Correlations of Plant Height and Canopy NDVI with Nitrogen Nutrition and Lint Yields of Cotton.

Measuring crop N nutrition status during the season by remote sensing of crop 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 applications. This study was designed to evaluate the correlations of plant height and canopy normalized difference vegetation index (NDVI) with leaf N nutrition and lint yields of cotton in Tennessee. A field experiment was conducted near Jackson and Milan, Tennessee from 2008 through 2009. Complete combinations of six N application rates (0, 40, 80, 120, 160, and 200 lb N/acre) and two N application timings (at planting, between first square and first bloom) were evaluated in a randomized complete block design with four replicates at both locations each year. Plant height, canopy NDVI, leaf N concentrations, and lint yield of cotton were measured on an individual plot basis at keying growing stages each site-year. There were significant positive relationships of lint yields with plant heights and canopy NDVI indices at some key growing stages. Correlations of lint yields with plant heights and canopy NDVI became stronger as the growing season moved forward. Relationships of lint yields with plant heights were stronger than those of lint yields with canopy NDVI at the same growing stage. Relationships of lint yields with plant heights and canopy NDVI were stronger with cotton under pre-planting N application than those with in-season N application. In summary, both plant height and canopy NDVI at key growing stages can be used to develop algorithms for in-season variable rate N applications on cotton.