Measurements on a 1/10-acre sample of brigalow forest indicated a total biomass of 293x 103 kg/ha, 46% of which consisted of dead materiai, either on the ground or standing. The presence of large amounts of dead material is attributed to the semiarid climate, which results in low decomposition rates, hardness of the wood, absence of termite activity above ground, and lack of running fires. Moisture percentages were low, varying from 4-6% for dead material to 65% for living leaves plus twigs. Amounts of elements immobilized in the biomass were 1600, 38, 300, 100, 2230, and 180 kg/ha for nitrogen, phosphorus, potassium, sodium, calcium, and magnesium respectively. Brigalow showed high nitrogen/phosphorus and calcium/potassium ratios compared with lucerne and grasses grown on a similar cleared area. No differences in sodium and calcium concentrations were found in different components of brigalow, but the canopy showed higher levels of nitrogen, phosphorus, potassium, and magnesium than the trunks, with branches and roots intermediate. In addition the canopies of larger trees showed higher concentrations of nitrogen, phosphorus, and potassium than those of smaller trees. The uneven spatial distribution of living trees associated with the gilgai topography resulted in large sampling errors. The dead material and roots, being more uniformly distributed, showed lower errors. Subsampling techniques used for obtaining samples for chemical analyses were adequate, as standard errors for nutrient concentration determinations were generally lower than those for dry matter determinations.

In a study of a brigalow (Acacia harpophylla F. Muell.) ecosystem the underlying soil material (0-90 cm) was intensively sampled in addition to complete harvesting of vegetative material. Microrelief contours were plotted and random sampling of soils within each of three microtopographic classes carried out. There was a tendency for larger trees to be confined to the higher portions of the microrelief. Differences in soil properties in various microtopographic positions appear to be related to canopy interception and leaf drip of these larger trees. Thus the apparent uniformity of soil salinity isopleths in corresponding layers at different topographic positions, in spite of run-off from higher portions of the microrelief, was attributed to the counteracting effect of canopy interception resulting in the concentration of incident rainfall on the higher parts. This effect was also considered to contribute to the higher soil exchangeable potassium values found on the upper portions of the microrelief. The higher values for soil organic carbon and nitrogen in the upper portions of the microrelief were attributed to the greater concentration of roots in these areas. Relationships between the chemical content of the various components of the ecosystem were examined. The relatively low phosphorus content of the soils and of the forest suggests the adaptation of brigalow to soils of low phosphorus status. The high uptake of calcium is of especial interest in view of the acidity and salinity of the soil. It seems probable that the trend of increasing acidity with depth in these soils is associated with the accumulation of calcium by brigalow and its release during litter decomposition, the low buffering capacity of the soil, and the increasing salinity of the soil with depth. The factors involved in the persistence of brigalow and its high dry matter production under the hot, dry climatic and saline soil conditions in this area are worthy of further study.

A lateritic podzolic soil and a solodized solonetz soil, with histories of organic matter increase under tropical and temperate pastures respectively, were incubated over a period of a year with a weekly wetting and drying cycle. Decreases in organic matter (7 and 11%), total nitrogen (12 and 10%), and non-distillable acid-soluble nitrogen (30 and 25%) occurred, but there were no significant changes in residual nitrogen. Although there were marked increases in mineral nitrogen at the beginning of the incubation in both soils, nitrification was relatively poor in both soils. In a short-term (4 weeks) incubation of a lateritic podzolic soil and a grey clay soil the addition of labelled nitrogen followed by fractionation allowed nitrogen transformations to be examined precisely. Although differences in total nitrogen (labelled + unlabelled) with time were not statistically significant (P = 0.05) in the sandy soil (lateritic podzolic) a loss (28%) of total labelled nitrogen did occur. Parallel with this was an increasing incorporation of labelled nitrogen in all three organic fractions and a disappearance of ammonium nitrogen without the appearance of an equivalent amount of nitrate nitrogen. On the other hand, in the clay soil there was no loss of total labelled nitrogen with time and little incorporation of labelled nitrogen in the organic fractions after the first week. There was little change in the pool of labelled mineral nitrogen between the first and fourth weeks, but virtually complete and quantitative conversion from ammonium nitrogen to nitrate nitrogen. Some of the results point to varying biological lability of chemical fractions of soil nitrogen. These fractions are unlikely to be of much use as indices for sensitive measurement of nitrogen changes in the field, however, possibly because of the continuing accretion and losses which occur in the field.

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