The effect of level of nitrogen nutrition on earliness in upland cotton (Gossypium hirsutum L.)

Abstract

The responses of both morphological and product quantity measures of earliness in two cotton cultivars to nitrogen stress applied either continuously or over specific developmental stages are reported. Continuous nitrogen stress increased the number of days to appearance of the first flower bud and first flower in both cultivars, had little or no effect on the main-stem node at which the first-fruiting branch appeared, and increased flower bud shedding only in the less determinate early cultivar Rex. The total number of fruiting points produced up to first flower appearance was reduced by nitrogen stress in both cultivars.

Nitrogen stress from planting to appearance of the first flower bud greatly increased the time taken for flowering to occur at the first 30 fruiting points through delaying first flower appearance in both cultivars and increasing the horizontal flowering interval in Rex. Nitrogen stress applied later generally had little effect on this earliness index. Nitrogen stress from planting to first flower bud appearance strongly reduced the production rate index in Rex. However, nitrogen stress from first flower bud to first flower appearance resulted in a rapid rate of seed cotton production in both cultivars. Stimulation over the control was particularly marked in cultivar Bar 7/8.

The relationship between earliness index and production rate index was explored, and the nitrogen effects on these indices evaluated. The combined use of these indices in field trials to identify factors limiting earliness is advocated.