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The quantified analysis of China's GM cotton yield capacity by C-D function and stochastic frontier model
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作者 张涛 薛宝娣 《Hunan Agricultural Science & Technology Newsletter》 2004年第1期11-13,共3页
Using a modified C D function and stochastic frontier model, the paper analyzed China's cotton yield capacity and found that the yield and technical efficiency of China's cotton planting system can be increas... Using a modified C D function and stochastic frontier model, the paper analyzed China's cotton yield capacity and found that the yield and technical efficiency of China's cotton planting system can be increased by the use of genetically modified (GM) varieties. 展开更多
关键词 GM cotton yield capacity C D function stochastic frontier model
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PREDICTION OF YIELD FUNCTIONS ON BCC POLYCRYSTALS 被引量:5
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作者 Huang Mojia Fu Mingfu Zheng Chaomei 《Acta Mechanica Solida Sinica》 SCIE EI 2006年第1期75-85,共11页
By the nonlinear optimization theory, we predict the yield function of single BCC crystals in Hill's criterion form. Then we give a formula on the macroscopic yield function of a BCC polycrystal Ω under Sachs' mode... By the nonlinear optimization theory, we predict the yield function of single BCC crystals in Hill's criterion form. Then we give a formula on the macroscopic yield function of a BCC polycrystal Ω under Sachs' model, where the volume average of the yield functions of all BCC crystallites in Ω is taken as the macroscopic yield function of the BCC polycrystal. In constructing the formula, we try to find the relationship among the macroscopic yield function, the orientation distribution function (ODF), and the single BCC crystal's plasticity. An expression for the yield stress of a uniaxial tensile problem is derived under Taylor's model in order to compare the expression with that of the macroscopic yield function. 展开更多
关键词 yield function the ODF BCC polycrystal single BCC crystals ANISOTROPY
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Effects of planting patterns plastic film mulching on soil temperature,moisture, functional bacteria and yield of winter wheat in the Loess Plateau of China 被引量:2
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作者 ZHAO Xiao-dong QIN Xiao-rui +2 位作者 LI Ting-liang CAO Han-bing XIE Ying-he 《Journal of Integrative Agriculture》 SCIE CAS CSCD 2023年第5期1560-1573,共14页
The yield of winter wheat is hindered by drought and low temperature in the Loess Plateau of China.Two common mulching methods to conserve soil moisture,ridge furrows with plastic film mulching (RP) and flat soil surf... The yield of winter wheat is hindered by drought and low temperature in the Loess Plateau of China.Two common mulching methods to conserve soil moisture,ridge furrows with plastic film mulching (RP) and flat soil surfaces with plastic film mulching (FP) are helpful for wheat production.Our previous study indicated that FP could improve wheat yield more effectively than RP,but the reason remains unclear.The effect of mulching method on functional bacteria also needs to be further studied.In this study,winter wheat was employed to evaluate the impacts of mulching method on soil temperature,moisture content,microorganisms and grain yield.The results showed that FP had a warming effect when the soil temperature was low and a cooling effect when the temperature was too high.However,the ability to regulate soil temperature in the RP method was unstable and varied with year.The lowest negative accumulated soil temperature was found in the FP treatment,which was 20–89 and 43–99%lower than that of the RP and flat sowing with non-film mulching control (NP) treatments,respectively.Deep soil moisture was better transferred to topsoil for wheat growth in the FP and RP treatments than the NP treatment,which made the topsoil moisture in the two treatments (especially FP) more sufficient than that in the NP treatment during the early growing stage of wheat.However,due to the limited water resources in the study area,there was almost no difference between treatments in topsoil water storage during the later stage.The wheat yield in the FP treatment was significantly higher,by 12–16and 23–56%,respectively,than in the RP and NP treatments.Significant positive correlations were observed among the negative accumulated soil temperature,spike number and wheat yield.The Chao1 and Shannon indices in the RP treatment were 17 and 3.9%higher than those in the NP treatment,respectively.However,according to network relationship analysis,the interspecific relationships of bacteria were weakened in the RP treatment.Phosphorus solubilizing,ammonification and nitrification bacteria were more active in the RP than in the FP treatment,and microbes with nitrate reduction ability and plant pathogens were inhibited in the RP treatment,which improved nutrient availability and habitat for wheat. 展开更多
