Grazing studies of a Hyparrhenia hirta (Coolatai grass) pasture in northern New South Wales
G. M. Lodge A C , L. H. McCormick B and S. Harden AA NSW Department of Primary Industries, Tamworth Agricultural Institute, 4 Marsden Park Road, Tamworth, NSW 2340, Australia.
B NSW Department of Primary Industries, PO Box 71, Manilla, NSW 2346, Australia.
C Corresponding author. Email: greg.lodge@dpi.nsw.gov.au
Australian Journal of Experimental Agriculture 45(12) 1603-1611 https://doi.org/10.1071/EA04086
Submitted: 2 May 2004 Accepted: 11 August 2004 Published: 19 January 2006
Abstract
Hyparrhenia hirta (L.) Stapf (Coolatai grass) has invaded large areas of grazed native grasslands on the North-West Slopes of New South Wales (NSW) and is widespread along roadsides and travelling stock routes. It is commonly regarded as an invasive, weedy species with low forage value when it is tall and rank, but may be more palatable when kept short, green and leafy.
A study (1990–2001) of a naturalised stand of Coolatai grass in the Manilla district of northern NSW examined its herbage mass (kg DM/ha), persistence (basal cover %), and grazing value under 2 contrasting grazing treatments: pastures that had either large amounts of dry, unpalatable herbage [light grazing at 5 dry sheep equivalents (DSE)/ha] or were short, green and leafy (strategic heavy grazing at a stocking rate of 37 DSE/ha). Effects of pre-grazing treatments (slashing, burning, and no defoliation) were also examined and data (litter mass, plant basal area, ground cover, and soil and litter microbial carbon and nitrogen) collected to assess the long term sustainability of these grazing systems.
Sheep grazed the light grazing treatment for about 34% of the experimental period, with the strategic heavy grazing treatment being grazed for about 7% of the time. Over the experimental period this equated to 6752 DSE grazing days/ha for the light grazing treatment compared with 10 120 DSE for the heavy grazing treatment. Herbage mass in the heavy grazing treatment declined to <1000 kg DM/ha within 6 months of the start of grazing and remained below this level until December 1998 when stocking rates were switched (i.e. plots previously grazed at low stocking rate were subjected to the heavier rate and vice versa). In contrast, mean herbage mass in the light grazing treatment was generally >3000 kg DM/ha from November 1990–98, but a high proportion of this was dead standing material that carried over from season to season. Mean Coolatai grass basal cover was 9.5% in November 1990, increasing over time to about 25% in both grazing treatments by December 2000.
Coolatai grass herbage accumulation was highly seasonal, ranging from as high as 70 kg DM/ha.day in summer to 0 in winter. In both grazing treatments, forage quality was low for both green and dead material, with mean crude protein being 6.0 (green) and 3.4% (dead). Digestible dry matter values ranged from 41 to 62% (green) and 32 to 51% (dead) and mean metabolisable energy values were 7 (green) and 5.3 MJ/kg DM (dead). After 8 years, the heavy grazing treatment had lower (P<0.05) litter mass, ground cover, plant basal area and soil microbial C and N levels than the light grazing treatment, but switching of the stocking rates restored most indicators, except the soil microbial values.
Additional keywords: degradation, forage quality, herbage mass, persistence, stocking rate.
Acknowledgments
We gratefully acknowledge the assistance of Ross and June Wicks, ‘Springmount’, Upper Manilla, in providing and maintaining the livestock used in this study and in moving stock to and from the plots as required. We also thank Brian Roworth, Michael Honess, Brian Sauer, Tina Schwenke, Andrew Schipp and Bruce Carter for their assistance in collecting and processing the data and Kath King, University of New England, Armidale, for analysing the soil and litter microbial biomass samples. Erik Dekkers and Wayne Garnsey, Rangers from the Tamworth Rural Lands Protection Board, also assisted with the selection of the site and its long term use. Funding from the NSW Agriculture R and D Initiatives Program (1995–98) provided for collection of the herbage accumulation data and the forage quality and soil chemical analyses.
Amato M, Ladd JN
(1988) Assay for microbial biomass based on ninhydrin-reactive nitrogen in extracts of fumigated soils. Soil Biology and Biochemistry 20, 107–114.
| Crossref | GoogleScholarGoogle Scholar |
(verified 22 November 2005)
McWilliam JR,
Shanker K, Knox RB
(1970) Effects of temperature and photoperiod on growth and reproductive development in Hyparrhenia hirta. Australian Journal of Agricultural Research 21, 557–569.
| Crossref | GoogleScholarGoogle Scholar |
Murphy SR, Lodge GM
(2002) Ground cover in temperate native perennial grass pastures. I. A comparison of four estimation methods. Rangeland Journal 24, 288–300.
| Crossref | GoogleScholarGoogle Scholar |
Orchard BA,
Cullis BR,
Coombes NE,
Virgona JM, Klein T
(2000) Grazing management studies in the Temperate Pasture Sustainability Key Program; experimental design and statistical analysis. Australian Journal of Experimental Agriculture 40, 143–154.
| Crossref | GoogleScholarGoogle Scholar |
Verbyla AP,
Cullis BR,
Kenward MG, Welham SJ
(1999) Analysis of designed experiments and longitudinal data by using smoothing splines (with discussion). Applied Statistics 48, 269–312.
