Ungrazed Research Articles

Grazing cover crops in continuous corn production in east‐central Mississippi

AbstractCover crop grazing can be used as a strategy to meet nutritional requirements for livestock while simultaneously enhancing soil ecosystem services without sacrificing subsequent crop yield. Field research was conducted in east‐central Mississippi from 2019 to 2021 on a sandy loam soil to assess the impacts that grazing, tillage, and cover crop species had on corn (Zea mays L.) grain yield and soil characteristics. The main plot was grazed (G) and un‐grazed (UG) cover crops, tillage (conventional and no‐till [NT]) was the subplot, and cover crop species the sub‐subplots. Cover crops were grazed using beef (Bos taurus) heifers at a stocking density of approximately 3300 kg ha−1 each growing season as forage mass (FM) allowed. No differences were observed in FM among cover crop treatments; however, FM, crude protein (CP), and total digestible nutrients (TDN) were affected by tillage and grazing. Corn grain yield was unaffected by grazing or tillage but was impacted by cover crop treatment. Cereal rye (Secale cereale L.; 11.99 Mg ha−1), crimson clover (Trifolium incarnatum L.; 11.67 Mg ha−1), and cereal rye + radish (Raphanus sativus L.; 12.07 Mg ha−1) had greater grain yield compared to the un‐planted control (10.99 Mg ha−1). The combination of G × no‐till (NT) resulted in greater penetration resistance (71.07 J); however, G plots contributed to greater organic matter(OM) concentrations. Overall, our data suggest that complimenting G and NT practices does not impact subsequent corn grain yield and could add value to cover cropping systems.

Partitioning evapotranspiration and carbon flux in ungrazed and grazed tallgrass prairie

The effect of cattle grazing on water and carbon cycling in grasslands is not fully understood. The goal of this study was to evaluate how grazing affects carbon and water cycles in a tallgrass prairie. Eddy covariance measurements were carried out from 2003 to 2005 growing seasons (from May to September) in Manhattan, Kansas, U.S., in grazed (GR) and ungrazed (UG) tallgrass prairie paddocks. Net ecosystem CO2 exchange (NEE) was partitioned into gross primary productivity (GPP) and ecosystem respiration (Reco) using the relationship between the air temperature and nighttime NEE data. Evapotranspiration (ET) was partitioned into transpiration (T) and evaporation (E) using an approach based on the concept of underlying water use efficiency. Our results revealed that grazing reduced maximum aboveground biomass (AGB) and green leaf area index (GLAI) by 22.5% and 24.3%, respectively. Grazing also reduced GPP, NEE and T in the middle of the growing seasons but enhanced these flux components at the end of the growing seasons compared to the UG paddock. Grazing reduced the growing season cumulative NEE by 11.9% and enhanced ET by 3.3% compared to the UG paddock. The reduction in NEE at UG was associated with an increase in Reco (9.4%). In turn, changes in ET in response to grazing were driven more by the increase in E (26.6%) than by the decrease in T (5.9%). Despite the reduction in AGB and GLAI caused by grazing, similar cumulative GPP values at the canopy scale at both paddocks suggest that there are compensatory mechanisms that maintain similar CO2 assimilation at UG and GR. Our findings suggest that the grazing regime adopted in this tallgrass prairie impacts the carbon cycle more strongly than the water cycle, given the higher reduction in NEE compared to the slight increase in ET on GR compared to UG. These results can be useful to outline strategies to improve management practices aimed at improving the efficiency of rangelands.

Moderate grazing is the best measure to achieve the optimal conservation and soil resource utilization (case study: Bozdaghin rangelands, North Khorasan, Iran).

