Forage Species Composition Research Articles

Plant-community characteristics of bahiagrass pasture during conversion to longleaf-pine silvopasture

Silvopasture is considered a sustainable agroforestry practice as a result of benefits the system offers for biodiversity, economic returns, and environmental quality. However, little is known about temporal and spatial dynamics of forage species composition of pastures being converted to silvopasture. Research objectives were to determine (1) the response of forage species composition to a young longleaf pine (Pinus palustris Mill.)-bahiagrass (Paspalum notatum Flugge) silvopasture versus open bahiagrass pasture, and (2) the impact that alley position relative to trees has on forage species composition in a young longleaf pine-bahiagrass silvopasture. The research was conducted in a randomized complete block design with three replications from 2003 to 2007 at Americus, Georgia, USA in a longleaf-pine silvopasture established in 2000 in an existing bahiagrass pasture and an adjoining bahiagrass open-pasture. Silvopasture forage-species composition was measured within alleys. Plant community diversity was greater in the silvopasture versus open-pasture early in the growing season, but open-pasture had greater diversity during the later growing season. Alley position in silvopasture also had a significant effect on understory forage species composition. This study indicated that conversion of bahiagrass pasture to longleaf-pine silvopasture in the Southern Coastal Plain can influence plant-community characteristics by the time trees are six to seven years old.

Landscape and field characteristics affecting winter waterfowl grazing damage to agricultural perennial forage crops on the lower Fraser River delta, BC, Canada

The lower Fraser River delta is an important waterfowl staging area on the lower coast of British Columbia, Canada. Since the early 1980s, wintering waterfowl have been causing economically significant damage to perennial forage fields (hay, pasture and silage). We examined the effect of farm management practices and landscape attributes on the extent of grazing damage on a total of 196 perennial forage fields between 2001 and 2005. Multiple regression analysis and an information-theoretic model comparison approach were used to identify field and landscape parameters that account for variation in damage. Rather than limit our evaluation to single-species use of forage crops, we considered the combined grazing impact of a complex of wintering waterfowl, including lesser snow goose (Chen caerulescens), American wigeon (Anas americana), mallard (Anas platyrhynchos), northern pintail (Anas acuta), and trumpeter swan (Cygnus buccinator) and identified which management practices might mitigate overall grazing damage. Forage species composition and availability of alternative feeding areas had an effect on waterfowl grazing damage to perennial forage fields. Fields with higher proportions of orchard grass showed higher levels of grazing damage; and damage was lower in years when abundant alternative feeding areas (AFAs) in the form of unharvested potatoes were available. Although these factors were found to be important in explaining variation in damage to perennial forage fields, our best model accounted for only 13% of the variation in damage. Mitigation efforts must be comprehensive and consider a wide range of factors that influence damage to perennial forage fields. Although manipulation of field characteristics and management of AFAs can contribute to waterfowl grazing damage mitigation, strategic geographic distribution of AFAs and management of human disturbance in designated AFA areas would further mitigate damage.

Effect of the physiological state of Criollo goats on the botanical composition of their diet in NE Mendoza, Argentina

The botanical composition of the diet and species preference of grazing goats in different physiological states were evaluated in the autumn and winter seasons. The study was performed in a desert rangeland in the northeast (NE) Mendoza region in Argentina. Food availability was estimated from forage species cover. Rectal grab faecal samples were collected from goats, and the botanical composition of the goat diet was determined using a microhistological technique. Goat preferences for each species consumed were calculated based on Ivlev's index. Nutritional composition and secondary compounds of forage species were determined. Correlations between diet and availability; and between goat preference and nutritional composition of forage species were also estimated. The habitat consisted of a dominant woody stratum associated with an herb stratum primarily composed of grasses. Goats in different physiological states utilised a significantly higher proportion of woody vegetation compared to grass (p<0.01). When grass availability was high (autumn), the herb stratum was more utilised by pregnant and lactating goats than by dry goats (p<0.05). In the winter, the diet of lactating goats consisted of more Atriplex lampa compared to the diet of dry goats (p<0.05), probably due to the high crude protein content of the plant. Goats consumed forage species with highly variable total phenol and tannin contents, which did not negatively affect selection. Correlations between diet and availability were high in the winter for dry (rs=0.88, p<0.02), pregnant (rs=0.93, p<0.01) and lactating goats (rs=0.97, p<0.01) but were not significant in the autumn. A significant correlation between preference and crude protein was shown during the autumn season for pregnant and lactating goats (rs=0.6, p<0.05). Forage availability was the main factor influencing diet selection in this arid environment. When food availability was not a limiting factor, goats selected a diet that most closely matched their nutritional requirements. Physiological state modified nutrient requirements and affected diet selection in that pregnant and lactating goats selected forage species with high protein contents.

