Organic rice (Oryza sativa L.) systems in California utilize a 30‐d drain approximately one month into the growing season to control weeds. This drain may result in N losses and reduce yields. Two field trials were initiated to evaluate whether top‐dressing fertilizer N following the drain period could mitigate this problem by increasing N uptake and yields. Treatments evaluated rates and sources of commercially available organic fertilizers varying in N content and C to N ratio. The six treatments were a control with no top‐dress fertilizer, and top‐dress applications of 12–3–0 (applied at 22, 45, and 67 kg N ha−1) and 6–3–2 and 4–1–4 applied at 45 kg N ha−1. Total plant N uptake at harvest increased linearly with increasing N rate at both locations. At both sites, grain yields increased linearly (by 15 to 22 kg ha−1 for every kg N ha−1 applied) up to 45 kg N ha−1 above which yields plateaued at one site but continued to increase linearly at the other site. Application of 12–3–0 increased yields relative to the control at both locations but yields were not significantly different between the three fertilizer sources at the 45 kg N ha−1 rate at either location. Total plant N uptake and N recovery were higher in the 12–3–0 treatment compared to the other fertilizer sources at only one location. An economic analysis indicates that at the yield responses reported here, top‐dress N fertilizer applications were economical.
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