Moderate Grazing Intensity Research Articles

Carbon and nitrogen cycling in an integrated soybean-beef cattle production system under different grazing intensities

Abstract:The objective of this work was to evaluate the effect of grazing intensity on the decomposition of cover crop pasture, dung, and soybean residues, as well as the C and N release rates from these residues in a long-term integrated soybean-beef cattle system under no-tillage. The experiment was initiated in 2001, with soybean cultivated in summer and black oat + Italian ryegrass in winter. The treatments consisted of four sward heights (10, 20, 30, and 40 cm), plus an ungrazed area, as the control. In 2009-2011, residues from pasture, dung, and soybean stems and leaves were placed in nylon-mesh litter bags and allowed to decompose for up to 258 days. With increasing grazing intensity, residual dry matter of the pasture decreased and that of dung increased. Pasture and dung lignin concentrations and C release rates were lower with moderate grazing intensity. C and N release rates from soybean residues are not affected by grazing intensity. The moderate grazing intensity produces higher quality residues, both for pasture and dung. Total C and N release is influenced by the greater residual dry matter produced when pastures were either lightly grazed or ungrazed.

Sheep Excreta as Source of Nitrous Oxide in Ryegrass Pasture in Southern Brazil

ABSTRACT Livestock urine and dung are important components of the N cycle in pastures, but little information on its effect on soil nitrous oxide (N2O) emissions is available. We conducted a short-term (39-day) trial to quantify the direct N2O-N emissions from sheep excreta on an experimental area of ryegrass pasture growing on a Typic Paleudult in southern Brazil. Four rates of urine-N (161, 242, 323, and 403 kg ha-1 N) and one of dung-N (13 kg ha-1 N) were applied, as well as a control plot receiving no excreta. The N2O-N emission factor (EF = % of added N released as N2O-N) for urine and dung was calculated, taking into account the N2O fluxes in the field, over a period of 39 days. The EF value of the urine and dung was used to estimate the emissions of N2O-N over a 90-day period of pasture in the winter under two grazing intensities (2.5 or 5.0 times the herbage intake potential of grazing lambs). The soil N2O-N fluxes ranged from 4 to 353 µg m-2h-1. The highest N2O-N fluxes occurred 16 days after application of urine and dung, when the highest soil nitrate content was also recorded and the water-filled pore space exceeded 60 %. The mean EF for urine was 0.25 % of applied N, much higher than that for dung (0.06 %). We found that N2O-N emissions for the 90-day winter pasture period were 0.54 kg ha-1 for low grazing intensity and 0.62 kg ha-1 for moderate grazing intensity. Comparison of the two forms of excreta show that urine was the main contributor to N2O-N emissions (mean of 36 %), whereas dung was responsible for less than 0.1 % of total soil N2O-N emissions.

Forage nutritive value and steer responses to grazing intensity and seed-head suppression of endophyte-free tall fescue in mixed pastures

ABSTRACT A 2-yr grazing experiment was conducted with 8- to 10-mo old steers on pastures of endophyte-free tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] in mixture with other grasses to assess the effect of seed-head suppression of fescue on steer performance and forage nutritive values. Treatments with and without seed-head suppression were each combined with either light or moderate grazing intensities for assignment to twelve 1.0-ha pastures of the grass mixtures. The experiment was conducted as a randomized complete block design with 3 replications. Steer ADG was measured, and CP and in vitro DM digestibility (IVDMD) of available forage, and leaf blade and sheaths of fescue tillers, were monitored. Averaged over grazing intensities, ADG was 16% greater (P 0.18) between suppressed and nonsuppressed vegetative tillers, and both had greater (P

