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1.
Leaf transmittance measurements can improve predictions of the nitrogen status for winter wheat crop
Dynamic crop models can be used to predict the occurrence of nitrogen deficiency during crop growth and optimize nitrogen fertilisation. However, prediction errors can be large and may lead to wrong recommendations. The objective of our work is to study the value of correcting the dynamic model Azodyn using transmittance measurements made with the N-Tester® (Yara) to predict the nitrogen status of a winter wheat crop. Our approach is to use a Bayesian method called the “interacting particle filter” to fit the model's state variables to measurements obtained over the course of the season. This approach was assessed on 44 experimental plots. Predictions of crop biomass, nitrogen uptake and nitrogen nutrition index were first performed for each plot by using the model without any correction. A second series of predictions was then performed for the same variables by correcting the model with N-Tester measurements at GS 7 on Feekes’ scale. The results showed that the second series of predictions were more accurate. Depending on the prediction dates, model corrections reduced the root mean squared error by 18.1–53.2% for nitrogen nutrition index, by 9.1–10.1% for biomass, and by 17.1–45.0% for nitrogen uptake. The predictions were improved up to 52 days after the measurement but the degree of improvement was higher when the prediction date was close to the measurement date. The results also showed that, when corrected, model predictions were very sensitive to values of N-Tester measurements. It is therefore necessary to use N-Tester measurements which are as precise as possible. 相似文献
2.
Background
We used a simple experimental design to test for the effects of microcosm scaling on the growth and survival of the mosquito, Culex pipiens. Microcosm and mesocosm studies are commonly used in ecology, and there is often an assumption that scaling doesn't affect experimental outcomes. The assumption is implicit in the design; choice of mesocosms may be arbitrary or based on convenience or cost. We tested the hypothesis that scale would influence larvae due to depth and surface area effects. Larvae were predicted to perform poorly in microcosms that were both deep and had small openings, due to buildup of waste products, less exchange with the environment, and increased competition. To determine if the choice of scale affected responses to other factors, we independently varied leaf litter quantity, whose effects on mosquitoes are well known. 相似文献3.
为在空间尺度上实现冬小麦LAI地面观测与遥感观测直接匹配,从1 m×1 m范围的实测LAI出发,通过优化采样方法扩展得到16 m×16 m范围的冬小麦LAI,然后利用空间分辨率为16 m的高分1号卫星的多光谱数据计算样本点的植被指数,建立其与冬小麦LAI的拟合模型,从四种植被指数的拟合模型中挑选表现最好的LAI估测模型,获得16 m×16 m尺度的LAI分布图,并经过重采样聚合为250 m×250 m尺度的LAI格点图,从而实现从地面点测量数据到卫星尺度数据的扩展。检验结果表明,16 m×16 m和250 m×250 m两个研究区域模拟点值和实测点值的相对误差分别为4.18%和3.64%,说明这种尺度扩展方法是科学可行的。 相似文献
4.
Background
One of the core issues of forest community ecology is the exploration of how ecological processes affect community structure. The relative importance of different processes is still under debate. This study addresses four questions: (1) how is the taxonomic structure of a forest community affected by spatial scale? (2) does the taxonomic structure reveal effects of local processes such as environmental filtering, dispersal limitation or interspecific competition at a local scale? (3) does the effect of local processes on the taxonomic structure vary with the spatial scale? (4) does the analysis based on taxonomic structures provide similar insights when compared with the use of phylogenetic information? Based on the data collected in two large forest observational field studies, the taxonomic structures of the plant communities were analyzed at different sampling scales using taxonomic ratios (number of genera/number of species, number of families/number of species), and the relationship between the number of higher taxa and the number of species. Two random null models were used and the “standardized effect size” (SES) of taxonomic ratios was calculated, to assess possible differences between the observed and simulated taxonomic structures, which may be caused by specific ecological processes. We further applied a phylogeny-based method to compare results with those of the taxonomic approach.Results
As expected, the taxonomic ratios decline with increasing grain size. The quantitative relationship between genera/families and species, described by a linearized power function, showed a good fit. With the exception of the family-species relationship in the Jiaohe study area, the exponents of the genus/family-species relationships did not show any scale dependent effects. The taxonomic ratios of the observed communities had significantly lower values than those of the simulated random community under the test of two null models at almost all scales. Null Model 2 which considered the spatial dispersion of species generated a taxonomic structure which proved to be more consistent with that in the observed community. As sampling sizes increased from 20 m × 20 m to 50 m × 50 m, the magnitudes of SESs of taxonomic ratios increased. Based on the phylogenetic analysis, we found that the Jiaohe plot was phylogenetically clustered at almost all scales. We detected significant phylogenetically overdispersion at the 20 m × 20 m and 30 m × 30 m scales in the Liangshui plot.Conclusions
The results suggest that the effect of abiotic filtering is greater than the effects of interspecific competition in shaping the local community at almost all scales. Local processes influence the taxonomic structures, but their combined effects vary with the spatial scale. The taxonomic approach provides similar insights as the phylogenetic approach, especially when we applied a more conservative null model. Analysing taxonomic structure may be a useful tool for communities where well-resolved phylogenetic data are not available.5.
