The Use of Red and Green Reflectance in the Calculation of NDVI for Wheat, Bermudagrass, and Corn Robert W. Mullen SOIL 4213 Robert W. Mullen SOIL 4213

Background of NDVI Normalized Vegetative Index –Current equation used in wheat and bermudagrass NDVI = (NIR ref - Red ref )/(NIR ref + Red ref ) Excellent predictor of biomass and N uptake in bermudagrass and wheat Normalized Vegetative Index –Current equation used in wheat and bermudagrass NDVI = (NIR ref - Red ref )/(NIR ref + Red ref ) Excellent predictor of biomass and N uptake in bermudagrass and wheat

What does the sensor see when measuring NDVI?

Biomass vs NDVI

N uptake vs NDVI

Red NDVI Limitations When a large amount of biomass is present red NDVI reaches an adsorption maxima –Plants are absorbing the maximum amount of red light –No longer able to differentiate yield levels in this region of red NDVI When a large amount of biomass is present red NDVI reaches an adsorption maxima –Plants are absorbing the maximum amount of red light –No longer able to differentiate yield levels in this region of red NDVI

Red Adsorption Maxima Red adsorption maxima

Green NDVI in Corn Work in corn shows that green NDVI is highly correlated with final grain yield (Shanahan et al., 2001) –Data collected using aerial imagery at 0.5 m resolution –Four bands were measured: blue ( nm), green ( nm), red ( ), and NIR ( nm) Work in corn shows that green NDVI is highly correlated with final grain yield (Shanahan et al., 2001) –Data collected using aerial imagery at 0.5 m resolution –Four bands were measured: blue ( nm), green ( nm), red ( ), and NIR ( nm)

Green NDVI in Corn Green NDVI calculated by: (NIR ref – Green ref )/(NIR ref + Green ref ) Corn ranged from stage V6 – R3 R values nearing 0.8 (highly significant) GNDVI more significant at later stages of growth (after tasseling) Green NDVI calculated by: (NIR ref – Green ref )/(NIR ref + Green ref ) Corn ranged from stage V6 – R3 R values nearing 0.8 (highly significant) GNDVI more significant at later stages of growth (after tasseling)

Green NDVI in Corn 1997 Data 1998 Data

Using an Index that Utilizes Both Red and Green May Be Possible Calculate NDVI using the following equation: –RGNDVI = (NIR ref – Green ref – Red ref ) (NIR ref + Green ref + Red ref ) Calculate NDVI using the following equation: –RGNDVI = (NIR ref – Green ref – Red ref ) (NIR ref + Green ref + Red ref )

So, how well does it work? Various indices versus biomass and forage N uptake in bermudagrass

How well does it work in wheat? Various indices versus biomass and forage N uptake in winter wheat

Discussion Currently, no wheat or corn yield data to verify this hypothesis If NDVI measures are made early enough in the season (prior to high biomass) Red NDVI may still be the more effective way of yield prediction Currently, no wheat or corn yield data to verify this hypothesis If NDVI measures are made early enough in the season (prior to high biomass) Red NDVI may still be the more effective way of yield prediction

Conclusions Calculation of NDVI using red and green reflectance may improve yield prediction of wheat and corn If sensor readings are collected at early growth stages this technique may not improve yield prediction This must be verified in wheat and corn Calculation of NDVI using red and green reflectance may improve yield prediction of wheat and corn If sensor readings are collected at early growth stages this technique may not improve yield prediction This must be verified in wheat and corn

Questions??