Productivity and nutrient cycling comparisons of perennial and annual forage systems

Brad Heins, U of MN WCROC & Sharon Weyers, USDA-ARS

Over the last decade, consumer demand has driven an increase in the number of organic dairy farms in the nation. The National Organic Program requires a minimum of 120 days of grazing per animal, typically met by a May-September grazing season.

Grazing cowsTo maintain the viability of organic dairy operations, best management practices and a consistent season-long supply of high quality forage are needed to ensure animal health and milk production. However, in the northern U.S., providing a season-long forage supply is a challenge due to variations in temperature and precipitation that cause a ‘summer slump’ in production of the predominant forage species, such as Kentucky bluegrass, quackgrass, smooth bromegrass, and white clover. 

We initiated a novel rotational grazing system to provide organic dairy cows with highly productive annual BMR sorghum-sudangrass and teff at a time when other perennial forages are typically at lowest productivity. 

We compared forage production, milk production and soil-plant nutrient dynamics in this alternative perennial+annual system to a traditional perennial-only system, across the grazing season.  Initial data indicate the perennial+annual forage system provided greater total net biomass production and intake, primarily due to the annual forages, than the perennial-only system.  This production and intake resulted in increased milk production.  Nutrient availability in the annual forage pastures was much higher during the annual growing season, than the perennial pastures, indicating that perennial grasses maintained a tighter hold on cycling nutrients than annual forages.

Despite the production benefits, the higher availability of N in the annual forage pastures indicate this system could be more susceptible to nutrient loss through leaching or runoff.  Future input expenses, should nutrient loss over time occur, will need to be taken into account in order to ensure the viability of this highly productive but apparently successful perennial+annual forage system. 

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