Grazing Efficiency Research Articles

Southern Ocean phytoplankton under climate change: a shifting balance of bottom-up and top-down control

Abstract. Phytoplankton form the base of the marine food web by transforming CO2 into organic carbon via photosynthesis. Despite the importance of phytoplankton for marine ecosystems and global carbon cycling, projections of phytoplankton biomass in response to climate change differ strongly across Earth system models, illustrating uncertainty in our understanding of the underlying processes. Differences are especially large in the Southern Ocean, a region that is notoriously difficult to represent in models. Here, we argue that total (depth-integrated) phytoplankton biomass in the Southern Ocean is projected to largely remain unchanged under climate change by the Coupled Model Intercomparison Project Phase 6 (CMIP6) multi-model ensemble because of a shifting balance of bottom-up and top-down processes driven by a shoaling mixed-layer depth. A shallower mixed layer is projected on average to improve growth conditions, consequently weaken bottom-up control, and confine phytoplankton closer to the surface. An increase in the phytoplankton concentration promotes zooplankton grazing efficiency, thus intensifying top-down control. However, large differences across the model ensemble exist, with some models simulating a decrease in surface phytoplankton concentrations. To reduce uncertainties in projections of surface phytoplankton concentrations, we employ an emergent constraint approach using the observed sensitivity of surface chlorophyll concentration, taken as an observable proxy for phytoplankton, to seasonal changes in the mixed-layer depth as an indicator for future changes in surface phytoplankton concentrations. The emergent constraint reduces uncertainties in surface phytoplankton concentration projections by around one-third and increases confidence that surface phytoplankton concentrations will indeed rise due to shoaling mixed layers under global warming, thus favouring intensified top-down control. Overall, our results suggest that while changes in bottom-up conditions stimulate enhanced growth, intensified top-down control opposes an increase in phytoplankton and becomes increasingly important for the phytoplankton response to climate change in the Southern Ocean.

Forage accumulation, nutritive value, and grazing efficiency on rotationally stocked ‘Zuri’ guineagrass pastures as affected by pre‐graze canopy height and N rate

AbstractGrazing management and nitrogen fertilisation may affect forage accumulation (FA), nutritive value, and grazing efficiency (GE) of the highly productive ‘Zuri’ guineagrass [Megathyrsus maximus (Jacq.) B.K.Simon & S.W.L. Jacobs syn. Panicum maximum Jacq.]. The objective of this study was to assess the effects of pre‐graze canopy heights [55 and 75 cm (H55 and H75, respectively)] and N fertilisation rates [150 and 300 kg N ha−1 year−1 (N150 and N300, respectively)] on FA, GE, grazing losses (GL), and nutritive value of Zuri under rotational stocking. The stubble height was 50% of the pre‐graze canopy height. The total FA was 20% greater under H75 than H55 (22,120 vs. 18,370 kg DM ha−1 year−1), as well as the GL was greater under H75 (85%) than under H55 (79%). Regardless of pre‐graze height, the upper stratum of the canopy was composed mostly of leaves contributing to similar crude protein (CP) (142 g kg−1) and in vitro digestible organic matter (IVDOM) (559 g kg−1) concentrations. Greater N rate (N300) increased FA (23,500 vs. 16,980 kg DM ha−1 year−1) and resulted in greater GE (84% vs. 80%) compared to N150. The CP and IVDOM concentrations under N300 (157 and 571 g kg−1, respectively) were greater than under N150 (128 and 547 g kg−1). Zuri guineagrass grazed at H75 has great FA and GE, maintaining a similar forage nutritive value compared to H55.

