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One of the key steps that would lead winegrowers to implement precision viticulture as a management tool would be the clear demonstration of the agronomic and oenological significance of the zones delineated within a vineyard based, totally or partially, on remote-acquired information. To perform this analysis, it is necessary to compare image-derived variables to crop characteristics. Classical ordinary least square (OLS) regression is not well suit for spatially structured data, while Moran’s index (MI) and local indicators of spatial autocorrelation (LISA) take autocorrelation into account. The aim of this work was to evaluate the performance of statistical methods to compare different maps of a vineyard, some including variables derived from UAV acquired imagery, and some from in situ ground characterization. The study was conducted during 2015 and 2016 seasons in an adult 7.5 ha cv. ‘Tempranillo’ vineyard located in Traibuenas, Navarra, Spain. The maps obtained out of UAV-imagery, volume index (VI) and normalized difference vegetation index (NDVI) were compared to the maps obtained for the agronomic variables measured (yield, berry weight and total soluble solids). The bivariate MI and the bivariate LISA cluster map obtained using Geoda software indicate depict the spatial cluster association between variables in 2015 and 2016 with different types of local spatial autocorrelation. The use of these methods that take into account data spatial structure, to compare ground autocorrelated data and spectral and geometric information derived from UAV-acquired imagery has been proved to be highly necessary and advisable.

Leaves are a significant component of the shoot system in grasses, functioning in light capture and photosynthesis. Leaf width, length, and angle are expressions of development that collectively define canopy architecture. Thus, the distinctive morphology of grass leaves is an interdependent readout of developmental patterning and growth along the proximal-distal, medial-lateral, and adaxial-abaxial axes. Here, we review the chronology of patterning and growth, namely along the proximal-distal axis, during maize leaf development. We underscore that patterning and growth occur simultaneously, making use of shared developmental gradients and molecular pathways.

Light in canopies is highly dynamic since the strength and composition of incoming radiation is determined by the wind and the Sun's trajectory and by canopy structure. For this highly dynamic environment, we mathematically defined sunflecks as periods of high irradiance relative to the background light environment. They can account for a large proportion of the light available for photosynthesis. Based on high-frequency irradiance measurements with a CCD array spectroradiometer, we investigated how the frequency of measurement affects what we define as sunflecks. Do different plant canopies produce sunflecks with different properties? How does the spectral composition and strength of irradiance in the shade vary during a sunfleck? Our results suggest that high-frequency measurements improved our description of light fluctuations and led to the detection of shorter, more frequent and intense sunflecks. We found that shorter wind-induced sunflecks contribute most of the irradiance attributable to sunflecks, contrary to previous reports from both forests and crops. Large variations in sunfleck properties related to canopy depth and species, including distinct spectral composition under shade and sunflecks, suggest that mapping canopy structural traits may help us model photosynthesis dynamically.

New remote sensing technologies have provided unprecedented results in vineyard monitoring. The aim of this work was to evaluate different sources of images and processing methodologies to describe spatial variability of spectral-based and canopy-based vegetation indices within a vineyard, and their relationship with productive and qualitative vine parameters. Comparison between image-derived indices from Sentinel 2 NDVI, unfiltered and filtered UAV NDVI and with agronomic features have been performed. UAV images allow calculating new non-spectral indices based on canopy architecture that provide additional and useful information to the growers with regards to within-vineyard management zone delineation.

Urban forest research and management requires improved methods for quantifying ecosystem structure and function. Regional equations for urban tree crown width and height can accordingly improve predictions of urban tree structure. Using a large regional dataset with 12 locations in the southeastern US, we developed diameter-based equations for 97 urban tree species. Whereas previously published urban equations have almost exclusively been developed with one location on public or commercial land, our data included both public and private land uses. For 5 widespread, common urban tree species (Acer rubrum, Cornus florida, Pinus taeda, Quercus nigra and Lagerstroemia spp.), we also assessed the inclusion of additional variables such as crown light exposure, land cover, basal area, and location. Overall, height and crown width models were improved when including additional predictors, although competition and location effects varied by species. Study city was a significant predictor of tree height in all species except C. florida, and a significant predictor of crown width for all species except C. florida and Q. nigra. This indicates that anthropogenically-influenced variation among cities can lead to significant differences in both tree form and structure and that future model development should utilize data encompassing multiple cities. Our predictive equations for urban tree crown characteristics provide an improved method for planning, management, and estimating the provision of ecosystem services to improve quality of life in cities. © 2016 Elsevier GmbH

