Row Canopy Research Articles

Evaluation of the SAIL Radiative Transfer Model for Simulating Canopy Reflectance of Row Crop Canopies

The widely used SAIL (Scattering by Arbitrarily Inclined Leaves) radiative transfer model (RTM) is designed for canopies that can be considered as homogeneous turbid media and thus should be inadequate for row canopies. However, numerous studies have employed the SAIL model for row crops (e.g., wheat and maize) to simulate canopy reflectance or retrieve vegetation properties with satisfactory accuracy. One crucial reason may be that under certain conditions, a row crop canopy can be considered as a turbid medium, fulfilling the assumption of the SAIL model. Yet, a comprehensive analysis about the performance of SAIL in row canopies under various conditions is currently absent. In this study, we employed field datasets of wheat canopies and synthetic datasets of wheat and maize canopies to explore the impacts of the vegetation cover fraction (fCover), solar angle and soil background on the performance of SAIL in row crops. In the numerical experiments, the LESS 3D RTM was used as a reference to evaluate the performance of SAIL for various scenarios. The results show that the fCover is the most significant factor, and the row canopy with a high fCover has a low soil background influence. For a non-black soil background, both the field measurement and simulation datasets showed that the SAIL model accuracy initially decreased, and then increased with an increasing fCover, with the most significant errors occurring when the fCover was between about 0.4 and 0.7. As for the solar angles, the accuracy of synthetic wheat canopy will be higher with a larger SZA (solar zenith angle), but that of a synthetic maize canopy is little affected by the SZA. The accuracy of the SAA (solar azimuth angle) in an across-row direction is always higher than that in an along-row direction. Additionally, when the SZA ranges from 65° to 75° and the fCover of wheat canopies are greater than 0.6, SAIL can simulate the canopy reflectance with satisfactory accuracy (rRMSE < 10%); the same accuracy can be achieved in maize canopies as long as the fCover is greater than 0.8. These findings provide insight into the applicability of SAIL in row crops and support the use of SAIL in row canopies under certain conditions (with rRMSE < 10%).

Observation and Assessment of Model Retrievals of Surface Exchange Components Over a Row Canopy Using Directional Thermal Data

Observation and Assessment of Model Retrievals of Surface Exchange Components Over a Row Canopy Using Directional Thermal Data

A Four-Component Parameterized Directional Thermal Radiance Model for Row Canopies

Directional brightness temperature (DBT) acquired by remote sensing instruments plays a significant role in characterizing the directional anisotropy of land surface, especially for row canopies. The difference between shaded vegetation and sunlit vegetation is ignored in the existing models. In this article, a four-component parameterized directional thermal radiance model (FCPMod) has been proposed to describe the DBT of the row canopy by considering the four components including the sunlit/shaded soil and sunlit/shaded leaf, the improved multiple scattering within the canopy, and the sensor&#x2019;s field of view (FOV). First, the sensor&#x2019;s FOV is divided into many tiny rectangles along the row direction and the probabilities of four components in each tiny rectangle are estimated based on the radiative transfer (RT) theory and the bidirectional gap probability. Second, the DBTs are weighted by the four components&#x2019; probabilities and brightness temperatures of tiny rectangles. Third, a modified multiple scattering model is proposed to improve the modeling accuracy by considering the contribution of the multiple scattering radiance between soil and canopy. The sensitivity analysis results show that the proposed method performed well compared to the FRA97 model proposed by Fran&#x00E7;ois <i>et al.</i> (1997) over continuous canopy and the RT model (FovMod) proposed by Ren <i>et al.</i> (2013) over row canopy. Finally, the field validations on a maize row canopy show that the proposed FCPMod performed better than about 0.4 K compared with the FovMod.

Assessment of Three Commercial Over-the-Row Sprayer Technologies in Eastern Washington Vineyards

Washington wine grape growers are rapidly adopting vineyard management technologies such as mechanical pruners and harvesters but have been slower to adopt new chemical application technologies. Therefore, this study was aimed at generating technical information about commercial over-the-row sprayers deposition and drift, which could be used by growers during sprayer selection and optimization for different vineyard systems and wine grape canopies. Three commercial sprayer technologies, i.e. multi-fan heads, pneumatic, and electrostatic sprayer, were evaluated for their canopy deposition and drift in the 2016 and 2017 production seasons. Data were collected in Vitis vinifera ‘Chardonnay’ and ‘Riesling’ vineyards at two application timings, early season and mid-season, to determine sprayer deposition patterns in opposed and unopposed application spray row canopy and in-field aerial as well as ground drift. All sprayer technologies showed consistent in-canopy deposition and drift patterns at both application timings. Regardless of sprayer technology, the most deposition was in the upper canopy compared to the fruiting zone of the vines. Similarly, the most aerial and ground drift was in the row closest to the sprayed row, indicating that drift is relatively low with the three evaluated sprayer technologies.

