2008 Joint Annual Meeting (5-9 Oct. 2008): Forage Yield and Nutritive Value of Selected Cool and Warm Season Forages Under Varying Rates of Nitrogen.

Cool season forages produce most of their biomass during spring, early summer and autumn, while warm season forages are productive during hot summers therefore filling in the slump left by cool season forages. To most livestock farmers, forage yield, crude protein (CP) and relative feed values (RFV) are the basis for making or buying hay for their livestock. Our objective was to determine yield, crude protein and relative feed values from a range of cool and warm season forages harvested as hay when grown under four different rates of nitrogen (N) of 0, 56, 112, & 168 kgha^-1. Cool season forages were: Fescue K-31, Max Q^TM fescue, CowPro fescue, Timothy, Smooth Bromegrass, and Orchard grass. Warm season forages were: Bermudagrass, Switchgrass, Eastern gamagrass, Indiangrass, Little bluestem, and Big bluestem. Forages were harvested at or near boot stage once each growing season near LaDue Missouri from 2003-5. Forage dry matter yields ranged between 1.6 and 5.0 Mgha^-1 for cool season forages and 3.0 to 8.3 Mgha^-1 for warm season forages for no nitrogen plots and plots receiving N at 168 kgha^-1 respectively. Significant differences in yields were observed with increasing rates of nitrogen. Percentage CP levels ranged from 6.4% to 9.2% and 3.4% to 7.1% for cool and warm season forages respectively. RFV levels ranged from 93 to 104 and 84 to 98 for cool and warm season forages respectively, and generally increased with increasing N rates. No significant differences in CP and RFV levels were observed for all the nitrogen rates except for CowPro fescue CP levels. Nitrogen highly influenced yield and to some extent CP and RFV but not as much as it influenced forage yield