Seasonal Dynamics of Nutrient Loading and Chlorophyll A in a Northern Prairies Reservoir, Saskatchewan, Canada

Harmful algae blooms have become an increasing concern in context with the safety of water resources around the globe;however, little is known about the dynamics and specific causes of such blooms in the prairie ecozone in North America. The aim of this study was to research the nitrogen (N) and phosphorous (P) content and nutrient limitation (defined as N and P limitation) of growth of cyanobacteria in a northern prairies reservoir (Lake Diefenbaker [LD], SK, Canada). A combination of concentration balance analysis for N and P, controlled bioassays with the natural consortium of phytoplankton or defined monocultures of cyanobacteria, and satellite imagery was applied to address this aim. The current trophic status of Lake Diefenbaker is one of moderate eutrophication. Primary production in the lake is P-limited, and N did not represent a limiting factor for algal production. There was no significant increase in TP con- centrations between the upper and lower portions of the reservoir, indicating that most of the phosphorus in LD comes from upstream sites in Alberta. Anabaena circinalis, a species that has the potential to seriously degrade lake ecosys- tems, was identified as the predominant cyanobacteria in LD. Together with the fact that TP influxes into the reservoir primarily originate from upstream sources, these results suggest the need for remedial measures in the upstream reach of the South Saskatchewan River. Satellite imaging represented a promising approach in support of monitoring for po- tential algal blooms in LD;however, due to limited sensitivity and issues associated with atmosphere interference this methodology should only be used in combination with in situ water quality monitoring. In summary, while this study indicated that Lake Diefenbaker is potentially at risk with cyanobacteria blooms (some of which such as Anabena sp. that can produce toxins) during late summer and fall, development of clear causal relationships and risk assessment strategies is currently limited due to lack of monitoring data and programs.

Short-term Intensive Sustainable Restoration of Grasslands and Prairies Invaded with High Densities of Nitrogen-fixing Weeds： A Test with the Invasive Plant Lespedeza Cuneata

This study examines a management strategy for restoring grassland and prairie communities that have become degraded due to high density stands of invasive nitrogen-fixing plants. The novel management applications minimize the use of herbicides and maximize the competitive interactions of native species. The management method includes two seasons of application of organic fertilizer （4-1-4）, an initial herbicide （Pasture Gard, Dow Agro） application, and mowing, where mowing was a necessary treatment to control secondary growth in prairie habitats, to control high density patches of Lespedeza （L.） Cuneata, in a completely randomized factorial experiment. The herbicide was effective in reducing L. Cuneate stem density 0 stems/m^2 from an initial 88 stems/m^2 with cover reduced to 0% from 16%. The fertilizer only treatment reduced L. Cuneata percent cover to 6% from initial cover of 16%, but did not reduce the number of stems. The management strategy is an effective fast step in restoring a native prairie invaded by a nitrogen-fixing plant.

Hybrid Prairie Dog and Beluga Whale Optimization Algorithm for Multi-Objective Load Balanced-Task Scheduling in Cloud Computing Environments

The cloud computing technology is utilized for achieving resource utilization of remotebased virtual computer to facilitate the consumers with rapid and accurate massive data services.It utilizes on-demand resource provisioning,but the necessitated constraints of rapid turnaround time,minimal execution cost,high rate of resource utilization and limited makespan transforms the Load Balancing(LB)process-based Task Scheduling(TS)problem into an NP-hard optimization issue.In this paper,Hybrid Prairie Dog and Beluga Whale Optimization Algorithm(HPDBWOA)is propounded for precise mapping of tasks to virtual machines with the due objective of addressing the dynamic nature of cloud environment.This capability of HPDBWOA helps in decreasing the SLA violations and Makespan with optimal resource management.It is modelled as a scheduling strategy which utilizes the merits of PDOA and BWOA for attaining reactive decisions making with respect to the process of assigning the tasks to virtual resources by considering their priorities into account.It addresses the problem of pre-convergence with wellbalanced exploration and exploitation to attain necessitated Quality of Service(QoS)for minimizing the waiting time incurred during TS process.It further balanced exploration and exploitation rates for reducing the makespan during the task allocation with complete awareness of VM state.The results of the proposed HPDBWOA confirmed minimized energy utilization of 32.18% and reduced cost of 28.94% better than approaches used for investigation.The statistical investigation of the proposed HPDBWOA conducted using ANOVA confirmed its efficacy over the benchmarked systems in terms of throughput,system,and response time.