The study of the variability of physical and chemical factors of soil due to different intensities of livestock grazing can help in the management and maintenance of soil and vegetation. Accordingly, the effect of livestock grazing intensities on soil properties and vegetation in Bozdaghin rangelands of North Khorasan province was investigated. To investigate the effect of different livestock grazing intensities, Three 5-hectare plots in the study area were determined under different treatments (ungrazed (UG), moderate grazing (MG), and heavy grazing (HG)), and the effect of three grazing intensities on vegetation and soil physicochemical and erodibility properties (SPEP) was evaluated. The soil sampling process was performed at depths of 0-15, 15-30cm and SPEP including soil saturation moisture (SSM), soil texture (percentage of clay, sand, and silt), absorbable potassium (K), electrical conductivity (EC), soil organic matter (SOM), absorbable phosphorus (P), acidity (pH), and bulk density were evaluated, and Soil Erodibility Index (SEI) was calculated by implementing the modified clay ratio relation. To assess the impact of various grazing intensities on all measured characteristics, multivariate analysis of variance (MANOVA) and Duncan tests were utilized to compare the means and their grouping. The results showed that HG compared to MG causes worrying consequences in the first soil depth. Also with increasing grazing intensity, plant production percentage (P <0.05) and vegetation density (P <0.01) decreased, and the amount of bare soil (P <0.01) increased. Also, with increasing grazing intensity, the amount of pH, EC, clay, saturated moisture, and N decreased (P < 0.01), but the amount of silt, sand, K, P, calcium (Ca), lime, and SOM increased (P <0.01). UG improves soil quality, MG intensity causes optimal conservation and utilization of soil resources, and HG intensity causes severe changes in rangeland soil properties. In areas with MG intensity, due to the increase of the percentage of vegetation (an increase of SOM and prevents the direct impact of raindrops on the soil aggregates) and as a result improvement of soil structure and texture, an increase of water infiltration, and decrease of runoff, and the rate of soil erodibility and water erosion, the rangeland soil decreases and results in sustainable production. This results in optimal conservation and utilization of soil resources. So to sustainably exploit and balance the conservation of biodiversity, livestock production, and soil carbon and nitrogen management, MG is recommended.

Soil Carbon Change Due to Land Conversion to Grassland in a Semi-Arid Environment

A 5-year study evaluated the change in the quantity of soil total C (STC), soil organic C (SOC), and soil inorganic C (SIC) stored in the surface 60 cm of the soil profile on two adjacent blocks of land with a long-term history of cropping (CH) or undisturbed grassland (NH) on similar soil types between 1999 and 2004. The NH area was tilled and a grass-legume species mix was seeded into plots on both the NH and the CH areas. Selected plots of restored grass were established so they could be grazed (GG) by livestock while other plots were left ungrazed (UG). Original undisturbed (and ungrazed) grassland plots within the NH area were used as a control treatment. Initially, STC and SOC in CH were lower than NH when compared under the semi-arid environmental conditions found in southwestern North Dakota. Over the study period, the undisturbed grass control plots had increases in STC and SOC levels in the soil profile of 3.90 kg·m−2 and 3.34 kg·m−2, respectively. Restored grass on the NH area with grazing showed increases in STC and SOC values of 2.11 and 1.26 kg·m−2, respectively, while without grazing, profile STC and SOC had values of 3.80 and 3.28 kg·m−2, respectively. Restored grass on the CH area showed increases in profile STC and SOC values of 0.55 and 1.96 kg·m−2, respectively, for the grazed plots and 0.78 and 2.11 kg·m−2, respectively, when left ungrazed. Soil inorganic C, though present in the soils, did not significantly change during the study. The lower C accumulation in the CH plots may be due to a lag time in the establishment of mycorrhizal associations with the seeded species, the inoculums of which were already present in the NH soils. Changes in STC were likely due to changes in water relationships in the soil profile where management changes affected water infiltration and its movement causing leaching of SIC below the 60 cm depth evaluated. Soils under undisturbed grassland continue to accumulate carbon while soils of the disturbed grassland or cropped prior to re-establishing grass showed losses that occurred due to either accumulating C at a lower rate or perhaps to C loss during the initial establishment period (1–2 years).

Plant diversity and botanical composition in an Atlantic heather-gorse dominated understory after horse grazing suspension: Comparison of a continuous and rotational management

