.5 a 70.5 b

CL = 0.16 to 0.23 steers ha-1 (~35% below recommended by NRCS); CH = 0.56 steers ha-1 (~ 33% above recommended stocking rate).


SOC stocks for soils from exclosed (EX), continuously, light grazed (CL), and continuously, heavy grazed (CH) (1982-2003) northern-mixed rangeland (Ingram et al., 2008)

Soil Depth (cm)

EX CL CH

_____________ SOC (Mg ha-1) _____________

0-5 10.8 b 13.8 a 10.9 a

5-15 16.5 18.1 15.1 NS

15-30 20.0 a 22.2 a 16.6 b

30-60 33.2 38.3 28.0 NS

0-15 27.3 b 32.0 a 26.0 b

0-30 47.3 b 54.2 a 42.5 b

0-60 80.5 b 92.5 a 70.5 b

Total above-ground biomass (kg ha-1)

1138 1188 960

C3-grasses (%) 62 64 33

C4-grasses (%) 4 11 42

Stubble Height†

Total C Total N Particulate C Litter OM mass

Lignin/N

cm --------------- Mg ha-1 -------------- % total kg ha-1

24 26 1.7 10.4 34 2510 7.8

16 23 1.5 8.6 29 2370 8.2

8 24 1.5 8.3 27 1725 9.2

SE 3 0.2 1.1 2.6 70 0.4

Polynomial Contrast

NS‡ NS L* L* L** L*

Total C and N content in bulk soil samples from pastures under different stocking densities (Liu et al., 2011; Silveira et al., 2013)

†Stocking density treatments were based on target stubble height. ‡NS = not significant ( P > 0.1). L =linear; * = P 0.05


Conclusions

• Grazing land intensification generally results in greater SOC stocks; however, these management practices need to be examined holistically, and take into consideration their impacts on the overall ecosystem services

• The direction and magnitude of SOC responses to management depend on the duration and intensity of these practices, region, and current SOC levels


THANKS

Maria L. SilveiraEmail: [email protected]

Phone: (863) 735-1314

Silveira solutions to new challenges

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