Accurate Estimates Of Leaf Area Index Research Articles

Indirect Measurement of Insect Defoliation

Leaf area index (LAI) after insect defoliation injury is closely related to yield, so measuring the LAI of defoliated plant canopies is of considerable importance. Unfortunately, direct measurement of LAI is laborious and time-consuming. This study was conducted to evaluate the LAI-2000, a commercially available instrument for rapidly and accurately measuring LAI of insect-defoliated soybeans, Glycine max (L.) Merr. The instrument’s indirect measurements of LAI were compared with direct measurement of LAI. Measurements were made in 2 fields, one with a50% defoliation and the other with a30% defoliation. The LAI range for direct measurement was 2.47–4.24. The instrument’s indirect LAI measurements exceeded the direct measurements, but by <15%. With respect to plant response to insect defoliation, an error rate of a15% is acceptable for most applied and research purposes. Additional comparison of LAI-2000 estimates to actual LAIs from 3 experiments revealed a linear relationship with a slope not significantly different from 1. Therefore, our work indicates the LAI-2000 provides accurate estimates of LAIs for insect defoliated soybeans, and would likely perform comparably in other crops.

An indirect method of estimating leaf area index in cordon trained spur pruned grapevines

The aim of this study was to validate an indirect method of estimating leaf area index (LAI) in cordon-trained spur-pruned grapevines. Indirect estimates were made using the LAI-2000 instrument, based on the principles of gap fraction theory. Results indicate that using an adjustment coefficient factor, this method could provide rapid and accurate estimates of LAI.

Leaf area index of boreal forests: Theory, techniques, and measurements

Leaf area index (LAI) is a key structural characteristic of forest ecosystems because of the role of green leaves in controlling many biological and physical processes in plant canopies. Accurate LAI estimates are required in studies of ecophysiology, atmosphere‐ecosystem interactions, and global change. The objective of this paper is to evaluate LAI values obtained by several research teams using different methods for a broad spectrum of boreal forest types in support of the international Boreal Ecosystem‐Atmosphere Study (BOREAS). These methods include destructive sampling and optical instruments: the tracing radiation and architecture of canopies (TRAC), the LAI‐2000 plant canopy analyzer, hemispherical photography, and the Sunfleck Ceptometer. The latter three calculate LAI from measured radiation transmittance (gap fraction) using inversion models that assume a random spatial distribution of leaves. It is shown that these instruments underestimate LAI of boreal forest stands where the foliage is clumped. The TRAC quantifies the clumping effect by measuring the canopy gap size distribution. For deciduous stands the clumping index measured from TRAC includes the clumping effect at all scales, but for conifer stands it only resolves the clumping effect at scales larger than the shoot (the basic collection of needles). To determine foliage clumping within conifer shoots, a video camera and rotational light table system was used. The major difficulties in determining the surface area of small conifer needles have been largely overcome by the use of an accurate volume displacement method. Hemispherical photography has the advantage that it also provides a permanent image record of the canopies. Typically, LAI falls in the range from 1 to 4 for jack pine and aspen forests and from 1 to 6 for black spruce. Our comparative studies provide the most comprehensive set of LAI estimates available for boreal forests and demonstrate that optical techniques, combined with limited direct foliage sampling, can be used to obtain quick and accurate LAI measurements.

Application of SORKAM to Simulate Shattercane Growth Using Forage Sorghum

AbstractShattercane [Sorghum bicolor (L.) Moench] is a serious weed problem. Few methods are available to assess the impact of shattercane competition on crop growth and yield. This study evaluated model sensitivity to variations in light, water, and plant density and assessed the applicability of the SORKAM model for simulating forage sorghum (used to represent shattercane) growth and development. Sensitivity analysis of SORKAM to photosynthetically active radiation (50, 75, and 100% of actual); water (50, 75, and 100% of actual precipitation, and no water stress); and plant densities of 3, 6, 12, 24, 48, and 96 plants m−2 was performed. ‘Rox Orange’ forage sorghum (used to represent shattercane) was grown at three densities, under irrigated and dryland environments over a 3‐yr period. Experiments were conducted on Eudora (coarse‐silty, mixed, mesic Fluventic Hapludoll) and Kahola silt loam (fine‐silty, mixed, mesic Cumulic Hapludoll) soils, in Manhattan, KS. The sensitivity analysis showed that SORKAM responded to a broad range of light, water, and plant density environments, with significant light by water interaction for biomass, and light by density interaction for biomass, leaf area index (LAI), and tillering. The SORKAM model simulated growth of Rox Orange from inputs of weather, soil, and plant data were compared with measured values. There was good agreement between simulated and measured LAI through 60 d after planting (r2 = 0.82, intercept not significantly different from 0, and slope = 0.83). Accurate estimation of LAI during this period of vegetative growth is important, because LAI determines the competition between a crop and shattercane for light and water. Agreement of measured and simulated biomass was good for low plant densities (slope and intercept not significantly different from 1 and 0 with high r2 = 0.78), with progressively greater underestimation at higher densities. Tiller number was generally underestimated, with no apparent correlation to model under‐ or overestimation of LAI or biomass. The sensitivity analysis and comparison of measured and simulated LAI indicates that the SORKAM model can be used to assess Rox Orange (shattercane) competition.

Non-destructive estimation of potato leaf area index using a fish-eye radiometer

Leaf area index (LAI) is widely used in many facets of potato (Solanum tuberosum L.) modelling but direct measurements have historically been difficult. This investigation tested the accuracy of a commercially available instrument (LI-COR LAI-2000) for measuring LAI non-destructively on a potato crop. Accurate estimates of LAI were difficult to obtain with small plots of≈1 m2. Results from larger field plots were extremely favourable and indicate that non-destructive measurements of LAI in situ can routinely be estimated within 5 to 10% of the destructively measured LAI. Six thinning tests performed on four potato cultivars produced average root mean square error measurements of LAI that ranged from 0.09 to 0.27.

Estimation of tree canopy leaf area index by gap fraction analysis

We estimated leaf area index (LAI) in a needle-leaved forest and a broad-leaved orchard using four instruments which measure fractional light penetration through the canopy. Gap fraction data were analyzed by a one-dimensional inversion model or by using the Beer-Lambert Law. Instrument and analytical technique both had a strong influence on calculated LAI. There was no consistent pattern of LAI results among instruments so no simple cross-calibration can be offered. Three of the four instruments accurately estimated orchard LAI when used with one or the other analytical technique. In addition to performance, practical considerations including cost, sampling, and data analysis were also compared among the instruments. Because the instruments do not provide consistently accurate LAI estimates, LAI should be independently corroborated before use in any particular situation. These instruments may be most useful for relative LAI comparisons in a specific canopy type when a single combination of instrument and analytical technique is employed.