Sugar beet (Beta vulgaris L.) was an endemic sugar crop and played an important role in agricultural production in north China. Yields of sugar beet were not high and the total output was instable, particularly sugar content showed a downward trend in Heilongjiang province and the national. All had become the obstacle factors to the development of sugar beet. Unreasonable application of nitrogen was one of the main reasons. Nitrate reductase was a key and limited enzyme in nitrogen metabolism. The fu...