The so-far studies on the physical determinants of roughness sensation of fabrics have considered only the profile amplitude of fabric surface, while it is poor to discriminate regular surfaces and doesn’t involve the interlocking interaction between fabric morphology and fingerprint. This work aims to compare the capability of the amplitude and spectral contents of fabric morphology in scaling the tactual roughness sensation by fingertip touching method. A set of experiments ranking fabrics on perceived tactual roughness by fingertip touching method were designed, and the Mean Deviation of the Surface profile (SMD), the texture spatial period, the maximum harmonic amplitude and the harmonic frequency were extracted from the fabric morphology. The concordance between the roughness sensation rank and the rank of each of four morphology indexes were compared. The experimental results showed that the spatial-intensive cues, i.e. the amplitude and the texture spatial periods were equivalent in scaling tactual roughness sensation of fabrics and the single spectral component was poor. Furthermore, it was observed that the features with a large length scale could dominate in subjects perceiving physical roughness. Accordingly, the speculation of this domination was tested, and it was confirmed that the texture spatial period dominated in the tactual roughness judgment of fabrics with texture-patterns spacing more than human fingerprint wavelength. It was concluded that the spatial coding works for the tactual roughness judgment of fabrics and the contribution of the spatial amplitude intensity depended on the contrast of texture spatial period to human fingerprint wavelength. 相似文献
6.
区域尺度冬小麦叶绿素含量的高光谱预测和空间变异研究 总被引：3，自引：0，他引：3
为从区域尺度探讨小麦SPAD的近地高光谱遥感监测技术,采用ASDField Spec 3.0型便携式高光谱仪获取的冬小麦冠层高光谱数据,利用相关分析和偏最小二乘法(PLSR)对SPAD进行建模预测,并采用地统计学方法进行空间变异制图。结果表明,冬小麦叶片SPAD值在不同生长阶段存在一定的差异,但在不同区域之间差异不显著。基于PLSR建立模型,并利用原始光谱和二阶导数光谱进行预测,R~2分别为0.653和0.995,均方根误差分别为2.622和0.327,相对析误差分别为1.549和13.66。综合来看,二阶导数光谱所建立的模型预测能力比原始光谱好。选择拔节期和成熟期进行区域化表达,与实测得到的SPAD空间分布图相比,采用全光谱数据和二阶导数光谱数据预测的SPAD均表现出了较高的空间相似性,其中二阶导数接近实测值。 相似文献
7.
Regional‐scale ecological processes are mediated by processes occurring at local scales. Spatially explicit models are needed to understand the broad‐scale consequences of a large number of local processes, driven by factors which are heterogeneous at a broad scale. A Geographic Information System (GIS)‐based mechanistic model, which can be used as a flexible tool to investigate the regional‐scale effects of changes in environmental factors on herbage production from a Lolium perenne sward, was developed and used to investigate the consequences of aggregating driving variables at different resolutions. The model allows rigorous scaling up of previously existing field‐based modelling approaches within a GIS context. The model's mechanistic approach allows flexibility in the simulation of the separate effects of environmental driving variables and of cutting regimes. The driving variables (temperature, solar radiation, available soil moisture and soil nitrogen status) are scaled up using geostatistical techniques. The model is used to evaluate weekly changes in herbage production under environmental conditions, variable both in space and time, under different cutting regimes. It is shown that, in this model, aggregation at 1 km2 is a good compromise between accuracy and practical feasibility, and that, while ignoring heterogeneity over many square kilometres can induce large errors, their magnitude and direction also depend on the model response curve to an input variable. The results obtained were consistent with the known trends in influential environmental factors. The programming within a GIS makes the model flexible in its application and, therefore, makes it easy to apply at a variety of scales. 相似文献
8.