Based on airborne LIDAR data on canopy morphology and height of Amazon forest trees, we developed allometric models to estimate dry biomass stored in the boles of dominant and co-dominant individuals and compared these results with those from equations based on traditional variables such as diameter at breast height (DBH). The database consisted of 142 trees of interest for logging in a forest under management for timber in Brazil's state of Acre. The trees chosen for study were selected through proportional sampling by diameter class (ranging from 45 to 165 cm DBH) in order to properly represent the dominant and co-dominant tree populations with diameters appropriate for harvest. Subsequent to LIDAR profiling of these trees, they were felled, subjected to a battery of dimensional measurements and sampled for wood-density determination. A set of models was generated, followed by model selection and identity testing in order to compare groups of basic wood density (low, medium and high). The morphometric variables of the crown had high explanatory power for bole biomass independent of whether the allometric equations included DBH. When calculating bole biomass with equations that include basic wood density, the best estimate is obtained using variables for both DBH and crown morphology. To obtain an allometric equation that encompasses species in all three classes of basic density, one should either use only independent variables representing crown dimensions or complement these with variables for basic density (BD) and total height (Ht). The study demonstrates the feasibility of using ground-based measurements to calibrate biomass models that include only LIDAR-based variables, allowing much larger areas to be surveyed with reasonable accuracy. The present study is designed to produce data needed for forest management, but the methods developed here can be adapted to studies aimed at reducing the uncertainty in biomass estimates of whole forests (not just harvestable trees) for use in quantifying carbon emissions from forest loss and degradation. © 2016 The Author(s)

The use of digital cameras for monitoring natural vegetation and agricultural ecosystems is particularly attractive since it necessitates neither expensive equipment nor extensive skill. In this study we tested the use of digital images (DIs) to generate 3D plant reconstruction for retrieving the main plant architectural features (leaf area, leaf inclination, leaf azimuth) of olive tree branches. High resolution image of tree branches were firstly used to generate 3D reconstruction of plant structures using a Structure From Motion approach; we therefore answered the question whether these 3D models may be segmented to discriminate main plant structures (leaves and branch) proposing a simple classification algorithm (Random Forest, RF) with saliency features and color indices as predictors. Finally, on the good and robust performances of the proposed classification algorithm, the single leaves were analyzed to retrieve the relevant area, inclination and orientation and compared to the relevant observed data. The calibration of the RF model indicated that color indices better discriminated leaves and stem than the sole use of saliency features. The classification performances were further improved by tuning the scale at which saliency features were calculated and by filtering the final result to reduce misclassified points. A RF model calibrated on a single plant was successfully applied to 5 others, indicating the robustness of the calibration strategy. The analysis of single leaves, as segmented after the classification process, indicated that plant architecture was satisfactorily reproduced with strong correlations obtained between measured and calculated values of leaf inclination and azimuth, while biases were observed for leaf area. These results emphasize the effectiveness of SFM in reproducing complex arrangements of leaves like on an olive tree. The use of such a system can be therefore suggested as a first step towards an improved low cost plant phenotyping platform to speed up our understanding of plant responses to environment. Further experiments are required to test the effectiveness of the approach also under outdoor conditions. (C) 2016 Elsevier B.V. All rights reserved.

Plant architectural traits are important selection criteria in plant breeding that relate to photosynthetic efficiency and crop productivity. Conventional manual measures of architectural traits for large breeding trials are labour- and time-consuming. In this study, we proposed a new method to reconstruct three-dimensional (3D) canopy architectural models for high-throughput phenotyping of canopy architectural traits using image sequences acquired by an unmanned aerial vehicle (UAV) platform. The accuracy of UAV-derived models is evaluated by comparisons with models from 3D digitizing and measured values. The results indicated that the proposed method could obtain full canopy architecture in the early growth stages and the upper parts of the canopy architecture in the later growth stages. The leaf number, plant height, individual leaf area, and vertical and horizontal distributions of the leaf area estimated from UAV-derived models were in good agreements with the reference values for maize. The derived length and maximum width of individual leaves were close to the field measurements for maize (R2 > 0.92 for both, RMSE 0.85 and RMSE

