Effect of fertigation frequency on soil nitrogen distribution and tomato yield under alternate partial root-zone drip irrigation

Alternate partial root-zone drip fertigation (ADF) is a combination of alternating irrigation and drip fertigation,with the potential to save water and increase nitrogen (N) fertilizer efficiency.A 2-year greenhouse experiment was conducted to evaluate the effect of different fertigation frequencies on the distribution of soil moisture and nutrients and tomato yield under ADF.The treatments included three ADF frequencies with intervals of 3 days (F3),6 days (F6) and 12 days (F12),and conventional drip fertigation as a control (CK),which was fertilized once every 6 days.For the ADF treatments,two drip tapes were placed 10 cm away on each side of the tomato row,and alternate drip irrigation was realized using a manual valve on the distribution tapes.For the CK treatment,a drip tape was located close to the roots of the tomato plants.The total N application rate of all treatments was 180 kg ha^(-1).The total irrigation amounts applied to the CK treatment were450.6 and 446.1 mm in 2019 and 2020,respectively;and the irrigation amounts applied to the ADF treatments were 60%of those of the CK treatment.The F3 treatment resulted in water and N being distributed mainly in the 0–40-cm soil layer with less water and N being distributed in the 40–60-cm soil layer.The F6 treatment led to 21.0 and 29.0%higher 2-year average concentration of mineral N in the 0–20 and 20–40-cm soil layer,respectively and a 23.0%lower N concentration in the 40–60-cm soil layer than in the CK treatment.The 2-year average tomato yields of the F3,F6,F12,and CK treatments were 107.5,102.6,87.2,and 98.7 t ha^(-1),respectively.The tomato yield of F3 was significantly higher (23.3%) than that in the F12 treatment,whereas there was no significant difference between the F3 and F6 treatment.The F6 treatment resulted in yield similar to the CK treatment,indicating that ADF could maintain tomato yield with a 40%saving in water use.Based on the distribution of water and N,and tomato yield,a fertigation frequency of 6 days under ADF should be considered as a water-saving strategy for greenhouse tomato production.

On the calibration and verification of Voronoi-based discontinuous deformation analysis for modeling rock fracture

Since its introduction,discontinuous deformation analysis(DDA)has been widely used in different areas of rock mechanics.By dividing large blocks into subblocks and introducing artificial joints,DDA can be applied to rock fracture simulation.However,parameter calibration,a fundamental issue in discontinuum methods,has not received enough attention in DDA.In this study,the parameter calibration of DDA for intact rock is carefully studied.To this end,a subblock DDA with Voronoi tessellation is presented first.Then,a modified contact constitutive law is introduced,in which the tensile and shear meso-strengths are modified to be independent of the bond lengths.This improvement can prevent the unjustified preferential failure of short edges.A method for imposing confining pressure is also introduced.Thereafter,sensitivity analysis is performed to investigate the influence of the calculated parameters and meso-parameters on the mechanical properties of modeled rock.Based on the sensitivity analysis,a unified calibration procedure is suggested for both cases with and without confining pressure.Finally,the calibration procedure is applied to two examples,including a biaxial compression test.The results show that the proposed Voronoi-based DDA can simulate rock fracture with and without confining pressure very well after careful parameter calibration.

Estimating distribution of water uptake with depth of winter wheat by hydrogen and oxygen stable isotopes under different irrigation depths

Crop root system plays an important role in the water cycle of the soil-plant-atmosphere continuum. In this study, com- bined isotope techniques, root length density and root cell activity analysis were used to investigate the root water uptake mechanisms of winter wheat （Triticum aesfivum L.） under different irrigation depths in the North China Plain. Both direct inference approach and multisource linear mixing model were applied to estimate the distribution of water uptake with depth in six growing stages. Results showed that winter wheat under land surface irrigation treatment （Ts） mainly absorbed water from 10-20 cm soil layers in the wintering and green stages （66.9 and 72.0%, respectively）; 0-20 cm （57.0%） in the jointing stage; 0-40 （15.3%） and 80-180 cm （58.1%） in the heading stage; 60-80 （13.2%） and 180-220 cm （35.5%） in the filling stage; and 0-40 （46.8%） and 80-100 cm （31.0%） in the ripening stage. Winter wheat under whole soil layers irrigation treatment （Tw） absorbed more water from deep soil layer than Ts in heading, filling and ripening stages. Moreover, root cell activity and root length density of winter wheat under TW were significantly greater than that of Ts in the three stages. We concluded that distribution of water uptake with depth was affected by the availability of water sources, the root length density and root cell activity. Implementation of the whole soil layers irrigation method can affect root system distribution and thereby increase water use from deeper soil and enhance water use efficiency.