Mineral composition of lucerne ( Medicago sativa) and white melilot ( Melilotus albus) is affected by NaCl salinity of the irrigation water

Most glycophytic forage legumes exhibit large reductions in biomass in response to saline growing conditions, although differences among species in salt tolerance exist. As several plant metabolic processes are affected by salinity, the nutritive value of these species to animals may be altered. Mineral concentration is an important component of plant nutritive value, and was evaluated in lucerne and white melilot under salt concentrations of 0, 55 and 110 mM NaCl in a glasshouse. Lucerne consistently accumulated higher concentrations of Na and Cl than white melilot. Calculated NaCl concentrations per unit DM reached 125 g/kg in lucerne and 39 g/kg in white melilot when irrigated with water containing 110 mM NaCl. In leaves of both species the Ca and Mg concentration decreased (P < 0.0001) with increasing salinity level, and there was an interaction (P < 0.0001) for these elements in which lucerne stems had decreases. The P concentration increased (P < 0.0001) in both species and the K concentration was affected only in lucerne stems. Among trace elements, Zn and Fe had marked decreases. Leaf and stem Zn concentration decreased in both species and Fe decreased more in leaves than in stems, but most analyzed microelements remained at acceptable levels for animal production. Detrimental changes in the mineral composition of forage species in response to salinity can be minimized by selecting appropriate species, such as white melilot. This may lead to improved animal production if biomass production, voluntary animal intake and digestibility can be maintained.

Seasonal cycles in whole-body proximate composition and energy content of forage fish vary with water depth

Quantifying the nutritional quality of forage fish is integral for understanding upper trophic levels as forage fish are the dominant prey for top predator fish, marine mammals, and sea birds. Many existing reports documenting body composition of forage species are not comparable due to confounding effects. This study systematically assessed the variability in proximate composition and energy content of 16 forage species in southeastern Alaska (57.2626 N/133.7394 W) between 2001 and 2004. Variation in energy and lipid contents was related to habitat, epipelagic planktivores varying most, mesopelagics intermediate, and demersal species relatively invariable. Season was the greatest source of variation as a result of short growing seasons at high latitude and energy allocation strategies for reproduction and growth. Among species that varied seasonally, energy and lipid increased over summer and declined during winter. Annual differences in body composition occurred during periods of peak energy content. Sampling recommendations and guidance for bioenergetics models are provided.Electronic supplementary materialThe online version of this article (doi:10.1007/s00227-010-1569-3) contains supplementary material, which is available to authorized users.

Proximate composition and energy content of forage species from the Bay of Biscay: high- or low-quality food?

Abstract Spitz, J., Mourocq, E., Schoen, V., and Ridoux, V. 2010. Proximate composition and energy content of forage species from the Bay of Biscay: high- or low-quality food? – ICES Journal of Marine Science, 67: 909–915. Collapses of high-energy dense concentrations of prey species induce negative effects on populations of top predators. Knowledge of prey quality appears to be crucial in ecosystem modelling and management. The aim here was to provide baseline data of forage species quality in the Bay of Biscay. Proximate composition (water, ash, protein, and lipid) and energy content have been determined to assess the quality of 78 species, including jellyfish, crustaceans, cephalopods, cartilaginous fish, and bony fish. Results show broad variations between species, with energy densities ranging from 2 to 10 kJ g−1. Lipids are the most structuring component and largely determined prey quality, and prey species are not necessarily interchangeable for the fulfilment of a predator's energy and food requirements. In ecosystem models, therefore, multispecies compartments of forage organisms would ideally be constituted using prey species of equivalent quality and hence of equivalent benefit to top predators.

