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Digital Images Estimate Canopy Coverage

February 18, 2009

Canopy light interception (LI) is an important factor for crop growth and fruit yield. Crop yield depends on a canopy’s ability to intercept incident solar radiation, which in turn depends on the available leaf area, its structure, and its efficiency in the process of photosynthesis.

Maximizing leaf growth through light interception is an important consideration when studying different agricultural or environmental factors on crop yield, and it is the main source of data in the most widely used methods for estimating crop water needs.

A study conducted by C. Campillo, M.H. Prieto, C. Daza, M.J. Monino, and M.I. Garcia, and published the October 2008 volume of HortScience, looked at how digital images can characterize canopy coverage and light interception in processing tomato crops. Digital images offer a series of advantages over other methods of LI estimation, including the possibility to directly process images by computer using free software.

According to Campillo, “The objectives of the study were to develop a simple, economical method for determining LI in low-lying crops such as processing tomato using digital images obtained with a standard, commercial camera and free software and to evaluate the influence of different types of soil coverage (bare soil and plastic mulch) on canopy light interception.”

The resulting images were processed and analyzed using the free software GIMP 2.2 and IMAGE J. Three different methods were used in the analysis: soil area (SA), soil contour (SC) and reclassification (SR), in order to quantify the percentage of groundcover (PGC). A close relationship between LI and estimated PGC was found with all three methods and for different soil cover regimes.

Many practical advantages to the methods were found. Most important, stated the researchers, measurements using a digital camera can be taken at any time of day, and bright sunshine is not necessary. In contrast, another common method that uses active radiation bars for measurement must be taken at solar noon and requires bright sunlight for accurate results.

By: Michael W. Neff, mwneff@ashs.org

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American Society for Horticultural Science




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