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Light penetration measurements have not been possible in turfgrass environments due to the large size of commercial light bars relative to the low height of the turfgrass canopy. A light bar was designed and constructed for use in turfgrass canopies mowed as short as 1.3 cm. The instrument uses four miniature solar cells connected in parallel and mounted to a high density polyethylene (HDPE) bar measuring 3.5-mm wide, 6-mm tall, and 200-mm long. The constructed light bar was calibrated against a Li-Cor (Li-Cor, Lincoln, NE) pyranometer sensor and obtained a relationship of Y = [1.0293e.sup.16.039x] with an [R.sup.2] value of 0.96. Data demonstrate measured differences in light penetration through an annual ryegrass (Lolium multiflorum Lam.) canopy maintained at three mowing heights. Light penetration measured at the base of annual ryegrass canopies maintained at cutting heights of 3.2, 5.7. and 8.3 cm amounted to 5.36 to 7.48%, 1.21 to 3.43%, and 0.10 to 0.40%, of full sunlight, respectively. This device should allow researchers the ability to assess canopy light penetration in low-growing vegetation including turfgrasses. doi: 10.2135/cropsci2009.06.0359

Potted experiments of rice (Oryza sativa L.) plants were conducted to produce various scales of brown planthopper [Nilaparvata lugens (Stal), Homoptera:Delphacidae] and leaffolder [Cnaphalocrosis mediualis Guenee (Lep., Pyralidae)] infestations, respectively, for canopy hyperspectral reflectance measurements, and then to identify spectral characteristics (SCs) associated with insect infestations leading to the establishment of spectral models for severity assessment. By linear correlation intensity analysis, correlation coefficients (r) along the spectral domain of 350 to 2400 nm were determined and narrow bands related to infestation severity were selected as SCs. The reflectance at green light (490-560 nm) maximum ([R.sub.GREEN]), red light (640-740 nm) minimum ([R.sub.RED]), and near-infrared (740-1300 nm) peak ([R.sub.NIR]) were also considered. For canopies infested with brown planthopper, r value at 426 nm was the highest (r = 0.878 **). Among the calculated spectral indices using two SCs, the determination coefficient of [R.sub.NIR]/[R.sub.RED] ratio was the highest ([R.sup.2] = 0.922, P < 0.001). For leaffolder infested canopies, the most negative r value located at 757 nm (r =-0.613 *) in active tillering stage but shifted to 445 nm (r = -0.928 **) in heading stage. The index [R.sub.NIR]-[R.sub.RED] in the active tillering increased [R.sup.2] value to 0.422 (P < 0.001), while no increase in [R.sup.2] was found in the examined Sis in heading stage. Models with more than two SCs yielded from multiple linear regression analysis exhibited a further improvement for discriminating infestation severity.

Cotton (Gossypium hirsutum L.) genotypes exhibit variation in leaf types and leaf area index (LAI). The objective of this research was to characterize canop development and yield of two cotton leaf types grown in varying plant populatio densities. Field experiments were conducted in 1991, 1992, and 1993 with both the okra-leaf (low LAI) and normal-leaf (high LAI) isolines of 'DES 24-8ne' cotton with selected plant population densities (5, 10, and 15 plants [m.sup.-2]). Photosynthetic photon flux density (PPFD) interception (1991-1992) and LAI (1991-1993) were determined periodically and final lint yield was determined at maturity. Averaged across years, yields of okra-leaf in narrow rows were 6 to 7% greater at 10 and 15 plants [m.sup.-2] than at 5 plants [m.sup.-2]. In 1991 and 1992, early-season PPFD interception of okra-leaf at 10 and 15 plants [m.sup.-2] was greater than at 5 plants [m.sup.-2]. In 1992 and 1993, okra-leaf at 10 and 15 plants [m.sup.-2] attained an LAI of 4.0 to 4.5 whereas the 5 plants [m.sup.-2] density failed to reach 4.0. Therefore, both PPFD interception and LAI limited yield of okra-leaf at 5 plants [m.sup.-2]. In contrast to okra-leaf, lint yields of normal-leaf were 4 to 8% greater at 5 plants [m.sup.-2] than at 10 and 15 plants [m.sup.-2]. In 1991 and 1992, the lower yields of normal-leaf at 10 and 15 plants [m.sup.-2] were apparently associated with late-season LAI values of 5.0 or greater, whereas the 5 plants [m.sup.-2] density developed late-season LAI values ranging from 4.0 to 4.8. These findings indicate that (i) optimal plant density was higher for okra-leaf than for normal-leaf and (ii) a maximum LAI between 4.0 and 5.0 was required to maximize cotton lint yields in this environment.

