Rice plant growth and nitrogen accumulation in drill-seeded and water-seeded culture

Nitrogen fertilization strategies for flooded rice (Oryza sativa L.) depend on understanding plant N demand. Seasonal N accumulation research in general is limited, and is nonexistent in water-seeded (WS) culture. A field study was conducted for 3 yr in Louisiana and 1 yr in Arkansas to characterize plant growth and N accumulation by rite at different development stages, and to compare these factors in drill-seeded (DS) and WS culture. 'Cypress' rice was grown on a Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf). Straw, grain, roots, and soil were collected at eight growth stages. Nitrogen-15-labeled urea was applied to 75 by 75 cm microplots enclosed by stainless steel retainers. Total dry matter increased each season, and grain dry matter was similar each year. In 1994 and 1995, both surface and subsurface root growth increased linearly until 90% heading. Fertilizer N accumulation increased to the four-leaf plus 21-d or panicle differentiation (PD) stages. Native soil N and remobilization of N from straw provided N needed for maturing grain. From heading plus 21 d to maturity, factors did not differ under either DS or WS each year. At early and late stages of development, factors did not differ under DS and WS in Louisiana. Differences in N accumulation and fertilizer N recovery were seen in Arkansas. This suggests that, under Louisiana conditions, results from experiments in DS and WS are interchangeable. Variation of the measured factors among years was significant, suggesting that even when labeled N is used, results from multiple seasons are required for accurate interpretation.