Potential for Delayed Orchardgrass Seeding during Glyphosate‐Resistant Alfalfa Establishment

Few herbicides are labeled for weed control when establishing alfalfa (Medicago sativa L.)‐grass mixtures. Varying the planting date of the grass in relation to alfalfa and adjusting herbicide application timing could improve weed control and forage grass safety. The research objective was to evaluate the use of glyphosate [N‐(phosphonomethyl) glycine] for weed control in seedling glyphosate‐resistant alfalfa mixed with orchardgrass (Dactylis glomerata L.). Orchardgrass was seeded with alfalfa or 4 and 5 wk after alfalfa; while glyphosate was applied 4 wk after planting and all treatments included an untreated check. First year harvests varied in composition and orchardgrass was slower to establish than alfalfa. At the first harvest, glyphosate treatments had 17 to 35% higher alfalfa content, reduced or similar orchardgrass content, and 75 to 90% lower weed content than treatments without glyphosate. By the third harvest of the establishment year, weed biomass in the 4 and 5 wk after planting treatments not treated with herbicide was at least 4.5 times greater and orchardgrass content was the same or less than the comparable glyphosate treatments. Forage species composition and weed control differences present during the establishment year dissipated during the second year of the study. By 2 yr after establishment, orchardgrass content was lower only in the first two cuttings when orchardgrass was seeded with the alfalfa and a glyphosate application followed, a practice not generally recommended. This study demonstrates the utility of glyphosate in glyphosate‐resistant alfalfa and should provide some guidance for establishment of successful alfalfa‐grass mixtures.

Evaluación de criterios de lectura microhistológica para la cuantificación de Sphaeralcea bonariensis (cav.), pl Lorentz en mezclas manuales

Sphaeralcea bonariensis (mallow) is a frequent component in goat diets in the semiarid silvopastoral systems of Santiago del Estero Province, Argentina. Quantification of mallow using the microhistological technique is difficult because trichomes often appear alone in the microscopic field of vision, detached from the epidermis. In an effort to better estimate the botanical composition of forage species in ruminant diets, four mixtures were prepared with different proportions of S. bonarieinsis, Tillandsia sp., Prosopis nigra and Sorghum halepensis. After collection, the botanical material was oven-dried, milled and prepared following the microhistological method, with 20 slides per mixture. Appearance frequency of species was determined microscopically to estimate the botanical composition of the mixtures. Readings were considered positive according to one of two criteria: 1) epidermis fragments only, and 2) epidermis fragments, or three or more detached hairs. A similarity index was used to compare the resulting values. The similarity index results were statistically analized (ANOVA) as a factorial experiment with a totally randomized design (4x2). The Anova between similarity index values showed significant differences between criterion x mixture. Criterion 1 was most accurate in quantifying mixtures with low (10 %) mallow content, and Criterion 2 was more effective in quantifying mixtures with more than 50% mallow. Proportions of 80 % mallow resulted in underestimation, independent of the estimation criterion applied.

Pasture and Cattle Responses in Rotationally Stocked Grazing Systems Sown with Differing Levels of Species Richness

Increasing species richness of temperate pastures beyond one or two forage species could improve grazing system productivity. An experiment in western Illinois, USA, was initiated in August 2001 to test this idea. The main study objective was to determine how pastures sown with increasing levels of species richness would affect herbage yield and cow‐calf performance. Three seed mixtures that contained three, five, or eight forage species were sown into 3‐ to 6‐ha pastures. Mixtures were replicated three times and rotationally stocked with beef cow–calf groups. Herbage mass and accumulation were estimated by a rising plate meter method and weight gain evaluated cow–calf performance. We also evaluated forage nutritive value indices and changes in forage species composition. After pasture establishment in 2001, herbage mass was marginally higher (P= 0.15) in eight‐species mixtures (98 g m−2) compared with three‐species mixes (43 g m−2). Once grazing started, pasture mix had no effect on herbage responses or stocking rate (P&gt; 0.05). Cow–calf performance was also unaffected by pasture mix, although average daily gain (ADG) was higher in 2003 (P&lt; 0.05). Cow and calf ADG averaged 0.33 and 1.17 kg d−1, respectively, in 2003 compared with 0.05 and 1.01 kg d−1in other years. Overall, species richness in pastures had minimal effects on forage yield and cattle performance. Grazing management (e.g., stocking rate) and climatic conditions more strongly influence grazing system productivity.

