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1.
Apera spica-venti is an important weed problem in winter cereals in Europe. Spatial and temporal dynamics of A. spica-venti were investigated to test the hypothesis that this species has a spatially aggregated distribution. A. spica-venti distribution was quantified over several crop rotation sequences in three commercial fields. From 1999 to 2006, the spatial pattern of A. spica-venti was sampled yearly at the same grid points. Geostatistical techniques were used to characterise the spatial and temporal variability of A. spica-venti density. The spatial pattern was analysed by Lloyd's index of patchiness. From year to year, differing aggregation of A. spica-venti resulted in weed patchiness. The Spearman Rank Correlation Coefficient (rs) was used to discover the strength of A. spica-venti occurrence in several years. For two sites there were significant correlations of weed occurrence between years but the relationship was less strong for the third field. Based on rank correlation coefficients, the temporal dynamics were marked by an overall continuity of distribution patterns. Knowing that spatial distributions of weeds vary little in time can reduce sampling efforts, and increases feasibility of site-specific weed control. 相似文献
2.
Tomokazu Haraguchi Kunihiko Hamagami Ken Mori Osamu Kato 《Paddy and Water Environment》2007,5(3):153-161
In areas where irrigation facilities are not available or in mountainous areas, reservoirs are used for paddy rice culture
in Japan. Water temperature must be adequately maintained because it affects water quality and has a significant impact on
the growth and yield of the rice crop. Stratification of water in a reservoir occurs due to heat storage on the water surface
by solar radiation, and destratification results from vertical mixing by wind-induced flow and heat convection. This study
used a simple topography model to estimate numerically the spatial distribution of longwave radiation on the water surface
of an agriculture reservoir surrounded by mountains. A radiation thermometer was used to estimate global longwave radiation.
The spatial and temporal variations of longwave radiation on the water surface were calculated using view factors of objects
surrounding the reservoir. The simulation showed that longwave radiation absorbed by the water surface increased with distance
from the center of the reservoir. The proposed procedure can be used to estimate the longwave radiation environment and heat
balance on a water body such as a reservoir and a stream. 相似文献
3.
Thirty‐year variations of above‐ground net primary production and precipitation‐use efficiency of an alpine meadow in the north‐eastern Qinghai‐Tibetan Plateau 
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下载免费PDF全文 Above‐ground net primary production (ANPP) and precipitation‐use efficiency (PUE) are key factors that can clarify the response of grassland ecosystem carbon and water cycles to ongoing climate change. The variations of ANPP and PUE were analysed based on long‐term in situ observations of a species‐rich alpine meadow in the north‐eastern Qinghai‐Tibetan Plateau from 1981 to 2010. ANPP and PUE increased markedly over time. ANPP was significantly controlled by post‐growing season length (from 1 September to the end of growing season in the previous year, R2 = 0·31, P < 0·01). Regression trees showed that air temperature during October of the previous year played a predominant role in ANPP annual variations. Results indicated that a strong thermal‐lagging effect on ANPP variations was present in the alpine meadow ecosystem. ANPP variations were undetectable during wet, normal and dry years (P = 0·25). Our finding supported the hypothesis that temporal site‐specific ANPP variations were less regulated by a single factor. The temporal PUE declined linearly with increasing annual precipitation, and the slope was obviously steeper than that of spatial patterns. More ANPP variability in an alpine meadow under warming conditions might occur via community transition in the north‐eastern Qinghai‐Tibetan Plateau. 相似文献
4.
Background
The temporal dynamics and formation of plant-pollinator networks are difficult to study as it requires detailed observations of how the networks change over time. Understanding the temporal dynamics might provide insight into sustainability and robustness of the networks and how they react to environmental changes, such as global warming. Here we study an Arctic plant-pollinator network in two consecutive years using a simple mathematical model and describe the temporal dynamics (daily assembly and disassembly of links) by random mechanisms. 相似文献5.
Won Ho Lee Seok Won Lee Tae Jin Kang Kwansoo Chung Jae Ryoun Youn 《Fibers and Polymers》2002,3(4):159-168
Polyurethane foams were produced by using a homogenizer as a mixing equipment. Effects of stirring speed on the foam structure
were investigated with SEM observations. Variation of the bubble size, density of the foam, compressive strength, and thermal
conductivity were studied. A hybrid foam consisting of polyurethane foam and commercial polystyrene foam is produced. Mechanical
and thermal properties of the hybrid foam were compared with those of pure polyurethane foam. Advancement of flow front during
mold filling was observed by using a digital camcorder. Four types of mold geometry were used for mold filling experiments.
