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  • Author or Editor: Lee Johnson x
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Airborne multispectral image data were compared with intercepted photosynthetic photon flux (PPF) in commercial winegrape (Vitis vinifera) vineyards of Napa Valley, Calif. An empirically based calibration was applied to transform raw image pixel values to surface reflectance. Reflectance data from the red and near-infrared spectral regions were combined into a normalized difference vegetation index. Strong linear response was observed between the vegetation index and PPF interception ranging from 0.15 to 0.50. Study results suggest the possibility of using optical remote sensing to monitor and map vineyard shaded area, thus providing spatially explicit input to water budget models that invoke evapotranspiration crop coefficient based calculations.

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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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Canopy cover (CC) is an important indicator of stage of growth and crop water use in horticultural crops. Remote sensing of CC has been studied in several major crops, but not in most horticultural crops. We measured CC of 11 different annual and perennial horticultural crops in various growth stages on 30 fields on the west side of California's San Joaquin Valley with a handheld multispectral digital camera. Canopy cover was compared with normalized difference vegetation index (NDVI) values calculated from Landsat 5 satellite imagery. The NDVI was highly correlated and linearly related with measured CC across the wide range of crops, canopy structures, and growth stages (R2 = 0.95, P < 0.01) and predicted CC with mean absolute error of 0.047 up to effective full cover. These results indicate that remotely sensed NDVI may be an efficient way to monitor growth stage, and potentially irrigation water demand, of horticultural crops.

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The influences of elevated iron concentrations in the nutrient solution and light intensity on growth and the chlorophyll and chloroplast development in Kentucky bluegrass (Poa pratensis) `Touchdown' (C3), creeping bentgrass (Agrostis palustris) `Penncross' (C3), and buffalograss (Buchloe dactyloides) (C4) were investigated. Plants established in peatlite medium in 11-cm pots were fertilized with a Hoagland solution containing various iron concentrations (0, 0.01, 0.1, 1, 2, 4, 6, 8, 10 mM Fe+2) under two different light regimes. Preliminary results indicated that no biomass reduction or toxic symptoms developed in buffalograss when grown with iron levels up to 8 mM under high light conditions. As Fe+' levels were raised, plants became progressively greener with both the chlorophyll-a and chlorophyll-b contents increased. In Kentucky bluegrass, the sizes of chloroplasts and grana stacks in the cell were larger when grown with 2 mM than 0.05 mM Fe+2 in the fertilizer solution. The interactions of iron concentration and light intensity on pigmentation and photosynthesis of the three species are currently being determined.

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Estimation of crop evapotranspiration supports efficient irrigation water management, which in turn supports water conservation, mitigation of groundwater depletion/degradation, energy savings, and crop quality maintenance. Past research in California has revealed strong relationships between fraction of the ground covered by photosynthetically active vegetation (Fc), crop coefficients (Kc), and evapotranspiration (ET) of cool-season vegetables and other specialty crops. Replicated irrigation trials for iceberg lettuce and broccoli were performed during 2012 and 2013 at the USDA Agricultural Research Station in Salinas, CA. The main objective was to compare crop yield and quality from ET-based irrigation scheduling with industry standard practice. Sprinkler irrigation was used to germinate and establish the crops, followed by surface drip irrigation during the treatment period. Each experiment compared three irrigation treatment schedules replicated five times in a randomized block design. Two decision-support models were evaluated as follows: 1) an FAO-56-based algorithm embedded in NASA’s prototype Satellite Information Management System (SIMS) based on observed Fc, and 2) CropManage (CM), an online database-driven irrigation scheduling tool based on modeled Fc. Both methods used daily reference ETo data from the California Irrigation Management Irrigation System (CIMIS) to translate Kc to crop ET, with a target of 100% replacement of water use during the drip irrigation phase. A third treatment followed an irrigation schedule representing grower standard practice (SP) at 150% to 175% ET replacement during the drip irrigation phase. No significant treatment differences were seen in lettuce head weight or total biomass. Marketable yields of lettuce (near 45.4 Mg·ha−1) and broccoli (near 17.4 Mg·ha−1) were in-line with industry averages during both years and all treatments. During 2012, CM yield was below lettuce SP, and above broccoli SP, while in 2013 no treatment differences were detected for either crop. No significant differences were detected between SIMS and SP yields during any trial.

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Strelitzia reginae Aiton is an iconic plant known for its vibrant orange and blue inflorescences. Floral pigments include carotenoids and the anthocyanin delphinidin-3-rutinoside. S. reginae has black seeds with vivid orange arils, yet the basis for the orange color is unknown. We recently discovered bilirubin in the arils of S. nicolai. Previously, this pigment was known only to exist in animals as a breakdown product of heme. Using high-performance liquid chromatography (HPLC) and HPLC/electrospray ionization–tandem mass spectrometry, we now show that bilirubin is the primary aril pigment of S. reginae and is also present in low concentrations in its sepals (less than 44.0 ng·g−1).

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