Enhanced Efficiency Nitrogen Formulation Effect on Tall Fescue - Red Clover Mixed Species Pasture Productivity.

The use of nitrogen (N) fertilizer is generally limited on mixed cool-season forage systems due to its stimulatory effect on grasses, which increases competition with legume species. Reduced legume growth from this competition can compromise forage nutritive value and prospective yields. The controlled-release nature of several enhanced efficiency fertilizer N products holds the potential to improve legume persistence in mixed species pastures while providing supplemental N required by the grass component. This study evaluated the effect of different enhanced efficiency N formulations [Environmentally Smart Nitrogen^® (ESN), Agrotain^®-treated urea (ATU), and a 75% ESN: 25% urea blend] and untreated urea on yield, nutritive value, and legume persistence in a ‘KY 31’ tall fescue [Schedonorus arundinaceus (Schreb.)] and ‘Kenland’ red clover (Trifolium pratense L.) mixture. Nitrogen was applied at four rates (0, 112, 224, and 336 kg N ha^-1) in three equal applications. During the first year, total seasonal yield increased with increasing N rates, but during the second growing season there was no difference in forage yield due to N rate or N source. Although clover content was greater than 50% throughout the duration of the study, red clover in the sward declined with increasing N rate. Environmentally Smart Nitrogen and the ESN+urea blend maintained more clover in the plots than ATU and urea. Forage nutritive value was not affected by N rate or N source. These results suggest that no N fertilization, regardless of N source, is required when red clover comprises more than 50% of the sward due to lack of yield benefit.