**4. Discussion**

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.

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

intervals based on binomial testing of the number of patches that showed a decrease over the total number with t = 0.1.

**Post-graze**

#Decrease/total Ave. vol. of

<19,000 28/38 73 (9) >19,000 11/22 50 (NS)

**cm3 cm3**

Spray/rotation 16,500 26/27 0 100 (1)

2013/2014 Mob 66,500 39/60 25,650 65 (10)

2013 Rotation 12,380 12/29 8830 41 (16)

2014 Summer recovery 2850 1/28 3 (NS)

and number that decreased in volume are presented.<sup>a</sup>

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

remaining

% Control<sup>a</sup>

Numbers in parentheses are confidence

vol.

Year Grazing system Pre graze ave.

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

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

the average height increased from 15 (May) to 86 cm (September). Because there was no tram-

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* 

pling and an increase in shoot height, this increase can be attributed to plant growth.

*absinthium* patch volume in mob-grazed areas influenced final *Artemisia absinthium* volume.

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

) to September (average volume = 151,200 cm3

). In addition,

plants in the sprayed patches were consumed with forage.

*3.2.2. Rotational grazing*

volume < or >19,000 cm3

62 Forage Groups

May (average volume = 2850 cm3

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

McCartney and Bittman [20] and others [29–31], suggest that timing and grazing capacity for optimal forage utilization and weed control, with minimal harm to desired species, requires thoughtful management to improve or maintain rangeland health. Our results show that mob grazing (225,000 or 50,000 kg of cattle ha−1 day−1) could reduce biomass of *Artemisia absinthium* a less palatable species in a pasture. In mob-grazed treatments, *Artemisia absinthium* plants appeared to be consumed if plants were small and, most likely, still had herbaceous, rather than woody, stems. Mob grazing offers the additional benefit of trampling which reduced *Artemisia absinthium* height, although not necessarily the volume, especially of larger plants. Effectiveness of mob grazing is dependent on plants species present, stocking density, and timing [14, 16, 20]. Grazing weeds should be avoided after seed set to minimize seed dispersal, as some weed seeds remain viable or increase in germination after ingestion and passing through the digestive tract of livestock [32, 33]. While we did not find literature that specifically addresses changes in *Artemisia absinthium* seed viability after animal ingestion, *Artemisia absinthium* seeds mature in late August or September [34], after the grazing events of our study, and was not investigated. If grazing an infested pasture must be delayed until a species is past its most palatable stage, or if a weed has inherently low palatability, higher stocking rates, as seen in this study and other studies [7] improved suppression.

parasites, which discourages multiple species grazing [41–43]. Cattle are, by far, the grazing animals of choice in South Dakota (1.8 million cattle vs. 260,000 sheep) [44] and across the

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

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

65

Herbicide applications are reported to be the most effective methods for *Artemisia absinthium* control [22, 45–47]. There are numerous reports about the enhanced effectiveness of combining weed control strategies for weed suppression in grazing lands [1, 7, 47–49]. In this study, using 2,4-D ester herbicide in combination with grazing, helped remove *Artemisia absinthium* growth for the first growing season. Some herbicides affect the palatability of certain plants, encouraging livestock to eat plants they would normally avoid, like poisonous plants [50]. However, precautions must be taken if spraying 2,4-D [24] because this herbicide can cause plants to accumulate excess nitrate, become more palatable, and result in nitrate poisoning of livestock [51]. There are a few grazing restrictions for 2,4-D ester [24]. For example, meat animals could be grazed immediately after application, but not within 7 days of slaughter; and restrictions for a dairy animals differed with no grazing within 7 days post-application.

Healthy rangelands grow more grass which aids in *Artemisia absinthium* control by preventing infestations and providing competition to newly establishing plants. Grass density can be optimized by managing livestock to minimize overgrazing through rotational grazing or avoiding heavy, early season grazing [22]. Based on *Artemisia absinthium* size increase in the 2014 recovery area after the early spring rotational grazing/summer rest, it appears that rotational grazing later in the growing season (as in 2013) achieved better suppression of *Artemisia* 

Once present, our study showed that grazing provided temporary reductions to *Artemisia absinthium* patches, with greater reductions in the mob-grazed and rotational/spray treatments than the rotational grazed treatment. Shoots of smaller plants and those in smaller patches appeared to be consumed in both mob grazing and rotational grazing when 2,4-D ester was applied. However, even the most decimated plants had shoots the following season. Once pastures are infested, long-term management plans are needed to keep *Artemisia absinthium* in check.

