Relationships of NDVI with Nitrogen Nutrition and Yields of Corn Under Different Cropping and Irrigation Systems.

Measuring crop N nutrition status during the season by remote sensing of the canopy seems to be a viable N management system for variable-rate N applications, emphasizing N application in the season, and minimizing the costs of N application. This study was designed to assess the relationships of canopy normalized difference vegetation index (NDVI) with crop N nutrition status and yields of corn under major cropping and irrigation systems in Tennessee. A field experiment was conducted near Milan, Tennessee from 2008 through 2009. Five N application rates of 0, 55, 110, 165, 220, and 275 lb N/acre were evaluated on corn under continuous corn, corn-soybean, and corn-cotton rotations and under non-irrigation and irrigation systems. A randomized complete block design was used with four replicates. Corn was planted on April 22, 2008 for all the trials. Canopy NDVI indices, leaf N concentrations, and plant heights at 49 and 59 days after planting and grain yields at harvest were measured on an individual plot basis in 2008. There were significant linear and quadratic relationships between corn yields and canopy NDVI indices and between corn yields and plant heights at 49 and 59 days after planting regardless of crop rotations and irrigation systems. The linear and quadratic relationships of corn yields with plant heights were stronger than those of corn yields with canopy NDVI indices, respectively, at the same growing stage under all the crop rotations. The relationships of corn yields with canopy NDVI indices and plant heights were stronger with corn rotated after soybean than those in continuous corn and corn rotated with cotton. Our results suggest that both canopy NDVI indices and plant heights at key growing stages can be used to develop algorithms for in-season N applications on corn under different crop rotations and irrigation systems.