The economics of coffee plantations is intrinsically linked to pruning, which can improve the canopy architecture and thereby increase use efficiency. However, in India, recommended pruning methods viz., light, medium and hard pruning on Arabica coffee plantations have been highly labour intensive. The labour constitutes about 60 % towards cost of cultivation of coffee. In this study, the modified pruning and planting systems were investigated on Arabica coffee cv. Chandragiri and assessed for growth, yield and labour productivity at Central Coffee Research Institute, India over a period of nine consecutive years (2010–2018). Experimental results revealed that all the growth attributes and clean coffee yield were significantly influenced by modified planting systems (hedge row and paired row) and pruning methods (cyclic and rock-n-roll). Correlation coefficient data indicated that growth parameters had shown positive and significant correlation with clean coffee yield (CC) due to effect of modified pruning and planting systems except plant height. Mean data showed that adoption of modified pruning and planting systems helped to get higher clean coffee yield (1316 kg/ha), about 22–55 % of labour savings and maximum cost: benefit ratio of 1:2 could be achieved over traditional system of pruning and planting system. These results suggest that modified pruning methods facilitate vertical growth of coffee plants and thereby provide huge scope for high density planting system without compromising the yield. Further, an efficient labour force and adequate supply of human labour is the basic requirement for successful commercial cultivation of coffee. Hence, modified pruning methods such as cyclic and rock-n-roll pruning could be an option for improving the labour productivity of Indian coffee plantation.

In wheat (Triticum aestivum L.) canopy architecture influences light penetration into the canopy and radiation use efficiency particularly during the period between stem elongation and anthesis which is the critical time for the determination of yield. Despite large differences in canopy architecture among spring wheat genotypes, ranging from erectophile to planophile upper leaves, there is little prior evidence to suggest that selection for canopy architecture influences yield. In this study we evaluated the variation for canopy architecture in a 4-way MAGIC population (n=∼ 1000 lines) developed from 4 Australian commercial spring wheats and an 8-way MAGIC population (n=∼ 300 lines) developed from 3 Australian and 5 northern hemisphere commercial wheats. The 4-way population was grown at both an irrigated and a dryland site in southern New South Wales whereas the 8-way population was grown at the irrigated site. We also measured grain yield, plant height and crop development stage at the irrigated site. Using a smaller subset of lines which we grouped into either erectophile or planophile we studied how canopy architecture influences grain yield and associated yield traits (above-ground biomass (AGBM), harvest index, yield components, flowering time and height). The grain yield in the latter experiments varied from 5 to 6 t ha−1. Averaged over two years and two sowing dates in each year lines that were erectophile yielded 13% more than the planophile lines and most of this yield advantage was associated with a higher AGBM (11%). Erectophile lines had 24% more grains per unit area but a 9% lower grain weight. Erectophile lines flowered 2 days later than planophile lines and they were 7 cm shorter. Lodging, although rare in these studies, was more evident in the planophile lines. In both MAGIC populations the most erectophile lines yielded 24% more grain than the most planophile lines. Mapping was conducted on the 1000 lines from the 4-way MAGIC population grown at the irrigated and the dryland site. It showed that genetic control of canopy architecture was complex but QTL were generally repeatable at both sites. Significant QTL were identified on most chromosomes. G x E was low for canopy architecture as the scores were repeatable across years (r2 = 0.85). This trait opens the way to improve wheat yields via increasing crop biomass which in the past has been largely intractable in breeding programs.