关键词 WINTER wheat soil temperature MOISTURE functional bacteria GRAIN yield
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Function fitting for modeling seasonal normalized difference vegetation index time series and early forecasting of soybean yield 被引量:2
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作者 Alexey Stepanov Konstantin Dubrovin Aleksei Sorokin 《The Crop Journal》 SCIE CSCD 2022年第5期1452-1459,共8页
Forecasting crop yields based on remote sensing data is one of the most important tasks in agriculture.Soybean is the main crop in the Russian Far East.It is desirable to forecast soybean yield as early as possible wh... Forecasting crop yields based on remote sensing data is one of the most important tasks in agriculture.Soybean is the main crop in the Russian Far East.It is desirable to forecast soybean yield as early as possible while maintaining high accuracy.This study aimed to investigate seasonal time series of the normalized difference vegetation index(NDVI) to achieve early forecasting of soybean yield.This research used data from the Moderate Resolution Image Spectroradiometer(MODIS),an arable-land mask obtained from the VEGA-Science web service,and soybean yield data for 2008-2017 for the Jewish Autonomous Region(JAR) districts.Four approximating functions were fitted to model the NDVI time series:Gaussian,double logistic(DL),and quadratic and cubic polynomials.In the period from calendar weeks 22-42(end of May to mid-October),averaged over two districts,the model using the DL function showed the highest accuracy(mean absolute percentage error-4.0%,root mean square error(RMSE)-0.029,P <0.01).The yield forecast accuracy of prediction in the period of weeks 25-30 in JAR municipalities using the parameters of the Gaussian function was higher(P <0.05) than that using the other functions.The mean forecast error for the Gaussian function was 14.9% in week 25(RMSE was0.21 t ha) and 5.1%-12.9% in weeks 26-30(RMSE varied from 0.06 to 0.15 t ha) according to the2013-2017 data.In weeks 31-32,the error was 5.0%-5.4%(RMSE was 0.07 t ha) using the Gaussian parameters and 7.4%-7.7%(RMSE was 0.09-0.11 t ha) for the DL function.When the method was applied to municipal districts of other soy-producing regions of the Russian Far East.RMSE was0.14-0.32 t hain weeks 25-26 and did not exceed 0.20 t hain subsequent weeks. 展开更多
关键词 NDVI function fitting Early prediction yield SOYBEAN
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Calibration of anisotropic yield function by introducing plane strain test instead of equi-biaxial tensile test 被引量:2
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作者 Jie ZHU Shang-yu HUANG +2 位作者 Wei LIU Jian-hua HU Xi-fan ZOU 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2018年第11期2308-2314,共7页
The equi-biaxial tensile test is often required for parameter identification of anisotropic yield function and it demands thespecial testing technique or device. Instead of the equi-biaxial tensile test, the plane str... The equi-biaxial tensile test is often required for parameter identification of anisotropic yield function and it demands thespecial testing technique or device. Instead of the equi-biaxial tensile test, the plane strain test carried out with the traditional uniaxialtesting machine is suggested to provide the experimental data for calibration of anisotropic yield function. This simplified method byusing plane strain test was adopted to identify the parameters of Yld2000-2d yield function for 5xxx aluminum alloy and AlMgSialloy sheets. The predicted results of yield stresses, anisotropic coefficients and yield loci by the proposed method were very similarwith the experimental data and those by the equi-biaxial tensile test. It is validated that the plane strain test is effective to provideexperimental data instead of equi-biaxial tensile test for calibration of Yld2000-2d yield function. 展开更多
关键词 aluminum alloy sheet anisotropic behavior yield function parameter identification plane strain test
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Improvement of the Yield Function of Continuum Mechanics of Textured Polycrystals
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作者 Da-wei Lin Ting-sheng Tu 《Advances in Manufacturing》 SCIE CAS 2000年第4期327-331,共5页
The calculation procedure of the continuum mechanics of textured polycrystals (CMTP) method is reviewed to estimate calculating time with various yield functions (YFs). A so called semi quadratic YF is proposed to ... The calculation procedure of the continuum mechanics of textured polycrystals (CMTP) method is reviewed to estimate calculating time with various yield functions (YFs). A so called semi quadratic YF is proposed to eliminate time consuming numerical calculation and avoid the decrease of prediction precision. The reasonability of the new YF is proved by making the comparisons between predicted R values and earing behaviour for some materials and the experimental results. 展开更多
