Grazing Treatments Research Articles

Grazing decreased soil organic carbon by decreasing aboveground biomass in a desert steppe in Inner Mongolia

The mechanisms through which stocking rates affect soil organic carbon in desert steppe landscapes are not fully understood. To address this research gap, we investigated changes in the biomass of Stipa breviflora plant communities and soils in a desert steppe. Through our research findings, we can establish an appropriate stocking rate for Stipa breviflora desert steppe. The establishment serves as a theoretical foundation for effectively maintaining elevated productivity levels and increasing the carbon sink, thereby offering a valuable contribution towards mitigate climate change.This study examined the effects of different stocking rates on soil organic carbon input, sequestration, and output and found: (1) For soil organic carbon input, the aboveground and litter biomass of plant communities decreased with increasing stocking rate. (2) Grazing treatments did not affect soil organic carbon retention. (3) Regarding soil organic carbon output, the grazing treatments exhibited no significant alteration in soil respiration when compared to the no grazing. In summary, the primary mechanisms through which increasing stocking rates affect the soil organic carbon pool are decreased inputs from plants and increased output through wind erosion. Therefore, decreasing grazing intensity is key to improving soil organic carbon retention in the desert steppe.

Grazing subirrigated meadow regrowth influences subsequent‐year plant production and nutritive value

AbstractSubirrigated and mesic meadow ecosystems are an important forage resource for livestock operations, being used for hay production, grazing, or a combination of both. Our study evaluated how timing and intensity of grazing meadow regrowth following a summer hay harvest influenced subsequent‐year plant production and forage nutritive value. Cattle grazed within established meadow paddocks during prefreeze (fall) or postfreeze (late‐fall/early‐winter) time periods at two utilization rates, moderate (53.0% ± 4.9%) or heavy (66.1% ± 4.9%), from 2018 to 2020 in four randomized compete blocks. Meadow regrowth available for grazing was 24% less between the prefreeze and postfreeze grazing periods, and forage crude protein (CP) decreased from 136 to 84 g kg−1 over the same period (p < 0.01). Prefreeze grazing reduced (p = 0.03) subsequent‐year graminoid production by 11.2% compared to grazing occurring during the postfreeze period and 10.5% (p = 0.08) compared to a non‐graze control; however, subsequent‐year total live plant production (graminoids and forb/legumes) did not differ among the grazing time and intensity treatments. Subsequent‐year forage nutritive value was variable by year and grazing treatment, but tended to follow the amount of forb/legumes present in total plant biomass (CP, R2 = 0.72; p < 0.01). Grazing meadow regrowth during the prefreeze period provides opportunities to better utilize greater forage quantity at a higher nutritive value, but periodically rotating grazing timing from prefreeze to postfreeze could limit negative effects of grazing during the prefreeze period on subsequent‐year graminoid biomass.

Symbiotic diazotrophs in response to yak grazing and Tibetan sheep grazing in Qinghai-Tibetan plateau grassland soils.

Grazing by local livestock is the traditional human practice in Qinghai-Tibetan Plateau grassland, and moderate intensity grazing can maintain high productivity and diversity of alpine grassland. Grazing ecosystems are often nitrogen-limited, but N2-fixing communities in response to yak grazing and Tibetan sheep grazing in Qinghai-Tibetan Plateau grassland have remained underexplored. In this study, we applied quantitative PCR quantitation and MiSeq sequencing of nifH under yak grazing and Tibetan grazing through a manipulated grazing experiment on an alpine grassland. The results showed that the grazing treatments significantly increased the soil ammonium nitrogen (AN) and total phosphorus (TP), but reduced the diazotrophs abundance. Compared with no grazing treatment, the composition of diazotrophs could be maximally maintained when the ratio of yak and Tibetan sheep were 1:2. The foraging strategies of grazing livestock reduced the legumes biomass, and thus reduced the diazotrophs abundance. Data analysis suggested that the direct key factors in regulating diazotrophs are AN and TP, and the changes of these two soil chemical properties were affected by the dung and urine of herbivore assemblages. Overall, these results indicated that the mixed grazing with a ratio of yak to Tibetan sheep as 1:2 can stabilize the soil diazotrophsic community, suggesting that MG12 are more reasonable grazing regimes in this region.

