scholarly journals Estimation of LAI in Winter Wheat from Multi-Angular Hyperspectral VNIR Data: Effects of View Angles and Plant Architecture

2018 ◽  
Vol 10 (10) ◽  
pp. 1630 ◽  
Author(s):  
Hanyue Chen ◽  
Wenjiang Huang ◽  
Wang Li ◽  
Zheng Niu ◽  
Liming Zhang ◽  
...  
Keyword(s):  
Winter Wheat ◽  
Zenith Angle ◽  
Plant Architecture ◽  
Broad Band ◽  
Forward Scattering ◽  
Crop Canopy ◽  
Plant Type ◽  
Area Index ◽  
View Zenith Angle ◽  
Band Combinations

View angle effects present in crop canopy spectra are critical for the retrieval of the crop canopy leaf area index (LAI). In the past, the angular effects on spectral vegetation indices (VIs) for estimating LAI, especially in crops with different plant architectures, have not been carefully assessed. In this study, we assessed the effects of the view zenith angle (VZA) on relationships between the spectral VIs and LAI. We measured the multi-angular hyperspectral reflectance and LAI of two cultivars of winter wheat, erectophile (W411) and planophile (W9507), across different growing seasons. The reflectance of each angle was used to calculate a variety of VIs that have already been published in the literature as well as all possible band combinations of Normalized Difference Spectral Indices (NDSIs). The above indices, along with the raw reflectance of representative bands, were evaluated with measured LAI across the view zenith angle for each cultivar of winter wheat. Data analysis was also supported by the use of the PROSAIL (PROSPECT + SAIL) model to simulate a range of bidirectional reflectance. The study confirmed that the strength of linear relationships between different spectral VIs and LAI did express different angular responses depending on plant type. LAI–VI correlations were generally stronger in erectophile than in planophile wheat types, especially at the zenith angle where the background is expected to be more evident for erectophile type wheat. The band combinations and formulas of the indices also played a role in shaping the angular signatures of the LAI–VI correlations. Overall, off-nadir angles served better than nadir angle and narrow-band indices, especially NDSIs with combinations of a red-edge (700~720 nm) and a green band, were more useful for LAI estimation than broad-band indices for both types of winter wheat. But the optimal angles much differed between two plant types and among various VIs. High significance (R2 > 0.9) could be obtained by selecting appropriate VIs and view angles on both the backward and forward scattering direction. These results from the in-situ measurements were also corroborated by the simulation analysis using the PROSAIL model. For the measured datasets, the highest coefficient was obtained by NDSI(536,720) at −35° in the backward (R2 = 0.971) and NDSI(571,707) at 55° in the forward scattering direction (R2 = 0.984) for the planophile and erectophile varieties, respectively. This work highlights the influence of view geometry and plant architecture. The identification of crop plant type is highly recommended before using remote sensing VIs for the large-scale mapping of vegetation biophysical variables.

Estimation of radiation interception by winter wheat from measurements of leaf area

1988 ◽  
Vol 110 (1) ◽  
pp. 101-108 ◽  
Author(s):  
G. N. Thorne ◽  
I. Pearman ◽  
W. Day ◽  
A. D. Todd
Keyword(s):  
Winter Wheat ◽  
Flag Leaf ◽  
Ground Cover ◽  
Mean Value ◽  
Crop Canopy ◽  
Projected Area ◽  
Senescent Leaf ◽  
Area Index ◽  
The Mean ◽  
Experimental Treatments

SummaryThe percentage (P) of incident photosynthetically active radiation (PAR) reaching the ground was measured in winter wheat crops throughout the season, and related to projected area index (L) of leaves, plus sheaths and stems when present. Between unfolding of the first leaf and appearance of the flag leaf the mean value for the exponential extinction coefficient (K) was 0·46±0·007. The value did not vary with the growth stage of the wheat and was scarcely affected by experimental treatments, apart from effects resulting from the presence of senescent tissues that intercepted light but whose area was not included in L. After anthesis, in crops having between 340 and 540 ears/m2, between 68 and 89% of incident PAR penetrated to below the ears. Relation between the further penetration to the base of the crop canopy and the area of green plus senescent leaf and stem tissue gave K = 0·50. The relation did not change significantly between anthesis and complete senescence.The relation between P and L was similar whether P was obtained from instantaneous measurements made near midday, 24 h integrals of PAR or percentage ground cover measured photographically.