关键词 CMTP method yield function plastic anisotr\
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Effect of hydrostatic stress on yield function and plastic constitutive relations
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作者 盖秉政 《Journal of Harbin Institute of Technology(New Series)》 EI CAS 2001年第4期328-333,共6页
A new yield function taking effect of hydrostatic stress into account is presented through establishing and solving the functional equation satisfied by the yield function, and its characteristic is simple in form and... A new yield function taking effect of hydrostatic stress into account is presented through establishing and solving the functional equation satisfied by the yield function, and its characteristic is simple in form and strong in generality. In order to reveal its availability, a comparison is made between the results obtained with it and the experimental results of grey cast iron has be done, both seem to be in good agreement. At the same time, taking the yield function obtained here as a potential function, a new associative plastic constitutive equation taking effect of hydrostatic stress into account is built, and the plastic volume change ratio of plastic deformation is given. 展开更多
关键词 hydrostatic stress yield function plastic constitutive relations
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NEW NON QUADRATIC ORTHOTROPIC YIELD FUNCTION FOR TRIAXIAL STRESS STATE
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作者 Zhou Weixian 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 1992年第2期62-67,共6页
A new Don-quadratic orthotropic yield function is developed in the present paper.It does not have those limitatioins which existing non-quadratic anisotropic yield functions have,such as being usable only for the plan... A new Don-quadratic orthotropic yield function is developed in the present paper.It does not have those limitatioins which existing non-quadratic anisotropic yield functions have,such as being usable only for the plane stress problems and in-plane isotropic sheet metals,and that the directions of principal stress or the ex ponent in yield function can not be arbitrary,etc.Furthermore all of the material constants involved in this yield function can be determined by performing only uniaxial tension lest.This yield function contains three new parameters,of which each one is present for one principal plane of anisotropy.Their values can be.generally,selected to equal 3.Other methods to determine the value of these parmeters are discussed and given in this paper.From the regression estimate for the yield stress in five directions of several kinds of titanium metal sheet.it is obtained that the suitable value of exponent in yield function for titanium sheets is 6 or 8.This is confirmed from the use for several plastic deformation problems of titanium sheets. 展开更多
关键词 ORTHOTROPY triaxial stress yield function
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A NEW ORTHOTROPIC YIELD FUNCTION DESCRIBABLE ANOMALOUS BEHAVIOR OF MATERIALS
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作者 Zhou,Weixian(Department of Aeronautical Manufacturing Engineering,Northwestern Polytechnical University,Xi’an 710072) 《中国有色金属学会会刊:英文版》 CSCD 1994年第2期37-41,共5页
ANEWORTHOTROPICYIELDFUNCTIONDESCRIBABLEANOMALOUSBEHAVIOROFMATERIALSANEWORTHOTROPICYIELDFUNCTIONDESCRIBABLEAN... ANEWORTHOTROPICYIELDFUNCTIONDESCRIBABLEANOMALOUSBEHAVIOROFMATERIALSANEWORTHOTROPICYIELDFUNCTIONDESCRIBABLEANOMALOUSBEHAVIOROF... 展开更多
关键词 ORTHOTROPY ANOMALOUS BEHAVIOR non-qudratic yield function
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Excessive manure application stimulates nitrogen cycling but only weakly promotes crop yields in an acidic Ultisol:Results from a 20-year field experiment
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作者 Song Wan Yongxin Lin +3 位作者 Hangwei Hu Milin Deng Jianbo Fan Jizheng He 《Journal of Integrative Agriculture》 SCIE CAS CSCD 2024年第7期2434-2445,共12页
