Comparison of the nutritive value of standover and regrowth Rhodes grass (Chloris gayana cv. Callide) during summer and autumn in a subtropical environment

Abstract

Animal Production in Australia 1998 Vol. 22 COMPARISON OF THE NUTRITIVE VALUE OF STANDOVER AND REGROWTH RHODES GRASS (Chloris gayana cv. Callide) DURING SUMMER AND AUTUMN IN A SUBTROPICAL ENVIRONMENT B.C. GRANZINAB and G. McL. DRYDEN A B A Dept of Animal Production, The University of Queensland Gatton, Qld 4345 Present address: NSW Agriculture, Wollongbar Agricultural Institute, Wollongbar, NSW 2477 Pasture availability is limited during late summer and autumn in subtropical dairying areas due to the low growth rates of both tropical and temperate pastures. One management option is to stand over tropical grasses from summer to autumn and then to graze this pasture. However, the opportunity cost of this practice is the loss of herbage that could be rotationally grazed during this standover period. Insufficient information is available to allow this opportunity cost in terms of yields and nutrient quality to be calculated. A trial was conducted at Mutdapilly Research Station in south-east Queensland where Rhodes grass (Chloris gayana cv. Callide) was stood over from 30 November 1994 to 19 April 1995. An adjacent area of the sward was cut on 28 December 1994, 8 February 1995 and 22 March 1995 with all cut material removed. The experimental plot received 656 mm of rainfall and irrigation during the experimental period. Urea was applied every six weeks at a rate of 100 kg/ha. Four quadrants (0.16 m2) were harvested to a height of 5 cm from each treatment every two weeks. Dry matter content was determined by drying herbage at 100oC for 24 h. Results shown in Table 1 for 30 November 1994, 14 December 1994 and 28 December are averages for the experimental area before the regrowth area was cut. The very low growth rates of Rhodes grass during April can be attributed to low minimum air temperatures (Ivory and Whiteman 1976). Although 3823 kg DM or 30 966 MJ ME/ha of leaf was available on 5 April 1995 after the sward was stood over, this was at the opportunity cost of 4802 kg DM or 39 464 MJ ME/ha of regrowth leaf during the same period indicating a marginal benefit for the regrowth system. Accompanying the standover leaf on 5 April 1995 was 8353 kg of stem which was of low nutritional quality (52 g crude protein/kg DM and 7.2 MJ of ME/kg DM). The high stem content of the standover sward would probably limit intakes of standover tropical grass pastures by dairy cows. Financial assistance from the Australian Research Council and the cooperation of T. Cowan and J. Ansell of the Queensland Department of Primary Industries is acknowledged. Table 1. Dry matter yields and nutrient content of standover and regr owth Rhodes grass leaf Sampling date 30.11.94 14.12.94 28.12.94 standover 11.01.95 25.01.95 08.02.95 22.02.95 08.03.95 22.03.95 05.04.95 19.04.95 A Leaf dry matter yields (kg/ha) 684 870 1490 Metabolisable energy (MJ/kg DM) 10.0 9.6 9.5 regrowth 9.9 9.6 7.2 9.5 9.1 7.5 10.0 9.2 A Neutral detergent fibre (g/kg DM) 609 642 623 Crude protein (g/kg DM) 167 146 149 regrowth standover 722 970 1302 893 1548 1666 344 368 8.8 9.1 8.9 8.0 9.3 8.8 8.1 6.6 standover 703 677 665 770 712 726 719 717 regrowth 580 626 646 644 734 720 628 611 standover regrowth 101 118 115 90 104 74 104 73 229 151 116 168 89 97 200 201 1828 2081 3111 2742 4389 4175 3823 2946 MJ ME/kg DM = 0.15 (In vitro dry matter digestibility(%) + 2% units) * (100 - ash%/100) (Wan Hassan 1981) IVORY, D.A. and WHITEMAN, P.C. (1978). Aust. J. Plant Physiol. 5, 131-148. WAN HASSAN, W.E. (1981). Proc. 5th Ann. Conf. Malay. Soc. Anim. Prod. pp. 192-201. 311