Floristic diversity changes substantially depending on the type of land management. We evaluated the impact of a continuous (CG) and rotational (RG) grazing system on the dynamics of plant diversity and community composition in a heather-gorse understory after a two and six-year pause from horse grazing. Previously grazed sites had higher total and rare species richness and diversity than ungrazed (UN), regardless the type of grazing system. The positive impact of previous grazing on species richness was higher in CG and continued after six years in both grazing systems. Seven species of high conservation interest in heathlands were present in the studied areas. Most of them were associated to CG management and none was exclusively in RG. The reduction of the shrub component by previous horse grazing led to a decrease of gorse dominance, thus potentially reducing fire risk and increasing plant diversity. The extent of the positive effect of horse grazing controlling excessive accumulation of combustible material and favoring species richness differed when relative abundance of species, and not solely the number of species, was taken into account (Simpson’s dominance increased and Pielou’s evenness decreased after six years). Overall, the effects of previous rotational and continuous grazing on plant diversity in an Atlantic heather-gorse dominated plant community were still apparent 2 or 6 years after grazing interruption, although declined after the six-year grazing interlude. Rotational management revealed a slight advantage upon the control of gorse biomass long term, and assisted to maintain the relative abundance of species more evenly over time. The alpha and beta diversity indices confirmed that plant diversity similarity between rotational and continuous management increased after six years.

Stocking rate impacts on tallgrass prairie landscape carbon fluxes

AbstractCarbon sequestration in ecosystems reduces atmospheric CO2, a major forcing factor in global warming. We aimed to determine the ecosystem C balance under heavy and moderate stocking rates or ungrazed (UG) pastures during the first 2 yr of a 3‐yr period and to determine if changing to moderate stocking on a previously heavily stocked pasture would result in compensatory ecosystem C retention. During 2003 and 2004, net ecosystem C exchange (NEEc) was measured with eddy correlation towers on pastures that were UG, stocked at 2 acres per steer until the middle of the grazing season [intensive early stocking (IES)], and season‐long stocking at the high rate of 2 acres per steer (SLS‐H). In 2005, the SLS‐H pasture changed to a season‐long moderate stocking rate of 4 acres per steer (SLS‐H‐M). Net ecosystem C exchange was summed over an entire year from the burn date to the burn date the following year minus the C lost from burning and livestock export to estimate C balance. During the growing season, SLS‐H reduced ecosystem C retention compared with UG and IES in 2003 and 2004 (+223, +212, and –669 lb acre–1 for UG, IES and SLS‐H). In 2005, when the stocking rate on the SLS‐H pasture was changed to SLS‐H‐M, C retention was greater than under UG and IES (+107, +89, and +205 lb acre–1 for UG, IES and SLS‐H‐M). We conclude that following stocking at an abusive rate, there is compensatory C retention resulting from greater nutrient and water availability.

Effects of long-term grazing on carbon isotope composition in plants and soils of different grassland

Grazing is a common human activity on grassland region. Long-term grazing exerts great effects on ecosystem carbon cycling. In this study, we collected leaf and soil samples from different grassland types across the growing season, separately from un-grazed (UG) and overgrazed (OG) plots. By analyzing the carbon isotope values of samples in laboratory, this study revealed the divergent Δ13C value (carbon isotope discriminative value) among different grassland ecosystems, as well as its influencing factors. The results showed that Δ13C value of soil at 0-5 cm significantly differed between UG and OG, but no difference at deeper layers (>5 cm). The grazing intensity had significant influence on the Δ13C value of vegetation leaves. After long-term grazing, most vegetation showed a significant increase in Δ13C value, especially in high altitude areas. In conclusion, grazing have significantly divergent impacts on the carbon processes under different grassland ecosystems, soil depths and altitudes. Therefore, a variety of grazing management strategies should be adopted for various grassland ecosystems.

Effects of Grazing Pattern on Ecosystem Respiration and Methane Flux in a Sown Pasture in Inner Mongolia, China

The establishment of sown pasture is an important agricultural practice in many landscapes. Although both native grassland and sown pasture play a key role in the global carbon cycle, due to lack of data and field experiments, our understanding of grassland CH4 fluxes and CO2 emissions remains limited, especially when it comes to sown pasture. We measured ecosystem respiration and CH4 fluxes in response to a variety of potential drivers (soil temperature, soil moisture, ammonium nitrogen, nitrate nitrogen and dissolved organic carbon) in CG (continuous grazing), RG (rotational grazing) and UG (ungrazed) plots in sown grassland for one year in Inner Mongolia. Fluxes of CH4 and ecosystem respiration were measured using static opaque chambers and gas chromatography. Grazing significantly reduced ecosystem respiration (p &lt; 0.01), and grazing pattern significantly influenced respiration in CG and RG plots (p &lt; 0.01). We find that the sown grassland is a net sink for atmospheric CH4. No influence of grazing pattern was observed on CH4 flux in CG, RG and UG (p &gt; 0.05). Soil temperature is the most important factor influencing ecosystem respiration and CH4 flux in the sown grassland, with soil moisture playing a secondary role to soil temperature. Variation in levels of ammonium nitrogen, nitrate nitrogen and dissolved organic carbon had little influence on ecosystem respiration or CH4 flux (except in UG plots). The values obtained for ecosystem respiration of grasslands have a large uncertainty range, which may be due to spatial variability as well as differences in research methods. Mean CH4 fluxes measured only during the growing season were much higher than the annual mean CH4 fluxes.