Population growth and growing demand for livestock products produce large amounts of manure,which can be harnessed to maintain soil sustainability and crop productivity.However,the impacts of excessive manure applicat... Population growth and growing demand for livestock products produce large amounts of manure,which can be harnessed to maintain soil sustainability and crop productivity.However,the impacts of excessive manure application on crop yields,nitrogen(N)-cycling processes and microorganisms remain unknown.Here,we explored the effects of 20-year of excessive rates(18 and 27 Mg ha^(–1)yr^(–1))of pig manure application on peanut crop yields,soil nutrient contents,N-cycling processes and the abundance of N-cycling microorganisms in an acidic Ultisol in summer and winter,compared with none and a regular rate(9 Mg ha^(–1)yr^(–1))of pig manure application.Long-term excessive pig manure application,especially at the high-rate,significantly increased soil nutrient contents,the abundance of N-cycling functional genes,potential nitrification and denitrification activity,while it had a weaker effect on peanut yield and plant biomass.Compared with manure application,seasonality had a much weaker effect on N-cycling gene abundance.Random forest analysis showed that available phosphorus(AP)content was the primary predictor for N-cycling gene abundance,with significant and positive associations with all tested N-cycling genes.Our study clearly illustrated that excessive manure application would increase N-cycling gene abundance and potential N loss with relatively weak promotion of crop yields,providing significant implications for sustainable agriculture in the acidic Ultisols. 展开更多
关键词 DENITRIFICATION manure amendment NITRIFICATION N-cycling functional genes peanut yields
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Numerical study of influence of anisotropy on flanging earing based on Barlat six-component yield function
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作者 李大永 张少睿 +1 位作者 彭颖红 胡平 《中国有色金属学会会刊:英文版》 CSCD 2003年第2期412-416,共5页
The anisotropy of stamped sheet metal exerts evident effects on the formability. Barlat six component yield function was introduced into the elastoplastic finite element formulation based on the principle of virtual v... The anisotropy of stamped sheet metal exerts evident effects on the formability. Barlat six component yield function was introduced into the elastoplastic finite element formulation based on the principle of virtual velocity and the discrete Kirchhoff triangular element model. The flanging earing in cylindrical cup drawing process of circular sheet metal was numerically simulated. The influence of anisotropy on the forming process was studied. 展开更多
关键词 各向异性 翻边 耳子 数值分析 凸缘 生产能力 金属板
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Effect of Nitrogen, Phosphorus and Potassium on the Content and Yield of DNJ of Mulberry Leaves in Spring 被引量:1
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作者 刘刚 殷浩 +5 位作者 佟万红 黄盖群 王丽 危玲 郑继川 帅小蓉 《Agricultural Science & Technology》 CAS 2012年第9期1937-1941,共5页
[Objective] This study aimed to scientifically improve the 1-deoxynojimycin (DNJ) yield of mulberry leaves in spring. [Method] "3414" experimental design was adopted to investigate the effects of different fertili... [Objective] This study aimed to scientifically improve the 1-deoxynojimycin (DNJ) yield of mulberry leaves in spring. [Method] "3414" experimental design was adopted to investigate the effects of different fertilizer application rates of nitrogen, phosphorus and potassium on the DNJ content in mulberry leaves. The regression relationship was further simulated with DNJ yield as the objective function and fertil- izer application rates of nitrogen, phosphorus and potassium as the regulatory factors. [Result] The results showed that nitrogen, phosphorus and potassium all have great effects on the DNJ content in mulberry leaves at different parts of mulberry tree (Morus alba); the DNJ content in mulberry leaves increases with the increasing single-factor fertilizer application rate and reaches the maximum under N2P2K2 level; different fertilizer application rates and combinations of nitrogen, phosphorus and potassium can significantly affect the DNJ content in mulberry leaves; according to the simulated fertilizer effect function, the optimal economic yield of total DNJ in mul- berry leaves was 23.23 kg/hm^2, the recommended fertilization indicators were 286.11 kg/hm^2 N, 95.22 kg/hm^2 P2O5 and 159.62 kg/hm^2 K20. [Conclusion] After confirmation in productive practice, this optimal fertilization program can provide reference for the construction of mulberry plantation with high yield and high quality of DNJ. 展开更多
关键词 Mulberry ieaves 1-deoxynojimycin yield Balanced iertilization Fertilizereffect function
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A New Economic Assessment Index for the Impact of Climate Change on Grain Yield 被引量:8
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作者 董文杰 丑洁明 封国林 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 2007年第2期336-342,共7页
