Timing of Maturity in Ultra-Narrow and Conventional Row Cotton as Affected by Nitrogen Fertilizer Rate

Ultra-narrow row (UNR) systems and N fertilizer can influence cotton (Gossypium hirsutum L.) crop maturation. Study objectives were to measure impacts of UNR systems and N fertilizer rates on cotton maturation and to identify mechanisms by which these effects occurred. The location was Burleson County, Texas. In the split plot design, whole plots were N rates ofO, 50, 101, and 151 kg ha -1 . Split plots were 19-, 38- (both UNR), and 76-cm (conventional row, CR) row spacings with 296,600, 195,400, and 136,300 plants ha -1 , respectively. Thirty, 60, and 85% harvestable seedcotton each occurred 1.5 to 2.9 d earlier in UNR than CR spacings. First boll set occurred 1 d later in 19-cm than in wider row spacings. Boll set rate m -2 was greater in 19- than 76-cm row spacing during a 5-d flowering period shortly after first boll set, but did not differ by row spacing during three flowering periods thereafter. The percentage first position bolls was lower with wider row spacing, suggesting greater potential for concurrent boll set at multiple sites on individual plants. Eventual development of nonfirst position fruiting sites in 76-cm row spacing may have contributed to confinement of faster boll set in 19-cm row spacing to early bloom. Nitrogen rates did not affect the timing of 30,60, or 85% harvest. Reductions in bolls plant -1 were counteracted by slower boll set rates with lower N. The limited observed interactions of N and row spacing do not suggest advantages from suboptimal N rates in UNR cotton.