High fertilizer prices might discourage stocker operators from fertilizing pastures, but Iowa State University forage specialist Steve Barnhart says the option for carrying more cattle per acre can make it cost-effective.

Grass-based pastures, he says, generally respond very efficiently to the first 40 to 50 pounds per acre of nitrogen. Bluegrass will continue to respond to nitrogen applications up to 150 to180 pounds per acre annually but at a decreasing rate of response.

Tall cool-season grasses such as bromegrass, orchardgrass and tall fescue respond to nitrogen levels of 250 to more than 300 pounds per acre, he says, but at a decreasing rate of response.

Barnhart offers these recommendations for nitrogen applications to grass-based pastures, which, he says, are modest yet efficient rates.

Kentucky Bluegrass

  • Early spring (March and April) 60 to 80 pounds per acre
  • Late spring (May to early June) (optional) additional 30 to 40 pounds per acre
  • And/or late summer (August to September) (optional) additional 30 to 40 pounds per acre

Tall, Cool-season Grasses

  • Early spring (March and April) 80 to 120 pounds per acre
  • Late spring (May to early June) (optional) extra 40 to 60 pounds per acre
  • And/or late summer (August to September) (optional) extra 40 to 60 pounds per acre

Legume-grass Mixed Pastures

  • If less than 1/3 legume, treat as a grass pasture
  • If more than 1/3 legume, no nitrogen is recommended

Barnhart points out that in legume-grass mixed pastures, heavy nitrogen applications, particularly in the spring, can make the grass component more competitive and limit legume production. To encourage legumes, use modest nitrogen applications during summer or fall while maintaining optimum soil pH, phosphorus and potassium levels.

Adding phosphorus and potassium to pastures generally will not increase production dramatically, Barnhart says, and these nutrients are not depleted to the degree nitrogen is in a pasture environment. If levels of these nutrients are low, applications will improve forage productivity and response to nitrogen.