MICROBIAL CHARACTERISTICS OF SOILS UNDER AN INTEGRATED CROP-LIVESTOCK SYSTEM

Integrated crop-livestock systems (ICLs) are a viable strategy for the recovery and maintenance of soil characteristics. In the present study, an ICL experiment was conducted by the Instituto Agronômico do Paraná in the municipality of Xambre, Parana (PR), Brazil, to evaluate the effects of various grazing intensities. The objective of the present study was to quantify the levels of microbial biomass carbon (MBC) and soil enzymatic activity in an ICL of soybean (summer) and Brachiaria ruziziensis (winter), with B. ruziziensis subjected to various grazing intensities. Treatments consisted of varying pasture heights and grazing intensities (GI): 10, 20, 30, and 40 cm (GI-10, GI-20, GI-30, and GI-40, respectively) and a no grazing (NG) control. The microbial characteristics analysed were MBC, microbial respiration (MR), metabolic quotient (qCO2), the activities of acid phosphatase, β-glucosidase, arylsuphatase, and cellulase, and fluorescein diacetate (FDA) hydrolysis. Following the second grazing cycle, the GI-20 treatment (20-cm - moderate) grazing intensity) contained the highest MBC concentrations and lowest qCO2 concentrations. Following the second soybean cycle, the treatment with the highest grazing intensity (GI-10) contained the lowest MBC concentration. Soil MBC concentrations in the pasture were favoured by the introduction of animals to the system. High grazing intensity (10-cm pasture height) during the pasture cycle may cause a decrease in soil MBC and have a negative effect on the microbial biomass during the succeeding crop. Of all the enzymes analyzed, only arylsuphatase and cellulase activities were altered by ICL management, with differences between the moderate grazing intensity (GI-20) and no grazing (NG) treatments.

Eaten out of house and home: impacts of grazing on ground-dwelling reptiles in Australian grasslands and grassy woodlands.

Large mammalian grazers can alter the biotic and abiotic features of their environment through their impacts on vegetation. Grazing at moderate intensity has been recommended for biodiversity conservation. Few studies, however, have empirically tested the benefits of moderate grazing intensity in systems dominated by native grazers. Here we investigated the relationship between (1) density of native eastern grey kangaroos, Macropus giganteus, and grass structure, and (2) grass structure and reptiles (i.e. abundance, richness, diversity and occurrence) across 18 grassland and grassy Eucalyptus woodland properties in south-eastern Australia. There was a strong negative relationship between kangaroo density and grass structure after controlling for tree canopy cover. We therefore used grass structure as a surrogate for grazing intensity. Changes in grazing intensity (i.e. grass structure) significantly affected reptile abundance, reptile species richness, reptile species diversity, and the occurrence of several ground-dwelling reptiles. Reptile abundance, species richness and diversity were highest where grazing intensity was low. Importantly, no species of reptile was more likely to occur at high grazing intensities. Legless lizards (Delma impar, D. inornata) were more likely to be detected in areas subject to moderate grazing intensity, whereas one species (Hemiergis talbingoensis) was less likely to be detected in areas subject to intense grazing and three species (Menetia greyii, Morethia boulengeri, and Lampropholis delicata) did not appear to be affected by grazing intensity. Our data indicate that to maximize reptile abundance, species richness, species diversity, and occurrence of several individual species of reptile, managers will need to subject different areas of the landscape to moderate and low grazing intensities and limit the occurrence and extent of high grazing.

Carbon and nitrogen reserves in marandu palisade grass subjected to intensities of continuous stocking management

SUMMARYPlant organic reserves and sward leaf area index (LAI) influence plant growth, persistency and herbage accumulation in grazed swards. The present study was conducted to describe patterns of variation in herbage accumulation and carbohydrate and nitrogen (N) reserves in shoot and root of marandu palisade grass subjected to intensities of continuous stocking management throughout the year. Treatments corresponded to four levels of grazing intensity – severe (S), severe/moderate (S/M), moderate (M) and lenient (L) – and were implemented in the field using bands of sward surface height (SSH – 10, 20, 30 and 40 cm ± 10%, respectively) maintained through continuous stocking and variable stocking rate. Total N concentration was higher in the shoot relative to the root compartment during autumn, early and late spring. On the other hand, the concentration of non-structural carbohydrates (NSC) and soluble N was higher in the root compartment, regardless of grazing intensity and season of the year. When taking into account the pool of C and N reserves, the shoot compartment represented the main storage organ, since it corresponded to the largest pool of NSC (averages of 0·102 ± 0·0038 and 0·201 ± 0·0088 kg/m2 for root and shoot, respectively) and soluble N (averages of 2·7 ± 0·26 and 5·3 ± 0·59 kg/m2 for root and shoot, respectively). During late spring, the time of active plant growth, there was a clear contrast in herbage accumulation and sward LAI among grazing intensities, particularly between the severe and lenient grazing treatments. The results show that even with larger pools of soluble N and NSC in the shoot compartment, herbage accumulation was limited by the reduced leaf area of swards subjected to the severe grazing treatment, indicating that under continuous stocking growth seems to be sustained by current assimilates instead of organic reserves. Therefore, targets of grazing management for maximizing herbage accumulation throughout the year should provide adequate combinations between quantity and quality of sward leaf area. This condition was obtained in the severe/moderate and moderate grazing intensities, and corresponded to sward heights between 20 and 30 cm for marandu palisade grass.

