Selected soil physical properties and aggregate-associated carbon and nitrogen as influenced by gypsum, crop residue, and glucose

Soil physical properties play an important role in maintaining proper soil conditions for sustainable plant growth and development. These properties can be improved through addition of soil amendments, but little information is available of the effect of gypsum applied alone or in combination with various C sources on selected soil properties. A greenhouse study was conducted involving two contrasting soil types (Wooster silt loam and Hoytville clay loam) from Ohio, USA to which were applied gypsum (8.9 and 26.9 Mg ha(-1)), two contrasting C sources (i.e. crop residues at 13.4 Mg ha(-1) and glucose at 4.5 Mg ha(-1)), their combinations and an untreated control. Response variables included soil bulk density, porosity, water stable aggregates, and aggregated-associated total C and N. A significant (P < 0.10) reduction in soil bulk density and increased porosity by glucose as compared to the control was observed. Crop residue addition also decreased bulk density. There was no significant effect on bulk density due to gypsum. Addition of glucose combined with gypsum (26.9 Mg ha(-1)) or crop residue resulted in more water stable aggregates (WSA), greater mean weight diameter (MWD), and greater geometric mean diameter (GMD) as compared to other treatments. The differences were attributed to multiple factors such as the gluing activity of the polysaccharides promoted by glucose, and the inorganic binding/stabilizing activity brought about by Ca2+ in the gypsum. Addition of C amendments increased aggregate formation and lowered soil bulk density. It also caused a C increase within aggregates. Both, highly labile C (i.e. glucose) and more stable C in the form of plant residues provided benefit by improving soil physical properties. These benefits were also enhanced in some instances when gypsum was applied in combination with the C amendments.