Estimation of the lower limit of the canopy-air temperature differential, (T(sub c)-T(sub a))(sub LL), is required for calculation of an empirically-based crop water stress, index. This research determined the complexity of model needed for accurate estimation of (T(sub c) - T(sub a))(sub LL) for several field grown cultivars of Kentucky bluegrass (Poa pratensis L.) and for creeping bentgrass (Agrostis stolonifera L. var. palustris (Huds.) Farw.). Regression models using vapor pressure deficit of the air (VPD), net radiation load (R(sub n)), and wind speed (WS) were developed for predicting (T(sub c) - T(sub a))(sub LL). The best one to three-variable regression models for predicting (T(sub c) - T(sub a))(sub LL) used variable groups of VPD (r squared = 0.47); VPD and R(sub n) (R squared = 0.66); and VPD, R(sub n), and WS (R squared = 0.82). Models developed for predicting (T(sub c) - T(sub a))(sub LL) on individual Kentucky bluegrass cultivars, across Kentucky bluegrass, and across both species were tested on a validation data set. Models using only VPD accounted for

Interception of solar irradiation by leaf canopies is influenced by the canopy architecture of crops, which is a function of shape, distribution, and orientation of the leaves that constitute the canopy. The objective of this study was to test the hypothesis that leaf azimuthal distribution in a maize (Zea mays L.) canopy is not influenced by plant density and row width. Experiments were conducted at Elora, Ontario, with maize grown at 4, 7, and 10 plants m to the -2 at a 0.76-m row width in 1991 and 1992 and with maize grown at 7 and 10 plants m to the -2 at a 0.5-m row width in 1992. Leaf orientation was recorded in 16 azimuthal classes for leaves from the bottom to the topmost leaf position. Results showed that the orientation of leaves in the topmost layer (twelfth to sixteenth leaf) was more perpendicular to the row for high than for low plant densities. An azimuthal shift of leaves from the bottom to the top in maize plants was apparent in all canopies, but the shift was larger for plants grown at high plant densities than for those grown at low plant densities and a similar trend was apparent for the comparison of maize grown at 0.76-m vs. 0.5-m row widths. Results of this study suggest that the orientation of leaves in a maize canopy is altered by intraspecific interference, thereby more effectively intercepting incident solar irradiance.

Measurement of changes in canopy reflectance of tall rescue (Festuca arundinacea Schreb.), which result from deterioration of tissues caused by disease organisms, is a potential unbiased method for quantifying disease. Canopy reflectance in eight spectral bands between 430 and 840 nm and 18 vegetation indices derived from the spectral bands were regressed against visual severity estimates of Rhizoctonia blight, caused by Rhizoctonia solani Kuhn, and gray leaf spot, caused by Pyricularia grisea (Cooke) Sacc. Reflectance within the 810-nm band exhibited the strongest relationship (19% [is less than or equal to] [r.sup.2] [is less than or equal to] 63%) with visual severity estimates of Rhizoctonia blight and gray leaf spot. Reflectance in the visible or near infra-red wavelengths was similar to tall rescue blighted by either fungal pathogen. A significant (P [is less than or equal to] 0.05) negative linear relationship was observed between canopy reflectance in the 810-nm band and the severity of either Rhizoctonia blight or gray leaf spot. As Rhizoctonia blight decreased with increases in the application rate of the fungicide flutolanil (N-[3-(1-methylethoxy)-phenyl]-2-(trifluoromethyl)benzamide) and the proportion of a resistant cultivar in tall rescue blends, canopy reflectance in the 810-nm band increased. However, models based on canopy reflectance had twice as much unexplained variability than models based on visual severity estimates of Rhizoctonia blight. Factors other than disease influenced variability in reflectance of light from tall fescue canopies., Tall fescue is a perennial, coarse-textured, bunch-type (non-stoloniferous) grass with a deep root structure and an optimum temperature range of 15 to 25 ° C. It is one of the [...]

Grain yields of eight representative semidwarf spring wheat (Triticum aestivum L.) cultivars released in northwest Mexico between 1962 and 1988 have increased linearly across years as measured in this region during 6 yr under favorable management mad irrigation. To understand the physiological basis of this progress and possibly assist future selection for grain yield, leaf traits were determined during 3 yr in the same study. Stomatal conductance ([g.sub.s), maximum photosynthetic rate ([A.sub.max]), and canopy temperature depression (CTD), averaged over the 3 yr, were closely and positively correlated with progress in the 6-yr mean yield. The correlation was greatest with [g.sub.s] (r = 0.94, P [is less than] 0.01). Compared with the overall yield increase of 27%, [g.sub.s] increased 63%, [A.sub.max] increased 23%, and canopies were 0.6 ° C cooler. Carbon-13 isotope discrimination was also positively associated with yield progress (r = 0.71, P [is less than] 0.05), but other leaf traits such as flag leaf area, specific leaf weight, percentage N and greeness were not, nor was crop growth rate around anthesis. The causal basis of the leaf activity interrelationships is reasonably clear, with both increased intercellular [CO.sub.2] concentration and increased mesophyll activity contributing to the increase in [A.sub.max]. However, causal links to the yield progress, and the accompanying increase in kernels per square meter, are not clear. It is concluded that [g.sub.s] and CTD should be further investigated as potential indirect selection criteria for yield., During the last 30 yr, wheat breeders at the International Maize and Wheat Improvement Center (CIMMYT) have achieved significant yield potential advances for bread wheat cultivars of semidwarf spring habit, [...]