**3. Measured impacts of grazing systems**

#### **3.1. Forage utilization**

#### *3.1.1. Mob grazing*

Pre-graze forage coverage averaged 85% (grass and forb) in 2013 and neared 100% in 2014. In 2013, pre-graze forage biomass was estimated to be 2910 (±816) kg ha−1 with the clipped method and 2720 kg ha−1 with the grazing stick. These measurements were statistically similar. Pre-grazing biomass in 2014 averaged 4640 kg ha−1, the grazing stick method estimated 3980 kg ha−1, with estimates statistically similar. The discrepancy between direct biomass sampling and grazing stick can be partially explained by sampling method, as forage was cut to within 1 cm of soil level, but the grazing stick calculation subtracts 7.6 cm from forage height to account for unconsumed stubble. Whereas the clipping method provided excellent data, the process was labor intensive, slow, and required preweighing, drying, and postweighing. In addition, it was found that after mob grazing there was no biomass to clip. The grazing stick method provided a reasonable estimate of available forage.

pre- and post-graze forage was 4530 and 2610 kg ha−1, respectively, which indicated that forage consumption neared 57%. As in the rotational area, there was little newly trampled litter.

Mob vs. Rotational Grazing: Impact on Forage Use and *Artemisia absinthium*

http://dx.doi.org/10.5772/intechopen.79085

61

The 2014 rotational pasture was grazed in April, which allowed recovery during the summer/ fall of 2014. Forage after grazing was 870 kg ha−1. The rancher follows the 'take half, leave half' utilization recommendation [12, 13], so a reasonable pre-graze forage estimate would have been about 1300 kg ha−1. Grass forage increased from 11 (May) to 23 (September) cm in height

A pre-grazing assessment of *Artemisia absinthium* was conducted with the volume of the patch related to its dry biomass by recording patch volume and comparing with clipped dried biomass. In mid-June of 2013, 30 *Artemisia absinthium* patches were quantified for volume, plants clipped, and dry biomass determined before grazing. Regression analysis of biomass (expressed as log biomass +1) on plant volume (expressed as log plant volume + 1) for these 30 patches resulted in the equation: log (biomass+1) = 1.35 log (volume + 1) − 5.89, [23] which implies a direct increase in biomass as patch volume increased. This regression fit the data very well (r2 = 0.90; *P* < 0.001), and was intended to be used to express differences in *Artemisia absinthium* biomass pre- and postgrazing. However, trampling dramatically increased *Artemisia absinthium* plant volume, as the shoots spread apart, in the mob-grazed areas (**Figure 3**) but because the samplings were within a few days of each other, it would not have been possible to increase biomass as the equation suggests. Therefore, data are presented and discussed in terms of plant volume, rather than biomass.

Matched-pair analysis of 2013 and 2014 combined indicated that about 65% of the *Artemisia absinthium* patches had less volume after mob grazing (**Table 3**). In 2013 the decrease averaged 75%, whereas in 2014, the decrease was about 20%. In 2014, grass surrounding the *Artemisia absinthium* patches had 60% of the forage consumed. Therefore, it appeared that cattle were grazing close to,

**Figure 3.** Example of the impact of mob grazing on a single *Artemisia absinthium* plant (pre and post grazing).

(*P* < 0.001) with fall forage biomass estimated at 2090 kg ha−1.

**3.2. Grazing impact on** *Artemisia absinthium*

*3.2.1. Mob grazing*

In 2013, mob grazing forage utilization was about 80% (**Table 2**; **Figure 2**) with a harvest efficiency (amount consumed) of 62% (~1800 kg ha−1). The remaining 20% of the vegetation was trampled. In 2014, the same stocking rate (125 cow-calf pairs) was used, but the area was two times larger, had about 1.5 times greater pre-graze biomass, and grazing time was doubled from 12 to 24 h. Forage utilization in 2014 was 75%, similar to 2013. The amount consumed was 1600 kg ha−1, similar to the amount consumed in 2013, but due to the greater starting biomass, the harvest efficiency (percent consumed) was 34%, and the trampled amount was 40%.

