Nitrogen fertilization timing and rate influence N recovery efficiency and rice yield

Nitrogen (N) fertilizer management in rice (Oryza sativa L.) varies with production practices. In drill-seeded, delayed-flood production systems, the most common production practice in Louisiana N fertilizer is applied at two application timings. The first application timing is just before the permanent flood is established. The second application is at midseason. Nitrogen fertilization before flooding is critical for maximum N uptake, nitrogen recovery efficiency (NRE), and yield. Field experiments were conducted from 2017 to 2020 to evaluate N timing effects on N uptake, NRE, and rice yield. The rice cultivar CL153 was drill-seeded into a stale seedbed at a seed rate of 85 kg ha⁻¹. Fertilizer-N was applied utilizing multiple application timings and rates adding up to a seasonal rate of 155 kg ha⁻¹ across treatments. A single N application 1-day before flooding significantly increased grain yield in all trials, ranging from 8523 kg ha⁻¹ in 2019 to 11,322 kg ha⁻¹ in 2018. Compared to post-flood applications, preflood N increased plant height, N uptake, and NRE. Split N application rates and timings after flooding did not impact rice yield or its agronomics, such as height, aboveground biomass, and time of heading. NRE and yield were significantly correlated (r = 0.805; p < 0.001). Our results indicated that a single N application before flooding has the potential to be an alternative option for N management in the drill-seeded, delayed-flood rice system.