首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 62 毫秒
1.
This 9-yr study tested steer gains, residual aboveground biomass (AGB) in mid-July and early October, and economic returns and risk for tallgrass prairie grazed annually under season-long stocking (SLS) at 1.62 ha · steer−1 until early October or intensive early stocking (IES) at 0.81 ha · steer−1 until mid-July compared to a composite grazing system. The three-pasture, three-herd “IES+ System” is a 3-yr fixed sequence of SLS, IES, and IES (0.81 ha · steer−1) plus late-season grazing (LSG; 1.62 ha · steer−1) until early October (IES/LSG). All grazing treatments began in late April. Average gains per steer for SLS and SLS in the IES+ System did not differ, but were significantly less than gains for steers that grazed the entire season under IES/LSG. Gains per steer in mid-July under IES alone or in combination with LSG were similar to the same repeated grazing treatments, but were significantly less than those for steers grazed season-long. Gains per hectare under SLS did not differ, but were significantly less than those for IES treatments and the IES+ System. Gain per hectare in July was similar for IES repeated annually and IES/LSG, but there was greater gain per hectare for IES-treated pastures rotated within the system. Residual grass and total aboveground biomass (AGB) in mid-July did not vary among years and was generally greater on SLS than IES. In early October, grass AGB was similar for all treatments except IES/LSG, which had less residual AGB. When pasture rent was charged per head, the IES+ System increased the 20-yr mean return per hectare by $5.98 compared to repeated use of IES, and $8.52 compared to using only SLS. Measures of economic risk were generally intermediate for the IES+ system compared to IES, which consistently had the highest risk, and SLS.  相似文献   

2.
A comparison of animal gains and vegetation trends was made from 2002–2008 between a continuous season-long stocking (SLS) system and a modified intensive–early stocking system (IES) with late-season grazing (IES 1.6× + 1; 1.6 times the number of animals of the SLS system from May 1 to July 15, and 1 times the number of animals of SLS from July 15 to October 1) on shortgrass native rangeland of western Kansas. The continuous season-long stocked system placed animals at a density of 1.37 ha · steer?1 from May through October, or 2.63 animal unit months (AUM) · ha?1, whereas the intensive–early stocked system with late-season grazing (3.33 AUM · ha?1) stocked pastures at 0.85 ha · steer?1 from May through the middle of July, and then stocked pastures at 1.37 ha · steer?1 for the remainder of the grazing season by removing the heaviest animals mid-July each yr. Average daily gains (0.78 vs. 0.70 kg · d?1, P = 0.039) and total animal gain (58 vs. 52 kg, P = 0.042) were different between the continuous season-long stocked and the intensive–early stocked animals during the first half of the grazing season. No difference was found between average daily gain (0.61 vs. 0.62 kg · d?1, P = 0.726) and total animal gain (48 vs. 49 kg, P = 0.711) for the continuous season-long stocked and intensive–early stocked with late-season grazing animals during the last half of the season. Total individual animal gain (106 vs. 101 kg, P = 0.154) and average daily gain (0.70 vs. 0.66 kg · d?1, P = 0.152) was not different between the continuous season-long stocked and the intensive–early stocked system animals that were on pasture the entire grazing season. Total beef gain on a land-area basis (96 vs. 77 kg · ha?1, P = 0.008) was greater for the modified intensive–early stocked system with late-season grazing with greater animal densities. Changes in residual biomass and most key vegetation components at the end of the grazing season were not different between the two systems.  相似文献   