Plant Diversity and Chemical Soil Composition of Rocky Pastures in Relation to the Sheep Grazing Intensity on the Northern Adriatic Islands (Croatia)

Abstract Optimal grazing pressure on rocky pastures is beneficial to the development of plant species and maintenance of plant diversity. Both abandonment of grazing and overgrazing gradually reduce plant diversity. This paper correlated abundance patterns of the flora on rocky pastures with the values of the chemical composition of the soil resulting from the degree of sheep grazing intensity. The study was carried out in the period from 2008 to 2010 on the islands of Pag, Krk and Cres. At 30 sites, 310 taxa of vascular plants were found. The highest plant diversity and 220 plant taxa were found on moderately grazed pastures. Abandoned pastures with a total of 93 plant taxa observed show the dominance of phanerophytes (35.5%) and the highest proportion of the Mediterranean floral element when compared to pastures of moderate and heavy grazing intensity. The highest concentration of total nitrogen in the soil (0.71%) was recorded on plots of heavy grazing intensity. The results of the study indicate that moderate grazing intensity, from 1 to 1.5 sheep ha−1, can be recommended on the northern Adriatic islands. This should contribute not only to the preservation of plant diversity, but also to the improvement of ecological sheep farming.

Influence of combined grazing by wild boar and small ruminant on soil and plant nutrient contents in a coppice oak forest

AbstractLimited information is available about the impact of grazing on soil and plant nutrient contents in Mediterranean deciduous oak forests grazed by both livestock and wild life. Thus, the main objective of this study was to investigate the effect of wild boar and small ruminants grazing in a coppice oak forest in N Greece. Eight even‐aged stands of similar canopy cover and site quality were selected: four stands with long‐time grazing mainly by wild boar and four stands with long‐time grazing by sheep and goats. A plot of 150 m2in each of the stands was fenced in order to be protected from grazing. A similarly sized plot open to grazing was assigned next to the fenced plot. Species composition was recorded in fenced and grazed plots. Soil samples and individual plants of the dominant palatable grass speciesDactylis glomerata andBrachypodium sylvaticumwere collected in every fenced and grazed plot. These samples were analysed for contents of nutrients. The results indicated that grazing increased organic matter, C, and total N, P and Ca, while it had no effect on the plant nutrients Mg, Na, K and all micronutrients, and pH as well. Wild boar grazing had a significantly negative impact on the concentrations of Na, Fe, Zn, and Mn in the soil. Beside a decrease in K and Mn, grazing had minimal effects on the contents of plant nutrients. Conversely, wild boar grazing increased the contents of several nutrients such as N, Na, Cu and Fe in plant tissue. It seems that species composition was more affected by the topography and management than by the soil features as revealed by RDA analysis. The results of this study indicate that it is important to maintain moderate small ruminant grazing intensity for the sustainable multi‐disciplinary management of coppice oak forests. It is also important to control wild boar population in order to facilitate ecosystem process, soil preservation and forage quality.

Italian ryegrass establishment by self-seeding in integrated crop–livestock systems: Effects of grazing management and crop rotation strategies

We evaluated the re-establishment of an Italian ryegrass pasture by self-seeding on a no-till integrated crop–livestock systems (ICLS) in the southern region of Brazil. This work is part of a long-term experimental protocol initiated in 2003. We tested the effects of various management practices, such as summer crop systems (soybean vs. maize–soybean rotation), stocking methods (continuous vs. rotational) and grazing intensities (low vs. moderate), on Italian ryegrass pasture establishment. In addition, we tested resilience of the system by testing pasture's ability to re-establish following a year without seed head production. The experiment consisted in the rotation, on the same area, of Italian ryegrass pasture grazed by sheep during the winter and up to the end of the grass production cycle, and soybean or soybean–maize grain crops rotation cultivated during the summer. The pasture established itself by self-seeding since 2005. Data were collected in 2011 and 2012 stocking season. The soybean summer crop, continuous stocking and low grazing intensity, all positively affected the production of reproductive tillers in 2011. Grazing intensity in 2011 strongly influenced early vegetative tiller densities (before crop harvest) in 2012. However, none of the grazing intensity or the stocking method treatments affected herbage mass at the end of pasture establishment in 2011 or 2012. On the other hand, the soybean summer crop positively affected pasture establishment, both in term of tiller densities and herbage mass at the end of pasture establishment. The removal of all seed heads in 2011 (preventing seed production) resulted in the total failure of pasture establishment in 2012. Overall, Italian ryegrass establishment by self-seeding relies on the annual replacement of the soil seed bank. This experiment demonstrated that under various stocking methods, moderate grazing intensity and maize or soybean summer crop, Italian ryegrass pasture establishment by self-seeding remains successful even when the stocking periods extended up to the end of the grass production cycle. Self-seeding with moderate grazing intensity ensures successful pasture establishment, reduces labour and costs and allows to increase the stocking period and so animal live weight gain over the grazing season.

