Assessing fertilizer nitrogen sources and application timing for water‐seeded rice systems

Abstract In California's water‐seeded rice systems, both high yields and nitrogen (N) use efficiency are achieved when the pre‐plant N fertilizer (usually aqueous‐ammonia [aqua‐N]) is injected into a dry seedbed before flooding planting. However, there situations where applying in this manner not possible. The objective of study was to evaluate alternative management practices by testing different sources application times. 2020, we tested 13 treatments 2021, six more were added. following evaluated: urea, ammonium sulfate, three enhanced fertilizers (EENFs). Application times for EENFs, sulfate one day after 2 weeks flooding. Urea also applied four‐way split. additional added with aqua‐N, urea flooding, applications at 3, 4, 5 Grain yield agronomic (ANUE) used comparison. All increased grain relative zero‐N control, which averaged 5093 kg ha −1 . Applying aqua‐N or preplant soil resulted highest ANUE. EENF performed similarly worse than alone. If field already flooded, splitting best option. Only split treatment evaluated study; warrants further research on fine‐tuning splits these systems.