Adaptation of winter cereal species to shade and competition in a winter/spring cereal forage mixture

1996 ◽  
Vol 76 (2) ◽  
pp. 251-257 ◽  
Author(s):  
V. S. Baron ◽  
E. A. de St Remy ◽  
D. F. Salmon ◽  
A. C. Dick
Keyword(s):  
Winter Wheat ◽  
Dark Respiration ◽  
Dominant Factor ◽  
Carbon Exchange ◽  
Area Index ◽  
Winter Cereal ◽  
Winter Triticale ◽  
Winter Cereals ◽  
Cereal Species ◽  
Shoot Weight

Spring planted mixtures of spring and winter cereals maximize dry matter yield and provide fall pasture by regrowth of the winter cereal. However, delay of initial harvest may reduce the winter cereal component and therefore subsequent regrowth yield. Research was conducted at Lacombe, Alberta to investigate the effect of time of initial cut (stage), winter cereal species (species) and cropping system (monocrop and mixture) on winter cereal shoot weight, leaf carbon exchange efficiency and shoot morphology. These parameters may be related to adaptation of winter cereals to growth and survival in the mixture. Winter cereal plants were grown in pails embedded in monocrop plots of fall rye (Secale cereale L.), winter triticale (X Triticosecale Wittmack) and winter wheat (Triticum aestivum L.) and in binary mixtures with Leduc barley (Hordeum vulgare L.). The plants were removed when the barley reached the boot (B), heads emerged (H), H + 2, H + 4 and H + 6 wk stages. Shoot weight was generally smaller in the mixture than in the monocrop and wheat was reduced more than fall rye and triticale in the mixture compared to the monocrop. Dark respiration rate (r = −0.54) and carbon exchange (r = 0.36) under low light intensity were correlated (P < 0.05) to shoot size in the mixture. Fall rye and winter triticale had lower dark respiration rates than winter wheat. Leaf area index (LAI) was closely correlated (r = 0.83 and 0.84) with shoot weight in both the mixture and monocrop. While species failed to exhibit clear cut differences for LAI, fall rye and winter triticale were reduced less than winter wheat in the mixture relative to the monocrop. Stage was the dominant factor affecting winter cereal growth in both cropping systems, but fall rye and triticale exhibited superior morphological features, and their carbon exchange responses to light were more efficient than wheat, which should allow them to be sustained longer under the shaded conditions of a mixture. Key words: Delayed harvest, shade, spring and winter cereal mixtures, adaptation, carbon exchange, respiration

scholarly journals Representing winter wheat in the Community Land Model (version 4.5)

2017 ◽  
Vol 10 (5) ◽  
pp. 1873-1888 ◽  
Author(s):  
Yaqiong Lu ◽  
Ian N. Williams ◽  
Justin E. Bagley ◽  
Margaret S. Torn ◽  
Lara M. Kueppers
Keyword(s):  
Heat Flux ◽  
Winter Wheat ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Latent Heat Flux ◽  
Carbon Allocation ◽  
Net Ecosystem Exchange ◽  
Area Index ◽  
Community Land Model ◽  
The Us

