Volume 27, 94

Tropical Grasslands (1993) Volume 27, 94–99

Response of Desmanthus to clipping on a phosphatic clay mine-spoil

M.B. ADJEl¹ and W.D. PITMAN²

¹University of the Virgin Islands, Agricultural Experiment Station, St. Croix, U.S. Virgin Islands
²University of Florida, Agricultural Research and Education Centre, Ona, Florida, USA

Abstract

Defoliation treatments of 1, 2, and 3 harvests annually were imposed on three Desmanthus accessions established on a phosphatic clay minespoil to evaluate yield and quality of edible forage and seed production. Total dry matter (leaf + stem) yields from 2 and 3 harvests annually were 26.2 and 16.0 t/ha (P < 0.01), respectively, across all accessions. However, annual yield of the temperate perennial D. illinoensis (Illinois bundleflower) from 1 harvest was only 7.1 t/ha compared with 37.1 and 53.2 t/ha for the tropical D. virgatus accessions IRFL 1857 and IRFL 1854, respectively. The proportion of leaf decreased (P < 0.01) from 50 to 10% with decreasing frequency of harvest. Mean leaf crude protein (CP) content for the 2 and 3 harvests averaged 22.4% but decreased (P < 0.05) to 20% for the single harvest. The average stem CP declined (P < 0.05) from 8.0 to 5.4% with maturation. Contrary to the expected trend, leaf in vitro organic matter digestibility (IVOMD) of all accessions was low (34–41 %) and increased (P < 0.05) with decreasing harvest frequency, perhaps as a result of a dilution of tannins with later growth. No appreciable amount of seed was produced under the most frequent harvest schedule. Highest annual seed yield (845–3380 kg/ha at 12% moisture, depending on year) for Illinois bundleflower was obtained with 2 harvests per year and for D. virgatus accessions (369–900 kg/ha) with 1 harvest per year. These data suggest that differential clipping schedules are required to optimise forage quality and seed production from the various Desmanthus accessions. Also, because of the low leaf IVOMD, feeding trials are needed to ascertain the feeding value of Desmanthus forage to livestock. Both temperate and tropical Desmanthus species were productive on this subtropical phosphatic clay site, with herbage and seed production occurring during the warm season for both species.