Cool Season, Mixed Species, Forage Response to Nutrient Additions.

Nutrient availability is a key determinant of plant biomass and species composition in forage systems, and is commonly manipulated via fertilizer applications.  Therefore, understanding forage species responses to micro- and macro-nutrient applications is necessary to predict changes in species assemblages and forage production associated with altering nutrient regimes.  To explore the relationships between forage species composition and production and nutrient availability we performed a full factorial design of N, P, and K plus micronutrient applications on a mixed tall fescue, orchardgrass, Kentucky bluegrass, clover, and vetch hay pasture in central Kentucky.  We collected biomass by functional group (graminoids, forbs, legumes, and dead litter) and species cover data for two consecutive years (2008 and 2009) of fertilizer applications.  Nitrogen additions favored grass species, promoting grass production and cover, and negatively impacted forbs.   Phosphorus additions had little impact on the vegetation parameters measured, presumably because of the high phosphorus soils prevalent at the site.  However, the K plus micronutrient treatment significantly increased production and cover of Big Flowered Vetch, a legume, which resulted in significant declines in grass production in these plots over time.  Additional testing revealed that K was the nutrient the Big Flowered Vetch was responding to.  In this central Kentucky hay field, total forage production was most stimulated by N additions increasing grass biomass; however, K additions most affected the species composition of the site by promoting legumes (specifically Big Flowered Vetch).  This alteration in species composition was immediate and appears likely to have long-lasting effects on the vegetative community.