89 Improving cattle grazing efficiency with multi-functional cover crops

Abstract Grazing cool-season cover crops provides a sustainable way of extending the grazing season and reducing the impact row-crop farming systems on the environment. Cover crops promote soil health; however, the impacts of grazing cover crops on soil health in the Southeast are not well understood. The objective of the current study was to determine the effects of different cover crop mixtures on a cotton (Gossypium hirsutum)-peanut (Arachis hypogaea) cropping system. The experiment consisted of 18 paddocks, planted in mixtures of grass [‘Coker’ oat (Avena sativa)], grass + legume [‘Dixie’ crimson clover (Trifolium incarnatum)], or grass + legume + brassica [(‘T-raptor’ brassica (Brassica napus × B. rapa)] planted at the Wiregrass Research and Extension Center (Headland, AL). Paddocks were randomly allocated to grazed or not grazed (n = 3). Grazed paddocks were grazed with yearling beef steers (266 ± 44 kg) using the put and take method to maintain a forage alloance of 1 kg DM per kg BW. Forage samples were collected every 2 wk, for biomass, botanical compositions, and nutritive value. Paddocks were grazed from 17 Jan – 22 Mar 2023 (65 d) and steer BW were taken at the beginning and end of the grazing season for calculation of average daily gain Data were analyzed using Proc Glimmix of SAS 9.4 (SAS Institute, Cary, NC) with forage sampling date considered a repeated measure. No difference in steer average daily gain was detected among grazed treatments (1.5 kg/d; P > 0.44). Cover crop (forage) biomass was also not different among all grazed and ungrazed treatments (1,097 kg DM/ha; P = 0.56). According to the results, grazing cool-season annual cover crops may reduce the supplementation required to maintain cattle through the winter months in the Southeast.

Replacing Fertilizer with Dried Distillers' Grains in Stocker Cattle Systems on Southern Great Plains Old World Bluestem, USA.

The objective was to examine the effects of dried distillers' grains supplementation and fertilization strategies on the cattle performance and resource use efficiency of stocker cattle grazing on Plains Old World bluestem. Over 4 consecutive years, heifers and steers (average n = 239) were randomly assigned to 1 of 4 treatments: (1) low input, low stocking density, and no fertilizer or distillers grains supplementation (LOW); (2) high stocking density and no fertilizer with distillers grains supplementation (DDGS); (3) high stocking density and 90 kg of nitrogen/ha with no distillers grains supplementation (NFERT); (4) high stocking density, 90 kg of nitrogen/ha, and 39 kg of phosphorus/ha with no distillers grains supplementation (NPFERT). Cattle grazed in the pastures from mid-May to mid-September each year, except for 2011, when the experiment ended in July due to lack of forage. Data were analyzed using a linear model with fixed effects of treatment, year, and treatment × year (R software). Nitrogen use efficiency (retained/inputs) was affected by a treatment × year interaction, where LOW had the greatest efficiency in all years and DDGS was greater than NFERT and NPFERT in all years except 2012, with NFERT and NPFERT being not different in all years. The estimated total carbon equivalent emissions were greater for DDGS, NFERT, and NPFERT than LOW, but the carbon footprint (kg CO2eq/kg weight gain) was lesser for LOW and DDGS, which were not different, than NFERT and NPFERT, which were also not different. Replacing nitrogen fertilizer with dried distiller's grains improved the cattle performance and the efficiency of resource use, and could be a viable economic alternative to traditional systems.

Efficiency of Amino Acid Utilization in Nellore Cattle Grazing Low-Quality Forage Supplemented with Different Sources of Nitrogen.

This study aimed to evaluate the effects of supplementation with non-protein nitrogen (NPN) or ruminal undegradable protein (RUP) on intake, digestibility, and amino acid (AA) use efficiency of Nellore cattle grazing during the dry season. Eight Nellore steers (12 ± 2 months old) were used in quadruplicate Latin squares (2 × 2). The animals were placed on Urochloa brizantha cv. Xaraés under continuous grazing. The treatments included the following: (1) urea supplementation (NPN) and (2) supplementation of corn gluten meal 60 (CGM, RUP). Animals supplemented with CGM showed higher intakes of dry matter (DM) supplement, total AA, essential AA, and individual AA. The supplementation did not affect the total AA digestibility, total AA flux, and the AA fluxes of microbial origin and RUP from the diet (p > 0.05). The ruminal microorganism origin flux of total AA to the duodenum was 44.5% and 52.7% for animals supplemented with NPN and CGM, respectively. Animals supplemented with CGM showed an increase in blood concentrations of isoleucine (+19.09 μmol/L), cystine (+27.29 μmol/L), and albumin (+0.11 g/dL) (p < 0.05), but this increase was not accompanied by an improvement in N use efficiency of steers (p > 0.05). RUP supplementation via CGM can be an efficient nutritional strategy to enhance the intake and absorption of AA by Nellore cattle grazing low-quality forage during the dry season.