Effects of daytime or night-time grazing on animal performance, diurnal behaviour and enteric methane emissions from dairy cows at high latitudes

ABSTRACT This study compared animal performance and enteric methane (CH4) emissions from dairy cows in a part-time grazing (PTG) system in northern Sweden. Twenty-four Nordic Red dairy cows were allocated to one of two treatments: DAY (10 h daytime pasture access) or NIGHT (12 h night-time pasture access). The cows in each treatment received the same ad libitum partial mixed ration (PMR) indoors and ad libitum herbage allowance. Methane was recorded using two linked GreenFeedTM emissions monitoring (GEM) units, on pasture and indoors. Day or night grazing showed no statistical differences in estimated grass or PMR intake, milk production or daily enteric CH4 emissions. There was a rapid decrease in diurnal CH4 emissions (28%) when the cows were moved from indoors to pasture in both grazing treatments. Using two GEM units (indoor, outdoor) in combination improved the diurnal assessment of enteric CH4 emissions during PTG conditions in the mixed feeding system.

Fecal NIRS to estimate intake and diet composition in Sarda dairy ewes fed mixed diets or part-time grazing forage crops

Knowledge on the intake and diet composition is a key to efficiently and sustainably drive ruminant production systems. Near infra-red spectroscopy of fecal samples (F.NIRS) has been proposed as a tool to estimate intake, diet composition and digestibility of ruminants. This study was aimed at ascertaining if F.NIRS can precisely and accurately predict 1) individual dietary intake and composition in dairy sheep fed mixed diets in confinement; 2) group dietary intake and composition in grazing dairy ewes using spot sampled faeces. We used two main datasets consisting of pairs of NIRS fecal spectra and reference values for intake, nutrient digestibility and composition of the diet: STALL, based on the results of digestibility trials carried out on a total of 120 sheep individually fed mixed diets including fresh forages, hays and concentrates (29 diets) and GRAZE based on results of already published grazing experiments. GRAZE encompassed a total of 102 pairs of group fecal spectra and group reference values regarding 6 grazing treatments differing in forage species, supplementation type and access time to pasture, in which reference data were obtained by double weighing procedure for herbage intake and hand-plucking for herbage composition. Group fecal samples were collected the day after. Data of the two datasets were separately used to calibrate F.NIRS using partial least square regression analysis and subsequent cross-validation. The quality of calibrations was evaluated using the ratio performance deviation (RPDcv). The diet attributes showing RPDcv in a range good to excellent (RPD > 3) in cross-validation were submitted to a validation exercise, on a subset of data previously excluded from calibration. Validation performance were evaluated as RPDval. Under confined conditions, individual herbage intake was predicted with good precision R2val = 0.90 and accuracy, SEP = 11.6% (RDPval = 3.2). The intake of hay was also well predicted (R2val = 0.97, SEP = 9.9%, RPDval = 4.6), whereas that of concentrates was just fairly predicted with R2val = 0.88 but a lower accuracy (SEP = 26.7%, RPDval = 2.9). The estimation of individual diet composition (% ingredients) was excellent for herbage and hay and good for concentrate, with R2val = 0.97, SEP = 11.2% and RPDval = 4.9 for hay; R2val = 0.97, SEP = 6.7% and RPDval = 5.5 for herbage; and R2val = 0.95, SEP = 26.7% and RPDval = 4.5 for concentrates. Prediction of nutrient proportion in the diet (% DM) was good for NDF, ADF, EE (RPDval ≥ 3) but inadequate for NFC (RPDval = 1.5). Cross-validation models were rather imprecise for CP and OM. Individual digestibility coefficients were poorly estimated in cross-validation, being the best models those estimating the digestibility of NFC (R2cv = 0.83, SECV% = 2.3, RPDcv = 2.4) and ADF (R2cv = 0.81, SECV% = 9.3, RPDcv= 2.3). Under grazing conditions, after cross-validation all models showed RPD < 3. The group intake of herbage was estimated with a modest precision and accuracy (R2cv = 0.75, SECV% = 14.2, RPDcv = 2.0). The proportion of herbage in the diet and its NDF content showed a higher accuracy, and equal or better precision, although models were adequate only for rough screening (RPDcv = 2 and 2.3, respectively). To conclude, this research confirms for dairy sheep the usefulness of F.NIRS to estimate individual intake and individual diet composition in ruminants fed mixed diets in confinement. Moreover, this study shows a modest cross-validation performance of F.NIRS for estimating group average proportion of herbage and NDF in the diet of grazing ewes by spot-sampling their faeces. Further validation of these models is needed to assess the applicability of the above results to farm conditions.

