基于夏玉米冠层内辐射分布的不同层叶面积指数模拟

为了模拟夏玉米冠层内各层叶面积指数垂直分布,光合有效辐射（photosynthetically active radiation, PAR）是研究作物群体光合作用和长势的重要特征参数,阐明冠层内PAR的垂直分布规律与冠层结构等参数之间的相关关系,可为遥感定量反演冠层结构参数提供模型基础。该文基于PAR在冠层内的辐射传输规律结合冠层结构模拟不同太阳高度角的PAR透过率垂直分布模型,并用地面冠层分析仪测量值进行验证,结果表明模型对封垄前玉米抽雄期冠层内PAR透过率垂直分布模拟精度较高。通过不同太阳高度角PAR透过率的垂直分布模型结合消光系数运用不同算法分别反演层叶面积指数（leaf area index, LAI）,并与不同高度层LAI实测值进行比较。结果显示：Bonhomme& Chartier算法反演不同高度层LAI精度较高,上层均方根误差（root mean square error,RMSE）为0.18,中层RMSE为0.55,下层RMSE为0.09。不同太阳高度角反演结果存在差异,30°和45°高度角均能较好地反演下层LAI,RMSE分别为0.11与0.09;30°高度角反演中层LAI精度较高,RMSE为0.30;45°高度角反演上层LAI精度较高,RMSE为0.18。结果表明基于不同太阳高度角构建的层LAI反演模型更适于实现夏玉米不同高度层LAI的遥感估算。该研究可为模拟垄行结构冠层内LAI垂直分布提供参考。     

Ultraviolet-B radiation in a row-crop canopy: an extended 1-D model

A decrease in stratospheric ozone may result in a serious threat to plants, since biologically active short-wavelength ultraviolet-B (UV-B 280–320 nm) radiation will increase even with a relatively small decrease in ozone. Numerous investigations have demonstrated that the effect of UV-B enhancements on plants includes reduction in grain yield, alteration in species competition, susceptibility to disease, and changes in plant structure and pigmentation. To determine the physiological effects on plants of any increases in UV-B radiation, the irradiances at the potential sensitive plant surface need to be known. A number of radiative transfer models exist but because of the importance of sky diffuse radiation to the global UV-B irradiance, models designed to estimate photosynthetically active radiation or total solar radiation may not accurately model the UV-B. This paper compares spatially and temporally averaged measurements of the UV-B canopy transmittance of a relatively dense maize canopy (sky view: 0.27°) to the estimations of two one-dimensional models differing mainly in the handling of sky radiance. The model that considered the distribution of sky radiance tended to underestimate the canopy transmittance, the model that assumed an isotropic sky radiance distribution tended to overestimate the canopy transmittance. However, the assumption concerning the sky radiance distribution accounted for only about 0.01 of the model error. Consequently, the sky radiance distribution is probably not important in modeling such dense crop canopies. The model that overestimated transmittance and had the generally larger errors, a modified Meyers model, used the assumption of uniform leaf angle distribution, whereas in the other model, designated the UVRT model, leaf angle distributions were estimated by sample measurements. Generally this model would be satisfactory in describing the statistically average UV-B irradiance conditions in the canopy. This model may also be applied to other dense plant canopies including forests.     

利用3D模型模拟天空与叶面散射对玉米冠层截光率的影响

该文利用并行蒙特卡罗光线跟踪模型定量分析了天空散射与叶片散射对玉米冠层截光率的影响.模拟试验表明:相同辐射强度时,冠层截获的光强与受剑照射的叶片在天空散射时都比直接辐射时多;当太阳高度角小于60°时,冠层在阴大截获的总光强小于晴大,但至少60%的叶片在阴大截获的光强大于晴大时截获的光强;叶片散射对冠层光分布的影响与波长...     