4 Developing a Dry Matter Intake Prediction Equation for Grazing Animals based on Real-Time Enteric Emissions Measurements

Abstract Cattle dry matter intake (DMI) is an essential component of calculating cattle stocking rates, determining nutrient requirements, and evaluating grazing efficiency. Cattle DMI and digestion of forages impact enteric greenhouse gas (CO2e) emissions. Enteric emissions include methane (CH4) and carbon dioxide (CO2), that are eructated by ruminants. The amount of methane produced is affected by consumption, quality, and type of feedstuffs. Intake of grazing animals varies on environmental factors and physiological stage. Additionally, increased GHG levels indicate energy loss during the rumen fermentation process. However, there may be a silver lining to enteric GHG emissions to predict DMI of grazing animals since they are highly correlated with DMI and forage composition. There is limited data on the relationship of DMI and GHG on extensive rangeland systems. Obtaining data for beef cattle DMI and enteric emissions on forage-based diets similar to extensive rangelands is needed to develop an equation capable of predicting DMI for grazing cattle. Therefore, our objective was to determine the relationship between CH4, CO2, oxygen (O2), and hydrogen (H2) emissions and DMI of dry beef cows to develop a mathematical model that predicts grazing DMI from enteric emissions. The predictive equation or precision system model (PSM; Menendez et al., 2022) was developed using data from two feeding trials that were conducted using GreenFeed, SmartFeed Pro, and SmartScale (C-Lock Inc. Rapid City, SD). This study was conducted at the SDSU Cottonwood Field Station (Cottonwood, SD). The two feeding trials consisted of dry beef cows (n=10) receiving low (8% CP) or high (15% CP) quality grass hay using a 14-day adaptation period and a 14-day period of data collection. Regression, artificial neural network, and dynamic-mechanistic models were developed using these data and assessed to identify a model that accurately and precisely predicts forage DMI for dry beef cows on pasture. Model evaluation of the machine learning algorithms used a training, testing, and cross-validation scheme to determine model accuracy. Evaluation of mechanistic models used the Model Evaluation System (MES; Tedeschi, 2006) to measure accuracy (mean bias, Cb, RMSEP), precision (R2, MEF, CCC), and screening for systematic errors. This study successfully integrated three precision technologies which improve research capabilities on extensive rangeland systems through precision enhanced data collection. Deploying a precision-based DMI algorithm enhances research-based capabilities to manage range beef cattle on an individual level by more precisely setting stocking rates, providing supplementation, and evaluating individual animal efficiency; ultimately leading to lower cost, optimized resources, and enhanced environmental sustainability. Further, the enteric emissions data collected fills a gap for missing GHG data of dry beef cows in maintenance phase in semi-arid western South Dakota rangelands.

The Repeatability of Grazing Efficiency as a Perennial Ryegrass Variety Trait

The ‘Grazing Utilization’ sub-index within the Pasture Profit Index identifies perennial ryegrass varieties with high grazing efficiency. Grazing efficiency is assessed in plot trials conducted over a number of years. The objective of this study was to investigate the repeatability of variety grazing efficiency. Correlations were derived between variety performance in separate evaluation years and between variety performances in separate trials. Grazing efficiency was found to be moderately repeatable, with correlation values ranging from 0.47 to 0.86 between years and ranging from 0.51 to 0.84 between trials. The results will provide commercial seed companies with increased confidence when developing variety mixes intended for intensive grazing. Farmers will benefit from improved variety selection and animal performance from their farms.

