W. TRUJILLO,^1,2 W.D. PITMAN,^1,4 C.G. CHAMBLISS³ and K. WILLIAMS²

¹University of Florida, Agricultural Research Center, Ona, and
²Botany Department, Gainesville, and
³Agronomy Department, Gainesville, Florida, USA
⁴Present address: Rosepine Research Station, Rosepine, Louisiana, USA

Abstract

Desmanthus virgatus has demonstrated potential as a pasture legume, particularly on tropical and subtropical clay soils that are neutral to alkaline. To increase understanding of its responses to defoliation, a factorial combination of 5, 25 and 100-cm stubble heights and 2, 4 and 12-week harvest intervals was imposed on field plots of D. virgatus accession IRFL 1857 over 2 years. Leaf and stem yield, in vitro digestibility, crude protein and number of growing points following defoliation were determined. Total non-structural carbohydrate (TNC) concentrations in roots and stems were also measured following each of 2 growing seasons of defoliation.
Both total dry matter harvested and leaf yield were greatest when plants were harvested every 2 weeks at a stubble height of 100 cm. TNC levels were highest and leaf digestibility was among the lowest in 1990 with this treatment combination. Close and frequent harvesting resulted in low yields, low TNC concentrations, very few shoots, and stand loss following 1 year of defoliation. These results indicate that frequent but light defoliation will maximise productivity. However, leaf digestibility can be lower under such utilisation, perhaps due to high tannin levels. No plants survived into the fourth year.