Plant functional traits and biodiversity can reveal the response of ecosystem functions to grazing

Plant functional traits can elucidate the response of plant communities and ecosystems to biotic and abiotic disturbances. However, whether livestock consume more aboveground biomass (AGB) in communities dominated by species with ‘acquisitive’ traits or in communities where biodiversity is high is not well known. Here, we measured 22 functional traits of the grazing communities and control communities in a Mongolian Plateau desert steppe. The effects of grazing on AGB, CWM traits, species diversity, and functional diversity (FD) were analysed, furthermore, we estimated the grazing impact by using the log response ratio (LRR, an increasing value shows a higher grazing impact) and investigated the correlations between the LRR, plant growth, and community-weighted mean (CWM) traits and diversity indices. We found that grazing significantly increased the CWM dry matter content and carbon-to‑nitrogen ratio and decreased the CWM height, specific leaf area (SLA), and nitrogen and phosphorus contents. The AGB decreased, while species diversity and FD increased under grazing treatments. Additionally, we found that plant traits and biodiversity could predict the response of AGB to grazing, the LRR was higher in patches dominated by species with ‘acquisitive’ foliage and in patches with higher biodiversity; in these patches, plant growth was lower. In the study area, the response of CWM traits to grazing suggests an avoidance strategy, which may be more conducive for adapting to low resource utilization environments. Also, the relationship between the CWM traits and the LRR indicated that the effect of grazing on AGB was mainly related to the selective foraging of herbivores. In addition, patches preferred by livestock may not recover quickly, leading to slow growth and thus reduced biomass under grazing treatments after prolonged grazing.

Impact of cattle grazing corn residue in spring on soil and subsequent soybean yield

AbstractThe effects of spring corn (Zea mays) residue grazing and stocking density on soil physical properties and subsequent soybean (Glycine max) yield were evaluated in an experiment with three treatments: no grazing (NG), normal stocking density (NSD), and high stocking density (HSD). The study was conducted over 2 years with four replicates per treatment each year. Steers (277 ± 4.4 kg) were stocked at 7.5 steers/ha for NSD with a target grazing of 45 days starting in mid‐February, and 22.5 steers/ha for HSD with a target grazing of 15 days in mid‐March, such that the stocking rate was equal. Bulk density, penetration resistance, and surface roughness were measured pre‐ and post‐planting. At 0‐to‐5‐ and 5‐to‐10‐cm depths, bulk density and penetration resistance were greater (p &lt; 0.01) for NSD than NG. There was no difference in bulk density (p ≥ 0.45) between grazed treatments. At 0–5 cm, penetration resistance was not different (p = 0.29) between grazed treatments. For 5–10 cm, penetration resistance was greater (p = 0.02) for HSD compared to NSD. Surface roughness was greater (p &lt; 0.01) for NSD than NG, and greater (p &lt; 0.01) for HSD than NSD. There was no difference (p ≥ 0.34) in soybean emergence among treatments. Soybean yield was less (p &lt; 0.01) for NG than NSD, but did not differ (p = 0.06) between NSD and HSD. The results indicate that spring grazing may cause minor compaction without reducing subsequent soybean yield.