Local and regional long‐term diversity changes and biotic homogenization in two temperate grasslands

AbstractQuestionsAre there losses in species richness due to extinctions? Is the input of new species lower in environments with strong resource limitation? Is there a decrease in abundance and diversity of native species due to anthropogenic disturbance at local and regional scale? Has abundance of exotic species been favoured by grazing increased? Are floristic changes associated with homogenization processes?LocationTwo grassland community types of the Argentine Flooding Pampas: the mesophyte prairie and the halophyte steppe.MethodsGrassland sites (n = 51) were resurveyed with the same methodology after 35 yr. At the local scale (0.25 ha), we analysed alpha diversity, site colonization and extinction rates, and changes in species and functional type composition. Site colonization rates were calculated separately for new species (not recorded in the original inventory) and old species (present in the first survey at other sample sites of the community). Correspondence analysis was applied to the presence/absence species matrix for all sites in both periods. At regional scale, we evaluated gamma diversity, heterogeneity within and between communities, changes in proportion of functional types (growth season, longevity and life form) and species origin.ResultsIn the mesophytic prairie, average local species richness increased 46% and regional richness 28%, while in the halophytic steppe changes were not significant. The colonization rate was higher and the extinction rate lower in the richest community (mesophytic prairie). Differences in colonization rates between natives and exotics were not found. Principal variability between sites in species composition was associated with abiotic conditions explaining 20.9% of inertia, temporal changes were relegated to the second axis with 6.38%. Proportions of warm‐season exotics among new arrivals were higher than expected. Biotic homogenization was evidenced in the mesophytic prairie as a significant reduction in species turnover between sampling dates.ConclusionsAfter 35 yr under moderate grazing intensity we found increases in species richness, no biodiversity loss and no losses of native species. Instead of those species favoured by grazing, as expected, warm season species increased. Different grassland communities showed clear differences in richness changes, in degree of homogenization and in species turnover.

Grazing intensity and stocking methods on animal production and methane emission by grazing sheep: Implications for integrated crop–livestock system

Among the various sources with a potential negative impact on the environment, methane (CH4) emissions from livestock origin have been highlighted as important for the agricultural sector. Research to mitigate CH4 emissions and understand how integrated crop and livestock production systems may contribute to the reduction of greenhouse gases, is essential for the development of public policies for environmental preservation. We hypothesized that combinations of stocking methods and grazing intensities provokes differences in the quantity and quality of herbage ingested, thus altering animal production and CH4 emissions by the grazing animal. Experiments were carried out in 2011 (Experiment 1) and 2012 (Experiment 2), when the production of pasture and CH4 emissions from sheep were studied in a system that integrates soybean (Glycine max. (L.) Merr.) and maize (Zea mays L.) in the summer/autumn, in rotation with Italian ryegrass (Lolium multiflorum Lam.) in winter/spring. Two stocking methods (continuous or rotational) and two grazing intensities (herbage allowance: moderate and low, 2.5 and 5 times the potential daily dry matter intake, respectively) in a randomized complete block design with three replicates were studied. Lambs were used in the first experiment, while lactating ewes (all with a single lamb) were used in the second experiment. Average daily gain (ADG) of lambs was greater (P<0.05) in continuous than in rotational stocking, regardless of grazing intensity (150 vs. 89gday−1 and 241 vs. 209gday−1 in Experiments 1 and 2, respectively). Ewe ADG did not differ (P>0.05) between treatments. Live weight gain per hectare (LWGHA) showed the same response in both experiments, with greater LWGHA in moderate grazing intensity (P<0.05). In Experiment 1, the dry matter intake (DMI) was on average 21% greater (P<0.05) for continuous stocking than rotational stocking (1345gday−1 vs. 1075gday−1, respectively), while in Experiment 2, no differences (P>0.05) between stocking methods and grazing intensities were observed (1673±83gday−1). The CH4 emissions per animal did not differ (P>0.05) among treatments in both experiments (22.7±1.0 and 39.9±1.3gday−1, Experiments 1 and 2, respectively), but when expressed in g CH4kgADG−1 emissions were on average 35 and 15% greater (Experiments 1 and 2, respectively) (P<0.05) under rotational than continuous stocking, independent of grazing intensity (171 vs. 263g CH4kgADG−1 and 171 vs. 202g CH4kgADG−1 in Experiments 1 and 2, respectively). Stocking method was more important than grazing intensity in determining methane production by grazing sheep. Continuous stocking was the most efficient grazing management in reducing methane emissions per unit animal production.

