Evaluation of forage grass response to nitrogen rate in a controlled greenhouse study

Productive forage with sufficient nutritive value is essential to profitable grazing operations. Application of nitrogen (N) fertilizer directly impacts pasture growth, but N rates must be carefully calibrated to minimize production costs and losses to the environment. We evaluated forage accumulation response, nitrogen use efficiency (NUE), and % 15 N recovery of meadow fescue [ Schedonorus pratensis (Huds.) P. Beauv.], orchardgrass ( Dactylis glomerata L.), and endophyte‐free tall fescue [ Schedonorus phoenix (Scop.) Holub] in response to N rate in a controlled greenhouse environment using two soil types. Nitrogen was split‐applied at cumulative annual rates of 0, 67, 135, 202, 269, and 336 kg N/ha. The first N application was 15 N‐enriched 5% atom ammonium nitrate (NH 4 NO 3 ) solution, while the three subsequent N applications were made following harvest events with reagent‐grade NH 4 NO 3 . Nitrogen recovery from the first application was estimated from the atom % 15 N in the dry matter (DM) sample from each harvest event. For all species, DM forage accumulation increased with N rate up to 202 kg N/ha, and orchardgrass had the greatest DM accumulation at all N rates. NUE in all species declined with increased N. % 15 N recovery of the first fertilizer application was significantly different across species and N rates, ranging from 35% to 70%. In pasture systems with these species in warm summer continental climates, N fertilizer timing and application strategy should be calibrated with weather, pasture conditions, and livestock demand.