3.
Our objective was to compare the performance of weaned steer calves managed with intensive-early stocking (IES; 12.4 steers per ha for 70 d) or season-long stocking (SLS; 6.2 steers per ha for 140 d) with and without supplementation (2 × 2 factorial). Beginning on May 15, 90 steers (BW = 217 ± 0.8 kg) were randomly assigned to one of 12 common bermudagrass (Cynodon dactylon [L.] Pers.) pastures (0.81 ha each) fertilized with 168 kg of nitrogen/ha. One of the following four treatments was randomly applied to three pastures: i) SLS plus no supplement, ii) SLS plus 0.45 kg/steer of ground corn daily, iii) IES plus no supplement, and iv) IES plus 0.45 kg/steer of ground corn daily. Steers on IES were lighter (P=0.01) than SLS steers on d 70. By d 140, SLS steers supplemented with corn were 33 kg heavier (P=0.02) than nonsupplemented steers. When using SLS, corn increased the BW gain 0.5 kg/kg of corn fed; however, when IES was used, there was no benefit from corn supplementation. Total BW gain/ha did not differ (P>0.17) among treatments, but SLS with corn supplementation could have the potential to produce more BW gain/ha compared to the other treatments. Grazing systems did not affect feedlot ADG (P>0.53), but IES (175 d on feed) steers did have a higher (P<0.01) feedlot total BW gain than the SLS steers (154 d on feed). Using IES positively affected (P<0.08) dressing percentage and longissimus area compared to SLS; however, these differences in carcass characteristics were probably the result of the longer feeding period.  相似文献   

4.
Shrub encroachment can be explained by the abandonment of extensive livestock farming and changes to land use, and it is a common problem in the Mediterranean mountain pastures of Europe, with direct effects on biodiversity and landscape quality. In this paper, the effects of livestock exclusion vs. grazing on the dynamics of shrub and herbaceous vegetation were analyzed in a Spanish natural park located in a dry Mediterranean mountain area over a 5-yr period. Twelve 10 × 10 m exclosures were set up in six representative pasture areas of the park (with two replicates per location). Each year, the shrub number, volume, and biomass were measured in April, and the herbage height, biomass, and quality were measured in April and December (which represent the start and end of the vegetative growth season). A sustained increase of the shrub population and individual biomass was observed throughout the study, which was reflected in total shrub biomass per ha. Growth was greater in nongrazed exclosures (2 563 kg dry matter [DM] · ha?1 · yr?1), but it also happened in the grazed control areas (1 173 kg DM · ha?1 · yr?1), with different patterns depending on the location and shrub species. Herbage biomass did not change when grazing was maintained, but it did increase in places where grazing was excluded (291 kg DM · ha?1 · yr?1), mostly as a consequence of the accumulation of dead material, with a concomitant reduction in herbage quality. It was concluded that at the current stocking rates and management regimes, grazing alone is not enough to prevent the intense dynamics of shrub encroachment, and further reductions in grazing pressure should be avoided.  相似文献   

5.
A 4-yr study was conducted to determine performance of stocker calves on tallgrass prairie under three grazing management strategies. Pastures were assigned to one of three grazing treatments. Grazing was initiated in June, and pastures were grazed only during the summer months for 57 to 104 d (79.5 ± 20.7 d). Two of the pastures were grazed season-long. Calves in one of the season-long treatments were fed a protein supplement during the second half of the grazing season; calves in the other season-long treatment were not supplemented (control group). The third pasture, an intensive early stocking (IES) treatment, was grazed at twice the stocking rate used in the season-long pastures for the first half of the grazing season (40 ± 11 d) and rested for the second half (39.5 ± 10 d). Individual stocker performance during the first half of the summer was similar among grazing treatments. Providing supplemental protein during the second half of the grazing season increased BW gain by 30 kg/ha during the last 40 d of the 80-d grazing season and increased BW gain by 12 kg/ha for the entire summer. Over the summer, IES stocker calves produced 24% more gain/ha than season-long stocked calves. Nonetheless, IES management was not more profitable than season-long grazing with or without protein supplementation. Under short-term ownership of calves in the IES system, fixed costs represented a large portion of the total cost.  相似文献   

