Nitrogen fertilization and critical nitrogen concentration for contemporary high yielding cotton under no-tillage

Nitrogen (N) management strategies for cotton may need to be modified because of the use of new high yielding cultivars and improved cropping systems. The objective of this research was to determine the optimal N application rate and critical leaf N concentration for contemporary high yielding cotton under no-tillage systems. A strip-plot trial was conducted on eleven private farms in Crockett, Fayette, Gibson, Haywood, Lake, and Lauderdale counties from 2009 through 2010 in Tennessee. Five N treatments of 0, 45, 90, 134, and 179 kg N ha(-1) were evaluated as side-dress N of urea and ammonium nitrate solution in strip plots in a randomized complete block design with three replicates. Eight out of the eleven location-years showed significant yield responses to side-dress N applications. Applying 45-146 kg N ha(-1) (including pre-plant and side-dress N) was sufficient for maximum cotton yields at the N responsive location-years. The results of this study indicate that the current N fertilizer recommendations for cotton may be more than adequate for some upland soils but inadequate for some other upland fields. A range of 34.4-47.4 g kg(-1) of leaf N concentration at early bloom is required for cotton to reach to maximum lint yield. These critical leaf N values were somewhat greater than the current sufficient N range, which suggests that the current critical leaf N concentrations for cotton in the southern U.S. may need to be modified; contemporary high yielding varieties require slightly higher N application rates to maximize yields.