Effects of N and Harvest Frequency on Forage Quality and Yield of Native Grasses.

Five native warm-season grass species and mixtures were grown in east-central Mississippi on a coarse-loamy, siliceous, semiactive, thermic Glossic Fragiudult, to determine their potential as forage grasses in response to harvest frequency and N application. Established stands were harvested at 30, 40, 60, and 120 d intervals, and were fertilized with N rates of 0, 56, 112, 168, and 224 kg N ha^-1 for two consecutive years (2016 and 2017). Dry matter (DM) yield, agronomic nitrogen use efficiency (aNUE), and forage quality (crude protein, CP; acid detergent fiber, ADF; neutral detergent fiber, NDF; and total digestible nutrients, TDN) were analyzed. Year, treated as a repeated measure, was the main source of variation affecting DM yields. Within year, harvest frequency had the greatest effect on cumulative yields in 2016, accounting for 44% of the variation observed. This effect was not observed in 2017. Frequent defoliations led to overall lower yields in 2017. Nitrogen was significant, but moderately, accounting for 2 and 4% of variation for 2016 and 2017, respectively. Species was also significant for both years. Agronomic N use efficiency varied between year, species, N rate, and harvest frequency. Eastern gamagrass [Tripsacum dactyloides (L.) L.] was the only species in which cumulative DM yield remained consistent across both years of the study, regardless of harvest frequency or N application. In terms of forage quality parameters, year was again significant for each characteristic. Harvest frequency had the greatest effect on CP (64%), ADF (57%), NDF (55%), and TDN (60%) of variation observed. More frequent harvests resulted in greater forage quality values. However, harvest frequencies should be based on species present, and less frequent harvests are required for sustained DM yields.