Integrating Ranch Forage Production,Cattle Performance,and Economics in Ranch Management Systems for Southern Florida

The presence of grazing cattle near open waterways has created environmental concerns related to the potential for water contamination. In Florida the removal of cattle from grazing landscapes or decreasing stocking density is being investigated as one option to improve the quality of surface water runoff draining into Lake Okeechobee, Florida. The objective of this study was to determine the effects of stocking rate on cow-calf performance, forage availability and quality, and ranch economic performance. Experimental pastures were established on a southern Florida cow-calf operation with stocking rates of 0.58, 1.01, and 1.35 ha·cow^-1 on summer pastures and 0.93, 1.62, and 2.16 ha·cow^-1 on winter pastures, corresponding to high, medium, and low rates, respectively. The study was conducted over 4 consecutive production years. Cow body condition scores (BCS), pregnancy rate, and calf average daily gain were used as measures of animal performance. Forage utilization was estimated by measuring the difference between forage yield inside and outside grazing exclusion cages and forage quality by crude protein and in vitro organic matter digestibility. Forage yield, utilization, and quality were not significantly affected by stocking rate. Although statistically not significant (P = 0.17), cattle in the high stocking rate experienced a numerically greater loss of BCS following the winter grazing period, but stocking rate did not affect pregnancy rate or calf gains. Production (kg weaned calves·ha^-1) was increased (P < 0.01) for a high stocking rate compared with medium and low stocking rates. Overall ranch profitability will decrease as stocking rates decline. Ranch revenues decrease one-for-one as stocking rates decrease. At the same time, unit cow costs increase at an increasing rate as fewer brood cows are left to support the ranch's fixed cost structure.     

Spatial Redistribution of Nitrogen by Cattle in Semiarid Rangeland

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 NO_x 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.     

Livestock Grazing Impacts on Herbage and Shrub Dynamics in a Mediterranean Natural Park

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.     

Integrated Ecological and Economic Analysis of Ranch Management Systems: An Example From South Central Florida

Developing sustainable ranch management systems requires integrated research that examines interrelations among ecological and economic factors. In south central Florida, where phosphorus (P) loading is an overriding environmental concern, we established an interdisciplinary experiment to address the effects of cattle stocking density and pasture type on P loading and other ecological and economic factors in subtropical Florida ranchlands through a partnership including ecologists, agricultural faculty, agency personnel, and producers. Here we present an overview of all project components detailed in 3 accompanying papers in this issue of Rangeland Ecology & Management. We describe the experimental design, which included 2 replicates of 4 different cattle stocking density treatments (control, low, middle, and high [0, 15, 20, and 35 cow–calf pairs per pasture]) maintained on 8 improved summer pastures (∼ 20 ha each), and 8 seminative winter pastures (∼ 32 ha each) from 1998 to 2003. Stocking densities did not significantly affect P loads and concentrations in surface runoff, soil chemistry, or soil nematode communities, but did affect cattle production and economic performance. Cattle production was greater at the high than at the middle or low stocking density; economic performance declined significantly with decreasing stocking density (break-even was $1.89·kg^-1 for high and $2.66·kg^-1 for low density). Pasture type significantly affected environmental factors; average P runoff from improved summer pastures (1.71 kg P·ha^-1·y^-1) was much greater than from seminative winter pastures (0.25 kg P·ha^-1·y^-1), most likely because of past P fertilizer use in improved pastures. We integrate results from all the papers within the context of a conceptual model and a P budget, and emphasize that management practices targeted at specific environmental factors on beef cattle ranches, such as nutrient loading, must include consideration of economic impacts and broader ecosystem implications.     

