Long‐Term Tillage and Crop Rotation Effects on Bulk Density and Soil Impedance in Northern Idaho

Abstract

Conservation tillage management for winter wheat (Triticum aestivum L.) production in northern Idaho may increase bulk density (ρ_b) and soil impedance (SI) of surface layers and limit crop growth, particularly when combined with spring cropping practices which require cultural or tillage operations during moist soil conditions. Bulk density and SI were measured in a long‐term tillage‐crop rotation experiment after 10 yr of continuous management to determine if differences resulting from tillage or cropping practices existed. Soils of the experimental site were two similar series, Palouse (fine‐silty, mixed, mesic Pachic Ultic Haploxeroll) and Naff (finesilty, mixed, mesic Ultic Argixeroll) silt loams. Tillage treatments included conventional (CON, moldboard plow), minimum (MIN, chisel), and no‐tillage (NOT). Crop rotations were a 2‐yr winter wheat‐spring pea (Pisum sativum L.)rotation and a 3 yr winter‐spring barley (Hordeum vulgare L.)‐spring pea rotation. Bulk density was determined on intact cores using gamma attenuation. Soil impedance was measured with a constant‐rate penetrometer. Tillage had a significant (P < 0.05) effect on ρ_b, but not SI. Crop rotation did not significantly influence either soil property. The main effect of depth and a tillage × depth interaction, however, produced significant (P < 0.01) differences on ρ_b and SI. Both MIN and NOT had SI values exceeding 1.5 MPa at a depth of 0.05 to 0.15 m, which were 0.5 to 1.0 MPa greater than CON. Higher SI values under reduced tillage while not preventing root growth may, when combined with cool, wet soil conditions during the spring, limit root function and decrease crop growth potential.