INFLUENCE OF SAMPLE-SIZE ON CHEMICAL AND PHYSICAL SOIL MEASUREMENTS

Understanding the distribution of soil properties with respect to samp le size is essential for designing efficient soil sampling strategies. This study was conducted to evaluate the influence of the size of soi l samples on the distribution of estimated soil physical (bulk density and water content), chemical (pH and orthophosphate P), and biologica l (NO3-N and denitrification rates) properties. The experiment was con ducted at Beltsville, MD, on a Beltsville silt loam soil (fine-loamy, mixed, mesic Typic Fragiudult). Soil samples were collected from the s urface layer (0-16 cm) using five different sized soil coring tubes, 1 .7 to 5.4 cm in diameter, and one 20 by 30 cm block. Thirty-six sample s of each sample size were collected twice before and twice after plan ting corn (Zea mays L.). Frequency distributions of denitrification ra tes, NO3-N, and orthophosphate P values were approximately log-normal, while the values for bulk density, water content, and pH were approxi mately Gaussian. Ah soil parameters except bulk density exhibited spat ially dependent results. The effect of sample size varied with the soi l property. The most consistent size effect was that smaller diameter samples gave smaller means, greater skewness, and higher variances com pared with the large-block sample statistics.