Impact of Stocking Rate and Rainfall on Sheep Performance in a Desert Steppe

Livestock performance is a critical indicator of grassland production systems and is influenced strongly by precipitation and stocking rates. However, these relationships require further investigation in the arid Desert Steppe region of northeastern China. We employed a randomized complete block design with three replications and four grazing treatments (nongrazed exclosure [Control]), lightly grazed [LG], moderately grazed [MG], and heavily grazed [HG]) by sheep in a continuously grazed system (June to November), to test the effect of stocking rate on sheep performance. The planned stocking rates were 0, 0.15, 0.30, and 0.45 sheep · ha^?1 · mo^?1, for the control, LG, MG, and HG treatments, respectively. However, actual stocking rates were calculated for each paddock in each year based on a 50-kg sheep equivalent (SE). Annual net primary production (ANPP) was determined at peak standing crop in August 2004 to 2008. Live weight gain was determined for the summer and fall periods, as well as the total grazing period, in each year. ANPP decreased with increasing stocking rate, and daily live weight gain per head decreased linearly with increasing stocking rates over the total grazing period but in a quadratic manner over the summer period with a plateau at the lower rates. Maximum sheep production per unit area over the total grazing season occurred at about 2 SE ha^?1 for about a 5-mo grazing period, but individual gains per sheep were predicted to decline after about 1 SE ha^?1 presumably because of forage limitations. However, in order to achieve stable annual production, we recommend that the Desert Steppe be grazed at about 0.77 SE ha^?1 for a 5-mo period (0.15 SE ha^?1 · mo^?1). This estimate is based on published grazing strategies that consider an average ANPP with a recommended utilization rate of 30%.     

Comparison of Season-Long Grazing Applied Annually and a 2-Year Rotation of Intensive Early Stocking Plus Late-Season Grazing and Season-Long Grazing

This research measured steer gains, aboveground biomass remaining at the end of the growing season, and economic returns of tallgrass prairie grazed under season-long stocking (SLS-C) and a grazing system that included a 2-yr rotation of SLS-rotated (SLS-R) and intensive early stocking (IES; 2× normal stocking rate) + late-season grazing at the normal stocking rate (IES + LSG-R). We hypothesized that even though the stocking rate on the IES + LSG-R pasture was above the recommended rate, the greater regrowth availability in the late season would result in steers gaining as well as or better than those stocked SLS at the normal rate. By rotating the IES + LSG treatment with SLS over 2 yr, we anticipated that the aboveground biomass productive capacity of the IES + LSG pasture would be restored in one growing season. Further, we hypothesized that the increased stocking rate with IES + LSG would increase net profit. Comparing traditional season-long stocking to the system, which was a combination of SLS and IES + LSG rotated sequentially over a 2-yr period, the system increased steer gains by 7 kg · hd^?1 and by 30 kg · ha^?1, had a consistent reduction of 429 kg · ha^?1 biomass productivity, and increased net profit by $55.19 per steer and $34.28 per hectare.     

Grazing-Induced Modifications to Peak Standing Crop in Northern Mixed-grass Prairie

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.     

Soil Phosphorus,Cattle Stocking Rates,and Water Quality in Subtropical Pastures in Florida,USA

Minimizing nonpoint source nutrient pollution is important to the sustainability of grazing lands. Increased nutrient loads have reduced water quality in Lake Okeechobee in south Florida, prompting establishment of a Total Maximum Daily Load (TMDL) that will require large reductions in phosphorus (P) runoff into the lake. A significant portion of this reduction must come from beef cattle ranches, the major land use in the region. A large-scale research project, consisting of a 420-ha array of 8 improved summer and 8 semi-improved winter pastures, was established from 1998–2003 to investigate the influence of beef cattle stocking rate on nutrient loads in surface runoff. Each pasture type had two replicates of four different cattle stocking rates including a control with no cattle and stocked pastures with low, medium, and high stocking rates (1.3, 1.0, 0.6 ha·AU^-1 [animal unit] in summer pastures; 2.1, 1.6, and 0.9 ha·AU^-1 in winter pastures). Cattle stocking rate did not affect nutrient concentrations or loads in surface runoff during the study period. Average annual P discharges were 1.71 kg·ha^-1 from summer pastures and 0.25 kg·ha^-1 from winter pastures. Average total P concentrations in runoff were 0.63 mg·L^-1 for summer pastures and 0.15 mg·L^-1 for winter pastures. Differences in runoff P were related to differences in soil P test results, a difference believed to be due to prior fertilization practices. Our findings show that reducing cattle stocking rates on beef cattle pastures is not an effective practice for reducing nutrient loads, and that accumulation of P in soil from historical fertilization has an overriding influence on P loads in surface runoff. Results indicate that reducing the overall volume of surface discharges would be a more effective strategy than altering cattle stocking practices to reduce nonpoint runoff of P from cattle pastures in this region.     

