Impact of Nitrogen on Cotton Growth, Lint Yield, Fiber Quality and Verticillium Wilt

Aim: To examine the response of cotton varieties with varying reactions to Verticillium dahliae to nitrogen.
Study Design: The experimental design was a randomized complete block in a split-plot arrangement with four replications. Nitrogen rate served as whole plots and cotton variety as sub-plot.
Locations: Trials were conducted at the Texas Tech University New Deal and Quaker Farms in Lubbock, County (2011 and 2012), and the Texas A&M AgriLife Research Halfway Farm in Hale County (1 trial in 2011 and 2 trials in 2012).
Methodology: Plots measured 4.1 m wide (four rows on a 1.2-m spacing) by 10.6 m long. Composite soil samples were collected from four depths to determine nitrogen concentrations and fungal populations. Nitrogen treatments were applied prior to bloom. Plant growth, disease incidence, lint yield and fiber quality were used to compare treatments.
Results: Overall, the application of nitrogen had little affect on cotton growth. Appreciable levels of disease were only observed in one trial. The application of nitrogen slightly increased disease incidence; however, a two-fold increase in disease was observed in susceptible versus partially resistant varieties. Lint yields were only increased with the application of nitrogen in 2011. Subtle differences in fiber quality were observed between nitrogen rates, while varietal effects were observed for most all parameters. The fungus was recovered from the entire soil profile with fewer propagates found in the upper layer. Residual nitrate nitrogen increased over the two years and concentrations were highest in the uppermost layer.
Conclusion: Although confounded by adverse environmental conditions, these studies suggest that interactions between V. dahliae and nitrogen may exist. Furthermore, variety selection and the vertical distribution of the fungus may affect disease development. Additional studies are needed under more conducive conditions to better understand the interactions between these factors.