Influence of streambank fencing on vegetation and soil of the Mixed prairie component in a complex corridor pasture

A 5 yr (2011–2015) field study was conducted to test the hypothesis that streambank fencing had a significant effect on selected vegetation and soil properties of the Mixed prairie component of a complex corridor pasture. The grazing treatments [ungrazed (UG) – periodic grazing (PG)] inside the corridor pasture were 11 yr (2001–2012) of cattle exclusion (UG), followed by 3 yr (2013–2015) of periodic grazing (PG) when the riparian soil was dry. A control treatment outside the fencing was continuous grazing (CG). Selected vegetation and soil properties were measured over the growing season at 10 paired locations in each treatment (nonreplicated) pasture over 5 yr (2011–2015), and rangeland health was measured in 2011. The UG–PG treatment significantly (P ≤ 0.10) increased the total biomass by 2- to 5-fold in all 5 yr compared with CG treatment and improved the rangeland health score of the UG phase of the UG–PG (63%) treatment compared with the CG treatment (50%) in 2011. It also significantly reduced surface soil temperature by 2.2–5.2 °C, significantly increased volumetric water content of the surface soil by 7%–10% in 3 of 5 yr, and significantly increased surface soil CO2 efflux (instantaneous) by 17%–60% in all 5 yr. Overall, the UG–PG treatment improved rangeland health, increased total biomass, soil water, and soil CO2 efflux of the Mixed prairie, but decreased soil temperature compared with the CG treatment. Excessive dead biomass, greater fire risk, and an increase in noxious weeds caused by cattle exclusion suggested that periodic grazing may be the preferred option.

Overgrazing depresses soil carbon stock through changing plant diversity in temperate grassland of the Loess Plateau

This study mainly estimates the effect of grazing on plant diversity and soil storages on the northern Loess Plateau of China. Four grazing intensities of ungrazed (UG), light (LG), moderate (MG), and heavy (HG) grassland were selected according to the vegetation utilization across the study area, in which plant diversity, heights, above- and belowground biomass, and soil carbon (C) stock were investigated. The results showed that overgrazing negatively affected plant growth and soil C stock. Plant cover, height, litter, above- and belowground productivity, as well as soil C stock significantly decreased with the increasing grazing intensity. Meanwhile, the UG and LG had higher grasses biomass together with lower forbs (P &amp;lt; 0.01) compared with MG and HG. The abundance of dominating grasses species, such as Stipa bungeana and S. grandis were decreased through long-term grazing as grasses species are palatable for herbivores, and the dominating forbs species, such as Artemisia capillaries and Thymus mongolicus were significantly increased with increasing grazing intensities. The results indicated that grazing exclusion or light grazing had positive effects on the sustainable development of grassland ecosystems. Therefore, a balanced use and a long-term efficient management of grasslands were better measures to counteract their local degradations.

