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Carlos Campillo, M.I. García, C. Daza and M.H. Prieto

the plant in the biomass ( Gifford et al., 1984 ). One estimate of a crop's ability to capture light energy is the leaf area index (LAI). The concept of the LAI was first introduced by Watson (1947) and defined as the ratio of leaf area to a given

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Wayne F. Whitehead and Bharat P. Singh

The effect of in-row plant densities on gas exchange, chlorophyll content and leaf area index of okra (Abelmoschus esculentus (L.) Moench) was studied. The six in-row plant densities ranged from 8 cm to 48 cm (D1 - D6). On 11 and 27 July 1990, the photosynthetically active radiation (PAR), transpiration (E), net photosynthesis (Pn) and chlorophyll content (Chl) at top- and mid-canopy levels and leaf area index (LAI) were measured. Mid-canopy PAR was 86 ± 6% less than that of the top-canopy and E, Pn and Chl at mid-canopy were respectively 55, 90 and 10% lower than those of the top-canopy. The interaction of plant density with canopy position was significant for E and Pn. The highest E and Pn, (12.28 mmol m-2 s-1 and 22.01 μmol CO2 m-2 s-1, respectively) were recorded at the D5 top-canopy. In-contrast, the lowest E and Pn, (4.17 mmol m-2 s-l and 1.23 μmol CO2 m-2 s-1, respectively) at the D6 mid-canopy were recorded. The LAI also exhibited significant variation among plant densities with a range of 4.65 to 4.97 for D5 and D3, respectively. These results indicate that 40 cm in-row density was the most suited for gas exchange of okra.

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David A. Grantz and Larry E. Williams

Leaf area development and canopy structure are important characteristics affecting yield and fruit quality of grapevines. Trellising systems and wide row spacing are common viticultural practices that violate key assumptions of currently available indirect methods of leaf area determination. We have developed a protocol for using a commercially available instrument to determine leaf area index (LAI) indirectly in a trellised vineyard. From knowledge of plant spacing, leaf area per vine can be calculated as required. A derived calibration equation resulted in a near 1:1 relationship (y = 0.00 + 1.00 X; r2 = 0.998) between actual and indirectly determined LAI over a range of LAI induced by irrigation treatments. The protocol involved covering 75% of the sensor with a manufacturer-supplied field of view delimiter and masking data from the outer three (of five) concentric radiation sensors. The protocol could form the basis for a general measurement technique, but may require local calibration.

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Lee F. Johnson and Lars L. Pierce

The performance of the LI-COR LAI-2000 Plant Canopy Analyzer (PCA) for indirect measurement of leaf area index (LAI) was evaluated in vineyards of California's North Coast region. Twelve plots were established, representing vineyards of differing trellis, cultivar, and planting density. Mean LAI ranged from 0.5- to 2.25-m2 leaf area per m2 ground area by direct measurement (defoliation). Indirect LAI derived by a standard two-azimuth, diagonal-transect measurement protocol was significantly related to direct LAI (r2 = 0.78, P ≤ 0.001). However, the PCA underestimated direct LAI by about a factor of two. Narrowing the instrument's conical field of view from 148° to 56° increased indirect LAI by 13% to 60% in vertically trained plots, but still resulted in substantial underestimation of direct values. Use of this PCA protocol in vineyards should therefore be accompanied by direct measurement for calibration purposes.

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Libertad Mascarini, Gabriel A. Lorenzo and Fernando Vilella

In roses (Rosa ×hybrida L.), the bending of branches is a technique that modifies the canopy of the plant and could affect such parameters as the leaf area index (LAI), the quality of reflected light, and the water index (WI) of the plant. The measurement of spectral reflectance with remote sensors is a nondestructive, quick, and simple method to study these parameters. The aim of this paper is to quantify the modification of reflected radiation quality, the LAI and the water index of the plant with different canopies, and its impact on flowering and the number and quality of flowers produced. In R. ×hybrida `Terracotta', using the spectral crop reflectance, the red: far red ratio [red (R) = 680 nm; far red (FR) = 730 nm], percentage of blue light of reflected radiation, and vegetation indices [normalized difference vegetation index (NDVI), simple ratio index (SRI), water index (WI)] were calculated in two architectural managements: traditional (upright hedge) and bent shoot. NDVI had a greater correlation with LAI than SRI (r2 = 0.98 and 0.85, respectively), but SRI was more reliable for LAI values of 1 to 3.5. The bent shoot system compared to the traditional one decreased the R:FR ratio of reflected radiation and increased LAI and plant water content. These changes were related to a higher commercial quality of the flowers (longer flowering shoots with a larger stem diameter and fresh weight), although there was no significant difference in the number of flowers harvested. The period that showed the largest difference in the quality of the flower using the bent shoot system had a LAI of 2.8 vs. 1.8 with traditional management and a marked reduction in the R:FR of the light reflected by bent plants. The bent shoot system advanced the peak production by 1 month at the end of winter and improved the flowers at a time when sun radiation is limiting factor for production.