Flow during mold filling was analyzed by using a two-dimensional control volume finite element method. Variation of foam density
with respect to time was experimentally measured. Creeping flow, uniform density, uniform conversion, and uniform temperature
were assumed for the numerical simulation. It was assumed for the numerical analysis that the cavity has thin planar geometry
and the viscosity is constant. The theoretical predictions were compared with the experimental results and showed good agreement. 相似文献
6.
Seong-Joon Kim Hyung-Joong Kwon In-Kyun Jung Geun-Ae Park 《Paddy and Water Environment》2003,1(3):149-155
The simulated streamflow from Thiessen average rainfall (T) and spatially distributed rainfall (R) may be significantly different from each other. To identify the hydrologic effects quantitatively, the grid-based kinematic wave storm runoff model was adopted. The model predicts temporal and spatial variations of surface and subsurface flow at each cell by calculating the water balance, and routes the streamflow to the outlet. The model was tested at the Yeoncheondam watershed (1,875 km2), one third of which belongs to North Korea. The watershed is elongated to north and south directions crossing the border. Four rain gauges cover the watershed within the territory of South Korea, while no records from North Korea are given. The simulated results showed the large differences in runoff volume and peak flow rates between T and R when rain moves in a north to south direction. The simulated results of east-to-west-direction storms showed little difference in the hydrographs. The hydrograph was strongly affected by the spatial variations of the rainfall moving along the stream of the watershed. 相似文献
7.
This paper introduces an irrigation system developed in the floodplain of a lake and studies the water management technique
of the irrigation system by estimating the total water balance of the whole system. The system is characterized by a reservoir
combined with a dike system in the floodplain of the Tonle Sap Great Lake and an irrigation system. Two main models are used
for calculating the total water balance. The first model is the water balance of the reservoir. The inputs to the model are
water level of the reservoir, precipitation, lake evaporation, infiltration, and area–volume curve of the reservoir. The outputs
are inflow and outflow of the reservoir. The supply from the reservoir to paddy fields is computed from the outflow. The second
model is the water balance of paddy fields, based on which the water requirement in paddy fields is derived. The reference
evapotranspiration needed to calculate the water requirement is simulated for monthly time series using the FAO Penman–Monteith
model. Since there is no drainage network in the irrigation system, surface drainage and runoff are not included in the calculation
of the water balance, and seepage is considered negligible in the flat floodplain area. The evapotranspiration, rice variety,
soil type and irrigated area are used to simulate water consumption in paddy fields. Finally, the two models are connected
to produce the total water balance from the reservoir to paddy fields. The total outflow from the reservoir is estimated and
the total water consumption for dry season cultivation is also determined. Finally, the efficiency of the whole system is
examined. 相似文献
8.
In closed water bodies with significant organic pollution, anoxification due to thermal stratification leads to the elution of nitrogen and phosphorus from the bottom sediment and the generation of sulfide, resulting in further degradation of the water environment. This study focuses on the water quality dynamics in an organically polluted reservoir exhibiting long-term anoxification using two approaches: (1) field observations of seasonal changes in vertical profiles of dissolved oxygen, nitrogen, phosphorus, and sulfide and (2) construction of a water quality prediction model based on an ecosystem model incorporated with anaerobic biochemical processes. Iron and sulfate reduction occurred simultaneously because nitrate–nitrogen was reduced by denitrifying bacteria after the anoxification, and iron reduction became the main factor of the increase in ammonium–nitrogen and phosphate–phosphorus. The redox state of the bottom sediment surface, when anoxification began to occur, greatly affected the water quality dynamics caused by gradual reductive reactions under anaerobic conditions. Furthermore, the calculation accuracy of ammonium–nitrogen, phosphate–phosphorus, and sulfide was highly improved by modifying the conventional model based on the field observations. The characteristics of water quality under anaerobic conditions were sufficiently reflected in the upgraded ecosystem model. The proposed water quality prediction model could be used to quantitatively estimate the water environment dynamics in organically polluted water bodies. The model could be developed further in the future to solve the problems caused by long-term anoxification. 相似文献
9.