Simulation of Sandsage-Bluestem Forage Growth Under Varying Stocking Rates

The effect of stocking rate on forage growth has attracted much research attention in forage science. Findings show that forage growth may be affected by stocking rate, and there is a consensus that high stocking rates lead to soil compaction, which could also in turn affect forage growth because of the changing soil hydrology and increased soil impedance to forage root penetration. In this study we used a modeling approach to investigate the effect of stocking rates on the growth of sand-bluestem forage at Fort Supply, Oklahoma. The GPFARM-Range model, which was originally developed and validated for Cheyenne, Wyoming, was recalibrated and enhanced to simulate soil compaction effects on forage growth at Fort Supply. Simulations without the consideration of soil compaction effects overestimated the forage growth under high stocking rate conditions (mean bias [MBE] = –591 kg · ha^?1), and the agreement between the simulated and observed forage growth was poor (Willmott’s d = 0.47). The implementation in the model of soil compaction effects associated with high stocking rates reduced the bias (MBE = –222 kg · ha^?1) and improved the overall agreement between the observed and the simulated forage growth (d = 0.68). It was concluded that forage growth under increasing soil compaction could be predicted provided such sensitivities are included in forage growth models.     

Performance of Nellore heifers, forage mass, and structural and nutritional characteristics of Brachiaria brizantha grass in integrated production systems

Our objective was to evaluate production, nutritive value and carrying capacity of piatã grass (Brachiaria brizantha cv. BRS Piatã), and performance of Nellore heifers in agrosilvopastoral systems (ASPS) with three eucalyptus (Eucalyptus urograndis) tree densities, during winter, spring, summer, and fall. Three integrated systems were evaluated: ASPS-1 (357 trees ha^?1), ASPS-2 (227 trees ha^?1), and CON (5 trees ha^?1). In each system, two sward heights were evaluated: short and tall. A total of 80 11-month-old Nellore heifers were randomly allocated in a randomized split-plot block, 3?×?2 factorial. Greater dry matter availability was observed on CON pastures during the fall season. Greater percentage of leaf lamina was detected on ASPS-1 with short sward height and greater during summer, compared with other seasons. A greater forage production was observed between tree rows and for tall sward height. Spring was the season with less forage nutritive value. Average daily gain was greater during summer and fall. Gain per hectare and stocking rate were greater on CON system and on ASPS-2. Pastures with short sward height had greater gain per hectare and stocking rate. Agrosilvopastoral systems with intermediate tree density seem to be a good choice for producers willing to diversify their revenue sources without decreasing animal production.     

Long-Term Production and Profitability From Grazing Cattle in the Northern Mixed Grass Prairie

Conventional wisdom among rangeland professionals has been that for long-term sustainability of grazing livestock operations, rangeland should be kept in high good to low excellent range condition. Our objective was to analyze production parameters, costs, returns, and profit using data generated over a 34-yr period (1969–2002) from grazing a Clayey range site in the mixed-grass prairie of western South Dakota with variable stocking rates to maintain pastures in low–fair, good, and excellent range condition classes. Cattle weights were measured at turnout and at the end of the grazing season. Gross income · ha^?1 was the product of gain · ha^?1 and price. Prices were based on historical National Agricultural Statistics Services feeder cattle prices. Annual variable costs were estimated using a yearling cattle budget developed by South Dakota State University agricultural economists. All economic values were adjusted to a constant dollar using the Bureau of Labor Statistics' Consumer Price Index. Stocking rate, average daily gain, total gain, net profit, gross revenue, and annual costs · ha^?1 varied among range condition classes. Net income for low–fair range condition ($27.61 · ha^?1) and good range condition ($29.43 · ha^?1) were not different, but both were greater than excellent range condition ($23.01 · ha^?1). Over the life of the study, real profit (adjusted for inflation) steadily increased for the low–fair and good treatments, whereas it remained level for the excellent treatment. Neither drought nor wet springs impacted profit differently for the three treatments. These results support generally observed rancher behavior regarding range condition: to maintain their rangeland in lower range condition than would be recommended by rangeland professionals. Ecosystem goods and services of increasing interest to society and associated with high range condition, such as floristic diversity, hydrologic function, and some species of wildlife, come at an opportunity cost to the rancher.     

Effects of Forage Management on Pasture Productivity and Phosphorus Content

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.     