Water storage changes in North America retrieved from GRACE gravity and GPS data

As global warming continues,the monitoring of changes in terrestrial water storage becomes increasingly important since it plays a critical role in understanding global change and water resource management.In North America as elsewhere in the world,changes in water resources strongly impact agriculture and animal husbandry.From a combination of Gravity Recovery and Climate Experiment（GRACE） gravity and Global Positioning System（GPS） data,it is recently found that water storage from August,2002 to March,2011 recovered after the extreme Canadian Prairies drought between 1999 and 2005.In this paper,we use GRACE monthly gravity data of Release 5 to track the water storage change from August,2002 to June,2014.In Canadian Prairies and the Great Lakes areas,the total water storage is found to have increased during the last decade by a rate of 73.8 ± 14.5 Gt/a,which is larger than that found in the previous study due to the longer time span of GRACE observations used and the reduction of the leakage error.We also find a long term decrease of water storage at a rate of-12.0 ± 4.2 Gt/a in Ungava Peninsula,possibly due to permafrost degradation and less snow accumulation during the winter in the region.In addition,the effect of total mass gain in the surveyed area,on present-day sea level,amounts to-0.18 mm/a,and thus should be taken into account in studies of global sea level change.

End-Member Selection in Two-Component Isotope-Based Hydrograph Separation

The science that underpins our knowledge and understanding of Isotope-Based Hydrograph separation (IHS) has gained grounds, over the last few decades, in the identification of streamflow sources. However, challenges still exist in identifying appropriate tracers and the right combination of end-members for the IHS process. In a two-component IHS analysis, the application of the dual isotopes tracers, δ18O and (or) δ2H, is regarded as the simplest method. We undertook an IHS study within a nested system of eight Prairie watersheds located in South central Manitoba, Canada. The work evaluated about 17,000 results emanating from the application of a combination of two potential tracers (δ18O and δ2H) and eight each of potential “old” and “new” water end-members in a two-component IHS process. The outcome showed occurrences of many mathematically possible but hydrologically unacceptable IHS results. The observation was particularly predominant within relatively larger perennial sub-catchments of the watershed. It is also shown that inter-site sub-catchment isotopic end-member transferability is possible within watersheds of similar physio-hydrographic characteristics. We suggest that a careful evaluation of the physio-hydrographic characteristics of catchments be considered in IHS studies in addition to the recommended guidelines in the selection of tracers and end-members.

Drought changes and the mechanism analysis for the North American Prairie

The worst droughts in the central part of the North American Prairie in the past several hundred years have been reconstructed from tree-ring chronologies, suggesting that some drought years have exceeded the se- verity shown by the gauge record. A general circulation model of the Geophysical Fluid Dynamics Laboratory （GFDL） has simulated climate changes for the area during the past 250 years driven by c^imatic forces, providing scenarios of extreme climate that can further diagnose the mechanisms. This study refined the drought signals from the tree ring data and GFDL modeling at inter-annual and decadal time scales and analyzed the potential mecha- nisms driving the droughts. Results showed that drought years with summer precipitation Ilower than the 10th per- centiles occurred during 1777-1789, 1847-1861 and 1886-1879 AD in the area. Both tree rings and model re- vealed that the frequency of droughts has been relatively consistent in a similar timing andl frequency with climate change. Monte Carlo analysis have detected that the tree ring chronologies have recorded drought years with probabilities of 9.3%-12.8%, and the model has simulated the droughts with probabilities 5..7%-17.8%. Under CO2 and aerosol forcing, the GFDL modeled the drought recurrences of 13 years and 25 years, which are very syn- chronous changes with tree rings and consistent with gauge records. The 20-a and 10-a time scale reoccurrences of droughts are very consistent with solar radiation cycles, and similar to the length of cycles in oceanic records, suggesting that terrestrial precipitation modeling is properly driven from sun-land-sea dynamics. Detected severity, variability and return periods of droughts from the present study make potential improvements in drought predictions and constructing scenarios for climate impacts and adaptation strategies.

