S.A. DALZELL¹, N.J. BRANDON² and R.M. JONES²

¹Department of Agriculture, University of Queensland, Brisbane, Queensland, Australia
²CSIRO Tropical Agriculture, Brisbane, Queensland, Australia

Abstract

Two promising ley legumes, Macroptilium bracteatum (CPI 27404) and Macrotyloma daltonii (CPI 60303), were compared under glasshouse conditions with the widely used Lablab purpureus cv. Highworth in terms of response to defoliation and nutritive value. Plants were grown for 5 weeks prior to cutting at 2-, 4- or 6-weekly intervals at 7 or 15 cm height. The treatments were applied over 12 weeks and compared with uncut controls.
M. bracteatum was the most persistent and productive legume under frequent defoliation, producing more growing points than the other species when cut at 7 cm. It had the highest yields of roots under all cutting regimes and set seed under the most lenient regime.
All M. daltonii plants died when cut at 7 cm, mostly after the initial cutting. Although survival was much better when cut at 15 cm, this species gave lower top-growth and root yields than M. bracteatum and L. purpureus. It set seed only under the most lenient cutting regime.
L. purpureus out yielded the other 2 species in the uncut controls. However, the relative decline in top-growth yield with increasing severity of cutting was greater than for M. bracteatum. Half the plants died under the combination of frequent (2- or 4-week) and intense defoliation (7 cm). It did not flower during the experiment.
The main difference in quality, as assessed by N%, P%, acid detergent fibre and grinding energy, was between leaf and stem. Differences in leaf or stem quality between the 3 species were relatively minor.
Macroptilium bracteatum was identified as a productive legume more tolerant of severe defoliation than L. purpureus.