Managing Medusahead Using Dormant Season Grazing in the Northern Great Basin

The invasive annual grass, medusahead, infests rangelands throughout the West, from the Columbia Plateau to the California Annual Grasslands and the Great Basin. Dominating secondary succession in the sagebrush steppe, medusahead can degrade the habitat of threatened species such as the greater sage-grouse. This research explores the potential of dormant season grazing as an applied management strategy to reduce the negative impacts of medusahead while promoting recovery of perennial vegetation at the landscape scale. In particular, it assessed grazing with four treatments from 2018 to 2020: traditional grazing (May–October), dormant season grazing (October–February), traditional + dormant season grazing (May–February), and no grazing. After 2 yr of grazing treatments, biomass, density, cover, and fuel continuity did not differ between treatments (P > 0.05). However, biomass measurements were significantly different between years, which is likely due to greater than normal precipitation in 2019 and 2020. Between 2018 and 2019, annual grass biomass increased by 81% (666–1 212 kg ha−1) and perennial grass biomass increased by 165% (118–313 kg ha−1). Litter biomass decreased by approximately 15% in every year since 2018 (2 374, 2 012, and 1 678 kg ha−1 in 2018–2020). There were not significant differences in cover or density of annual and perennial grasses between treatments and years. Our results indicate that 2 yr may not be adequate time for dormant season grazing treatments to be effective in reducing the abundance of medusahead and that after 2 yr of treatments, dormant season grazing does not have a detrimental effect on perennial vegetation.

Grazing facilitates litter-derived soil organic carbon formation in grasslands by fostering microbial involvement through microenvironment modification

Grasslands store 10–30 % of the global soil organic carbon (SOC) and have the potential to mitigate the increase in atmospheric CO2 concentrations. Grazing plays a crucial role in regulating SOC storage in grassland ecosystems. However, the mechanistic understanding of how grazing influences the SOC dynamic still needs to be improved. We investigated how grazing-induced microenvironment changes influence the microbial assimilation of plant litter C and SOC formation from decomposed litter C in a multi-year field experiment, where grazing was simulated with mowing, dung and urine return, and trampling. We incubated 13C labeled litter in PVC collars to trace the microbial assimilation of litter C and the fate of litter C in the SOC after decomposition. While the grazing treatments changed soil properties marginally, mowing decreased above-ground plant biomass, litter mass, plant height, and plant cover (−12 % to −79 %). Accordingly, mowing treatment increased the exposure of litter to UV radiation (+38 %) and therefore facilitated the microbial assimilation of litter C (+20 %) and the SOC formation (+15 %). Trampling treatment promoted the transformation of litter C to SOC pools by mixing litter and soil (+34 %). Dung and urea return treatment did not affect SOC formation due to a marginal change in available nitrogen. Collectively, our results suggest that grazing facilitates litter-derived SOC formation by regulating microbial involvement through changes in the microenvironment. Our study indicates that grazing promotes SOC formation from plant litter, which maintains SOC storage in grasslands. Accurate quantification of the contribution of plant C input to SOC pools in different grasslands under various utilization is the next step to better predict SOC dynamics.

Multi-species rotational grazing of small ruminants regenerates undergrowth vegetation while controlling weeds in the oil palm silvopastoral system

CONTEXT.Prolonged use of synthetic herbicides to control weeds may cause adverse effects on the environment and human wellbeing. As a mitigation effort, commercial oil palm growers have been encouraged to adopt livestock integration as a holistic approach to manage weeds. Previous studies have suggested utilizing a multi-species livestock grazing may optimize the grazing impacts in silvopastoral agroforestry systems. OBJECTIVEPresent study examined the effects of small ruminant grazing (i.e., goats, sheep and multi-species) on undergrowth vegetation with the following specific objectives: 1) to investigate the effects of small ruminant grazing treatments on undergrowth vegetation composition in oil palm plantations; 2) to examine the variables (canopy cover, grazing treatments, and cycles) that influenced undergrowth vegetation (species richness, coverage, height, and dry weight) in oil palm plantations. METHODSWe established quadrats on experimental plots to detect changes in undergrowth vegetation composition, species diversity, coverage, height, and dry weight resulting from different grazing treatments. RESULTS AND CONCLUSIONSWe found that undergrowth vegetation composition varied between different grazing treatments. The multi-species livestock grazing effectively supress unwanted weeds (i.e., woody broadleaves) compared to single–species livestock grazing (i.e., goats, sheep). The use of single-species livestock grazing is likely to cause oil palm growers to use herbicides to control undesirable weeds. Hence, we concluded managing undergrowth vegetation in oil palm plantations using multi-species livestock grazing is a practical approach, and it should be fine-tuned for example by choosing livestock species based on the targeted objectives and the grazing sequence that will be practiced to regenerate the oil palm silvopastoral system. SIGNIFICANCEMulti-species livestock grazing can reduce oil palm growers' dependence on synthetic herbicides for weed control and optimize land use in oil palm plantation sector. On the other hand, the use of single species, whether goat or sheep-only, has caused unwanted undergrowth to increase after several grazing rotations have been carried out. Therefore, the use of multi-species grazing is a promising biological tool to reduce synthetic herbicide application in environmentally-sustainable oil palm plantations.

