SAMPLING SOUTHERN ALBERTA SOILS FOR N AND P SOIL TESTING

The number of subsamples that should be composited to obtain a soil sample representative of a given area in southern Alberta, Canada was determined. Five locations were selected from each of the brown, dark-brown and thin black soil zones. Samples were dried, crushed, sieved and analyzed for available NO3-N and available P. The results were summarized for a surface soil sample (0-15 cm) and combined for 0-60 cm or 0-120 cm depths. The depths were selected because the Alberta Soil and Feed Testing Laboratory bases its fertilizer P recommendation on the P level to a 15 cm depth and its fertilizer N recommendation on a 60 cm soil sample. Results indicate that the usual degree of compositing of soil samples by farmers and researchers is inadequate.