Using Remote Sensing to Estimate Soybean Leaf Area

D.L. Holshouser

Soybean leaf area is directly related to yield.  Research has shown that a leaf area index (LAI) of approximately 4.0 is needed to maximize yield potential.  Yield increases little when LAI is greater than 4.0, but yield is linearly related to LAI when less than this level.  Leaf area index can be used to select cultivars, adjust seeding rates or row spacing, and determine insect defoliation thresholds.  However, obtaining LAI information from multiple fields can be difficult and time consuming.  Our objective was to determine if the normalized difference vegetation index (NDVI) obtained from infrared photographs could be used to estimate soybean LAI.  Experiments were conducted in 2002 and 2003.  A very strong relationship of NDVI with soybean LAI was evident.  Altitude that photograph was taken and soybean development stage affected NDVI estimates, but their influence on the NDVI-LAI relationship was minimal.