9. Improving nitrogen fertilization in mechanized rice culture

Abstract

Rice is produced in highly mechanized and energy intensive water-seeded and dry-seeded systems in the United States. Nitrogen fertilization management relative to N source and time of application differs in the two systems because of the timing of soil submergence which influences N retention in the soil. Nitrogen management studies show that N fertilizer efficiency is maximized in water-seeded rice when ammonical N is placed 5 to 10 cm in the soil immediately before flooding. Nitrogen applied on a dry soil surface immediately before flooding dry-seeded rice results in N movement into the soil and retention for plant utilization. Nitrogen application preplant or into water after flooding results in N losses in dry-seeded rice. Split N application gives acceptable N efficiency when 65 to 75% of the total N fertilizer requirement is applied preflood followed by a midseason N topdressing. Sulfur-coated urea and nitrapyrin soil incorporated with urea reduce N loss in dry-seeded rice. Total N requirements of rice in the cultural systems is dependent on cultivar, soil N fertility and other factors. Plant analysis research establishes critical N concentrations in semidwarf and tall rice cultivars in the water-seeded system.