Effects of selected conditioners and tillage on the physical quality of a clay loam soil

Field-crop yields are below their genetic and climatic potentials on many fine-textured soils due to low organic carbon content (OC), high bulk density (ρb), low hydraulic conductivity (Ks), insufficient air capacity (AC) and low plant-available water capacity (PAWC). Although soil conditioners derived from municipal, agricultural and industrial wastes are frequently used to improve soils, their effects on overall soil physical quality are still poorly understood. Hence, the objective of this laboratory soil core study was to determine for a Brookston clay loam the effectiveness of masonry sand, greenhouse rockwool waste, yard waste compost and swine manure compost for improving soil physical quality relative to “ideal” levels proposed in the literature, and relative to “benchmark” levels found in the soil under virgin conditions, long-term conventional tillage and long-term no-tillage. The virgin soil produced near-surface (0.05–0.15 m depth) values for ρb(0.88 Mg m-3), AC (0.19 m3m-3) and PAWC (0.22 m3m-3) that fell within the optimal ranges proposed in the literature, while OC (68.2 g C kg-1) was slightly above optimal. The soil under long-term conventional tillage and no-tillage (cornsoybean rotation) produced below-optimal organic carbon content (21.9–22.5 g C kg-1), excessive ρb (1.45–1.47 Mg m-3), insufficient AC (0.06 m3m-3) and low PAWC (0.14–0.19 m3m-3). Conventional tillage also produced below-optimal Ks (10−6 m s-1). Each conditioner could improve one or more of the above parameters, but not all five. Adding sand at 20–100 wt. % improved AC, but caused excessive reductions in OC and PAWC, and excessive increases in ρb and Ks. Greenhouse rockwool waste added at 2.5–10 wt. % improved AC and ρb, but did not improve OC and PAWC. Yard waste compost added at 3.8–20 wt. % improved OC, ρb and PAWC, but did not improve AC. Adding swine manure compost at 3.8–20 wt. % improved OC and ρb, but did not improve AC or PAWC, and decreased Ks. As no single conditioner could optimize all soil physical quality parameters, future studies using combinations of conditioners are proposed.