The shift of rural laborers out of the agricultural sector led to a steady decrease of intercropping in the North China Plain (NCP). Strip intercropping facilitates mechanized management, and has the potential to out yield monocropping by an optimized resource use of the intercropped species. Therefore we developed a light partitioning model, that calculates the available amount of photosynthetically active radiation (PAR) at the top of the canopy for a given point within a strip of a smaller, subordinate crop. The model was described, evaluated on various simulation time steps and tested for the purpose of designing strip–intercropping systems. PAR reaching the top of the canopy of various rows of the strip subordinate bush bean (Phaseolus vulgaris L. var. nana) was measured continuously under different sky conditions. In the dominant strip, maize (Zea mays L.) was grown. Then the model was tested for its ability to account for the influence of different widths of the bush bean strip, strip orientations and maize canopy architecture (height, leaf area index, and leaf angle distributions). Comparison between hourly averaged simulated and observed values of PAR across the bush bean strip showed a high accuracy of the simulations, under both, clear and cloudy conditions. Overall, simulations of hourly values of PAR across the bean strip showed a root mean square error (RMSE) ranging between 47 and 87 μmol m−2 s−1 and a percent bias (PBIAS) ranging between −3.4 and 10.0%. A simulation time step of 20 min is recommended to preserve the accuracy of the model across the strip. The model captured reasonably the influence of strip design (width and orientation) and maize canopy architecture. Results suggested that the highest potential to increase PAR across the bush bean strip is by reducing height and leaf area index of maize, especially in the most shaded border row adjacent to the maize strip. The model proved to be a helpful tool for understanding the characteristics of light availability across the strip of the subordinate species and can be further used to examine a number of strip intercropping arrangements prior to labor and time consuming field trials.

Acid deposition as a widely concerned environmental problem in China has been less studied in plantation forests compared to urban and secondary forests, albeit they constitute 1/3 of the total forested areas of the country. We measured the rainwater amount and chemistry outside and beneath the canopies of two widely distributed plantations (Acacia mangium and Dimocarpus longan) in the severe acid rain influenced Pearl River Delta region of southeastern China for two years. Our results showed that the frequency of acid rain was 96% on the basis of pH value 88%) and NH4+ (10–38%). The two tree species showed distinct impacts on rainfall redistribution and rainwater chemistry due to their differences in canopy architecture and leaf/bark texture, suggesting that species-specific effects should not be overlooked while assessing the acid deposition in forested areas.

Atrazine is the most widely used herbicide in North American corn production; however, additional restrictions on its use in the near future are conceivable. Currently, a majority of commercial sweet corn fields suffer losses due to weeds, despite widespread use of atrazine. Field experiments were conducted in the primary North American production areas of sweet corn grown for processing to determine the implications of further reductions in atrazine use on weed control and crop yield. A range of atrazine doses (0–1120 g ha−1) applied postemergence with tembotrione (31 g ha−1) were tested in two hybrids differing in canopy architecture and competitive ability with weeds. Atrazine applied postemergence reduced risk (i.e. more variable outcomes) of poor herbicide performance. Atrazine doses up to 1120 g ha−1 with tembotrione improved grass control and broadleaf weed control in five of eight and seven of eight environments, respectively. Of the three environments which had particularly low broadleaf weed control (

43 Pag., 8 Fig., 2 Tabl. The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774, Maize (Zea mays L.) and alfalfa (Medicago sativa L.) were simultaneously irrigated in two adjoining plots with the same sprinkler solid-set system under the same operational and technical conditions. The Christiansen's uniformity coefficient (CUC) and the wind drift and evaporation losses (WDEL) were assessed from the irrigation depth (IDC) collected into pluviometers above each crop. A network of pluviometers was located above the maize canopy. Two networks of pluviometers were located above the alfalfa, one above the canopy and the other at the same level as that above the maize. The latter was used to analyze the effects of the water collecting plane. The wind velocity (WV) profile was measured above each crop using anemometers located at three levels. Both the CUC and the WDEL differed between maize and alfalfa. The crops modified both the wind velocity above the canopy and the water interception plane. Both effects were related to the height of the crops (h). When h increased, the water interception plane increased, and the overlap of the sprinklers decreased. The CUC of the IDC increased with the overlap. Because h was greater for maize than for alfalfa, the CUC was noticeably smaller for maize. The WV greatly decreased in proximity to the canopy. The WV at the level of the nozzles was smaller above the maize because the top of the canopy was closer to the nozzles than it was for alfalfa. However, the CUC of the IDC mainly depended on the WV at higher levels, where the WV was similar above both maize and alfalfa. The logarithmic wind profile overestimated the vertical variation of the WV in the space where the sprinklers distributed the water. The WDEL was greater above the maize than above the alfalfa. This finding was related to the underestimation of the IDC above maize, especially under windy conditions, because the pluviometers were located very close to the nozzles., This research was funded by the CICYT of the Government of Spain through grants AGL2004-06675-C03-03/AGR and AGL2007-66716-C03, and by the Government of Aragón through grant 13 PIP090/2005 and by the INIA and CITA through the PhD grants program.