We found that mob grazing with cattle for 12 or 24 h in pastures where *Artemisia absinthium* was present did indeed improve *Artemisia absinthium* control of smaller plants (as measured in plant volume) with concomitant high forage utilization. Rotational grazing at lower stocking rates for 20 days (late-May through mid-June), when combined with 2,4-D application, also suppressed *Artemisia absinthium* for that growing season. Early (mid-April) rotational grazing with a summer rest resulted in much larger *Artemisia absinthium* plants and patches in the fall. We could not verify the statements that mob grazing would result in (1) an increase of two or more cm of soil per year, nor (2) a species composition change due to the intense grazing, which are two positive benefits of mob grazing often discussed in trade journal articles [15, 19, 52]. In addition, we did not assess the impact of mob grazing on animal performance, although in a single one-time grazing situation, a change in this parameter would not be

*absinthium* patches, although cattle did not necessarily consume *Artemisia absinthium*.

Northern Great Plains of the US.

**5. Conclusions**

Mob grazing with cattle has been proposed as a grazing system to increase forage use efficiency and help in landscape restoration [14] and is likened to grazing patterns of the native plains bison. Kohl et al. [35] reported that bison and cattle differ in grazing, standing, bedding, and moving behaviors, with bison moving from 50 to 99% faster and foraging up to double the land area than cattle during the same duration. This is the precedent for the frequent moves when mob grazing cattle. In addition, cattle, when not pressured, tend to select high plant biomass, whereas bison tend to select intermediate plant biomass [35]. Regardless of the inherent differences between these two species, when managed correctly, mob grazing with cattle can diversify grazing time, with frequent moves, and long rest periods [30]. However, if managed incorrectly, high intensity grazing systems could increase weed infestations [31]. For example, in 3 years, under medium grazing intensity (grazed five times year−1 with 6 cm of vegetation remaining after each grazing event) weeds increased by about 4 plants m−2, whereas under high intensity (grazed seven times year−1 until surface exposure), weed densities increased by 51 plants m−2 [36]. Hart et al. [37] reported that stocking rates that alter grazing frequency and defoliation intensity, rather than grazing system, have greater potential to impact species composition. Plant diversity and complex mixtures of forage species are integral to healthy ecosystems and consistent yields [38, 39]. However, mob grazing, if repeatedly used in the same area and at the same seasonal timing, could decrease plant species diversity and richness, change functional plant traits (e.g., tall vs. short), but improve productivity of the remaining plants [40].

The animal of choice for grazing also can influence grazing results. Goats (*Capra aegagrus hircus*) and sheep (*Ovis aries*) [7, 41] are often suggested to control brush and other undesirable vegetation, as they are more efficient at foraging and have faster growth rate than cattle. However, there are to numerous disadvantages to using goats and sheep which include: poor return on investment due to low per capita consumption of their meat products in the US and low wool prices; limited genetic improvement in milk or meat production; high predation rates compared with cattle; difficulty in fencing confinement; and susceptibility to internal parasites, which discourages multiple species grazing [41–43]. Cattle are, by far, the grazing animals of choice in South Dakota (1.8 million cattle vs. 260,000 sheep) [44] and across the Northern Great Plains of the US.

Herbicide applications are reported to be the most effective methods for *Artemisia absinthium* control [22, 45–47]. There are numerous reports about the enhanced effectiveness of combining weed control strategies for weed suppression in grazing lands [1, 7, 47–49]. In this study, using 2,4-D ester herbicide in combination with grazing, helped remove *Artemisia absinthium* growth for the first growing season. Some herbicides affect the palatability of certain plants, encouraging livestock to eat plants they would normally avoid, like poisonous plants [50]. However, precautions must be taken if spraying 2,4-D [24] because this herbicide can cause plants to accumulate excess nitrate, become more palatable, and result in nitrate poisoning of livestock [51]. There are a few grazing restrictions for 2,4-D ester [24]. For example, meat animals could be grazed immediately after application, but not within 7 days of slaughter; and restrictions for a dairy animals differed with no grazing within 7 days post-application.
