A pound of N is a pound of N, regardless of the carrier (Urea or Ammonium Nitrate) or if it is a liquid or solid. Liquids may become tied-up in surface organic matter residue and not available. Both products may burn green foliage depending on temperature and application rates. Cost should be the primary factor in selecting nitrogen or phosphorus sources.
Because grass plants accumulate nitrogen very fast and trans-locate it throughout the plant, avoid grazing livestock on fertilized fields. Fertilize no earlier than 3-5 days prior to livestock removal. Hay yield and grazing studies at Spur Ranch on Piceance Creek illustrated fertilizer application should be delayed until after spring grazing.
Liquids and solids are subject to loss from volatilization from high heat, so apply during cool temperatures.
One ton of additional hay production takes about 100 pounds of nitrogen, 34 pounds are removed in hay and 66 pounds are utilized through grazing, natural loss, run off and non-harvested plant parts.
Split your application in a two cutting system, 2/3 applied in early spring and 1/3 applied after first cutting.
With a single late cutting the most economical responses are with an application of 60 to 100 pounds of nitrogen per acre.