Characteristics of Exposed Subsoil—At Exposure and 23 Years Later1
- Harold V. Eck2
The effects of topsoil removal on subsoil characteristics and productivity are usually studied at or soon after removal, with little attention to changes with time. The objective of this study was to evaluate the effects of 23 yr of exposure on the chemical and physical characteristics and productivity of various layers of Pullman clay loam (fine, mixed, thermic Torrertic Paleustolls). An area on a 1% slope was leveled in 1960, giving plots with 0, 0.10, 0.20, 0.30, and 0.41 m of topsoil removal. The area was cropped to grain sorghum [Sorghum bicolor (L.) Moench] in fertility studies for 6 yr, fallowed for 2 yr, then planted to tall wheatgrass (Agropyron elongatum) and left undisturbed until 1983. The study was then reactivated with grain sorghum being grown without fertilizer 1 yr to determine fertilizer residual effects. In 1984 the previous N fertilizer treatments were reinstituted. During the 23 yr, organic matter (OM) and total N decreased in uncut surface soil but increased in exposed subsoil where initial levels were low. Extractable P levels and particle size distribution remained essentially unchanged. The proportion of large water-stable aggregates (4.0-12.7 mm) decreased, especially in the surface soil where OM decreased with time. Decreases in large aggregates were accompanied by increases in the 0.25- to 1.0-mm size range. Productivity of exposed subsoil layers increased over time. In relation to yields on similarly treated surface soil, yield reductions from soil removal (avg 0.10, 0.20, 0.30, and 0.41 m) in 1960 to 1962 and 1984 were as follows: unfertilized, 55 and 33%; P fertilized, 52 and 38%; N fertilized, 31 and 16%; N and P fertilized, 2 and 14%. Productivity increases were associated with increases in both N and P supplying capacity.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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