Nobuaki Kimura Wen-Cheng Liu Chih-Yu Chiu T. K. Kratz Wei-Bo Chen 《Paddy and Water Environment》2012,10(1):17-30
A nowcasting system integrating observations and a numerical model was developed to better understand the spatial distributions
and temporal variations in the dynamics of a small, subtropical lake occasionally influenced by severe rainstorms. The nowcasting
system was used to monitor real-time meteorological conditions and thermal structures, to provide spatial information on the
thermal and flow dynamics from model predictions, and to compare the predictions with the observations. The system was also
able to determine whether the instruments collecting field data were performing correctly using telemetry operations. The
nowcasting system was initially operated in the spring of 2009 in Yuan-Yang Lake, Taiwan. Rainstorm-induced mixing occurred
due to Typhoon Morakot during August 7–9, 2009. The mixing was observed by the instruments, and the spatial distributions
and temporal variations during the mixing were successfully predicted by the three-dimensional hydrodynamic lake model. A
quantitative comparison of the energy balances among the heat, wind, and water inflow inputs to the lake implied that the
typhoon-induced mixing was primarily caused by strong winds. The model predictions showed that the lake experienced mixing
and flooding (large amounts of inflow/outflow discharges), resulting in homogenous temperatures and flows that moved to the
outlet of the lake. 相似文献
9.
《Field Crops Research》2005,91(2-3):273-285
The linearity of harvest index (HI) increase has been used as a simple means to analyze and predict crop yield in experimental and simulation studies. It has been shown that this approach may introduce significant error in grain yield predictions when applied to diverse environments. This error has been ascribed to variability in the rate of linear increase in HI with time (dHI/dt). Data from two field experiments indicated in chickpea (Cicer arietinum L.) that dHI/dt varied among sowing dates. This variation was related to the length of pre-seed growth phase and vegetative growth (dry matter production) during this phase and could be described by the mean daily temperature from sowing to beginning seed growth. dHI/dt increased linearly with increase in the temperature up to 17 °C when it reached to its maximum value and remained constant. Simulation of these field experiments using a chickpea crop model including a constant dHI/dt resulted in yield over-prediction for some sowing dates. However, a modified HI-based approach greatly improved model predictions. In this approach, potential seed growth rate (SGR) is calculated using the linear HI concept, but actual SGR is limited to current biomass production and the remobilisation of dry matter accumulated in vegetative organs before the seed growth period. This modification well accounted for temperature and drought effects on HI and resulted in better yield predictions under conditions of major chickpea producing areas of Iran. Therefore, we recommend that the modification to be applied in the other HI-based models. 相似文献
10.
为快速、准确获取江淮麦区县域冬小麦赤霉病发生信息,选用中、高空间分辨率卫星遥感影像做多尺度信息融合研究。在筛选适宜冬小麦田块分布特征的空间尺度遥感影像基础上,通过分析冬小麦长势指标和赤霉病病情指数之间的互作关系,构建基于多农学参数的冬小麦赤霉病估测模型,并对县域冬小麦赤霉病空间变化进行遥感监测。结果表明:(1)2m×2m、8m×8m和16m×16m三种空间尺度融合影像的均值相差不大,平均梯度和标准差存在明显差异。16m×16m融合影像的清晰度最好,信息量也多,比较适合研究区域冬小麦田块分布特征。(2)16m×16m融合影像提取的归一化植被指数(NDVI)和比值植被指数(RVI)值明显高于2m×2m和8m×8m融合影像,说明16m×16m融合影像光谱信息量较丰富,有利于冬小麦的识别。(3)冬小麦叶面积指数、叶片叶绿素含量和地上部生物量是影响赤霉病发生的主要长势指标。基于主要长势指标构建冬小麦赤霉病估测模型,平方根误差(REMS)为10.5%,相对误差为14.6%。该方法可以实现对县域冬小麦赤霉病空间变化的有效监测。 相似文献
11.
Warren K. Coleman Danielle J. Donnelly Shirlyn E. Coleman 《American Journal of Potato Research》2001,78(1):47-55
Although invitro production of potato tubers or microtuberization was achieved more than 40 years ago, the application of microtubers in reliable model research systems has been slow to develop. Several factors such as the use of growth regulators in microtu-ber induction and growth media, the mixotropic nature of thein vitro system, and cultivar-specific responses have led to interpretive difficulties. A cautionary note is also necessary in view of apparent growth and development differences, metabolic alterations, and soma-clonal variation encountered in microtubers that may not be found in field-grown tubers. Evidence for strong and consistent analogies between microtubers and field-grown tubers for their induction, growth and development, and metabolism often is lacking. However, several components such as the rapid and near-synchronous induction and growth, which can be modified by a range of exogenous compounds or conditions, make the microtuber a valuable model system. Complex problems such as dormancy also appear to be particularly amenable to examination by the microtuber system. In addition, the use of microtubers as experimental research tools has potential in the areas of plant metabolism, germplasm selection and evaluation, genetic transformation, somatic hybridization, and molecular farming. 相似文献
12.
