Volume 42, 96-103

Tropical Grasslands (2008) Volume 42, 96–103

Forage production and potential nutritive value of 24 shrubby Indigofera accessions under field conditions in South Africa

ABUBEKER HASSEN¹, N.F.G. RETHMAN², Z. APOSTOLIDES³ AND W.A. VAN NIEKERK¹

¹ Department of Animal and Wildlife Sciences,
² Department of Plant Production and Soil Science, and
³ Department of Biochemistry, University of Pretoria, Pretoria, South Africa

Abstract

Twenty-four shrubby Indigofera accessions from 7 species were evaluated in terms of their forage production, potential nutritive value and indospicine levels in the forage biomass over two growing seasons. Eighteen seedlings per plot were transplanted into field plots measuring 1.5 × 3 m in January 2003 at spacings of 50 cm between and within rows, with 3 replicates. In both seasons, differences between and within species for plant height, canopy spread diameter, fodder yield and leaf percentage of the biomass were significant (P<0.05). I. amorphoides 7570, I. cryptantha 7070 and I. arrecta 7709 were superior in terms of forage yield in the first season, while I. amorphoides 7549, I. cryptantha 7067 and I. arrecta 10350 were superior in the subsequent season. Yields as high as 21 t/ha DM (total) and 5 t/ha DM (leaf) were obtained in some accessions in Year 2. Crude protein concentrations were high for I. cryptantha (29.8%) and I. amorphoides (27.7%), while the lowest were recorded for I. coerulea (15.9%) and I. vicioides (20.1%). Phosphorus concentrations in the forage biomass were higher for I. cryptantha (0.37%), I. brevicalyx (0.35%) and I. amorphoides (0.33%) than for I. costata (0.23%). The in vitro organic matter digestibility ranged from 74.8% for I. amorphoides to 63.8% for I. brevicalyx.
Indospicine levels in the forage biomass varied dramatically both between and within species. Concentrations were insignificant (0–2 mg/kg DM) in I. brevicalyx, and reached 706 mg/kg DM in I. vicioides. Within I. arrecta, levels varied 10-fold (26–289 mg/kg DM). The variation, which exists in this genus in the various parameters, indicates considerable opportunity to select accessions for possible feeding studies with animals to determine acceptability and possible deleterious effects.