Indicators of good soil physical quality: density and storage parameters

Abstract

Optimal values of soil physical quality (SPQ) parameters for enhancing field-crop productivity while maintaining or improving environmental health are still largely unknown. We hypothesized that progress toward identifying optimal values for some SPQ parameters might be made by comparing parameters obtained from long-term conventional tillage cropping (CT), long-term no-tillage cropping (NT), and virgin woodlot (WL) treatments located on Fox sand (Psammentic Hapludalf), Guelph loam (Mollic Hapludalf), and Brookston clay loam (Typic Argiaquoll) soils. Undisturbed 100-mm diameter soil cores were collected from the 0–100-mm depth range and the SPQ parameters, organic carbon (OC), bulk density (BD), porosity (POR), air capacity (AC), field capacity (FC), permanent wilting point (PWP), and plant-available water capacity (PAWC) were determined using standard laboratory methods. Regardless of soil type, OC, POR, and AC were smaller by 12–74% under NT and CT relative to WL, while BD was greater by 28–56%. The FC, PWP, and PAWC parameters showed no consistent differences among WL, CT, and NT. There was no clear advantage of NT over CT or vice versa with respect to any of the parameters measured. The SPQ indicator parameters, OC, BD, AC, and PAWC, all fell within their established “optimum” ranges or limits for the WL management on the loam and clay loam soils. However, these parameters fell outside their optimum ranges for the NT and CT managements on these soils, as well as for all three managements on the sandy soil. The recently proposed guidelines, FC/POR=0.66 and AC/POR=0.34, for “ideal” storage capacity of soil water and soil air appear to be useful as additional indicators of good SPQ, given that they yield results consistent with existing guidelines, and they incorporate aspects of soil quality that are not included in other indicator parameters.