Response of cotton to water and nitrogen in a tropical environment: I. Frequency of watering and method of application of nitrogen

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Abstract
SUMMARY: Two experiments were made in successive years in which three frequencies of watering were combined factorially with several rates and methods of applying nitrogen. Soil water content and leaf water potential were measured. The least frequent watering treatment decreased yield and nitrogen applications increased yield. All of the effect of water and most of the effect of nitrogen were associated with changes in the number rather than the weight of bolls. Although the combination of heavy nitrogen with frequent watering caused the crop initially to set fruit more slowly than did heavy nitrogen with infrequent watering, it prolonged flowering and increased the number of fruit ultimately set. Thus yield and the potential duration and cost of insect control were also increased. There were no differences in yield nor rate of setting between the following methods of application of the nitrogen: all applied to the seed bed; split application between the seed bed and side dressing 2 months later; and split application between the seed bed, side dressing, and irrigation water. However, when application was split so that most was applied in the water, the response was not as great. Application of nitrogen combined with frequent watering decreased the weight of the early bolls by decreasing fibre per seed. Nitrogen increased the weight of later bolls by increasing the number and weight of seeds. The practical and physiological implications of these results are discussed and a crop nutritional hypothesis for cotton developed further.