Vertical root distribution and root cohesion of typical tree species on the Loess Plateau, China

Black locust（Robinia pseudoacacia L.） and Chinese pine（Pinus tabulaeformis Carr.） are two woody plants that are widely planted on the Loess Plateau for controlling soil erosion and land desertification. In this study, we conducted an excavation experiment in 2008 to investigate the overall vertical root distribution characteristics of black locust and Chinese pine. We also performed triaxial compression tests to evaluate the root cohesion（additional soil cohesion increased by roots） of black locust. Two types of root distribution, namely, vertical root（VR） and horizontal root（HR）, were used as samples and tested under four soil water content（SWC） conditions（12.7%, 15.0%, 18.0% and 20.0%, respectively）. Results showed that the root lengths of the two species were mainly concentrated in the root diameter of 5–20 mm. A comparison of root distribution between the two species indicated that the root length of black locust was significantly greater than that of Chinese pine in nearly all root diameters, although the black locust used in the comparison was 10 years younger than the Chinese pine. Root biomass was also significantly greater in black locust than in Chinese pine, particularly in the root diameters of 3–5 and 5–10 mm. These two species were both found to be deep-rooted. The triaxial compression tests showed that root cohesion was greater in the VR samples than in the HR samples. SWC was negatively related to both soil shear strength and root cohesion. These results could provide useful information on the architectural characteristics of woody root system and expand the knowledge on shallow slope stabilization and soil erosion control by plant roots on the Loess Plateau.

Effects of loading rate on root pullout performance of two plants in the eastern Loess Plateau,China

Root pullout performance of plants is an important mechanical basis for soil reinforcement by plant roots in the semi-arid areas.Studies have shown that it is affected by plant factors(species,ages,root geometry,etc.)and soil factors(soil types,soil moisture,soil bulk densities,etc.).However,the effects of loading rates on root pullout performance are not well studied.To explore the mechanical interactions under different loading rates,we conducted pullout tests on Medicago sativa L.and Hippophae rhamnoides L.roots under five loading rates,i.e.,5,50,100,150,and 200 mm/min.In addition,tensile tests were conducted on the roots in diameters of 0.5-2.0 mm to compare the relationship between root tensile properties and root pullout properties.Results showed that two root failure modes,slippage and breakage,were observed during root pullout tests.All M.sativa roots were pulled out,while 72.2%of H.rhamnoides roots were broken.The maximum fracture diameter and fracture root length of H.rhamnoides were 1.22 mm and 7.44 cm under 100 mm/min loading rate,respectively.Root displacement values were 4.63%(±0.43%)and 8.91%(±0.52%)of the total root length for M.sativa and H.rhamnoides,respectively.The values of maximum pullout force were 14.6(±0.7)and 17.7(±1.8)N under 100 mm/min for M.sativa and H.rhamnoides,respectively.Values of the maximum pullout strength for M.sativa and H.rhamnoides were 38.38(±5.48)MPa under 150 mm/min and 12.47(±1.43)MPa under 100 mm/min,respectively.Root-soil friction coefficient under 100 mm/min was significantly larger than those under other loading rates for both the two species.Values of the maximum root pullout energy for M.sativa and H.rhamnoides were 87.83(±21.55)mm•N under 100 mm/min and 173.53(±38.53)mm•N under 200 mm/min,respectively.Root pullout force was significantly related to root diameter(P<0.01).Peak root pullout force was significantly affected by loading rates when the effect of root diameter was included(P<0.01),and vice versa.Except for the failure mode and peak pullout force,other pullout parameters,including root pullout strength,root displacement,root-soil friction coefficient,and root pullout energy were not significantly affected by loading rates(P>0.05).Root pullout strength was greater than root tensile strength for the two species.The results suggested that there was no need to deliberately control loading rate in root pullout tests in the semi-arid soil,and root pullout force and pullout strength could be better parameters for root reinforcement model compared with root tensile strength as root pullout force and pullout strength could more realistically reflect the working state of roots in the semi-arid soil.

