LIGHT INTERCEPTION, RESERVE STATUS, AND PERSISTENCE OF CLIPPED MOTT ELEPHANTGRASS SWARDS

Defoliation management is an important determinant of persistence of p erennial forages. Persistence and related responses of 'Mott' elephant grass (Pennisetum purpureum Schum.) have not been studied under a wide range of defoliation management practices. The objective of this stud y was to determine the effect of defoliation frequency and stubble hei ght on Mott canopy Light interception, rhizome mass and reserve status at season end, tiller number in spring, and persistence. Treatments i mposed in 1989 through 1991 included all 16 treatment combinations of four defoliation heights (10-, 22-, 34-, and 46-cm stubble) and four d efoliation frequencies (3, 6, 9, and 12 wk). Treatments were replicate d three times in a randomized block design, and the soil was a hyperth ermic, uncoated Aquic Quartzipsamment. Data were analyzed by fitting m ultiple regression equations starting with a second order polynomial m odel. Light interception after harvest ranged from 11 to 60% and was a ffected only by defoliation height. Light interception increased as de foliation height increased, but at a decreasing rate. Light intercepti on before harvest ranged from 52 to 96% and was lowest for the 3-wk de foliation frequency, 10-cm stubble height treatment. In December follo wing 2 yr of defoliation, rhizome total nonstructural carbohydrate con centration (TNC) ranged from 135 to 271 g kg(-1) dry matter (DM), rhiz ome mass ranged from 24 to 733 g DM m(-2), rhizome TNC content was fro m nearly 0 to 197 g TNC m(-2), and rhizome N concentration was from 10 .9 to 14.2 g kg(-1) DM. Plants defoliated every 3 wk at a 10-cm stubbl e height had the lowest rhizome mass, TNC concentration and content, a nd N concentration, while values were greatest for those defoliated ev ery 12 wk at a 46-cm defoliation height. Number of tillers per plant i n May of 1990 and 1991 followed a similar trend. We conclude that Mott elephantgrass is persistent over a relatively wide range of clipping management practices, but close and frequent defoliation results in de pletion of reserves and stand decline.