Effect of rotation frequency and weaning date on forage measurements and growth performance by cows and calves grazing endophyte-infected tall fescue pastures overseeded with crabgrass and legumes1

A grazing study was initiated in April 2000 and continued through three calving and weaning cycles (ending July 2003) to investigate the effects of rotational grazing management (twice monthly [2M] vs. twice weekly [2W]) and weaning date (mid-April [EARLY] vs. early June [LATE]) on production of fall-calving cow-calf pairs (495 +/- 9.6 kg initial BW) grazing Neotyphodium coenophialum-infected tall fescue (Festuca arundinacea Schreb.) overseeded with legumes and crabgrass. Secondary objectives of the experiment were to monitor differences in quantity and quality of available forage and to evaluate changes in forage species composition. Pastures were dominated by tall fescue throughout the study, and the proportion of basal cover was greater (P < 0.05) in 2M than in 2W pastures. The percentage of legumes was very low across all treatment combinations, but the percentage of crabgrass continued to increase (P < 0.05) linearly and quadratically across years for both summer and fall sampling periods, regardless of rotation or weaning program. In vitro DM disappearance and mineral concentrations varied minimally because of rotation frequency or weaning date. Rotation frequency did not substantially affect (P = 0.11 to 0.97) cow BW, hay offered, milk production, calving interval, calf birth weight, or actual or adjusted weaning weights; however, 2M cows had 0.3 units higher (P < 0.05) BCS at the time of breeding than 2W cows. Calves weaned late had greater (P < 0.05) actual weaning weight and weighed more (P < 0.05) on the LATE weaning date than on the EARLY weaning date, but 205-d adjusted weaning weights did not differ (P = 0.74) across weaning dates. Therefore, rotation frequency and/or weaning date had little effect on forage species composition or forage quality. In addition, the rapid rotation program offered little advantage with respect to animal performance, and weaning fall-born calves grazing endophyte-infected tall fescue pastures at approximately 189 d of age seemed to be detrimental to calf performance compared with delaying weaning until 243 d of age.

Forage Yield and Species Composition in Years following Kura Clover Sod‐Seeding into Grass Swards

Sod‐seeding legumes into grass pastures improves forage productivity and quality, but legumes currently used lack persistence. Field experiments were established in Québec and Minnesota to compare postseeding year performance of two cultivars (‘Cossack’ and ‘Endura’) of Kura clover (Trifolium ambiguum M. Bieb.) against that of red clover (Trifolium pratense L.) and white clover (Trifolium repens L.) sod‐seeded using different intensities of herbicide sod suppression [paraquat (0.9 kg a.i. ha−1) and glyphosate (0.8 or 3.3 kg a.i. ha−1)] with or without seeding year N fertilization (110 kg N ha−1). Red clover had the greatest yield and contribution to total forage yield in the first postseeding year [avg. 2.7 Mg dry matter (DM) ha−1, 50% clover], white clover (WC) was intermediate (avg. 1.5 Mg DM ha−1, 32% clover), and Kura clover (KC) ranked last (avg. 1.2 DM Mg ha−1, 27% clover). Yields of KC were, however, similar to WC in three of five sites. Clover yields and content in the first postseeding year were positively associated with intensity of sod suppression. Kura clover content increased over time; at the first harvest of the second postseeding year, it had greater clover yield and content (avg. 750 kg DM ha−1, 45% clover) than red clover (avg. 160 kg DM ha−1, 25% clover) and WC (avg. 60 kg DM ha−1, 11% clover). Seeding year N fertilization, which enhanced seeding year yields, had inconsistent effects on postseeding year yield and botanical composition but rarely had negative effects on clover. Kura clover can be established in permanent pastures via sod‐seeding.

The Impact of Underseeding Barley (Hordeum vulgare L.) on Timothy (Phleum pratense L.)‐Clover (Trifolium pratense L.; Trifolium hybridum L.) Forage Production in a Cool Maritime Climate