Incorporation of the grazing utilization subindex and new updates to the Pasture Profit Index

Grazing efficiency has been shown to differ between perennial ryegrass varieties. Such differences affect the utilization of grass within grazing systems, influencing the profitability of grass-based ruminant production systems. The Pasture Profit Index (PPI) is an economic merit grass variety selection tool developed to identify varieties with the greatest economic potential for grass-based dairy production systems. A new grass utilization subindex was developed and incorporated into the PPI to identify varieties with superior grazing efficiency. The subindex rewards varieties with superior grazing efficiency, measured as Residual grazed height, as these varieties allow increased amounts of herbage dry matter to be used by grazing animals. The economic values of all other traits within the PPI were reviewed and updated to ensure that the index was reflective of the current economic scenarios with appropriate assumptions included in the models, thus ensuring that varieties excelling in the agronomic traits with the greatest effect on profitability were recognized. The difference between the highest and lowest performing varieties for the grass utilization trait ranged from €23 to -€24. A range of €211 to €43 was recorded between the highest and lowest ranked varieties within the updated PPI. Spearman's rank correlation between the updated and original PPI lists was 0.96. The introduction of the utilization subindex will allow farmers to make informed variety selection decisions when reseeding pasture, particularly on their grazing platforms and it will allow a demand-based communication process between the farmer and the grass merchant or breeder, ultimately affecting trait selection for future breeding strategies.

Seasonal effects on the stoichiometry of microbes, primary production, and nutrient cycling

We develop a compartment model inspired by producer–herbivore–microbe soil food webs and determine how the naturally occurring seasonal variation in producer and detrital quality affects microbial nutrient cycling and the feedback to primary production. We show that seasonal changes in the stoichiometric quality of the producer coupled with the efficiency of herbivore grazing could induce a switch in the stoichiometric signature and therefore the functioning of the microbial community. Microbial decomposers are responsible for the flux of essential nutrients through an ecosystem. Our model enables one to quantitatively understand the tipping points between bacterially or fungally dominated decomposer communities, and more generally, the complex relationships between microbial decomposers, primary production, and nutrient cycling.

Shrub cover impacts on yak growth performance and herbaceous forage quality on the Qinghai-Tibet Plateau, China

Shrub cover in alpine meadows around the world has experienced significant changes during the past 20 yr. An increase in shrub cover has often been associated with large influences in ecosystem functions. The objectives of the present study were to investigate the impact of shrub cover on herbaceous forage quality and yak grazing efficiency on the Qinghai-Tibetan Plateau, China. Forty-eight yak steers were randomly assigned to four grazing pastures with different shrub cover rates (control, low, middle, and high). The whole grazing period was categorized as vegetative stage (June to July), bloom stage (August to October), and senescent stage (November to December). Herbaceous forage chemical composition and body weight of yaks were measured, and serum and rumen samples were analyzed. Although shrub cover had no effect on herbaceous forage chemical composition and serum biochemical parameters of yaks, total herbaceous forage production in pastures and crude protein intake of yaks decreased with increasing shrub cover. Such changes decreased average daily gain of yaks. As expected, increasing the herbaceous forage maturation significantly decreased crude protein content while increased dry matter, neutral detergent fiber and acid detergent fiber contents, consequently, reduced herbaceous forage crude protein and organic matter intakes and average daily gain of yaks. The rumen of yaks has higher ammonia nitrogen and total volatile fatty acid concentrations and butyrate proportion in the bloom stage of forage compared with those of the senescent stage. The results indicate that shrub cover on the Qinghai-Tibetan Plateau needs a certain level of control for the sustainable grazing yak production, although it has little negative effect on blood health and rumen fermentation. Additionally, it is vital to select the optimum time to market livestock or supplement feed with yaks during the cold season on the Qinghai-Tibetan Plateau.