Impact of height heterogeneity on canopy turbulence

The flow development above and within homogeneous and heterogeneous canopies was experimentally studied using particle image velocimetry in a refractive-index-matching channel. The experiments were designed to gain insight into the effect of height heterogeneity on the structure and spatial distribution of the turbulence. The homogeneous model (base case) is constituted of elements of height$h$arranged in a staggered configuration; whereas the heterogeneous canopy resembled a row canopy and consisted of elements of two heights$h_{1}=h+(1/3)h$and$h_{2}=h-(1/3)h$alternated every two rows. Both canopies had the same density, element geometry and mean height. The flow was studied under three submergences$H/h=2$, 3 and 4, where$H$denotes the flow depth. The experiments were performed at Reynolds number$Re_{H}\simeq 6500$, 11 300 and 12 300 and nearly constant Froude number$Fr\simeq 0.1$. Turbulence statistics complemented with quadrant analysis and proper orthogonal decomposition reveal richer flow dynamics induced by height heterogeneity. Topography-induced spatially periodic mean flows are observed for the heterogeneous canopy. Furthermore, and in contrast to the homogeneous case, non-vanishing vertical velocity is maintained across the entire length of the heterogeneous canopy with increased levels at lower submergence depths. Further alternations were induced in the magnitude and distribution of the turbulent kinetic energy, Reynolds shear stress and characteristics of the canopy mixing layer, evidencing enhanced mixing and turbulent transport for the heterogeneous canopy especially at lower submergence depths. Overall, the results indicate that heterogeneous canopies exhibit greater vertical turbulent exchange at the canopy interface, suggesting a potential for greater scalar exchange and a greater impact on channel hydraulic resistance than a homogeneous canopy of similar roughness density.

Towards Automated Large-Scale 3D Phenotyping of Vineyards under Field Conditions.

In viticulture, phenotypic data are traditionally collected directly in the field via visual and manual means by an experienced person. This approach is time consuming, subjective and prone to human errors. In recent years, research therefore has focused strongly on developing automated and non-invasive sensor-based methods to increase data acquisition speed, enhance measurement accuracy and objectivity and to reduce labor costs. While many 2D methods based on image processing have been proposed for field phenotyping, only a few 3D solutions are found in the literature. A track-driven vehicle consisting of a camera system, a real-time-kinematic GPS system for positioning, as well as hardware for vehicle control, image storage and acquisition is used to visually capture a whole vine row canopy with georeferenced RGB images. In the first post-processing step, these images were used within a multi-view-stereo software to reconstruct a textured 3D point cloud of the whole grapevine row. A classification algorithm is then used in the second step to automatically classify the raw point cloud data into the semantic plant components, grape bunches and canopy. In the third step, phenotypic data for the semantic objects is gathered using the classification results obtaining the quantity of grape bunches, berries and the berry diameter.

Simulated impact of sensor field of view and distance on field measurements of bidirectional reflectance factors for row crops

It is well established that a natural surface exhibits anisotropic reflectance properties that depend on the characteristics of the surface. Spectral measurements of the bidirectional reflectance factor (BRF) at ground level provide us a method to capture the directional characteristics of the observed surface. Various spectro-radiometers with different field of views (FOVs) were used under different mounting conditions to measure crop reflectance. The impact and uncertainty of sensor FOV and distance from the target have rarely been considered. The issue can be compounded with the characteristic reflectance of heterogeneous row crops. Because of the difficulty of accurately obtaining field measurements of crop reflectance under natural environments, a method of computer simulation was proposed to study the impact of sensor FOV and distance on field measured BRFs. A Monte Carlo model was built to combine the photon spread method and the weight reduction concept to develop the weighted photon spread (WPS) model to simulate radiation transfer in architecturally realistic canopies. Comparisons of the Monte Carlo model with both field BRF measurements and the RAMI Online Model Checker (ROMC) showed good agreement. BRFs were then simulated for a range of sensor FOV and distance combinations and compared with the reference values (distance at infinity) for two typical row canopy scenes. Sensors with a finite FOV and distance from the target approximate the reflectance anisotropy and yield average values over FOV. Moreover, the perspective projection of the sensor causes a proportional distortion in the sensor FOV from the ideal directional observations. Though such factors inducing the measurement error exist, it was found that the BRF can be obtained with a tolerable bias on ground level with a proper combination of sensor FOV and distance, except for the hotspot direction and the directions around it. Recommendations for the choice of sensor FOV and distance are also made to reduce the bias from the real angular signatures in field BRF measurement for row crops.