#### *3.1.2. Rotational grazing*

In 2013, pre-graze forage amount averaged 2600 kg ha−1 and post-graze was 1190 kg ha−1 (**Table 2**). Both harvest efficiency (amount consumed) and utilization (amount consumed + trampled) were 45%, as new trampled litter was not observed. In the rotational/spray treatment,

**Figure 2.** Pre-graze forage and post-graze results, the impact of mob grazing.

pre- and post-graze forage was 4530 and 2610 kg ha−1, respectively, which indicated that forage consumption neared 57%. As in the rotational area, there was little newly trampled litter.

The 2014 rotational pasture was grazed in April, which allowed recovery during the summer/ fall of 2014. Forage after grazing was 870 kg ha−1. The rancher follows the 'take half, leave half' utilization recommendation [12, 13], so a reasonable pre-graze forage estimate would have been about 1300 kg ha−1. Grass forage increased from 11 (May) to 23 (September) cm in height (*P* < 0.001) with fall forage biomass estimated at 2090 kg ha−1.

## **3.2. Grazing impact on** *Artemisia absinthium*

A pre-grazing assessment of *Artemisia absinthium* was conducted with the volume of the patch related to its dry biomass by recording patch volume and comparing with clipped dried biomass. In mid-June of 2013, 30 *Artemisia absinthium* patches were quantified for volume, plants clipped, and dry biomass determined before grazing. Regression analysis of biomass (expressed as log biomass +1) on plant volume (expressed as log plant volume + 1) for these 30 patches resulted in the equation: log (biomass+1) = 1.35 log (volume + 1) − 5.89, [23] which implies a direct increase in biomass as patch volume increased. This regression fit the data very well (r2 = 0.90; *P* < 0.001), and was intended to be used to express differences in *Artemisia absinthium* biomass pre- and postgrazing. However, trampling dramatically increased *Artemisia absinthium* plant volume, as the shoots spread apart, in the mob-grazed areas (**Figure 3**) but because the samplings were within a few days of each other, it would not have been possible to increase biomass as the equation suggests. Therefore, data are presented and discussed in terms of plant volume, rather than biomass.

#### *3.2.1. Mob grazing*

**Figure 2.** Pre-graze forage and post-graze results, the impact of mob grazing.

**3. Measured impacts of grazing systems**

stick method provided a reasonable estimate of available forage.

Pre-graze forage coverage averaged 85% (grass and forb) in 2013 and neared 100% in 2014. In 2013, pre-graze forage biomass was estimated to be 2910 (±816) kg ha−1 with the clipped method and 2720 kg ha−1 with the grazing stick. These measurements were statistically similar. Pre-grazing biomass in 2014 averaged 4640 kg ha−1, the grazing stick method estimated 3980 kg ha−1, with estimates statistically similar. The discrepancy between direct biomass sampling and grazing stick can be partially explained by sampling method, as forage was cut to within 1 cm of soil level, but the grazing stick calculation subtracts 7.6 cm from forage height to account for unconsumed stubble. Whereas the clipping method provided excellent data, the process was labor intensive, slow, and required preweighing, drying, and postweighing. In addition, it was found that after mob grazing there was no biomass to clip. The grazing

In 2013, mob grazing forage utilization was about 80% (**Table 2**; **Figure 2**) with a harvest efficiency (amount consumed) of 62% (~1800 kg ha−1). The remaining 20% of the vegetation was trampled. In 2014, the same stocking rate (125 cow-calf pairs) was used, but the area was two times larger, had about 1.5 times greater pre-graze biomass, and grazing time was doubled from 12 to 24 h. Forage utilization in 2014 was 75%, similar to 2013. The amount consumed was 1600 kg ha−1, similar to the amount consumed in 2013, but due to the greater starting biomass, the harvest efficiency (percent consumed) was 34%, and the trampled amount was 40%.