The relationship between the grazing efficiency and the production, morphology and nutritional traits of perennial ryegrass varieties

AbstractRuminant grazing systems aim to optimize the proportion of grazed forage within the diet and perennial ryegrass grazing efficiency influences both the quantity and quality of herbage utilized. The objective of this study was to examine morphological and chemical plant characteristics and test for any associations with grazing efficiency. The leading perennial ryegrass varieties from the 2016 Irish Recommended List were established in a plot study and rotationally grazed by dairy cows over 3 years. Pre-grazing plant characteristics were measured and related to grazing efficiency, as measured by ‘residual grazed height’. Data were analysed using the PROC MIXED procedure to test for trait differences between varieties, and their corresponding ploidy and heading categorizations. Traits displaying significant variety variability were then tested for their correlation to grazing efficiency using the PROC GLM procedure. Tetraploid varieties exhibited superior grazing efficiency over diploids, due to their superior performance in traits correlated with grazing efficiency. Increasing organic matter digestibility and leaf proportion and decreasing neutral detergent fibre and stem height within the sward were found to increase grazing efficiency. The observed link between these plant traits and grazing efficiency indicates a possibility that they could be used to develop proxy measures to aid breeders to select for, and evaluators to measure, varietal grazing efficiency without involving animal assessments. It was concluded that this would make it logistically practical to assess large numbers of varieties in small plot trials to both breed and evaluate perennial ryegrass varieties for superior grazing efficiency.

An investigation into the grazing efficiency of perennial ryegrass varieties

AbstractThe objective of this study was to compare the grazing efficiency of 30 perennial ryegrass varieties, differing in ploidy and heading date. Plots were grazed by lactating dairy cows and managed under a rotational grazing system with 19 grazing events occurring over two years. Pre‐grazing and post‐grazing compressed sward heights were measured with a rising plate meter. A mixed model was used to predict the post‐grazing sward height of each variety based on year, grazing event, block and pre‐grazing sward height. Residual grazed height (RGH) was derived as the difference between the actual and predicted post‐grazing sward height and was used as the measure of grazing efficiency. Negative RGH values indicated that the actual herbage removed was greater than that predicted and so indicated a superior grazing efficiency. Varieties differed in their level of grazing efficiency (p &lt; .001), with RGH values ranging from −0.38 to +0.34 cm. Tetraploid varieties exhibited significantly greater grazing efficiency performance than diploids (p &lt; .001), with average RGH values of −0.13 and +0.13 cm respectively. A significant difference in grazing efficiency was found among recommended perennial ryegrass varieties that are not being recorded by mechanically harvested simulated grazing protocols. A variety reappraisal that included grazing efficiency could identify varieties capable of improving on‐farm livestock productivity from grass.

The Use of Remote Sensing Data to Improve the Efficiency of Pastoral Sheep

in the study of agricultural land, the priority is the use of remote monitoring techniques using unmanned aerial vehicles, technological portable devices. Obtaining materials by remote methods will expand the possibilities of introducing grazing livestock, increase the yield and thereby improve the efficiency of production indicators. The article considers the issues of assessing the nutritional value of pasture fodder, in particular, the amino acid composition in combination with the vegetation index in the conditions of pasture livestock raising in the Stavropol Territory. Productive qualities of replacement young animals directly depend on the quality of feed. Monitoring the amino acid composition of feeds allows you to optimize the technology of growing sheep, taking into account their productivity direction. The combination of remote methods for assessing the vegetation index and the in-depth composition of the nutritional value of feeds makes it possible to optimize the production schedule for the use of pasture plots by various sex and age groups of animals and increase the average daily gain in live weight of young fattening groups by 8-10%. It has been shown that the introduction of top-dressing with roughage in especially dry periods contributes to preserve of animal growth energy when changing grazing areas. Remote assessment of pasture vegetation was carried out using a special camera to calculate the NDVI (Normalized Difference Vegetation Index), which was installed on an unmanned aerial vehicle. At the same time, the dynamics of the NDVI using a portable manual nitrogen sensor was studied in the same pasture plots. The obtained results of monitoring of the vegetative index on pasture plots were compared with the results of chemical analysis of plant feed. Information on the availability of gross amount of plant biomass in the fields was used for priority selection of a specific site for grazing animals and optimizing the use of agricultural territories. It was proven that the parameters of the NDVI for the pasture keeping of young sheep should not be lower than 0.4. The development and implementation of innovative methods of aerospace monitoring makes it possible to increase the efficiency of land use and increase the efficiency of grazing.

