Interaction of water and nitrogen stress on the growth and development of cotton

Water and nitrogen fertilizer are two important management inputs in cotton production. Although the individual affects of water and nitrogen have been studied extensively, their interaction has not. The goal of this research was to further understand the individual and combined affects of water and nitrogen on cotton growth and development.; A study investigating the effects and interactions of water and nitrogen stress on field grown cotton (Gossypium hisutum L.) was performed over three years at the University of California's Westside Field Station. Measurements of growth, development, biomass partitioning, leaf area development, leaf water potential, soil water extraction, nutrient concentration, single leaf gas exchange, fruit retention patterns, seedcotton yields, and lint yield and quality were made.; Both water and nitrogen stress reduced mainstem growth. Water stress had the greatest impact in 1988 and nitrogen stress impacted growth prior to first bloom in 1989 and 1990. Both water and nitrogen stress had minor impacts on mainstem node development. The number of mainstem nodes required to produce 95 percent of the harvestable bolls (MSN95) was decreased significantly. Relative yield was directly related to final plant height, mainstem nodes, and MSN95. The impact of water and nitrogen stress on retention was greatest at higher mainstem nodes and at sympodial branch positions greater than one.; With increased nitrogen fertilization, leaf water potentials were lower than nitrogen deficient treatments. The increase in leaf water potential with increasing nitrogen stress was evident at equivalent volumetric soil water contents.; Water extraction patterns indicated that increasing nitrogen rates reduced the depth of soil explored by roots.; Single leaf gas exchange was reduced by both water and nitrogen stress. There was no compensation by nitrogen for water stress. The opposite was also true, namely that adequate water did not increase photosynthetic rates when nitrogen was the limiting factor.; Both water use efficiency and nitrogen use efficiency were maximized at input levels which did not provide for maximum lint yields. The water use efficiency response surface indicated that 250 mm of water were necessary for lint production. The nitrogen use efficiency rose as nitrogen rates declined.; Conclusions reached from this research include: (1) if severe enough, nitrogen deficiencies can impact cotton growth prior to the development of a reproductive sink; (2) an anatomical change in the water conducting system of cotton plants may reduce the resistance to water flow under nitrogen stress; and (3) though nitrogen can ameliorate the impact of water stress on lint yield, nitrogen affects must occur at some physiological level other than gas exchange.