2D approximation of realistic 3D vineyard row canopy representation for light interception ( fIPAR) and light intensity distribution on leaves ( LIDIL)

A detailed dynamic 3D architecture model coupled with a soil water balance model is used to explore the pertinence of 2D approximations of the row structure and describe the light regime and canopy photosynthesis in vineyard. The fraction of intercepted light ( fIPAR), the fraction of illuminated leaf area ( fILA) and the distribution of light intensity on illuminated leaves ( LIDIL) were calculated using Z-buffer and ray tracing techniques under both direct (black-sky) and diffuse (white-sky) conditions. The 2D approximations of the row were based on parallelepiped infinitely extended bounding boxes whose height and width was either defined by the outer envelope of the leaves (2D max) or effective dimensions (2D eff) adjusted to simulate the same instantaneous fIPAR diurnal time course as that of the reference 3D model (3D). The results showed consistent simulations between 2D eff and the reference 3D model for the three light regime variables investigated. Conversely, discrepancies were observed between 2D max and the reference 3D model both for fIPAR and fILA: the 2D max model overestimates the actual fIPAR (up to 22%) and fILA (up to 50% in some cases). These differences increased with LAI values, and are associated to an overestimation of row height. Conversely, LIDIL simulated for the 2D max were consistent with those obtained with both 3D and 2D eff models. The canopy level photosynthesis rates, computed using the leaf model of Schultz (2003), confirmed the adequacy of a 2D effective row structure approximation. The 2D max approximation leads to systematic overestimation of photosynthesis rates that can reach up to 36%. Although an effective 2D approximation seems very pertinent for light regime simulations in the PAR domain where multiple scattering is marginal, it was difficult to relate the effective dimensions to other canopy architecture features easy to measure in the field, row height being the most sensitive characteristic.

The effect of fungicide seed protectants, seeding rates, and reduced rates of herbicides on no-till soybean

A field study was conducted to determine if fungicide seed protectants, reduced rates of a complete preemergence or a complete postemergence herbicide program, and soybean seeding rates affect weed control and yield in a no-till system. Asgrow 3237, Pioneer 9273, and Pioneer 9342 soybean cultivars were planted into corn stubble at Urbana, Illinois in 1995 and 1996. Fungicide seed protectants increased soybean population density and reduced time to canopy closure in 1995, but had no effect in 1996. As seeding rates increased from 34.6 to 54.3 seeds m −2, yields increased, and time to row canopy closure was decreased. In general, adequate weed control and soybean yields were maintained using reduced rates (⩾0.5 X) of herbicides. In 1996, the purple seed stain fungus, Cercospora kikuchii, was isolated more often from Pioneer 9273 seed and Asgrow 3237 seed harvested from the no-herbicide, weedy control plots compared to plots treated with herbicides.

Direct solar radiation penetration into row crop canopies in a lean-to greenhouse

Experiments were conducted using model row crop canopies inside a model lean-to greenhouse (ratio 1 : 15) under artificial light to investigate the relations between row orientations and amount of direct solar radiation received by the canopy leaves. The model leaves were round in shape, horizontal in leaf inclination. The difference between the azimuthal directions of every two vertically neighbouring leaves was 90°. The east–west (E–W) and north–south (N–S) row canopies consist of 110 (5 rows × 22 plants/row) and 98 (14 rows × 7 plants/row) plants, respectively, and both gave a leaf area index of 1.16. Solar cells, each with a detecting area of 1.0 cm × 1.0 cm, were set on the surface of the upper 10 leaves of each measuring plant to detect the solar radiation reaching it. At 35°N, E–W row canopy showed higher normalized daily canopy irradiance than that of N–S row canopy during the winter and early spring months, while the results became the opposite for the rest of the year. At 45 and 55°N, on the other hand, N–S row canopy showed higher normalized daily canopy irradiance than E–W row canopy throughout the year. Moreover, magnitude of the differences in normalized daily canopy irradiance between row orientations was bigger in summer and late spring months than in winter and early spring months. Further analyses showed that the differences between E–W and N–S row canopies mentioned above were mainly due to the differences of normalized canopy irradiance during almost the whole day in spring and summer, and the differences in the integral value over the day of normalized canopy irradiance in winter.