Observing eddy dye patches induced by shear instabilities in the surf zone on a plane beach

The effects of surf zone eddy generated by alongshore currents on the deformation and transport of dye are still poorly understood,and related tracer release experiments are lacking.Therefore,a tracer release laboratory experiment was conducted under monochromatic,unidirectional incident waves with a large incident angle(30°)on a plane beach with a 1:100 slope in a large wave basin.A charge-coupled device suspended above the basin recorded the dye patch image.The evolution of eddy dye patch was observed and the transport and diffusion were analyzed based on the collected images.Subsequently,a linear instability numerical model was adopted to calculate the perturbation velocity field at the initial stage.The observation and image processing results show that surf zone eddy patches occurred and were separated from the original dye patches.Our numerical analysis results demonstrate that the structure of the perturbation velocity field is consistent with the experimental observations,and that the ejection of eddy patches shoreward or offshore may be ascribed to the double vortex.

Influence of soil moisture content on pullout properties of Hippophae rhamnoides Linn. roots

Plant root system plays an important role in preventing soil erosion and improving slope stability.However,its performance is significantly affected by soil moisture content,and the role of soil moisture in root reinforcement is not fully understood.In this study,the influence of soil moisture on root pullout properties was studied by experiments.Vertical in-situ pullout tests under four different levels of soil matric suction(12 kPa,18 kPa,24 kPa,30 kPa)were carried out on roots of sea buckthorn plants(Hippophae rhamnoides Linn.)which were artificially cultivated for 7 months.Diameter and length of the root system of sea buckthorn were investigated.The results showed that a very significant correlation was observed between root diameter(D)and root length(L)(P<0.01),and root diameter decreased with soil depth.When soil bulk density was constant,peak pullout force(F)and friction coefficient of root-soil interface(μ)decreased with increasing gravimetric soil moisture content in power functions.Soil moisture content significantly affected root pullout resistance because the increase of soil moisture content decreased the friction coefficient between the roots and soil.Root diameter at breakage point(Db)and length of root segment left in soil(Lb)were increased with soil moisture content.In addition,peak pullout force of the roots increased in a power function with root diameter at the soil surface(D0)and in a linear function with total root length(L).The results provided an experimental basis for quantifying the effects of soil moisture content on soil reinforcement by plant roots.

Untangling the influence of soil moisture on root pullout property of alfafa plant

Root pullout property of plants was of key importance to the soil reinforcement and the improvement of slope stability. To investigate the influence of soil moisture on root pullout resistance and failure modes in soil reinforcement process, we conducted pullout tests on alfalfa(Medicago sativa L.) roots at five levels(40, 30, 20, 10 and 6 kPa) of soil matric suction, corresponding to respectively 7.84%, 9.66%, 13.02%, 19.35% and 27.06% gravimetric soil moisture contents. Results showed that the maximal root pullout force of M. sativa decreased in a power function with increasing soil moisture content from 7.84% to 27.06%. Root slippage rate increased and breakage rate decreased with increasing soil moisture content. At 9.66% soil moisture content, root slippage rate and breakage rate was 56.41% and 43.58%, respectively. The threshold value of soil moisture content was about 9.00% for alfalfa roots in the loess soil. The maximal pullout force of M. sativa increased with root diameter in a power function. The threshold value of root diameter was 1.15 mm, because root slipping force was greater than root breaking force when diameter >1.15 mm, while diameter ≤1.15 mm, root slipping force tended to be less than root breaking force. No significant difference in pullout forces was observed between slipping roots and breaking roots when they had similar diameters. More easily obtained root tensile force(strength) is suggested to be used in root reinforcement models under the condition that the effect of root diameter is excluded as the pullout force of breaking roots measured in pullout tests is similar to the root tensile force obtained by tensile tests.