Nutrient Intake, Excretion and Use Efficiency of Grazing Lactating Herds on Commercial Dairy Farms.

Simple SummaryExcess nutrients on dairy farms can affect soil and animal health and have negative impacts on the environment. More nutrients are usually brought onto farms in animal feed than in fertilizer and, as dairy cows do not efficiently use feed nutrients to produce milk, most consumed nutrients are excreted in dung and urine. Estimating nutrients excreted by cows relies on measuring feed and nutrient intake. However, measuring pasture nutrients consumed by cows that graze on commercial farms is complicated. We modified the ‘Feeding Standards’ approach to estimate daily pasture dry matter and nutrient intake and nutrients excreted using data and samples readily available on commercial dairy farms. These data were collected on five visits in different seasons from 43 grazing system farms located in diverse climatic zones. Although these herds graze daily, the lactating cows only obtained slightly more than half their dry matter intake from pasture. Each day, on average, we estimated that a grazing cow excretes 433 g nitrogen, 61 g phosphorus, 341 g potassium, 44 g sulphur, 92 g calcium and 52 g magnesium on these farms. Using this approach to estimate nutrients excreted by grazing animals on dairy farms can assist farmers improve nutrient distribution and fertilizer requirements.Estimating excreted nutrients is important for farm nutrient management, but seldom occurs on commercial grazing system farms due to difficulties in quantifying pasture intake. Nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca) and magnesium (Mg) intake, excretion and use efficiency of 43 commercial dairy herds grazing pasture were calculated to understand the range in nutrient intake and excretion in these systems. Milk production, feed (grazed and supplement), as well as farm and herd management data were collected quarterly on representative farms located in temperate, arid, subtropical and tropical regions of Australia. Lactating herd sizes on these farms averaged 267 (30 to 1350) cows, with an average daily milk yield of 22 (9 to 36) kg/cow per day and the herds walked from <0.01 to 4 km/day on a variety of terrains. The mean total metabolizable energy (ME) required by cows in the herds was estimated to be 195 (116 to 289) MJ/cow per day. Although these farms are considered grazing systems, feeding strategies ranged from total dependence on pasture to total mixed rations (TMRTMR) and consisted of a wide variety of nutrient and energy contents. Mean pasture dry matter intake (DMI) (9 kg/cow per day, from 0.1 to 22 kg/cow per day) was just over half of total DMI. Dietary concentration of crude protein, P, K, S, Ca and Mg concentrations were, on average, 19%, 0.45%, 2.1%, 0.29%, 0.65%, and 0.3%, respectively, for all herds and, except for N, supplement nutrient concentrations were always more variable than pasture. Approximately 72% and 88% of diets provided greater than recommended P and N intakes, respectively. Calculated mean N, P, K, S, Ca and Mg excretions were 433, 61, 341, 44, 92 and 52 g/cow per day, respectively. Of the farm characteristics examined, residual maximum likelihood (REML) analysis indicated that daily excreted N, P and S were significantly related to per ha milk production, and excreted P, K and Mg were related to percentage of herd DMI provided as supplement. Mean use efficiencies by cows of N, P, K, S, Ca and Mg were 21%, 25%, 9%, 16%, 23% and 4%, respectively. These estimates of nutrient excretion and feed nutrient use efficiencies can be used to improve nutrient management on grazing system commercial dairy farms.

Zooplankton grazing selectivity regulates herbivory and dominance of toxic phytoplankton over multiple prey generations