6.
Understanding the long-term effect of summer grazing date and fall stocking rate on herbage production is critical to extending the grazing season in the Nebraska Sandhills. A study was conducted from 1997 to 2002 at the Gudmundsen Sandhills Laboratory located near Whitman, Nebraska, to determine the herbage production response to summer grazing date and October stocking rate on two different sites. Site 1 was dominated by warm-season grasses and site 2 was dominated by cool-season graminoids. At each site, three 0.37-ha pastures were constructed in each of four blocks before application of summer grazing treatments. Pastures in each block were grazed at 0.5 animal-unit months (AUM) · ha?1 in June or July, or were deferred from summer grazing. Following summer grazing treatments, October stocking rate treatments (no grazing or 1.0, 2.0, or 3.0 AUM · ha?1) were applied to subunits of each summer grazing date pasture during mid-October. Vegetation was sampled in each pasture in mid-June and mid-August and sorted by functional group to determine the effect of 5 yr of grazing treatments on herbage production and residual herbage. Herbage production was not affected by summer or October grazing treatments on the warm-season grass–dominated site. Increasing October stocking rate, however, reduced cool-season graminoid production and subsequent herbage production 25% by year 5 of the study. Residual herbage at both sites at the end of the October grazing periods explained as much as 16% to 34% of subsequent year’s herbage production. Grazing managers in the Nebraska Sandhills can extend the grazing season by lightly stocking pastures in the summer to facilitate additional fall grazing. Heavy stocking in October over several years on cool-season–, but not warm-season–, dominated sites will reduce production of cool-season graminoids on these sites.  相似文献   

7.
Nitrogen (N) availability can strongly influence forage quality and the capacity for semiarid rangelands to respond to increasing atmospheric CO2. Although many pathways of nitrogen input and loss from rangelands have been carefully quantified, cattle-mediated N losses are often poorly understood. We used measurements of cattle N consumption rate, weight gains, and spatial distribution in shortgrass rangeland of northeastern Colorado to evaluate the influence of cattle on rangeland N balance. Specifically, we estimated annual rates of N loss via cattle weight gains and spatial redistribution of N into pasture corners and areas near water tanks, and used previous studies to calculate ammonia volatilization from urine patches. Using measurements of plant biomass and N content inside and outside grazing cages over 13 yr, we estimate that cattle stocked at 0.65 animal unit months (AUM) · ha?1 consumed 3.34 kg N · ha?1 · yr?1. Using an independent animal-based method, we estimate that cattle consumed 3.58 kg N · ha?1 · yr?1 for the same stocking rate and years. A global positioning system tracking study revealed that cattle spent an average of 27% of their time in pasture corners or adjacent to water tanks, even though these areas represented only 2.5% of pasture area. Based on these measurements, we estimate that cattle stocked at 0.65 AUM · ha?1 during the summer can remove 0.60 kg N · ha?1 in cattle biomass gain and spatially redistribute 0.73 kg N · ha?1 to areas near corners and water tanks. An additional 0.17 kg N · ha?1 can be lost as NH3 volatilization from urine patches. Cumulatively, these cattle-mediated pathways (1.50 kg N · ha?1) may explain the imbalance between current estimates of atmospheric inputs and trace gas losses. While NOx emission remains the largest pathway of N loss, spatial N redistribution by cattle and N removed in cattle biomass are the second and third largest losses, respectively. Management of cattle-mediated N fluxes should be recognized as one means to influence long-term sustainability of semiarid rangelands.  相似文献   

8.
Complete rest or grazing deferment is a general recommendation to encourage vegetative recovery following fire in the western United States. However, effects of grazing deferments on animal performance have not been determined. Prescribed fires were individually applied to nine separate, 1.5-ha pastures each year (2006 and 2007) for a total of 18 pastures. Grazing was deferred until spring (16 May), early summer (19 June), or late summer (1 August) the growing season after fire. At the end of each deferment, a 70-d (2007) or 41-d (2008) grazing period was initiated. Stocking rates were consistent between treatments within year, but were adjusted between years to achieve the targeted residual biomass of approximately 300 kg · ha?1. Diet quality was assessed approximately every 15 d throughout each grazing period (three pastures · period?1) via collection of rumen extrusa throughout the 2-yr study. Ewe body weight was measured on and off-test for each grazing period. Diet extrusa samples for in vitro organic matter disappearance was less (P = 0.03) for late summer than early summer grazing periods and equal to the spring period (62.9, 64.6, and 61.0 ± 0.90%, respectively for spring, early summer, and late summer grazing periods). In vitro neutral detergent fiber disappearance decreased (P = 0.01) by 10.6 percentage units from early grazing to late grazing period in 2007, whereas no differences were observed in 2008. Ewe average daily gain did not differ between spring and early summer grazing periods and were greater (P = 0.03) than the negligible body weight gains of the late summer grazing period. Total gain was 10.9 kg · ha?1 greater in 2008, and a quadratic response was measured for grazing period in 2007. Results indicate that deferment until early summer may be preferable so that stocking rates can be more accurately determined and animal performance is not diminished.  相似文献   