FIELD TEST RESULTS WITH MECHANICAL HARVESTING EQUIPMENT IN FLORIDA ORANGES

During the 1996-1997 season, mechanical harvesting tests were conducted with a canopy shaker, a trunk shake-catch harvester, and a fruit pickup machine. The canopy shaker, which moved continuously down one side of the tree row canopy, operated at 1.2 to 2.4 km/h. Orange removals ranged from 55% in larger diameter tree canopies to 95% in smaller tree canopies with machine capacities up to 25 t/h. The trunk shake-catch harvester removed 84 to 94% of oranges shaking 5 to 10 s per tree with machine capacities up to 10 t/h. The fruit pickup machine picked up oranges at 15 to 20 t/h at 97% efficiency and caused 3 to 7% split peels from handling.

The influence of orchard row canopy discontinuity on irradiance and leaf area distribution iii apple trees

SummaryPhotosynthetic irradiance and leaf area distributions were determined in individual trees of ten year old ‘Royal Gala’/ MM.106 apple planted at 4.5 × 2.0 m and 5.0 × 3.0 m. Since tree height, across-row profile, and management history were similar, the extent of canopy discontinuity between trees along the row in response to tree spacing represented the main difference between the planting systems. Total daily photosynthetic photon flux (PPF) to deep within canopies was higher in the wider-spaced trees because attenuation of PPF from mid to lower canopy regions was less pronounced than with close-spaced trees. The differences were evident under both diffuse and direct light conditions, although in direct light, decline in irradiance occurred mainly in the eastern and southern aspects of the canopy. The patterns of irradiance under partially cloudy conditions were very similar to those in direct light. Light interception was 59% by trees spaced 3.0 m apart in the row and 64% by trees spaced 2.0 m apart in the row. LAI was significantly higher in trees planted at 4.5 m × 2.0 m, the difference caused by greater shoot leaf area in the mid and upper canopy regions. LAD was higher in all parts of the canopy in the closer-spaced trees. Many of the irradiance and leaf canopy properties of trees planted at 5.0 × 3.0 m approached optimum values modelled for efficient orchard production systems. The roles of the conical tree form and discontinuity between adjacent trees along rows or in beds are discussed in relation to orchard canopy efficiency.

Comparisons of Moisture and Energy Balance Components as Influenced by Two Row Orientations of Soybean.

When a crop is grown in rows, the row direction influences the energy balance and moisture budget of the soil-canopy system of the crop. Attempts were made to compare energy balance and moisture budget of E-W row soybeans with those of N-S rows at partial cover during the summer of 1996. The energy balance and moisture budget were considered for the soil and canopy separately. Daily fluctuations and diurnal patterns of energy and water balance of field, soil and canopy were strongly influenced by row orientations. Average latent heat flux density (LE) observed in N-S row soybean field was 6.6% larger as compared to E-W row soybean field. Average ratios of -LE to net radiation (Rn) were found 0.85 and 0.87 for E-W and N-S rows, respectively. Soil heat flux (G) accounted for 14 to 20% of Rn for E-W rows and 6 to 9% for N-S rows. Soil surface net radiation (Rns) of E-W rows was about 25% larger than that of N-S rows. Latent heat flux from the soil (LEs) was about 13% larger in E-W rows as compared to N-S rows. The -LEs/Rns ratios often exceeded 1.0 in both the cases. The sensible heat flux from the soil showed a positive trend in both the cases indicating soil surface was absorbing convective heat. The -G/Rns ratios were found 0.41 and 0.26 for E-W and N-S rows, respectively. Average net radiation of E-W row canopy (Rnc) was 20% smaller as compared to N-S row canopy. Latent heat flux from the E-W row canopy (LEc) was 19% smaller as compared to N-S row canopy. The -LEc/Rnc ratios were found 0.80 and 0.79 for E-W and N-S rows, respectively. Sensible heat flux from the canopy showed negative trends in both the cases. Results suggest that only field energy balance measurements would not provide sufficient information on how energy balances of the soil and canopy are partitioned.

Vertical and horizontal distribution of wind speed and air temperature in a dense vegetation canopy

Wind speed and temperature were measured within a corn row canopy to investigate horizontal and vertical variability of the mean wind speed and temperature. It appears that the mean wind speed can vary between 20% and 30% from its horizontal mean value. In the narrow row crop, the horizontal mean air temperature varies between 0.1°C (night-time) and 0.35°C (daytime) from the spatial mean value. Exceptions occur around noon in daytime when direct irradiation dominates and where the direct beam illuminates the within-row space of the canopy. Then, deviations of 1°C or more from the horizontal mean value are observed. Attention was focused on finding adequate scaling parameters of the within-canopy wind speed and air temperature profiles under various atmospheric stratification states. During daytime and night-time, the above-canopy friction velocity appears to be a good scaling parameter. Clear nights, however, are exceptions, when the above-crop wind speed drops to a very low value. Then, the within-canopy free convection velocity scale appears to be an appropriate scaling parameter for within-canopy processes. During daytime, the within-canopy temperature profiles scale well with the above-canopy temperature scale, T ∗ , for stationary irradiation and wind speed regimes. On calm nights, however, the relative within-canopy temperature profile scales very well with the within-canopy free convection temperature scale, Θ ∗.