The slope effect and correction methods for estimation of canopy gap fraction, leaf area index (LAI), mean leaf angle and clumping index using hemispherical photography, were investigated. The evaluation was carried out in tropical cloud forest and plantations in South-East Kenya in order to consider a range of canopy architecture and slopes up to 65%. The aim was to compare two acquisition techniques and various correction procedures. All estimates assume uniform slope, canopy parallel to ground and homogeneous canopy structure at the photo site level.

This study samples 247 saguaros ( Carnegiea gigantea ) and their nurses in 30 populations in the northern Sonoran Desert to determine whether saguaros are randomly distributed beneath their nurses’ canopies. Saguaro–nurse association patterns are compared across three nurse groups distinguished by canopy architecture characteristics (leguminous trees, small dense Ambrosia spp. shrubs, and the larger, open-canopied shrub Larrea tridentata ). For all three nurse types, saguaros are significantly clustered near the center of their nurse's base. Clustering varies with nurse architecture, as saguaros are most tightly clumped under the most open-canopied species ( L. tridentata ), as more than 80% of saguaros were under the innermost 10% of L. tridentata 's subcanopy area. Saguaros showed the least basal clustering about tree nurses, though not significantly less than Ambrosia spp. nurses. More saguaros establish under Ambrosia relative to its cover in sampled populations, while saguaros were underrepresented under L. tridentata . All analyses suggest that L. tridentata is an inferior nurse for saguaros. Different canopy architecture influences the extent of ground available to a nursed species to benefit from, for establishment and survival. While herbivory, rodents or other factors may play a role in these patterns, ultimately microclimate differences are the most likely factor shaping cacti–nurse associations in the harsh desert environment.

The relationship between wind speed and drag coefficient was experimentally investigated in two mixed conifer forests of the Italian Alps. Drag coefficient was calculated from the mean momentum equation while canopy architecture was described using optical measurements of gap fraction. Two different formulations of the momentum equation were tested: the common one, where drag forces are expressed in terms of the squared mean velocity ( ¯ u 2 ), and an alternative one in which drag forces depend on the averaged product of instantaneous wind intensity and instantaneous longitudinal wind component |U|u. Values of drag coefficients computed according to the first approach, decrease with increasing wind speed in both sites and show different average values between sites (0.15 ± 0.14 and 0.34 ± 0.45). Drag coefficients obtained with the second approach do not show a clear dependence on wind intensity, and the mean drag coefficients of the two sites become more similar (0.09 ± 0.06 and 0.12 ± 0.12). According to these results the scaling based on |U|u seems more appropriate to characterise the physics of the phenomenon. © 2003 Elsevier B.V. All rights reserved.

Leaf area and its spatial distribution are key parameters in describing canopy characteristics. They determine radiation regimes and influence mass and energy exchange with the atmosphere. The evaluation of leaf area in conifer stands is particularly challenging due to their open nature and clumping on the needle, shoot and tree scale. The overall objective of our study was to characterize leaf area index (LAI) (Lh ,m 2 half-surface area foliage m 2 ground) in the vicinity of our old-growth and 14-year-old ponderosa pine (Pinus ponderosa, var. Laws) eddy covariance flux sites, with future plans to scale from the flux sites to the pine region using ecosystem models and remote sensing. From the combination of optical and canopy geometry measurements, sapwood and litter-fall measurements, and one- and three-dimensional (3-D) models, we evaluated the variation in estimates of Lh in a mixed-age stand at the old-growth flux site. We also compared sapwood area estimates from a local allometric equation with LAI-2000 estimates that have been corrected for clumping and the interception of light by stems and branches (Lhc ,m 2 half-surface area m 2 ground) across a range of age classes and stand densities of ponderosa pine forests along a 15 km swath in Central Oregon that encompassed the flux sites. In the old-growth stand, the litter-fall and sapwood estimates tended to be higher than the optical and 3-D radiative transfer model estimates. Across the 15 km east‐west gradient from the crest of the Cascade Mountains, Lhc was typically lower than the sapwood estimates (Lhsw; slope 0.38). The Lhc data, as well as aboveground production estimates for the 17 pine plots will be useful for scaling flux measurements to the region using ecosystem models that have been validated with these data. © 2001 Elsevier Science B.V. All rights reserved.

