Response of ultra-narrow and conventional spaced cotton to variable nitrogen rates

Insufficient nitrogen (N) uptake in cotton (Gossypium hirsutum L.) has been shown to delay maturity and decrease lint yields, while excessive amounts will cause a host of disadvantages, ranging from increased insect damage to defoliation difficulties. Proper nitrogen fertilization rates are therefore essential to maximizing lint production while minimizing input costs. This test was designed to determine if ultra-narrow row cotton (UNRC) has similar nitrogen requirements as conventional row cotton (CRC). Two sites, one in peanuts and the other fallow the previous growing season, and four nitrogen rates (45, 67, 90, and 112 kg N ha(-1)) were used to compare soil fertility and nitrogen effects on petiole nitrate concentrations, lint yields, and ginning percentages. Although petiole nitrate concentrations between early and peak bloom were lower in ultra-narrow row cotton with 45 and 67 kg N ha(-1) there was no cor relation between petiole nitrate concentrations and lint yield. Conventional spacing receiving 67 kg N ha(-1) had the highest lint production at both locations, while application of 90 kg N ha(-1) produced the highest yields in UNRC at both locations. Ultra-narrow row cotton produced numerically higher yields than conventional row at all nitrogen rates at the location without a previous legume crop, but no significant trend was observed. Ultra-narrow row cotton lint percentages were significantly lower than conventional spacing, independent of nitrogen application rate.