Errors resulting from thickness of point quadrats

1963 ◽  
Vol 11 (2) ◽  
pp. 178 ◽  
Author(s):  
JW Wilson
Keyword(s):  
Leaf Area ◽  
Relative Frequency ◽  
Theoretical Study ◽  
Sufficient Accuracy ◽  
Correction Factors ◽  
Resultant Error ◽  
Point Quadrat

When the needles used for point quadrat analyses have appreciable thickness, this causes overestimation of leaf area. A theoretical study, supported by practical trials, shows that the resultant error in estimates of "relative frequency" doubles with a doubling of quadrat diameter or a halving of leaf breadth. With the point quadrat techniques that have been in normal use the errors often exceed 50% and the estimates obtained are usually less accurate than visual estimates. However, results of sufficient accuracy for rough work can be obtained by using a narrow quadrat needle and applying correction factors; and errors can be altogether avoided by recording contacts with the sharpened point, but not the sides, of a needle gradually lowered through the vegetation.

scholarly journals Measurement of grapevine canopy leaf area by using an ultrasonic-based method

OENO One ◽  
2013 ◽  
Vol 47 (3) ◽  
pp. 183 ◽  
Author(s):  
Marco Vitali ◽  
Mario Tamagnone ◽  
Tiziana La Iacona ◽  
Claudio Lovisolo
Keyword(s):  
Leaf Area ◽  
Large Scale ◽  
Irrigation Management ◽  
Management Training ◽  
Ultrasonic Sensors ◽  
Leaf Sample ◽  
Area Index ◽  
Canopy Area ◽  
Point Quadrat ◽  
Leaf Canopy

<p style="text-align: justify;"><strong>Aim</strong>: Measurement of leaf area in grapevine has always been a critical point in researches focused on irrigation management, training systems, source-sink interrelationships and efficiency of spray application to canopies. In this work, we propose the use of ultrasonic sensors as a fast and accurate tool for the estimation of large portions of leaf canopy area.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Through outputs of ultrasonic sensors installed on a tractor moving along vineyard rows, we calculated an ultrasonic-based leaf density index that we correlated with three measurements or estimates of canopy area: I) direct measurement of the area of a canopy portion (LAØ), assessed by summing the areas of all the leaves, where each single-leaf area was assessed by regressing the leaf diameter (the maximum width perpendicular to the main rip) against the related leaf area calculated on the basis of a relation between the leaf diameter and the leaf area, previously assessed through an area meter on a 20-leaf sample; II) the point quadrat output (LApq); and III) the canopy leaf area index (LAI) obtained through LAI-2000 (Li-Cor) technology. The measurements were assessed on six cultivars in three replicate rows (8-12 plants per cultivar per row) in a vineyard trained to a vertical trellis system.</p><p style="text-align: justify;"><strong>Conclusion</strong>: When we correlated the three independent control parameters with each other, we obtained highly significant correlations between LApq and LAØ, but less significant correlations between these two and LAI-2000 outputs. Also, the correlations between ultrasonic outputsoutputs and LAØ and LApq were significant, with R2 ranging between 0.84 and 0.85. On the contrary, no significant correlation was found between ultrasonic outputs and LAI-2000 outputs. These results were obtained by averaging all the values belonging to each replicated cultivar (10.5 m along the row, i.e., twelve contiguous vines); on the contrary, when the analysis was done over a shorter distance (3.5 m, i.e., four contiguous vines), the reliability of the ultrasonic-based method decreased.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: These results point to the ultrasonic technology as a powerful tool to estimate large-scale leaf canopy area, with potential applications in precision farming. At the moment, however, the limitation of this approach is the requirement of reference values for leaf area (e.g., assessed by point quadrat) to obtain absolute and not only relative outputs. With this application we can quantify, in a few hours, the canopy of a whole vineyard, in order to analyze different vegetation zones or to follow canopy development.</p>

Divergence-slit intensity corrections for Bragg–Brentano diffractometers with circular sample surfaces and known beam intensity distribution

2004 ◽  
Vol 37 (3) ◽  
pp. 472-476 ◽  
Author(s):  
H. Krüger ◽  
R. X. Fischer
Keyword(s):  
Intensity Distribution ◽  
Sample Surface ◽  
Sufficient Accuracy ◽  
Beam Intensity ◽  
Correction Factors ◽  
A Value

Bragg–Brentano powder diffractometers equipped with fixed-divergence slits show a loss of intensity at small 2θ angles as a result of the overflow of the beam exceeding the sample surface. To correct this effect, geometrically derived algorithms are presented to calculate correction factors for circular sample surfaces. It is shown that the algorithms for rectangular samples can be applied to circular samples with sufficient accuracy if the value for the length of the sample is replaced by a value intermediate between the diameter of the circular sample and the length of the corresponding rectangular sample. Inhomogeneous beam intensity distribution also has serious effects on the correction factors, especially for wide divergence-slit apertures.

