Effect of Disturbed Soil Thickness on Soil Water Use and Movement under Perennial Grass

Abstract

AbstractPrevious research has shown that plant growth on minespoil of lower plant productivity is dependent upon thickness of soil replaced. Sodium‐affected strip‐mine spoils are a significant reclamation problem in the northern Great Plains. The purpose of this work was to develop understanding of plant growth response to soil thickness over sodic minespoils by measurement of water movement, water use, and root growth. Soil water storage and use were measured in each of three growing seasons under crested wheatgrass (Agropyron desertorum) grown on 0.25‐, 0.5‐, 0.75‐, and 1.0‐m thicknesses of disturbed soil. Soil profiles were constructed from Haploboroll topsoil (0.2 m for all treatments), placed over varying thicknesses of subsoil (B and C horizon materials), which in turn was placed over sodic (Sodium adsorption ratio = 30) drag‐line spoil at a semiarid, steppe‐land site in western North Dakota. Forage yield was 2‐ to 3.5‐fold greater on 1.0 m soil thickness than on 0.25 m. Both total soil water potentials and root weight densities were similar in minespoil and in subsoil at the same profile depths. Root water uptake was much less from the minespoil (mean saturated hydraulic conductivity (HC) = 1 × 10−3 cm/d) than from subsoil (mean HC = 0.2 cm/d). Low HC per se appeared to be the dominant factor limiting sodic minespoil as a plant growth medium because low HC resulted in less use of stored soil water from minespoil compared to subsoil. Depletion from a 120‐cm profile was 0.2, 3.3, 7.9 and 9.8 cm for 0.25‐, 0.50‐, 0.75‐ and 1.0‐m soil thickness, respectively. Relative differences in evapotranspiration (ET) between the 0.25‐m and 1.0‐m soil thickness treatments were much less than yield differences, reflecting progressively reduced water use efficiency with less soil thickness.