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  • Author or Editor: Jim Thomas x
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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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St. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is considered to be one of the most shade-tolerant warm-season turfgrasses, yet information is lacking on intraspecies developmental responses and performance in shade. This greenhouse study was conducted to 1) compare quality, development, and physiological responses of 10 commercial and experimental lines of st. augustinegrass in moderate and heavy [32% and 15% photosynthetic photon flux (PPF), respectively] shade environments’ and 2) evaluate physiological and morphological indicators that could be used in rapid screening for shade tolerance among st. augustinegrass progeny from a segregating population. A range of shade tolerance was observed between the entries, as noted by quality and percent green cover after 10 weeks of imposed shade conditions. In moderate shade, most entries maintained acceptable (6 or greater) quality and greater than 50% green cover. However, in heavy shade, only ‘Captiva’, ‘Amerishade’, and ‘PI 600734’ maintained acceptable quality, with only PI 600734 and Captiva maintaining greater than 50% cover. ‘TAES 5732-6’, an embryo rescue-derived hybrid from ‘Floratam’, exhibited the least shade tolerance of the group in both shade environments. Neither chlorophyll content nor total nonstructural carbohydrates related well to observed shade quality differences between the entries. A strong correlation existed between shoot elongation rate of a cultivar and its corresponding final percent green cover in moderate shade (R 2 = 0.66) but not in heavy shade (R 2 = 0.19), suggesting that moderate shade may be the better environment for discriminating genetic differences among st. augustinegrass germplasm for shade tolerance.

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