为了解决作物长势遥感监测中星机协同性问题，在田块尺度上通过设置小麦氮素和灌溉梯度试验，在各关键生育时期测定SPAD和LAI两个长势指标并获取无人机遥感数据，构建小麦长势多光谱监测模型，并将优化的波段比值修正法与Sentinel-2A影像结合进行模型升尺度应用。结果表明，在拔节期、孕穗期、开花期和灌浆期，分别利用Clgreen、Clrededge、OSAVI和OSAVI构建的三次函数、指数函数、指数函数和幂函数对小麦SPAD的拟合效果最佳，升尺度应用至孕穗期、开花期和灌浆期卫星遥感监测后验证精度均较好；上述四个生育时期分别利用Clgreen、Clrededge、DATT和OSAVI构建的幂函数、二次函数、指数函数和指数函数对LAI拟合效果最佳，升尺度应用验证精度均较好。基于该星机协同方法对咸阳市冬小麦长势进行监测发现，2021年武功县、兴平市、三原县等区域小麦各生育时期长势均较优，永寿县、淳化县、彬州市等地的小麦长势均较差。这说明通过对无人机和卫星遥感影像融合方法的完善，可提高冬小麦长势监测中星机协同性。 相似文献
13.
大麦顶端发育和物候期的模拟 总被引：10，自引：1，他引：9
为了能直观反映大麦生长发育进程,利用生理发育时问恒定的原理,建立了系统预测大麦顶端发育阶段和物候期的模拟模型。模型的检验结果表明,模型对大麦大多数发育阶段的绝对模拟误差都在0～6d,平均差平方和的根值（Root mean square error,RMSE）不超过4d。模型对出苗期、成熟期的模拟误差较小,RMSE分别为1．0和1．6d;对雌雄蕊分化期的模拟误差较大,RMSE为3．7d;对于比较重要的单棱期和药隔形成期,RMSE分别为1．8和3．2d,均没有超过4d。模型表现出较强的机理性和实用性。 相似文献
14.
A mathematical model which simulates a single-cut forage conservation system is described. It was designed to investigate the effect of machine performance on the nutrient content of conserved forage but its scope is much wider, so that the effects of such aspects as crop growth characteristics, climatic differences and management policy can be assessed. An example of the use of the model to determine the value of chemical additives to high moisture content hay is described in detail. Various uses of the model are discussed and some of its limitations are shown to be caused by a lack of data on factors determining dry matter losses. 相似文献
15.
Kwang-Wook Jung Sang-Woo Lee Ha-Sun Hwang Jae-Ho Jang 《Paddy and Water Environment》2008,6(3):275-284
Researchers generally accept that land use types within a watershed closely relate with the water quality characteristics
of streams. Despite numerous studies investigating the relationships between water quality and land use, there are increasing
concerns about the geographical variation and lack of spatial integration in previous studies. We investigated the relationships
between land use and water quality characteristics including biological oxygen demand (BOD5), total nitrogen (TN), total phosphorus (TP), and Escherichia coli in the Wha-Ong estuarine reservoir watershed in Korea, which has spatially integrated land uses. Residential and paddy areas
appear to be positively and negatively correlated, respectively, with degraded water quality. The spatial variations of these
relationships were also examined using zonal analysis. Some results contrasted with those of previous studies that were conducted
mostly in developed Western countries and may reflect the different land use intensities and agricultural practices in Korea.
Relationships across zones, distinguished by distances from streams, were inconsistent and erratic, suggesting that the relationships
between remote land uses and water quality may be affected more significantly by sub-basin characteristics than by the land
use itself. The geographical differences and spatial variations found in this study indicate that caution must be taken in
generalizing the relationship between land use and water quality. 相似文献
16.
The major uncertainty in the climate change impact study inherits from applying the predictions of General Circulation Models
(GCMs). Different results might be obtained by using various GCMs’ predictions, which causes difficulties on the decision
making of water resources management. This study proposed an integrated hydrological simulations and optimization framework,
consisting of a fuzzy linear programming model with interval numbers, a streamflow simulation model, and agricultural water
demand projections, to evaluate the impacts of climate change on reservoir active storage. The reservoir inflows are simulated
by the WatBal model, while agricultural water demands are predicted based on the projected change of potential evapotranspiration.