Optimization schemes for grassland ecosystem services under climate change

Ecosystem and associated services in arid and semiarid areas are sensitive to climate change and human activities. Guiding human activities based on the optimization of ecosystem services can help humans adapt to climate change effectively, which is vital for regional sustainability. We evaluated the distribution of five ecosystem services: net primary productivity (NPP), soil conservation (SC), water yield (WY), water retention (WR), and livestock supply in the grassland and agro-pastoral transitional zone of China (GAPTZ) under the future climate scenarios of representative concentration pathway (RCP) 4.5 and RCP8.5 in 2050. We designed the four grazing-intensity scenarios of ungrazed (UG), lightly grazed (LG), moderately grazed (MG), and heavily grazed (HG) and analyzed the impacts of climate change and grazing on the ecosystem services. Finally, we presented the optimization schemes of grazing intensity in the GAPTZ under the objectives of “strong sustainability” and “weak sustainability”. “Strong sustainability” objective means that the total change rate of ecosystem services compared to the ungrazed scenario is maximal and should not be less than 0. “Weak sustainability” objective means that the livestock supply is preferential and the total change rate of ecosystem services compared to the ungrazed scenario is maximal but could be less than 0. The results showed that both climate change and grazing exert great influence on the supply and interrelation of ecosystem services. In the northeast of the GAPTZ, LG and MG can stimulate grassland to tiller and enlarge ecosystem services integrally. HG has the severest negative effect on ecosystem services overall. Under the “weak sustainability” objective, LG can be widely adopted in the GAPTZ. Under the “strong sustainability” objective, grazing should be limited in the northwestern and north-central GAPTZ. Reasonable planning of grazing intensity and its spatial patterns can promote effective utilization of grassland resource and realization of regional sustainability.

Grazing effects on ecosystem CO2 fluxes regulated by interannual climate fluctuation in a temperate grassland steppe in northern China

The dynamics of CO2 fluxes on grassland ecosystem can be highly affected by grazing intensity and climate variation. To determine the role of grazing intensity on grassland ecosystem CO2 fluxes, we used static chamber methods to measure net ecosystem exchange for CO2 (NEE) and its two components, gross ecosystem production (GEP) and ecosystem respiration (Re), during three growing seasons on a steppe site located at the southeastern edge of the Mongolian Plateau in China. Objectives were to document how NEE, GEP and Re varied seasonally and interannually, and to examine how environmental factors and grazing intensity influenced the C budget. Sheep grazed during the growing seasons of 2012–14 at a stocking rate of 0, 1.43 and 2.33 sheep units ha −1year−1 for ungrazed (UG), moderately grazed (MG) and heavily grazed (HG) sites, respectively. Results showed that both grazing intensity and climatic variability significantly affected NEE, GEP and Re. Precipitation or soil water content and aboveground biomass (AGB) critically controlled NEE and GEP. Precipitation during the growing season of 2013 was 34% greater than that in 2014 and 2012, and 38% higher than long-term mean precipitation (244mm, 1953–2012). Precipitation was low between days 150–260 in 2012 and 2013 compared to that in 2014 with lower precipitation during days 205–260. Despite strong intra- and interannual influences on ecosystem CO2 fluxes, interaction of year and grazing intensity only affected NEE (P=0.026) and not GEP (P=0.286) or Re (P=0.984). Seasonal values of NEE (-7.5μmol CO2 m−2s−1), GEP (-12.2μmol CO2 m−2s−1), and Re (3.4μmol CO2 m−2s−1) in 2013 were approximately 47% (46–48%), 34% (33–35%), and 22% (6–38%) higher than those in 2012 and 2014, respectively. The temperate steppe in northern China was a sink for C during the growing season for the grazing intensities evaluated in our study with the MG site exhibiting the greatest NEE and GEP. Mean cumulative carbon uptake for MG was 1005±45gCm−2, which was 31 and 98% greater than that for UG and HG, respectively. Results from our study suggested that both no grazing and heavy grazing significantly decreased C fixation of the steppe grassland (P<0.05) in northern China. In addition, annual precipitation and its associated distribution mediated the magnitude of reduction in C fluxes.

Non-growing season soil CO2 efflux patterns in five land-use types in northern China