Abstract. Winter wheat is a staple crop for global food security, and is the dominant vegetation cover for a significant fraction of Earth's croplands. As such, it plays an important role in carbon cycling and land–atmosphere interactions in these key regions. Accurate simulation of winter wheat growth is not only crucial for future yield prediction under a changing climate, but also for accurately predicting the energy and water cycles for winter wheat dominated regions. We modified the winter wheat model in the Community Land Model (CLM) to better simulate winter wheat leaf area index, latent heat flux, net ecosystem exchange of CO2, and grain yield. These included schemes to represent vernalization as well as frost tolerance and damage. We calibrated three key parameters (minimum planting temperature, maximum crop growth days, and initial value of leaf carbon allocation coefficient) and modified the grain carbon allocation algorithm for simulations at the US Southern Great Plains ARM site (US-ARM), and validated the model performance at eight additional sites across North America. We found that the new winter wheat model improved the prediction of monthly variation in leaf area index, reduced latent heat flux, and net ecosystem exchange root mean square error (RMSE) by 41 and 35 % during the spring growing season. The model accurately simulated the interannual variation in yield at the US-ARM site, but underestimated yield at sites and in regions (northwestern and southeastern US) with historically greater yields by 35 %.

Weed Seedling Emergence and Survival as Affected by Crop Canopy

2008 ◽  
Vol 22 (4) ◽  
pp. 736-740 ◽  
Author(s):  
Randy L. Anderson
Keyword(s):  
Winter Wheat ◽  
Seed Production ◽  
Spring Wheat ◽  
Seedling Emergence ◽  
Crop Canopy ◽  
Cool Season ◽  
Common Lambsquarters ◽  
Green Foxtail ◽  
Seedling Emergence And Survival ◽  
Weed Dynamics

This study measured impact of cool-season crops on seedling emergence, survival, and seed production of weeds common in corn and soybean. Weed dynamics were monitored in permanently marked quadrats in winter wheat, spring wheat, and canola. Three species, green foxtail, yellow foxtail, and common lambsquarters, comprised more than 80% of the weeds observed in the study. Seedling emergence was reduced by winter wheat, but not by spring wheat or canola, when compared with adjacent quadrats without a crop canopy. Approximately 10% of seedlings in spring wheat and canola developed into seed-bearing plants, but no seed-bearing plants were present in winter wheat at harvest. Common lambsquarters produced more than 1,100 seeds/plant, whereas a foxtail plant produced 85 seeds, averaged across spring wheat and canola. At harvest, new seedlings were present in all crops; thus, control after harvest will be required to prevent seed production in the fall. Winter wheat may provide an opportunity to disrupt population dynamics of weeds common in corn and soybean without requiring herbicides.

Spring top-dressings of ‘Nitro-Chalk’ and late sprays of a liquid N-fertilizer and a broad spectrum fungicide for consecutive crops of winter wheat at Saxmundham, Suffolk

1978 ◽  
Vol 90 (3) ◽  
pp. 509-516 ◽  
Author(s):  
A. Penny ◽  
F. V. Widdowson ◽  
J. F. Jenkyn
Keyword(s):  
Calcium Carbonate ◽  
Winter Wheat ◽  
Leaf Area Index ◽  
Ammonium Nitrate ◽  
Leaf Area ◽  
Broad Spectrum ◽  
N Fertilizer ◽  
N Content ◽  
Area Index ◽  
Liquid Fertilizer

SummaryAn experiment at Saxmundham, Suffolk, during 1974–6, tested late sprays of a liquid N-fertilizer (ammonium nitrate/urea) supplying 50 kg N/ha, and a broad spectrum fungicide (benomyl and maneb with mancozeb) on winter wheat given, 0, 50, 100 or 150 kg N/ha as ‘Nitro-Chalk’ (ammonium nitrate/calcium carbonate) in springMildew (Erysiphe graminisf. sp. tritici) was most severe in 1974. It was increased by N and decreased by the fungicide in both 1974 and 1975, but was negligible in 1976. Septoria (S. nodorum) was very slight in 1974 and none was observed in 1976. It was much more severe in 1975, but was unaffected by the fungicide perhaps because this was applied too late.Yield and N content, number of ears and leaf area index were determined during summer on samples taken from all plots given 100 or 150 kg N/ha in spring; each was larger with 150 than with 100 kg N/ha. The effects of the liquid N-fertilizer on yield and N content varied, but leaf area index was consistently increased. None was affected consistently by the fungicide.Yields, percentages of N in, and amounts of N removed by grain and straw were greatly and consistently increased by each increment of ‘Nitro-Chalk’. Yields of grain were increased (average, 9%) by the liquid fertilizer in 1974 and 1975, and most where most ‘Nitro-Chalk’ had been given, but not in 1976 when the wheat ripened in July; however, both the percentage of N in and the amount of N removed by the grain were increased by the liquid fertilizer each year. The fungicide increased the response to the liquid N-fertilizer in 1974, but not in 1975 when Septoria was not controlled, nor in 1976 when leaf diseases were virtually absent.The weight of 1000 grains was increased by each increment of ‘Nitro-Chalk’ in 1975 but only by the first one (50 kg N/ha) in 1974 and 1976; it was very slightly increased by the liquid fertilizer and by fungicide each year.