9.
Our objective was to compare the performance of weaned steer calves managed with intensive-early stocking (IES; 12.4 steers per ha for 70 d) or season-long stocking (SLS; 6.2 steers per ha for 140 d) with and without supplementation (2 x 2 factorial). Beginning on May 15, 90 steers (BW = 217 ± 0.8 kg) were randomly assigned to one of 12 common bermudagrass (Cynodon dactylon [L.] Pers.) pastures (0.81 ha each) fertilized with 168 kg of nitrogen/ ha. One of the following four treatments was randomly applied to three pastures: i) SLS plus no supplement, ii) SLS plus 0.45 kg/steer of ground corn daily, iii) IES plus no supplement, and iv) IES plus 0.45 kg/steer of ground corn daily. Steers on IES were lighter (P=0.01) than SLS steers on d 70. By d 140, SLS steers supplemented with corn were 33 kg heavier (P=0.02) than nonsupplemented steers. When using SLS, corn increased the BW gain 0.5 kg/kg of corn fed; however, when IES was used, there was no benefit from corn supplementation. Total BW gain/ha did not differ (P>0.17) among treatments, but SLS with corn supplementation could have the potential to produce more BW gain/ ha compared to the other treatments. Grazing systems did not affect feedlot ADG (P>0.53), but IES (175 d on feed) steers did have a higher (P<0.01) feedlot total BW gain than the SLS steers (154 d on feed). Using IES positively affected (P<0.08) dressing percentage and longissimus area compared to SLS; however, these differences in carcass characteristics were probably the result of the longer feeding period.  相似文献   

10.
An experiment was conducted to evaluate the influence of forest fuels reduction on diet quality, botanical composition, relative preference, and foraging efficiency of beef cattle grazing at different stocking rates. A split plot factorial design was used, with whole plots (3 ha) being fuel reduced or no treatment (control), and split plots (1 ha) within whole plots were grazed to three levels of forage utilization; (low) 3 heifers · ha?1, (moderate) 6 heifers · ha?1, (high) 9 heifers · ha?1, with a 48-h grazing duration. Grazing treatments were applied in August of 2005 and 2006. Cattle diet composition and masticate samples were collected during 20-min grazing bouts using six ruminally cannulated cows in each experimental unit. Relative preference indices indicated a strong preference for grass regardless of treatment and stocking rate. Grass consumption was lower in control pastures (P < 0.05) and tended (P < 0.095) to decrease with increased stocking rates. Shrub use was higher in control pastures displaying a quadratic effect (P < 0.05) due to stocking, whereas shrub use increased with stocking rate across all treatments. Cattle grazing control pastures consumed diets higher in crude protein compared to cattle grazing treated pastures (P < 0.05). In vitro dry matter digestibility values were lower (P < 0.05) in control sites and tended (P = 0.10) to decrease with increased stocking rates. In both control and treated pastures, bites per minute and grams consumed per minute declined (P = 0.003) with increased stocking, indicating foraging efficiency of cattle decreases with increased stocking rates. Our data indicated cattle grazing late season grand fir habitat types have a strong preference for grasses regardless of treatment or stocking rate. However, as stocking rate increased in both control and treated pastures, grass consumption decreased, shrub consumption increased, and foraging efficiency decreased.  相似文献   

