A Statistical Study of Several Methods used in Determining the Botanical Composition of a Sward: I. A Study of Established Pastures<sup>1</sup>

VanKeuren, R. W.; Ahlgren, H. L.

doi:10.2134/agronj1957.00021962004900100004x

Cited by 9 publications

(11 citation statements)

References 3 publications

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“…Some support for this expectation is given by the observations of VanKeuren and Ahlgren (1957), who found that percentage contribution (dry matter basis) was in general more highly correlated with inclined than with vertical point quadrat estimates.…”

Section: Introductionmentioning

confidence: 88%

Inclined Point Quadrats

1960

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With 5 figures in the text) SUMMARY 'Relative frequency' recorded by point quadrats measures not the actual area of foliage but the area projected in the direction in which the quadrat lies. Accordingly the relative frequency varies both with the slope of the foliage and also -when inclined quadrats are used -with the inclination of the quadrat. A theoretical study reveals that variation in relative frequency resulting from difi^erences in foliage angle is greatest for vertical quadrats, is considerably reduced when (as suggested by Tinney, Aamodt and Ahlgren) quadrats are inclined at 45°, and is least when quadrat inclination is 32.5°. Accordingly the usual, vertical position for point quadrats is the worst possible one, since it results in the most erroneous estimates of percentage contribution (area basis); while with quadrats inclined at 32.5° errors are greatly reduced and are of an order acceptable in general survey work.

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Section: Introductionmentioning

confidence: 88%

Inclined Point Quadrats

1960

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“…However, determining the legume content in a grass–legume pasture directly is difficult due to the heterogeneity of the distribution. A number of indirect methods for estimating legume content of grass–legume mixtures have been developed, such as visual estimation (Marten 1964), point quadrat method (Vankeuren and Ahlgren 1957), and the dry‐weight rank method (Mannetje and Haydock 1963). However, accuracy of visual estimation depends on the experience of the observer, and hand‐separation of samples to estimate the legume content is time‐consuming (Shibayama 2003).…”

Section: Introductionmentioning

confidence: 99%

Waveband selection using a phased regression with a bootstrap procedure for estimating legume content in a mixed sown pasture

et al. 2011

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Legume content in grass–legume mixtures is a key parameter for deciding the forage quality and the amount of fertilizer application to the pasture due to nitrogen (N) fixation. To estimate legume content in a grass‐white clover (WC) mixed pasture in Hokkaido, we searched for robust hyperspectral wavebands from in situ canopy reflectance spectra over the 400–2350 nm range comparing a phased regression with a bootstrap procedure (PHR‐BS) (Ferwerda et al. 2006) and forward stepwise multiple linear regression (FS‐MLR). Canopy reflectance data and plant samples were obtained from 50 selected sites during two seasons (n = 100); spring (May) and summer (July) 2007. Although selected wavebands were similar in the PHR‐BS and FS‐MLR, PHR‐BS gave a higher predictive accuracy (44–74%) than FS‐MLR (35–73%). Selected wavebands in the final models were blue (400–456 nm) and red bands (659–670 nm) in visible wavelength, red‐edge region (704–724 nm), near infrared regions (813, 937, and 1121 nm), and shortwave infrared regions (2303–2344 nm) that are mainly linked to known biochemical components such as chlorophyll, N, lignin and cellulose. These results suggest that legume content in grass–legume mixtures can be predicted by in situ canopy reflectance, and that the predictive ability of the model can be improved by wavelength selection using the PHR‐BS method.

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“…Charpentier & Saarela (1941) e Crocker & Tiver (1948 afirmaram não haver correlação entre os dados obtidos com o método de pontos e o peso seco. Outros autores também não obtiveram essa relação e propuseram o uso de fatores de correção, passíveis de serem usados com a porcentagem de contribuição na composição ou com a porcentagem de cobertura (Arny & Schid, 1942;Amy, 1944;Hanson, 1950a;Hughes, 1962;Van Keuren & Ahlgren, 1957). Esses fatores devem variar conforme as espécies, período do ano e o desenvolvimento da vegetação, como salientou Amy (1944), para quem o peso seco por toque, obtido na análise de uma pastagem mista, foi maior para a alfafa do que para as gramíneas e elevou-se com o aumento da altura da vegetação .…”

Section: Os Resultados Obtidos Com O Emprego Do Método De Agulhas Incunclassified

O método de pontos

Mantovani

Martins

1990

Acta Bot. Bras.

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RESUMO -O método de pontos foi usado em diversas situações, comparado com outros métodos , modificado e amplamente discutido e criticado , podendo-se ter através da revisão bibliográfica uma visão de suas vantagens e limitações, salientando-se naquelas a sua rapidez, precisão e pouca perturbação causada na vegetação e nestas, o diâmetro da agulha e a ação do vento. Neste trabalho está sendo introdu zido e discutido um novo índice, denominado ín-dice de cobertura (lC) , obtido da soma dos valores absolutos de freqüência, que representa a cobertura e de vigor. associado à biomassa.Palavras-chave: fitossociologia, método de pontos.ABSTRACT -The point method has been utilized in many situations, with or without modifications: it has also been compared to other methods and critically discussed. A review of the literature reveals the advantages (speed precision, minimum disturbance of the stand) and disadvantages (dependence on diameter of the needle , wind action) . A new index is introduced and discussed. It is referred to as the cover index (CI) and is obtained by summing absolute frequency , which represents cover, and absolute vigor, which is associated with biomass.

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A Statistical Study of Several Methods used in Determining the Botanical Composition of a Sward: I. A Study of Established Pastures¹

Cited by 9 publications

References 3 publications

Inclined Point Quadrats

Inclined Point Quadrats

Waveband selection using a phased regression with a bootstrap procedure for estimating legume content in a mixed sown pasture

O método de pontos

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A Statistical Study of Several Methods used in Determining the Botanical Composition of a Sward: I. A Study of Established Pastures1

Cited by 9 publications

References 3 publications

Inclined Point Quadrats

Inclined Point Quadrats

Waveband selection using a phased regression with a bootstrap procedure for estimating legume content in a mixed sown pasture

O método de pontos

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A Statistical Study of Several Methods used in Determining the Botanical Composition of a Sward: I. A Study of Established Pastures¹