Animal and Vegetation Response to Modified Intensive–Early Stocking on Shortgrass Rangeland

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.     

Animal-Driven Rotational Grazing Patterns on Seasonally Grazed New Mexico Rangeland

Global positioning system (GPS) data collected over a 4-yr period on 52 crossbred young cows grazing a 146-ha pasture were used to determine whether cattle establish patch-scale rotational patterns within pastures. Cow positions at 5-min intervals were recorded during 20 d in late winter/early spring. Estimated per capita forage allowance (PCFA) was 347 kg herbage · cow^-1, 438 kg herbage · cow^-1, 1 104 kg herbage · cow^-1, and 1 884 kg herbage · cow^-1 in 2004, 2005, 2006, and 2007, respectively. Cumulative winter/early spring precipitation (CPPT) was low in 2004 and 2006 (35 mm and 30 mm, respectively) and high in 2005 and 2007 (119 mm and 112 mm, respectively). Structured query language codes developed for this study were used to 1) select grazing GPS points with movement velocities between 1 m · min^-1 and 20 m · min^-1, 2) overlay location data on a pasture map subdivided into 30 × 30 m pixels, and 3) calculate percentage of grazed pixels (% GP), pixel residence time (RT), revisit rate (RR), and return interval (RI) for each animal. Cows grazed 31% ± 5.9 SEM of all pixels for 21 min ± 3.7 SEM, visited grazed pixels 1.6 times ± 0.18 SEM, and returned to grazed pixels after 5 D ± 2 SEM. As PCFA increased, % GP decreased (r = -0.42) and RI increased (r = 0.73) significantly (P < 0.01); however, RT decreased (r = -0.46) and RR increased (r = 0.6) significantly (P < 0.01) with increasing CPPT. Pixel attributes (elevation, aspect, slope, percentage of tree cover, and distance from water, roads, and fences) failed to explain variation in pixel RT (R² = 0.28) regardless of PCFA. The same predictors explained most of the variation in pixel RR and RI when PCFA was high (R² = 0.86 and R² = 00.76, respectively). Cows appear to establish their own patch-scale rotational patterns within pastures. Nonforage pixel attributes appear to have a strong influence on such patterns.     

Reproductive Effort and Seed Establishment in Grazed Tussock Grass Populations of Patagonia

The importance of sexual reproduction in tussock grasses that regenerate through vegetative growth is unclear. Festuca gracillima Hook. f. was studied as a model because it is a perennial tussock-forming grass that produces abundant seed but rarely regenerates through seedlings. The Study area was the Magellanic Steppe, Patagonia, Argentina (182 mm rainfall), managed with sheep-grazing regimes of 0.65 (high), 0.21 (low), and 0 (exclosure) ewe equivalents · ha^?1 · yr^?1. Tussock size and spikelet production of 358 individuals were recorded over 5 yr. Yearly models of reproductive effort in relation to plant size were tested using a maximum likelihood procedure. Seed was collected and soil cores were tested for germination and viability. Survival and growth of cohorts of seedlings sown in nylon bags were recorded. Eighteen experimental plots were cleared, and seed establishment under protected and grazed conditions was registered. Reproductive effort varied with years and plant size, with a mean of 2.41%. Florets were produced at mean density of 544 ± 217 · m^?2. Predispersal losses reduced viable seed production to 187 ± 48 seeds · m^?2. Seed weighed 2–2.5 mg, with 65–95% germination. Postdispersal losses reduced the seed bank in spring to 33 ± 1.3 seeds · m^?2. Seedling survival curves were negatively exponential, with 95% mortality in the first year. Up to 5% of resources were used for sexual reproduction in favorable years and a recruitment of 1–3 new seedlings · m^?2 · yr^?1 was expected. These new plants were not observed in undisturbed plots, but established naturally in cleared plots and reached a density of 1 plant · m^?2 after 10 yr, together with 44 plants · m^?2 of other species. Competition might block the final establishment in these grasslands. Grazing does not appear to interfere in any stage of seed reproduction. Seed production may not maintain population numbers but could enhance genetic variation in these clonal plant populations and enable dispersal and recolonization of disturbed areas.     

Stocking Rate and Fuels Reduction Effects on Beef Cattle Diet Composition and Quality

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.     