Effectivity of arbuscular mycorrhizal fungi collected from reclaimed mine soil and tallgrass prairie

We examined suitability of arbuscular mycorrhizal fungi (AMF) associated with cool-season nonnative forages on reclaimed surface-mined land in southeast Ohio for establishment of native warm-season grasses. The goal of establishing these grasses is to diversify a post-reclamation landscape that is incapable of supporting native forest species. A 16-week glasshouse study compared AMF from a 30-year reclaimed mine soil (WL) with AMF from native Ohio tallgrass prairie soil (CL). Four native grasses were examined from seedling through 16 weeks of growth. Comparisons were made between CL and WL AMF on colonized (+AMF) and non-colonized plants (–AMF) at three levels of soil phosphorus (P). Leaves were counted at 4 week intervals. Shoot and root biomass and percent AMF root colonization were measured at termination. We found no difference between WL and CL AMF. Added soil P did not reduce AMF colonization, but did reduce AMF efficacy. Big bluestem (Andropogon gerardii Vitman), Indiangrass (Sorghastrum nutans (L.) Nash), and tall dropseed (Sporobolus asper (Michx.) Kunth) benefited from AMF only at low soil P while slender wheatgrass (Elymus trachycaulus (Link) Gould ex Shinners) exhibited no benefit. Establishment of tallgrass prairie dominants big blue-stem and Indiangrass would be supported by the mine soil AMF. It appears that the non-native forage species have supported AMF equally functional as AMF from a regionally native tallgrass prairie. Tall dropseed and slender wheatgrass were found to be less dependent on AMF than big bluestem or Indiangrass and thus would be useful in areas with little or no AMF inoculum.

Soil compaction and arbuscular mycorrhizae affect seedling growth of three grasses

Soil compaction is a limitation to establishment of native forest species on reclaimed surfacemined lands in Appalachia. Previously, non-native forage species such as tall fescue (Schedonorus arundinaceus(Schreb.) Dumort., nom. cons.) have been planted because they easily established on reclaimed mine soil. There is now interest in establishing robust native prairie species to enhance biodiversity and provide greater potential for root activity in the compacted soil. We conducted a 10-week glasshouse study comparing growth of “Pete” eastern gamagrass (Tripsacum dactyloidesL.), “Bison” big bluestem (Andropogon gerardiiVitman), and “Jesup MaxQ” tall fescue at soil bulk densities (BD) of 1.0, 1.3, and 1.5 g·cm-3. We also examined effects of arbuscular-mycorrhizal fungi (AMF) on plant growthin relation to compaction. Sources of AMF were a reclaimed surface coal mine soil and a native tallgrass prairie soil. Shoot and root biomass of tall fescue and big bluestem were reduced at 1.5 BD while eastern gamagrass growth was not affected. Growth ofbig bluestem and eastern gamagrass was greaterwith AMF than without, butsimilar between AMF sources. Tall fescue growthwas not enhanced by AMF. Overall, tall fescue biomass was 3 times greater than eastern gamagrass and 6 times greater than big bluestem when comparing only AMF-colonized grasses. Eastern gamagrass and big bluestem are both slower to establish than tall fescue. Eastern gamagrass appears to be more tolerant of compaction, while big bluestem appears somewhat less tolerant.

Effects of Land Use Change, Cultivation, and Landscape Position on Prairie Soil Organic Carbon Stocks

Temperate grassland soils are typically a sink for carbon. However, it is estimated that up to 99% of tallgrass prairies in North America have been converted to another land use. These conversions can lead to increased soil erosion and soil organic carbon (SOC) mineralization rates, turning a large carbon sink into a source. The purpose of this study was to compare by land use the retention of SOC, TSN, and fly ash on sloping landscapes with an emphasis on measuring the subsoil in addition to the surface soil. Eight paired plots were established on adjacent, sloping landscape profiles in western Iowa;one site a cropland and the other a remnant tallgrass prairie. The prairie landscape had a baseline SOC stock of 232 Mg-C ha-1. After roughly 150 years of agriculture the cropland had 52% less SOC, 39% less TSN, and 22% less fly ash which equates to annual losses of 0.55 Mg-C ha-1 yr-1, 0.04 Mg-N ha-1 yr-1, and 0.0002 Mg-fly ash ha-1 yr-1.