Soil carbon and nitrogen stocks and fractions in a long-term integrated crop–livestock system under no-tillage in southern Brazil

Managing grazing stocks in integrated crop–livestock (ICL) systems under no-tillage is a key variable for reaching equilibrium in soil C and N budgets. Understanding how different plant and animal residues affect soil C and N stocks in these systems goes beyond soil dynamics since these elements are crucial for the functioning of the soil–plant–atmosphere system. The objective of this research was to determine soil C and N fractions, stocks, budgets and the carbon management index as affected by nine years of ICL with grazing intensities under no-tillage conditions. The experiment established in May 2001 in a Rhodic Hapludult (Oxisol) of southern Brazil was composed of black oat (Avena sativa) plus ryegrass (Lolium multiflorum) pasture in winter and soybean (Glycine max) crop in summer. Treatments were regulated by grazing pressures to maintain forage at 10, 20, 30 and 40cm high (G10, G20, G30 and G40, respectively). Non-grazed (NG) treatment was the control. Changes in soil C and N stocks and fractions (particulate and mineral-associated) were assessed in the ninth year of the experiment. Moderate and light grazing intensities (G20, G30 and G40) resulted in similar increases in total organic C, particulate organic C, total N, and particulate organic N compared with NG treatment. Soil C additions ranged from 0.54 to 8.68Mgha−1 from NG to the other grazing treatments. The G10 led to a soil N loss of 1.17Mgha−1 due to soil organic matter degradation. The carbon management index (CMI) values, compared with native forest (NF) as a reference, indicated soil quality loss and degradation under high grazing intensity (G10). For a positive contribution to the soil system, ICL must be managed with moderate grazing intensities and adjustment of N additions through N fixation or fertilization.

Italian ryegrass establishment by self-seeding in integrated crop-livestock systems: Effects of grazing management and crop rotation strategies

We evaluated the re-establishment of an Italian ryegrass pasture by self-seeding on a no-till integrated crop-livestock systems (ICLS) in the southern region of Brazil. This work is part of a long-term experimental protocol initiated in 2003. We tested the effects of various management practices, such as summer crop systems (soybean vs. maize–soybean rotation), stocking methods (continuous vs. rotational) and grazing intensities (low vs. moderate), on Italian ryegrass pasture establishment. In addition, we tested resilience of the system by testing pasture's ability to re-establish following a year without seed head production. The experiment consisted in the rotation, on the same area, of Italian ryegrass pasture grazed by sheep during the winter and up to the end of the grass production cycle, and soybean or soybean-maize grain crops rotation cultivated during the summer. The pasture established itself by self-seeding since 2005. Data were collected in 2011 and 2012 stocking season. The soybean summer crop, continuous stocking and low grazing intensity, all positively affected the production of reproductive tillers in 2011. Grazing intensity in 2011 strongly influenced early vegetative tiller densities (before crop harvest) in 2012. However, none of the grazing intensity or the stocking method treatments affected herbage mass at the end of pasture establishment in 2011 or 2012. On the other hand, the soybean summer crop positively affected pasture establishment, both in term of tiller densities and herbage mass at the end of pasture establishment. The removal of all seed heads in 2011 (preventing seed production) resulted in the total failure of pasture establishment in 2012. Overall, Italian ryegrass establishment by self-seeding relies on the annual replacement of the soil seed bank. This experiment demonstrated that under various stocking methods, moderate grazing intensity and maize or soybean summer crop, Italian ryegrass pasture establishment by self-seeding remains successful even when the stocking periods extended up to the end of the grass production cycle. Self-seeding with moderate grazing intensity ensures successful pasture establishment, reduces labour and costs and allows to increase the stocking period and so animal live weight gain over the grazing season.