11.
Beef cattle production from rangelands in the Southern Great Plains has decreased in concert with herbaceous forage production declines in response to woody plant encroachment by honey mesquite (Prosopis glandulosa Torr.) over the past 120 yr. Combinations of livestock overstocking and fire suppression are considered to be primary drivers of these changes. This experiment evaluated cow–calf production responses over a 7-yr (1995–2001) period to ranch-scale (1 294–2 130 ha) integrated restoration strategies involving prescribed fire and grazing management. Restoration strategies tested in this year-round grazing ecosystem were 4-pasture, 1-herd rotation with fire (25% of pasture acreage burned each year; 4:1F); an 8-pasture, 1-herd rotation, with fire (8:1F); and a 4-pasture, 1-herd, with fire and aerial application of 0.28 kg · ha?1 clopyralid + 0.28 kg · ha?1 triclopyr herbicide (4:1F / H). Restoration strategies were compared to a continuous grazing strategy with no mesquite treatment. All cattle stocking rates were moderate (7.5–15 ha · animal unit?1 · year?1) and all fires were applied during late winter. Beef cattle (cow–calf) production variables measured included conception rate, weaned calf percentage, weaning weight, weight of calf per exposed cow, weight of calf per hectare, and supplement fed per cow. We observed significant differences in beef production among strategies primarily during the first 2 yr where the continuous grazing strategy exhibited better overall livestock production than the integrated restoration strategies. Differences in livestock production among strategies were minimal over the last 5 yr of the study. These livestock production results suggest livestock and management adapted to restoration strategies after the first 2 yr. Results point to the need to cautiously transition into integrated grazing and fire restoration strategies when cattle and management are changed and intensified from prior historical protocols.  相似文献   

12.
Monoculture and mixed pastures in Florida provide habitat for a variety of resident and migratory bird species. The objectives of this study were to investigate the effects of grazing on vegetation structure and bird species richness and abundance in grazed monoculture and mixed pastures. Study pasture units were subject to four cattle grazing intensities: 0 = nongrazed (control), 15 = low, 20 = medium, or 35 = high animal units (AU) per pasture unit (no cattle, 1.3, 1.0, and 0.6 ha · AU?1, on monoculture pastures and no cattle, 2.1, 1.6, and 0.9 ha · AU?1, on mixed pastures). Monoculture pastures displayed a greater decrease in spatial heterogeneity of the vegetative community in the presence of grazing than mixed pastures. An increase in grazing intensity led to declines in total avian species richness and abundance and species richness within short-distance migrant, neotropical migrant, and permanent resident guilds on monoculture pastures. Declines in total species richness and abundance and neotropical migrant guild species richness and abundance were observed on mixed pastures subject to increasing grazing intensity. However, species richness within short-distance migrant and urban guilds and abundance within the grassland guild increased on this pasture type in the presence of grazing. Loss of spatial heterogeneity typically results in a lack of suitable habitat for birds that occupy the extremes of the vegetation structure gradient. This can lead to a loss of species richness and abundance. For the majority of avian guilds, a low grazing intensity of 1.3 ha · AU?1 and 2.1 ha · AU?1 on monoculture and mixed pasture, respectively, is recommended to maintain abundance. However, these grazing intensities may result in declines in species richness. Ultimately, if a range of avian species are to be supported on monoculture and mixed pastures, spatial heterogeneity of plant structure and composition must be maintained.  相似文献   

13.
A study was conducted on upland range in the Nebraska Sandhills to determine differences in plant species frequency of occurrence and standing crop at various topographic positions on pastures grazed with short-duration grazing (SDG) and deferred-rotation grazing (DRG). Pastures within each grazing treatment were grazed at comparable stocking rates (SDG = 1.84 animal unit months (AUM) · ha?1; DRG = 1.94 AUM · ha?1) by cow–calf pairs from 1999 to 2005 and cow–calf pairs and spayed heifers from 2006 to 2008. Plant frequency of occurrence data were collected from permanently marked transects prior to, midway through, and at the conclusion of the study (1998, 2003, and 2008, respectively) and standing crop data were collected annually from 2001 to 2008 at four topographic positions (dune top, interdune, north slope, and south slope). Livestock performance data were collected during the last 3 yr of the study (2006 to 2008). Positive change in frequency of occurrence of prairie sandreed (Calamovilfa longifolia [Hook.] Scribn.) was 42% greater on DRG pastures than SDG after 10 yr. Total live standing crop did not differ between DRG and SDG except in 2001 when standing crop was 23% greater on DRG pastures. Standing crop of forbs and sedge was variable between grazing methods on interdune topographic positions depending on year. Average daily gain of spayed heifers (0.84 ±  kg · d?1 SE) did not differ between SDG and DRG. Overall, SDG was not superior to a less intensively managed grazing method (i.e., DRG) in terms of vegetation characteristics and livestock performance.  相似文献   