Near-Surface Soil Nutrient Changes over Time under Native Prairie and Managed Agriculture in Arkansas

Landuse change from native prairie to managed agriculture can have substantial impacts on soil nutrient properties. Nutrient release from soil organic matter decomposition is the soil’s inherent source of long-term fertility; thus it is imperative to understand the effects of continued landuse over time to avoid mistaking actual soil property changes with simple inter-annual variability from one year to the next. The objective of this study was to evaluate the effects of landuse (i.e. managed agriculture and native prairie) in two contrasting physiographic regions (i.e. the Ozark Highlands region of northwest Arkansas and the Grand Prairie region of east-central Arkansas) on the change in extractable soil nutrients over a 15-yr period from 2001 to 2016. Extractable soil Ca, Mg, and Zn increased at least two times more over time (P < 0.05) under cultivated agriculture in the Grand Prairie than under native prairie in the Grand Prairie or either landuse in the Ozark Highlands. Averaged across landuse, extractable soil S increased nine times more over time (P < 0.05) in the Ozark Highlands than in the Grand Prairie, while extractable soil Na and Mn increased at least six times more over time (P < 0.05) in the Grand Prairie than in the Ozark Highlands. Averaged across region, extractable soil Mn increased 2.5 times more over time (P < 0.05) under native prairie than under agricultural landuse. Results from this long-term field study clearly demonstrate how landuse and regional soil characteristics can affect near-surface soil nutrient contents, which should be taken into consideration when implementing conservation and/or ecosystem restoration activities.

Destination and Alienation:Spiritual Belongingness in My Antonia

The backdrop of Willa Cather's works is usually set on the prairie of West Nebraska.She focuses on the depiction of the life style and spirit of the farmers working in the harsh environment of the west,and her work is a loving tribute to the tough and pioneering spirit of its people.She also depicts the spiritual alienation of the various immigrants who move away from home to settle down in the west,exploring their hardship and disillusionment.My Antonia is just this kind of work,which features Jim Burden and his quest of an Antonianized prairie,pregnant with touching nostalgia for a rural past in the west threatened by the multiple complications of an overdeveloping modern world.The thesis aims to dissect the state of spiritual belongingness of the novel's several characters,and analyze their respective implication.

Opportunities of Inner Mongolia's economic development under the background of the “Silk Road Economic Belt”

"The Silk Road Economic Belt" is a great strategic thought, through which China deepens allround reform and opening up, especially in the major move of opening up to the west. Inner Mongolia autonomous region owns the superior geographical position and was closely related to the Silk Road in ancient times. In the new stage, Inner Mongolia autonomous region should seize the opportunity of the development strategy, and strive to develop economic construction under the background of the belt of Prairie Silk Road, and play an important role in the economic belt of the "Prairie Silk Road".

A Diagnostic Approach towards the Causes of Energy Balance Closure Problem

Hydrometeorological models are often evaluated and optimized on the basis of micrometeorological measurements. However, it has been known for more than three decades that surface measurements of sensible and latent heat energy (LE) are systematically underestimated. We studied this problem using six years of eddy-correlation measurements for four fields (corn, soybean, and prairie) in central Iowa, USA. We recorded major components of the energy equation (i.e. net radiation, sensible heat flux, LE, and soil heat flux, photosynthesis), and indirectly estimated most of the minor components of energy balance (namely storage in the soil, canopy and air). Storage in the canopy was related to leaf area index (LAI) acquired from Moderate Resolution Imaging Spectrometer (MODIS). In this paper, a diagnostic approach is investigated where systematic error is identified first. Three dimensional (3D) plots of the residual of energy equation vs. potential variables indicated the imbalance was largest mainly during the cold non-growing season when the soil was dry. Correlations between energy balance residual (EBR) and energy components showed that soil storage was not precisely estimated. Finally, an a-posteriori analysis (constrained linear multiple regression (CMLR)) was conducted to quantify the contribution of major/minor components of the energy equation towards EBR. The result highlights that the contribution of pertinent components of energy to EBR is mainly controlled by prevailing monthly hydrometeorological conditions;however, precise quantification of causes of imbalance is site-specific. A comparison between the a-posteriori analysis technique and the Bowen-ratio method demonstrates that the Bowen-ratio basically presumes a higher level of underestimation in LE. The results obtained in this study suggest that a-posteriori analysis may offer a superior methodology to correct measured eddy-correlation measurements. Furthermore, the overall trends in the correction of LE measurements suggest that there is a potential for rough monthly corrections of LE, irrespective of the type of crop.