Heavy grazing and unsuitable farming practices have led to grassland degradation in northern China. This study examined soil CO2 efflux (Fc) from five land-use types during the non-growing season on the southeastern edge of the Mongolian Plateau in China. The land-use types included three native vegetation steppes subjected to differing stocking rates [ungrazed (UG), moderately grazed (MG) and heavily grazed (HG)], a fertilized annual cropland (CL) and a perennial pasture (PP) used for haying and winter grazing. Values of Fc were measured at 3-day to 2-week intervals during the non-growing season in two contrasting hydrological years (2012-13 and 2013-14) using closed chambers. The Fc during 1 Oct. 2013 to 30 April 2014 averaged 475 mg C m−2 for all sites compared to a significantly (P < 0.05) lower Fc (102 mg C m−2) during 1 Oct. 2012 to 30 April 2013. The seasonal Fc patterns followed the same trend during the two non-growing seasons with greater Fc observed in the autumn and spring freeze-thaw periods compared to the winter permanently frozen period, which accounted for 4.8% of accumulated total non-growing season Fc. The heavily grazed site showed less soil CO2 efflux compared to UG, MG, PP and CL land-use types due to a larger reduction in gross primary productivity (GPP) compared to ecosystem respiration. Grazing reduced Fc by 23% for MG and 32% for HG compared to UG. Soil CO2 efflux from the PP land-use type, which was grazed during the non-growing season, was 23% greater than that from the UG and CL land-use types. Air temperature during the non-growing season was the main factor controlling soil CO2 efflux (R2 = 0.40, P < 0.001), although soil water content also played a role. Precipitation received during the growing season had a large legacy effect on Fc. Annual weather variation overshadowed the influence of land-use types on Fc.

Grazing effects on soil characteristics and vegetation of grassland in northern China

Abstract. Large areas of grassland in the agro-pastoral region of northern China were converted into cropland for grain production, and the remaining grasslands are being overgrazed and seriously degraded. The objective of this study was to evaluate how reductions in grazing intensity affect the soil and vegetation characteristics in grasslands of northern China. Soil heterogeneity and vegetation characteristics were evaluated for ungrazed (UG), moderate grazing (MG), and heavy grazing (HG) sites. Grazing increased diversity, but heavy grazing decreased aboveground biomass and increased the non-grass component. The non-grass proportion of total biomass increased with grazing intensity, which was 8, 16 and 48 % for UG, MG and HG sites, respectively. Species richness at the MG and HG sites was significantly higher than at the UG site (P&lt; 0.05) with 3.6, 5.5 and 5.7 for UG, MG and HG sites, respectively. Strong spatial dependence of the examined soil properties at 10 m scale for all grazed sites was revealed by the ratio of nugget to total variation (0–23 %). Overgrazing homogenized soil characteristics at a 10 m scale. The ranges of spatial autocorrelation for soil organic C (SOC) and total N were both &gt; 120 m at the HG site, which was considerably larger than that at the MG and UG sites with corresponding distances of 17.3 and 20.8 m for the MG site and 8.6 and 15.0 m for the UG site, respectively. The sampling density and sampling space for the HG site could be decreased under this scale sampling interval (10 m). Therefore, MG was recommended as the preferred management alternative for grasslands in northern China because of increased plant diversity without negative consequences related to decreased forage quality, forage quantity and soil heterogeneity for the investigated soil properties in northern China's grasslands.

Responses of Plant Community and Soil Properties to Inter-Annual Precipitation Variability and Grazing Durations in a Desert Steppe in Inner Mongolia

Grazing can dramatically affect arid grassland communities that are very vulnerable to environmental changes due to its relatively short and sparse ground coverage, low biomass, sandy soil and inter-annual precipitation found in the desert steppe. The study investigates the effects of different grazing durations on vegetation and soil properties of a desert steppe community. The experiment was conducted in Xisu Banner in Inner Mongolia with five treatments: CG (continuous grazing), 40UG (40 d ungrazed), 50UG (50 d ungrazed), 60UG (60 d ungrazed) and UG (ungrazed). The biomass of both shrub and annual-biennial plant communities were significantly decreased by CG. Continuous grazing and 40UG significantly reduced the ANPP (aboveground net primary productivity) by the end of the three year study. 60UG treatment increased soil organic carbon (OC), total nitrogen concentration (TN) and total phosphorus concentration (TP) concentrations and 50UG increased the TN and total phosphorus concentration (TK) concentrations, whereas CG, 40UG and 50UG decreased soil OC, TP and available phosphorus concentration (AP) concentrations. The perennial plant species of the desert steppe were generally tolerant for grazing. The annual-biennial plant species had large variability in ANPP because of the inter-annual precipitation. Our results highlight that inter-annual precipitation variations could strongly modify the community responses to grazing in arid ecosystems.

Response of vegetation and soil carbon and nitrogen storage to grazing intensity in semi-arid grasslands in the agro-pastoral zone of northern china.

