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Abstract
Approximately one-third of the rice (Oryza sativa L.) in the United States is established by aerial application of pre-germinated rice into flooded fields. In the upper Mississippi alluvial region, no-till water-seeded rice farmers apply all of the nitrogen fertilizer on fields after flooding. The objective of a field experiment initiated in 1996 was to determine the optimum timing for making the first N application in this system. Rice seeds (L202 cv.) were broadcast by airplane into an established flood on a Gideon clay loam soil (fine-loamy, mixed, thermic Mollic Fluvaquent) in Missouri. Rice tillering and yield response to six N rates and six application timings were examined in small plots. Urea fertilizer (45.5% N) was broadcast applied at 15, 20, 25, 30, 35, 40 days after seeding (DAS) at the rates of 0, 28, 56, 84, 112, and 140 kg N ha−1. This was followed by two mid-season 28 kg N ha−1 applications on all plots. Two-year results showed that significantly more early tillers and yield were obtained when the first N application was made at 30 to 35 DAS [350 to 430 growing degree days base temperature 10°C (GDD10) after seeding]. Averaged across years and N rates, rice with the first N applied 30 DAS yielded 7817 kg ha−1. Rice receiving the first N applied 15 DAS yielded 5819 kg ha−1. Regression analysis showed that the optimum first N rate for the first N application was 35 DAS at a rate of 101 kg N ha−1.