Nitrogen and Defoliation Management: Effects on Yield and Nutritive Value of Flaccidgrass

Abstract

Abstract‘Carostan’ flaccidgrass (Pennisetum flaccidum Griseb.), a C4 perennial grass, has shown high quality potential in animal trials. Its yield response to defoliation frequency and N fertilization, however, has not been reported. We examined the influence of stubble height and of a range of N applications in two defoliation experiments over 4 yr. Experiment 1 (Raleigh, NC) combined two harvest heights, 76 and 38 cm, with two stubble heights, 25 and 15 cm (76–25, 76–15, 38–25, 38–15); all treatments received 380 kg N ha−1 yr−1. After Year 1, the 76–15 defoliation produced higher yields than 76–25 (Year 2: 11 330 vs. 7930 kg ha−1, P < 0.001; Year 3:8950 vs. 6270 g kg−1, P < 0.001), while in vitro dry matter disappearance (IVDMD) was similar (Year 3) (mean = 582 g kg−1). Compared with 38–15, the 38–8 defoliation resulted in lower yields (Year 2: 8638 vs. 9344 kg ha−1, P = 0.001; Year 3, 6173 vs. 8090 kg ha−1, P = 0.07) but higher IVDMD (Year 3, 651 vs. 635 g kg−1, P < 0.01). Experiment 2 (Raleigh, NC, and Watkinsville, GA) had four defoliations: clipping to 5 cm at 20 and 51 cm (vegetative) and to 8 cm at boot and anthesis stages (20–5, 51–5, Boot—8, Anthesis—8). All defoliation treatments were topdressed with 291 kg N ha−1, and 51–5 and Boot—8 were also evaluated with 179 and 403 kg N ha−1 (eight N—defoliation treatments in all). At both locations, highest yields were obtained with Anthesis—8, averaging 19 010 kg ha−1 at Raleigh and 12 390 kg ha−1 at Watkinsville. The 20–5 defoliation resulted in lowest yields at both locations, averaging 7648 kg ha−1 at Raleigh and 5100 kg ha−1 at Watkinsville. Defoliation frequency altered IVDMD (range = 550 to 789 g kg−1), but N application did not; however, increasing N application increased N concentrations linearly (P = 0.05). Flaccidgrass had high yield potential and high nutritive value at the Raleigh location, and warrants further evaluation in the upper South.