Grazing Intensity Research in the Missouri Coteau of North Dakota


Forage Production and Utilization Treatment Effects

 

The first year in which the amount of forage produced under the various grazing treatments was significantly different was 1992 on silty range sites and 1993 on overflow range sites. Table 6 gives the average forage production by treatment on silty range sites at the beginning of the grazing season, mid-season, peak of the season and end of the season for the period from 1992 to 2001. Table 7 gives the same information for overflow range sites averaged over the period from 1993 to 2001. For both range sites the extreme grazing treatment produces the least forage. However the ungrazed treatment is not the most productive, although it is only slightly less productive than the light treatment on the silty range site at the beginning of the grazing season. The light treatment is the most productive on silty range sites. There is little difference between light, moderate and heavy treatments on overflow range site but moderate tends to be the most productive. There is no year X treatment interaction between treatments on overflow range sites. That means the effect of grazing intensity on forage production is consistent across all of these years. However there is year X treatment interaction on silty range sites at the beginning and end of the grazing season. This indicates that the weather for the year, or the previous year may affect which grazing treatment produces the most forage. At the beginning of the grazing season the most productive site varied between the ungrazed, light and moderate treatments with the extreme or heavy always being least productive. At the end of the season the light or moderate was most productive and the extreme or heavy was least productive although ungrazed produced the least in 1994. Although there were no significant differences in biomass production in 1991 the fact that there were differences at the beginning of the 1992 grazing season indicates that grazing must have reduced the amount of carbohydrate reserves that the plants were able to carry over to the next season. Part of the variability in production on the ungrazed treatment may be the result of litter buildup that can prevent rainfall and sunlight from reaching the ground. In 1992 and 1993 the ungrazed treatment produced the most forage on silty range sites and production decreased as grazing intensity increased. Annual rainfall in 1993 was the second highest of any year during this study and the greatest forage production on silty range sites occurred during that year (see table 2). The buildup of litter in that year may have been the factor that caused the ungrazed treatment to be the least productive treatment in 1994.

 

Table 6. Average above ground biomass production by grazing treatment on silty range sites from 1992 to 2001.

 

Above ground biomass (lbs/acre)

Treatment

Beginning

of season

Middle of

season

Total

yield

End of

season

Ungrazed

Light

Moderate

Heavy

Extreme

LSD(0.05)

1,396 a1

 1,467 a

1,289 b

  928 c

  751 d

105

2,571 b

 2,944 a

  2,615 b

 2,237 c

 1,825 d

204

2,836 b

3,365 a

3,055 b

2,514 c

2,229 d

268

2,617 b

  3,188 a

2,906 a

  2,399 bc

2,205 c

284

1Means in the same column followed by the same letter are not significantly different at P=0.05.


 

Table 7. Average above ground biomass production by grazing treatment on overflow range sites 

from 1993 to 2001.

 

Above ground biomass (lbs/acre)

Treatment

Beginning

of season

Middle of

season

Total

yield

End of

season

Ungrazed

Light

Moderate

Heavy

Extreme

LSD(0.05)

1,121 b1

1,206 ab

1,333 a

1,300 a

   893 c

128

3,349 b

4,131 a

4,055 a

3,967 a

2,421 c

387

3,416 b

4,390 a

4,584 a

4,327 a

2,922 c

401

2,784 b

4,030 a

  4,384 a

4,286 a

2,846 b

425

1Means in the same column followed by the same letter are not significantly different at P=0.05.


Soil Water and Forage Production

 

Soil water has been sampled bi-monthly throughout the growing season on each of the vegetation monitoring sites and differences in available water have developed between the different grazing treatments. On overflow range sites, lightly grazed pastures have more available water than heavily grazed pastures. The differences in available water occur during both soil water recharge and discharge. This indicates that on heavily grazed sites more water runs off during a rain and sunlight evaporates more water from the soil surface. On silty range sites, moderately grazed pastures have more available water than ungrazed or heavily grazed pastures. The ungrazed treatment has less available water because the plants on that treatment have more leaf area than the grazed plants, and more water is removed from the soil by transpiration.

 

Forage Quality


The nutritional quality of the forage was sampled at the middle of the grazing season each year for the first 10 years of the study. The average forage quality by treatment is shown in table 8. On silty range sites the grasses have higher crude protein and digestibility and lower fiber components at the higher grazing intensities. On the heavily grazed treatments the grass that is available for grazing is mostly regrowth that is of higher quality. However on overflow sites both grasses and forbs are highest in fiber components on the heavy grazing treatment. Perhaps on these sites cattle are selecting species of higher quality and leaving those that are higher in fiber. On silty sites forbs are highest in neutral detergent fiber on the ungrazed and extreme grazing treatments. As the ungrazed forage matures on the ungrazed treatment it becomes higher in fiber. On the heavily grazed treatments only forbs of lower quality would remain ungrazed. These differences in nutritional quality have occurred gradually over the course of the study.


Table 8. Average nutritional quality of forage on the grazing intensity trial 1989-1998.

Treatment

Crude

Protein

 (%)

In Vitro

Dry Matter 

Digestibility

   (%)

Acid

Detergent

Lignin

 (%)

Acid

Detergent

Fiber

 (%)

Neutral

Detergent

Fiber

 (%)

Overflow sites—forbs

None

Light

Moderate

Heavy

Extreme

  9.17 c1

  8.80 c

  9.13 c

10.42 a

  9.87 b

61.86

60.53

61.74

59.99

60.14

6.80 c

7.52 ab

7.31 abc

7.81 a

7.23 bc

35.98

38.08

37.67

37.19

36.82

43.06 b

44.85 ab

44.79 ab

46.40 a

44.64 ab

Overflow sites—grasses

None

Light

Moderate

Heavy

Extreme

 6.57 d

 7.03 bc

 6.73 cd

 7.29 ab

 7.57 a

50.65

51.38

50.63

49.91

52.12

4.67

4.42

4.58

4.61

4.57

42.56 b

42.80 ab

43.02 ab

43.85 a

41.01 c

67.03 c

67.69 bc

68.46 ab

69.37 a

68.85 ab

Silty sites–forbs

None

Light

Moderate

Heavy

Extreme

10.40

10.75

10.88

10.79

10.76

59.22 b

61.94 a

60.48 ab

60.33 ab

62.00 a

7.80

7.35

7.41

7.73

7.31

36.58 a

36.15 ab

34.43 c

34.97 bc

33.86 c

50.01 a

45.40 b

44.85 b

45.42 b

48.70 a

Silty sites–grasses

None

Light

Moderate

Heavy

Extreme

7.35 c

7.36 c

7.88 b

8.40 a

8.55 a

49.11 c

46.68 d

50.55 bc

51.14 b

55.86 a

4.17 b

4.64 a

4.19 b

4.24 b

4.04 b

42.84 ab

43.64 a

42.32 b

40.83 c

39.31 d

69.44 bc

72.05 a

71.43 ab

71.48 ab

68.37 c

1Means in the same column followed by the same letter, or no letter, are not significantly different at P=0.05.

                                                                                                                                                                                                                                                 

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