Overgrazing has been the primary cause of grassland degradation in the semi-arid grasslands of the agro-pastoral transition zone in northern China. However, there has been little evidence regarding grazing intensity impacts on vegetation change and soil C and N dynamics in this region. This paper reports the effects of four grazing intensities namely un-grazed (UG), lightly grazed (LG), moderately grazed (MG) and heavily grazed (HG) on vegetation characteristics and soil properties of grasslands in the Guyuan county in the agro-pastoral transition region, Hebei province, northern China. Our study showed that the vegetation height, canopy cover, plant species abundance and aboveground biomass decreased significantly with increased grazing intensity. Similarly, soil organic carbon (SOC) and total nitrogen (STN) in the 0–50 cm were highest under UG (13.3 kg C m−2 and 1.69 kg N m−2) and lowest under HG (9.8 kg C m−2 and 1.22 kg N m−2). Soil available nitrogen (SAN) was significantly lower under HG (644 kg N hm−2) than under other treatments (725–731 kg N hm−2) in the 0–50 cm. Our results indicate that the pasture management of “take half-leave half” has potential benefits for primary production and livestock grazing in this region. However, grazing exclusion was perhaps the most effective choice for restoring degraded grasslands in this region. Therefore, flexible rangeland management should be adopted in this region.

The influence of grazing exclosure on soil C stocks and dynamics, and ecological indicators in upland arid and semi-arid rangelands

Soil carbon (C) storage and quality in rangeland ecosystems may change as a result of long-term heavy grazing, especially in upland arid and semi-arid rangelands characterized by low soil organic C contents. The impact of grazing exclosure on soil C stock and mineralization, microbial biomass C and the activities of invertase and alkaline phosphatase involved in C and P cycling as soil ecological indicators were studied in woody and non-woody rangeland ecosystems of two sites (viz., Sabzkouh with woody cover and Boroujen with non-woody cover) located in Zagros Mountains, Central Iran. At each site, soil samples were taken from 0 to 15cm depth of the two rangelands including heavy grazing (HG) and ungrazed (UG) regimes, and analyzed for their chemical and microbial properties. Results demonstrate that soil organic C and total N contents, and C/N ratios were not affected by grazing regime at Boroujen, while ungrazed rangelands had higher C (17%) and N (19%) contents compared with heavily grazed rangelands at Sabzkouh. Grazing exclosure increased soil C mineralization (44.7–73.6%) and turnover (24–64%) at both study sites, and increased the amount of soil microbial biomass C (5.4-fold) and decreased the metabolic quotient (90%) only at Sabzkouh. Soil invertase activity was significantly higher (1.3–2.1 times) in ungrazed than heavily grazed rangelands at both sites, whereas ungrazed rangelands had significantly greater soil alkaline phosphatase activity (19%) compared with heavily grazed rangelands only at Sabzkouh. The variations in the effect of grazing exclosure on soil organic matter (SOM) dynamics and C sequestration in these upland arid and semi-arid rangelands were due to differences between rangelands in initial SOM contents, and probably could be due to differences in plant productivity and composition, and the amount of rainfall between the study sites. Non-woody rangelands contained less soil C and N contents, and C mineralization but greater microbial biomass C than woody rangelands, reflecting a clear difference in substrate quality and soil C availability. Soil biochemical and microbial indices as ecological indicators can reflect grazing exclosure effects on soil restoration only in woody rangelands.

Contribution of grazing to soil atmosphere CH4 exchange during the growing season in a continental steppe

Degradation of steppes induced by overgrazing may affect the uptake of atmospheric methane (CH4) by soil sinks. However, uncertainty is associated with the very limited knowledge of gas fluxes in rapidly degrading steppe. In this study, we investigated the effects of grazing on CH4 uptake during the growing season in three types of steppe (meadow steppe, typical steppe and desert steppe and) in Inner Mongolia, China, to quantify and compare CH4 uptake in steppe ecosystems under different grazing management conditions. The CH4 fluxes were measured using an automatic cavity ring-down spectrophotometer at three steppe locations that differed primarily in grazing intensity. The results indicated that steppe soils were CH4 sinks throughout the growing season. CH4 uptake at all sites averaged 7.98 kg CH4-C ha−1 yr−1 (ranging from 1.53 to 18.74 kg CH4-C ha−1 yr−1), of which approximately 43.8% occurred in the desert steppe. CH4 uptake in the desert steppe increased 20.4% and 51.2% compared with the typical steppe and meadow steppe, respectively. Light grazing (LG) of steppe did not significantly change CH4 uptake compared with un-grazed (UG) steppe, but moderate and heavy grazing (MG, HG) reduced CH4 uptake significantly (by 6.8–37.9%, P < 0.05). These findings imply that reducing the grazing pressure on steppe would help increase the atmospheric CH4 sinks in steppe soils. Our results suggest that HG exerts a considerable negative impact on CH4 uptake in a continental steppe. Further studies involving year-round, intensive measurements of CH4 uptake are needed.