An experimental study of the spatial structures of the instabilities of longshore currents on plane beaches

A laboratory experiment on alongshore currents is conducted for two plane beaches with slopes 1：40 and 1：i00 to investigate the instability of alongshore currents. The dye release experiment is also performed synchronously in surf zone. Complicated and strongly unstable motions of alongshore currents are observed in the experiment. To examine the spatial and temporal variations of the shear instabilities of longshore clearly, dye batches are released in surf zone. The deformation of the dye patch is observed efficiently and effectively with charge coupled device （CCD） system. Some essential characteristics of the shear instability are validated from the results of image analyses of the temporal variation of the dye patch. The influences of alongshore currents, Stokes drift, large-scale vorticity and the shear instabilities on the transport of dye are analyzed using the collected images. The spatial structure of the instabilities of longshore currents is studied by analyzing collected images of the dye patch. And the phase velocity of the meandering movements is obtained through measuring the movement distances of the oscillations of dye patch in alongshore direction with time. The results suggest that the propagation speed of the shear instability is approximately 5070 7570 of maximum of mean alongshore currents for irregular and regular waves. The calculated propagation speed using a linear instability analysis theory is compared with the experimental results. The comparison shows agreements between them.

Characteristics of sea ice kinematics from the marginal ice zone to the packed ice zone observed by buoys deployed during the 9th Chinese Arctic Expedition

Sea ice growth and consolidation play a significant role in heat and momentum exchange between the atmosphere and the ocean.However,few in situ observations of sea ice kinematics have been reported owing to difficulties of deployment of buoys in the marginal ice zone(MIZ).To investigate the characteristics of sea ice kinematics from MIZ to packed ice zone(PIZ),eight drifting buoys designed by Taiyuan University of Technology were deployed in the open water at the ice edge of the Canadian Basin.Sea ice near the buoy constantly increased as the buoy drifted,and the kinematics of the buoy changed as the buoy was frozen into the ice.This process can be determined using sea ice concentration,sea skin temperature,and drift speed of buoy together.Sea ice concentration data showed that buoys entered the PIZ in mid-October as the ice grew and consolidated around the buoys,with high amplitude,high frequency buoy motions almost ceasing.Our results confirmed that good correlation coefficient in monthly scale between buoy drift and the wind only happened in the ice zone.The correlation coefficient between buoys and wind was below 0.3 while the buoys were in open water.As buoys entered the ice zone,the buoy speed was normally distributed at wind speeds above 6 m/s.The buoy drifted mainly to the right of the wind within 45°at wind speeds above 8 m/s.During further consolidation of the ice in MIZ,the direct forcing on the ice through winds will be lessened.The correlation coefficient value increased to 0.9 in November,and gradually decreased to 0.7 in April.

Research on ultrasonic-based investigation of mechanical properties of ice

Arctic sea ice area and thickness have declined dramatically during the recent decades.Sea ice physical and mechanical properties become increasingly important.Traditional methods of studying ice mechanical parameters such as ice-coring cannot realize field test and long-term observation.A new principle of measuring mechanical properties of ice using ultrasonic was studied and an ultrasonic system was proposed to achieve automatic observation of ice mechanical parameters(Young’s modulus,shear modulus and bulk modulus).The ultrasonic system can measure the ultrasonic velocity through ice at different temperature,salinity and density of ice.When ambient temperature decreased from 0°C to-30°C,ultrasonic velocity and mechanical properties of ice increased,and vice versa.The shear modulus of the freshwater ice and sea ice varied from 2.098 GPa to 2.48 GPa and 2.927 GPa to 4.374 GPa,respectively.The bulk modulus of freshwater ice remained between 3.074 GPa and4.566 GPa and the sea ice bulk modulus varied from 1.211 GPa to 3.089 GPa.The freshwater ice Young’s modulus kept between 5.156 GPa and 6.264 GPa and sea ice Young’s modulus varied from 3.793 GPa to 7.492 GPa.The results of ultrasonic measurement are consistent with previous studies and there is a consistent trend of mechanical modulus of ice between the process of ice temperature rising and falling.Finally,this ultrasonic method and the ultrasonic system will help to achieve the long-term observation of ice mechanical properties of ice and improve accuracy of sea ice models.