Mixing by wind-induced flow and thermal convection in a small, shallow and stratified lake 总被引：1，自引：1，他引：0
Thermal stratification is one of the important features in closed water bodies, which primarily depend on meteorological conditions,
and has strong impact on the ecological environment in lakes or reservoirs. Data monitored in 3 days were analyzed for factors
that affect heat mixing processes to examine the diurnal stratification cycles in the Shikinawa Lake, a study area in Fukuoka
prefecture, Japan. We found that wind speeds and directions played an important role in the thermal mixing in the lake. High
solar heating mainly caused stratification state, but with less effect under stronger wind action. Development of mixed layer
depth in a natural lake due to wind-induced flow and thermal convection were calculated. Functional relationships between
entrainment rate and Richardson number or Wedderburn number were found and represented in this paper. Besides, heats exchanged
at the air–water interface and energy stored in the water column were also analyzed and discussed. 相似文献
10.
《Plant Production Science》2013,16(1):30-36
AbstractSpatial and temporal variations of photosynthetic photon flux density (PFD) measured using small photodiodes (Hamamatsu, model G1118) attached on the leaf surface of rice (Oryza sativa L.) differed with the orientation and inclination even at the same height of the canopy. Under sunny conditions, the fluctuation pattern of PFD was mainly determined by the orientation and inclination of the leaf surface, and not by the daily change of PFD in the open, e. g., high peaks of PFD were observed in the morning on east-oriented leaves, but only low peaks on north-oriented leaves. Under overcast conditions, however, the PFD on the leaf surface depended highly on the PFD in the open irrespective of the leaf orientation and inclination. The present study suggests that the orientation and inclination should be considered as the major factors influencing the PFD regime (spatial variation and daily total PFD) within the rice canopy. To determine the effects of spatial and temporal variations of PFD on crop productivity, the daily net assimilation of each leaf was estimated from the obtained data and the light-photosynthesis curve. 相似文献
11.
Recent studies have provided detail of the mechanisms by which plants and animals interact, but attempts to apply this knowledge to understand function at the scale of whole fields or grazed ecosystems can be fraught with difficulties. Faced with a plethora of detail, and yet demands to make models more comprehensive, modellers face pressure to revert to simplified accounts for what are assumed to be well-established biological phenomena, for example, for describing plant growth and intake, but this raises the risk that important insights may be lost, or that the analyses may face errors of scaling.
The predictions of a previously described spatial model are compared with those of a non-spatial rendition of the same model to identify the differences in predictions and the sources of these differences. In particular, the use of the conventional empirical growth functions and their interaction with temporal and spatial scaling errors are examined. The comparison exposed how substantial errors could be made in predicting yield and stability under grazing. It is proposed that such errors might be avoided by ensuring that the functional responses used capture the insights of more detailed studies, and by recognizing the difficulties of scaling-up from the level of processes to the field scale and beyond. 相似文献
The predictions of a previously described spatial model are compared with those of a non-spatial rendition of the same model to identify the differences in predictions and the sources of these differences. In particular, the use of the conventional empirical growth functions and their interaction with temporal and spatial scaling errors are examined. The comparison exposed how substantial errors could be made in predicting yield and stability under grazing. It is proposed that such errors might be avoided by ensuring that the functional responses used capture the insights of more detailed studies, and by recognizing the difficulties of scaling-up from the level of processes to the field scale and beyond. 相似文献
12.
Grant L. Pilkay Francis P. F. Reay-Jones Michael D. Toews Jeremy K. Greene William C. Bridges 《Journal of insect science (Online)》2015,15(1)
A 3-yr study (2009–2011) was conducted to examine the spatial and temporal dynamics of stink bugs in three commercial farmscapes. Study locations were replicated in South Carolina and Georgia, in an agriculturally diverse region known as the southeastern coastal plain. Crops included wheat, Triticum aestivum (L.), corn, Zea mays (L.), soybean, Glycine max (L.), cotton, Gossypium hirsutum (L.), and peanut, Arachis hypogaea (L.). Farmscapes were sampled weekly using whole-plant examinations for corn, with all other crops sampled using sweep nets. The predominant pest species of phytophagous stink bugs were the brown stink bug, Euschistus servus (Say), the green stink bug, Chinavia hilaris (Say), and the southern green stink bug, Nezara viridula (L.). Chi-square tests indicated a departure from a normal distribution in 77% of analyses of the variance to mean ratio, with 37% of slopes of Taylor’s power law and 30% of coefficient β of Iwao’s patchiness regression significantly greater than one, indicating aggregated distributions. Spatial Analyses by Distance IndicEs (SADIE) indicated aggregated patterns of stink bugs in 18% of year-end totals and 42% of weekly counts, with 80% of adults and nymphs positively associated using the SADIE association tool. Maximum stink bug densities in each crop occurred when the plants were producing fruit. Stink bugs exhibited greater densities in crops adjacent to soybean in Barnwell and Lee Counties compared with crops adjacent to corn or fallow areas. The diversity of crops and relatively small size of fields in the Southeast leads to colonization of patches within a farmscape. The ecological and management implications of the spatial and temporal distribution of stink bugs within farmscapes are discussed. 相似文献
13.