黄土高原间作大豆对幼龄果园土壤水分及氮素累积的影响

为探明间作豆科作物对幼龄果园土壤水分、硝态氮含量以及树木生长的影响，并对黄土高原旱作果园土壤肥力提升与可持续发展提供指导，以黄土丘陵区苹果/黄豆复合系统为研究对象，通过测定种植黄豆整个生育期内试验小区水分、硝态氮含量以及果树叶片含氮量和生理指标的变化来评价不同间作密度黄豆对果树生长的影响。结果表明：(1)相较于清耕果园，中密度间作在黄豆花期前对果园土壤水分含量有一定的提升作用，而高密度间作加剧行间水分的消耗，显著降低土壤含水量。(2)不同土层硝态氮相对累积量随黄豆生育期后移呈现逐渐下移且分布逐渐均衡的趋势，土壤总硝态氮累积量处理间未表现出显著差异。(3)中、高密度间作均可有效提升果树叶片氮含量，促进果树生长，而中密度间作黄豆使土壤含水量最高提升17.6%,叶片氮含量最高增加8.04%。因此，中密度间作黄豆在黄土高原旱作苹果园更具有间作优势。     

Total reflected solar radiation calculated from multi-band sensor data

Reflected solar radiation is a significant term in the net radiation equation and is the one most strongly affected by surface conditions. The evaluation of net radiation over a heterogeneous area requires a detailed knowledge of the areal distribution of the reflected solar radiation. Remote sensing offers a means to obtain this areal distribution, provided that the total reflected solar spectrum can be estimated from discrete band multispectral radiometric data. A radiative transfer model was used to calculate the irradiance at the earth's surface for a number of atmospheric scattering and adsorption conditions. Response functions of two multiband radiometers were used to obtain the partial spectrum/total spectrum (P/T) ratio for each radiometer at each atmospheric condition. It was found that the P/T ratio was essentially independent of atmospheric scattering and only mildly dependent on water vapor absorption. Reflectance spectral distributions for 14 different surface conditions (bare soil to full green canopy) were used along with the irradiance data to determine the P/T ratio for reflected solar radiation. Multispectral data, with the appropriate P/T ratio, were used to calculate the total incoming radiation and the total reflected radiation from a wheat canopy. The calculated data differed from wide band pyranometer data by about 5%. It was concluded that both total incoming and reflected solar radiation can be evaluated from multispectral radiometric data. This development is a step towards regional net radiation maps, and possibly regional evapotranspiration maps.     

农作物冠层结构参数自动测量系统设计与试验

农作物冠层的结构参数,如叶面积指数与平均叶倾角,是影响太阳辐射在农田内进行重新分配的重要参数。在农业工程中,以玉米与小麦为例,这些参数的测量以传统的手持仪器为主,需要消耗较大的人力和时间,难以被应用于大区域尺度、长时间序列结构参数获取。该文设计并实现了一种基于无线传感器网络技术的农作物结构参数自动测量系统。系统由冠层上、下部光强测量节点、数据汇聚节点以及数据无线传输的路由节点组成,通过测量不同太阳高度角下冠层透过率来求解冠层的结构参数。数值模拟结果与野外实测结果表明,该文所用的结构参数反演算法稳定,测量系统可以较好的探测一天之中不同太阳高度角下的植被冠层太阳辐射透过率,基于方向透过率计算得到的叶面积指数与LAI2000仪器测量结果有较好的相关性,平均叶倾角和理论分布模式计算结果基本一致。该系统可以应用于对大区域尺度上的农作物长时间序列连续观测,提高农作物结构参数测量的自动化程度。     