EVAPOTRANSPIRATION OF LOW-LYING PRAIRIE WETLAND IN MIDDLE REACHES OF HEIHE RIVER IN NORTHWEST CHINA

Low-lying prairie wetland, which has characteristics of both grassland and wetland, has irreplaceable ecological functions in inland river basins of Northwest China. Owing to its small-scale distribution, so far, the observation and research on it are rare. The estimation of evapotranspiration is significant to ecological and environmental construction, scientific management of pasture and protection of wetland. For studying the evapotranspiration （ET） of low-lying prairie wetland in the middle reaches of the Heihe River, an inland river, in Northwest China, the automatic weather station in Linze Ecological Experimental Station of Lanzhou University （39°15′ 3″N, 100°03′ 52″ E）, Linze, Gansu Province, was selected as a case study. Based on meteorological data collected, Bowen-Ratio Energy Balance （BREB） method was used to calculate the evapotranspiration （ET） of low-lying prairie wetland. The analysis results showed that in a whole year （September 2003 -August 2004）, the total ET was 611.5mm and mean daily 1.67mm/d. The ET varied with different growing stages. In non-growing stage （NGS）, initial growing stage （IGS）, middle growing stage （MGS） and end growing stage （EGS）, the ET was 0.57, 2.01, 3.82 and 1.49mrrdd, with a percentage of total ET of 18.26%, 9.20%, 61.83% and 10.71% respectively. In March, ET began to increase. But in April, the ET increased most. After that, it increased gradually and got the maximal value in July. From then on, the ET decreased gradually. In September, the ET decreased rapidly. With the ending of growing and the freezing of soil, the ET stopped from the middle of November to February in next year. Hourly ET analysis showed that at 8：00 a.m. （during MGS at 7：00 a.m.）, the evapotranspiration began, at 13：00 p.m. got its maximal value and at 19：00 p.m. （during MGS at 20：00 p.m.）, the evapotranspiration stopped. The intensity of ET in sunny day was much larger than that in cloudy day in the same growing stage.

Effects of inclusion of purple prairie clover (Dalea purpurea Vent.)with native coolseason grasses on in vitro fermentation and in situ digestibility of mixed forages

Background:Incorporation of legume species into native North American pastures is considered an effective method to increase native pasture productivity and improve the nutritive value of forage.This study evaluated the effects of inclusion of purple prairie clover(PPC,Dalea purpurea Vent.),a native legume forage,with native coolseason grasses on the in vitro fermentation and in situ digestibility of mixed forages.Methods:Whole plant PPC and mixtures of cool-season grasses were harvested when the PPC reached the vegetative(VEG),full flower(FL)and seedpod(SP)stages,and were combined in ratios(DM basis)of 0:100,25:75,50:50,75:25 and 100:0 at each maturity.In vitro ruminal incubations using these mixtures were conducted for 48 h to determine gas production(GP),in vitro DM disappearance(IVDMD),total volatile fatty acids(VFA)and ammonia-N production.Mixtures of forages harvested when the PPC reached the FL stage and 50:50 mixture of forages harvested at VEG,FL and SP stages were incubated in the rumen of three heifers for 0,2,6,12,24,48,72 and 96 h to determine in situ degradabilities of DM,neutral detergent fibre(aNDF)and crude protein(CP).Results:Contents of aNDF and ADF increased(P<0.01),while CP decreased(P<0.001)as PPC matured.Concentrations of extractable condensed tannins in PPC ranked as FL>VEG>SP(P<0.05).Regardless of PPC proportions in the mixture,GP decreased(P<0.05)with increasing PPC maturity.Increasing PPC proportions linearly increased(P<0.001)GP,IVDMD and total VFA at VEG,but linearly decreased(P<0.001)them at SP.Irrespective of PPC maturity,ammonia-N production linearly increased(P<0.01)with increasing proportions of PPC and the concentration was higher(P<0.05)at VEG than at FL and SP stages.Increasing proportion of PPC at either maturity linearly increased(P<0.001)molar percentage of acetate(A)and branched-chain VFA,but linearly decreased(P<0.001)molar percentage of propionate(P),resulting in a linearly increase(P<0.001)in the A:P ratio.Increasing FL PPC in the mixture linearly and quadratically(P<0.01)increased a(soluble fraction),but linearly and quadratically decreased(P<0.01)b(potentially degradable fraction)for DM and aNDF,resulting in linear(P<0.05)and quadratic(P<0.01)increases in DM and aNDF maximum potential degradabilities(a+b).Effective degradabilities of DM and aNDF were also linearly and quadratically increased(P<0.05),and CP was quadratically increased(P<0.05)with increasing FL PPC,with the greatest effective degradability being observed with ratios between 50:50 and 75:25.Ruminal maximum potential degradabilities of DM and aNDF decreased(P<0.001)as the forage matured.Effective degradability of DM ranked as VEG>FL>SP(P<0.001),whereas the effective degradability of aNDF was similar between VEG and FL and both were greater(P<0.01)than SP.Conclusions:Inclusion of vegetative PPC in a mixed forage diet resulted in the greatest digestibility and incorporation of PPC before seedpod stage with native grasses had a positive effect on ruminal fermentation.Effects of PPC on ruminal digestion depend on both the stage of maturity and its proportion in mixed legume-grass pastures.Pastures containing 50%of PPC in full flower stage would likely provide the greatest quality diet to grazing ruminants subject to potential animal selectivity.

