Nondestructive Measurement of Vegetative Cover Using Digital Image Analysis
| Autor: | Stephanie L. Greene, Robert L. Wample, Mercy A. Olmstead, Julie M. Tarara |
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| Rok vydání: | 2004 |
| Předmět: | |
| Zdroj: | HortScience. 39:55-59 |
| ISSN: | 2327-9834 0018-5345 |
| DOI: | 10.21273/hortsci.39.1.55 |
| Popis: | Traditionally, vegetative cover has been subjectively assessed by visual assessment. However, visual assessment is thought to overestimate percent vegetative cover. Thus, a repeatable method to objectively quantify percent cover is desirable. In two vineyards near Prosser, Wash., the percentage of ground surface covered by up to 15 different cover crops was assessed both visually and by computer-assisted digital image analysis. Quadrats in the cover crop were photographed digitally and the images analyzed with commercially available software. Areas of green vegetation in each image were identifi ed and measured. Weeds in some images were differentiated from the cover crop by user- defi ned thresholds. Subjective visual estimates of percent vegetative cover were generally higher than those digitally estimated. Values for the visual estimates ranged from 5% to 70% in 1998 (mean = 52.4%) and 7.5% to 55% in 1999 (mean = 30.7%), compared to digital readings ranging from 0.5% to 24% (mean = 11.1%) and 10.3% to 36.6% cover (mean = 20.1%), respectively. The visual assessments had lower coeffi cients of variability in 1998 (CV 28.1) than the digital image analysis (CV 52.3), but in 1999, the values for the two techniques were similar (CV 41.2 vs. CV 45.7). Despite initial variations between the two methods, the accuracy of digital image analysis for measuring percentage vegetative cover is superior. Soil erosion by wind is a signifi cant concern in vineyards in eastern Washington, in part, because of low rainfall. Both the Columbia and Yakima valleys, where the majority of the stateʼs vineyards are located, lie in the rainshadow of the Cascade Mountains and experience frequent high winds. In some seasons, 2 to 5 cm of topsoil can be lost by wind erosion. Soil eroded from bare ground accumulates in areas with vegetative cover (Coldwell et al., 1942). Cover crops mitigate |
| Databáze: | OpenAIRE |
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