Abstract:
Proc. Aust. Soc. Anim. Prod. (1978)112: 230 COMPARATIVE SUMMER MILK PRODUCTION FROM TROPICAL GRASS-LEGUME AND NITROGEN FERTILIZED PASTURES T.M. DAVISON* and R.T. COWAN* During periods of high pasture growth on the Atherton Tablelands, dairy farmers can choose between grass-legume (GL) and nitrogen fertilized grass (GN) pastures for summer milk production. With increasing fertilizer costs it is important to compare the levels of milk production from the two systems. As part of a largier grazing experiment, four Friesian cows grazed four pasture replicates oflGattoplpanic (Panicum maximum - CT. Gattpn) fertilized-at 200 kg N ha (N200) and 400 kg N ha year- (N400) year or Gatton panic - Glycine wightii cv. Tinaroo, Desmodium intortum pasture (GL) . Treatments were ~grazed on a rptational basis of one week grazing, three weeks spelling at 2.0 cowsha . Nitrogen fertilizer was applied in mid-Nov. 1976 at 15% of the annual rate. Pre-grazing pasture data were collected from three replicates by cutting and sorting into leaf, stem and legume. Two Friesian heifers with oesophageal fistulas were used to samnle each of the threie replicates. Milk data were recorded durincl eight weeks of grazing in Jan. and Feb. 1977. Milk yield per cow was higher (P(O.01) on GL than GN pastures, but milk yields for N2OO and N400 (Table 1) were similar. Solids not fat. levels of GN cows were lower (P(O.01) than for GL cows and below the legal standard of 8.5 percent. There was no significant difference (PjO.05) between treatments in diet leaf percent. Legume averaged la percent of the diet ofGL cows. TABLE 1: Milk yield and composition, pasture and diet parameters. Higher milk yield by GL cows was attributed to the legume component of the diet. Since pasture on offer was not limiting (Cowan and O'Grady 1976) milk yield was mainly a function of diet quality. Few experiments have compared milk production from GN and GL systems in tropical areas. The superiority of the GL over the GN pastures for milk production in this experiment is- consistent with results for meat production from tropical pastures (Jones 1974). The study indicates major savings in fertilizer costs can be obtained by grazing GL pastures during summer. COWAN, R.T., and O'GRADY, P. (1976). Trop. Grasslds. 10 : 213. JONES, R. J. (1974). Proc. Aust. Soc. Anim. Prod. 10 : 540. * Queensland Department of Primary Industries, Kairi, 4872. 230.