In 2013, pre-graze forage amount averaged 2600 kg ha−1 and post-graze was 1190 kg ha−1 (**Table 2**). Both harvest efficiency (amount consumed) and utilization (amount consumed + trampled) were 45%, as new trampled litter was not observed. In the rotational/spray treatment,

**3.1. Forage utilization**

*3.1.2. Rotational grazing*

*3.1.1. Mob grazing*

60 Forage Groups

Matched-pair analysis of 2013 and 2014 combined indicated that about 65% of the *Artemisia absinthium* patches had less volume after mob grazing (**Table 3**). In 2013 the decrease averaged 75%, whereas in 2014, the decrease was about 20%. In 2014, grass surrounding the *Artemisia absinthium* patches had 60% of the forage consumed. Therefore, it appeared that cattle were grazing close to,

**Figure 3.** Example of the impact of mob grazing on a single *Artemisia absinthium* plant (pre and post grazing).


When data were combined over both years, 28 of 38 *Artemisia absinthium* patches <19,000 cm3 decreased in volume with reductions ranging from 43 to 84% (data not shown). The other 10 patches in this category increased in volume by about 50%. There were 22 *Artemisia absin-*

ume increase in the other 11 patches averaged 150%. Based on the height of the surrounding forage and *Artemisia absinthium* plant condition, it appears that *Artemisia absinthium* patches

*Artemisia absinthium* plant height also was used to evaluate treatment effects. The average height of 30 *Artemisia absinthium* plants was similar before (average height 39 cm) and after (average height 37 cm) rotational grazing in 2013, which may be considered avoidance. The initial height [tall (>33 cm) vs. short (<33 cm)] did not influence rotational grazing impact. Before grazing, *Artemisia absinthium* plant height in the mob-grazed treatment averaged 58 cm. After mob grazing, 75% (± 9) of the *Artemisia absinthium* plants were 37% shorter, with no plants increasing in height. Even plants that were very tall (>97 cm) were reduced in height by about 50%. These data were consistent with either trampling or consuming. We concluded that animals in the rotation pasture had enough area and forage to selectively avoid *Artemisia absinthium* plants. Spraying 2, 4-D followed by rotational grazing (spray/rotation treatment), however, resulted in a height reduction of 96% of the *Artemisia absinthium*

In 2014, all tagged patches in the 2013 pastures were reevaluated to determine if patches and plants in the patches were still present and the amount of regrowth. Plants in the treated patches of the rotation/spray treatment, which provided excellent control of *Artemisia absinthium* in 2013, had less volume than those originally measured in 2013, but *Artemisia absinthium* plants were still present at the same location as the original patches (data not shown). Rotational grazing, with a 2,4-D application just prior to grazing, helped manage *Artemisia absinthium* plants in the same growing season as the herbicide application as they were no longer visible just after grazing. However, this treatment did not eliminate this perennial weed, as plants regrew the year after this treatment. Plants in the mob-grazed

Rotational grazing for 20 days at 25 cow/calf pairs in 8 ha had comparable results in forage consumption to mob grazing with 125 cow/calf pairs for 12 or 24 h. in 0.65 or 1.3 ha, respectively. There were other differences between the systems, most notably the vegetative growth stage of forage, which was more mature during mob grazing. Trampled vegetation was observed in the mob grazing areas but not the rotational grazing treatments. However, claims about building soil at rates of cm per year, or significantly increasing N and C content (which was measured and reported in Myer [23]), as often discussed in popular press articles [15, 19], could not be substantiated in this study. However, trampled litter and manure patches (measured as manure patches along the transects and reported in Myer [23]) were greater post-mob grazing

and rotational grazed areas were also present and had no observed injury.

compared to both pre-mob and post-rotational grazing.

were consumed with forage, whereas plants in the larger patches were trampled

. Of these, 11 patches had a slight decrease in volume. The vol-

Mob vs. Rotational Grazing: Impact on Forage Use and *Artemisia absinthium*

http://dx.doi.org/10.5772/intechopen.79085

63

*thium* patches >19,000 cm3

<19,000 cm3

and not browsed.

plants (from 54 to 9 cm).

**4. Discussion**

The average pre-graze volume, the number of patches from the initial number that decreased in volume post-graze, and the average volume of the patch remaining. Patches in the mob-grazed pastures were separated into those with an initial volume < or >19,000 cm3 and number that decreased in volume are presented.<sup>a</sup> Numbers in parentheses are confidence intervals based on binomial testing of the number of patches that showed a decrease over the total number with t = 0.1.