AbstractGrowing barley (Hordeum vulgare L.) in the year of forage establishment is a common agronomic practice in marginal growing regions, but is often not recommended to growers. We examined the effect of silage barley production over an establishing timothy (Phleum pratense L.)‐clover (Trifolium pratense L.; Trifolium hybridum L.) forage sward in a 4‐year study near St. John's, Newfoundland, Canada. The experiment compared two barley varieties differing in plant height (semidwarf Chapais and Leger), three barley seeding rates and the effect of a forage understorey on forage (barley) production in the establishment year and forage (timothy‐clover) production in the subsequent year. The taller Leger yielded similar forage biomass to Chapais in the year of forage establishment, which (when planted at 375 plants m−2) was roughly twice that of a pure‐stand timothy‐clover mix. Increasing the barley seeding rate from 125 to 375 plants m−2 resulted in a linear increase in forage yield in the year of planting. The production of barley forage in the establishment year resulted in reduced timothy‐clover forage yield in the year following barley planted at 125 and 375 seeds m−2, but not for barley planted at 250 seeds m−2. Companion planting also altered forage species composition in that higher barley seeding rates resulted in 12–18 % less timothy and 2–4 % lower fibre levels in the year following planting. Barley seeded at rates of 250–375 seeds m−2 and undersown with a timothy‐clover mixture (harvested at mid‐milk) resulted in greater forage yield of poorer quality than pure‐stand timothy‐clover in the planting year, and a barley seeding rate of 250 seeds m−2 did not impede forage production in the subsequent year.

The impact of underseeding forage mixtures on barley grain production in northern North America

Livestock farmers in Newfoundland grow most of their required forage, yet must import most feed grain. Growing barley (Hordeum vulgare L.) in the year of forage establishment may allow for the incorporation of grain production into local cropping schemes. We examined the effect of barley grain production over an establishing timothy (Phleum pratense L.)-clover (Trifolium pratense L.; T. hybridum L.) forage sward in a 4-yr study near St. John’s. The experiment compared two barley varieties (differing in plant height), three barley seeding rates and the effect of a forage under-story on grain production in the establishment year, and forage production in the subsequent year. Increasing barley seeding rate from 125 to 375 plants m-2 resulted in a linear increase in spikes m-2, which led to a linear increase in barley yield. Pure-stand grain yields did not differ from those undersown to forage mixtures. The production of barley grain in the establishment year did not alter forage yield in the subsequent year (at any barley seeding rate or cultivar archetype). The barley crop did alter forage species composition in that higher seeding rates resulted in 15% less timothy in the forage production year. Barley undersown at a rate of 375 seeds m-2 with a timothy-clover mixture can be produced successfully in Newfoundland. Key words: Hordeum vulgare L., alsike clover, red clover, underseeding, companion planting, Newfoundland

Yield response of long-term mixed grassland swards and nutrient cycling under different nutrient sources and management regimes

The response of a long-term, mixed-species hayfield in Maine, USA, to commercial fertilizers and liquid dairy manure was evaluated over a 6-year period, including the effects on yield, nutrient concentration and cycling, forage species composition and soil nutrient levels. Nutrient treatments included an unamended control, N fertilizer, NPK fertilizer and liquid dairy manure (LDM). The application rates of plant-available N, P, and K were constant across treatments. Application of nutrients in any form increased forage yield, generally by 2–4 t dry matter (DM) ha−1 year−1. Yield from NPK fertilizer was 0·05–0·25 higher than from LDM, due to differences in N availability. Yield responses to P and K were minimal and there appeared to be no difference between P and K in fertilizer and manure. The forage sward became increasingly dominated by grass species as the experiment progressed; application of P and K in fertilizer or LDM allowed Agropyron repens to increase at the expense of Poa pratensis. Forage nutrient removal accounted for all applied N and K, and nearly all applied P, throughout the study period, demonstrating the important role these forages can play in whole-farm nutrient management.

Field activities and blood profile of pregnant South African indigenous goats after receiving dihydroxy pyridone-degrading rumen bacteria and grazing Leucaena leucocephala-grass or natural pastures

