The Dollars and Sense of Nitrogen Application on Summer Annual Forage Mixtures.

Increasing botanical diversity in perennial pastures has traditionally been linked with increased productivity, especially when legumes are included. This often leads to a reduced need for nitrogen fertilizer, which should lead to increased economic efficiency. However, limited information exits as to whether these same phenomena are realized in summer annual pastures. A study was conducted in 2018 and 2019 at two locations in Kentucky (Princeton, Zanesville silt loam with a fragipan; Lexington, Maury silt loam) to determine the effects of nitrogen application rate (0, 50, 100, 150, and 200 lb N/A) on three different sudangrass based forage treatments: monoculture, simple mixture (3 species) and complex mixture (12 species); both mixtures contained legumes. Plots were harvested three times each year at 30-40 in. In three out of the four location+year combinations (environments), forage treatment had no effect on yield (p>0.06). However, for three out of the four environments, N treatment still had a linear effect on yield (p<0.01), even though legumes were included in mixtures. These results indicate that increasing biodiversity in summer annual pastures may not offer any additional yield benefit, as well as the need to still apply nitrogen fertilizer on these pastures even with legume inclusion. These findings indicate that sudangrass monocultures fertilized with optimal nitrogen rates may be the most economic option of those studied, however, diverse summer annual mixtures may offer other environmental benefits.