Correction - Soil nitrogen status and pasture productivity after clearing of brigalow (acacia harpophylla)

At 31 sites of solodized solonetz and solodic soil in central Queensland, the total soil nitrogen (N) and organic carbon (OC) levels of pasture and crop areas were compared with matched uncleared areas of A. harpophylla-Dawson gum (Eucalyptus cambageana) forests. Reductions in total N content (kg per ha) occurred only at 8 of the 31 sites and ranged from 16-34% of the virgin levels (about 300 to 700 kg N ha). There was no association between changes in N reserves and age of development. Reductions in the concentration (%) of N and OC were measured under pasture (group 1) and crop (group 3) areas but not where pasture areas had been ploughed (group 2). The bulk density of soils developed to pasture was higher than those of the uncleared areas. In a pot experiment, both nitrogen uptake and dry matter (DM) yield were significantly (P< 0.01) correlated (r = 0.78, r = 0.81, respectively) with the percentage N content of soils. Also, reductions in potential DM yield were positively correlated (r = 0.76) with reductions in the N percentage. Old buffel grass (Cenchrus ciliaris) pastures were moderately deficient in nitrogen, and DM yield increased curvilinearly in response to nitrogen applied as NH4NO3 at rates of 0, 40, 80, 120, 160, 200, 240 and 300 kg N haCurrent pasture production is about 60% below the potential possible if adequate nitrogen is available. Summer yields of 3200 kg DM ha-l were doubled, with a response efficiency of about 31 kg DM per kg N, by applying 120 kg N haThe pasture potential of sites of differing N status was influenced by the weather. It is concluded that the deterioration of pastures on brigalow lands is influenced more by reduced nitrogen availability than changes in N reserves