In this paper a model for estimating actual evapotranspiration ( ET ) is tested at two experimental sites in Europe (southern Italy and southern France), using data for soybean crops temporarily stressed, grown under a typical Mediterranean climate. The present ET model is based on the Penman-Monteith approach, but uses a canopy r v value that takes account of both stomatal resistance and canopy architecture. In this mode, r v appears only as r v r a , where r a is aerodynamic resistance. r v r a is set to a fraction of the ratio r ∗ r a (with r ∗ called the critical resistance, similar to the isothermal resistance). The function r v r a = f( r ∗ r a ) depends on crop water status as specified by the predawn leaf water potential. The model gives very good results for both sites on hourly, daily and seasonal time scales.

A study was conducted in a lowland dipterocarp rain forest in Sumatra to assess the structure and dynamics of the forest canopy. The canopy structure was analysed at different scales, including a previous mapping of a 5 ha forest mosaic and an interpretation of the canopy architecture, along a horizontal gradient between the high forest and a 320 m2 treefall. Canopy geometry was ascertained by analysis of digitized zenithal hemispherical photographs sampled at 25 near-ground sites. Gap size, morphology and dispersion varied continuously from the high forest to the treefall. An asymmetric pattern of gaps about the zenith was characteristic of almost all forest sites. The spatial dispersion of gaps was random in the high forest. It tended to be dumped in the forest border and in the treefall. Plant area indices ranged from 6.5 in the high forest to 2.9 in the treefall. These values reflect a reduced leaf area during a severe dry spell, at the time of measurements. Inclination angles of canopy elements were highly correlated with gap dispersion and canopy openness, as observed from the high forest to the treefall. Implications of canopy heterogeneity on the distribution of light were analysed. The importance of lateral light penetrating from the forest border into the high forest is stressed. The canopy gradient of architecture and geometry from the high forest to the treefall and the very diverse structure of the high forest are emphasized.

The first transgenic crop with a modified seed compositionlauric-oil rapeseed as cultivated for commercial use in 1995, and many additional transgenic rapeseed varieties, expressing a variety of novel seed-oils or proteins, are under development. Research advances in Arabidopsis molecular genetics, and the emerging Brassica-Arabidopsis genome relatedness, will enable the radical manipulation of many key agronomic traits in rapeseed, ranging from greatly improved seed-oil yield and quality, to improved disease resistance, pod shattering and canopy architecture. Many of these advances will be directly applicable to other oil crops, including high-yielding tropical perennials such as oil palm.

Thermal stresses adversely affect plant growth and development worldwide and the resultant reductions in yield limit profitability of agricultural production. The identification of an optimal thermal range provides a means for quantifying thermal stress experienced by a plant. The thermal dependence of apparent K m and variable fluorescence are two procedures for estimating optimal thermal ranges. The ability of a plant to resist thermal stress can be increased through alteration of plant temperature and/or alteration of the optimal thermal range. Optimization of temperature can be accomplished through alteration of canopy architecture, optimization of plant root systems, and irrigation management based on plant temperature. Alteration of optimal thermal range of a species may be accomplished through breeding or molecular engineering methodologies.

We examined the influence of canopy architecture on light penetration in unmanaged lodgepole pine (Pinus contorta var latifolia) forests of the Rocky Mountains. Light extinction coefficients were estimated for 19 stands of varying age and structure from measured light interception using the Beer-Lambert equation. Estimates of G (k corrected for solar angle) varied between 0.28 and 0.70 and were negatively correlated with estimates of leaf area index (LAI) and the percent gap in the canopy. We also simulated the effects of changing canopy architecture on light penetration. Simulation results suggested that the order of importance of the characteristics of canopy architecture on light penetration was: (1) LAI; (2) foliage aggregation; (3) average leaf inclination angle; (4) vertical distribution of foliage. Direct measurement and simulation of light penetration suggested that increased LAI and increased within-crown foliage aggregation result in a reduced light capture efficiency (light capture/unit LAI). Canopy gaps tend to be more pronounced in dense, older lodgepole pine forests. High LAI and aggregated foliage distributions associated with this forest structure would cause increased foliage overlap and foliage self shading, thus reducing light capture efficiency.