日光温室黄瓜群体结构参数及群体内辐射分布分析

为研究作物群体结构与环境要素的关系，观测了日光温室内黄瓜不同生育时期的群体结构参数和群体内太阳总辐射的水平分布和垂直分布。发现叶面积指数、叶面积密度、叶倾角、叶方位角等结构要素在不同生育时期有明显的变化：随生育的进展，叶面积指数稳定增加，叶面积密度生育前期明显上升、后期有所下降，最大叶面积密度所在高度随黄瓜生长逐渐上移；叶倾角分布主要以水平叶为主；叶方位角以偏南居多，偏北叶所占比例较少；不同黄瓜品种间叶方位角和叶倾角也存在差异。这些变化与差异对黄瓜群体的辐射分布有重要影响，也直接影响群体叶的光合速率，此结果可为建立黄瓜群体辐射分布模型进一步优化日光温室结构，建立日光温室内作物生长模型、环境调节控制策略等提供理论依据，另外，对植株的调控技术(如整枝打杈技术等)也有一定的参考意义。     

Root growth and phosphorus uptake in wide‐ and narrow‐row soybeans

Most of the research comparing the effect of different row spacing on seed yield in soybeans [Glycine max (L.) Merr.] has been focused on row spacing effects on aboveground crop characteristics such as leaf area, right interception, pod number, or biomass accumulation and their relationships with seed yield. Little work has been done on the effects of narrow‐row spacing on root distribution. Plant distribution may also affect root distribution and interroot competition, and therefore, exploration and use of soil resources. A field experiment was carried out on the Pampas (Argentina) to determine the effect of narrow‐row spacing on root distribution within the topsoil in soybean, and whether different root distributions affect phosphorus uptake. In December 1993, soybeans were planted at two row spacings, narrow rows (0.35 m) and wide rows (0.70 m). Root density was measured during seed filling (92 days after planting) at several points within the inter‐row space down to a soil depth of 30 cm. Aboveground biomass was harvested at maturity and phosphorus (P) uptake was measured. Below the row line, narrow‐row soybeans showed a greater root density than the wide row treatment at 5–10 cm depth, while roots of the wide‐row soybeans had more lateral growth. Root density at both sides of the row down to a depth of 5 cm was greater for the wide‐row treatment. Average root density for each depth for a section of 70 cm wide across the row line indicated there was no significant difference between treatments at any depth. The fewer number of rows for the wide‐row spacing was compensated by a greater lateral extension of roots within the interrow space. This compensation resulted in a similar root density at each depth for both planting patterns, narrow and wide rows. Aboveground biomass and phosphorus concentration in plant tissue at maturity were not affected by row spacing. A similar phosphorus uptake for both treatments was consistent with the lack of effect of the different plant distribution on soil exploration by roots and on aboveground biomass accumulation.     

风送喷雾雾滴冠层穿透模型构建及应用

研究雾滴在树冠内的分布规律,对优化喷雾参数,提高喷雾效果有重要意义。该文以叶密度、出口风速和取样深度为试验变量,用试验法研究了树冠内雾滴穿透比例分布规律;试验结果表明:雾滴穿透比例随叶密度、取样深度的增加而减小,随喷雾机出口风速的增大而增大,其中取样深度对穿透比例影响最为显著。在此基础上,结合试验数据与统计学方法,构建了雾滴穿透比例二次指数数学模型,并确定了模型的待定系数,其模型精度R2高于0.95,经检验模型有一定的合理性和可靠性。基于此模型,计算了雾滴冠后飘移率,与实测值相比,平均相对误差为16.73%。进一步对雾滴冠后飘移率影响因素、双面喷雾机理、喷雾参数优化进行了分析,拓展了模型应用,对模型局限性和进一步优化模型的后续研究设想展开了说明。研究对风送喷雾雾滴分布规律研究具有一定的参考价值。     

Analysis of the effects of soil management on runoff generation in olive orchards using a physically based model.