Effect of residual leaf area index on spatial components of Tifton 85 pastures and ingestive behaviour of sheep

2017 ◽  
Vol 57 (5) ◽  
pp. 903 ◽  
Author(s):  
W. L. Silva ◽  
J. P. R. Costa ◽  
G. P. Caputti ◽  
A. L. S. Valente ◽  
D. Tsuzukibashi ◽  
...  
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Rainy Season ◽  
Structural Characteristics ◽  
Light Interception ◽  
Dry Season ◽  
Area Index ◽  
Dead Material ◽  
Point Quadrat ◽  
Ingestive Behaviour

This study compared the effect of residual leaf area index (rLAI) on the spatial distribution of morphological components of Tifton 85 (Cynodon spp.) pastures and the ingestive behaviour of grazing sheep. Also, it was investigated whether any specific correlation could be found between pasture structural characteristics and sheep ingestive behaviour. Four rLAI treatments (0.8; 1.4; 2.0 and 2.6) with four replications were evaluated per period. Sheep grazed under rotational stocking management and they grazed for 4 days in each pasture while pasture regrowth period was determined by the 95% light interception requirement. Pasture structure was evaluated using inclined point-quadrat, LAI estimates, light interception and leaf : stem ratio. The 2.6 rLAI yielded the highest proportion of dead material in the lower canopy. In the post-grazing period the proportion of leaves increased with increasing rLAI, especially on the canopy surface during the rainy season. In the pre-grazing average pasture height ranged between 19 and 26 cm with dead material and stem observed up to the canopy surface in the dry season. The animals grazed longer on the last day (89.72%) compared with the first day (80.25%) in the dry season. However, they spent less time (11.45%) ruminating in the dry season compared with the rainy season (15.38%), regardless of the grazing day. Grazing time decreased and rumination time increased as rLAI increased. Sheep grazing time correlated negatively with pasture height, before and after grazing. The sheep tend to graze longer on Tifton 85 pastures when rLAI was lower and forage supply was possibly less as on the last grazing day and in the dry season.

Laser point-quadrat sampling for estimating foliage-height profiles in broad-leaved forests

2001 ◽  
Vol 31 (3) ◽  
pp. 410-418 ◽  
Author(s):  
Philip J Radtke ◽  
Paul V Bolstad
Keyword(s):  
North Carolina ◽  
Leaf Area ◽  
Field Studies ◽  
Area Index ◽  
Quadrat Sampling ◽  
Range Finding ◽  
The North ◽  
Broad Leaved Forest ◽  
Western North Carolina ◽  
Point Quadrat

A technique for estimating the vertical distribution of foliage area in broad-leaved forests was developed. The technique is similar to optical point-quadrat sampling, where estimates are based on heights to the lowest leaves above numerous sample locations beneath a canopy. In optical point-quadrat sampling, heights to lowest leaves are measured with a telephoto lens. Here, heights were measured using a commercially available laser range-finding instrument. The laser point-quadrat technique was tested in field studies conducted under broad-leaved forest canopies in western North Carolina and east-central Minnesota, U.S.A. Foliage-height profiles obtained by laser point-quadrat sampling were consistent with two of four published foliage-height profiles observed in 1995 at the North Carolina field locations. Total leaf area estimates obtained by laser point quadrats were not significantly correlated with values of leaf area index estimated by recent litter fall analyses at the North Carolina and Minnesota field locations. Although further evaluation and refinement of the technique is needed, laser point-quadrat sampling shows promise as a means of obtaining foliage-height profiles at a significantly reduced effort and with greater accuracy than methods commonly in use today.

Zur Eliminierung des Einflusses von Zellgruppen bei der Ermittlung der Inaktivierungsrate für Einzelzellen

1957 ◽  
Vol 12 (8-9) ◽  
pp. 542-546 ◽  
Author(s):  
Werner Stein ◽  
Wolfgang Laskowski
Keyword(s):  
Survival Rate ◽  
Relative Frequency ◽  
Single Cells ◽  
Characteristic Number ◽  
Sufficient Accuracy ◽  
Numerical Examples ◽  
Cell Groups

If one uses as criterium of inactivation of microorganisms the inability to form macrocolonies and if the culture under investigation is a mixture of single cells and cell groups the problem arises to determine from the survival rate Ü of the mixture the rate ü1 of single cells. The frequently used formula (hn is the relative frequency of the cell groups with n cells) may be replaced with sufficient accuracy by the formula for the correction of where . Thus the possibility is given to express a given distribution hn by a single characteristic number E . The validity of this approximation is discussed by numerical examples and in general.

scholarly journals Germination potential of Hymenaea courbaril L. in different maturation stages

2021 ◽  
Vol 42 (6supl2) ◽  
pp. 3667-3684
Author(s):  
Hugo Roldi Guariz ◽  
◽  
Halley Caixeta de Oliveira ◽  
Huezer Viganô Sperandio ◽  
Jean Carlo Baudraz de Paula ◽  
...  
Keyword(s):  
Leaf Area ◽  
Relative Frequency ◽  
Germination Rate ◽  
Germination Percentage ◽  
Seedling Production ◽  
Hymenaea Courbaril ◽  
Germination Time ◽  
Germination Potential ◽  
The Matrix ◽  
Maturation Stages

The production of quality forest seedlings in large quantities is essential for the restoration of environments that have been deforested and degraded. However, obtaining seeds with high vigor is a challenge for several tree species native to Brazil. The objective of this work was to verify the germination potential of jatobá-da-mata seeds at different stages of maturation, in order to favor the production of seedlings of this species in nurseries. The seeds were extracted from green and ripe fruits detached from the mother plant and ripe fruits collected from the ground. The germination percentage, average germination time, emergence speed index, average speed, relative frequency, leaf area of the seedling, and length of the aerial part and root were measured. The planting was carried out with mechanically scarified and intact seeds from each maturation group. The results indicated that non-scarified green seeds can be used for planting and seedling production, as they do not require pre-germination treatment and have a favorable germination percentage (79%). Fruit seeds harvested from the ground, on the other hand, needed a method to overcome integumentary dormancy, such as mechanical scarification, obtaining a germination rate of 85%. The seeds of ripe fruits harvested in the matrix showed greater vigor, with a higher percentage of germination (96 to 100%), a higher emergence speed index, shorter average germination time, and seedlings with greater leaf area and greater length of shoot.

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