Mesquites Limit Targeted Grazing Effects on Texas Wintergrass Growth and Reproduction Responses

In mixed C3/C4 grasslands of the southern Great Plains of North America, honey mesquite (Prosopis glandulosa Torr.) invasion facilitates the dominance of the C3 midgrass Texas wintergrass (Nassella leucotricha [Trin. & Rupr.] Pohl) to the detriment of warm-season grasses. Little is known about the viability of targeted grazing as a treatment method for reducing Texas wintergrass biomass and reproduction, particularly under mesquite canopies. We quantified the effects of targeted grazing treatments (grazed once [G1], grazed twice [G2], and control) and mesquite canopy position (under canopy [UC] and outside of canopy [OC]) on Texas wintergrass basal area, total dry matter (DMY) per basal area, live DMY per basal area, dead DMY per basal area, leaf length, total number of reproductive culms per plant, number of fungus-infected reproductive culms per plant, and rate of reproductive culm development over 2 yr at two study sites. Targeted grazing reduced leaf length and biomass and slowed reproductive development of the wintergrass plants that cattle could more easily access. Environmental factors and differences in mesquite physiognomy at the two study sites likely interacted with grazing treatments, making it challenging to separate the impacts of targeted grazing treatments from other factors. Results suggest mesquite removal is likely necessary to increase cattle access to Texas wintergrass, particularly in stands with multistemmed trees.

Reversing habitat loss: An experimental test of the interactive effects of grazing exclusion and surface rock restoration on reptile conservation

Abstract Restoring structural elements of habitats and understanding how restoration interacts with environmental factors such as grazing management can be crucial for improving conservation outcomes in agricultural landscapes. Surface rock is a structural habitat type that is critical for a range of reptile species; yet, it is often poorly managed and protected. Using a Before/After, Control/Impact (BACI) design, we experimentally quantified the response of reptiles to surface rock restoration in an agricultural landscape, and tested whether its effects interacted with livestock grazing treatments to influence various reptile diversity measures. To implement our crossed factorial design, we added approximately 50 tonnes of rock and 1 km of grazing exclusion fencing across 10 sites in south‐eastern Australia. We found increases in the number of total reptile captures, total individuals and species richness when comparing rock addition plots to non‐rock plots. There was no significant overall grazing exclusion effect or interactive effect of grazing and rock treatment on reptile measures. Synthesis and applications. Our study provides experimental evidence that surface rock addition is an effective restoration method for reptiles in agricultural landscapes. We recommend that the addition of surface rock is prioritised as a restoration tool for reptiles, and that existing surface rock areas are protected from clearing.

Soil organic carbon changed by grazing determinates the abundance, diversity and composition of aerobic methanotroph communities in cyanobacteria-dominated biological soil crusts in desert steppes

Aerobic methanotrophic bacteria (AMB) are widely present in biological soil crusts (BSCs) and are important methane-oxidizing groups in desert ecosystems. Grazing disturbance can destroy BSCs, but how it affects AMB is unclear. In this study, the AMB in BSCs under no-, moderate- and heavy-grazing intensities and continuous grazing for 10 years were studied using high-throughput sequencing technology and bioinformatics analysis. The results showed that soil total organic carbon (TOC), dissolved organic carbon (DOC), available phosphorus, and leucine aminopeptidase significantly reduced, while nitrate and ammonium nitrogen and β-1,4-acetylglucosaminidase enzyme activities increased, with increasing grazing intensity. The AMB were highly diverse, with an absolute abundance from 2.97 to 4.95 × 105 (in no and heavy grazing treatments, respectively). Grazing disturbance especially influenced the relative abundance of AMB communities at the genus level. Members belonging to Methylocystis, Methylosinus, and Methylobacter were the top three genera and core methanotrophs in AMB communities, and closely related to the stability of AMB community networks under grazing disturbance. AMB community structure were majorly affected by TOC and DOC. We provide novel insights into grazing could change the soil organic matter, which determinates the abundance, diversity and composition of AMB communities in cyanobacteria-dominated BSCs in desert steppes.