Effects of fertigation strategies on water and nitrogen distribution under water storage pit irrigation for orchards

Water storage pit(WSP)irrigation is a simple and inexpensive technology suitable for orchards in semiarid and arid regions of North China.This study compared the effects of different fertigation strategies on water and nitrogen distribution,and ammonia volatilization.A fertigation experiment was conducted using a 30°wedge-shaped plexiglass soil container,which represents one-twelfth of the complete storage pit.The height of the container was 120 cm,and a plexiglass damper for simulating the zero flux plane of adjacent water storage pits was located at the 40 cm radius.Four fertigation strategies were used for WSP irrigation:solution application during the first half(N-W),the last half(W-N),the middle half of an irrigation cycle(W-N-W),and during the entire irrigation(N-N).Surface(SF)irrigation was used as a control treatment with solution application during the entire irrigation(SN-N).The experimental results showed that the soil water and ammonium contents at 0-10 cm soil depth under WSP irrigation were only 10.51%and 18.42% of those under SF irrigation,respectively.The cumulative NH3 volatilization under WSP irrigation was 51.71%-68.72% lower compared with that under SF irrigation.The soil water distributions were similar for all four fertigation strategies.NH3 volatilization mainly occurred at the pit wall interface,and cumulative NH3 volatilization loss followed the trend N-N>W-N>W-N-W>N-W.Ammonium was adsorbed into the soil and thus mostly remained near the pit wall.Low concentrations of ammonium were found near the edge of the wetting zone under all strategies.Compared to N-W,N-N and W-N-W treatments,W-N treatment decreased the nitrate accumulation at 80-90 cm by 38.6%,19.0%and 10.3%,respectively.The W-N strategy was suggested for minimizing potential nitrate leaching.

Effective root depth and water uptake ability of winter wheat by using water stable isotopes in the Loess Plateau of China

A field experiment using PVC growth tubes was conducted in the Loess Plateau of China to determine the effective root depth(ERD)of winter wheat and its relationship with root distributions and soil water conditions.The water stable isotopes technique was used to estimate the water uptake contributions of different root depths during the growth stages.On the basis of IsoSource and the Romero-Saltos model,the ERD was 0-40 cm in the majority of the growth stage.However,in the heading and filling stages,the ERD could reach 60%-75%of the maximum root depth.Furthermore,the contributions to water uptake of different root depths were correlated with variations in soil water and root length density(r=0.395 and 0.368,respectively;p<0.05).However,by path analysis,the low decisive coefficient indicated that root distribution and soil water content did not always follow the same trend as water uptake.The conclusions of this study can help with understanding winter wheat water uptake mechanisms in arid and semi-arid regions and increasing water use efficiency.

Characteristic analysis of ecosystem service value of water system in Taiyuan urban district based on LUCC

Changes in the land use and ecosystem service value of the 600 m buffer zone of Jinyang Lake and the 1000 m riparian zone of the Fenhe River in the Taiyuan urban district in China,were studied using satellite image data collected in June 2006 and June 2013.According to the ecosystem services assessment system based on expert knowledge,the ecosystem service value(ESV)per unit area was determined for various land-use types and the value of the water system and its buffer regions in the Taiyuan urban district were determined.And then the relationship between LUCC(Land Use/Cover Change)and ESV was discussed.Moreover,the accuracy and validity of the results was analyzed.The results showed that:(1)the areas of green vegetation and water bodies of Jinyang Lake and its buffer region decreased by 24.96%and 3.22%,respectively,between June 2006 and June 2013,whereas the areas of farmland and built-up land increased by 15.81%and 12.37%,respectively.At Jinyang Lake,the degree of dynamic change for green vegetation,water bodies,farmland,built-up land,and unused land was−0.13,−0.02,0.17,0.09,and−0.05,respectively.In the Fenhe River’s buffer region,the areas of green vegetation,farmland and unused land decreased by 1.36%,6.36%and 0.3%,respectively,but those of built-up land and water bodies increased by 1.41%and 6.61%,respectively.Their degree of dynamic change was−0.03,−0.02,−0.04,0.01 and 0.32,respectively;(2)In 2006,the landscape fragmentation indices(LFI)of Jinyang Lake buffer of 0-200 m zone were greater than 2,but those of 200-600 m buffer zone were less than 0.3,the water-body index not included.However,in 2013,the landscape fragmentation indices of green vegetation and water bodies of 0-600 m buffer zone were both high,meaning that the land-use pattern had improved.The fragmentation index of green vegetation of the 0-200 m buffer increased from 0.1(the minimum for the year)to 1.7(the maximum for the year)during the seven years of this study along the Fenhe River.The fragmentation index of built-up land increased from 0.007 to 0.01 in the 200-500 m buffer and from 0.007 to 0.06 in the 500-1000 m buffer.(3)The total ecosystem service value of Jinyang Lake and its buffer region decreased by 22.673%,whereas during the same period,that of the Fenhe River and its buffer region increased by 41.345%.The total ecosystem service value of the water bodies and their buffer regions in the Taiyuan urban area increased by 13.725%overall.(4)The change rate of the ecosystem service value of the 0-600 m buffer region decreased by 1.579%at Jinyang Lake,while that of the 0-1000 m buffer region increased 5.079%at the Fenhe River over the seven years.