The impact of climate change on agriculture has received wide attention by the scientific community. This paper studies how to assess the grain yield impact of climate change, according to the climate change over a lo... The impact of climate change on agriculture has received wide attention by the scientific community. This paper studies how to assess the grain yield impact of climate change, according to the climate change over a long time period in the future as predicted by a climate system model. The application of the concept of a traditional "yield impact of meteorological factor (YIMF)" or "yield impact of weather factor" to the grain yield assessment of a decadal or even a longer timescale would be suffocated at the outset because the YIMF is for studying the phenomenon on an interannual timescale, and it is difficult to distinguish between the trend caused by climate change and the one resulting from changes in non-climatic factors. Therefore, the concept of the yield impact of climatic change (YICC), which is defined as the difference in the per unit area yields (PUAY) of a grain crop under a changing and an envisaged invariant climate conditions, is presented in this paper to assess the impact of global climate change on grain yields. The climatic factor has been introduced into the renowned economic Cobb-Douglas model, yielding a quantitative assessment method of YICC using real data. The method has been tested using the historical data of Northeast China, and the results show that it has an encouraging application outlook. 展开更多
关键词 global change yield impact of meteorological factor CLIMATE production function
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Derivation of Plastic Work Rate Done per Unit Volume for Mean Yield Criterion and Its Application 被引量:8
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作者 Dewen ZHAO Yingjie XIE +1 位作者 Xiaowen WANG Xianghua LIU 《Journal of Materials Science & Technology》 SCIE EI CAS CSCD 2005年第4期433-436,共4页
In Haigh Westergaard stress space linear combination of twin shear stress and Tresca yield functions is called the mean yield (MY) criterion. The mathematical relationship of the criterion and its plastic work rate ... In Haigh Westergaard stress space linear combination of twin shear stress and Tresca yield functions is called the mean yield (MY) criterion. The mathematical relationship of the criterion and its plastic work rate done per unit volume were derived. A generalized worked example of slab forging was analyzed by the criterion and its corresponding plastic work rate done per unit volume. Then, the precision of the solution was compared with those by Mises and Twin shear stress yield criterions, respectively. It turned out that the calculated results by MY criterion were in good agreement with those by Mises criterion. 展开更多
关键词 Mean yield criterion Plastic work rate done per unit volume functional linearization Slab forging
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Determination of rock resistant coefficient based on Mohr-Coulomb criterion for underwater tunnel 被引量:5
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作者 Zhong-ren TU Qiang YANG +1 位作者 Qi-ming SHEN Xiao-wen WANG 《Journal of Zhejiang University-Science A(Applied Physics & Engineering)》 SCIE EI CAS CSCD 2008年第9期1239-1244,共6页
According to the load-structure method, the wall rock with lining can bear the load caused by the surrounding rock, and the rock resistant coefficient (RRC) is a key parameter for evaluating the capacity of this wall ... According to the load-structure method, the wall rock with lining can bear the load caused by the surrounding rock, and the rock resistant coefficient (RRC) is a key parameter for evaluating the capacity of this wall rock. Based on the Mohr-Coulomb yield criterion, this paper develops a formula for calculating the RRC, which has been applied to the real engi-neering project, such as Xiamen Xiang’an East Passage Underwater Tunnel Project. The fact shows that this formula is helpful for designers to determine the RRC value. 展开更多
关键词 Rock resistant coefficient (RRC) mohr-coulomb yield criterion Rock mechanics Underwater tunnel
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A practical constitutive theory based on egg-shaped function in elasto-plastic modeling for soft clay 被引量:4
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作者 JIANG Jia-qi XU Ri-qing +3 位作者 YU Jian-lin QIU Zhi-jian QIN Jian-she ZHAN Xiao-bo 《Journal of Central South University》 SCIE EI CAS CSCD 2020年第8期2424-2439,共16页
