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Nitrogen (N) is important for cotton production but if poorly managed it can lead to reduced lint yield and low N use efficiency. This study was conducted to evaluate cotton’s ability to recover from early season N deficiency and determine if a sensor-based N rate calculator (SBNRC) can be used to make mid-season N recommendations in cotton. The effect of sidedress N fertilizer (0, 33, 67, 101, and 134 kg N ha-1) applied at early pinhead square (EPHS), first white flower (FWF), 30 d after first white flower (30 DAFWF), and four levels of preplant N (0, 33, 67, and 101 kg ha-1), on cotton lint yield was investigated at two locations in Oklahoma. The results indicated that at 0 and 33 kg ha-1 preplant N applications, cotton yield was significantly impacted by the timing of sidedress N. However, at Altus in 2009 and Lake Carl Blackwell (LCB) in 2010, cotton recovered from early season N deficiency and attained near maximum lint yield when sidedress N fertilizer was applied at EPHS or FWF. At Altus in 2010, cotton recovered when sidedress N was applied at EPHS and reduced when sidedress N was delayed until FWF. Yields were significantly (P < 0.05) reduced when application was delayed to 30 DAFWF at all sites. The results indicate normalized difference vegetative index (NDVI) could be used to make sidedress N recommendation for cotton at EPHS or FWF stage. This research validates the use of the SBNRC to improve in-season N recommendations in cotton production.