14.
Because of concerns about the impact of grazing management on surface water quality, a 3-yr study was conducted to determine grazing management and microclimate impacts on cattle distribution relative to a pasture stream and shade. Three treatments, continuous stocking with unrestricted stream access (CSU), continuous stocking with restricted stream access (CSR), and rotational stocking (RS), were evaluated on six 12.1-ha cool-season grass pastures stocked with 15 fall-calving Angus cows (Bos taurus L.) from mid-May through mid-October of each year. On 2 d · mo?1 from May through September of each year, a trained observer in each pasture recorded cattle position and activity every 10 min from 0600 to 1800 hours. In years 2 and 3, position of one cow per pasture was recorded with a Global Positioning System (GPS) collar at 10-min intervals 24 h · d?1 for 2 wk · mo?1 from May through September. In week 2 of collar deployment in May, July, and September, cattle had access to off-stream water. Ambient temperature, black globe temperature, relative humidity, and wind speed were recorded at 10-min intervals and temperature humidity (THI), black globe temperature humidity (BGTHI), and heat load (HLI) indices were calculated. Based on GPS collars, mean percentage of time cows in CSU pastures were in the stream (1.1%) and streamside zone (10.5%) were greater (P < 0.05) than cows in CSR (0.2% and 1.8%) or RS (0.1% and 1.5%) pastures. Based on GPS collar data, off-stream water did not affect the percentage of time cattle in CSU or CSR pastures spent in the stream. Probabilities that cattle in CSU and CSR pastures were in the stream or riparian zones increased (P < 0.05) as ambient temperature, black globe temperature, THI, BGTHI, and HLI increased. Rotational stocking and restricted stream access were effective strategies to decrease the amount of time cattle spent in or near a pasture stream.  相似文献   

15.
Questions have been raised about whether herbaceous productivity declines linearly with grazing or whether low levels of grazing can increase productivity. This paper reports the response of forage production to cattle grazing on prairie dominated by Kentucky bluegrass (Poa pratensis L.) in south-central North Dakota through the growing season at 5 grazing intensities: no grazing, light grazing (1.3 ±  animal unit months [AUM] · ha-1), moderate grazing (2.7 ±  AUM · ha-1), heavy grazing (4.4 ±  AUM · ha-1), and extreme grazing (6.9 ±  AUM · ha-1; mean ± SD). Annual herbage production data were collected on silty and overflow range sites from 1989 to 2005. Precipitation and sod temperature were used as covariates in the analysis. On silty range sites, the light treatment produced the most herbage (3 410 kg · ha-1), and production was reduced as the grazing intensity increased. Average total production for the season was 545 kg · ha-1 less on the ungrazed treatment and 909 kg · ha-1 less on the extreme treatment than on the light treatment. On overflow range sites, there were no significant differences between the light (4 131 kg · ha-1), moderate (4 360 kg · ha-1), and heavy treatments (4 362 kg · ha-1; P &spigt; 0.05). Total production on overflow range sites interacted with precipitation, and production on the grazed treatments was greater than on the ungrazed treatment when precipitation (from the end of the growing season in the previous year to the end of the grazing season in the current year) was greater than 267.0, 248.4, 262.4, or 531.5 mm on the light, moderate, heavy, and extreme treatments, respectively. However, production on the extreme treatment was less than on the ungrazed treatment if precipitation was less than 315.2 mm. We conclude that low to moderate levels of grazing can increase production over no grazing, but that the level of grazing that maximizes production depends upon the growing conditions of the current year.  相似文献   