AbstractHow grazer selectivity regulates the primary producer community is a core topic in ecology. Yet, the role of zooplankton grazing selection on phytoplankton dynamics is poorly understood. Few studies have compared the effect of grazers with contrasting selectivity on mixed phytoplankton prey, and none over multiple phytoplankton generations. We tested the hypothesis that a selectively grazing copepod (Eudiaptomus gracilis) would facilitate the dominance of a toxic cyanobacterium (Microcystis aeruginosa) by grazing on a competing eukaryotic microalga (Cryptomonas pyrenoidifera), while a generalist cladoceran (Daphnia magna) would have no effect on the dominance of cyanobacteria in 4‐d laboratory cocultures. Experiments started with a ninefold initial dominance of Cryptomonas over Microcystis by biomass. Each grazer type was added to cocultured phytoplankton and the abundance of phytoplankton was compared to no‐grazer controls. As predicted, Daphnia had no effect on the relative abundance of its prey and the copepod facilitated Microcystis dominance, although the strength of facilitation slightly declined with time. As the copepod reduced mostly the biomass of the edible algae, it pushed the system toward the dominance of toxic prey, which likely reduced the efficiency of selective grazing on the last day. Hence, while the selective grazer promoted cyanobacterial dominance, the effect may be weaker than predicted from extrapolating grazing rates obtained from short‐term (i.e., hourly) assays. Overall, predicting the role of zooplankton selectivity on phytoplankton dynamics—especially harmful algal blooms—would benefit from accounting for fluctuations in grazer effects due to shifting abundance and growth of each prey over time.

Regulation of protist grazing on bacterioplankton by hydrological conditions in coastal waters

A series of dilution experiments were conducted along an environmental gradient in coastal waters during April to September 2016, in order to examine the regulation of protist grazing on bacterioplankton by physical processes. Our results suggested that the density gradient in the frontal zone and the pycnocline played a significant role in regulating protist grazing on bacterioplankton in marine environments. The highest bacterial growth rate (1.33 d−1) and grazing rate (1.05 d−1) occurred in the frontal zone along the inshore-offshore transect and in the deep chlorophyll maximum (DCM) that always matched with the pycnocline in terms of the vertical profile in offshore waters. Spatial variability in bacterial growth rate and grazing rate was related to the presence of the density gradient in the front and the DCM. The density gradient aggregated phytoplankton and bacterial cells, enhancing their biomass. Meanwhile, high phytoplankton biomass provided more labile organic carbon to bacterioplankton in the front and the DCM, improving bacterial growth. Hence, the density gradient improved bacterial abundance, consequently enhancing the efficiency of protist grazing. Our findings implied that the density gradient improved bacterial carbon converted to high trophic levels and altered carbon flow in microbial food web in marine environments.

Fir expansion not controlled by moderate densities of large herbivores: a Mediterranean mountain grassland conservation issue

Whilst livestock has maintained grasslands over centuries in south European mountains, current ungulate densities are insufficient to control tree and forest expansion effectively. The present results based on fir population dynamics and radial/height growth raise questions about the sustainable management of new forests that are former mountain grasslands. This empirical case study contributes to debate about methods for long-term management of grasslands in Mediterranean mountains. Forest expansion following the cessation of grazing is a threat to biodiversity in mountain grasslands that are components of Mediterranean cultural landscapes. We hypothesised that ungulates could mitigate tree recruitment, thus conserving mountain grasslands. We tested the efficiency of grazing and browsing by domestic and wild ungulates (sheep, roe and red deer) at inhibiting silver fir (Abies alba Mill.) encroachment in a conservation area, one of the main browsed trees. The fir trees’ age structure was analysed by dendrochronology, and the individual growth patterns and scars were recorded in their tree-ring series. Fir density has increased since the 1960s, simultaneously with the increase in ungulate populations. The scar occurrences only appeared during the 1970s. Most scars were observed on seedlings and small saplings. The impacts of ungulates are observed on the radial and height growth of trees, mostly on trees < 100 cm, but it did not however result in controlling the recruitment of fir. The hypothesis that a moderate density of ungulates might inhibit tree encroachment is therefore rejected, even in the case of a highly palatable species such as silver fir. Ungulates, solely, would not be an appropriate policy for grassland conservation in Mediterranean mountains.