Abstract. A numerical model that incorporates the spatial variability of infiltration, surface storage and resistance to overland flow was developed, calibrated and validated for olive orchards. The model reproduced accurately amounts of runoff used in validation, and predicted runoff in olive orchards managed in different ways, in line with published results. The model was used to analyse the runoff generation in a virtual, 180 m length, 5% steep, olive grove, using 54 different scenarios which combined three different soil types, two tree canopy sizes and nine soil management techniques (four tillage scenarios: freshly or degraded tillage with and without a compacted plough layer; no-till, and four cover crops in strips differing in width and plant density). The results of the numerical experiment showed that no-till had the highest runoff coefficient, while a dense cover crop had the lowest. Recently tilled soils also exhibited some of the lowest runoff coefficients. The effects of increasing soil cover due to a greater tree canopy on runoff were significant and caused by the greater area of high infiltration beneath the canopy. Effects of tree canopy size were less important than the impact of soil management practices on runoff.     

Measurement variability in soybean water status and soil‐nutrient extraction in a row spacing study in the U.S. southeastern coastal plain

Abstract

Full‐season determinate soybean [Glycine max (L.) Merrill] was grown in the field in a humid climate for three seasons (1979–81). The objective was to examine variability in several methods of determining basic relationships between soil and plant water status in a range of canopy configurations and to examine treatment effects on soil‐nutrient extraction. In each year, two cultivars, “Davis” (group VI) and “Coker 338” (group VIII) were planted in four row spacings. In 1980 and 1981 the experiment was expanded and split for irrigation and row orientation (N—S or E‐W). Post‐harvest soil samples were collected and analyzed to determine if irrigation, row spacing, or cultivar influenced K, Ca, and Mg extraction patterns.

During the growing seasons, parallel leaf diffusive resistance (R_s) was poorly correlated with xylem pressure potential (ψ_x), canopy s x temperature (T_c), canopy minus air temperature (?T), leaf vapor pressure deficit (LVPD), and atmospheric vapor pressure deficit (VPD) in single factor correlations. Xylem pressure potential was highly correlated with T_c , ?T, VPD, and LVPD, but was poorly correlated with soil water potential. Both ψ_x and T_c were significantly affected by the imposition of shade from a 60% shading cloth within as little as 1 minute of shade imposition. The impact of cultivar on seasonal ψ_x was significant and was nearly half the magnitude of the observed difference caused by irrigation. Irrigation raised ψ_x by only 2.2 bars over the two—year observation period, in spite of large differences in soil water potential when irrigation was imposed. The impact of canopy configuration was not measureable in any water relations parameter except infrared‐determined T_c. Correlation of T and ψ_x was significantly more reliable when limited to a single variety, row spacing, and row orientation. Aspect of infrared temperature measurement also significantly affected observed T_c.

Analysis of post‐harvest soil samples indicated that narrow (50 cm) row spacing in 1980 and irrigation in 1981 significantly decreased post—harvest Mehlich No. I extractable K, but none of the cultural practices influenced extractable Ca or Mg at P(0.05). In 1980, ex‐tractable K within soybean rows was significantly greater than between rows. Similar trends were observed for Ca and Mg in 1980 and for all 3 nutrients in 1981, but those differences were not significant at P(0.05). Overall, these measurements quantify the difficulty in relating soil and plant water status and identifying nutrient extraction patterns in sandy soils within the humid U.S. Southeastern Coastal Plain.     

我国4种主要苹果树形冠层结构和辐射三维分布比较研究

树体结构和辐射分布是影响果树冠层光合生产力和果实产量品质的主要因素。本文以"富士"苹果(Malus domestica Borkh.cv.‘Fuji’)为试材,采用田间调查方法,系统研究了我国苹果生产中4种主要树形的树体结构参数以及叶面积密度(LAD)和光合有效辐射(PAR)的三维分布特征。结果表明,开心形树冠的枝量(894×103·hm-2)和叶面积指数(LAI,2.53)最小,其他3种树形中小冠疏层形分别为2 280×103·hm-2、4.14,疏散分层形分别为2 119×103·hm-2、3.98,纺锤形分别为2 190×103·hm-2、3.88。不同树形LAD三维分布各不相同,小冠疏层形苹果树的叶片主要分布在树冠的0.5~1.5 m之间,疏散分层形和纺锤形主要分布在0.5~2.0 m之间,开心形主要分布在1.0~2.0 m之间。通过对不同树形LAD和PAR三维分布比较发现,每种树形的PAR都随树冠深度的增加而降低,在树冠中部LAD最大部位辐射消减最快,PAR的三维分布主要与叶片分布有关。其中开心形树冠的平均PAR最高,分布最均匀。4种树冠内叶片得到的平均相对PAR小冠疏层形为24.85%,疏散分层形为28.84%,纺锤形为27.71%,开心形为37.28%。开心形树冠内低光区的叶片所占比例只有35%,其他树形都超过50%。研究表明,不同相对PAR范围内的叶片比例能够更好地反映果树冠层的辐射情况,开心形树冠在辐射分布上优于其他3种树形。     