Twenty-four multiparous female South African indigenous goats were used. Once a week during the 2nd (weeks 8, 11 and 14) and 3rd (weeks 18, 19 and 20) trimesters, between 08·00 and 15·00 h, four females per treatment were randomly selected and observed every 1 min for time spent grazing, browsing, ruminating and idling. Blood samples were taken once a week during the 2nd (weeks 8, 11 and 14) and 3rd (weeks 18, 19, 20 and 21) trimesters for measurements of some mineral elements and protein metabolites. Goats on natural pasture (NP) grazed 54·8 min (P&lt;0·001) more and browsed 53 min (P&lt;0·001) less than goats on Leucaena leucocephala-grass pasture (LGP) during the 2nd trimester. During the 3rd trimester, goats on NP treatments grazed and idled more (24·7 min, P = 0·004; 15·8 min, P = 0·044, respectively) but ruminated less (−24·1 min, P&lt;0·001) than LGP goats. Time allotted to each field activity by the goats on both treatments within trimester seemed to be dependent on forage species composition while activity between trimesters was possibly influenced by seasons, plant type, herbage quantity, environment and quality, and changes in stage of gestation of the goats. Blood Mg level on NP was higher (P = 0·051) than on LGP during the 2nd trimester while blood Cu and albumin contents on LGP were significantly higher (P = 0·029 and 0·022, respectively) than on NP during the 3rd trimester. Furthermore, blood concentrations of the haematological parameters (except serum protein) on both treatments were within the normal range for goats in the tropics and subtropics and perhaps explain the absence of mineral and nutrient deficiency symptoms. The absence of visible symptoms of mineral deficiency and mimosine toxicity in LGP goats can be attributed to the transfer of DHP-degrading rumen bacteria. The bacteria effectively detoxified mimosine and its metabolites, thereby overcoming chelating tendency of mimosine and its metabolites. Mimosine-susceptible pregnant SAIG can be safely grazed on LGP once their rumen is completely colonized by the DHP-degrading rumen bacteria (Synergistes jonesii).

Snow cover and snow goose Anser caerulescens caerulescens distribution during spring migration

Arctic geese often use spring migration stopover areas when feeding habitats are partially snow covered. Melting of snow during the stopover period causes spatial and temporal variability in distribution and abundance of feeding habitat. We recorded changes in snow cover and lesser snow goose Anser caerulescens caerulescens distribution on a spring migration stopover area in south‐central Alaska during aerial surveys in 1993–1994. Our objectives were to determine whether geese selected among areas with different amounts of snow cover and to assess how temporal changes in snow cover affected goose distribution. We also measured temporal changes in chemical composition of forage species after snow melt. We divided an Arc/Info coverage of the approximately 210 km2 coastal stopover area into 2‐km2 cells, and measured snow cover and snow goose use of cells. Cells that had 10–49.9% snow cover were selected by snow geese, whereas cells that lacked snow cover were avoided. In both years, snow cover diminished along the coast between mid‐April and early May. Flock distribution changed as snow geese abandoned snow‐free areas in favour of cells where snow patches were interspersed with bare ground. Snow‐free areas may have been less attractive to geese because available forage had been quickly exploited as bare ground was exposed, and because soils became drier making extraction of underground forage more difficult. Fiber content of two forage species increased whereas non‐structural carbohydrate concentrations of forage plants appeared to diminish after snow melt, but changes in nutrient concentrations likely occurred too slowly to account for abandonment of snow‐free areas by snow geese.

Pasture Renovation and Grazing Management Impacts on Cool-Season Grass Pastures

Legumes have been shown to increase production in cool-season grass pastures. However, they are included in relatively few acres of pasture. A split plot experiment with six replications was conducted to evaluate the impact of pasture renovation and grazing management on forage production and species composition of cool-season grass pastures. Grazing management main plots were grazed to leave low (2-4 in.), medium (4-6 in.), or high (6-8 in.) residue levels. Main plots were intensively grazed (50 000-70 000 lb of cows per acre) five or six times per grazing season by lactating Holstein cows. Subplot pasture renovation treatments were (i) an untreated check, or sprayed with glyphosate and interseeded with (ii) alfalfa (Medicago sativa L.), (iii) red clover (Trifolium pratense L.) and birdsfoot trefoil (Lotus corniculatus L.), or (iv) graziers mix (a mixture of legumes and grasses). Areas that were grazed to leave low residue level produced less forage mass (4.7 ton/acre) than areas grazed to medium (5.4 ton/acre) or high (5.5 ton/acre) residue levels. When averaged across years and grazing management treatments, renovated areas produced 1.8 ton/acre (46%) more forage than the control. Of interseeded species, alfalfa, red clover, and orchardgrass persisted through the study (more than 25% of the dry matter in at least one of the pasture renovation treatments). By June 1998, thistle (Carduus and Cirsium spp.) was present in all treatments. Fewer thistle was present in areas that were grazed to leave low residue (10 sq yd) than high residue (18 sq yd) and in renovated areas (9 sq yd) than the control (22 sq yd). The additional forage produced as a result of pasture renovation cost from $8.07/ton to $12.81/ton. Tbis study indicates that pasture renovation can be a valuable tool for increasing forage production in cool-season grass pastures.

