DEFOLIATION EFFECTS ON AGRONOMIC PERFORMANCE OF SEEDED PENNISETUM HEXAPLOID HYBRIDS

Interspecific Pennisetum hybrids between pearl millet [P glaucum (L.) R.Br.) and elephantgrass (P. purpureum Schum.) have been developed tha t are seed propagated, productive, and high in nutritive value, but de foliation effects on hybrid agronomic performance have not been assess ed. A field experiment was conducted on an Adamsville soil (hypertherm ic, uncoated Aquic Quartzipsamment) in 1991 and 1992 to determine the effect of three clipping treatments (every 6 or 12 wk to 15 cm and eve ry 6 wk to 30 cm) on dry matter (DM) yield, nutritive value, and persi stence of 10 seeded hybrids and 'Mott' elephantgrass. In the first yea r of defoliation, Mott and the hybrids had similar yields when harvest ed at 6-wk intervals (9.7 vs. 9.2 Mg ha-1 yr-1), but hybrids had great er yields than Mott when harvested at 12-wk intervals (17.9 vs. 13.0 M g ha-1 yr-1). Yields were greater for Mott than hybrids in the second year, regardless of clipping treatment. In 1991, crude protein (CP) co ncentration was not different when cut every 6 wk (139 g kg-1 DM), but Mott had higher CP than the hybrids when clipped every 12 wk (H2 vs. 95 g kg-1). Across clipping treatments, in vitro digestible organic ma tter (IVDOM) was greater for Mott than for the hybrids (638 vs. 602 g kg-1 OM) in 1991. In 1992 there were no differences in CP or IVDOM bet ween Mott and hybrids. After 1 yr of defoliation, winter survival of h ybrid plants was 18%, while Mott survival was 100%. Comparison of rese rve status of hybrids and Mott showed that hybrids had lower rhizome m ass (0.46 vs. 1.1 kg m-2), total nonstructural carbohydrate (TNC) conc entration (115 vs. 276 g kg-1 DM), and TNC pool (56 vs. 304 g m-2) . T hese data indicate that seeded hybrids are productive and high in nutr itive value. Their potential for use in the U.S. Gulf Coast, however, depends on development of lines that are more persistent under defolia tion.