Effects of different grazing intensities on grassland production in China: a meta-analysis.

BackgroundGrazing is one of the main grassland disturbances in China, and it is essential to quantitatively evaluate the effects of different grazing intensities on grassland production for grassland carbon budget and sustainable use.MethodsA meta-analysis was conducted to reveal general response patterns of grassland production to grazing in China. We used weighted log response ratio to assess the effect size, and 95% confidence intervals to give a sense of the precision of the estimate. Grazing effects were estimated as a percentage change relative to control (%).ResultsA total of 48 studies, including 251 data sets, were included in the meta-analysis. Grazing significantly decreased total biomass by 58.34% (95% CI: −72.04%∼−37.94%, CI: Confidence Interval), increased root/shoot ratio by 30.58% and decreased litter by 51.41% (95% CI: −63.31%∼−35.64%). Aboveground biomass and belowground biomass decreased significantly by 42.77% (95% CI: −48.88%∼−35.93%) and 23.13% (95% CI: −39.61%∼−2.17%), respectively. However, biomass responses were dependent on grazing intensity and environmental conditions. Percentage changes in aboveground biomass to grazing showed a quadratic relationship with precipitation in light grazing intensity treatment and a linear relationship in moderate and heavy grazing intensity treatment, but did not change with temperature. Grazing effects on belowground biomass did not change with precipitation or temperature. Compared to the global average value, grazing had greater negative effects on grassland production in China.ConclusionsGrazing has negative effects on grassland biomass and the grazing effects change with environmental conditions and grazing intensity, therefore flexible rangeland management tactics that suit local circumstances are necessary to take into consideration for balancing the demand of grassland utilization and conservation.

Perfilhamento em pastagens de azevém em sucessão a soja ou milho, sob diferentes métodos e intensidades de pastejo

O objetivo deste trabalho foi avaliar a densidade populacional de perfilhos, a massa de forragem, o padrão populacional de perfilhamento e o índice de estabilidade de pastagens de azevém anual (Lolium multiflorum) estabelecidas após os cultivos de soja ou milho, submetidas a diferentes métodos e intensidades de pastejo por cordeiros. Foram avaliados os métodos de pastejo rotativo e contínuo, sob as intensidades moderada (oferta de forragem correspondente a 2,5 vezes o potencial de consumo de cordeiros) e baixa (correspondente a 5,0 vezes). Utilizou-se o delineamento experimental de blocos ao acaso, em arranjo fatorial 2x2x2, com quatro repetições. As avaliações foram feitas mensalmente, entre agosto e outubro de 2010, durante a fase de pastejo. A densidade populacional de perfilhos apresentou diferenças significativas para métodos e intensidades de pastejo, e foi maior na área previamente cultivada com soja. As maiores massas de forragem foram observadas em pastagens subsequentes à soja e com baixa intensidade de pastejo, enquanto as menores, nas pastagens subsequentes ao milho e com moderada intensidade de pastejo. No período de florescimento, a densidade de perfilhos reduziu-se e suas massas individuais aumentaram. A intensidade de pastejo moderada reduz o percentual de perfilhos florescidos. A redução da densidade de perfilhos durante o florescimento não compromete o índice de estabilidade do pasto.