Enabling Regenerative Agriculture Using Remote Sensing and Machine Learning

The emergence of cloud computing, big data analytics, and machine learning has catalysed the use of remote sensing technologies to enable more timely management of sustainability indicators, given the uncertainty of future climate conditions. Here, we examine the potential of “regenerative agriculture”, as an adaptive grazing management strategy to minimise bare ground exposure while improving pasture productivity. High-intensity sheep grazing treatments were conducted in small fields (less than 1 ha) for short durations (typically less than 1 day). Paddocks were subsequently spelled to allow pasture biomass recovery (treatments comprising 3, 6, 9, 12, and 15 months), with each compared with controls characterised by lighter stocking rates for longer periods (2000 DSE/ha). Pastures were composed of wallaby grass (Austrodanthonia species), kangaroo grass (Themeda triandra), Phalaris (Phalaris aquatica), and cocksfoot (Dactylis glomerata), and were destructively sampled to estimate total standing dry matter (TSDM), standing green biomass, standing dry biomass and trampled biomass. We invoked a machine learning model forced with Sentinel-2 imagery to quantify TSDM, standing green and dry biomass. Faced with La Nina conditions, regenerative grazing did not significantly impact pasture productivity, with all treatments showing similar TSDM, green biomass and recovery. However, regenerative treatments significantly impacted litterfall and trampled material, with high-intensity grazing treatments trampling more biomass, increasing litter, enhancing surface organic matter and decomposition rates thereof. Pasture digestibility and sward uniformity were greatest for treatments with minimal spelling (3 months), whereas both standing senescent and trampled material were greater for the 15-month spelling treatment. TSDM prognostics from machine learning were lower than measured TSDM, although predictions from the machine learning approach closely matched observed spatiotemporal variability within and across treatments. The root mean square error between the measured and modelled TSDM was 903 kg DM/ha, which was less than the variability measured in the field. We conclude that regenerative grazing with short recovery periods (3–6 months) was more conducive to increasing pasture production under high rainfall conditions, and we speculate that – in this environment - high-intensity grazing with 3-month spelling is likely to improve soil organic carbon through increased litterfall and trampling. Our study paves the way for using machine learning with satellite imagery to quantify pasture biomass at small scales, enabling the management of pastures within small fields from afar.

Moderate Grazing Promotes Arthropod Species Diversity in an Alpine Meadow.

Livestock grazing is an important tool used in grassland land management practices. Studies have substantially addressed the effect of grazing on plant species diversity, revealing that moderate grazing increases plant species diversity. However, few studies have dealt with the relationship between grazing and arthropod species diversity, which remains unclear. Here, we hypothesize that moderate grazing promotes arthropod species diversity because arthropods are directly or indirectly dependent on plant diversity. In this study, we conducted a two-year plant and arthropod survey from 2020 to 2021 at four levels of grazing intensity, i.e., nongrazing (as a control), light grazing, moderate grazing, and heavy grazing, of the long-term grazing experiment starting in 2016. The data show that plant species diversity peaked in the moderate grazing treatment, and herbivore species diversity was positively correlated with plant species diversity (and hence peaked in the moderate grazing treatment). Moderate grazing promoted parasitoid species diversity, which was positively correlated with herbivore species diversity. However, predator species diversity did not significantly differ among the four treatments. In addition, saprophage species diversity decreased, whereas coprophages increased with increasing grazing levels, such that species richness (but not species diversity of detritivores statistically) was highest in the moderate grazing treatment. Consequently, the species diversity of arthropods as a whole peaked at the moderate grazing level, a phenomenology that is consistent with the intermediate disturbance hypothesis. Considering that moderate grazing has been found to increase plant species diversity, facilitate soil carbon accumulation, and prevent soil erosion, we suggest that moderate grazing would maximize multi-functional ecosystem services.