《Journal of Cereal Science》1998,27(2):179-189
A 10-gram Mixograph was used to analyse 39 bread wheat cultivars having various agricultural characteristics and origins. Eleven parameters obtained during the first 8 minutes of the mixing procedure were selected using a repeatability analysis in order to investigate variations between genotypes. Several flour protein fractions characterised by their extractability properties and size distributions were quantified. In addition grain hardness, water-extractable arabinoxylan contents and relative arabinoxylan viscosity were also determined and correlated with dough formation during mixing. Dough consistency, as measured by the height of the Mixogram, was correlated with grain hardness, as expressed by the starch damage content and the proportion (%) of flour particles larger than 37·8 μm. No significant relation was found with the water-extractable arabinoxylan content or the relative arabinoxylan viscosity. The width and height of the Mixogram was related to the proportion of unaggregated proteins before the mixing peak and to polymeric proteins after the dough consistency reached a maximum. The Mixograph proved to be a powerful tool to investigate indices of bread making quality. 相似文献
14.
The characterization of the dynamics of canopy coverage represents a relevant matter of study in the field of crop physiology.
The objective of this work was to calibrate a model able to simulate potato canopy coverage as a function of thermal time,
but including the error structure in such model. This was accomplished by using a mixed effects modelling approach where random
effects were added to the average response model. By applying this modelling approach, the structure of the data was taken
into account. Calibration data for the model were obtained from canopy coverage estimates derived from image processing analysis.
Digital images were taken periodically within 11 potato fields located in the Mantaro Valley (Peru) during the 2005–2006 growing
season. This model gave a better fit in comparison with the traditional fixed parameters model. An additional uncertainty
analysis with the objective of estimating the confidence region for the predictions of the mixed effects model was carried
out. By exploring the data structure, a more comprehensive overview of the potato canopy coverage was achieved with the mixed
effects model. 相似文献
15.
《Field Crops Research》1995,40(2):119-127
Seasonal patterns and vertical distributions of alfalfa root systems were investigated with field experiments and a simulation model. We carried out root excavations on an established alfalfa stand at Davis, California, in 1982 and 1983. Thirty-six soil cores to a depth of 150 cm were taken seven times in 1982 and seventy-two soil cores to 30 cm were taken nine times in 1983 over the growth seasons. Live fine roots were recovered through six (in 1982) or seven (in 1983) procedures, including detailed hand sorting for removing debris. Our studies revealed that fine root mass was generally greatest in spring and fall and least during summer. Secondary minima were found within each harvest cycle. At all samplings, root mass declined exponentially with depth.A simulation model was developed for studying dynamics of alfalfa fine roots. The model has two components: root growth and death. Actual growth rate of fine roots was determined by potential growth rate and dependent on soil temperature, water and carbohydrate supply. Root death was controlled by the maximum death rate and influenced by soil temperature and nonstructural carbohydrate in roots. Through differential changes in simulated growth and death rates, the model predicted well the temporal and vertical distributions of fine root mass. A high amount of fine root mass was maintained in spring by rapid growth and moderate death rates. Frequent harvests reduced root mass in summer. Root mass increased in fall again due to a prolonged high growth rate. Sensitivity analyses indicated vertical distributions varied strongly with carbohydrate supply and soil temperature. 相似文献
16.