An exploratory discussion is presented on the application of egg-shaped function in elasto-plastic constitutive analysis for soft clay.Two main tasks of the paper are:1)to propose a complete yield criterion based on e... An exploratory discussion is presented on the application of egg-shaped function in elasto-plastic constitutive analysis for soft clay.Two main tasks of the paper are:1)to propose a complete yield criterion based on egg-shaped function and supplement its definition in the deviatoric section,and then a yield criterion suitable for 3D stress conditions is obtained;2)to elaborate its numerical implementation based on the drained triaxial tests.During the above discussion,a non-associated flow rule is proposed,in which the stress-dilatancy relationship in most classical theory is replaced by a linear dependence between the stress state parameterηand the rotation angleγof the plastic potential surface.Thereafter,isotropic and kinematic hardening behavior is considered by employing the hardening parameter H,which can be expressed as the function of plastic work Wp.Finally,comparisons between numerical results and test data on Taizhou soft clay are made to verify the effectiveness of the proposed model. 展开更多
关键词 egg-shaped function elastoplasticity yield criterion non-associated flow
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Evaluation of the water conservation function in the Ili River Delta of Central Asia based on the InVEST model 被引量:2
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作者 CAO Yijie MA Yonggang +2 位作者 BAO Anming CHANG Cun LIU Tie 《Journal of Arid Land》 SCIE CSCD 2023年第12期1455-1473,共19页
The Ili River Delta(IRD)is an ecological security barrier for the Lake Balkhash and an important water conservation area in Central Asia.In this study,we selected the IRD as a typical research area,and simulated the w... The Ili River Delta(IRD)is an ecological security barrier for the Lake Balkhash and an important water conservation area in Central Asia.In this study,we selected the IRD as a typical research area,and simulated the water yield and water conservation from 1975 to 2020 using the water yield module of the Integrated Valuation of Ecosystem Services and Tradeoffs(InVEST)model.We further analyzed the temporal and spatial variations in the water yield and water conservation in the IRD from 1975 to 2020,and investigated the main driving factors(precipitation,potential evapotranspiration,land use/land cover change,and inflow from the Ili River)of the water conservation variation based on the linear regression,piecewise linear regression,and Pearson's correlation coefficient analyses.The results indicated that from 1975 to 2020,the water yield and water conservation in the IRD showed a decreasing trend,and the spatial distribution pattern was"high in the east and low in the west";overall,the water conservation of all land use types decreased slightly.The water conservation volume of grassland was the most reduced,although the area of grassland increased owing to the increased inflow from the Ili River.At the same time,the increased inflow has led to the expansion of wetland areas,the improvement of vegetation growth,and the increase of regional evapotranspiration,thus resulting in an overall reduction in the water conservation.The water conservation depth and precipitation had similar spatial distribution patterns;the change in climate factors was the main reason for the decline in the water conservation function in the delta.The reservoir in the upper reaches of the IRD regulated runoff into the Lake Balkhash,promoted vegetation restoration,and had a positive effect on the water conservation;however,this positive effect cannot offset the negative effect of enhanced evapotranspiration.These results provide a reference for the rational allocation of water resources and ecosystem protection in the IRD. 展开更多
关键词 water conservation function water yield Integrated Valuation of Ecosystem Services and Tradeoffs(InVEST)model climate change land use/land cover change(LUCC) Ili River Delta Lake Balkhash
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IMPACT OF CLIMATE ON GRAIN YIELD PER UNIT AREA IN CHINA DURING THE YEARS OF 1949~1992
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作者 谢云 刘继东 《Chinese Geographical Science》 SCIE CSCD 1998年第4期22-29,共8页
The grain yield per unit area in China has been increasing from 1949 to 1992 with annual fluctuations, which was caused by both policies and monsoon climate. The total grain yield is divided into trend yield, which r... The grain yield per unit area in China has been increasing from 1949 to 1992 with annual fluctuations, which was caused by both policies and monsoon climate. The total grain yield is divided into trend yield, which reflects the influence of economic factors, and climate yield, which reflects the impact of climate factors. The results of grain and climate yield by EOF (empirical orthogonal function) method show that the grain yield in the eastern China is higher and more fluctuating than that in the western region. The spatial and temporal distributions of climate yield were divided into four patterns. Regional unanimity of climate yield variation is the first and main spatial pattern, and then there are the spatial patterns of north-south difference and east-west difference in some years. Generally, climate conditions are good for grain yield during the 1950s and 1980s all over the country. 展开更多
