Light Interception, Reserve Status, and Persistence of Clipped Mott Elephantgrass Swards

Abstract

Defoliation management is an important determinant of persistence of perennial forages. Persistence and related responses of ‘Mott’ elephantgrass (Pennisetum purpureum Schum.) have not been studied under a wide range of defoliation management practices. The objective of this study was to determine the effect of defoliation frequency and stubble height on Mott canopy light interception, rhizome mass and reserve status at season end, tiller number in spring, and persistence. Treatments imposed in 1989 through 1991 included all 16 treatment combinations of four defoliation heights (10‐, 22‐, 34‐, and 46‐cm stubble) and four defoliation frequencies (3, 6, 9, and 12 wk). Treatments were replicated three times in a randomized block design, and the soil was a hyperthermic, uncoated Aquic Quartzipsamment. Data were analyzed by litting multiple regression equations starting with a second order polynomial model. Light interception after harvest ranged from 11 to 60% and was affected only by defoliation height. Light interception increased as defoliation height increased, but at a decreasing rate. Light interception before harvest ranged from 52 to 96% and was lowest for the 3‐wk defoliation frequency, 10‐cm stubble height treatment. In December following 2 yr of defoliation, rhizome total nonstructural carbohydrate concentration (TNC) ranged from 135 to 271 g kg−1 dry matter (DM), rhizome mass ranged from 24 to 733 g DM m−2, rhizome TNC content was from 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 stubble height had the lowest rhizome mass, TNC concentration and content, and N concentration, while values were greatest for those defoliated every 12 wk at a 46‐cm defoliation height. Number of tillers per plant in 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 depletion of reserves and stand decline.