Long-Term Grazing Exclusion Increases Ecosystem Carbon Stock but Decreases Nitrogen Stock in the Karst Alpine Grassland of China

Grazing management practices are a major factor regulating nutrient cycling and plant growth in grasslands. However, the response of long-term grazing regimes to ecosystem carbon and nitrogen accumulation and plant productivity remains uncertain in karst landscapes. The purpose of this research is to assess the effects of long-term management measures on plant biomass and ecosystem organic carbon (EOCS), total nitrogen (ETNS), and phosphorus (ETPS) stocks in a karst alpine grassland. A 17 year-long field experiment, constituting the methods of grazing exclusion (GE), continuous grazing (CG), mowing and grazing (MG), and rotational grazing (RG) was established in 2001. Plant and soil samples were collected in 2017. Grazing treatments significantly reduced the aboveground and root biomass (MG and RG) compared to GE. SOC of GE was higher than that of CG, MG, and RG in each soil layer. Grazing promoted the mean TN content with a significant increase in CG and RG. GE significantly increased the EOCS and decreased the ETNS and ETPS. The EOCS increased by 22.29% (MG) and 16.31% (RG) and ETNS increased by 7.76% (RG), and MG significantly decreased ETNS compared to CG. EOCS were positively related to SOC, stoichiometry, and aboveground biomass, while being negatively correlated with TP; ETNS were positively related to TN and TP, while being negatively correlated with C/N, C/P, aboveground biomass, and root biomass; ETPS were positively correlated with TN and TP and negatively correlated with NH4+-N and stoichiometry. GE can provide significant improvements in plant recovery and ecosystem carbon stock, whereas RG is beneficial for promoting ecosystem nutrient stock under the condition of pasturing utilisation in the karst grasslands.

117 Effects of Cattle Removal Date on Sustainability of Cool-Season Annual Grazed Cover Crop Systems

Abstract Grazing of cool-season cover crops has been shown to be a viable tool in extending the grazing season while mitigating environmental risks associated with row crop farming systems. While there is a vast amount of research available on cover crops in relation to soil health, a more novel approach would be to focus on forage production and animal performance when grazing cover crops. Therefore, our objective was to evaluate the effects of cattle removal date on forage yield, forage quality, and steer performance when grazing cool-season cover crops. A cool-season forage mix consisting of ‘Cosaque’ oats (Avena strigose), ‘FL401’ cereal rye (Secale cereal), ‘AU Sunrise’ crimson clover (Trifolium incarnatum), and ‘T-raptor’ brassica (Brassica napus × B. rapa) was established in twelve, 0.62 ha paddocks in Headland, AL. Each paddock was then randomly allocated to one of four cattle removal treatments: 1) no grazing (CON); 2) February removal (FEB); 3) March removal (MAR); or 4) April removal (APR). Three tester steers were randomly allotted, based on body weight (BW), to each of the grazing treatments, excluding CON. The tester steers were weighed every 30 d for calculation of initial BW, final BW, and average daily gain (ADG). At inception and every subsequent two weeks, forage was harvested to analyze average forage yield, neutral detergent fiber (NDF), acid detergent fiber (ADF), and crude protein (CP). All data were analyzed using GLIMMIX procedure of SAS version 9.4 (SAS Inst., Cary, NC). Significant differences in forage yield were detected between CON and FEB (3,913 vs. 2,261 kg/ha; P &amp;lt; 0.001), CON and MAR (3,913 vs. 1,790 kg/ha; P &amp;lt; 0.001), and CON and APR (3,913 vs. 1,810 kg/ha; P &amp;lt; 0.001). There were no differences found for ADG (1.2 kg/day; P = 0.56), NDF (50.94%; P = 0.46), or ADF (30.34%; P = 0.25) among treatments. Results indicate that grazing of cool-season annual cover crops will reduce forage yield, but removal date of cattle will not further affect forage yield, quality, or individual cattle performance. Thus, we can reduce winter supplementation needs for cattle by increasing grazing days; however, under continuous grazing for stocker cattle production, forage availability may inevitably be the limiting factor.