Calibrating Vegetation Cover and Grassland Pollen Assemblages in the Flint Hills of Kansas, USA

Grassland cover and composition respond to climate and have undoubtedly changed during the Holocene, but quantitative reconstructions from fossil pollen have been vague about spatial scale and taxon-specific cover. Here, we estimate the relevant source area of pollen for sedimentary basins approximately 50 m in radius, and we report pollen productivity estimates for 12 plant taxa in the tallgrass prairies of central North America. Both relevant source area of pollen and pollen productivity estimates were calculated via the Extended R-Value Model. To obtain these estimates, we collected and quantified the pollen found in surface sediment samples from 24 ponds across the study area. Vegetation was surveyed in the field in a 100 m radius around each pond, and vegetation maps from the Kansas Gap Analysis Project (GAP) were used to a radius of 2 km. Pollen fall speeds were calculated according to Stoke’s Law. Pollen assemblages from basins approximately 50 m in radius have a relevant source area of 1060 m in this grassland landscape. Pollen productivity estimates range from 0.02 to over 30 among the 12 taxa: Artemisia, Ambrosia, Asteraceae, Chenopodiaceae, Cornus, Fabaceae, Juniperus, Maclura, Poaceae, Populus, Quercus, and Salix. Woody taxa generally have higher pollen productivity than herbaceous taxa (except for Chenopodiaceae and Ambrosia).

Biomass Production of Monocultures and Mixtures of Cup Plant and Native Grasses on Prime and Marginal Cropland

To date, most candidate systems for producing herbaceous cellulosic biomass have been composed of monocultures of perennial or annual grasses. Ecosystem goods and services provided from these biomass feedstock production systems could be increased dramatically with mixing of one or more forb species that would increase biodiversity and provide habitat for pollinators. Cup plant (Silphium perfoliatum L.) is featured with many desirable characteristics, such as high biomass potential, adaptation to marginal soils, and attractiveness to pollinators, desirable in a dicot species to grow in mixtures with perennial warm-season grasses. The objective of this study was to compare cup plant, switchgrass (Panicum virgatum L.), and prairie cordgrass (Spartina pectinata Link) monocultures to their mixtures for biomass production on prime and poorly drained marginal crop land for two years in both South Dakota and Wisconsin. In Wisconsin, monocultures of prairie cordgrass and cup plant and their mixture produced more biomass (8.1 Mg&middot;ha-1) than the switchgrass monoculture and switchgrass/cup plant mixture (5.3 Mg&middot;ha-1) on both prime and marginal land. While in South Dakota, drought and meristem destruction by the cup plant moth (Eucosma giganteana Riley) caused large reductions in biomass production (1.7 Mg&middot;ha-1) in both years, with the switchgrass/cup plant mixture on marginal land having the highest yield (2.1 Mg&middot;ha-1). Our study showed binary mixtures of cup plant and native warm-season grasses have great potential for increasing biodiversity and other ecosystem goods and services, relative to monocultures, for sustainable biomass feedstock production on poorly drained marginal land in the northcentral USA.

