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Simulation models addressing soil erosion and water quality issues on range sites should realistically simulate grass dry matter yields across a wide diversity of soils and climate regimes. This study was designed to evaluate the ...
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Simulation models addressing soil erosion and water quality issues on range sites should realistically simulate grass dry matter yields across a wide diversity of soils and climate regimes. This study was designed to evaluate the ability of the ALMANAC (Agricultural Land Management Alternatives with Numerical Assessment Criteria) model to simulate annual range grass biomass production under diverse climatic conditions and soils in Texas. The objective was to compare range grass production at rangeland ecological sites, as reported in the U.S. Department of Agriculture Natural Resources Conservation Service ((USDA NRCS) soil surveys, with production simulated by ALMANAC using the most common grasses for each site. The model was run with 60 years of daily weather data on 20 different soils from a diverse set of sites in Texas. The weather data was from seven sites. Model inputs included parameters for the soil series, grass species characteristics, and locally measured climate data. After allowing 10 years for the model to equilibrate, means for simulated production for the sites for the next 50 years were similar to reported means. Simulated production in high rainfall years and low rainfall years were also similar to reported values. The soils, climate, and grass parameter data sets developed here can be useful starting points for deriving data for additional range sites, giving model users examples of realistic input data. The model shows promise as a tool for realistically simulating grass production on a diverse group of soils and in diverse climatic conditions.
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Slow callus growth is a barrier to efficient genetic transformation in some gramineous species. A reformulation of Murashige and Skoog (MS) medium, with additional magnesium sulphate, potassium phosphate, copper sulphate, proline ...
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Slow callus growth is a barrier to efficient genetic transformation in some gramineous species. A reformulation of Murashige and Skoog (MS) medium, with additional magnesium sulphate, potassium phosphate, copper sulphate, proline and glutamine, termed WPBS medium, has been developed which improves all aspects of in vitro culture when compared with MS based media. Embryogenic callus could be produced more rapidly from responsive genotypes of sixteen cereal, forage, model and energy grass species, whether using embryos, shoot tips or proliferated meristems as explants. Three species were not transformed due to contamination or unsuitable explant, but thirteen species were transformed using an identical Agrobacterium-mediated transformation, selection and regeneration protocol, including Avena sativa and Oryza sativa. Readily transformable species such as Lolium perenne, Brachypodium distachyon and Festuca arundinacea and recalcitrant species such as Lolium temulentum and Miscanthus sinensis were reliably transformed, while two new species Phalaris arundinacea and viviparous Deschampsia cespitosa were transformed at the first attempt. It is hoped that the use of WPBS media and this general transformation protocol may help to improve the efficiency of grass and cereal transformation.
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Grazed pastures in south-eastern Australia are typically based on temperate (C3) species, such as perennial ryegrass (Lolium perenne). With predictions of warming to occur in this region, there has been growing interest in the per...
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Grazed pastures in south-eastern Australia are typically based on temperate (C3) species, such as perennial ryegrass (Lolium perenne). With predictions of warming to occur in this region, there has been growing interest in the performance of more heat-tolerant and deep-rooted subtropical (C4) pasture grasses, such as kikuyu (Pennisetum clandestinum). This study used an existing pasture model to estimate the production of kikuyu compared with the commonly used perennial ryegrass at seven sites in south-eastern Australia, using an historical baseline climate scenario between 1971 and 2010, and the daily temperature of the baseline scenario adjusted by +1, +2, and +3 degrees C to represent potential warming in the future. The seven sites were chosen to represent the range of climatic zones and soil types in the region. First, the model predictions of monthly kikuyu dry matter (DM) production were validated with measured data at Taree, Camden, and Bega, with results showing good agreement. Second, pasture production (tDM/ha), metabolisable energy (ME, MJ/kgDM) content, and ME yield (GJ/ha) were predicted using the baseline and warmer climate scenarios. The study was based on 56 simulations of the factorial arrangement of seven sites x four temperature scenarios x two pastures. The month and annual ME yield of a kikuyu-subterranean clover (Trifolium subterraneum) pasture and a perennial ryegrass-subterranean clover pasture were compared. This study showed that in summer-dominant rainfall locations, where the average maximum temperature is >23 degrees C, kikuyu was a more productive pasture species than perennial ryegrass. In winter-dominant rainfall locations during the warmer months of December-March, kikuyu can provide a useful source of ME when perennial ryegrass is less productive. With warming of up to 3 degrees C at the winter-dominant rainfall sites, the average ME yield per year of kikuyu was predicted to surpass that of perennial ryegrass, but inter-annual variation in kikuyu production was higher. The nutritive value, seasonal distribution of growth, total annual production, and its variability are all important considerations for producers when selecting pasture species.
