Root characteristics of temperate pasture in New South Wales after grazing at three stocking rates for 30 years

The distribution of length, diameter, surface area and volume of roots was measured in northern New South Wales, Australia, under temperate pasture that had been previously grazed at low and high stocking rates for 30 years; these root characteristics were compared with those of roots under ungrazed pasture. The ungrazed pasture was dominated by phalaris (Phalaris aquatica), whereas annual grasses and dicotyledons were a large component of the pasture at low and high stocking rates. A fine-meshed (0.250 mm) sieve was used for separating the roots from the soil, and the root charateristics were measured using image analysis techniques. With this sieve size, root length densities were many times higher than published data for pastures where a larger mesh sieve had been used for sample preparation. The lengths of root per unit of soil volume (root length densities) were high for all stocking rates and averaged 91 cm cm(-3) near the soil surface (0-5 cm) declining to 4.0 cm cm(-3) at the deepest depth measured (65-75 cm). There was a greater proportion of roots near the soil surface at the higher stocking rates. A greater proportion of fine roots occurred at the higher stocking rates, which was probably due to the differences in botanical composition. Reciprocal, power and logarithmic functions best described the distribution of root length density, root surface area density and root volume density with depth.