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W.F. Whitehead and B.P. Singh

A 2-year field study was conducted to determine the effects of within-row spacing (WRS) on CO2 exchange rate (CER), leaf-area index (LAI), and yield of okra [Abelmoschus esculentus (L.) Moench]. Okra cultivar Clemson Spineless was seeded at WRS of 8, 16, 24, 32, 40, and 48 cm in a randomized complete-block design replicated three times. CER and LAI were measured five times at about biweekly intervals between first flowering and final harvest. Fruits were harvested three times weekly for 7 weeks. There was no year-to-year variation in CER or LAI. Plants at 8 cm WRS attained maximum CER by 56 days after planting (DAP), while all other spacings took longer. CER at all WRS declined after 85 DAP. In 8 and 16 cm WRS, maximum LAI developed by 56 DAP, but 69 DAP were required at all other spacing. Depending on the spacing, LAI regressed linearly or cubically on DAP. Fruit number/plant (FNP), fruit fresh and dry weight/plant (FFW and FDW), and fresh and dry fruit yield/ha (FFY and DFY) were greater in 1991 than in 1990 as a result of more favorable weather during 1991. There was a linear increase in FNP, FFW, and FDW as WRS increased. Conversely, FFY and DFY were highest at 8 cm and decreased linearly in 1990 and quadratically in 1991 as WRS increased. Results of this study suggest that okra plants reach maximum CER and LAI earlier and produce higher fruit yield per unit area when spaced close together in the row.

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Wayne F. Whitehead and Bharat P. Singh

During the 2004–05 growing season, a study was conducted to determine effect of cover crop, their mixture and fertilizer N rates on above ground biomass (AGB) yields, and Leaf Area Index (LAI) of Bt sweet corn. The following cover crop nitrogen fertility treatments were applied using randomized complete-block design with three replications: 1) fall-0 N, fallow; spring-0 N, 2) fall-0 N, abruzzi rye; spring-0 N, 3) fall-0 N, hairy vetch; spring-0 N, 4) fall-0 N, abruzzi rye+hairy vetch; spring-0 N, 5) fall-0 N, fallow; spring-101 kg N/ha, 6) fall-0 N, abruzzi rye; spring-101 kg N/ha, 7) fall-0 N, hairy vetch; spring-101 kg N/ha, 8) fall-0 N, abruzzi rye+hairy vetch; spring-101 kg N/ha, 9) fall-0 N, fallow; spring-202 kg N/ha, 10) fall-0 N, abruzzi rye; spring-202 kg N/ha, 11) fall-0 N, hairy vetch; spring-202 kg N/ha, and 12) fall-0 N, abruzzi rye+hairy vetch; spring-202 kg N/ha. In Spring 2005, `Attribute BSS0977' bi-color (BC) supersweet (sh2) corn seeds were field planted. AGB yields were collected during harvest week while LAI was recorded at tasseling (6/27), silking (7/8) and one week after harvest (7/25). Hairy vetch; spring-101 kg N/ha produced highest LAI at tasseling (2.18), silking (2.73), and one week after harvest (2.57). Lowest LAI at tasseling (1.12) and silking(1.60) were produced by abruzzi rye; spring-0 N with fallow; spring-0 N producing lowest LAI (1.40) one week after harvest. Maximum AGB fresh (40.5 Mg/ha) and dry weight (12.1 Mg/ha) yields were produced by hairy vetch; spring-101kg N/ha, while minimum AGB fresh (9.6 Mg/ha) and dry weight (3.6 Mg/ha) yields were produced by abruzzi rye; spring-0 N. Results imply LAI at each growth stage and AGB yields of this BCsh2 corn variety are best supported by hairy vetch supplemented with N at 101 kg/ha.

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Ioannis Tsirogiannis, Nikolaos Katsoulas and Constantinos Kittas

reflection. Canopy radiation reflectance is mainly affected by crop leaf reflectance behavior, but also by the nonuniformity of incident solar radiation, by the plant structure, the leaf area index, possible shadows, and background reflectance ( Thenot et al

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Angela Knerl, Brendon Anthony, Sara Serra and Stefano Musacchi

As the Pacific Northwest fruit industry shifts to precision-based management strategies for their orchards, tools are needed to understand tree physiology in the orchard to optimize fruit quality. Leaf area index is the ratio between the summed area

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Jose G. Franco, Stephen R. King, Joseph G. Masabni and Astrid Volder

measurement dates. Little change in LAI between 43 and 63 DALP also indicates that the canopy had almost reached full maturity at 43 DALP. Fig. 6. Leaf area index [leaf area index (square meters leaf area per square meter soil surface)] of monoculture controls