Nitrogen effects on the fate of cotton bolls

Abstract

Nitrogen (N) affects the number, size, and disposition of cotton bolls. Also, high N rates have been linked to increased incidence of boll rot. Nitrogen is often applied to cotton (Gossypium spp.) at rates in excess of 112 kg ha^‐1 in the lower Red River Valley of central Louisiana. This study was conducted to determine the effect of N on boll disposition. Cotton was planted on a Norwood silt loam soil [fine‐silty, mixed (calcareous), thermic Typic Udifluvent] in 1990 and 1992 and fertilized with N at seven rates ranging from 0 to 168 kg ha^‐1 in 28‐kg increments. Plants were harvested from plots at maturity, and bolls were mapped for site and disposition. Bolls were classified as open (normal), missing, immature (closed), or rotten. Yield fit to a quadratic curve both years and increased with N to a maximum between 120 and 150 kg ha^‐1 and then decreased. All boll categories fit to a quadratic curve and increased with N to a maximum and then decreased except in 1990 when rotten bolls were not affected by N rate. The percentage of open and missing bolls changed significantly with N each year in a different manner. The percentage of immature bolls slightly increased with N in 1990 but was not affected in 1992. The percentage of rotten bolls was not affected by N in either year. In summary, high N rates usually did not adversely affect boll disposition except for a general increase in missing bolls percentages, which partially offset the yield advantage of additional bolls at high N rates.