Satellite‐Based Estimation of Particulate Organic Carbon Export in the Northern South China Sea

AbstractKnowledge of particulate organic carbon export flux (EP) is the key to understanding the marine biological carbon pump. In this study, a satellite remote sensing algorithm based on the food‐web model established by Siegel et al. (2014; https://doi.org/10.1002/2013GB004743) was used to estimate EP in the northern South China Sea (NSCS), which consists of direct sinking flux of large phytoplankton and associated aggregates by gravity and flux of zooplankton feces by grazing. This is the first time that fine spatiotemporal variation of satellite‐derived EP in the NSCS is unveiled. Compared with the results on 1° spatial scale products, the model results based on the satellite products with 1/3° and 1/12° resolutions showed better consistency with the observations. Validation with in situ EP showed that the model exhibited a good performance in the NSCS basin, but the predicted EP in the shelf regions were smaller compared with measurements. The satellite‐derived annual‐mean EP in the shelf areas was 8.47 and 5.56 mmol C·m−2·d−1 in the NSCS basin, on the 1/3° spatial scale, with relative differences from observations were about −50% and −15% for the shelf and basin, respectively. The flux of feces from zooplankton grazing, especially that from microzooplankton grazing, might account for the major fraction of the EP in the NSCS. Accurate products of ocean net primary production and empirical coefficients in the food web (e.g., export efficiency of zooplankton grazing and specific mortality rate of nongrazing phytoplankton) suitable for the NSCS, are essential for performance improvement of the satellite‐based EP model.

Behaviour of White Fulani calves grazing panicum/stylo pasture in Southwest Nigeria

The objective of this study was to investigate the behaviour of White Fulani (WF) yearling calves grazing a Panicum maximum/Stylosanthes guianensis mixture under traditional management system in south western Nigeria. The effects of two biomass spatial distribution (dense and sparse) were evaluated in association with three pasture heights (10, 15 and 20cm), with calves allowed access to the pasture for 2:00h. The experiment was laid out in a split plot design with the two biomass spatial distribution assigned to the main plot and sward height assigned to the sub plot to give six treatments; this was replicated three times. The experiment took place from November to December, 2015. Grazing behaviour was recorded with the aid of a Chloride UK 8 channel, H.264 digital video recorder and Chloride UK IR waterproof camera fitted with 3.6mm lens. Data on grazing time, walking time, idling/resting/rumination time and time spent by the animals exhibiting self-licking behavior were collected from the recorded CCTV video player. There was a significant difference in the time spent grazing by the calves with those grazing the pasture with dense biomass at 15cm height recording more grazing time (87.33min). Animals on the pasture with sparse biomass at 10cm height recorded more (p<0.05) idling/resting/rumination time (18.33min). The time spent by the calves walking was similar for the pasture with dense biomass at 10cm and 15cm above the ground. Self-licking behaviour was generally exhibited by the calves across the treatments. However, calves grazing in the plot with sparse biomass at 20cm height engaged in more self-licking behaviour than those in the dense biomass pasture. The differences observed in the behavioural parameters examined clearly indicated the capability of WF yearling calves to increase grazing time, reduce the time spent walking, idling/resting/rumination and self-licking time, thereby improving their efficiency of grazing. From management perspective, plots with dense pasture biomass cut to 15cm height is suggested for optimal production of grazing calves on sown Panicum/Stylosanthes mixture under the present production systems in south western Nigeria.

Technical efficiency and the impact of grassland use right leasing on livestock grazing on the Qinghai-Tibetan Plateau

This paper reviews changes in grassland property rights and measures the efficiency of livestock grazing on China’s Qinghai-Tibetan Plateau, where there is an extensive nomadic grazing system. A cross sectional data set from a field survey of 197 livestock grazing households is used to develop a stochastic translog distance function and technical inefficiency model; variables for livestock intensity and property rights are incorporated. The overall average technical efficiency of the extensive livestock grazing is estimated to be 0.62, lower than the value of 0.67 found for households who rent-in grassland. The results indicate that renting-in grassland improves the technical efficiency of livestock grazing significantly. Both household size and livestock intensity have an effect on technical efficiency, especially the dummy variable of whether the summer pasture is near the winter pasture. This may indicate that grassland fragmentation would be not ideal for extensive livestock production on the Qinghai-Tibetan Plateau.