Modelling soil water dynamics and root water uptake for apple trees under water storage pit irrigation

Water storage pit irrigation is a new method suitable for apple trees.It comes with advantages such as water saving,water retention and drought resistance.A precise study of soil water movement and root water uptake is essential to analyse and show the advantages of the method.In this study,a mathematical model(WSPI-WR model)for 3D soil water movement and root water uptake under water storage pit irrigation was established based on soil water dynamics and soil moisture and root distributions.Moreover,this model also considers the soil evaporation,pit wall evaporation and water level variation in the pit.The finite element method was used to solve the model,and the law of mass conservation was used to analyse the water level variation.The model was validated by experimental data of the sap flow of apple trees and soil moisture in the orchard.Results showed that the WSPI-WR model is highly accurate in simulating the root water uptake and soil water distributions.The WSPI-WR model can be used to simulate root water uptake and soil water movement under water storage pit irrigation.The simulation showed that orchard soil water content and root water uptake rate centers on the storage pit with an ellipsoid distribution.The maximum distribution region of soil water and root water uptake rate was near the bottom of the pit.Distribution can reduce soil evaporation in the orchard and improve the soil water use efficiency in the middle-deep soil.

A numerical model with Stokes drift for pollutant transport within the surf zone on a plane beach

This study examines the effects of Stokes drift on pollutant transport within the surf zone on a plane beach both numerically and experimentally. Firstly, the numerical model is described. The wave-induced current is modeled using the concept of the radiation stress. The wave propagation model is based on the wave energy conservation equation. And the advective diffusion model including the Stokes drift is used to describe the pollutant transport in the surf zone. Model validation was achieved in this case versus an analytical solution for an instantaneous point source in a uniform horizontal flow. This study also describes a laboratory experiment on dye release in the surf zone over a plane beach. We examined the final inclination angle required by a continuously released pollutant plume to reach the shoreline under both cases, and transport velocities in the alongshore and cross- shore directions were estimated by linearly fitting the location of a dye-patch front at different time. Results show that this dye patch moved shoreward with an approximate speed of 0.05 m/s (0.017 m/s) between 10 s and 40 s and 0.001 m/s (0.011 m/s) after 40 s for Case 1 (2). This model was then used to simulate pollutant transport in the surf zone on a plane beach as reproduced in the current experiment. Comparisons between our dye transport experiment and numerical results were then also conducted;the data showed that the numerical results including Stokes drift agreed more closely with experimental results than those without it. The data showed that the pollutant was generally transported obviously shoreward in addition to its expected drift along the shore. We also suggest that Stokes drift plays an important role in pollutant movement in the surf zone, especially shoreward.

3-D numerical investigation of the wall-bounded concentric annulus flow around a cylindrical body with a special array of cylinders

Concentric annulus flow around a combinational cylindrical body with a special array of cylinders at five high Reynolds numbers is investigated numerically using Fluent 6.3.26 in this paper. The numerical results show a good agreement with the experimental data in regard to the axial velocity of the flow. This study focuses on the flow structure and the hydrodynamic characteristics based on the velocity distribution, the pressure distribution, streamlines and vectors under I-D, 2-D and 3-D condi- tions. Meanwhile, some global parameters including the pressure coefficient, the drag coefficient and the lift coefficient are analyzed. Numerical results show that the high velocity region and the reverse wake zone with low velocity exist in some spaces due to the disturbance of the cylindrical body. Negative pressures appear in some regions. Neither a wide area vortex nor the vortex shedding appears in the wall-bounded domain. The drag along the axial direction is the main force acting on the cylindrical body in the pipe domain. The annulus flow around the cylindrical body is analyzed to reveal the hydrodynamic characteristics of the complex turbule- nt concentric annulus flow field due to the multi-effects in the pipeline.

