NITROGEN AND DEFOLIATION MANAGEMENT - EFFECTS ON YIELD AND NUTRITIVE-VALUE OF FLACCIDGRASS

'Carostan' flaccidgrass (Pennisetum flaccidum Griseb.), a C-4 perennia l grass, has shown high quality potential in animal trials. Its yield response to defoliation frequency and N fertilization, however, has no t been reported. We examined the influence of stubble height and of a range of N applications in two defoliation experiments over 4 yr. Expe riment 1 (Raleigh, NC) combined two harvest heights, 76 and 38 cm, wit h 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 de foliation produced higher yields than 76-25 (Year 2: 11 330 vs. 7930 k g 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, 617 3 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) a nd 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), an d 51-5 and Boot-8 were also evaluated with 179 and 403 kg N ha(-1) (ei ght N-defoliation treatments in all). At both locations, highest yield s were obtained with Anthesis-8, averaging 19 010 kg ha(-1) st Raleigh and 12 390 kg ha(-1) at Watkinsville. The 20-5 defoliation resulted i n lowest yields at both locations, averaging 7648 kg ha(-1) at Raleigh and 5100 kg ha(-1) at Watkinsville. Defoliation frequency altered IVD MD (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 t he Raleigh Location, and warrants further evaluation in the upper Sout h.