16.
The objectives of the current study were to determine the amounts of above- and below-ground plant biomass production, P uptake by forage, and P concentration of cool-season grass forage as influenced by management and season. Five forage management treatments were evaluated over 3 years in smooth bromegrass (Bromus inermis Leyss) pastures. Management practices were: ungrazed (U), hay harvest/fall stockpile grazing (HS), rotational stocking to residual sward heights of 10 (10R) or 5 (5R) cm, and continuous stocking to maintain sward height at 5 cm (5C). Forage samples were hand-clipped within and outside grazing exclosures monthly from April through November of each year and analyzed for mass and P concentration. Root samples were collected at the initiation and completion of the study for determination of root length density (RLD) and root surface area density (RSAD). Phosphorus concentrations of forage outside the grazing exclosures did not differ among 5C, 5R, and 10R treatments, which were greater than U paddocks in April and August and less than HS paddocks in June. Mean annual forage productivity was greater in HS, 10R, 5R, and 5C paddocks (6 744 ± 62 kg · ha-1 mean ± SE) than in the U paddocks (1 872 ± 255 kg · ha-1). Mean P concentration of forage outside exclosures was greatest during the spring (0.21 ± 0.01%), and lowest during the fall (0.13 ± 0.01%). Mean annual P uptake by forage followed the same trend as forage production, being greater in the HS, 10R, 5R, and 5C paddocks (13.9 ±  kg · ha-1) than in the U paddocks (3.7 ±  kg · ha-1). After 3 years, RLD decreased in the ungrazed paddocks, but was unchanged in the HS, 10R, 5R, and 5C paddocks. Forage production and P uptake by forage is stimulated by forage harvest, either by grazing or hay harvest in smooth bromegrass pastures.  相似文献   

17.
Grazing plays a key role in many ecosystems worldwide and can affect the structure and composition of terrestrial plant communities. Nonetheless, how grazing management, especially grazing regime (yearlong continuous and seasonal grazing), affects the relationship between grazing and vegetation on alpine grasslands has not been extensively studied. Here, we performed a grazing experiment in Gangcha county of Qinghai province of the Qinghai-Tibetan Plateau to test the effects of different stocking rates and grazing regimes on grassland biomass and plant structure and composition. Six stocking rates (ranging from 0 to 5.62 sheep ha? 1) were used for continuous grazing, and three grazing intensities (1.72, 2.87, and 5.62 sheep ha? 1) were used for seasonal grazing (grazed only in the growing season, from June to October) at the study sites. Plant biomass and grass functional community composition were characterized in two different yr (2011 and 2012). Additionally, species richness and plant diversity indexes were estimated to quantify the impacts of grazing on plant community composition. Our results indicated that grazing intensity best explained the plant biomass decrease in low-productivity environments, and different grazing regimes also influenced these results. The shifts in plant community structure and composition in response to increased grazing intensity differed considerably between continuous grazing and seasonal grazing. Seasonal grazing maintained greater amounts of palatable plant species, and fewer undesirable species in plant communities when compared with the composition after continuous grazing. Our results emphasize the importance of grazing regime in regulating the effects of grazing on plant communities and the importance of seasonal grazing for ecosystem maintenance, especially in the Qinghai-Tibetan Plateau. This suggests that periodic resting of grasslands could be a good management strategy to keep palatable species, thereby minimizing undesirable species in the overall species composition.  相似文献   

