Influence of Sample Size on Chemical and Physical Soil Measurements

Abstract

AbstractUnderstanding the distribution of soil properties with respect to sample size is essential for designing efficient soil sampling strategies. This study was conducted to evaluate the influence of the size of soil samples on the distribution of estimated soil physical (bulk density and water content), chemical (pH and orthophosphate P), and biological (NO3‐N and denitrification rates) properties. The experiment was conducted at Beltsville, MD, on a Beltsville silt loam soil (fine‐loamy, mixed, mesic Typic Fragiudult). Soil samples were collected from the surface 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 samples of each sample size were collected twice before and twice after planting corn (Zea mays L.). Frequency distributions of denitrification rates, NO3‐N, and orthophosphate P values were approximately lognormal, while the values for bulk density, water content, and pH were approximately Gaussian. All soil parameters except bulk density exhibited spatially dependent results. The effect of sample size varied with the soil property. The most consistent size effect was that smaller diameter samples gave smaller means, greater skewness, and higher variances compared with the large‐block sample statistics.