日光温室黄瓜非均质冠层光合生产的模拟

用均质冠层结构的光合模型来模拟非均质的日光温室黄瓜冠层光合速率则误差较大.该文所建立的日光温室黄瓜非均质冠层光合速率模型考虑到日光温室黄瓜冠层内光照分布以及叶片光合特性的不均匀性,其包含了非均匀冠层的透光模型和描述冠层叶片光合特性差异的经验公式.利用该模型对冠层光照分布和冠层光合速率的模拟结果表明:当模拟时所取的植株高度小于1.2 m,则冠层内直射光透光率和散射光透光率的模拟结果与验证值相比符合程度较好,但是对于模拟冠层单位体积内叶面积的总光合速率的结果还有待于进一步的验证.     

Previous Corn Row Effects on Potassium Nutrition and Yield of Subsequent No‐Till Soybeans

Abstract

Narrow‐row soybean [Glycine max (L.) Merr.] production in corn [Zea mays L.]–soybean rotations results in various distances of soybean rows from previous corn rows, yet little is known about soybean responses to proximity to prior corn rows in no‐till systems. The objective of this study was to evaluate the impacts of preceding corn rows on potassium (K) nutrition and yield of subsequent no‐till soybeans. Four field experiments involving a corn–soybean rotation were conducted on long‐term no‐till fields with low to medium K levels from 1998 to 2000 near Paris and Kirkton, Ontario, Canada. In the corn year, treatments included K application rate and placement in conjunction with tillage systems or corn hybrids. Before soybean flowering, soil exchangeable K concentrations (0–20 cm depth) in previous corn rows were significantly higher than those between corn rows. At the initial flowering stage, trifoliate leaf K concentrations of soybeans in preceding corn rows were 2.0 to 5.3 g kg^?1 higher than those from corresponding plants between corn rows. Yield of no‐till soybeans in previous corn rows increased 10 to 44% compared to those between previous corn rows. Positive impacts of prior corn rows on soil K fertility, soybean leaf K, and soybean yield occurred even when K fertilizer was not applied in the prior corn season. Deep banding of K fertilizer tended to accentuate row vs. between‐row effects on soybean leaf K concentrations in low‐testing soils. Corn row effects on soybeans were generally not affected by either tillage system or corn hybrid employed in the prior corn crop. Potassium management strategies for narrow‐row no‐till soybeans should take the potential preceding corn row impacts on soil K distribution into account; adjustments to current soil sampling protocols may be warranted when narrow‐row no‐till soybeans follow corn on soils with low to medium levels of exchangeable K.     

