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A Light Interception Method for Measuring Row Crop Ground Cover¹

ABSTRACT

Ground cover determined by light interception is the percentage of the soil surface shaded by the plant canopy; i.e., it is a measure of the shadow projected by the plant canopy. The best time to measure ground cover is near solar noon when changes in solar angle result in the least change in ground cover. Measurements of ground covered by canopy foliage are used to evaluate the effectiveness of sunlight interception in photosynthesis and evapotranspiration studies. Ground cover measurements are also useful indicators of the ability of various row crops and cropping systems to intercept rainfall and reduce runoff and erosion.

Ground cover of grain sorghum [Sorghum bicolor (L.) Moench], cotton [Gossipium hirsutum L.], sunflower [Helianthus annus (L.)], soybean [Glycine max (L.) Merr.], and corn [Zea mays (L.)] were determined using a meter stick, overhead photography, and photosensitive light sensors.

The meter-stick method is as accurate, faster, simpler, and more economical than any of the other methods used to determine ground cover. There were no significant differences in ground cover determinations using the meter-stick method, overhead photographs, spatial quantum sensor, or traversing quantum cell. Ground cover was not linearly related to Leaf area index (LAI). A single measurement of ground cover across the plant row (perpendicular) was as accurate as the average of 21 inter-row measurements parallel to the plant rows.

¹ Contribution from the Southern Region, USDA-ARS in cooperation with the Texas Agric. Exp. Stn., Texas A&M Univ.

² Soil scientist, USDA-ARS, Southern Region, and Assistant Professor, Texas Agric. Exp. Stn., Temple, Texas, respectively.

Received for publication November 5, 1976. Accepted for publication March 7, 1977.

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