Spatial Variability of a Cultivated Soil as Affected by Past and Present Microtopography

The effects of 30 yr of cultivation on the magnitude and spatial variance relationships of selected soil properties are examined. Soil cores (76‐mm diam) were taken every 1 m in 46‐m long transects in a native and adjacent cultivated field. The soil is a mixture of Typic Haploborolls and Typic Argiborolls. Spatial relationships observed in the native soil were used to construct a moving average model for predicting the soil surface on the cultivated site that existed before cultivation. The model along with 137 Cs distribution was used to separate the effects of tillage translocation and erosion on changes in solum mass and C. Tillage translocation during the initial years of cultivation resulted in considerable redistribution of soil. Spectral analysis indicated the redistribution was not random, but was related to the spatial distribution of the past surface curvature. The systematic redistribution resulted in higher overall variances for soil properties compared to the native site, but also resulted in significant increases in autocorrelation and the proportion of variance associated with deterministic cycling. A conceptual and mathematical filter model is presented for representing the effects of management, weathering, or other treatments on the soil. In profiles where no significant tillage translocation occurred, total C losses in the solum were 0.35% (of original C) per year. Soil erosion could account for 40% of the observed total C loss.