渭北果园土壤物理退化特征及其机理研究

【目的】针对我国渭北苹果主产区出现的随植果年限增加,果园土壤质量严重退化,树势衰弱、树体过早衰老、抗性降低、腐烂病及早期落叶病频繁发生,果品产量与品质下降等问题,开展了渭北苹果园土壤物理质量退化特征、退化机理及危害程度等问题的研究,以期查明制约果业可持续发展的因素,为果园土壤科学管理提供依据。【方法】在渭北黄土塬区选取了10 a、10 20 a、20 a 3个园龄段果园各4个,并以土壤条件相同的农田作对照,在果树冠层投影范围内距树干2/3处采取土样,测定土壤剖面不同层次容重、紧实度、孔隙度、饱和导水率、粘粒含量等物理性指标。【结果】渭北果园土壤容重和紧实度随园龄和土层深度的增加而增大,尤其在表层(20 cm)以下,土壤容重已经达到了1.45 1.61 g/cm3,紧实度达到933 2433 k Pa,严重超出果树健康生长的阈值。土壤孔隙度仅在0—20 cm土层能够保持在50%以上,属于良好状态,而20—60 cm土层维持在40%46%,已处于紧实和严重紧实状态。土壤饱和导水率在果园表层和紧实层均表现出随植果园龄的增大而减小的趋势,尤其是10 20 a和20 a的果园亚表层土壤饱和导水率低至46.88 cm/d和20.89 cm/d,制约着降水入渗和土壤蓄墒。3个园龄段果园土壤剖面上粘粒含量随土层深度呈递增趋势,且在0—30 cm土层随园龄的增加而明显减少,而在30 cm以下则随园龄的增加而呈递增趋势。进一步分析发现,粘粒含量与土壤容重、紧实度以及孔隙度之间呈极显著的相关关系。以压实密度(PD)为指标,对渭北果园土壤压实程度进行评估,发现渭北果园20 cm土层以下的土壤压实密度都在1.40 g/cm3以上,均达到了中度压实的程度,严重影响果树根系的健康生长及对养分的吸收。【结论】渭北果园20 cm以下的亚表层土壤孔隙密实、容重和紧实度增大,土壤饱和导水率递减是其土壤物理性质退化的主要特征,表层土壤粘粒的深层移动与淀积是土壤物理退化的主要过程和机理,果园土壤翻耕扰动少、对物理退化干预少是其土壤物理退化程度逐渐加剧的外在原因,土壤团聚体稳定性差是土壤物理状态退化的根本原因。     

The computation of foliage clumping index using hemispherical photography

Hemispherical photography (HP) is extensively used for both canopy architecture such as leaf area index (LAI), and solar radiation regime determinations under forest canopies. This is done mainly by assuming that foliage elements occur in a spatially random manner. However, the majority of world forests occur in heterogeneous ecosystems and topography with rather complex canopy architecture. To improve the estimates of canopy structures and solar radiation regimes, a non-random spatial distribution parameter called clumping index (CI) has been used. We compared varying methodologies of CI determination on real HP acquired in contrasting forest types growing on sloping ground, and on simulated HP representing different aggregation levels of foliage elements. The major aim was the comparative analysis of the effects of forest types, forest density, slope and gap fraction acquisition accuracy on estimation of CI using the five different approaches. The result indicated that CI estimates based on gap size distribution approaches performed the best and were less affected by topography and forest density compared to approaches based on solely logarithmic gap averaging techniques.     

Simulating sunflower canopy temperatures to infer root-zone soil water potential

A soil—plant—atmosphere model for sunflower (Helianthus annuus L.), together with clear sky weather data for several days, is used to study the relationship between canopy temperature and root-zone soil water potential. Considering the empirical dependence of stomatal resistance on insolation, air temperature and leaf water potential, a continuity equation for water flux in the soil—plant—atmosphere system is solved for the leaf water potential. The transpirational flux is calculated using Monteith's combination equation, while the canopy temperature is calculated from the energy balance equation. The simulation shows that, at high soil water potentials, canopy temperature is determined primarily by air and dew point temperatures. These results agree with an empirically derived linear regression equation relating canopy-air temperature differential to air vapor pressure deficit. The model predictions of leaf water potential are also in agreement with observations, indicating that measurements of canopy temperature together with a knowledge of air and dew point temperatures can provide a reliable estimate of the root-zone soil water potential.     

