Chemical curing of annual pastures in Southern Australia for beef cattle and sheep

Abstract

A desiccant herbicide (paraquat) was used to kill an annual pasture during the late spring months when the digestibility of the dry matter (DM) was 75%. The nutritive value of this standing herbage during the summer drought period was compared in field and pen studies with pasture allowed to mature naturally in the Mediterranean environment of South Australia. The herbicide treatment resulted in a significant reduction of standing herbage at the beginning of the summer period (5766 v. 2791 kg DM/ha). The DM digestibility by beef cattle of treated and untreated herbage was similar (52.4 v. 53.0% respectively). There was no difference between the paraquat-treated and the naturally matured pasture in the content or the apparent digestibility of organic matter, water-soluble carbohydrate, cellulose, or lignin; but nitrogen content, digestibility, and retention were significantly higher for paraquat-treated herbage. Rainfall between spraying and the beginning of the summer period was 140 mm. Indirect evidence from a separate study indicates that the fall in digestibility of the herbage after paraquat treatment was influenced by both rainfall and the spraying treatment. The productivity of beef cattle and sheep grazing the treated and untreated pastures during the dry summer confirmed the results of the digestibility studies, there being no difference between treatments in weight change or wool production. After the commencement of the autumn rainfall season the proportion of grass . on the sprayed area was greatly reduced, and the growth of cattle was significantly impaired. Thus the overall effect of the paraquat treatment was to reduce cattle growth.