Diurnal measurements of alfalfa leaf distribution and crop canopy reflectance were made in stressed and unstressed alfalfa plots in Phoenix, AZ. Measurements were made on three dates in January, May, and November. Results showed that heliotropic leaf movements were directly affected by crop water status. Under well-watered conditions, alfalfa leaves tended to track the sun throughout the day, in both the azimuthal and zenithal directions. In the stressed plots, diurnal tracking ability diminished as the day progressed and the canopy assumed a more vertical profile due to leaflet cupping. The stressed canopy then had a lower spectral reflectance (measured at nadir) than the unstressed canopy, in both the red and near-IR wavebands. The Perpendicular Vegetation Index (PVI) decreased with the stress-induced change in architecture while the near-IR/red ratio remained relatively constant. As a result, the near-IR / red ratio was more successful in estimating alfalfa biomass than was the PVI. These results emphasize the need to account for stress-induced architectural differences in plant canopies when using remotely sensed spectral data.

The influence of canopy architecture on the irradiance distribution on leaf surfaces in horizontally heterogeneous canopies was investigated using a procedural radiative transfer model. Four model canopies were abstracted as plant stands of 10 rows and 20 plants per row, and the procedural model was executed in conjunction with these digitized canopies. From the resulting distribution of the penetration function, the energy incident on leaf surfaces along the normal was calculated. The irradiance distribution was characterized by formally defining three kinds of irradiance — normal, diminished and null. Gross and net photosynthetic efficiencies due to irradiance in each energy class are presented. Canopy architecture was found to significantly influence the efficiency of energy use by affecting the interception pattern of solar radiation.

Several studies have shown that little movement of carbohydrate occurs in soybean ( Glycine max (L.) Merr.) from a leaf at one node to nodes more than two removed from the source node. Most light is intercepted in the upper periphery of the soybean canopy, but most of the seed yield occurs on the lower central nodes of the soybean plant. Thus, this study was designed to examine leaf area display and light interception patterns in the crop canopy in relation to yield production sites of two varieties of short-season indeterminate soybeans. Altona and Evans soybeans were planted in South Deerfield, MA on 19 May 1982 in rows 25 cm and 75 cm apart. Plots were overseeded by 50% into a fine sandy loam (Typic Udifluvents) and later thinned to populations of 25, 50 and 75 plants per m 2 . Light readings, taken weekly when weather permitted, were integrated over 1 m across and parallel to soybean rows, with the sensor placed on the ground, 25 and 50 cm above the ground and above the canopy dependent on plant height. Growth samples were taken biweekly with samples for leaf area determination divided into five strata, separated on the basis of point of attachment and display of the leaves. Soybean plants grown in narrow rows (25 cm) had a greater leaf area index, intercepted more light and yielded 23% more than soybeans grown in wide rows. For seed yield there was a variety-row width-density interaction, with Evans requiring a lower density for maximum yield than Altona in the 25-cm row width. Seed yield averaging 346.3 g m −2 for Evans was 32% greater than the average for Altona. Although most light interception, and therefore photosynthate production occurred in the upper regions of the plant canopy, many of the leaves displayed there were attached to nodes lower in the plant. Thus carbohydrates were suppled to lower regions of the plant, from these leaves, where most of the yield was found to occur. However leaves attached low in the canopy were still somewhat shaded by upper leaves, thus it is probable that greater efficiency of production could be obtained by concentrating breeding effects for improved canopy architecture with deeper light penetration into the canopy.

A model for radiative transfer in heterogeneous three-dimensional canopies such as those found in forests is proposed. Its use in estimating important biophysical variables such as leaf area index and canopy architecture from bidirectional canopy reflectance data is discussed. The model and its use in estimating canopy parameters through its inversion are validated with measured canopy reflectance data for corn canopies.