内蒙古荒漠草原主要草食动物食性及其营养生态位

PDF HTML阅读 XML下载 导出引用 引用提醒 内蒙古荒漠草原主要草食动物食性及其营养生态位 DOI: 10.5846/stxb201207281071 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 中国科学院"百人计划"优先资助项目(292005312D1102626);中国科学院知识创新工程方向性项目(KSCX2-YW-N-040)资助 The diet composition and trophic niche of main herbivores in the Inner Mongolia Desert steppe Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探讨荒漠草原主要食草动物(绵羊、达乌尔黄鼠和亚洲小车蝗)的食性及其种间生态位变化与草原退化的关系,以内蒙古苏尼特右旗荒漠草原为研究对象,于2003年7-8月运用饱和链烷技术研究小针茅群落不同放牧强度下绵羊、达乌尔黄鼠和亚洲小车蝗的食性及其生态位变化。结果表明:随牧压的增大,群落中小针茅数量显著减少,猪毛菜比例随着增加;绵羊、达乌尔黄鼠、亚洲小车蝗3种食草动物的主要食物均来源于猪毛菜,且采食比例随牧压增大而递增;3种食草动物对牧草的选择性指数随牧压的变化而变化,双齿葱和多根葱优先被采食;三者生态位重叠程度很高且生态位宽度随牧压的增加而变窄。重度放牧改变了小针茅群落的植物组成,使其演替为猪毛菜群落,3种食草动物对草地资源存在激烈的竞争,因此,控制鼠、虫的种群密度,防止鼠、虫害的发生对保证放牧家畜的食物安全具有十分重要的现实意义。 Abstract:In recent years, degradation of the natural grassland areas of Inner Mongolia has been particularly severe. Many factors have contributed to grassland degradation, including frequent grazing, trampling and damage by herbivores. These factors have not only changed the structure of the plant communities and plant species composition; they have also affected community succession. To examine the effects of grassland degradation on the dietary composition and trophic niches of the main herbivores of the Inner Mongolian desert steppe (Ovis aries, Spermophilus dauricus, Oedaleus asiaticus), we measured changes in the dietary composition and trophic niches occupied by these herbivores under different intensity grazing regimes in June-July 2003 using an n-alkane technique. The results showed that the richness of Stipa klemenzii-dominated communities decreased significantly with increased grazing intensity, whereas the proportion of Salsola collina in the community increased. Salsola collina was the main food source for Ovis aries, Spermophilus dauricus and Oedaleus asiaticus. Six to eight plant species were ingested by Ovis aries but Salsola collina made up the largest proportion of its diet. The other main species ingested by Ovis aries were Allium bidentatum,Cleistogenes songorica and Allium polyrhizum. Five to seven plant species were ingested by Spermophilus dauricus in Stipa klemenzii-dominated communities, but Allium bidentatum and Salsola collina were consumed to a greater extent than other species. Spermophilus dauricus fed less selectively on Salsola collina with increased levels of grazing intensity and more selectively on Stipa krylovii. Overall, Spermophilus dauricus fed most selectively on Allium bidentatum, which had the highest selectivity index score. Five plant species were ingested by Oedaleus asiaticus, but Cleistogenes songorica and Salsola collina constituted the largest proportion of its diet. The selectivity indices of Oedaleus asiaticus for Salsola collina and Allium polyrhizum were lower with increased grazing intensity, while the selectivity indices for Cleistogenes songorica and Stipa krylovii increased. The selectivity index of Oedaleus asiaticus for Allium bidentatum was highest at moderate grazing intensities. Analysis of variance tests on grazing intensity, herbivore identity and plant species factors revealed significant differences between each factor that we examined (P < 0.05) and significant (P < 0.01) interactions between any two factors or among the three factors. The proportion of plant species ingested by herbivores in ungrazed plots was significantly (P < 0.05) lower than that in grazed plots, but there was no significant difference between moderate grazing and heavy grazing intensity plots. The proportion of plant species ingested by Ovis aries was significantly (P < 0.05) lower than that ingested by Spermophilus dauricus and Oedaleus asiaticus, but multiple comparisons of the diets of different herbivores showed that there was no significant difference between Spermophilus dauricus and Oedaleus asiaticus. Trophic niche breadth of the three herbivores became increasingly narrow with increasing grazing intensity. There was a great deal of overlap among the three herbivores with the greatest trophic overlap occurring between Ovis aries and Spermophilus dauricus. There was also considerable overlap in the diets of Ovis aries and Oedaleus asiaticus, Spermophilus dauricus and Oedaleus asiaticus. In summary, heavy grazing on the Inner Mongolian desert steppe changed a Stipa klemenzii-dominated community into a Salsola collina-dominated community. This succession led to the degradation of the grassland, and to fierce competition for resources among the three main herbivorous species. Therefore, controlling pests and mice population densities to prevent outbreaks is important for grazing livestock and food safety. 参考文献 相似文献 引证文献

Variation in specific composition and cover in grassland exposed to various grazing pressures in the Monte Rionegrino

In the western Monte Phytogeographical Province of Rio Negro, vegetation is a shrubby-grassland steppe, where plants are interspersed within a bare soil matrix forming “phytogenic islands”. The objective of this study was to evaluate the specific composition and cover of the study ecological system under different grazing pressures. We selected areas with high, moderate and low grazing intensity at three sites. In each area we established five linear transects, where basal cover and all intercepted species were registered. Sites were arranged through a Principal Component Analysis using the Infostat software. We analyzed similarity between sites, considering basal cover and species present in islands and inter-islands, and in both situations together. Islands and inter-islands were separated especially by the presence of shrubby species. Exclosure areas showed a greater cover of <i>Poa ligularis</i>, litter and biological crusts, whereas intense grazed areas presented a greater cover of bare soil. Grazing by itself and different grazing pressures can modify the specific composition at an island and inter-island scale. Greater cover of biological crusts could help recovery of the study system.

