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Calcium Stimulation of Ammonium Absorption In Radish

Dep. of Soil and Crop Sci., Texas A&M Univ., 1380 A&M Circle, El Paso, TX 79927
Dep. of Horticulture, Texas A&M Univ., 1380 A&M Circle, El Paso, TX 79927

^* Corresponding author.

Nitrogen loss processes in soils have been widely studied and there have been many suggestions for improving N-use efficiency, such as using NH₄-NO₃ fertilizers, split fertilizer applications, application timing, and other techniques. The objective of this research was to examine the use of Ca as a means to increase the rate of NH₄ absorption by radish (Raphanus sativus L.). Short-term ¹⁵NH₄ absorption in the presence of variable Ca was measured in the greenhouse, long-term plant growth responses to NH₄ in the presence of variable Ca were measured both in the greenhouse and in field production trials. Ammonium absorption (¹⁵NH₄) increased in plants with increasing solution Ca to a Ca/NH₄ ratio of 0.5:1 in the tops and to 2:1 in the roots. Vegetative growth increased in two greenhouse experiments as Ca concentrations increased, all at a constant NH₄ concentration. As the Ca concentration increased, the total N concentration increased in foliar tissue and decreased in the roots. In the 2 yr of field testing, dry weight yield of roots increased 77 and 55%, respectively, in the urea + Ca treatment compared with the urea treatment alone. In the second year field data, total plant absorption of the added urea-N in the presence of added Ca increased by 109% compared with urea alone. Significant increases were found both in the root and foliar tissue N content, and growth in the 2 yr of field data. The addition of Ca with urea produced significantly improved plant N-use efficiency in the field as was suggested from the greenhouse data.

Received for publication November 28, 1988.