Spatial distribution of roots and cracks in soils cultivated with sunflower

The aim of this research was to investigate the spatial distribution of roots and cracks in two clay soils cropped with sunflower under different inter-row spacing in order to identify the optimal management. A latin square experimental design was applied to compare bare soil and soil cropped with sunflower, with three plant densities, obtained by keeping constant the number of plants on the row (3 plants m^?1) and varying the row spacing (0.4, 0.6, 0.8 m). The presence of the crop and the different distance between rows influenced soil moisture content as well as the root spatial distribution and thus the structural features of cracks. Increasingly lower values of moisture were found in both soils as the distance between rows decreased; an opposite trend was observed for both root density and crack size. The volume of cracks in the soil grown with sunflower at 0.4 m row spacing was 201.4 m³ ha^?1, thus 8 times higher than the value on the bare soil and 2.5 times higher compared to the one grown at 0.8 m between rows. Optimal results in terms of root density, soil moisture and crack size were obtained with an inter-row spacing of 0.6 m.     

Physiological interpretation of a hyperspectral time series in a citrus orchard

Hyperspectral remote sensing for monitoring horticultural production systems requires the understanding of how plant physiology, canopy structure, management and solar elevation affect the retrieved canopy reflectance during different stages of the phenological cycle. Hence, the objective of this study was to set up and to interpret a hyperspectral time series for a mature and healthy citrus orchard in the Western Cape province of South Africa considering these effects. Based on the remotely sensed data, biophysical parameters at the canopy level were derived and related to known observed physiological and phenological changes at the leaf level and to orchard management. Fractions of mature fruit, flowers, and sunburnt leaves were considered, and indices related to canopy structure chlorophyll content and canopy water status were calculated.Results revealed small cover fractions of mature fruit, flowers and sunburnt leaves of respectively 2.1%, 3.1% and 7.0%, but the high spectral contrast between flowers and leaves allowed a successful classification of flowering intensity. Furthermore, it was shown that canopy level time series of vegetation indices were sensitive to changes in solar elevation and soil reflectance which could be reduced by applying an empirical soil line correction for the most affected indices. Most trends in vegetation indices at the canopy level could be explained by a combination of changes at the leaf level (chlorophyll, carotenoids, dry matter), changes in canopy structure (leaf area index and leaf angle distribution) and changes in cover fractions of vegetative flushes, flowers and sunburnt leaves. The transformed chlorophyll absorption ratio index over the optimised soil adjusted vegetation index (MCARI/OSAVI) was best related to leaf level trends in chlorophyll content. Seasonal changes in the photochemical reflectance index (PRI) were linked to inverse changes in the carotenoid-to-chlorophyll ratio. Canopy structure indices (the modified triangular vegetation index or MTVI2 and the standardized leaf area index determining index or sLAIDI) were sensitive to changes in leaf area index, average leaf angle as well to management interactions (pruning and harvest). Canopy water status was highly impacted during the spring flush due to expanding leaves that concealed trends in the underlying mature leaves. Seasonal trends in soil and weeds reflectance were related to changes in volumetric soil water content and to the earlier and reduced growth period of non-irrigated weeds.     

夏玉米冠层光合有效辐射垂直分布模型

吸收光合有效辐射分量（FPAR）是研究植被群体光合作用和光能利用的重要参数,弄清冠层内FPAR的垂直分布规律及其与冠层结构等参数之间的定量关系,可以为遥感定量反演冠层FPAR提供模型基础。该文基于平均冠层的辐射传输过程,结合冠层结构建立玉米冠层内FPAR垂直分布计算模型,并就模型的参数如植被组分光学特性、株型、太阳高度角以及天空散射光比例等对FPAR垂直分布结果的影响进行了分析。利用实测结构参数模拟了玉米冠层内FPAR,并与SUNSCAN测量值进行了比较,结果表明模型对封垄后的玉米冠层内FPAR垂直分布的模拟精度较高,RMSE均小于0.18,并能较好地计算封垄前冠层内FPAR的垂直分布趋势。