This study aimed to evaluate the nitrogen use efficiency by different cotton varieties in an Acrisol. The design was com- pletely randomized in a 5x2x5 factorial. The factors consisted of five nitrogen rates (0, 250, 500, 750 and 1000 mg dm-3 of soil), two cotton genotypes (FiberMax 910 and FiberMax 966) and five repetitions, using urea as source N (45% N). The following variables were studied: dry matter production of plant shoots, nitrogen content, nitrogen concentration, N use efficiency, efficiency of nitrogen applied, physiological efficiency, agro-physiologic efficiency and recovery efficiency. The results showed that there was a significant linear effect of nitrogen application in the dry matter production, nitrogen content and nitrogen concentration of cotton plant. The nitrogen use efficiency varied with the genotypes and type of ef- ficiency calculated, and with increasing doses of N, less N was recovered by cotton plants.

Revista de Ciências Agrárias, vol. 36 n.º 1 (2013)