**Table 3.** Effect of grazing system on *Atremesia absinthium* average patch volume.

if not directly on, the *Artemisia absinthium* plants. The remaining patches increased in volume by 120% in 2013 and 154% in 2014. This volume increase at first does not seem correct, as pre- and post-grazing samples were taken within days of each other each year. However, the volume increase was due to an increase in patch width (**Figure 3**), and was attributed to trampling.

#### *3.2.2. Rotational grazing*

In 2013, 41% of the *Artemisia absinthium* patches in the rotational paddocks had a 30% decrease in volume and the remaining patches had similar volume pre- and post-grazing. Post-graze forage height of plant near the *Artemisia absinthium* patch averaged 15 cm (33%) shorter than pregrazing measurements (*P* < 0.001), which indicates that *Artemisia absinthium* may have been consumed. In the spray/rotation 2013 pasture, nearly 100% of the *Artemisia absinthium* patches decreased in volume by 100% after grazing (**Table 3**). Grass surrounding the *Artemisia absinthium* patches was 51% shorter (*P* < 0.001) post- grazing, which strongly suggests that plants in the sprayed patches were consumed with forage.

In 2014, with no grazing pressure during the summer season, only 1 (3%) of the *Artemisia absinthium* patches decreased in volume. The remainder had a volume increase of 5000% from May (average volume = 2850 cm3 ) to September (average volume = 151,200 cm3 ). In addition, the average height increased from 15 (May) to 86 cm (September). Because there was no trampling and an increase in shoot height, this increase can be attributed to plant growth.

#### *3.2.3. Influence of initial Artemisia absinthium patch volume on grazing system impact*

Initial *Artemisia absinthium* patch volume in the rotation and rotation/spray areas did not influence final volume. All *Artemisia absinthium* size categories in the rotationally grazed areas had about 50% of the patches increase and 50% decrease in volume. All *Artemisia absinthium* patches in the rotation/spray treatment were reduced to near 0, irrespective of initial plant volume. Initial *Artemisia absinthium* patch volume in mob-grazed areas influenced final *Artemisia absinthium* volume.

When data were combined over both years, 28 of 38 *Artemisia absinthium* patches <19,000 cm3 decreased in volume with reductions ranging from 43 to 84% (data not shown). The other 10 patches in this category increased in volume by about 50%. There were 22 *Artemisia absinthium* patches >19,000 cm3 . Of these, 11 patches had a slight decrease in volume. The volume increase in the other 11 patches averaged 150%. Based on the height of the surrounding forage and *Artemisia absinthium* plant condition, it appears that *Artemisia absinthium* patches <19,000 cm3 were consumed with forage, whereas plants in the larger patches were trampled and not browsed.

*Artemisia absinthium* plant height also was used to evaluate treatment effects. The average height of 30 *Artemisia absinthium* plants was similar before (average height 39 cm) and after (average height 37 cm) rotational grazing in 2013, which may be considered avoidance. The initial height [tall (>33 cm) vs. short (<33 cm)] did not influence rotational grazing impact. Before grazing, *Artemisia absinthium* plant height in the mob-grazed treatment averaged 58 cm. After mob grazing, 75% (± 9) of the *Artemisia absinthium* plants were 37% shorter, with no plants increasing in height. Even plants that were very tall (>97 cm) were reduced in height by about 50%. These data were consistent with either trampling or consuming. We concluded that animals in the rotation pasture had enough area and forage to selectively avoid *Artemisia absinthium* plants. Spraying 2, 4-D followed by rotational grazing (spray/rotation treatment), however, resulted in a height reduction of 96% of the *Artemisia absinthium* plants (from 54 to 9 cm).

In 2014, all tagged patches in the 2013 pastures were reevaluated to determine if patches and plants in the patches were still present and the amount of regrowth. Plants in the treated patches of the rotation/spray treatment, which provided excellent control of *Artemisia absinthium* in 2013, had less volume than those originally measured in 2013, but *Artemisia absinthium* plants were still present at the same location as the original patches (data not shown). Rotational grazing, with a 2,4-D application just prior to grazing, helped manage *Artemisia absinthium* plants in the same growing season as the herbicide application as they were no longer visible just after grazing. However, this treatment did not eliminate this perennial weed, as plants regrew the year after this treatment. Plants in the mob-grazed and rotational grazed areas were also present and had no observed injury.