scholarly journals Growth and clorophyll content dynamics of winter wheat (Triticum aestivum L.) in different cropyear

2013 ◽  
pp. 101-105
Author(s):  
Enikő Vári
Keyword(s):  
Winter Wheat ◽  
Grain Filling ◽  
Triticum Aestivum L ◽  
Area Index ◽  
Rotation System ◽  
Crop Rotation System ◽  
Two Parameters ◽  
The University ◽  
The Relationship

The experiments were carried out at the Látókép experimental station of the University of Debrecen on chernozem soil in a long term winter wheat experiment in the season of 2011 and 2012 in triculture (pea-wheat-maize) and biculture (wheat-maize) at three fertilisation levels (control, N50+P35K40, N150+P105K120). Two different cropyears were compared (2011 and 2012). The research focused on the effects of forecrop and fertilisation on the Leaf Area Index, SPAD values and the amount of yield in two different cropyears. We wanted to find out how the examined parameters were affected by the cropyear and what the relationship was between these two parameters and the changes of the amount of yield. Examining the effects of growing doses of fertilizers applied, results showed that yields increased significantly in both rotations until the N150+PK level in 2011 and 2012. By comparing the two years, results show that in 2011 there was a greater difference in yields between the rotations (7742 kg ha-1 at N150+PK in the biculture and 9830 kg ha-1 at N150+PK in the triculture). Though wheat yields following peas were greater in 2012, results equalized later on at N150+PK levels (8109–8203 kg ha-1). Due to the favorable agrotechnical factors, the leaf and the effects of the treatments grown to a great extent in 2011, while in 2012 the differences between treatments were moderate. Until the N150+PK level, nitrogen fertilisation had a notable effect on the maximum amount of SPAD values (59.1 in the case of the biculture and 54.0 in the triculture). The highest SPAD values were measured at the end of May (during the time of flowering and grain filling) in the biculture. In the triculture, showed high SPAD values from the beginning. The same tendency could be observed in the 2012 cropyear, although increasing doses of fertilizers resulted in higher SPAD values until N150+PK level only from the second measurement. Maximum SPAD values were reached at the end of May in both crop rotation system

scholarly journals Influence of Different Satellite Imagery on the Analysis of Riparian Leaf Density in a Mountain Stream

2020 ◽  
Vol 12 (20) ◽  
pp. 3376 ◽  
Author(s):  
Giovanni Romano ◽  
Giovanni Francesco Ricci ◽  
Francesco Gentile
Keyword(s):  
Winter Wheat ◽  
Satellite Imagery ◽  
Vegetation Cover ◽  
Riparian Vegetation ◽  
Deciduous Forests ◽  
Sensor Data ◽  
Mountain Stream ◽  
Landsat 8 ◽  
Area Index ◽  
Sentinel 2