Toshihiro Hasegawa Shinji Sawano Shinkichi Goto Pisarn Konghakote Anan Polthanee Yasushi Ishigooka Tsuneo Kuwagata Hitoshi Toritani Jun Furuya 《Paddy and Water Environment》2008,6(1):73-82
Climate change will have significant impacts on the rain-fed rice production ecosystem, and particularly on the ecosystem’s
hydrology and water resources. Under rain-fed lowland conditions, substantial variations among fields in grain yield are commonly
observed, but a method that can account for field-scale yield variability to produce regional-scale yield estimates is lacking,
thereby limiting our ability to predict future rice production under changing climate and variable water resources. In this
study, we developed a model for estimating regional yields of rain-fed lowland rice in Northeast Thailand, by combining a
simple crop model with a crop calendar model. The crop model incorporates the effects of two important resources (water and
nitrogen) on crop growth. The biomass accumulation is driven by water use, whereas the nitrogen supply determines canopy development
and thereby constrains crop water use. Accounting for the wide range of planting dates and the strong photoperiod-sensitive
characteristics of rice varieties through the calendar model is an essential component in determining regional yield estimates.
The present model does not account for the effects of mid-season drought or flooding, but was nonetheless able to explain
the spatial and temporal yield variations at the province level for the past 25 years. Thus, it can be used as a prototype
for simulating regional yields of rain-fed lowland rice. 相似文献
17.
基于RS和GIS的北京冬小麦面积多尺度时空变化研究 总被引：2，自引：0，他引：2
为了解小麦在不同空间尺度上的时空分布特征,基于冬小麦统计和遥感监测数据,利用空间统计分析方法,分别从北京市、区县和乡镇三个尺度,评价了2009-2014年冬小麦面积空间分布变化特征。结果表明：（1）北京市冬小麦面积从2009年的61 971.02 hm下降到2014年的26 814.87 hm,减少了56.73%;冬小麦成片种植的地块数量从11 243块降低到4 914块,减少了56.29%;地块平均面积也从4.76±0.19 hm减少到1.22±0.05 hm,降低了74.29%;（2）通州区、大兴区、房山区和顺义区的冬小麦面积减少量占总减少量的87.43%;每个乡镇的平均冬小麦面积从2009年的1 066.28±153.63 hm降低到2014年的388.21±59.17 hm,且大于1 000 hm和500~1 000 hm的乡镇数分别约减少了2/3和1/2;（3）四个典型乡镇冬小麦面积也均呈极显著减少趋势,地块平均面积降低幅度均在70%以上,并且面积大于5 hm的地块数量占总体的比例减少至不足8%。这说明2009-2014年北京市冬小麦种植面积显著减少,种植区域破碎化趋势严重。 相似文献
18.
为建立一种具有时空适应性、适用于稻麦轮作生产的管理决策支持系统,运用系统分析原理和数学建模技术,构建了具有较强机理性和预测性的稻麦轮作生长模拟模型,并进一步结合气象生成模型与策略分析评价模型,以C#.net为编程语言,应用面向对象的程序设计与软件技术,建立了综合性的稻麦轮作生产管理决策支持系统.系统具有农田信息管理、专家咨询、动态模拟、方案评估、因苗预测和系统维护等功能,实现了模拟预测、决策支持和人机交互技术的有机耦合.系统的建立为稻麦轮作生产管理和策略制定提供了定量化的辅助决策工具. 相似文献
19.
Although a lot of research has been performed on estimating irrigation water demand at the on-farm level, far less has been done on irrigation water demand for a region-wide basis, such as for a river basin or an area covering multiple river basins. The capture and management of the spatial variations in related data such as soil, climate, crops, and canal networks is the key to effective and efficient regional irrigation water demand estimations. The Geographic Information System (GIS), with its powerful spatial data management and analysis capabilities is used in this study to extend the scope of on-farm irrigation water estimation into a regional estimation. A command area covering several river basins in southern Taiwan was used to build a model prototype. The model framework shows the capability of the system to estimate regional irrigation water demand with most of the spatial variations preserved. The model also shows the capability for quickly reflecting changes in irrigation water demand in response to changes in cropping patterns, a feature that may be a necessary for regional water resource planning. 相似文献
20.
为利用高时空分辨率的航天数据对区域冬小麦播期实现尽早监测,对冬小麦播期的不同遥感监测时相精度进行了分析。首先利用耦合作物模型和辐射传输模型模拟不同播期冬小麦从播种至返青的冠层光谱反射率,分析不同播期的冠层光谱响应差异,选取对不同播种日期敏感的波段。然后,根据敏感波段的冠层光谱,选择训练样本并计算不同播期之间的J-M距离,初步判断出光谱可分性较好的时相。最后,对不同的播期进一步进行判别分析,判定未知类别样本的所属类别。根据正确分类的精度,在华北平原北部选择播期监测的最佳时相为12月中旬,精度达到89.5%。 相似文献