The large variability of plant available nitrogen (N) at small spatial scales is well established, and may why soil N tests can be unreliable predictors of crop requirements for N. The traditional method of soil sampling to test for N requirements combines soil cores that have a relatively small volume. In comparison, the root-ball of an established plant integrates a relatively large volume of soil. A description of the spatial variability of plant available N at the plant root-ball scale may be useful to improve soil sampling strategies for plant available N. Root-ball scale samples (7.5^-04m²) were collected at 300 mm centres within areas of 1.44 m². Soil core samples were collected in the same area at the same spatial scale, and either kept separate or combined into composited (bulked) samples. Nine sets of root-ball and soil core sample collections were made, each set at least 30 m apart. All sets were within a soil type and soils varied from silty, clayey to stony phases. Within the silty phase, land uses in the season preceding sample collection encompassed ryegrass seed production, wheat, and dairy pasture. Anaerobically mineralisable N was measured in all samples, as the difference between NH₄ and NO₃ extracted by KCl, with and without anaerobic incubation. Population distributions and geostatistical trends are compared within and between the sample sets.