Nighttime free convection characteristics within a plant canopy

An intensive measurement campaign within and above a maize row canopy was carried out to investigate flow characteristics within this vegetation. Attention was given to finding adequate scaling parameters of the within-canopy windspeed and air temperature profiles under above-canopy stable stratification. During clear and calm nights the within-canopy condition differs considerably from the abovecanopy state. In contrast to the daytime, the windspeed and temperature profiles do not scale with the above-canopy friction velocity,u * , and the scaling temperature,T * , respectively. A free convection flow regime is generated, forced by the soil heat flux at the canopy floor and by cooling at the top of the canopy. However, the windspeed and temperature profiles appear to scale well with the free convective velocity scale,w * , and the free convective temperature scale,T f , respectively. The free convective state within the canopy agrees well with the free convection criterion Gr>16Re2(u * ), where Gr is the Grashof number and Re(u * ) the Reynolds number, a criterion often used in technical flow problems. Also it is shown that under within-canopy free convection, there is a unique relation between the Grashof number, Gr, and the Reynolds number if the latter is based on the free convective velocity scale. Under within-canopy free convective conditions, it appears that within the canopy the fluxes of heat and water vapour can be estimated well with the relatively simple variance technique. Under these conditions, the Grashof, or Rayleigh number, represents a measure for the kinetic energy of the turbulence within the canopy.

Primocane Development and Early Yield of `Heritage' Red Raspberry in Relation to Initial Plant In-row Spacing

Micropropagated plants of `Heritage' primocane-fruiting (PF) red raspberry (Rubus idaeus L.) were planted at in-row spacings of 100, 50, or 25 cm. Yield per unit area during the first season was positively correlated with initial plant in-row spacing. During the first season of growth, initial plant in-row spacing did not affect the total number of primocanes that developed but was positively associated with the numbers of primocanes that fruited. Yield per primocane, primocane yield efficiency, total nodes per primocane, and number of fruiting nodes per primocane were not affected by plant in-row spacing in the first year. Average fruit weight and fruiting primocane diameter in the first year were negatively associated with plant in-row spacing. Photosynthetic photon flux density (PPFD) penetrating the row canopy as measured in the first season was not affected by treatment. Treatment did not influence percentage of fruit exhibiting solar injury, shattering, or infection by Botrytis cinerea. Plant in-row spacing did not influence yield during the second and third production seasons.

Horizontal and vertical distribution of wind speed in a vegetation canopy.

Wind speed measurements within a maize row canopy were carried out to investigate the horizontal and vertical variability of the mean wind speed and its standard deviation. Attention was given to finding adequate scaling parameters of the within-canopy wind speed profiles under various atmospheric stratification states. A validation of existing model simulations was also carried out. The horizontal mean wind speed and its standard deviation can vary about 20% from its spatial mean value. During day time and night time the friction velocity appears to be a good scaling parameter. Clear nights, however, are exceptions, when the wind speed above the crop drops to a very low value. Then the free convection velocity appears to be an appropriate scaling parameter for the within-canopy processes. The canopy models of Wilson &amp; Shaw [Journal of Applied Meteorology (1977) 16, 1197-1205] and Li et al. [Boundary-Layer Meteorology (1985) 33, 77-84] were found to simulate the spatially averaged mean wind profile within the range of the horizontal variability. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Row structure and foliage geometry as determinants of the interception of light rays in a sorghum row canopy

Row structure and foliage geometry as determinants of the interception of light rays in a sorghum row canopy

Row structure and foliage geometry as determinants of the interception of light rays in a sorghum row canopy

Abstract. The interception of light rays by the canopy of a widely spaced sorghum row crop was assessed from a series of hemispherical photographs taken on five occasions during its vegetative growth. Analysis of the photographs shows that most of the temporal and spatial variation in the canopy's interception could be accounted for by treating the row as an array of solid parallel walls with rectangular cross sections. Within the space occupied by rows, the effect of the distribution of foliage elements on interception could be assessed by the porosity of a single row. The north‐south asymmetry observed in the distribution of ray interception indicates that this sorghum canopy, grown under unirrigated, arid summer conditions, adopted a light‐avoiding growth pattern.