Ingestion and excretion of nitrogen and phosphorus by beef cattle under contrasting grazing intensities

AbstractThere is increased global interest in the environmental impacts of farming, including the need to prevent the contamination of soil, water and air with excessive amounts of nitrogen (N) and phosphorus (P) in grazed systems. Reduction in grazing intensity has frequently been recommended to meet biodiversity and production goals in sustainable grazing systems. The objective of this experiment was to measure N and P ingestion and excretion by beef cattle grazing semi‐natural pastures at two grazing intensities (Moderate or Lenient). The cattle grazing at Moderate grazing intensity had significantly more defaecations each day than those grazing at Lenient intensity (9·5 vs. 7·5) and tended to have more urinations (7·0 vs. 5·8). For the Moderate and Lenient treatments, respectively, 113 vs. 76 g N d−1 was excreted compared with 136 vs. 94 g N d−1 ingested; 12 vs. 8 g P d−1 was excreted compared with 13 vs. 10 g P d−1 ingested and urine N comprised 0·51 and 0·52 of the total N excreted each day. In improved, intensively managed grassland systems, urine N comprises a much higher proportion (approximately 0·70–0·85) of the daily total N excreted. The lower level found here is likely to impact on potential volatilization, denitrification and leaching losses, and these aspects should be examined further to see the extent to which semi‐improved grasslands containing increased plant diversity compared with improved grasslands can deliver higher resource protection, as well as enhanced grassland faunal diversity and abundance.

Recria de borregas sob diferentes métodos de pastoreio em azevém anual em sucessão a lavoura

O objetivo deste trabalho foi avaliar a recria de borregas em pastagem de azevém anual (Lolium multiflorum) em sucessão a lavouras de milho ou soja, manejadas em intensidades de pastejo moderada ou baixa, com métodos de pastoreio rotativo ou contínuo. Utilizou-se o delineamento experimental de blocos ao acaso em arranjo fatorial 2 intensidades x 2 métodos de pastoreio, com quatro repetições. Não houve interação entre os métodos e as intensidades de pastejo. A intensidade de pastejo baixa determinou maior massa média de forragem e altura do pasto. A altura e a massa de forragem foram maiores no pastoreio rotativo. Não houve diferença para ganho médio diário. Houve diferença significativa para carga animal para o método rotativo e a intensidade de pastejo moderada. O ganho de peso por hectare foi maior para intensidade de pastejo moderada. A intensidade de pastejo e o método de pastoreio empregados não afetaram a produtividade de soja ou milho em sucessão. A forragem disponível é a principal determinante da produtividade do sistema integrado, independentemente do método de pastoreio.

Diversidade metabólica e atividade microbiana no solo em sistema de integração lavoura-pecuária sob intensidades de pastejo

O objetivo deste trabalho foi avaliar a diversidade metabólica e a atividade microbiana, em sistema de integração lavoura-pecuária em plantio direto, sob diferentes intensidades de pastejo e produção de soja. O experimento foi realizado em São Miguel das Missões, RS, em Latossolo Vermelho distroférrico argiloso, submetido ao pastejo a 10, 20, 30 e 40 cm de altura de azevém + aveia-preta, e sem pastejo, no inverno. A diversidade metabólica foi avaliada com microplacas Biolog EcoPlate pelo índice de diversidade de Shannon, e a atividade microbiana pelo método de hidrólise do diacetato de fluoresceína. Houve maior diversidade funcional a intensidades moderadas de pastejo (20 a 40 cm). A maior atividade microbiológica no solo ocorreu no tratamento sem pastejo, em consequência da grande quantidade de resíduos vegetais remanescentes. A diversidade funcional da microbiota e a atividade microbiana tiveram alterações causadas pelas intensidades de pastejo, que podem ser utilizadas como indicadores de qualidade do solo, em sistema de integração lavoura-pecuária em plantio direto.