Cotton in ultra-narrow row spacing: Plant density and nitrogen fertilizer rates

Ultra-narrow row spacing (UNR) of 25 cm or less may be a viable alternative to wide-row spacing for cotton (Gossypium hirsutum L.) in the Mid-South USA but yield and quality in relation to wide-row cotton have been variable. Field experiments were conducted from 1997 through 2000 on Gigger silt loam (fine-silty, mixed, thermic Typic Fragiudalfs) to: (i) determine the effects of plant density (128 000, 256 000, and 385 000 plants ha(-1)) and N rate (90, 112, 134, and 157 kg ha-1) on irrigated and rain-fed UNR cotton and (ii) compare performance of UNR cotton to wide-row cotton (102-cm row spacing) at a density of 116 000 plants ha(-1) and fertilized with 90 kg N ha(-1). Increase in plant density decreased lint yield of irrigated cotton and had no effect on yield of rain-fed cotton. Increase in plant density of irrigated cotton decreased boll number plant(-1) and individual boll weight but had no effect on boll number m(-2). Yield components of rain-fed cotton were not affected by varying plant density. Increasing N rate did not affect yield or yield components of irrigated or rain-fed cotton. Plant density, N rate, and row spacing affected fiber properties but effects were small and would not affect value or utilization. Under irrigation, UNR cotton averaged 771 kg lint ha(-1) and wide-row cotton averaged 1069 kg lint ha(-1). Without irrigation, UNR cotton averaged 377 kg lint ha(-1) and wide-row cotton averaged 586 kg lint ha(-1). Maximum yields of UNR cotton were attained from plant densities in the range of 128 000 to 256 000 ha(-1) and a N rate of 90 kg ha(-1).