Eficiência agronômica no uso de nitrogênio mineral por cultivares de arroz de terras altas.

Rice is one of the most important cereals in the economy of developing countries, being highly demanding for nutrients, especially nitrogen. Thus, the selection of highly efficient rice genotypes in mineral nitrogen use is currently considered one of the most appropriate ways to decrease rice crop production costs. The aim of this work was to verify the existence of differences between improved rice varieties in terms of nitrogen use efficiency in upland soils. The cultivars evaluation was carried out in two environments, with low and high nitrogen rates. The experiment was carried out in randomized block design with four replications. To simulate the environments with low and high nitrogen rates, 20 and 120 kg ha-1 of N were applied, respectively. The cultivars BRS-Primavera and BRSMG-Conai had high agronomic efficiency and response to N fertilization and, therefore, are recommended for cultivation with any level of fertilization in the South region of the State of Tocantins. The highest yields are related to the highest chlorophyll indexes and the lowest ratios between chlorophyll indexes a and b. [ABSTRACT FROM AUTHOR]