Utility of Vegetation Indices in Assessing Canopy Closure in Soybean.

The yield potential of a soybean crop is related to its canopy leaf area.  The leaf area increases during crop development and declines after R5.  Defoliation due to soybean rust can rapidly decrease the canopy’s ability to intercept solar radiation.  Vegetation indices (VIs), such as NDVI (Normalize Difference Vegetation Index), WDRVI (Wide Dynamic Range Vegetation Index), and SR (Simple Ratio), quantify the amount of green leaf area.  However, they have difficulty detecting differences in LAIs (Leaf Area Indices) after canopy closure (when 95% or more of the light is intercepted).  For this study plots were established with different row widths (7.5”, 15”, and 30”), which had different times of canopy closure.  Vegetation indices, LAI, and LI (light interception) were measured at weekly intervals from R1 to R5.