Relationship Strength Comparisons of Cotton Yield and Leaf Nitrogen With Combined and Respective NDVI and Plant Height Measurements.

The strength of the relationships of cotton N nutrition and yield with combined normalized difference vegetation index (NDVI) and plant height measurements has been scarcely investigated. The objective of this study was to compare the strength in terms of determination coefficient (R²) among the relationships of cotton yield and leaf N with combined and respective NDVI and plant height measurements taken during the growing season of cotton under no-tillage. A field experiment was conducted at Jackson and Milan, Tennessee from 2008 through 2010. Six N treatments (0, 45, 90, 135, 180, and 225 kg N ha^-1) applied at two different timings and repeated four times were implemented at each location-year in a randomized complete block design. Slightly to markedly stronger regressions of cotton yield with NDVI × plant height and NDVI + plant height were often observed relative to those of cotton yield with NDVI alone in terms of R² values regardless of growth stage. Relationships of cotton yield with NDVI × plant height or NDVI + plant height were usually similar to but occasionally stronger than those of cotton yield with plant height alone. Regressions of leaf N concentration with NDVI × plant height and NDVI + plant height were similar to or slightly to remarkably stronger than those of leaf N with NDVI alone. Relationships of leaf N with NDVI × plant height or NDVI + plant height were usually similar to but occasionally stronger than those of leaf N with plant height alone. Our results suggest that the benefits are variable in using combined NDVI and plant height measurements to assess cotton N nutrition and/or predict corn yield relative to the utilization of NDVI or plant height alone during the growing season.