Carbon dioxide and temperature effects on forage establishment: tissue composition and nutritive value

SummaryAtmospheric CO2 concentration ([CO2]) and temperature are likely to increase in the future and may change plant growth and composition characteristics. Rhizoma peanut (Arachis glabrata Benth.) and bahiagrass (Paspalum notatum Flügge) were grown on a natural field soil in temperature‐gradient greenhouses to evaluate the effects of elevated [CO2] and temperature on tissue composition and digestibility during the establishment year. Carbon dioxide levels were maintained at 365 (ambient) and 640 μL CO2 L–1 air. The temperature‐gradient greenhouses were regulated to obtain air temperature sectors of 0.2, 1.5, 2.9, and 4.5 °C above ambient. Samples were taken of previously undefoliated herbage at 57, 86, 121, 148, and 217 days after planting and entire plots were harvested at 218 days after planting. Elevated [CO2] increased total nonstructural carbohydrate concentration in rhizoma peanut leaves by almost 50%. Rhizoma peanut leaf N concentration was 6% lower at elevated than at ambient [CO2]. The N concentration in new rhizomes of rhizoma peanut was increased by high [CO2], while the N concentration in bahiagrass was not affected by temperature or [CO2]. No effects of [CO2] and temperature were found on neutral detergent fibre in rhizoma peanut leaves or stems; however, elevated [CO2] increased neutral detergent fibre in bahiagrass leaves. Only at season end was in vitro organic matter digestion of rhizoma peanut higher at ambient (623 g kg–1) than at elevated [CO2] (609 g kg–1). Elevated [CO2] had a greater effect on tissue composition of rhizoma peanut than of bahiagrass. These data suggest that elevated temperature and CO2‐induced changes in chemical composition of forage species adapted to humid subtropics will be relatively small, particularly for C4 species.

Late Growing-Season Fire Effects in Mid-Successional Tallgrass Prairies

Wildfire in the growing season is relatively frequent and interest is increasing in using growing-season fire in management of tallgrass prairie. However, the influence of fire in the growing season on forage production and species composition, especially in mid-successional tallgrass prairie, is largely unknown. Our objective was to compare vegetation composition and production on Loamy Prairie and Very Shallow ecological sites in mid-successional stages in response to late growing-season fire at different frequencies. We applied 4 burning treatments (no burn, or 1, 2, or 3 burns in 5 years) in the late growing season in southern Oklahoma during a series of years of above-average precipitation. The sites were dominated at the beginning of the study by early- and mid-successional species including prairie threeawn (Aristida oligantha (Michx)), a species indicating a disturbance history. After the initial burns in 1990, tallgrasses, little bluestem, and perennial grasses were reduced by burning on the Loamy site. Forbs were more productive on burned plots (1,980 kg ha-1) than on plots that were not burned (1,290 kg ha-1) averaged across sites. Total production was not reduced by burning in 1990. Growing-season burns in 2 consecutive years had little influence on species composition or production as compared to a single burn in 2 years. Warm-season perennial grasses other than tallgrasses and little bluestem increased on the Loamy site, but decreased on the Shallow site. Production of cool-season perennial grasses increased to almost 40% of total production on twice-burned plots averaged across sites. Other than the effect on cool-season perennial grasses, 2 burns over a two-year period had little effect beyond the first growing season after the second burn. Twice-burned plots and plots burned 3 times produced more forbs than either plots that were burned once or not burned. Production of perennial grasses was opposite that of forb production. Total production was not reduced on either site regardless of fire frequency. Results indicate managers may expect a short-term reduction in production of forage grasses and an increase in forbs following late growing-season fire in mid-successional tallgrass prairies.

Impacts of Rotational Grazing on Mixed Prairie Soils and Vegetation

In this study the impact of a rotation grazing system on the soil and vegetation of a Stipa-Bouteloua-Agropyron community in the mixed prairie ecoregion was compared with the ungrazed treatment in exclosures. At a low stocking rate, grazing had no effect on the vegetation but did alter soil quality. Grazing pressure was so light in the rotational grazing treatment that recovery of productivity, as measured by standing crop and litter, was not significantly different from the ungrazed treatment. Conversely, the species distribution was unchanged but was indicative of a lower seral state for this mixed prairie. The effect of grazing on this community was indirect, possibly by altering the microenvironment. The relationships observed among forage production, soil chemistry, and species composition raise questions on the importance of any one variable expressing range condition on the mixed prairie.