Comparison of Prairie and Eroded Agricultural Lands on Soil Organic Carbon Retention (South Dakota)

The primary objective of this research was to predict changes in soil organic carbon (SOC) and total soil nitrogen (TSN) stocks as a result of land use change from prairie to agricultural land if the mesic-frigid temperature line moved north in the US and the former frigid soils were cultivated. The conversion of prairie to agricultural use, as a result of climate shift, would release SOC to atmosphere and enhance greenhouse gas emissions. The SOC and TSN differences between the prairie site and agricultural land were compared in South Dakota. The agricultural land had 18% less SOC and 16% less TSN or only half of the expected loss from prairie levels. An attempt was made to document the land use history of the prairie site to understand why SOC and TSN losses were less than anticipated. The fly ash concentration levels on prairie side slopes suggested that the prairie was historically disturbed and eroded. Intensive grazing and burning contributed to the disturbance. The SOC and TSN stock losses appear to represent the minimal change that would occur in the next 100-year time period if a prairie was shifted to agricultural use as a result of climate shift and the mesic-frigid temperature line in US was to move north.

Long-Term Drainage and Nitrate Leaching below Well-Drained Continuous Corn Agroecosystems and a Prairie

Many studies have evaluated nitrate-N leaching from tile-drained agricultural soils, but little longterm research has been performed on well-drained soils commonly throughout the Midwest. Equilibrium tension lysimeters installed at a depth of 1.4 m were used to measure year-round (12 month) nitrate-N leaching below chisel-plow (CP) and no-tillage (NT) continuous corn (Zea mays L.) agroecosystems to determine the potential effects of common agricultural practices on subsurface water quality. The corn systems were fertilized at a rate of 10 kg N ha-1 of starter fertilizer and 180 kg N ha-1 as NH4NO3. For comparison, nitrate-N leaching from a natural ecosystem was performed on a nearby prairie restoration (PR). Drainage, nitrate-N leaching loss, and flow-weighted mean nitrate-N concentrations for 8 years of data (1996-2003) are reported for the CP, NT and PR ecosystems. Results show that 52%, 37%, 16% of cumulative precipitation was collected as drainage, while 18%, 19%, 0.5% of the total N input was leached as nitrate-N in the CP, NT, and PR, respectively. Nearly three-quarters of the total nitrate-N was leached from each ecosystem during the period from 1 April to 30 June. The 8-yr, flow-weighted mean nitrate-N concentration measured in leachate was 9.5, 12.2 and -1 for the CP, NT and PR treatments. Annual drainage volumes and nitrate-N leaching losses were highly variable, stressing the importance of long-term studies capable of measuring year-round drainage for understanding N leaching dynamics and evaluating effects of cropping practices on potential groundwater quality.

Salinity Tolerance in Argentinean Population of <i>Bromus catharticus</i>. Variability and Direct and Indirect Effects on Seedling Characters

The aim of this research was to evaluate the salinity tolerance in prairie grass populations at the seedling stage quantifying the variability and the influence of physiological traits related to it. Salinity tolerance, in Bromus catharticus Vahl (prairie grass) populations collected in different environments of the Pampean Phytogeography region (Argentine) was evaluated at the seedling stage, using controlled condition of temperature and light. It was adopted a completely randomized design using 3 plots with three plants each one per population and two levels of treatment: 0 mM and 100 mM NaCl. Morphological, biomass and membrane stability root and shoot traits were studied. A factorial ANOVA with interaction was estimated. Then one way ANOVA for all seedling traits in both treatments allowed estimating variance components, coefficient of genotypic determination (CGD) and variation index (VI). Comparisons between populations were made using Tukey test (at 5% of probability). Phenotypic correlations among traits were calculated and then a path coefficient analysis separated direct and indirect effects at 100 and 0 mM NaCl. No significant interactions “Population × Treatment” were found for any character. The saline stress caused a pairing in the population means for the most traits. Coefficients of variation were mainly higher when the seedlings grew without stress (0 mM) because it allowed a greater potential genotypic expression. The absence of significant interactions denotes a good homeostatic capacity of the prairie grass facing that abiotic stress. Leaf length, shoot length and root dry matter were the variables with the largest direct and indirect effects. Our results showed an increase for them at salt and demonstrated intraspecific variation, possibly in relation with the origin sites. Plants under stress showed a marked resilience, in order to quickly restore the same biomass allocation patterns that occur in non-stress environment.