Numerical investigation of the concentric annulus flow around a cylindrical body with contrasted effecting factors

This paper studies the wall-bounded flow around a cylindrical at a high Reynolds numbers body in a determined computational domain, with simulations of the 3-D, turbulent concentric annulus flow in a straight pipe. Numerical results show that a reversing zone, appearing as a tongue zone with nested velocities higher than the surrounding area, exists behind the cylindrical body. The annulus space is a region of high velocity and low pressure. The zero velocity, of combined the X- velocity and the Y- velocity, exists in the cross sections and no vortex shedding is formed behind the attaching cylinders. Among all investigated effecting factors, the diameters of the attaching and the main cylinders affect the wake feature behind the cylindrical body while the main cylinder length does not affect the distribution tendency of the flow field. The diameters of the main cylinder and the pipe affect the pressure values and the distribution tendencies on the main cylinder surface. Obviously, the increase of the pipe diameter reduces the drag coefficient of the cylindrical body and the increase of the diameter of the main cylinder increases the drag coefficient greatly. The numerical investigation of the concentric annulus flow provides foundations for further improvements of the intricate flow studies.

Influence of reservoir construction on surrounding vegetation cover

Vegetation is a significant factor in the energy and water cycles.Changes in vegetation are affected by the natural environment and human activities.In this study,the Dalong Reservoir on the Ningyuan River in Sanya,Hainan,China,was taken as an example to set one type of buffer zone with the reservoir dam site as the center,and two types of horizontal and vertical buffer zones outwards from both banks of the river,and Landsat 5 remote sensing image data and the vegetation data were applied.A coverage estimation model was used to study the temporal and spatial changes in surface vegetation in three types of buffer zones,and the characteristics of the surface vegetation changes in the preterm,midterm and late-term reservoir construction periods were analyzed.The results showed that,(1)During the years 2000 and 2010,the vegetation coverage first decreased and then increased with time in the scope of the research.During preterm construction(2000-2004),the vegetation coverage in the upstream region decreased while that in the downstream region increased.During midterm construction(2004-2006),the declining rate of vegetation coverage downstream was greater than that upstream,but the influence of reservoir construction on vegetation coverage decreased over time in the late-term construction period(2007-2010);(2)Along the direction of the river length,the vegetation coverage showed a downtrend along with the river flow direction during the whole period(2000-2010),and the influence of reservoir construction on vegetation coverage gradually decreased as the distance from the reservoir increased;(3)Along the direction of the river width,the vegetation coverage in the preterm and midterm construction periods(2000-2006)increased with increasing distance from the riverbanks;(4)The vegetation coverage showed a significant increasing trend with increasing distance from the reservoir.The research results can provide a theoretical reference for reducing the risk of vegetation degradation,strengthening the governance of the ecological environment,and promoting the ecological construction of“landscapes,forests,fields,lakes and grass”.

Nitrogen use in double cropping soybean with non-fertilized winter oilseed crops

Sustainable intensification of cropping systems is a strategy to increase productivity and reduce disservices of conventional agroecosystems.Camelina[Camelina sativa(L.)Crantz]and field pennycress(Thlaspi arvense L.)are winter annual oilseed crops well suited to fill the fallow period between corn(Zea mays L.)and soybean[Glycine max(L.)Merr.]in the U.S.northern Corn Belt,but their inclusion may be limited by resource use limitations.A 2-year study was conducted from 2015 to 2017 in the U.S.upper Midwest to evaluate the effect of double cropping on winter oilseed crops and soybean productivity and economic performance.Treatments included relay-and sequential-cropped soybean with winter camelina and field pennycress,and monocrop soybean as control.Biomass and grain yield of winter oilseed crops were not affected by cropping system.Averaged over years and cropping systems,winter camelina resulted in more biomass,nitrogen(N)uptake and grain yield by 240,186 and 139% respectively,compared to field pennycress.Soybean biomass,N uptake and yield were higher in relay relative to sequential cropping.Relay soybean resulted in similar total grain yield(soybean+winter oilseed crop)compared to monocropped soybean.Double cropping soybean could maintain net return compared to monocropped soybean.Results indicate that double cropping winter oilseed crops with soybean can be economically viable in the U.S.upper Midwest.Yet,research aimed at optimizing yield through N and water use while improving ecosystem services is needed.