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

USDA-ARS and Dep. of Crop Science, North Carolina State Univ., Univ., Box 7620, Raleigh, NC 27695
Dep. Crop Science, North Carolina State Univ., Univ., Box 7620, Raleigh, NC 27695
Belesky, USDA-ARS, 224 Airport Rd., P.O. Box 400, Beaver, WV 25813.
USDA-ARS and Dep. of Crop Science, North Carolina State Univ., Box 7620, Raleigh, NC 27695
Dep. Crop Science, North Carolina State Univ., Box 7620, Raleigh, NC 27695

^* Corresponding author (jburns{at}cropservl.cropsci.ncsu.edu).

‘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 fertilizafion, however, has not been reported. We examined the influence of stubble height and of a range of N applicafions 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 defoliafion 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 defoliafion 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.

Received for publication July 15, 1997.