Soil Morphologic Properties and Cattle Stocking Rate Affect Dynamic Soil Properties

Soil properties that influence the capacity for infiltration and moisture retention are important determinants of rangeland productivity. Monitoring effects of grazing on dynamic soil properties can assist managers with stocking rate decisions, particularly if monitoring takes into account environmental variability associated with inherent soil morphological properties. On a Pacific Northwest Bunchgrass Prairie in northeast Oregon, we applied three cattle stocking rates (0.52, 1.04, and 1.56 animal unit months · ha^?1) and an ungrazed control in a randomized complete block design for two 42-d grazing seasons and measured the change in four dynamic soil properties: soil penetration resistance, soil aggregate stability, bare ground, and herbaceous litter cover. To address apparent environmental heterogeneity within experimental units, we also utilized a categorical soil factor (termed Edaphic Habitat Types or EHT), determined by characterizing soil depth, texture, and rock fragment content at sample sites. Stocking rate did not affect extent of bare ground or soil aggregate stability. Stocking rate had a significant effect on penetration resistance, which was greatest at the high stocking rate (1.6 J · cm^?1 ± 0.1 SE) and lowest in the control (1.1 J · cm^?1 ± 0.1 SE). For litter cover, the effects of stocking rate and EHT interacted. In two rocky EHTs, litter cover was highest in the controls (60% ± 6 SE; 50% ± 3 SE) and ranged from 27% ± 3 SE to 33% ± 6 SE in the stocking rate treatments. Measures of penetration resistance, aggregate stability, and bare ground were different across EHTs regardless of stocking rate, but did not interact with stocking rate. Our study demonstrates that response of dynamic soil properties to stocking rates should be considered as a useful and accessible approach for monitoring effects of livestock management decisions on rangeland conditions.     

Performance of spring-calving beef suckler cows and their progeny to slaughter on intensive and extensive grassland management systems

The performance of rotationally grazed beef suckler cows and their progeny to slaughter on two lowland grassland management systems differing in stocking rate (SR) and fertiliser nitrogen (N) level was compared over eight years. The two Systems were 1) Intensive (INT): SR of 0.56 (bull production) or 0.71 (steer production) ha cow^? 1 unit, 211 kg fertiliser N ha^? 1, two silage harvests, and 2) Extensive (EXT): SR of 0.69 (bull production) or 0.88 (steer production) ha cow^? 1 unit, 97 kg fertiliser N ha^? 1 and one staggered silage harvest. A cow unit was defined as a cow plus progeny to slaughter. On the silage harvesting area, the mean application rate for fertiliser N was 110 and 80 kg ha^? 1 for first and second harvests, respectively. Herbage dry matter digestibility both pre- and post-grazing was similar (P > 0.05) for the two systems, whereas herbage crude protein concentrations were generally significantly lower for the EXT than the INT system. There was no difference (P > 0.05) between the Systems in cow live weight, body condition score or their changes or in calf live weight gain from birth to weaning. Post-weaning, live weight gain, slaughter weight, carcass weight, kill-out proportion, estimated carcass gain, carcass conformation score or carcass fat score did not differ (P > 0.05) between the systems for heifer, steer or bull progeny. It can be concluded that similar animal performance levels can be expected in an extensive grassland-based suckler calf-to-beef system compatible with the EU, Rural Environmental Protection Scheme as that attained in a more intensive System comprising of both a moderately high SR (~ 1.25 higher) and fertiliser N application (~ 2.1 higher).     

Productivity,Respiration, and Light-Response Parameters of World Grassland and Agroecosystems Derived From Flux-Tower Measurements