Rehabilitating Invaded Rangeland in Central South Dakota with Grazing, Seeding, and Herbicides

Rangelands in the northern Great Plains are threatened by invasive C3 annual and perennial grasses that displace native C4 grasses. Rehabilitating these rangelands by reintroducing native C4 grass species could extend the season in which relatively higher-quality forage is available for livestock grazing and improve wildlife habitat. Three seeding treatments, four herbicide treatments, and two stocking densities were applied to a pasture in central South Dakota, United States, that was dominated by invasive C3 grasses. Grazing and herbicide treatments were designed to suppress exotic cool season grasses. Drought limited establishment during the first 2 yr, but C3 grasses were successfully controlled during this time. Plots drill-seeded and sprayed with glyphosate established a mean of 1.0 seeded grasses m−2 by the third yr. Unseeded plots and plots that did not receive glyphosate failed. This trend continued into yr 5, when the most successful treatments were composed of 10−14% seeded C4 grasses, as determined by a modified step-point count technique. Stocking density did not affect establishment success. It is possible to suppress C3 invasive grasses with herbicide and establish native C4 tallgrasses in central South Dakota, but drought makes it a risky proposition in this semiarid region.

The reciprocal changes in dominant species with complete metabolic functions explain the decoupling phenomenon of microbial taxonomic and functional composition in a grassland.

The decoupling of microbial functional and taxonomic components refers to the phenomenon that a drastic change in microbial taxonomic composition leads to no or only a gentle change in functional composition. Although many studies have identified this phenomenon, the mechanisms underlying it are still unclear. Here we demonstrate, using metagenomics data from a steppe grassland soil under different grazing and phosphorus addition treatments, that there is no "decoupling" in the variation of taxonomic and metabolic functional composition of the microbial community within functional groups at species level. In contrast, the high consistency and complementarity between the abundance and functional gene diversity of two dominant species made metabolic functions unaffected by grazing and phosphorus addition. This complementarity between the two dominant species shapes a bistability pattern that differs from functional redundancy in that only two species cannot form observable redundancy in a large microbial community. In other words, the "monopoly" of metabolic functions by the two most abundant species leads to the disappearance of functional redundancy. Our findings imply that for soil microbial communities, the impact of species identity on metabolic functions is much greater than that of species diversity, and it is more important to monitor the dynamics of key dominant microorganisms for accurately predicting the changes in the metabolic functions of the ecosystems.

Cascading effects of seed-stem-individual spatial patterns along a grazing gradient.

Studying the seed trait-stem trait-individual spatial pattern system is helpful for understanding the developmental direction of plant dynamics and populations under grazing disturbance as well as the antagonistic relationship between animals and plants, but few systematic analyses of this spatial pattern system have been carried out. Kobresia humilis is the dominant species in alpine grasslands. We studied K. humilis seed traits and their relationship with K. humilis reproductive individuals, the relationship between reproductive and vegetative stems, and the weights and spatial patterns of reproductive and nonreproductive individuals under four grazing treatments: no grazing (control), light grazing, moderate grazing and heavy grazing. We explored the relationship among seed size and seed number with reproductive stems and vegetative stems along the grazing gradient and assessed the spatial pattern changes between reproductive and nonreproductive individuals. The results showed the following: (1) Seed size increased with increasing grazing intensity, and the coefficient of variation for seed size and seed number in the heavy grazing treatment was greater than 0.6. (2) The structural equation model showed that grazing treatment had a positive effect on seed number, seed size and reproductive stem number and a negative effect on reproductive stem weight. (3) Grazing treatment did not affect the resource allocation to reproductive stems and vegetative stems per unit length of reproductive K. humilis individuals. (4) Compared with the number of reproductive individuals in the no grazing treatment, the number in the heavy grazing treatment decreased significantly, and the negative correlation between reproductive individuals and nonreproductive individuals changed from a full-scale negative correlation to a small-scale negative correlation and a large-scale positive correlation. Our study showed that grazing could activate and change the resource allocation pattern of dominant species in a grassland and have significant positive effects on reproductive stem number, reproductive stem weight, seed number and seed size. Along a grazing intensity gradient, with the increase in distance between reproductive and nonreproductive individuals, the transformation of intraspecific relationships from a negative correlation to a positive correlation is an ecological strategy conducive to population survival.