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Sedimentation resulting from soil erosion degrades the surface water environment. This study determines the sediment trapping capacity (STC) of grass filter strips and how slope gradient and vegetation cover affect it. STC is defi...
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Sedimentation resulting from soil erosion degrades the surface water environment. This study determines the sediment trapping capacity (STC) of grass filter strips and how slope gradient and vegetation cover affect it. STC is defined as the maximum sediment trapped within vegetative filter strips (VFS) under given conditions. An exponential model was derived to mirror the relationship between instantaneous sediment trapping efficiency and runoff duration, with findings that STC is closely related to the initial efficiency and attenuation coefficients. The model effectively describes the sediment trapping process, and demonstrates that STC decreases with increasing slope and increases with vegetation cover. Grass strips have a small sediment trapping thickness measured in mm or cm, and grass stems and leaves have little influence on STC, which indicates that reasonable forage cutting may have little influence on sediment removal. STC is an intrinsic characteristic of VFS, and it can be recommended to assess the VFS performance in trapping sediment in severe soil erosion areas. A sediment trapping modulus at the watershed scale based on STC, can offer help to effectively evaluate soil and water conservation engineering and transformation of cropland into forest and grassland in China.
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Tetraploid Brachiaria ruziziensis genotypes which reproduce sexually are essential for the breeding of other species of the Brachiaria genus which reproduce by apomixis. Aiming at studying the available phenotypic and genetic vari...
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Tetraploid Brachiaria ruziziensis genotypes which reproduce sexually are essential for the breeding of other species of the Brachiaria genus which reproduce by apomixis. Aiming at studying the available phenotypic and genetic variability in the breeding population of B. ruziziensis, it was estimated the parameters heritability and genetic and phenotypic correlations between the traits associated with flowering, and the traits responsible for forage yield and nutritional quality. Seventeen traits in 1180 individuals from 59 open pollinated families were studied, and the data were analyzed by mixed model methods. Individuals with sparse flowering presented higher breeding values for total dry matter, yield, and total number of panicles per plant than individuals with early or late flowering. Considering breeding population differences on flowering behavior, on individual narrow sense heritability and on genetic correlations between flowering, agronomic quality and nutritional quality traits have to be considered in intrapopulation breeding and in intrapopulational recurrent selection.
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In semi-arid areas, multiple equilibrium states of an ecosystem ( e. g., grassland and desert) are found to coexist, and the transition from grassland to desert is often abrupt at the boundary. A simple ecosystem model is develope...
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In semi-arid areas, multiple equilibrium states of an ecosystem ( e. g., grassland and desert) are found to coexist, and the transition from grassland to desert is often abrupt at the boundary. A simple ecosystem model is developed to provide the biophysical explanation of this phenomenon. The model has three variables: living biomass, wilted biomass, and soil wetness. The moisture index, which is the ratio of the annual precipitation to potential evaporation, is the only external climate driving force, and the key mechanism is the vegetation-soil interaction. It is found that the maintenance of a grassland requires a minimum moisture index, and the abrupt transition occurs when the moisture index is around this critical value. These results are robust within a wide range for most model parameters, suggesting that the model may be applicable to other temperate grasslands. The characteristics of the wilted biomass also strongly influence the ecosystem's dynamics. [References: 11]
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A dispersion model for continuous releases of pollutants in the atmospheric boundary layer is applied to study the influence on modelled concentrations of different estimates of the key micrometeorological variables that represent...
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A dispersion model for continuous releases of pollutants in the atmospheric boundary layer is applied to study the influence on modelled concentrations of different estimates of the key micrometeorological variables that represent the dispersion processes. The modelling approach is based on the advection-diffusion equation and includes profiles of wind and eddy diffusivity for the entire atmospheric boundary layer. Their functional forms depend on relevant parameters that represent the turbulent mechanisms in a wide range of stabilities. The Prairie Grass experiments were considered for the evaluation. The model performed satisfactorily in the estimation of the near surface crosswind integrated concentrations. The distinct micrometeorological parameters caused, in general, minor differences in the concentrations. However, a greater impact was found during very stable or unstable conditions. In consequence, in these particular situations, the methodologies to obtain the micrometeorological parameters must be carefully analysed.
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A dispersion model for continuous releases of pollutants in the atmospheric boundary layer is applied to study the influence on modelled concentrations of different estimates of the key micrometeorological variables that represent...