Grazing effects on the greenhouse gas balance of a temperate steppe ecosystem

Although a significant fraction of the global soil–atmosphere exchange of greenhouse gases (GHGs) occurs in semi-arid zones little is known about the magnitude of fluxes in grazed steppe ecosystems and the interference with grazing intensity. In order to assess GHG burdens and to identify options of climate-optimized livestock farming, GHG emissions of sheep grazing in Inner Mongolia steppe were analyzed. Carbon sequestration and field-fluxes of methane (CH4) and nitrous oxide (N2O) were measured at a range of steppe sites differing in grazing intensity and management, i.e. ungrazed (UG), ungrazed with hay cutting (HC), lightly grazed (LG), moderately grazed (MG), and heavily grazed (HG). In addition, GHG emissions from enteric fermentation, manure management, and farming inputs (i.e. fossil fuels) were quantified for LG, MG, and HG. Monte Carlo simulation was used to estimate uncertainty. Sheep grazing changed the net GHG balance of the steppe from a significant sink at UG (−1476 ± 2481 kg CO2eq ha−1 year−1) to a significant source at MG (2350 ± 1723 kg CO2eq ha−1 year−1) and HG (3115 ± 2327 kg CO2eq ha−1 year−1). In a similar way, the GHG intensity increased from 8.6 ± 79.2 kg CO2eq kg−1 liveweight gain at LG up to 62.2 ± 45.8 and 62.6 ± 46.7 kg CO2eq kg−1 liveweight gain at MG and HG, respectively. GHG balances were predominantly determined by CO2 from changes in topsoil organic carbon. In grazing systems, CH4 from enteric fermentation was the second most important component. The results suggest that sheep grazing under the current management changes this steppe ecosystem from a sink to a source of GHGs and that grazing exclusion holds large potential to restore soil organic carbon stocks and thus to sequester atmospheric CO2. The balance between grazing intensity and grazing exclusion predominantly determines GHG balances of grass-based sheep farming in this region. Therefore, a high proportion of ungrazed land is most important for reducing GHG balances of sheep farms. This can be either achieved by high grazing intensity on the remaining grazed land or by confined hay feeding of sheep.

Short‐term degradation of semiarid grasslands—results from a controlled‐grazing experiment in Northern China

AbstractThe assessment of grassland degradation due to overgrazing is a global challenge in semiarid environments. In particular, investigations of beginning steppe degradation after a change or intensification of the land use are needed in order to detect and adjust detrimental land‐use management rapidly and thus prevent severe damages in these sensitive ecosystems. A controlled‐grazing experiment was established in Inner Mongolia (China) in 2005 that included ungrazed (UG) and heavily grazed plots with grazing intensities of 4.5 (HG4.5) and 7.5 (HG7.5) sheep per hectare. Several soil and vegetation parameters were investigated at all sites before the start of the experiment. Topsoil samples were analyzed for soil organic C (SOC), total N (Ntot), total S (Stot), and bulk density (BD). As vegetation parameters, aboveground net primary productivity (ANPP), tiller density (TD), and leaf‐area index (LAI) were determined. After 3 y of the grazing experiment, BD increased and SOC, Ntot, Stot, ANPP, and LAI significantly decreased with increasing grazing intensity. These sensitive parameters can be regarded as early‐warning indicators for degradation of semiarid grasslands. Vegetation parameters were, however, more sensitive not only to grazing but also to temporal variation of precipitation between 2006 and 2008. Contrary, soil parameters were primarily affected by grazing and resistant against climatic variations. The assessment of starting conditions in the study area and the application of defined grazing intensities is essential for the investigation of short‐term degradation in semiarid environments.