In recent decades, technological advancements in sensors have generated increasing interest in remote sensing data for the study of vegetation features. Image pixel resolution can affect data analysis and results. This study evaluated the potential of three satellite images of differing resolution (Landsat 8, 30 m; Sentinel-2, 10 m; and Pleiades 1A, 2 m) in assessing the Leaf Area Index (LAI) of riparian vegetation in two Mediterranean streams, and in both a winter wheat field and a deciduous forest used to compare the accuracy of the results. In this study, three different retrieval methods—the Caraux-Garson, the Lambert-Beer, and the Campbell and Norman equations—are used to estimate LAI from the Normalized Difference Vegetation Index (NDVI). To validate sensor data, LAI values were measured in the field using the LAI 2200 Plant Canopy Analyzer. The statistical indices showed a better performance for Pleiades 1A and Landsat 8 images, the former particularly in sites characterized by high canopy closure, such as deciduous forests, or in areas with stable riparian vegetation, the latter where stable reaches of riparian vegetation cover are almost absent or very homogenous, as in winter wheat fields. Sentinel-2 images provided more accurate results in terms of the range of LAI values. Considering the different types of satellite imagery, the Lambert-Beer equation generally performed best in estimating LAI from the NDVI, especially in areas that are geomorphologically stable or have a denser vegetation cover, such as deciduous forests.

scholarly journals Upscaling from Instantaneous to Daily Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) for Satellite Products

2020 ◽  
Vol 12 (13) ◽  
pp. 2083
Author(s):  
Siyuan Chen ◽  
Liangyun Liu ◽  
Xue He ◽  
Zhigang Liu ◽  
Dailiang Peng
Keyword(s):  
Zenith Angle ◽  
Photosynthetically Active Radiation ◽  
Solar Zenith Angle ◽  
Field Measurements ◽  
Area Index ◽  
Active Radiation ◽  
Sensing Applications ◽  
Typical Satellite ◽  
Absorbed Photosynthetically Active Radiation ◽  
Local Noon

The fraction of absorbed photosynthetically active radiation (FAPAR) is an essential climate variable (ECV) widely used for various ecological and climate models. However, all the current FAPAR satellite products correspond to instantaneous FAPAR values acquired at the satellite transit time only, which cannot represent the variations in photosynthetic processes over the diurnal period. Most studies have directly used the instantaneous FAPAR as a reasonable approximation of the daily integrated value. However, clearly, FAPAR varies a lot according to the weather conditions and amount of incoming radiation. In this paper, a temporal upscaling method based on the cosine of the solar zenith angle (SZA) at local noon ( c o s ( S Z A n o o n ) ) is proposed for converting instantaneous FAPAR to daily integrated FAPAR. First, the diurnal variations in FAPAR were investigated using PROSAIL (a model of Leaf Optical Properties Spectra (PROSPECT) integrating a canopy radiative transfer model (Scattering from Arbitrarily Inclined Leaves, SAIL)) simulations with different leaf area index (LAI) values corresponding to different latitudes. It was found that the instantaneous black sky FAPAR at 09:30 AM provided a good approximation for the daily integrated black sky FAPAR; this gave the highest correlation (R2 = 0.995) and lowest Root Mean Square Error (RMSE = 0.013) among the instantaneous black sky FAPAR values observed at different times. Secondly, the difference between the instantaneous black sky FAPAR values acquired at different times and the daily integrated black sky FAPAR was analyzed; this could be accurately modelled using the cosine value of solar zenith angle at local noon ( c o s ( S Z A n o o n ) ) for a given vegetation scene. Therefore, a temporal upscaling method for typical satellite products was proposed using a cos(SZA)-based upscaling model. Finally, the proposed cos(SZA)-based upscaling model was validated using both the PROSAIL simulated data and the field measurements. The validated results indicated that the upscaled daily black sky FAPAR was highly consistent with the daily integrated black sky FAPAR, giving very high mean R2 values (0.998, 0.972), low RMSEs (0.007, 0.014), and low rMAEs (0.596%, 1.378%) for the simulations and the field measurements, respectively. Consequently, the cos(SZA)-based method performs well for upscaling the instantaneous black sky FAPAR to its daily value, which is a simple but extremely important approach for satellite remote sensing applications related to FAPAR.

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