Effect on cereal crop and sheep production of two rotations in a ley farming system in the south-west of Western Australia

The effects on pasture composition, soil nitrogen, cereal crop production and sheep production of two rotations in a subterranean clover (Trifolium subterraneum) ley farming system were studied over an eight-year period, 1965-1 972, in a 625 mm rainfall area at Bakers Hill, Western Australia. A short rotation (one year pasture-one year crop) commencing after either one or two years of pasture, was compared with a longer rotation (six years pasture-one year crop). Closed farm systems were usedwith the pastures continuously grazed by Merino wether sheep at two set-stocked rates. A two year rotation based on one year of subterranean clover followed by one year of cereal crop resulted in cereal grain yields in the third crop equal to that after six years pasture. Clover content of pastures was higher with alternate years of cropping. Soil mineral nitrogen was higher in the two year rotation before the third crop than after six years of pasture. The wheat crops did not respond to fertilizer nitrogen on either rotation. Grain yield was slightly lower following grazing at the high stocking rate. At the end of the experiment the grain yield from the second crop in the two year rotation was less than half that from the first crop and the difference in yield could not be eliminated by the use of fertilizer nitrogen up to 100 kg ha-1. The sheep on the short rotation were heavier and cut more wool per head at both stocking rates by the end of the experiment.