Yield of Native Warm‐Season Grasses in Response to Nitrogen and Harvest Frequency

Abstract

Core Ideas Within year, harvest frequency has the greatest effect on DM production of native warm‐season grasses. Nitrogen has little effect on native warm‐season grass DM yield. Eastern gamagrass can tolerate consecutive years of frequent defoliations and maintain yield. 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 and agronomic nitrogen use efficiency (aNUE) 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. Results suggest that rest periods should be based on species present, and that less frequent harvests are required for sustained DM yields.