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A dispersion model for continuous releases of pollutants in the atmospheric boundary layer is applied to study the influence on modelled concentrations of different estimates of the key micrometeorological variables that represent the dispersion processes. The modelling approach is based on the advection-diffusion equation and includes profiles of wind and eddy diffusivity for the entire atmospheric boundary layer. Their functional forms depend on relevant parameters that represent the turbulent mechanisms in a wide range of stabilities. The Prairie Grass experiments were considered for the evaluation. The model performed satisfactorily in the estimation of the near surface crosswind integrated concentrations. The distinct micrometeorological parameters caused, in general, minor differences in the concentrations. However, a greater impact was found during very stable or unstable conditions. In consequence, in these particular situations, the methodologies to obtain the micrometeorological parameters must be carefully analysed.
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In humid-temperate regions grazed grass is the most economical means of feeding ruminant livestock. Grass growth is often highly variable and therefore difficult to predict. It is influenced by many factors including climatic cond...
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In humid-temperate regions grazed grass is the most economical means of feeding ruminant livestock. Grass growth is often highly variable and therefore difficult to predict. It is influenced by many factors including climatic conditions, soil type and soil nutrients. The Moorepark St. Gilles Grass Growth model (MoSt GG model) is a dynamic model developed in C++ describing daily grass growth at the paddock level. It was developed by adapting an existing grass growth model to include a nitrogen (N) component and a soil water component. The model is effective in grazing and cutting scenarios. Inputs include weather data, grazing management decisions and N fertiliser application. Outputs include daily grass growth, soil mineral N content, grass N uptake, grass N content and NO3?leaching. The MoSt GG model was evaluated against measured data using 2 years data from an experimental farm; the predicted and measured biomass for each paddock was compared. The mean root mean square prediction error (RMSPE) at the measurement level was 505?kg DM/ha. When averaged by week of year, the RMSPE was reduced to 321?kg DM/ha. The MoSt GG model was also evaluated against a range of management scenarios including N fertiliser application rate (from 0 to 650?kg N/ha per year) and defoliation management, and weather conditions. The grass growth response to N fertiliser application was, on average, 9.6?kg DM/kg N applied with a minimum response of 0.8?kg DM/kg N applied and a maximum response of 16.2?kg DM/kg N applied, which is in the range of previously published studies. The MoSt GG model responds to daily weather conditions, patterns and methods of sward defoliation, and describes daily variations in soil mineral and organic N content.
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Simulation models are frequently applied to determine the production potential of forage grasses under various scenarios, including climate change. Thorough calibrations and evaluations of forage grass models can help improve thei...
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Simulation models are frequently applied to determine the production potential of forage grasses under various scenarios, including climate change. Thorough calibrations and evaluations of forage grass models can help improve their applicability. This study evaluated the ability of the Light Interception and Utilization Simulator-GRAss (LINGRA) model to predict biomass yield of timothy (Phleum pratense L. cv. Grindstad) in the Nordic countries. Variety trial data for the first and second year after establishment were obtained for seven locations: Jokioinen, Finland (60 degrees 48'N; 23 degrees 29'E), Maaninka, Finland (63 degrees 09'N; 27 degrees 18'E), Korpa, Iceland (64 degrees 09'N; 21 degrees 45'W), Saerheim, Norway (58 degrees 41'N; 5 degrees 39'E), Lillerud, Sweden (59 degrees 24'N; 13 degrees 16'E), Ostersund, Sweden (63 degrees 15'N; 14 degrees 34'E) and Umea, Sweden (63 degrees 49'N; 20 degrees 13'E) from 1992 to 2012. Two calibrations of the LINGRA model were carried out using Bayesian techniques. In the first of these (Saerheim calibration), data on biomass yield and underlying variables obtained from independent field trials at Saerheim were used. In the second (Nordic calibration), biomass data from the other locations were used as well. The model was validated against the remaining set of biomass yields from all locations not included in the Nordic calibration. The observed total seasonal yield the first and second year after establishment was 913 and 991 g DM m-2 respectively on average across the locations. The corresponding average simulated yield after the Saerheim calibration was 1044 (root mean square error (RMSE) 258) and 1112 g DM m-2 (RMSE 312), respectively. After the Nordic calibration, the simulated average total seasonal yield was 863 (RMSE 242) the first year and 927 g DM m-2 (RMSE 271) the second year after establishment. The differences between the observed and simulated first cut yield followed the same patterns, whereas the prediction accuracy for second cut yield did not differ substantially between the calibration approaches. Using the parameter set from the Nordic region decreased the model predictability at Saerheim compared with only using model parameters derived from this location. These results show that using biomass data from several locations, instead of only one specific location, in the calibration of the LINGRA model improved the overall prediction accuracy of first cut dry matter yield and total seasonal dry matter yield across an environmentally heterogeneous region. To further analyse the usefulness of including multi-site data in forage grass model calibrations, other forage grass models could be evaluated against the same dataset.
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