Temporal Variability of Selected Properties of Loessial Soil as Affected by Cropping

Quantification of the relationships between short‐ and long‐term variability of soil properties is needed to understand the effects of cropping on soils. These relationships were studied in four adjacent fields of a Typic Albaqualf or a Typic Glossaqualf which included a prairie and three fields that had been cropped for 3, 14, or 32 yr. The fields were sampled monthly from March 1989 to March 1990. Soil samples were collected at depth intervals of 0 to 5 cm and 5 to 10 cm at each sampling time. The statistical model assumed that the fields studied represented a random sample of fields from a large population. One of the ways in which these fields differ is in cropping duration. Field and sampling time variabilities were treated as random effects in a mixed model including soil depth. We defined the variability among fields as long‐term and the variability among sampling times within a field as short‐term. Statistical analyses indicated that the soil properties vary with cropping, depth interval, and sampling time within a year. The highest ratio of long‐ to short‐term variability ( r ) was found to be 26 with total C, and the lowest ratio was 0.52 with saturated hydraulic conductivity ( K sat ). Values of r for most of the soil properties examined ranged between 1.7 and 2.8 and tended to be higher in the first depth interval. The large estimated standard errors for these ratios indicated that even though r was greater than 1.0, the long‐term variability was not statistically significantly greater than the short‐term variability at α = 0.05.