Soil Organic Matter

Soil property comparisons in long-term grazed and ungrazed rangeland in the Southern Great Plains

W. R. Teague, J. K. Foy and S. L. Dowhower, TAES-Vernon; and
C. A. Cambardella, National Soil Tilth Laboratory , ARS, Ames, Iowa

Soil organic carbon is extremely important in range ecosystems since it significantly improves soil texture, enhances infiltration, soil water availability, soil water retention and soil fertility. The degree to which these properties are enhanced with increasing soil organic carbon differs according to soil texture (Bowman et al. 1990; Bauer and Black 1992). Research in northern Great Plains rangelands indicates that grazing over long periods has reduced soil organic carbon in range soils relative to relict grassland sites (Bauer et al. 1987). The effects of frequent fire have also been shown to decrease soil organic carbon (Ojima et al. 1990). Simulations using the CENTURY model (Seastedt et al. 1994) indicate that the management inputs of burning and grazing are by far the most important factors influencing soil organic carbon values. Predictions over a period of 100 years are that; with no burning or grazing, soil organic carbon would increase 10-12%; burning every 4 years would maintain soil organic carbon; and light grazing would slightly increase soil organic carbon. Annual burning or heavier grazing would decrease soil organic carbon about 15% over the same time period. The SPUR model (Foy 1993; Foy et al. 1997, 2 manuscripts in prep) gives similar predictions following grazing.

This project was funded, but soil sampling was delayed by the 1995-1996 drought. Bob Cross and Jan Worrall began sampling these soils in March 1997. Soil sampling was completed in the summer of 1997 with grateful help from Cody Bradley and Diane Conover. Diane Conover completed soil texture analysis and pH determinations in January 1998. C and N analyses were completed by C. Cambardella's lab in Ames, Iowa, in early 1998. Some preliminary results are presented below. All values are in grams per meter squared (unless otherwise indicated).

STOCKING RATE

%clay

%silt

pH

BD

TotalC

TotalN

SlowC

SlowN
Exclosures

35.6

27.3

8.07

1.39

3169

320

1898

182
Moderate continuous

33.6

33.6

7.80

1.40

2805

286

1017

95
Heavy continuous

32.4

32.4

7.51

1.41

3310

282

2075

170
Teague, W. R., Foy, J. K., Dowhower, S., & Cambardella, C. A. (1997). Soil property comparisons in long-term grazed and ungrazed rangeland in the Southern Great Plains--preliminary results. Retrieved from http://juniper.tamu.edu/IRM/rangecol/Som.htm

Long-term changes in soil carbon, nitrogen and bulk density in root-plowed mesquite rangeland

Cross, B. T., W. R. Teague, and J. K. Foy, TAES-Vernon

This project was completed in early 1998. %C and %N was analyzed by the combustion method (Carlo-Erba) at Tom Boutton's lab in College Station. The completed results are presented below.

Comparison of Native and Root-Plowed Soils since time of treatment
TIME TREATMENT %clay %silt pH BD %C %N C/N gm-2C
22 years Native 30.3

39.0

6.72

1.27

0.836

0.0858

9.75

2167
Plowed

25.8

43.4

6.38

1.23

0.858

0.0862

9.98

2150
16 years Native

30.0

40.7

6.86

1.30

1.03

0.0992

10.4

2697
Plowed

30.9

39.3

7.08

1.26

0.989

0.0952

10.4

2528
11 years Native

30.5

38.7

6.90

1.29

0.996

0.0942

10.6

2616
Plowed

29.0

38.8

7.01

1.28

0.952

0.0898

10.6

2477
9 years Native

31.8

38.7

7.40

1.30

0.989

0.0932

10.6

2611
Plowed

32.0

39.8

7.39

1.31

0.979

0.0932

10.5

2601
4 years Native

31.0

39.7

6.72

1.35

0.963

0.0955

10.1

2632
Plowed

31.4

37.3

7.48

1.37

1.03

0.100

10.3

2861

Cross, B., Teague, W. R., & Foy, J. K. (1997). Long-term changes in soil carbon, nitrogen and bulk density in root-plowed mesquite rangeland--preliminary results. Retrieved from http://juniper.tamu.edu/IRM/rangecol/Som.htm

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Email: r-teague@tamu.edu
 Last modified: August 29, 2002 5:00pm CDT