Inflows and water demands are used to formulate an interval number fuzzy linear programming model. Fuzzy relationships are
used to describe tolerable deficits of water resources, and the interval number is employed to indicate ranges of possible
inflows and water demands. This systematic framework is applied to study the Tsengwen reservoir watershed to provide an optimal
interval of active storage. The results further indicate the higher tolerable deficit, the smaller difference between superior
and inferior active storage. 相似文献
17.
Richard M Sibly Jacob Nabe-Nielsen Mads C Forchhammer Valery E Forbes Christopher J Topping 《BMC ecology》2009,9(1):18-9
Background
Variation in carrying capacity and population return rates is generally ignored in traditional studies of population dynamics. Variation is hard to study in the field because of difficulties controlling the environment in order to obtain statistical replicates, and because of the scale and expense of experimenting on populations. There may also be ethical issues. To circumvent these problems we used detailed simulations of the simultaneous behaviours of interacting animals in an accurate facsimile of a real Danish landscape. The models incorporate as much as possible of the behaviour and ecology of skylarks Alauda arvensis, voles Microtus agrestis, a ground beetle Bembidion lampros and a linyphiid spider Erigone atra. This allows us to quantify and evaluate the importance of spatial and temporal heterogeneity on the population dynamics of the four species. 相似文献18.
A quantitative model of the ensilage process in lactate silages 总被引：2，自引：1，他引：1
A model of the ensilage process is presented which can be used to predict silage quality in lactate silages. The model simulates the major microbial and biochemical processes during ensilage, including aerobic respiration, hydrolysis of hemicellulose. growth and death of lactic acid bacteria and their production of lactic and acetic acids, reduction in pH, change in soluble sugar content, increase in osmotic potential, and proteolysis. The model is designed to operate on mixtures of grasses, legumes, or whole-plant corn. Parameters for the model are developed from published silage experiments and pure-culture bacterial studies. The model gives reasonably accurate predictions of key silage quality parameters, but further experimental work is needed on growth of lactic acid bacteria and on plant-enzyme proteolysis. Predicted final pH depends primarily on the pH at which bacterial growth and death rates are equal. Initial bacterial concentration affects the time to rapid pH change, while maximum bacterial growth rate affects the rate of decline thereafter. 相似文献
19.
Much of our understanding of weed communities and their interactions with crops comes from studies conducted at, or below, the spatial scale of individual fields. This scale allows for tight control of experimental variables, but systematically ignores the potential for regional-scale environmental variation to affect agronomic operations and thereby influence weed management outcomes. We quantified linkages among agronomic, environmental and weed management characteristics of 174 commercial sweet corn fields throughout the north central United States and evaluated crop and weed responses to these variables using classification and regression tree (CART) analysis. Multi-model selection indicated that characteristics of weed management systems, especially total cost and herbicide rate, were important predictors of weed diversity, interference and fecundity. Adding agronomic variables, such as planting date, or environmental variables, such as latitude, explained additional variation in weed floristic measures. We tested yield predictions of the most parsimonious CART model against a verification data set comprised of over 1500 published observations from 25 experiments conducted in the major North American regions where sweet corn is grown for processing. Yield values fell within the 95% confidence interval of observed data for most branches of the tree, suggesting the experimental and analytical approaches were reasonably robust. Several characteristics favoring sweet corn productivity and weed management sustainability were identified. This work resulted in easily interpretable models, both by scientists and producers, which place crop and weed responses within the context of regional-scale variation in agricultural management and the environment. 相似文献
20.
The effects of transfusing cores of grass silage with mixtures of oxygen and nitrogen containing 0%, 0·2%, 2%, 5% and 20% oxygen were investigated. Changes in populations of yeasts, lactobacilli and streptococci were measured and the relationship between populations after 7 days' transfusion and oxygen concentration were tested against the predictions of two models, based on Monod and logistic growth functions. Yeasts were related to oxygen by the Monod model, while lactobacilli and streptococci were related by the logistic model. The differences were ascribed to yeasts initiating deterioration by growing aerobically, while lactobacilli and streptococci grew fermentatively once the environment had changed following yeast growth. Dry-matter losses were related to oxygen by the Monod model. Changes in temperature were related to dry matter loss (through measurements of CO2 evolution) using a simple heat balance model. 相似文献