| Sumario: | Defficient Coffea arabica L. plants were treated with CaNO, (114%15N) in doses ranging from 25 to 200 kg/ha of N The effect of the treatments on the activity of nitrate reductase and on Nitrate Assimilation Potential was evaluated. Both parameters were equally sensitive to the nutritional status of the plants, but the use of the Nitrate Assimilation Potential is preferred as a diagnostic tool for it compensates for fluctuations in activity due lo environmental factors. Nitrate Assimilation Potentid zalues lower than 1.6 were evidenced by adeguately nonrished plants, while defficient ones presented values higher than 2. In leaves, 25 per cent of the N was derived from the fertilizer when a dose of 100 kg/ha was supplied, and 40 per cent was derived from it tohen supplymg 200 kg/ha At 150 ke/ha of N, an incipient saturation of the nitrate absorbing system was evidenced, while the activity of the nitrate assimilation system became stable from he 100 kg/ha dose on.
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