Grasslands and agroecosystems occupy one-third of the terrestrial area, but their contribution to the global carbon cycle remains uncertain. We used a set of 316 site-years of CO₂ exchange measurements to quantify gross primary productivity, respiration, and light-response parameters of grasslands, shrublands/savanna, wetlands, and cropland ecosystems worldwide. We analyzed data from 72 global flux-tower sites partitioned into gross photosynthesis and ecosystem respiration with the use of the light-response method (Gilmanov, T. G., D. A. Johnson, and N. Z. Saliendra. 2003. Growing season CO₂ fluxes in a sagebrush-steppe ecosystem in Idaho: Bowen ratio/energy balance measurements and modeling. Basic and Applied Ecology 4:167–183) from the RANGEFLUX and WORLDGRASSAGRIFLUX data sets supplemented by 46 sites from the FLUXNET La Thuile data set partitioned with the use of the temperature-response method (Reichstein, M., E. Falge, D. Baldocchi, D. Papale, R. Valentini, M. Aubinet, P. Berbigier, C. Bernhofer, N. Buchmann, M. Falk, T. Gilmanov, A. Granier, T. Grünwald, K. Havránková, D. Janous, A. Knohl, T. Laurela, A. Lohila, D. Loustau, G. Matteucci, T. Meyers, F. Miglietta, J. M. Ourcival, D. Perrin, J. Pumpanen, S. Rambal, E. Rotenberg, M. Sanz, J. Tenhunen, G. Seufert, F. Vaccari, T. Vesala, and D. Yakir. 2005. On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm. Global Change Biology 11:1424–1439). Maximum values of the quantum yield (α=75 mmol · mol^?1), photosynthetic capacity (A_max=3.4 mg CO₂ · m^?2 · s^?1), gross photosynthesis (P_g,max=116 g CO₂ · m^?2 · d^?1), and ecological light-use efficiency (ε_ecol=59 mmol · mol^?1) of managed grasslands and high-production croplands exceeded those of most forest ecosystems, indicating the potential of nonforest ecosystems for uptake of atmospheric CO₂. Maximum values of gross primary production (8 600 g CO₂ · m^?2 · yr^?1), total ecosystem respiration (7 900 g CO₂ · m^?2 · yr^?1), and net CO₂ exchange (2 400 g CO₂ · m^?2 · yr^?1) were observed for intensively managed grasslands and high-yield crops, and are comparable to or higher than those for forest ecosystems, excluding some tropical forests. On average, 80% of the nonforest sites were apparent sinks for atmospheric CO₂, with mean net uptake of 700 g CO₂ · m^?2 · yr^?1 for intensive grasslands and 933 g CO₂ · m^?2 · d^?1 for croplands. However, part of these apparent sinks is accumulated in crops and forage, which are carbon pools that are harvested, transported, and decomposed off site. Therefore, although agricultural fields may be predominantly sinks for atmospheric CO₂, this does not imply that they are necessarily increasing their carbon stock.     

Performance of spring-calving beef suckler cows and their progeny on four contrasting grassland management systems

Data were collected over four consecutive years from four, rotationally grazed, grassland management systems each with 15 spring-calving beef suckler cows and their progeny to 13 months of age. The Systems were high stocking rate (SR), high fertiliser nitrogen (N), 2 silage harvests — HH2; high SR, low N, 2 silage harvests — HL2; low SR, low N, 2 silage harvests — LL2, and low SR, low N, 1 silage harvest — LL1. High and low SR were 0.49 and 0.59 ha cow^− 1 unit, respectively, and high and low N amounted to an annual input of 239 and 57 kg ha^− 1 on the grazing areas, respectively. Where applicable, the four Systems received 114 and 80 kg of N ha^− 1 for the first and second silage harvests, respectively. Equal areas of Systems HH2, HL2 and LL2 were conserved as silage (0.29 and 0.21 ha for first (24 May) and second (4 August) harvests, respectively cow^− 1 unit) each year. Silage from System LL1 (0.37 ha cow^− 1 unit) was conserved 14 days after the other first harvests. Following the final harvesting for silage within any System these areas of grassland were then grazed. During the winter all animals were housed and cows were offered grass silage and calves were offered silage plus 1 kg of concentrate per head daily. Good cow and calf performance at pasture were obtained at both high SR and high N or low SR and low N. At the high SR, increasing the level of fertiliser N application increased cow liveweight gain at pasture by 24 kg, improved body condition score (BCS) gain at pasture by 0.36 units and prolonged the grazing season by 7 days. Similarly, at the low level of fertiliser N, reducing the SR, increased cow liveweight gain at pasture by 21 kg, improved BCS gain at pasture by 0.23 units and prolonged the grazing season by 7 days. At the low SR all the winter silage requirements could be provided in one as opposed to two harvests thereby reducing the conservation area. However, delayed harvesting of silage resulted in lower silage digestibility and reduced calf performance in winter. The results indicate the specifications for a planned lower N grassland system, particularly where qualification for EU environmental schemes is dependent on moderate stocking densities.