关键词 GRAIN yield CLIMATE yield empirical ORTHOGONAL function spatial and TEMPORAL distribution
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Responses of vegetation yield to precipitation and reference evapotranspiration in a desert steppe in Inner Mongolia,China
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作者 LI Hongfang WANG Jian +2 位作者 LIU Hu MIAO Henglu LIU Jianfeng 《Journal of Arid Land》 SCIE CSCD 2023年第4期477-490,共14页
Drought,which restricts the sustainable development of agriculture,ecological health,and social economy,is affected by a variety of factors.It is widely accepted that a single variable cannot fully reflect the charact... Drought,which restricts the sustainable development of agriculture,ecological health,and social economy,is affected by a variety of factors.It is widely accepted that a single variable cannot fully reflect the characteristics of drought events.Studying precipitation,reference evapotranspiration(ET_(0)),and vegetation yield can derive information to help conserve water resources in grassland ecosystems in arid and semi-arid regions.In this study,the interactions of precipitation,ET_(0),and vegetation yield in Darhan Muminggan Joint Banner(DMJB),a desert steppe in Inner Mongolia Autonomous Region,China were explored using two-dimensional(2D)and three-dimensional(3D)joint distribution models.Three types of Copula functions were applied to quantitatively analyze the joint distribution probability of different combinations of precipitation,ET_(0),and vegetation yield.For the precipitation–ET_(0)dry–wet type,the 2D joint distribution probability with precipitation≤245.69 mm/a or ET_(0)≥959.20 mm/a in DMJB was approximately 0.60,while the joint distribution probability with precipitation≤245.69 mm/a and ET_(0)≥959.20 mm/a was approximately 0.20.Correspondingly,the joint return period that at least one of the two events(precipitation was dry or ET_(0)was wet)occurred was 2 a,and the co-occurrence return period that both events(precipitation was dry and ET_(0)was wet)occurred was 5 a.Under this condition,the interval between dry and wet events would be short,the water supply and demand were unbalanced,and the water demand of vegetation would not be met.In addition,when precipitation remained stable and ET_(0)increased,the 3D joint distribution probability that vegetation yield would decrease due to water shortage in the precipitation–ET_(0)dry–wet years could reach up to 0.60–0.70.In future work,irrigation activities and water allocation criteria need to be implemented to increase vegetation yield and the safety of water resources in the desert steppe of Inner Mongolia. 展开更多
关键词 PRECIPITATION reference evapotranspiration vegetation yield Copula functions desert steppe dry and wet events Inner Mongolia
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Importance of a Well-distributed Frequency of Measurements in the Senescence Monitoring of Winter Wheat and Yield Estimates
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作者 Louis Kouadio Bakary Djaby Moussa El Jarroudi Bernard Tychon 《Journal of Agricultural Science and Technology(B)》 2012年第12期1203-1213,共11页
Theoretical frequencies of green area index (GAI) measurements were assessed in order to bring out the optimum frequencies for the monitoring of the senescence of winter wheat as well as the relationships between me... Theoretical frequencies of green area index (GAI) measurements were assessed in order to bring out the optimum frequencies for the monitoring of the senescence of winter wheat as well as the relationships between metrics which could be derived and the final grain yield. Several profiles of GAI decreasing curves were elaborated based on field measurements. Two functions, usually employed in green leaf area decreasing curves fitting (i.e., modified Gompertz and logistic functions) were then used to characterize the senescence phase and to calculate their metrics. These analyses showed that the two curve fitting functions satisfactorily described the senescence phase on frequencies of four to six GAI measurements, well distributed throughout a period of 30-35 days. The regression-based modeling showed that those involving metrics from logistic function (i.e., maximum value of GAI, green area duration and senescent rate) were more suitable than that of the modified Gompertz function for wheat yield estimates. Such results could be useful for studies at larger scales (involving remote sensing airplane or satellite data) and focused on the senescence in terms of optimum number of measurements and frequencies for developing models for yield estimates. 展开更多
关键词 Green area index SENESCENCE logistic function yield wheat.
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