18.
Selective grazing can modify the productive capacity of rangelands by reducing competitiveness of productive, palatable species and increasing the composition of more grazing-resistant species. A grazing system (season-long and short-duration rotational grazing) × stocking rate (light: 16 steers · 80 ha-1, moderate: 4 steers · 12 ha-1, and heavy: 4 steers · 9 ha-1) study was initiated in 1982 on northern mixed-grass prairie. Here, we report on the final 16 years of this study (1991–2006). Spring (April + May + June) precipitation explained at least 54% of the variation in peak standing crop. The percentage of variation explained by spring precipitation was similar between stocking rates with short-duration grazing but decreased with increasing stocking rate for season-long grazing. April precipitation explained the greatest percentage of the variation in peak standing crop for the light stocking rate (45%), May precipitation for the moderate stocking rate (49%), and June precipitation for the heavy stocking rate (34%). Peak standing crop was 23%–29% greater with light (1 495 ± 66 kg · ha-1, mean ± 1 SE) compared to moderate (1 218 ± 64 kg · ha-1) and heavy (1 156 ± 56 kg · ha-1) stocking rates, which did not differ. Differences in peak standing crop among stocking rates occurred during average and wet but not dry springs. Neither the interaction of grazing system and stocking rate nor grazing system alone affected standing crop across all years or dry, average, or wet springs. Grazing-induced modification of productive capacity in this northern mixed-grass prairie is attributed to changes in species composition with increasing stocking rate as the less productive, warm-season shortgrass blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Griffiths) increases at the expense of more productive, cool-season midheight grasses. Land managers may need to substantially modify management to offset these losses in productive capacity.  相似文献   

19.
Prescribed fire is used to reduce the rate of woody plant encroachment in grassland ecosystems. However, fire is challenging to apply in continuously grazed pastures because of the difficulty in accumulating sufficient herbaceous fine fuel for fire. We evaluated the potential of rotationally grazing cattle in fenced paddocks as a means to defer grazing in selected paddocks to provide fine fuel for burning. Canopy cover changes from 1995 to 2000 of the dominant woody plant, honey mesquite (Prosopis glandulosa Torr.), were compared in three landscape-scale grazing and mesquite treatment restoration strategies: 4-paddock, 1-herd with fire (4:1F), 8-paddock, 1-herd with fire (8:1F), and 4:1 with fire or aerial application of 0.28 kg · ha?1 clopyralid + 0.28 kg · ha?1 triclopyr herbicide (4:1F/H), and a continuously grazed control with mesquite untreated (CU). Prescribed burning took place in late winter (February–March). Droughts limited burning during the 5-yr period to half the paddocks in the 4:1F and 8:1F strategies, and one paddock in each 4:1F/H strategy. Mesquite cover was measured using digitized aerial images in 1995 (pretreatment) and 2000. Mesquite cover was reduced in all paddocks that received prescribed fire, independent of grazing strategy. Net change in mesquite cover in each strategy, scaled to account for soil types and paddock sizes, was +34%, +15%, +5%, and -41% in the CU, 4:1F, 8:1F, and 4:1F/H strategies, respectively. Thus, rotational grazing and fire strategies slowed the rate of mesquite cover increase but did not reduce it. Fire was more effective in the 8:1F than the 4:1F strategy during drought because a smaller portion of the total management area (12.5% vs. 25%) could be isolated to accumulate fine fuel for fire. Herbaceous fine fuel and relative humidity were the most important factors in determining mesquite top-kill by fire.  相似文献   

20.
Low larkspur (Delphinium nuttallianum Pritz.) poisoning causes serious economic loss to livestock producers that graze cattle on foothill and mountain ranges in western North America. In general, all Delphinium spp. are five times less toxic to sheep than to cattle. Because low larkspurs are less toxic to sheep than cattle, grazing sheep before cattle on rangelands with dense populations of low larkspur can reduce larkspur density and risk of poisoning to grazing cattle. All previous published work on sheep and larkspur interactions has involved tall larkspurs. This series of studies was conducted to determine if sheep would consume sufficient low larkspur to reduce subsequent risk to cattle. Four summer trials were conducted in Collbran, Colorado, and Soda Springs, Idaho on pastures with dense (> 9 plants · m?2) low larkspur populations. In all trials, sheep ate very little low larkspur (< 0.5% of bites). During one final trial using high sheep density (two sheep · 0.015 ha?1 for 9 d), sheep consumed little low larkspur, but animals appeared to trample much of the low larkspur. Toxic alkaloid concentrations in low larkspur ranged from 1.1 mg · g?1 to 1.6 mg · g?1 in all trials. The use of sheep to graze low larkspurs to reduce subsequent consumption by grazing cattle does not appear to be a viable option.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号