ABSTRACT
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.
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