There is increasing evidence which suggests that the presence of Ca in concentrations greater than that for adequate plant nutrition increases NH₄⁺ absorption. The objectives of this study were to evaluate the effects of cotton age on Ca-stimulated NH₄⁺ absorption under greenhouse conditions and long-term responses of cotton to Ca/NH₄⁺ treatments under field conditions. Greenhouse results indicated that plant age had a significant effect on NH₄⁺ absorption. Young (37-d) seedlings preferred N in the NO₃- form. Increasing levels of Ca (added to NH₄⁺-N solution) increased plant N and growth of 57-d cotton. Older (78-d) cotton showed no preference for either N form or did not significantly responded to added Ca. Under field conditions, Ca increased the N content in all vegetative structures of 59-d cotton, regardless of water management or mode of treatment application. Added Ca tended to improve boll size and significantly increased fiber length. However, lint yields were unaffected. This could be due to an inadequate amount of soil-applied N. Both greenhouse and field results showed that luxurious amounts of soluble Ca increased NH₄⁺ absorption and stimulated cotton growth. Long-term benefits of CS/NH₄ to cotton require further evaluation.