Tropical Grasslands (1986) Volume 20, 145–156

INFLUENCE OF TEMPERATURE ON THE DIGESTIBILITY AND GROWTH OF MACROPTILIUM ATROPURPUREUM AND PANICUM MAXIMUM VAR. TRICHOGLUME IN SUBTROPICAL AND TROPICAL AUSTRALIA

J.R. WILSON,1P.N. JONES,2 D.J. MINSON1and

Officers of the N.S.W. Department of Agriculture, Qld Department of Primary Industries, N.T. Department of Primary Production, and CSIRO, Division of Tropical Crops and Pastures.3

1CSIRO, Division of Tropical Crops and Pastures, 306 Carmody Road, St Lucia, Queensland, 4067.
2CSIRO, Division of Mathematics and Statistics, 306 Carmody Road, St Lucia, Queensland, 4067.
3see footnote.

Abstract

Herbage from a multi-site trial of bred lines of the legume Macroptilium atropurpureum was collected at regular six-weekly harvests over two growing seasons to determine the effect of temperature on dry matter digestibility (DMD) under field conditions. The 18 sites were located throughout the subtropics and tropics of Australia (30°S to 13.5°S). At 10 sites, Panicum maximum var. trichoglume (green panic) was sown as an associate grass. Whole tops and the most recent fully expanded leaves for two of the Macroptilium lines and for green panic were collected.
Regression analysis showed that for each rise of 1°C in daily maximum or minimum temperature the DMD of Macroptilium decreased respectively by 0.25 or 0.26 percentage units for tops and 0.19 or 0.14 units for leaf. The decrease in DMD for the grass was larger, being 0.43 and 0.74 units for tops and 0.29 and 0.18 units for leaf. The average DMD was lower for the tropical northern sites (21°S–13°S) than the sub-tropical southern sites (30°S–23°S) by 2.5 and 1.9 units for tops and leaf of Macroptilium, and by 3.0 and, 1.5 units for tops and leaf of green panic. The DMD advantage of the sub-tropical sites was generally greater in spring and autumn than in summer. The DMD of tops tended to increase with water stress.
Active growth of both Macroptilium and green panic was initiated at, a daily minimum temperature above c. 12°C (daily mean temperature 17°C) but the responsiveness to temperature of the legume (4.8 kg ha-1 day-1 per °C) was only half that of the grass (10.8 kg ha-1 per day-1 per °C).
The DMD responses to temperature are considered in relation to temperature effects on yield, leaf/stem ratio and leaf development. Some practical implications of the adverse effect of high temperature on herbage quality are considered.

The following Officers took part in this investigation:-
P.T. Mears, G.P.M. Wilson, H. Mathers (Department of Agriculture, N.S.W.); K.F. Lowe, B.G. Cook, G.B. Robbins, B. Walker, M.T. Rutherford, C.H. Middleton, J.M. Hopkinson (Department of Primary Industries, Qld); P.G. Harrison (Department of Primary Production, N.T.); R.M. Jones, R.J. Jones, R. Delves (Division of Tropical Crops and Pastures, CSIRO).

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