Nitrogen Timing for Boot Stage Triticale Forage Yield and Phosphorus Uptake

Boot‐stage winter triticale (× Triticosecale rampaui Wittm.) is a popular double‐crop option for dairymen that increases forage production and phosphorus (P) removal in the Pacific Northwest USA. Optimal nitrogen (N) management for forage yield and P removal and a convenient plant assay of N sufficiency for this option are not well established. Thus, the objective was (i) to refine N fertilizer rate and timing and (ii) to evaluate forage crude protein (CP) as a reasonable diagnostic for plant N sufficiency. Irrigated winter triticale in low and compost‐P‐enriched soil was treated with eight N fertilizer treatments: a non‐fertilized control; five fall pre‐plant urea N rates, (60, 120, 180, 240, and 300 lb/acre); and two late‐winter urea N rates (120 and 240 lb/acre). Applied N increased boot‐stage forage biomass, CP, nitrates, and N and P uptake. Compared to late‐winter N, fall pre‐plant N increased boot‐stage forage yield as much as 33% and P uptake as much as 22% in P enriched soil. More N was required for maximizing P removal than was required for maximizing forage production. Forage CP provided a reasonable estimate of plant N sufficiency with 10.0 to 11.0% CP indicating sufficient available N for maximum forage production. In summary, pre‐plant N is preferable to delayed late‐winter topdressed N for maximum boot‐stage triticale forage yield and soil P removal.